Anisotropy-mediated stress regulation in Mn-substituted VOPO₄ enables aqueous zinc batteries with long cycle life

Abstract

The structural integrity of layered VOPO₄ frameworks critically determines their electrochemical performance in aqueous zinc-ion batteries, yet the highly ordered stacking of VOPO₄ renders it susceptible to lattice stress accumulation and chemo-mechanical degradation during cycling, causing rapid capacity fading and a shortened battery lifespan. Herein, we show a strategy to alleviate these limitations through partial metal substitution in the VOPO₄ lattice, enabling the modulation of local coordination environments and mitigating lattice and cycling induced stress. As a proof-of-concept, theoretical calculations and experimental validation on Mn-substituted VOPO₄ reveal shortened M–O bond along the c-axis and the formation of Mn–O–P–O–V delocalized structure. These modifications introduce subtle lattice distortions and generate percolation channels that enable more facile, ordered Zn²⁺ migration, facilitating uniform lattice stress distribution. Real-time monitoring of interfacial stress during cycling identifies that Mn incorporation induces electronic redistribution and lattice anisotropy, promoting balanced intra-layer (a/b-axis) stress accommodation. Therefore, Mn-substituted VOPO₄ exhibits higher specific capacity and cycling stability, with 91.0% capacity retention over 2000 cycles at 1 A g⁻¹. This intra-layer anisotropy engineering strategy offers a practical route for mitigating dissolution and strain effects during cycling, paving ways for the development of high-energy-density positive electrodes with cycling durability.

The structural integrity of layered VOPO₄ frameworks critically determines their electrochemical performance in aqueous zinc ion batteries. Herein, the authors use partial metal substitution in VOPO₄ to modulate local coordination and mitigate cycling induced stress, enabling enhanced cycling stability.

Introduction

The rapid integration of renewable energy sources and increasing demand for grid-scale energy storage has propelled aqueous zinc ion batteries (AZIBs) to the forefront of next-generation electrochemical technology, owing to their high capacity, inherent safety and cost effectiveness. However, AZIBs are currently constrained by the limited availability of high-energy-density and durable positive electrode materials. In this context, polyanionic vanadium oxides (VOPO₄) have emerged as candidates due to their strong P − O covalent bond induction effect, which attracts the electrons adjacent to the V − O bonds, polarizes the V − O bonds, and reduces the electron density in the Vd orbitals, enabling elevated discharge plateaus (≈ 1.1 − 1.8 V vs Zn²⁺/Zn). Furthermore, VOPO₄ offers a high theoretical capacity (> 300 mAh g⁻¹) and a distinct layered structure conductive to ion transport. Nevertheless, the intra-layer lattice of VOPO₄ has an alternating connection of VO₆ octahedra and PO₄ tetrahedra, forming a rigid, highly ordered two-dimensional network with strong interlayer coupling, resulting in a high-order stacking sequence. During Zn²⁺ insertion and extraction, lattice strain is readily induced, leading to dislocation formation and localized stress accumulation, thereby accelerating structural degradation. During the electrochemical cycling, particularly Zn²⁺extraction, anisotropic lattice strain inevitably arises, inducing crystal fatigue and resulting in substantial capacity fading and limited cycle life¹. This degradation can be attributed to several mechanisms. First, the extraction of Zn²⁺ induces contraction of the VO₆ octahedra, reducing the a/b lattice parameter of VOPO₄². Subsequent migration of vanadium ions and loss of polyanionic PO₄³⁻ groups may ultimately lead to the irreversible transformation into VO_x phases, compromising voltage and cycling stability. Second, strong electrostatic interactions of Zn²⁺ and VOPO₄ during Zn²⁺ insertion impede ion diffusion kinetics and reduce active material utilization, culminating in structural collapse and diminished specific capacity³. These anisotropic lattice displacements give rise to accumulated strain to irreversible mechanical fatigue, which regarded as the primary cause of degradation in layered oxide positive electrodes.

To address these challenges, a variety of strategies have been pursued, including pre-embedding in conductive matrices (e.g., graphene⁴, polypyrrole⁵), defect engineering (e.g., oxygen vacancies⁶), or electrolyte optimization (e.g., ZnSO₄/graphitic carbon nitride quantum dots⁷, ZnCl₂/H₃PO₄⁸). The intercalated species within the VOPO₄ layers can interact with insert Zn²⁺ ions, thereby weakening their binding affinity to the host lattice, improving electronic conductivity and facilitating Zn²⁺ transport by expanding interlayer spacing and providing additional ion diffusion pathways. Introducing structural defects diminish electrostatic interactions between Zn²⁺ and the VOPO₄ framework, enhancing ion diffusion kinetics. In parallel, the incorporation of PO₄³⁻ additives and the use of high concentration electrolytes suppress dissolution by minimizing ion concentration gradients and reducing diffusion coefficients that comply with Fick’s law. Additionally, lowering water activity through hydroxyl-rich additives, capable of integrating into the hydrogen bonding network, effectively mitigates phosphate leaching then dissolution. Although these approaches have alleviated material dissolution and led to incremental improvements in electrochemical performance, the intrinsic lattice evolution of VOPO₄ during cycling remains a fundamental challenge. Consequently, the development of integrated strategies that combine intrinsic structural stabilization with modulation of lattice and cycling induced stress is urgently needed to enhance the electrochemical resilience of VOPO₄ based positive electrodes.

In this work, a series of metals were incorporated into the VOPO₄ lattice to tune the local coordination environment, among which Mn proved most effective in enhancing lattice strain adaptability under deep charge states. Owing to its higher electronegativity, Mn induces pronounced electron redistribution, regulates the anisotropy of both the c-axis and a/b-plane lattices, and modifies lattice distortion and ion migration pathways. Simultaneously, the M–O bond length along the c-axis shortens, weakening interlayer coupling and enabling interlayer slippage, thereby regulating crystal periodicity and dispersing localized stress over a broader area to achieve effective stress relaxation. Spectroscopic analyses reveal the formation of a stable Mn−O − P − O − V delocalized electronic structure. The delocalization configuration suppresses spontaneous migration of transition metal ions during Zn²⁺ extraction, mitigates VOPO₄ dissolution and decomposition and preserving lattice integrity. Real-time monitoring of the interfacial stress under Zn²⁺ insertion and extraction process indicates Mn-induced electronic redistribution and lattice anisotropy promotes balanced intra-layer (a/b-axis) stress accommodation. Simultaneously, the stabilized lattice framework and interconnected percolation channels facilitate directional Zn²⁺ migration, suppress volume fluctuations, and minimize residual strain (σ‘_residual = 0.46 MPa). As a result, the Mn-substituted VOPO₄ demonstrates a high Zn²⁺ storage specific capacity of 258 mAh g⁻¹ and a markedly enhanced cycling stability, retaining 91.0% of its capacity after 2000 cycles. X-ray 3D nano-computed tomography (nano-CT) analysis shows a slight increase in porosity after cycling (from 20.5% to 21.9%), corroborating the role of intralayer anisotropy tuning in constructing stabilized delocalized structures and achieving homogeneous stress distribution, both essential for mechanical stability and dissolution suppression. This work demonstrates that partial metal ion substitution is a viable strategy for enhancing the reversibility and mechanical stability of VOPO₄.

Results and discussion

Structural evolution upon metal incorporation: lattice distortion and stress redistribution

During the charge/discharge process of VOPO₄ in AZIBs, a sequential phase transformation from VOPO₄ → Zn_0.5VOPO₄ → ZnVOPO₄ occurs. Analysis of the voltage profiles (Fig. 1a) reveals a continuous decline in the discharge/charge voltage plateaus from the 2nd to the 200th cycle. This trend is more distinctly reflected in the corresponding differential capacity (dQ/dV) curves (Fig. 1b), which display four pairs of redox peaks. The low voltage plateaus associated with VO_x redox couples (0.73/0.58 V and 0.97/0.89 V, corresponding to the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ transitions, respectively) gradually intensify with cycling, while the high voltage plateaus induced by the PO₄³⁻ polyanion (1.28/1.07 V and 1.61/1.55 V) progressively weaken and nearly vanish by the 100th cycle. As a result, the discharge capacity retention after 200 cycles is only 73% of the initial value, indicating substantial voltage and capacity decay. Further evidence from V 2p X-ray photoelectron spectroscopy (XPS) reveals a downshift in both V 2p_1/2 and V 2p_3/2 binding energies, accompanied by an increased proportion of V⁴⁺ oxidation state over cycling, which originates from the loss of the PO₄³⁻ groups, weakening the inductive effect and lowering overall binding energy (Fig. 1c). Consistently, the P component detected by XPS decreases markedly from 11.57 to 1.48 at.% (Fig. 1d and Supplementaty Table S1), indicating substantial PO₄³⁻ dissolution. These results demonstrate that VOPO₄ undergoes irreversible PO₄³⁻ leaching during cycling, transforming into VO_x, resulting in structural collapse and continuous voltage/capacity degradation.

Fig. 1. Microstructure lattice and stress distribution of VOPO₄ and 2% Mn-VOPO₄.

a, b Voltage profiles and the associated dQ/dV curves of the VOPO₄ cycled at 0.1 A g⁻¹ with 3 m Zn(OTf)₂ electrolytes. c, d V 2p XPS fitting and P/V ratios of pre-cycle and post-cycle of VOPO₄ over 200 cycles. e, f HRTEM images of VOPO₄ and 2% Mn-VOPO₄. g, h IFFT images of VOPO₄ and 2% Mn-VOPO₄. i, j The intra-layer atomic lattice vectors along the c-axis of the VOPO₄ and 2% Mn-VOPO₄, enumerating the angular distances in their direct and reciprocal spaces. k, l Strain distributions in the Exx direction within the VOPO₄ and 2% Mn-VOPO₄ structures performed by GPA. m, o Surface morphology and (n, p) Young’s modulus images of VOPO₄ and 2% Mn-VOPO₄ analyzed from AFM. Source data for Fig. 1a–c are provided as a Source Data file.

