Synergetic modulation on ionic association and solvation structure by electron-withdrawing effect for aqueous zinc-ion batteries

Significance

Aqueous zinc-ion batteries (ZIBs) possess the advantages of low cost and high safety. However, their Zn anodes are usually confronting with the challenge of side reactions and Zn dendrite formation. Herein, we developed low ionic association electrolytes by introducing 2, 2, 2-trifluoroethanol (TFE) into 30 m ZnCl₂. TFE will construct H-bonds with H₂O in Zn²⁺ solvation structures and results in low ionic association due to the electron-withdrawing effect of -CF₃ groups in TFE molecules. Therefore, Zn anodes in such electrolyte display a fast Zn²⁺ plating/stripping kinetics and high Coulombic efficiency. The resultant full batteries exhibit enhanced rate performance and stable cycling behavior.

Abstract

Aqueous zinc-ion batteries are emerging as one of the most promising large-scale energy storage systems due to their low cost and high safety. However, Zn anodes often encounter the problems of Zn dendrite growth, hydrogen evolution reaction, and formation of by-products. Herein, we developed the low ionic association electrolytes (LIAEs) by introducing 2, 2, 2-trifluoroethanol (TFE) into 30 m ZnCl₂ electrolyte. Owing to the electron-withdrawing effect of -CF₃ groups in TFE molecules, in LIAEs, the Zn²⁺ solvation structures convert from larger aggregate clusters into smaller parts and TFE will construct H-bonds with H₂O in Zn²⁺ solvation structure simultaneously. Consequently, ionic migration kinetics are significantly enhanced and the ionization of solvated H₂O is effectively suppressed in LIAEs. As a result, Zn anodes in LIAE display a fast plating/stripping kinetics and high Coulombic efficiency of 99.74%. The corresponding full batteries exhibit an improved comprehensive performance such as high-rate capability and long cycling life.

Aqueous zinc-ion batteries (ZIBs) hold great promise for large-scale energy storage because of their high safety, low cost, and environmental benignity (1–7). As a common anode material in ZIBs, Zn metal possesses the advantages of abundant resources, high theoretical specific capacity (820 mAh g⁻¹ and 5,854 mAh cm⁻³), and low Zn/Zn²⁺ redox potential (−0.76 V vs. standard hydrogen electrode) (8–11). However, Zn metal also suffers from the issues of side reactions and Zn dendrite formation in traditional aqueous electrolytes. The side reactions, including Zn anode corrosion and cathodic hydrogen evolution reaction (HER), will consume electrolytes irreversibly and induce the formation of insoluble by-products on the surface of Zn anode (12–14). Zn dendrites that originated from inhomogeneous Zn deposition often pierce the separators, and this thus results in the short circuit of batteries. Simultaneously, some Zn dendrites are usually detached from the Zn anode easily and convert into form “dead Zn”. Therefore, side reactions and Zn dendrites will lead to low Coulombic efficiency and severe capacity degeneration of aqueous ZIBs.

Recently, “water-in-salt” electrolytes were developed to overcome the issues of Zn anodes (15–19). The H₂O molecules in “water-in-salt” electrolytes are mainly restrained in Zn²⁺ ion-solvated shells. As a result, the redox potentials of these H₂O molecules are largely extended and their activities are limited, achieving the suppression of HER. In addition, “water-in-salt” electrolytes can provide abundant Zn²⁺ ions at the surface of Zn anodes, which will homogenize the Zn²⁺ ion flux and thus inhibit the growth of Zn dendrites. Compared with other zinc salts that were used in “water-in-salt” electrolytes, ZnCl₂ displays much lower cost, as a result, the high-concentration ZnCl₂ “water-in-salt” electrolyte is attracting great attention (20–22). In 30 m ZnCl₂ electrolyte, the activity of H₂O molecules would be effectively suppressed in their Zn²⁺ solvation structures, however, the ionization of solvated H₂O could be still induced by the interaction between Zn²⁺ ions and them. As a result, the HER often takes place at the surface of Zn anodes easily along with the formation of by-products (23–26). Furthermore, bivalent Zn²⁺ ions in the solvation structure will coordinate with the Cl⁻ ions in neighboring solvation structures to form aggregates by the strong electrostatic interaction (27, 28). The existence of these aggregates results in that 30 m ZnCl₂ electrolyte usually displays high viscosity with low ionic transport rate, limiting the power density of corresponding ZIBs. Thus, the solvation structures of 30 m ZnCl₂ electrolyte have to be modified to inhibit the ionization of solvated H₂O and weaken the interaction between Zn²⁺ ions and Cl⁻ ions.