To mitigate the structural decomposition of VOPO₄, a series of cation-substituted VOPO₄ materials (M = Mn, Fe, Co, Nb, Mo, Ta, and W) were synthesized via an oil bath reflux method⁷, all of which retained the typical VOPO₄ rectangular plate like morphology (length ≈ 17 μm, width ≈ 14 μm) (Supplementary Fig. S1a). Under identical reaction conditions, replacing V₂O₅ with equimolar Mn salts yielded MnPO₄, composed of alternating MnO₆ octahedra and PO₄ tetrahedra. Its X-ray diffraction (XRD) pattern (Supplementary Fig. S2) matches perfectly with PDF#78-1082, confirming successful low temperature substitution of transition metals into the VOPO₄ lattice. Notably, Mn-substituted VOPO₄ processes a distinct helically stacked rosette morphology (Supplementary Fig. S1b, c), attributed to the similar coordination chemistry between Mn and V, which enables Mn to substitute V more effectively than the other larger metal ions in the series. Mn, with its higher electronegativity (1.91) compared to V (1.79), leads to a shortened c-axis M − O bond, thereby reducing interlayer electrostatic interactions in the two-dimensional (2D) lattice and facilitating stress relaxation through sliding of the layers^9–11. Moreover, Mn substitution promotes intra-layer electron transfer along the a/b-axes, enhancing lattice polarization and strengthening interatomic interactions, which collectively stabilize the helical dislocation stacking structure¹². Although Fe and Co possess comparable ionic radii to V, their lower electronegativities (Fe: 1.65, Co: 1.69) elongate the c-axis M − O bonds, preventing the discussed effects and leading to the undermine of structural integrity and morphological fragmentation (Supplementary Fig. S1d, e). While Nb, Mo, Ta, and W are highly electronegative (Nb: 1.86, Mo: 2.10, Ta: 1.92, W: 2.18), their strong d-orbital electrons localization inhibits efficient intra-layer electron transport along a/b-axes, preserving the nanosheet morphology of pristine VOPO₄ but yielding structures with weak interlayer cohesion (Supplementary Fig. S1f–i). This localized electronic structure results in unstable, low-density morphologies that are suboptimal for electrochemical applications.

XRD analysis reveals that Mn substitution leads to a downshift in the (001) diffraction peak of VOPO₄, accompanied by an increase in the interlayer spacing from 0.747 nm to 0.751 nm (Supplementary Fig. S3). This shift derives from the weakened interlayer interactions induced by Mn incorporation, resulting in an c-axis lattice expansion. In contrast, the larger ionic radii of Fe and Co (Fe: 0.63 Å, Co: 0.69 Å, V: 0.59 Å) strengthens interlayer interactions and causes c-axis lattice contraction. Similarly, incorporation of Nb, Mo, Ta, and W (Nb: 0.69 Å, Mo: 0.62 Å, Ta: 0.68 Å, W: 0.62 Å) also results in lattice contraction due to increased electron localization, which strengthens M − O bonding and interlayer coupling. Therefore, Mn was chosen as the metal for cation substitution to demonstrate its effectiveness in modulating the microstructure of VOPO₄. To optimize substitution levels, VOPO₄ materials with varying Mn contents (1%, 2% and 5% molar ratios, denoted as 1% Mn-VOPO₄, 2% Mn-VOPO₄, and 5% Mn-VOPO₄) were prepared and systematically evaluated.

The anisotropy of VOPO₄ increases progressively with Mn substitution, with 2% Mn substitution exhibiting a well-developed helical rosette structure. In contrast, low Mn concentrations fail to induce sufficient lattice distortion, while excessive Mn led to structural fragmentation (Supplementary Fig. S4). As the Mn content increases, the diffraction peak corresponding to the (001) c-axis crystal plane of VOPO₄ gradually shifts to lower angles (JCPDS: 36-1472), and the interlayer spacing expands to 0.757 nm (Supplementary Fig. S5)^13–15. Neutron diffraction spectra (Supplementary Fig. S6) revealed concomitant contraction along the a/b planes, the d₂₀₀ spacing decreased from 3.13 to 3.11 nm and d₂₂₀ from 2.23 to 2.20 nm, evidencing anisotropic lattice tuning along the c- and a/b-axes by Mn substitution. Electron paramagnetic resonance (EPR) spectra reveal a g-factor of 2.008, indicative of oxygen vacancies typically associated with redox-active transition metals. The concentration of oxygen vacancies decreases with increasing Mn content (Supplementary Fig. S7)⁶. Among the evaluated compositions, the sample with 2% Mn substitution presents the most coherent helical stacking and the lowest oxygen vacancy concentration, thus 2% Mn-VOPO₄ was selected as the focus material for further study.

High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images confirm the uniform distribution of V, O, P, and Mn elements in the 2% Mn-VOPO₄, with no detectable impurities (Supplementary Fig. S8). High-resolution transmission electron microscopy (HRTEM) reveals that pristine VOPO₄ nanosheets exhibit well-ordered lattice fringes with a crystallographic spacing of 0.32 nm, corresponding to the (200) crystal plane (Fig. 1e and Supplementary Fig. S9a). Notably, 2% Mn-VOPO₄ displays a wavy lattice structure with an expanded spacing of 0.37 nm, attributed to partial substitution of V by Mn atoms (Fig. 1f and Supplementary Fig. S9b). Brunauer Emmett Teller (BET) (Supplementary Fig. S10) analysis showed that 2% Mn-VOPO₄ possesses a significantly larger surface area than pristine VOPO₄ (0.89 m² g⁻¹), providing enhanced ion transport pathways and more Zn²⁺ storage sites. This lattice expansion in principle would give more space for ion transport and facilitate Zn²⁺ deposition. Inverse Fourier transform (IFFT) images further illustrate the ordered lattice fringes of VOPO₄ and the pronounced wavy lattice distortion following Mn substitution (Fig. 1g, h). This distortion is ascribed to electron redistribution induced by the higher electronegativity of Mn, which enhances the intra-layer anisotropy and distorts the lattice. Consequently, the modified lattice texture and connectivity of Zn²⁺ migration channels form in this sample a percolated network that mitigates the detrimental effects of ion migration on the material’s integrity¹⁶. Simulated diffraction halo from the (001) selected area electron diffraction (SAED) patterns confirm that the crystalline surface of VOPO₄ remains consistent before and after Mn substitution (Fig. 1i and Supplementary Fig. S11)¹⁷. The sharp, cubic-arranged diffraction spots verify that Mn effectively replaces the V sites while preserving the single-crystalline nature of the tetragonal phase. Furthermore, Mn-induced electron redistribution generates intra-facial anisotropy, altering the crystal face pitch angle and leading to a lattice twisted helical stacking morphology (Fig. 1j and Supplementary Fig. S12). These lattice modifications offer an additional mechanism for mechanical stress distribution. Geometric phase analysis (GPA) reveals that the pristine VOPO₄ nanosheets experience localized stress concentration (Fig. 1h). Atomic force microscopy (AFM) further demonstrates that the stress distribution in VOPO₄ nanosheets is uneven, with higher stress at the center and lower stress at the edges (Fig. 1k, m, n and Supplementary Fig. S13). This uneven structural stress distribution originates from the ordered atomic lattice within VOPO₄, where the central region is subjected to multiple constraints, leading to stress concentration and inhomogeneity, rendering the nanosheets to be more prone to rupture and dissolution. In contrast, 2% Mn-VOPO₄ exhibits significantly alleviated stress accumulation with a more uniform stress distribution (Fig. 1l, o, p). The Mn-induced anisotropic lattice adjustment generates lattice distortions and helical dislocations, modulating the crystal periodicity, generating natural strain fields that distribute stress across a larger area, effectively mitigating stress accumulation and crack formation, and thereby enhancing the structural stability of the materials^18–20.

Electronic delocalization structure: strengthened domination of π-symmetric electrons

To elucidate the Mn-induced electronic delocalized structure, Raman analysis (Fig. 2a) was performed. The characteristic bands located at approximately 540, 575, 950, and 1037 cm⁻¹ correspond to δ(O − P − O), υ(Mn−O), υ(O − P), and υ(V = O) vibrational modes, respectively^6,21. The formation of Mn−O bonds upon Mn incorporation is particularly evident in the 560–590 cm⁻¹ region (Supplementary Fig. S14)^22,23. Due to the asymmetry of the VO₆ octahedra, the V = O bonding stretching modes in the 1020–1060 cm⁻¹ exhibit an upshift, indicative of lattice distortion (Fig. 2b). The interlayer strain (δ) can be estimated using the following Eq. (1)⁴:

$$\Delta \omega =\delta \times \omega /2.66$$ 1

where ω is the Raman shift, and Δω denotes the shift in Raman peak position. The incorporation of Mn induces approximately 1.0% tensile strain in the shorter c-axis V = O bond, enhancing the symmetry of the VO₆ octahedron, improving structural stability, and introducing facet-specific anisotropy that leads to controlled lattice distortion⁴. Detailed electronic interactions following Mn incorporation was investigated through XPS. The XPS survey spectra (Supplementary Fig. S15a) of VOPO₄ and 2% Mn-VOPO₄ confirm the presence of V, O, and P. Quantitative analysis of the V 2p spectrum (Fig. 2c and Supplementary Table S2) reveals that both materials are dominated by V⁵⁺ species, with a minor fraction of V⁴⁺. The proportion of V⁵⁺ increased from 82.65% in pristine VOPO₄ to 86.95% in 2% Mn-VOPO₄. Moreover, the V 2p peak of 2% Mn-VOPO₄ shifted to higher binding energies, while the O 1s and P 2p peaks (Supplementary Fig. S15b, c) shifted to lower energies, indicating electron redistribution caused by Mn substitution, resulting in an increase in V⁵⁺ content and a decrease in V⁴⁺ content. The Mn 2p_1/2 peak (Supplementary Fig. S15d) can be deconvoluted into two distinct components at 652.8 eV (Mn³⁺) and 654.8 eV (Mn⁴⁺), confirming that Mn exists predominantly in the + 3 and + 4 oxidation states in 2% Mn-VOPO₄. The disparity in positive charge density at metal sites is compensated by an increased electron density within the anionic framework. These observations suggest that Mn incorporation, due to its stronger electron-withdrawing capacity, promotes electron transfer from the V centers to Mn through the PO₄ tetrahedral resonance structure^12,13,24,25. This electron delocalization facilitates the redistribution of lattice charges along the a/b-axis, dispersing stress throughout the network and mitigating localized stress concentrations by the soft delocalized electrons^26,27.

Fig. 2. Electronic structure analysis.

a, b Raman spectrum of VOPO₄, 1% Mn-VOPO₄, 2% Mn-VOPO₄ and 5% Mn-VOPO₄. c High-resolution V 2p XPS of VOPO₄ and 2% Mn-VOPO₄. d V L-edge XANES spectra of VOPO₄ and 2% Mn-VOPO₄. e, f V K-edge XANES spectra and FT curves of V K-edge EXAFS k³χ (k) functions of VOPO₄ and 2% Mn-VOPO₄. g, h Mn K-edge XANES spectra and FT curves of Mn K-edge EXAFS k³χ (k) functions of VOPO₄ and 2% Mn-VOPO₄. i The fitted average oxidation states of Mn from XANES spectra. j Magnetic susceptibility of VOPO₄ and 2% Mn-VOPO₄. The dotted lines are the fitting results by a Curie-Weiss law. k Schematic representations of the electronic coupling among V and Mn in VOPO₄ and 2% Mn-VOPO₄. Source data for Fig. 2a–h and Fig. 2j are provided as a Source Data file.

The electronic delocalization and lattice bonding environment were further examined using X-ray absorption near-edge structure (XANES)¹³. The V L-edge XANES (Fig. 2d) reveals that incorporating Mn in 2% Mn-VOPO₄ shifts the V absorption to higher energies at both the L₃- and L₂-edges and decreases the L₃/L₂ intensity ratio from 1.054 to 1.038, suggesting an increase in the V⁵⁺ oxidation state²¹. The V K-edge XANES (Fig. 2e) presents a reduced leading-edge peak, reflecting a more symmetric octahedral structure at the V-site after Mn substitution²⁸, consistent with the Raman results. In addition, the slightly shift of the absorption edge towards higher energies further suggests electron depletion and an increased average V valence state in 2% Mn-VOPO₄, which aligns with the XPS and L-edge XANES findings. Comparative analysis of Fourier transforms extended X-ray absorption fine structure (FT-EXAFS) of the V K-edge k³ χ(k) function (Fig. 2f and Supplementary Fig. S16) and the pair distribution function (PDF) (Supplementary Fig.S17) proclaim similar structural evolution. The V − O distance in the first shell decreased from 1.68 Å to 1.56 Å, and the V − P distance in the second shell shortens from 2.65 Å to 2.50 Å upon Mn incorporation. These changes imply that Mn modulates the local structure and chemical environment of the V centers, shortened the V − O and V − P bonds, generates localized Coulombic forces that induce helical dislocations and lattice distortions, thereby enhancing structural stability²⁵. The Mn K-edge XANES spectra (Fig. 2g and Supplementary Fig. S18) indicate that the absorption edge of 2% Mn-VOPO₄ lie between those of MnO₂ and metallic Mn, confirming that Mn exists in a higher oxidation state. The corresponding FT-EXAFS of the Mn K-edge (Fig. 2h) reveals a Mn−O bond length of 1.43 Å, validating the successful replacement of Mn for V within the lattice. The average oxidation state of Mn, determined from XANES fitting, is calculated to be + 3.6 (Fig. 2i), close to the + 4 oxidation state in MnO₂. Furthermore, the wavelet transform (WT) analysis of 2% Mn-VOPO₄ (Supplementary Figs. S19, S20) discloses two distinguishable intensities associated with V − O and V − P coordination environments, in agreement with the FT-EXAFS results²⁹. Radial distribution function (RDF) calculations (Supplementary Fig. S21) further corroborate the atomic distances obtained from EXAFS and WT analyses. To probe the electronic spin configuration, temperature-dependent zero-field cooling (ZFC) magnetization was performed (Fig. 2j, Supplementary Fig. S22 and Supplementary Table S3). The effective magnetic moments (μ_eff) for 2% Mn-VOPO₄ and MnO₂ were calculated to be 3.04 μ_eff and 2.83 μ_eff, respectively. The number of unpaired d-electrons (n) was determined by Eq. (2)³⁰:

$${\mu }_{eff}=\sqrt{n\left(n+2\right)}$$ 2

The unpaired electron number (n) in 2% Mn-VOPO₄ is approximately 3.6, indicating that the Mn ions adopt a high-spin configuration. Mn−O − P − O − V structural model is shown in Fig. 2k to elucidate the valence electron distribution and electronic interactions was constructed. In this structural motif, Mn³⁺, with an electronegativity close to 1.91, significantly higher than that of V⁴⁺ (1.79), exerts a stronger domination of π-symmetric electrons³¹. In the case of V⁴⁺, unpaired electrons occupying π-symmetric t_2g orbitals are transferred to the bridging O²⁻ via π-donation. The phosphate group (PO₄³⁻) adopts a resonance structure with delocalized electrons, forming four equivalent P − O bonds. Meanwhile, the π-symmetric e_g orbitals of Mn³⁺ remain partially unoccupied and accept electrons through resonance mediated interactions with the phosphate framework. The formation of this extended delocalized Mn−O − P − O − V network facilitates rapid electron transfer, alters the M − O bonds, and induces helical dislocations and lattice anisotropy, which contribute to lattice distortion, stress dispersion alongside mechanical stability improvement. Moreover, Mn incorporation not only strengthens the binding between metal ions and oxygen but also enhances the conjugation with phosphate units, forming a stable Mn−O − P − O − V delocalized structure that may improve the cycling stability of 2% Mn-VOPO₄ during repeated charge/discharge processes.

Charge reconfiguration: optimizing Zn²⁺ diffusion and dynamic bond stability

Density functional theory (DFT) calculations were conducted to understand the variations in charge and bond lengths. The calculated charge density differences (Fig. 3a, b and Supplementary Fig. S23) verify substantial charge redistribution and delocalized electron transfer between V and Mn atoms, with a pronounced reduction in charge accumulation around Mn. Bader’s charge analysis further indicates that the charge on Mn atoms (– 2.12 e) is less negative than the one on V atoms (– 2.30 e), giving another evident of the electron transfer from V to Mn, consistent with EXAFS and XPS findings³². Density of states (DOS) and partial density of states (PDOS) analyses (Fig. 3c) clarify that Mn incorporation promotes electronic reconfiguration, narrowing the energy band gap by 0.51 eV compared to pristine VOPO₄, thereby accelerating charge carrier migration. Charge migration induced by Mn led to a shortening of the c-axis M–O bond from 2.06 Å to 1.64 Å thereby weakening the interaction between the apical oxygen and Zn²⁺ (Fig. 3d, e and Supplementary Fig. S24). Simultaneously, the a/b-axis M–O bond contracted slightly from 1.90 Å to 1.89 Å, strengthening the binding interaction with the PO₄³⁻ group. Climbing Image Driven Elastic Bands (CI-NEB) simulations were then carried out to examine the Zn²⁺ diffusion kinetics (Fig. 3f and Supplementary Fig. S25, S26), which manifests that dense covalent bonding and increased electron density within the anionic substructure effectively reduce the Zn²⁺ diffusion energy barrier from 1.03 eV to 0.65 eV, significantly improving ion diffusion kinetics. To further explore the Zn²⁺ storage mechanism, in situ Raman spectroscopy was employed to monitor chemical bonding dynamics throughout the electrochemical cycling process. During Zn²⁺ insertion, the electrostatic interactions between Zn²⁺ and the apical O atoms of VO₆ units induce tensile stress within the lattice, weakening the P − O and V = O bonds, which results in a downshift in Raman bands. Upon Zn²⁺ extraction, the releases of electrostatic force results in a corresponding upshift of the P − O and V = O bands^33–36. Since the instability of the lattice structure of VOPO₄, excessive tensile strain presents a situation where the P − O bonds cannot fully recover their initial positions, predisposing the material to irreversible dissolution of PO₄³⁻ (Fig. 3g and Supplementary Fig. S27). In contrast, a stable Mn−O − P − O − V delocalized electronic structure in 2% Mn-VOPO₄ effectively buffers the electrostatic stress originated from intercalated Zn²⁺ since a reduced c-axis M − O bond, thereby enabling the lattice to recover its initial state, achieving full reversible Zn²⁺ storage (Fig. 3h and Supplementary Fig. S28). In situ XRD was conducted to evaluate the structural reversibility and mechanical stability provided by this Mn-VOPO₄ structure. Repeated deep insertion and extraction of Zn²⁺ cause severe lattice expansion and contraction, which is typically the cause of crack formation and structural degradation^37–39. During discharge, the (001) and (220) diffraction peaks of both VOPO₄ and 2% Mn-VOPO₄ gradually shift to higher 2θ values, considering the c-axis and a/b-axis lattice contraction induced by electrostatic attraction with intercalated Zn²⁺⁴⁰. Conversely, during charging, Zn²⁺ extraction increases the electrostatic repulsion of interlayer oxygen, leading to c-axis and a/b-axis expansion. However, pristine VOPO₄ exhibits irreversible structural deformation: the c-axis and a/b-axis spacing continuously decrease (from 0.665 nm to 0.663 nm, from 0.233 nm to 0.232 nm) after complete Zn²⁺ extraction (Fig. 3i, j). This irreversibility is attributed to the V − O bond elongation, partial conversion of VOPO₄ into amorphous VO_x, and the release of PO₄³⁻ to the solution, resulting in lattice mismatch and structural collapse. These processes further promote the nucleation and accumulation of inter- and intracrystalline microcracks during cycling^20,41. In contrast, Mn modification by Mn−O − P − O − V delocalized structure stabilizes the host lattice by modulating interlayer interactions and shortening the M − O bond along both c-axis and a/b-axis. This enables the reversible recovery of the (001) and (220) crystal planes to their original positions after full Zn²⁺ extraction (Fig. 3k, l), indicating high structural reversibility. The associated polarization induced buffering effect mitigates mechanical strain during Zn²⁺ insertion/extraction, improving both the reversibility and mechanical stability of the electrode⁶.

Fig. 3. Charge configuration and dynamic structure analysis.

a, b Differential charge density image of VOPO₄ and 2% Mn-VOPO₄, the yellow and blue regions represent charge accumulation and decrease, respectively. The atomic coordinates are provided in Supplementary Data 1. c The total DOS and PDOS of VOPO₄ and 2% Mn-VOPO₄. d, e Configuration models and Zn²⁺ diffusion path diagrams for 2% Mn-VOPO₄ in top-view and side-view modes. The atomic coordinates are provided in Supplementary Data 1. f Diffusion energy barrier profiles of Zn²⁺ transport in VOPO₄ and 2% Mn-VOPO₄. g, h In situ Raman spectra of VOPO₄ and 2% Mn-VOPO₄ during one charge/discharge cycles. i–l In situ XRD plots of VOPO₄ and 2% Mn-VOPO₄ (001) and (220) crystal planes over one charge/discharge cycle at 0.5 A g⁻¹. Source data for Fig. 3c, f, 3g–l are provided as a Source Data file.