In this work, we designed the low ionic association electrolytes (LIAEs) by introducing 2, 2, 2-trifluoroethanol (TFE) into 30 m ZnCl₂. In such LIAEs, owing to the electron-withdrawing effect of trifluoromethyl (-CF₃) groups in TFE molecules, TFE will construct H-bonds with H₂O in the Zn²⁺ solvation structure instead of coordinating with Zn²⁺ ions, which suppresses the ionization of H₂O in Zn²⁺ solvation structure and reduces the electrostatic interaction between Zn²⁺ ions and Cl⁻ ions (Fig. 1). Simultaneously, ionic association will be weakened and the aggregate clusters are divided into smaller solvation structures, resulting in enhanced ionic migration kinetics. Therefore, the Zn anodes in LIAE exhibit faster plating/stripping kinetics and higher Coulombic efficiency. The corresponding full batteries demonstrate superior rate performance and stable cycling behavior.

Fig. 1.

Schematic diagrams of the Zn²⁺ solvation structures and interfacial side reactions in 30 m ZnCl₂ and LIAE-20%.

Results

The LIAEs were prepared by adding TFE into 30 m ZnCl₂ electrolyte under stirring until the solution became transparent and stable. The molar ratios of TFE and H₂O are adjusted in a range of 10 to 50% (SI Appendix, Fig. S1). In the LIAEs, there are some aggregate clusters with polymer-like characteristic in electrolytes, which can be reflected by their glass transition temperature (T_g) in differential scanning calorimetry (DSC) (SI Appendix, Fig. S2). The DSC curves of LIAEs display an endothermic peak that represents the T_g of electrolytes. When more TFE was added into the LIAEs, the T_g values of LIAEs decreased obviously, indicating that aggregate clusters are divided into smaller parts. Dynamic light scattering (DLS) further displays the size distribution of aggregate clusters accurately, as shown in Fig. 2A and SI Appendix, Fig. S3. The average size of aggregates in LIAEs varies from 2.94 to 1.31 nm with the addition of TFE molecules from 10 to 50%. Simultaneously, the amount of aggregates with smaller sizes will be increased, as suggested by the Tyndall effect (Fig. 2B). When the amount of TFE is increased, the intensity of scattered light in LIAEs is gradually enhanced, indicating the existence of more aggregates with smaller sizes (29). Combining with low viscosity and shear stress (Fig. 2C), LIAE-20% displays an improved ionic conductivity of 17.7 mS cm⁻¹ (Fig. 2D), which is higher than the case of 30 m ZnCl₂ electrolyte. However, when more TFE is added in the range of 30 to 50%, the ionic conductivity of LIAEs will be gradually reduced due to the drop of ZnCl₂ concentration.

Fig. 2.

The characteristics of LIAEs with different molar ratios. (A) Distribution of particle size. (B) Tyndall effect. (C) Viscosity and shear stress. (D) Ionic conductivity. (E) Raman spectra. (F) FTIR spectra. (G) LSV curves.