Internal stress evolution in cells: lattice strain adaptation and cycling stress relaxation

In order to investigate the impact of lattice stress distribution on Zn²⁺ storage, an lab-made Swagelok cell integrated with a single mode optical Fiber Bragg grating (FBG) sensor was developed, with the FBG positioned on top of the positive electrode (Fig. 4a)⁴². Such a configuration was found not to affect the Zn²⁺ insertion/extraction behavior. The FBG sensor serves as a reflector for a specific wavelength, enabling real-time tracking of wavelength variations as light propagates through the optical fiber. The Bragg wavelength (λ_B), defined as ${\lambda }_B=2n_{eff}\Lambda$, where n_eff is the effective refractive index, and Λ is the Bragg grating period, represents the characteristic reflection wavelength of FBG. Variations in temperature, hydraulic pressure, or mechanical strain surrounding the FBG sensor alter n_eff and/or Λ, resulting in a shift in the reflected wavelength. In turn, the stress (σ) in the positive electrode can be directly calculated using the simplified version of Hooke’s Law Eq. (3)^42,43:

$$\sigma =\frac{{\mathrm{\Delta }\lambda }_B}{{\lambda }_{B,0}}\times \frac{1}{0.8}\times 69.9GPa$$ 3

where λ_B,0 is the initial Bragg wavelength and Δλ_B is the change in Bragg wavelength. The evolution of Zn²⁺ induced strain during galvanostatic charge/discharge cycling is illustrated in Fig. 4b–d. In pristine VOPO₄, the strains arise from multiple factors during Zn²⁺ insertion/extraction cycling, including volume fluctuations, phase transitions, and parasitic side reactions at the positive electrode. These collectively result in a substantial increase in residual strain (σ_residual) from an initial 0 MPa to 6.81 MPa (Fig. 4b). A 2D stack view of the reflected spectra obtained from the FBG sensor positioned at the positive electrode/electrolyte interface (Fig. 4c) is presented in chronological order from bottom to top, with the initial λ_B denoted as λ_B,0. Each recorded spectrum exhibits a single Bragg reflection peak. During the charging process, the λ_B peak progressively shifts to longer wavelengths (rightward), whereas during discharge, it shifts back to shorter wavelengths (leftward). Notably, with continued cycling, a gradual overall leftward drift of the λ_B peak is observed, indicating deviation from the expected linear trend. This drift is likely attributed to lattice structural instability, which hinders Zn²⁺ diffusion and results in stress accumulation. Comparative stress evolution in different transition metal substituted VOPO₄ (M = Mn, Fe, Co, Nb, Mo, Ta, W) (Supplementary Fig. S29 and Supplementary Table S4) reveals distinct behaviors. In Fe- and Co-substituted systems, elongated c-axis M − O bonds enhance interlayer coupling, but the resulting rigid lattices cannot accommodate volume changes through slip, producing excessive local stress and particle fragmentation, particularly in Co-VOPO₄, σ_residual = 7.93 MPa. In contrast, Nb-, Mo-, Ta-, and W-substituted compounds exhibit strong d-orbital localization and poor intra-layer electron transport, weakening interlayer cohesion and causing morphological instability. These structures disintegrate upon cycling, generating high internal friction and large residual stresses (8.27 MPa in W-VOPO₄). By comparison, ions with similar radii to vanadium (Mn) have a similar coordination structure. Meanwhile, the highly electronegative Mn shortens c-axis M − O bonds, weakens interlayer electrostatic interactions, and facilitates interlayer slip that dissipates stress during Zn²⁺ (de)insertion. Consequently, the σ‘_residual increases by only 0.46 MPa after 13 cycles. The 2D stacked reflection spectra (Fig. 4e) show consistent cyclic right-left oscillations, demonstrating that Mn-induced electronic reconfiguration and lattice anisotropy effectively accommodate cyclic stress fluctuations, ensuring lattice reversibility.

Fig. 4. Dynamic stress evolution mechanism.

a Schematic diagram of the integration of an FBG into a lab-made Swagelok cell and the principle of an FBG optical sensor. b Time-resolved voltage profile (top) and internal cycling strain Δσ (bottom) evolution from the FBG sensor of Zn | |VOPO₄ at 0.5 A g⁻¹. c 2D stack-view of the reflected spectra given by the FBG sensor located at the positive electrode/electrolyte interface for the cycles shown in (b). d, e Analogous plots to (b, c), for a cell with the FBG sensor embedded within the Zn | |2%Mn-VOPO₄ electrode. f, g The charge-discharge curves and simultaneous stress response analysis were conducted for the initial two cycles of Zn | |VOPO₄ and Zn | |2%Mn-VOPO₄ cells at 0.5 A g⁻¹. h, i Comparison of the first cycle dQ/dV plots (top) and the strain Δσ evolution of the FBG sensors located above the corresponding electrodes (bottom) of Zn | |VOPO₄ and Zn | |2%Mn-VOPO₄ cells. Source data for Fig. 4b–i is provided as a Source Data file.

During the first charging process (Fig. 4f), Zn²⁺ is initially extracted in an orderly manner from the edge insertion sites of VOPO₄ within the voltage range of 0.50 V − 1.19 V. This stage features unrestricted Zn²⁺ migration pathways and minor interlayer expansion, where elastic deformation dominates, resulting in a steady increase in strain (σ₁). As the voltage increases to 1.53 V, Zn²⁺ migration enters a diffusion-controlled regime since the internal Zn²⁺ undergoes an increased ion transfer distance and sluggish kinetics. The intrinsic structural rigidity of VOPO₄ causes anisotropic lattice expansion, and in combination with the strong electrostatic interactions between Zn²⁺ and VO₆ units, it gives rise to localized structural rupture, PO₄³⁻ leaching, or potential phase transitions. These structural disruptions further exacerbate Zn²⁺ migration disorder, enhance electrolyte infiltration and promote rapid volumetric expansion, collectively intensifying strain accumulation and contributing to a pronounced rinse in strain (σ₂)⁴⁴. Upon increasing the voltage to 1.80 V, the remaining Zn²⁺ continues to be extracted from VOPO₄ crystallites, which approaches a new equilibrium state, and strain (σ₃) steadily increases. When the electric field reversed, Zn²⁺ ions are preferentially reinserted into the interlayer in a controlled manner within the voltage window of 1.80 V to 1.23 V, primarily governed by surface active sites. This process induces an alight contraction of the interlayer spacing. However, the structure does not fully recover its elastic deformation, resulting in residual strain (σ₄). As the voltage drops to 0.88 V, saturation of surface sites drives Zn²⁺ to diffuse into the bulk, which may induce interlayer sliding and local structural contraction along the c-axis limited migration pathways, lead to a sharp reduction in strain (σ₅). As the voltage approaching 0.50 V, Zn²⁺ continues to intercalate, whereas previously inserted Zn²⁺ forms a physical shielding layer that suppresses further insertion. This coordinated intercalation behavior of Zn²⁺ a gradual decline in strain (σ₆)⁴⁵.

In the case of 2% Mn-VOPO₄, a rapid increasing σ‘₂ strain is observed during the first charging process within the voltage range of 0.50 V − 1.43 V (Fig. 4g). This behavior is assigned to the distinct Mn−O − P − O − V delocalized framework and anisotropic lattice induced percolation channel, which accelerates fast and orderly Zn²⁺ extraction, promotes efficient intra-layer stress dispersion, suppress the structural degradation and enables controlled volumetric expansion. Even under diffusion limited Zn²⁺ extraction from deep lattice sites at 1.80 V, the σ‘₃ strain remains steadily increase since the robust lattice network of Mn-VOPO₄. Upon discharging, the reduced c-axis M − O bond and interconnected percolation channel enable low diffusion barriers, achieving efficient Zn²⁺ reinsertion with minimal interlayer contraction over 1.80 V − 1.30 V and a gradual, smooth evolution in σ‘₄ strain. With the voltage further decreasing to 0.50 V, the elastic lattice continues to accommodate Zn²⁺ intercalation from both surface and bulk regions, leading to further gradual σ‘₅ strain reduction.