To further understand the solvated structures of aggregate clusters in LIAEs, the LIAEs with different TFE contents were characterized by Raman spectra. As shown in Fig. 2E, the peak at around 240 cm⁻¹ is attributed to the ionic aggregates of [Zn_xCl_2x+2]²⁻ (30), which are induced by electrostatic interaction between Zn²⁺ ions and Cl⁻ ions in neighboring solvation structures. The peaks at around 293 and 337 cm⁻¹ are assigned to the solvation structures of [Zn(H₂O)₂Cl₄]²⁻ and [Zn(H₂O)Cl₃]⁻, respectively. After introducing TFE into LIAEs, the peak intensity of [Zn_xCl_2x+2]²⁻ is weakened, whereas [Zn(H₂O)₂Cl₄]²⁻ and [Zn(H₂O)Cl₃]⁻ peaks are significantly enhanced. These suggest the solvation structure conversion from [Zn_xCl_2x+2]²⁻ to [Zn(H₂O)₂Cl₄]²⁻ and [Zn(H₂O)Cl₃]⁻ in LIAEs due to the addition of TFE, which is different from the case of dilute electrolytes (SI Appendix, Fig. S4). However, it is noted that the peaks of [Zn(H₂O)₂Cl₄]²⁻ and [Zn(H₂O)Cl₃]⁻ shift to high wavenumber with the increase of TFE contents. It is ascribed to the H-bonds interaction between TFE and the H₂O molecules in solvation structures, which were further identified by the FTIR spectra, as shown in Fig. 2F and SI Appendix, Fig. S5. In FTIR spectra, the characteristic peak at 1,277 cm⁻¹ corresponds to the -CF₃ group of TFE molecules (31). It is gradually enhanced and shifts to low wavenumber with the addition of TFE molecules. Besides, the peaks of O–H bending vibration (1,615 cm⁻¹), O–H symmetric (3,200 cm⁻¹), and asymmetric (3,380 cm⁻¹) stretches in H₂O are weakened and exhibit a blue shift. These indicate the formation of H-bonds between TFE and H₂O molecules. Furthermore, with the increase of TFE contents in LIAEs, more H-bonds between TFE and H₂O molecules will be achieved.

The electron-withdrawing effect of -CF₃ group in TFE determines the Zn²⁺ solvation structures and the H-bonds between TFE and H₂O molecules in LIAEs. In order to demonstrate the distribution of charges on the surfaces of solvent molecules, the molecular electrostatic potential (MESP) mappings of solvents were calculated, as shown in Fig. 3A. The O atom in H₂O molecules exhibits a negative MESP (blue region) of −0.0672 Ha, which tends to coordinate with positive Zn²⁺ ions to induce Zn²⁺-H₂O coordination structures. In contrast, the electron density of O atom in TFE molecule is reduced and corresponding MESP value is more positive since -CF₃ group possesses a strong electron-withdrawing effect. As a result, TFE molecules are hard to coordinate with Zn²⁺ ions and will only interact with the H₂O molecules in the solvation structures by H-bonds. It is different from the case of common aqueous solvent, where MESP value of O atom in hydroxyl is often more negative than the case of H₂O molecules (SI Appendix, Fig. S6). They tend to coordinate with Zn²⁺ ions preferentially in 30 m ZnCl₂ electrolyte (SI Appendix, Fig. S7), resulting in the separation of H₂O molecules from solvation structures and the generation of free H₂O in the electrolyte (SI Appendix, Fig. S8). The binding energies between Zn²⁺ ions and solvents can be compared by the density functional theory (DFT) calculation (Fig. 3B and SI Appendix, Figs. S9–S13). The binding energies of Zn²⁺-TFE with different coordination numbers are lower than the case of Zn²⁺-H₂O. It further confirms that TFE is difficult to coordinate with Zn²⁺ ion in LIAE-20%, ensuring that the H₂O molecules will be not separated from solvation structures and Zn²⁺ ion coordination in LIAE-20% is similar to the case in 30 m ZnCl₂ even the aggregate clusters are divided into smaller parts in LIAE-20%.

Fig. 3.

(A) MESP mappings of H₂O and TFE molecules. (B) Binding energies of Zn²⁺-H₂O and Zn²⁺-TFE with different coordination numbers. MD simulation snapshots of (C) 30 m ZnCl₂ and (D) LIAE-20%. (E) RDFs and corresponding average coordination number of 30 m ZnCl₂ and LIAE-20%. (F) Ionization energies of H₂O molecules in different Zn²⁺ solvation structures.

The Zn²⁺ solvation structures and the distributions of their neighboring molecules can be further understood by molecular dynamics (MD) simulations (Fig. 3 C and D). The MD simulations suggest that there are some aggregates of [Zn_xCl_2x+2]²⁻ ions in 30 m ZnCl₂ electrolyte due to the strong electrostatic interaction between Zn²⁺ ions and Cl⁻ ions. After adding TFE, the Zn²⁺ solvation structure [Zn_xCl_2x+2]²⁻ converts to the [Zn(H₂O)₂Cl₄]²⁻ and [Zn(H₂O)Cl₃]⁻ in LIAEs-20%. Furthermore, TFE molecules will not coordinate with Zn²⁺ ions and only interact with the H₂O molecules in these solvation structures by H-bonds. The corresponding radial distribution functions (RDFs) and coordination number distribution functions were further achieved (Fig. 3E). The LIAE-20% displays a broad Zn-O_TFE peak at 0.53 nm, indicating that TFE molecules construct H-bonds with H₂O instead of coordinating with Zn²⁺ ions, which inhibits the ionization of H₂O (32). Different from LIAE-20%, 30 m ZnCl₂ electrolyte shows the sharp Zn-O_H2O peak at 0.21 nm, suggesting the coordination structure of Zn²⁺-H₂O. These results are consistent with the discussion of the above MESP calculation. Moreover, the ionization energies of H₂O in different electrolytes were also calculated to understand the activity of H₂O in them (Fig. 3F). It is noted that the ionization energies of [Zn(H₂O)₂Cl₄]²⁻-TFE (330.46 Kcal mol⁻¹) and [Zn(H₂O)Cl₃]⁻-TFE (507.17 Kcal mol⁻¹) are much higher than the cases of [Zn(H₂O)₂Cl₄]²⁻ (241.89 Kcal mol⁻¹) and [Zn(H₂O)Cl₃]⁻ (426.43 Kcal mol⁻¹), respectively. Therefore, the H-bonds between TFE and H₂O molecules will suppress the ionization of H₂O in the Zn²⁺ solvation structure in LIAE-20%. As shown in linear sweep voltammetry (LSV) curves (Fig. 2G), H₂ evolution potential in LIAE-20% is delayed and its decomposition current is smaller than the case of 30 m ZnCl₂ electrolyte. Moreover, the chemical corrosion of Zn anodes is also inhibited in LIAE-20% (SI Appendix, Fig. S14). As a result, LIAE-20% was selected for further electrochemical analysis.

The symmetric cells with Zn foils (denoted as Zn||Zn-LIAE-20% and Zn||Zn-30 m ZnCl₂) were utilized to illustrate the plating/stripping behavior of Zn electrodes in electrolytes. Their Zn²⁺ ion plating curves show that the nucleation overpotential of Zn²⁺ ions in LIAE-20% is 6.1 mV (Fig. 4A), which is lower than the case (10.1 mV) of 30 m ZnCl₂ electrolyte. Moreover, the CV curve of Zn||Ti cells also displays a small nucleation overpotential in LIAE-20% (SI Appendix, Fig. S15). It is attributed to the enhanced wettability of LIAE-20% for Zn metal and the lower charge-transfer resistance at the interface between Zn metal and electrolyte (SI Appendix, Figs. S16 and S17). Such low nucleation overpotential will be beneficial to reduce the energy barrier of Zn²⁺ ion plating (33), which can be further reflected by the active energy (E_a) of desolvation during Zn²⁺ ions plating at Zn–electrolyte interface (Fig. 4C). The E_a is evaluated by electrochemical impedance spectroscopy (EIS) and can be calculated based on the Arrhenius equation (34):

$$ln\left(T/R_{\mathit{ct}}\right)=E_a/RT+ln\mathrm{A,}$$ [1]

Fig. 4.