To elucidate stress evolution across different voltage plateaus during cycling, the differential capacity (dQ/dV) curves and corresponding strain (Δσ) profiles for the first cycle of the Zn | |VOPO₄ cell were analyzed in parallel (Fig. 4h). Combined with in situ XRD analysis (Fig. 3i, j), the variations in the (001) and (220) lattice spacings were monitored to quantitatively evaluate the evolution of the a/b- and c-axis parameters, thereby revealing the underlying mechanism of strain generation during charge and discharge. During charging, Zn²⁺ ions were extracted from the interlayers of VOPO₄, disrupting the electrostatic stabilization originally provided by interlayer Zn²⁺ and leading to structural expansion. Concurrently, vanadium underwent gradual oxidation. In Stage I, V³⁺ is oxidized to V⁴⁺, causing contraction of the VO₆ octahedra. Simultaneously, the removal of Zn²⁺ exerts tensile stress on the apical oxygen atoms, resulting in an almost unchanged a/b-axis spacing (0.233 nm) while the c-axis expands to 0.666 nm. The combined effect of the lattice evolution along the a/b axis and the c axis leads to a steady increase in strain (σ₁). At stage II, further oxidation of V⁴⁺ to V⁵⁺ induced continued VO₆ contraction, with the a/b-axis stretching to 0.234 nm and the c-axis to 0.667 nm, producing a moderate and continuous strain increase (σ₂). In Stage III, PO₄³⁻ induced the redox potential of vanadium, accelerating the conversion of residual V³⁺ to V⁴⁺. The a/b-axis remained at 0.234 nm, whereas the c-axis abruptly expanded to 0.672 nm, likely due to local structural adjustments of the PO₄³⁻ groups, resulting in a drastic change in the c lattice parameters. Meanwhile, slow Zn²⁺ diffusion combined with the intrinsic rigidity of VOPO₄ caused anisotropic lattice expansion and strong Zn²⁺−O electrostatic interactions, which triggered local collapse, microcrack formation, and partial PO₄³⁻ dissolution. These structural degradations increased the Zn²⁺ migration barrier, enhanced electrolyte infiltration, and promoted rapid volume expansion, leading to a sharp strain rise (σ₃). In Stage IV, deep Zn extraction occurred with concurrent oxidation of V⁴⁺ to V⁵⁺ and progressive PO₄³⁻ dissolution, the transformation of VOPO₄ to the amorphous VO_x phase. The a/b- and c-axis expanded to 0.235 and 0.674 nm, respectively, though the expansion rate slowed, indicating structural stabilization. Continuous Zn²⁺ extraction from microcrystalline domains caused a gradual strain increase (σ₄). During discharge, Zn²⁺ reinsertion established electrostatic interactions with the apical oxygens of VO₆ units, inducing structural contraction and progressive vanadium reduction. In Stage V, Zn²⁺ insertion initially occurred at surface sites, where PO₄³⁻ induced reduction of V⁵⁺ to V⁴⁺ caused a slight a/b-axis contraction (0.236 → 0.235 nm), while the c-axis remained at 0.675 nm. This is due to the structural defects and microcracks formed at the end of charging, which hinder the initial insertion of Zn²⁺ at the defect sites, resulting in a temporary accumulation of strain and a slow increase in strain (σ₅). In Stage VI, PO₄³⁻ induced reduction of V⁴⁺ to V³⁺ led to further contraction (a/b = 0.234 nm, c = 0.671 nm). As surface sites became saturated, Zn²⁺ diffusion into the bulk increased, and the enhanced interlayer electrostatic attraction caused rapid contraction along the c-axis pathway, yielding a sharp strain decrease (σ₆). In Stages VII and VIII, sequential reduction of V⁵⁺ → V⁴⁺ → V³⁺ further contracted both axes, with the a/b-axis shrinking to 0.232 nm and the c-axis shrinking to 0.663 nm. At this stage, interstitial Zn²⁺ saturation formed a physical shielding layer that inhibited further contraction. Simultaneously, PO₄³⁻ dissolution weakened lattice rigidity, and the contraction efficiency of strains (σ₇) and (σ₈) decreases. After full discharge, neither lattice parameter returned to its original value, due to irreversible phase change, PO₄³⁻ dissolution, and associated structural fractures, which generated σ_residual.

In contrast, the Zn | |2% Mn-VOPO₄ battery exhibited a distinct strain profile (Figs. 4i, 3k, l). In Stage I, strain (σ‘₁) increased slowly, as the oxidation of V³⁺ → V⁴⁺ contracted the VO₆ octahedra, but the stable Mn framework counteracts the octahedral contraction under the tensile effect of the released Zn²⁺, resulting in an increase in the a/b-axis from 0.235 nm to 0.236 nm. At the same time, the free removal of edge Zn²⁺ leads to an increase in the c-axis from 0.685 nm to 0.686 nm. This was attributed to the initial lattice expansion induced by Mn substitution, providing more space for ion migration. The Mn−O − P − O − V delocalized network buffered local stress, resulting in mild strain growth. In Stage II, V⁴⁺ → V⁵⁺ oxidation dominated, causing VO₆ contraction and a/b-axis reduction to 0.235 nm. Simultaneously, Mn-induced shortening of the c-axis M–O bonds weakened interlayer coupling, promoting ordered Zn²⁺ extraction and moderate c-axis expansion to 0.690 nm. This is because the anisotropy induced by Mn causes the lattice of the a/b-axis to contract and the lattice of the c-axis to expand to reach a balance, inhibiting structural degradation and achieving controlled volume expansion, yielding a stable strain increase (σ‘₂). In Stage III, Mn mediated PO₄³⁻ induces the rapid oxidation of V³⁺ → V⁴⁺, slightly increasing the a/b-axis (0.236 nm) and expanding the c-axis to 0.698 nm, resulting in a significant increase in the strain (σ‘₃). Despite transient lattice reorganization, the presence of anisotropy induced dislocations and diffusion channels effectively released local stress, preventing microcrack formation. In Stage IV, PO₄³⁻ assisted oxidation of V⁴⁺ → V⁵⁺ expanded the a/b- and c-axes to 0.240 and 0.717 nm, respectively. The stable Mn−O − P − O − V delocalized lattice structure, the uniform stress distribution induced by anisotropic lattice, and the infiltration channels guiding the orderly exodus of internal Zn²⁺ prevent local collapse, resulting in a stable increase in strain (σ‘₄). During discharge, Zn²⁺ reinsertion into the Mn-VOPO₄ lattice established electrostatic interactions with VO₆, accompanied by gradual V reduction. In Stage V, Zn²⁺ occupation of surface sites (V⁵⁺ → V⁴⁺) caused minor contractions (a/b = 0.239 nm, c = 0.710 nm). The shortened c-axis bonds, resilient Mn−O − P − O − V framework, and interconnected percolation channels enabled low barrier Zn²⁺ insertion and balanced octahedral contraction, keeping σ‘₅ nearly constant. In Stage VI, V⁴⁺ → V³⁺ reduction and rapid Zn²⁺ diffusion through percolation channels caused uniform contraction (a/b = 0.238 nm, c = 0.699 nm) and a sharp strain drop (σ‘₆). In Stages VII and VIII, further reduction of V⁵⁺ → V⁴⁺ → V³⁺. The stable localized structure formed flow channels, and the uniform stress distribution induced by the anisotropic lattice facilitates the free and orderly embedding of Zn²⁺ deep within the phase, allowing for the accommodation of more Zn²⁺, causing the a/b-axis and c-axis lattices to continuously contract and return to their initial positions (0.235 nm, 0.685 nm). The strains (σ‘₇) and (σ‘₈) continue to decrease, approaching the reversible state. The Mn substitution effectively inhibited PO₄³⁻ dissolution and suppressed irreversible phase transitions. The shortened c-axis bonds reduced Zn²⁺−O electrostatic interactions, while the combined effects of dislocations and anisotropic stress distribution promoted stress redistribution and buffering, and realized the highly reversible strain during the Zn²⁺ storage process. Consequently, the σ‘_residual increased to only 0.46 MP after 13 cycles, showing only a minor change and revealing the reversible structural evolution stage of Zn²⁺ insertion/extraction. These findings confirm that Mn-induced lattice stress regulation effectively harmonizes electrochemical and mechanical processes, enhancing positive electrode durability, mitigating structural degradation, and providing direct in situ evidence for the dynamic coupling between mechanical strain and Zn²⁺ storage in layered positive electrode materials.

Stable Mn-VOPO₄ positive electrode: the strengthening effect on driving Zn²⁺ storage