Electrochemical performance of Zn anodes. (A) Voltage profiles during Zn²⁺ ion plating at 0.2 mA cm⁻². (B) Rate performance of Zn||Zn-LIAE-20% and Zn||Zn-30 m ZnCl₂. (C) Fitted Arrhenius curves and corresponding activation energies of Zn²⁺ desolvation in LIAE-20% and 30 m ZnCl₂. (D) Tafel polarization curves in LIAE-20% and 30 m ZnCl₂. (E) Coulombic efficiency of Zn||Zn-LIAE-20% and Zn||Zn-30 m ZnCl₂. (F) X-ray diffraction (XRD) patterns after cycling in LIAE-20% and 30 m ZnCl₂ for 200 cycles. (G) Cycling performance of Zn||Zn-LIAE-20% and Zn||Zn-30 m ZnCl₂.

where R_ct, T, R, and A represent charge-transfer resistance, absolute temperature, standard gas constant, and preexponential constant, respectively. The E_a of Zn²⁺ desolvation in LIAE-20% is 41.5 kJ mol⁻¹, which is smaller than that (63.7 kJ mol⁻¹) in 30 m ZnCl₂ electrolyte. The H-bonds between TFE and H₂O molecules in Zn²⁺ solvation structures result in the reduced E_a and simultaneously lead to the weakened coordination interaction between Zn²⁺ ions and H₂O molecules, which benefits the desolvation of solvated Zn²⁺ ions at the Zn–electrolyte interface and accelerates the Zn²⁺ ion-transfer kinetics.

The fast Zn²⁺ ion-transfer kinetics at electrode–electrolyte interface endow the Zn||Zn-LIAE-20% with excellent rate capability, as shown in Fig. 4B. The voltage hysteresis of Zn||Zn-LIAE-20% and Zn||Zn-30 m ZnCl₂ are comparable under low current density (0.2 mA cm⁻²) (SI Appendix, Fig. S18). However, at large current densities, the Zn||Zn-LIAE-20% exhibits lower voltage hysteresis in comparison with Zn||Zn-30 m ZnCl₂, and even Zn||Zn-30 m ZnCl₂ will suddenly break down at 3 mA cm⁻², demonstrating the excellent electrochemical stability of Zn||Zn-LIAE-20% under high current density. In addition, the corrosion of Zn electrodes is also suppressed in LIAE-20%, as reflected by Tafel polarization curves (Fig. 4D). Generally, the corrosion current determines the corrosion kinetics of electrodes. The Zn anode in LIAE-20% displays a lower corrosion current density (0.13 mA cm⁻²) in comparison with the case of 30 m ZnCl₂ electrolyte, indicating the diminished corrosion rate of the Zn anode in LIAE-20%. Therefore, the reversibility of Zn²⁺ plating/stripping process is enhanced in LIAE-20%. The average CE of Zn²⁺ plating/stripping in LIAE-20% can reach 99.74% after 100 cycles at 1 mAh cm⁻² (Fig. 4E). Furthermore, at larger current density, average CE of Zn²⁺ plating/stripping is still high (SI Appendix, Fig. S19). In addition, there is nearly no dendrite on the Zn surface after cycling in LIAE-20%, which is different from the case of 30 m ZnCl₂ electrolyte (Fig. 4F and SI Appendix, Figs. S20 and S21). As a result, the Zn||Zn-LIAE-20% displays a long cycle life with stable voltage hysteresis over 4,000 h (Fig. 4G). In contrast, the surface of Zn anode in Zn||Zn-30 m ZnCl₂ is tarnished after cycling, and many irregular flake-like ZnCl₄·4Zn(OH)₂·H₂O by-products are piled up on the Zn surface, resulting in the uneven Zn²⁺ ions plating and eventually causing the internal short circuit in cell.