The electrochemical properties of the proposed Mn-VOPO₄ positive electrode are evaluated in Zn(OTF)₂ + triethyl phosphate electrolyte. As shown in Fig. 5a, Supplementary Fig S30, and Supplementary Table S4, substitution with Fe and Co induced c-axis lattice contraction, narrowing Zn²⁺ migration channels and impeding ion diffusion, leading to rate retentions of 51.4% and 36.3%, respectively. Nb, Mo, Ta, and W are characterized by strongly localized d electrons and hindered charge transfer. Despite preserved morphology, these materials exhibited sluggish kinetics and poor rate performance, with W-VOPO₄ retaining only 26.8% of its specific capacity. In contrast, Mn substitution, owing to its high electronegativity, facilitated rapid planar electron transitions, markedly reducing internal charge transfer resistance and delivering fast kinetics (66.3%). Upon returning the current density to 0.1 A g⁻¹, 2% Mn-VOPO₄ recovered a discharge specific capacity of 250 mAh g⁻¹, nearly matching the initial value, demonstrating rate reversibility and achieving a high energy density of 325 Wh kg⁻¹. Under long-term cycling at 1.0 A g⁻¹ for 2000 cycles (Fig. 5b, Supplementary Fig. S31, and Supplementary Table S4), VOPO₄ substituted with Fe, Co, Nb, Mo, Ta, or W experienced small lattice spacings and high residual stress accumulation. This mechanical strain caused repeated structural fatigue, crack propagation, and particle fragmentation, significantly reducing capacity retention (W-VOPO₄ only 14.9%). Although Fe-VOPO₄ displayed slightly improved stability, it still exhibited considerable stress (4.53 MPa) and limited rate capability. In contrast, 2% Mn substitution shortened the c-axis M − O bond, inducing controlled lattice distortion, uniform stress distribution, and permeation channels that facilitated efficient Zn²⁺ transport. Concurrently, local charge compensation formed a Mn−O − P − O − V delocalized structure, suppressing PO₄³⁻ dissolution and preserving structural integrity, resulting in a high specific capacity of 258 mAh g⁻¹, 91.0% capacity retention, and an energy density of 273 Wh kg⁻¹. Thus, Mn substitution in 2% Mn-VOPO₄ introduces controlled intra-layer anisotropy and stabilizes the Mn−O − P − O − V delocalized electronic structure. This reconfiguration promotes lattice distortion mediated permeation channels and uniform stress distribution, accelerating Zn²⁺ transport kinetics while mitigating cycling-induced degradation. The combination of open ionic channels, fast electron conduction, and structural toughness, enabled by Mn’s electronegativity and compatible ionic radius, coordinates lattice and electronic reconstruction, ensuring stable Zn²⁺ storage. In contrast, the pristine VOPO₄ discloses a relevant low specific capacity of 87.9 mAh g⁻¹ at 1.0 A g⁻¹, while 49.6% capacity retention is sustained primarily due to notorious structural degradation and positive electrode material loss. Notably, excessive Mn incorporation in 5% Mn-VOPO₄ decreases the density of electrochemically active sites and disrupts the redox activity of vanadium. Incidental pulverization induces exorbitant lattice distortion and heterogeneous interfacial stress, collectively compromising overall electrochemical performance, yielding only marginal improvement over the pristine VOPO₄¹⁶. To further assess the proximity of the experimental capacity to the theoretical limit, peak deconvolution and integration of the V 2p XPS spectra were conducted for 2% Mn-VOPO₄ in the fully charged and fully discharged states after 1000 cycles at 1 A g⁻¹ (Supplementary Fig. S32 and Supplementary Table S5). In the fully charged state, V⁵⁺ and V⁴⁺ account for 63.78% and 36.22%, respectively, corresponding to an average oxidation state of + 4.6. In the fully discharged state, V³⁺ (85.67%) and V⁴⁺ (14.33%) dominate, yielding an average oxidation state of + 3.1. These results indicate that each vanadium atom participates in the transfer of approximately 1.5 electrons during electrochemical cycling. Using the theoretical capacity expression $C=nF/\left(3.6M\right)$(mAh g⁻¹), where n is the number of transferred electrons, F is the Faraday constant (96,485 C mol⁻¹), and M is the molar mass (g mol⁻¹), the theoretical capacity contributed by vanadium is calculated to be 203.0 mAh g⁻¹. When the additional, minor contribution from manganese redox activity is included (Supplementary Fig. S15d), the total calculated capacity closely matches the experimentally measured value of 208.3 mAh g⁻¹, indicating near-theoretical utilization of the redox-active species. This efficient electron transfer and the good agreement between theoretical and experimental capacities originate from the redistribution of π electrons within the Mn−O − P − O − V delocalized framework. Such delocalization strengthens the covalent anchoring of PO₄³⁻ tetrahedra, promotes uniform charge distribution, and facilitates rapid electronic compensation during cycling. Consequently, the vanadium centers reversibly participate in 1.5 electron redox processes while enabling reversible lattice adjustment during Zn²⁺ deintercalation, thereby allowing the electrode to achieve capacities approaching its theoretical limit. ICP-OES analysis of electrolyte samples after 1000 cycles at 1 A g⁻¹ (Supplementary Table S6) revealed that pristine VOPO₄ suffered significant V dissolution (28.2 mg L⁻¹) due to PO₄³⁻ loss, resulting in 49.6% capacity retention after 2000 cycles. In contrast, 2% Mn-VOPO₄ limited V dissolution to 2.57 mg L⁻¹ and Mn loss to 0.06 mg L⁻¹, preserving 91.0% capacity retention. Therefore, the impact of minor Mn loss on capacity decay was negligible. Meanwhile, we prepared thin layer VOPO₄ (Supplementary Fig. S33) as a comparison⁴. Thin-layer VOPO₄ increased specific surface area and active sites, slightly enhancing specific capacity (124 mAh g⁻¹) but remaining far below that of 2% Mn-VOPO₄ (223.3 mAh g⁻¹). The distinguished capacity of 2% Mn-VOPO₄ arises from minor lattice distortion at active sites, shortened c-axis M − O bonds, and the Mn−O − P − O − V delocalized framework, enabling deeper and more orderly Zn²⁺ insertion while balancing internal stress. Additionally, the capacity of 2% Mn-VOPO₄ in the thin layer after 2000 cycles was 36.8%, indicating that the fragile VOPO₄ was more prone to delamination and structural degradation upon cycling. To evaluate the suppression of voltage and capacity decay achieved by Mn substitution, long-term cycling tests were performed on 2% Mn-VOPO₄ at a current density of 0.1 A g⁻¹. The charge–discharge profiles collected over different cycles (Fig. 5c and Supplementary Table S7) show that the primary voltage plateau remains highly stable over 200 cycles, with a voltage shift of less than 0.02 V. This behavior clearly demonstrates that Mn substitution effectively suppresses voltage decay. Consistently, the corresponding dQ/dV curves (Supplementary Fig. S34) from the 2nd to the 20th cycle exhibit only a slight attenuation of the PO₄³⁻ induced high-voltage peak, with its capacity contribution maintained between approximately 45% and 63%. Even by the 200th cycle, changes are negligible, and the high-voltage peak remains dominant, delivering a total specific capacity of 256.3 mAh g⁻¹ with a capacity retention of 102%. In stark contrast, pristine VOPO₄ exhibits complete disappearance of the high-voltage redox peak between the 2nd and 100th cycles, accompanied by a rapid decline in its capacity contribution from 70% to 22%. Consequently, the electrochemical response becomes dominated by low-voltage redox processes, leading to pronounced capacity fading, with only 73% of the initial capacity retained after 200 cycles. The high cycling stability of 2% Mn-VOPO₄ originates from Mn-substitution-induced lattice anisotropy and the formation of a stable Mn–O–P–O–V delocalized electronic structure. This framework enables efficient sharing and redistribution of π-symmetric electrons throughout the polyanionic network, significantly enhancing the covalent integrity of the PO₄³⁻ tetrahedra and strengthening their conjugation with adjacent VO_x octahedra. Consequently, the phosphate groups are firmly anchored within the lattice, ensuring that the high-voltage contribution remains dominant in the overall capacity while effectively suppressing PO₄³⁻ dissolution during repeated Zn²⁺ extraction/insertion cycles. These synergistic effects markedly enhance the structural stability of the layered polyanionic framework and mitigate intrinsic voltage and capacity decay. The dQ/dV curves of (Fig. 5d) Mn-VOPO₄ demonstrate consistent redox peaks corresponding to vanadium’s multivalent transitions, like those observed in pristine VOPO₄. One oxidation peak gradually shifts from 1.31 V to 1.33 V with increasing Mn content, which derives from the incorporation of Mn weakens the V − O bonds within the VO₆ octahedra, hence intensifying the interaction with PO₄ tetrahedra through a strengthened inductive effect. This enhanced inductive interaction stabilizes the Mn-VOPO₄ frameworks and modulates its redox behavior. Further electrochemical impedance spectroscopy (EIS) analysis (Supplementary Fig. S35 and Supplementary Table S8) revealed that 2% Mn-VOPO₄ exhibits the smallest semicircle and the steepest slope, indicating an enhanced charge transfer process. This improvement can be attributed to the high electronegativity of Mn, which induces electronic redistribution and promotes the formation of a Mn−O − P − O − V delocalized electronic structure. Such a structure facilitates interfacial charge transfer and increases the effective specific surface area, thereby enhancing Zn²⁺ desolvation and accelerating ion/electron transport across the interface. To assess the long-term stability, post-cycling EIS measurements after 1000 cycles at 1 A g⁻¹ (Supplementary Fig. S36 and Supplementary Table S9) showed that the Rct of 2% Mn-VOPO₄ remained as low as 29 Ω. This low resistance results from the Mn−O − P − O − V delocalized electronic structure, the formation of anisotropic electron/ion transport pathways, and weakened interlayer interactions that enable adaptive layer sliding. These features mitigate lattice pulverization and maintain low impedance. In addition, the reduced Zn²⁺ occupancy lowers vacancy defect concentrations, enhances interfacial contact, increases the exchange current density, and further suppresses impedance growth. In contrast, the pristine VOPO₄ electrode exhibited a substantial increase in Rct to 475 Ω after cycling, owing to its fragile lattice structure. The repeated volume expansion and contraction during Zn²⁺ insertion/extraction generate internal stress, leading to particle fracture, disruption of the continuous electronic conduction network, and a pronounced increase in impedance.

Fig. 5. Electrochemical characteristics in AZIBs.

Comparison of (a) rate performance and (b) long-term cycle performance at 1.0 A g⁻¹ of the (i) VOPO₄, (ii) 1%Mn-VOPO₄, (iii) 2%Mn-VOPO₄, and (iv) 5%Mn-VOPO₄ in 3 M Zn(OTF)₂ (containing 5% triethyl phosphate) electrolyte, respectively. c Galvanostatic charge/discharge curves of 2%Mn-VOPO₄ at 0.1 A g⁻¹. d dQ/dV curves of the (i) VOPO₄, (ii) 1%Mn-VOPO₄, (iii) 2%Mn-VOPO₄, and (iv) 5%Mn-VOPO₄ at 2nd cycle. e The relationship curves of log (i, current density) and log (v, scan rate) in CV at scan rate of 0.1 − 100 mV s⁻¹, f The relationship between normalized capacity and v^−1/2. g GITT curves at 0.05 A g⁻¹ of 5 min and a relaxation time of 30 min. h Calculated Zn²⁺ diffusion coefficient in (i) VOPO₄, (ii) 1%Mn-VOPO₄, (iii) 2%Mn-VOPO₄, and (iv) 5%Mn-VOPO₄, respectively. Source data for Fig. 5a–d and Fig. 5g, h are provided as a Source Data file.

To probe the Zn storage mechanism, a kinetic analysis based on cyclic voltammetry measurements was carried out. The relationship between peak current (i) and scan rate (v) was examined using the equation ${i=av}^b$, where a, b are adjustable parameters. A b value of 0.5 indicates a diffusion-controlled process, while the one of 1 represents a surface controlled electric field driven (capacitive) process. The fitting results of log(i) versus log(v) (Fig. 5e and Supplementary Fig. S37–40) reveal a linear correlation, yielding b values of 0.91/0.81, 0.96/0.93, 1.00/0.99 and 0.93/0.88 for VOPO₄, 1% Mn-VOPO₄, 2% Mn-VOPO₄, 5% Mn-VOPO₄, respectively (Supplementary Table S10), indicating Zn²⁺ transport throughout insertion/extraction in these positive electrodes is predominantly governed by capacitive processes. Also, at a high scan rate of 10 mV s⁻¹ (Supplementary Fig. S41), the b values remain above 1.00/0.89, demonstrating that its electrochemical performance enhancement is not merely a result of increased surface area. To quantify the respective contributions of diffusion and capacitive controlled processes, the current response i was deconvoluted according to $i=k_{1}v+k_2{v}^{1/2}$. At a scan rate of 2 mV s⁻¹, the capacitive contribution for 2% Mn-VOPO₄ is calculated to be approximately 64%. This capacitive dominated Zn²⁺ storage mechanism implies a pseudocapacitive insertion/extraction process with negligible phase transformation or structural degradation. The rate-limiting step in this Zn²⁺ storage mechanism is elucidated through plotting the relationship between capacity (Q) and scan rate (v) over a range of 0.1 to 100 mV s⁻¹ (Fig. 5f). In Region I (v < 10 mV s⁻¹), the capacity remains largely invariant with respect to scan rate, confirming that capacitive control dominates the kinetics at lower scan rates. Conversely, in Region II (10 < v < 100 mV s⁻¹), the capacity decreases linearly with v^−1/2, indicating that the Zn²⁺ storage process becomes increasingly diffusion-limited at higher scan rates. The linear dependence in this regime reflects a capacity limitation governed by semi-infinite linear diffusion, whereas capacitive contributions remain scan rate independent. The pseudocapacitive dominated nature of the electrochemical process accounts for the fast Zn²⁺ storage kinetics in 2% Mn-VOPO₄. Furthermore, the anodic and cathodic peaks exhibit minimal potential separation (< 0.1 V) at scan rates below 2 mV s⁻¹ (Supplementary Fig. S42), indicative of rapid charge transfer and high-rate capability. These findings underpin the distinguished rate performance and long-term cycling stability of the 2% Mn-VOPO₄ positive electrode, desired for efficient energy storage applications. Additional galvanostatic intermittent titration technique is used to further monitor the Zn²⁺ migration behaviors (Fig. 5g). The Zn²⁺ diffusion coefficient in 2% Mn-VOPO₄ is calculated to be 2.63 × 10⁻⁹ cm² s⁻¹, which is nearly four orders of magnitude higher than that of pristine VOPO₄ (9.20 × 10⁻¹³ cm² s⁻¹) (Fig. 5h). This substantial enhancement reaffirms that incorporating Mn facilitates efficient Zn²⁺ transport, primarily by inducing lattice twisted percolation channels. Such structural tuning migrates the electrostatic interaction between Zn²⁺ and lattice oxygen, resulting in an enlarged two-dimensional interlayer pathway that enhances both ion accessibility and diffusion kinetics⁴⁶. These findings demonstrate that moderate Mn incorporation not only optimizes the lattice framework and electronic conductivity but also improves structural reversibility, mechanical stability, and Zn²⁺ storage/migration efficiency. Comparison of key electrochemical parameters (voltage, capacity, rate performance, and cycle life) of 2% Mn-VOPO₄ with leading vanadium-based materials (Supplementary Table S11) shows its significant competitive advantage. While materials such as diethylene glycol VOPO₄⁴⁷, V₂O₅·pyridine⁴⁸, VO polymers⁴⁹, V₂O_4.85⁵⁰, and Zn₂V₂O₇⁵¹ exhibit comparable voltages, their inherently fragile lattices and associated stress limit rate and cycling stability. In contrast, 2% Mn-VOPO₄ combines a Mn−O − P − O − V delocalized electronic structure with anisotropic stress regulation, delivering high specific capacity, rate capability, and cycle life, achieving an energy density of 325 Wh kg⁻¹ at 0.1 A g⁻¹. This structural and electrochemical advantage underscores the potential of 2% Mn-VOPO₄ for grid-scale energy storage applications.

Robust lattice structure and electrode integrity under operating condition

The VOPO₄ degradation processes was investigated, and samples with varying Mn content were immersed in 3 M Zn(OTF)₂ for 48 hours. Static observations (Supplementary Fig. S43) revealed a color transition of pristine VOPO₄ from green to orange, accompanied by yellowing of the solution. As Mn content increases, the samples retain their original color more effectively, and the solution become increasingly clearer. This visual change verifies that Mn incorporation strengthens the structural stability during Zn²⁺ exposure in the electrolyte. To further gain insight into the structural evolution after electrochemical cycling, post-mortem characterization was conducted on the positive electrode after 500 cycles of Zn²⁺ insertion/extraction. The VOPO₄ holds a two-dimensional morphology with extensive fragmentation (Fig. 6a). High-resolution TEM images demonstrate severe lattice distortion and closure of the percolation channels (Fig. 6b), which hinders Zn²⁺ intercalation. Elemental mapping detects only trace Zn²⁺ signals (Supplementary Fig. S44), corroborating the hypothesis that PO₄³⁻ leaching leads to structural collapse. In contrast, the 2% Mn-VOPO₄ retains its intact polycrystalline morphology and well-defined anisotropic percolation channels with preserved lattice striations (Fig. 6c, d and Supplementary Fig. S45), evidencing a robust structural integrity under rigorous electrochemical test.

Fig. 6. Analysis of lattice structure and electrode integrity.

TEM and HRTEM images of (a, b) VOPO₄, (c, d) 2% Mn-VOPO₄ after 500 cycles. X-ray 3D nano CT images of (e, f) VOPO₄, and (h, i) 2% Mn-VOPO₄ positive electrode before and after cycling. Ratio of void features on (g) VOPO₄ and (j) 2% Mn-VOPO₄ positive electrode. k Galvanostatic charge/discharge curves of the pouch cells with 2% Mn-VOPO₄ positive electrode under different bending states (normal, 45°, 90°, 135°, and 180°). l Long-term cycle performance of VOPO₄ and 2% Mn-VOPO₄ pouch cells at 1 A g⁻¹. The insert shows the pouch cell device. m Schematic illustration of the structural degradation and storage mechanisms of VOPO₄ and 2% Mn-VOPO₄ during cycling. Source data for Fig. 6g, j, and k, l is provided as a Source Data file.

Non-destructive X-ray nano-computed tomography (X-ray nano-CT) was then employed to in situ visualize the evolution of morphological features in three-dimensional space, and the pore characteristics of the positive electrode were analyzed. Given the varying x-ray attenuation coefficients of different elements, the reconstructed contrast images enable the precise identification of distinct phase species within the positive electrode. After cycling, pristine VOPO₄ positive electrode displays prominent red void regions, indicative of progressive structural dissolution and active material loss (Fig. 6e, f). The particle size of VOPO₄ is significantly reduced due to pulverization, which arises from cycling induced stress concentration and structural degradation. Quantitative analysis revealed an increase in void ratio from 22.2% to 35.8%, accompanied by a significant reduction in the concentration of active material from 47.8% to 24.1% (Fig. 6g). On the other hand, negligible changes in both void regions and particle sizes after cycling can be noticed in the 2% Mn-VOPO₄ (Fig. 6h, i), with only a slight increase in porosity from 20.5% to 21.9% (Fig. 6j), proving again the structural robustness and integrity of the Mn-VOPO₄ framework. The practical applicability of the positive electrode was further assessed in pouch cells (Fig. 6l). The pristine Zn | |VOPO₄ cell retained only 39.6% of its initial capacity after 500 cycles, whereas the Zn | |2%Mn-VOPO₄ cell maintained 94.6% under identical conditions. Increasing the loading to 10 mg cm⁻² (Supplementary Fig. S46) exacerbated performance degradation in pristine VOPO₄, yielding only 24.4% capacity retention at 1 A g⁻¹ after 500 cycles. In contrast, the Mn−O − P − O − V delocalized structure in 2% Mn-VOPO₄ mitigated mechanical stress and suppressed dissolution, preserving 80.5% of capacity, highlighting its promise for practical energy storage applications. Moreover, charge/discharge profiles recorded under bending angles (0°, 45°, 90°, 135°, and 180°) showed negligible variation. Two flexible pouch cells connected in series could stably power a red LED (1.2–2.2 V, Supplementary Fig. S47). These underscore the mechanical flexibility of the Mn-VOPO₄ positive electrode, and importantly, provide supplementary proof that its structural features effectively accommodate mechanical deformation, including lattice strain and cycling stress, thereby preserving electrochemical stability under dynamic conditions. Furthermore, a schematic illustration of the degradation pathway and Zn²⁺ storage mechanisms is proposed (Fig. 6m). The pristine VOPO₄ undergoes volume contraction upon Zn²⁺ insertion, ascribing to the strong electrostatic interaction of Zn²⁺ and lattice oxygen within VO₆. This interaction in turn tend to disrupt the connectivity of VO₆ and PO₄ units during Zn²⁺ extraction, leading to the dissolution of PO₄³⁻ into the electrolyte. While Mn incorporation shortens the c-axis M − O bonds within MO₆ octahedra, hence weakening the Zn²⁺−O electrostatic interactions, and a stable Mn−O − P − O − V network enhances electron delocalization and strengthens the coupling between MO₆ and PO₄ units. In addition, the subtly lattice distortion introduces efficient percolation pathways and homogenizes lattice stress, which facilitate Zn²⁺ diffusion kinetics and mitigate cycling induced strain, all in concert suppressing the structural degradation, alleviating the deformation stress, and improving both the electrochemical reversibility and mechanical stability of the material⁴¹.

In summary, this study proposes a partial metal substitution strategy to enhance the structural integrity, electrochemical reversibility, and mechanical flexibility of VOPO₄ positive electrodes in aqueous zinc ion batteries. As a typical example, the introduction of Mn induces controlled intra-layer anisotropy, leading to the formation of a robust Mn–O–P–O–V delocalized electronic framework. This structural reconfiguration facilitates the development of lattice distorted percolation pathways and homogenized structural stress distribution, thereby accelerating rapid Zn²⁺ transport kinetics and mitigating cycling-induced degradation. Real-time interfacial stress monitoring reveals improved intra-layer (a/b-axis) stress accommodation and c-axis stress relaxation during Zn²⁺ insertion and extraction in Mn-VOPO₄. Comprehensive electrochemical and morphological analyses, including post-mortem TEM, in situ 3D nano-computed tomography and long-term electrochemical cycling tests, confirm the high performance of the 2% Mn-VOPO₄ positive electrode, which retains 91.0% of initial capacity over 2000 cycles and delivers stable output under mechanical deformation while preserving high structural integrity. These findings not only elucidate the fundamental structure–function relationships in layered vanadophosphate systems but also offer a promising pathway toward the rational design of high-performance, flexible zinc ion energy storage devices.

Methods

Synthesis of VOPO₄

VOPO₄ was synthesized using a typical oil-bath reflux method. Briefly, 4.8 g of V₂O₅ (AR, 99.5%, Shanghai Aladdin Biochemical Technology Co., Ltd.), 26.6 mL of H₃PO₄ (AR, 85%, Shanghai Lingfeng Chemical Reagent Co., Ltd.), and 115.4 mL of deionized water (resistivity ≥ 18.2 MΩ·cm; TE-S20 laboratory water purification system, Haitai Instrument Co., Ltd.) were added to a round-bottom flask. The mixture was magnetically stirred for 30 min using a magnetic stirrer (84-1 A, Shanghai Sile Instrument Co., Ltd.) to ensure thorough mixing, and was then heated under reflux in an oil bath (DF-101S, Yuhua Instrument Co., Ltd.) at 115 °C for 20 h. The resulting product was washed three times with acetone (AR, 99.5%, Sinopharm Chemical Reagent Co., Ltd.) and dried in a vacuum oven at 60 °C to obtain a rectangular plate-like VOPO₄.

Synthesis of Mn-substituted VOPO₄ (Mn-VOPO₄)

A series of Mn-substituted VOPO₄ materials with different Mn contents was synthesized using the same procedure, except that 0.09, 0.23, or 0.49 g of Mn(NO₃)₂⋅4H₂O (CP, 98%, Shanghai Macklin Biochemical Co., Ltd.) was added to the precursor mixture. The resulting products were denoted as 2% Mn-VOPO₄, 5% Mn-VOPO₄, and 10% Mn-VOPO₄, respectively.

Material characterizations

The crystal properties of Mn-VOPO₄ were analyzed using X-ray diffraction (XRD, MiniFlex600, Cu Kα radiation, Rigaku Corporation). X-ray photoelectron spectroscopy (XPS, ESCALAB250Xi, Thermo Fisher Scientific) was employed to analyze the electronic delocalization effects in 2% Mn-VOPO₄. Peak calibration was conducted using the standard position of the C 1s peak (284.8 eV). A cold field emission transmission electron microscope (TEM, JEM-F200, 200 kV) was used to examine the morphology of the prepared materials. High-resolution TEM (HRTEM, JEOL JEM-2100F, JEOL Ltd.) was utilized to study the lattice evolution and stress distribution of VOPO₄ and 2% Mn-VOPO₄. High-angle annular dark-field scanning TEM (HAADF-STEM, 200 kV, 1 eV) was used to explore the uniform distribution of elements in the materials. Electron paramagnetic resonance (EPR, Bruker A300, 298 K, 9.85 GHz) spectroscopy was employed to investigate oxygen vacancies. Measure the BET of materials using the TriStar 3020 micro-analyzer. Study the elemental content in the electrolyte after material recycling using inductively coupled plasma optical emission spectroscopy (ICP-OES). Raman spectroscopy (Raman, Leica Microsystems CMS GmbH, Ernst-Leitz-Str in Via, 250 mW, 532 nm) was used to detect chemical bonds and in-plane strain information in the materials. An atomic force microscope (AFM, Dimension Icon, Bruker Corporation) was used to analyze stress distribution in the nanosheet lattice. Hard X-ray (BL17B1, Shanghai Synchrotron Radiation Facility) was used to test V/Mn K-edge X-ray Absorption Fine Structure (XAFS), and soft X-ray (NSRL, BL12B-α, National Synchrotron Radiation Laboratory, Hefei) was used to test V L-edge X-ray Absorption Near Edge Structure (XANES) to evaluate electronic delocalization structure and coordination bond length. XAS data were analyzed using the Athena software package⁵¹. Temperature-dependent magnetization was measured using a SQUID-VSM (H = 1 k Oe) system. The PDF curves for high-energy X-ray (BL13SSW, Shanghai Synchrotron Radiation Facility, Synchrotron Radiation Light Source, CeO₂ specimen, λ = 0.248 Å) total scattering were measured. The sample detector distance and detector tilt angle relative to the incident radiation and polarization direction were corrected using the Fit2D software. Pair distribution function and neutron diffraction spectra were then processed using PDFGetX3 software to extract anisotropic atomic displacement parameters and coordination bond lengths. Single-mode fiber Bragg gratings (FBG, AG-1550-H, Shandong Shenghai Optical Fiber Technology Co., Ltd.) were used to investigate the internal stress distribution and release mechanisms within the material lattice.

Electrochemical measurements

The as-prepared VOPO₄ and Mn-VOPO₄ were used as active materials. The active material, acetylene black (Kejing Zhida Technology Co., Ltd.), and poly(vinylidene fluoride) (PVDF, Kejing Zhida Technology Co., Ltd.) were mixed in N-methyl-2-pyrrolidone (NMP; AR, 99.5%, Shanghai Aladdin Biochemical Technology Co., Ltd.) at a mass ratio of 7:2:1 to form a homogeneous slurry. The slurry was coated onto stainless-steel (99.5%, Wuhu Maotouying Materials Technology Co., Ltd.) or graphene-foil current collectors (99.9%, thickness: 0.1 mm, Qingdao Dongkai Graphite Co., Ltd.) and dried in a vacuum oven (DZF-6050, Shanghai Yiheng Co., Ltd.) at 60 °C for 12 h. The mass loading of the active material was maintained in the range of 1–2 mg cm⁻².

The electrochemical performance of VOPO₄ and Mn-VOPO₄ was evaluated using CR2032 coin cells. The VOPO₄ and Mn-VOPO₄ electrodes (diameter: 1.2 cm) were used as the positive electrodes, Zn foil (99.9%, thickness: 0.05 mm, diameter: 1.2 cm, Qinghe Shenghang Metal Materials Co., Ltd.) was used as the negative electrode, and a glass-fiber membrane (thickness: 0.29 mm, pore size: 1.63 μm, diameter: 1.9 cm, Ouleji New Materials Co., Ltd.) served as the separator. The electrolyte consisted of 100 μL of 3 M Zn(OTF)₂ (AR, 99.5%, Shanghai Aladdin Biochemical Technology Co., Ltd.) or 100 μL of 3 M Zn(OTF)₂ containing 5% triethyl phosphate (TPE; AR, 99.9%, Bide Pharmatech Co., Ltd.).

For pouch cells, PVDF and graphene foil were used as the binder and current collector, respectively. For single-layer pouch cells (3 × 4 cm²), the mass loading of 2% Mn-VOPO₄ was 1 mg cm⁻². A 0.05 mm Zn foil, cleaned with water and ethanol, was used as the negative electrode. The electrolyte consisted of 400 μL of 3 M Zn(OTF)₂ containing 5% TPE. The applied current was 12 mA, corresponding to an areal current density of 1 mA cm⁻². The cell delivered a capacity of 2.5 mAh, corresponding to an areal capacity of 0.21 mAh cm⁻². The N/P ratio was 13.5, and the N/P mass loading ratio was 35.2:1. During testing, clamps were applied at the four corners of the rectangular pouch cell with a load of 30 kg to ensure full contact between the positive and negative electrodes and the separator.

Electrochemical impedance spectroscopy (EIS) measurements were carried out using CR2032 coin cells on an electrochemical workstation (VMP3, Bio-Logic, Wuhan Koster Instrument Co., Ltd.) to investigate the charge-transfer resistance of the Mn-VOPO₄ electrode. The measurements were performed at the open-circuit voltage with a perturbation amplitude of 10 mV over a frequency range from 200 kHz to 10 mHz, using automatic frequency scanning from high to low frequency. All impedance spectra were fitted using equivalent circuits in ZView software, and the fitted curves showed good agreement with the experimental data. The fitting errors are listed numerically in Supplementary Tables S8 and S9.

Cyclic voltammetry (CV) measurements were performed using an electrochemical workstation (VMP3, Bio-Logic, Wuhan Koster Instrument Co., Ltd.) over the voltage range of 0.5–1.8 V at scan rates of 0.1, 0.2, 0.5, 1, 2, 4, 6, 8, 10, 20, 40, 60, 80, and 100 mV s⁻¹ to investigate the reaction mechanism of the Mn-VOPO₄ electrode.

Galvanostatic intermittent titration technique (GITT) measurements were conducted using an electrochemical workstation (LAND-CT3002A, Wuhan LAND Electronics Co., Ltd.) for Mn-VOPO₄ at a specific current of 0.05 A g⁻¹. A constant current was applied for 300 s, followed by a rest period of 1800 s, with one data point recorded every 5 s.

Galvanostatic charge/discharge, rate capability, and long-term cycling tests were also carried out using the LAND-CT3002A system. The Coulombic efficiency was calculated as the ratio of discharge capacity to charge capacity.

All the above electrochemical measurements were performed in a constant-temperature chamber at 25 °C.

DFT calculations

First-principles calculations were performed using the Vienna Ab initio Simulation Package (VASP) within the spin-polarized framework, employing a plane-wave basis set for density functional theory (DFT) calculations^52,53. The exchange-correlation functional was described using the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA)⁵⁴. All calculations employed the DFT + D3 method to account for van der Waals (vdW) interactions. The valence states of all atoms were projected onto a plane-wave basis set with a cutoff energy of 400 eV. A 2 × 2 × 1 k-point grid was used to sample the Brillouin zone. The energy convergence criterion for the self-consistent steps was set at 10⁻⁵eV, and the force threshold for geometric optimization was 0.05 eV/atom⁵⁵. The optimized coordinates for VOPO₄ and 2%Mn-VOPO₄ is provided in Supplementary Data 1.

The climbing image nudged elastic band (CI-NEB) method was employed to evaluate the energy barriers along the Zn²⁺ migration pathway^56,57. During the calculations, all atoms in the intermediate images were relaxed, while the atomic structures of the reactants and products were kept fixed. The reaction free energy (ΔG) was calculated using the following equation:

$$\Delta G=\Delta E\mathrm{–}T\Delta S+\Delta ZPE$$ 4

where ΔG represents the free energy, ΔE is the total energy from the DFT calculations, TΔS is the entropy contribution, and ΔZPE is the zero-point energy.

Supplementary information

Supplementary Information ^{(2.7MB, pdf)}

Peer Review file ^{(2.3MB, pdf)}

41467_2026_74444_MOESM3_ESM.pdf ^{(172.7KB, pdf)}

Description of Additional Supplementary Files

Supplementary Data 1 ^{(19.7KB, pdf)}

Source data

Source Data ^{(21.3MB, zip)}

Author contributions

Z.Y. contributed to Methodology, Validation, Formal analysis, Data Curation, Visualization and Writing - Original Draft. W.Z. contributed to Conceptualization, Formal analysis, Investigation, Writing - Review & Editing, Supervision, Project administration and Funding acquisition. X.C. contributed to Software and Visualization. J.C., B.Z., J.T., Y.H., J.C., and L.T. contributed to Validation and Investigation. J.Z., H.J., and M.A. contributed to Writing - Review & Editing. J.Z. contributed to conceptualization, Supervision, Project administration and Funding acquisition.

Peer review

Peer review information

Nature Communications thanks Jeongin Han and the other anonymous reviewers for their contribution to the peer review of this work. A peer review file is available.

Funding

This work was supported by the Natural Science Foundation of China (Nos. 52125202, 52202100, and U24A2065), the Natural Science Foundation of Jiangsu Province (BK20243016), the National Key R&D Program of China (Grant No. 2024YFB3815301), Fundamental Research Funds for the Central Universities, China Postdoctoral Science Foundation (No. 2024T171166) and Postgraduate Research & Practice Innovation Program of Jiangsu Province (Nos. KYCX25_0720).

Data availability

The data generated in this study are provided in the Supplementary Information/Source Data file. Source data are provided in this paper.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at https://doi.org/10.1038/s41467-026-74444-8.