To illustrate the practical feasibility of LIAE-20%, aqueous ZIBs were assembled based on polyaniline (PANI) cathodes (SI Appendix, Fig. S22), Zn anodes, and LIAE-20%. The resultant aqueous ZIBs can deliver a discharge capacity of 128 mAh g⁻¹ at 0.1 A g⁻¹ (Fig. 5A), which is comparable to those of previously reported PANI-based ZIBs (35, 36). Impressively, even at 5 A g⁻¹, the discharge capacity of aqueous ZIBs can be still up to 49 mAh g⁻¹ (Fig. 5B). Moreover, when the current density goes back to 0.1 A g⁻¹, its capacity recovers to 127 mAh g⁻¹, demonstrating an excellent rate performance. The reaction kinetics of ZIBs can be further reflected by their cyclic voltammetry (CV) curves with different scan rates (Fig. 5C). The CV curves show two pairs of redox peaks and the relationship between the peak currents (i) and scan rates (v) can be described as the following equation (37–39):

$$i=a{v}^b$$ [2]

Fig. 5.

Electrochemical performance of Zn||PANI batteries. (A) Galvanostatic charge/discharge curves. (B) Rate performance. (C) CV curves at different scan rates. (D) The log (peak current) vs. log (scan rate) plots at each redox peak according to the CV curves. (E) Capacitive contributions at various scan rates. (F) The ion diffusion coefficient during discharging process. (G) Nyquist plots. (H) Cycling performance at 2 A g⁻¹.

where a and b are the variable parameters. When b value approaches 1, the pseudocapacitance will determine the electrochemical reaction. It is noted that the b values of peaks 1, 2, 3, and 4 in CV curves are 0.88, 0.98, 0.95, and 0.99, respectively (Fig. 5D), suggesting that the redox reaction of the PANI cathode is mainly dominated by pseudocapacitance-controlled behavior (40). Moreover, with the increase of scan rates, the capacitive contribution of the PANI cathode in ZIBs rises gradually and can reach to 77% at 1 mV s⁻¹ (Fig. 5E), which is higher than the case of ZIBs based on 30 m ZnCl₂ electrolyte (SI Appendix, Fig. S23). In addition, the fast kinetics can be further understood by the diffusion coefficient (D) of ions in PANI cathodes, which was calculated by the galvanostatic intermittent titration technique measurement (41–43). As shown in Fig. 5F, the D values of PANI cathodes in ZIBs are 10⁻¹¹ to 10⁻⁹ cm² s⁻¹, demonstrating a fast reaction kinetics of PANI cathodes in LIAE-20%. This is closely related to the small charge transfer resistance at the electrode/electrolyte interface (Fig. 5G). Furthermore, the ZIBs can still maintain 87.6% of its initial capacity even after charge/discharge for 2,000 cycles at 2 A g⁻¹ (Fig. 5H), exhibiting a superior cycling behavior. The enhanced cycling performance is ascribed to that the introduction of TFE into 30 m ZnCl₂ electrolyte will effectively suppress the dendrite and HER of Zn anodes in batteries (SI Appendix, Fig. S24). Therefore, the LIAE-20% endows the ZIBs with enhanced electrochemical performance.

Discussion

An LIAE was designed by introducing TFE into 30 m ZnCl₂ electrolyte. The introduction of TFE induces the solvation structure conversion from [Zn_xCl_2x+2]²⁻ to [Zn(H₂O)₂Cl₄]²⁻ and [Zn(H₂O)Cl₃]⁻ in LIAE and the formation of H-bonds between TFE and H₂O molecules in the solvation structures due to the electron-withdrawing effect of -CF₃ groups in TFE molecules. As a result, LIAE displays higher ionic transport rate and the lower charge transfer resistance at the interface between Zn anodes and LIAE, leading to a faster plating/stripping kinetics. Simultaneously, the H-bonds between TFE and H₂O molecules will suppress the ionization of H₂O in Zn²⁺ solvation structure in LIAE. Therefore, in LIAE, the reversibility of Zn²⁺ plating/stripping behaviors is improved and the formation of by-products is inhibited, which endows Zn anodes with high Coulombic efficiency of 99.74%. The aqueous ZIBs with LIAE exhibit an excellent rate performance and a high capacity retention of 87.5% after 2,000 cycles. This work will pave a route to design high-rate and stable aqueous ZIBs.

Materials and Methods

Materials.

ZnCl₂ (99.95%) and Zn foil (99.9%) were purchased from Alfa Aesar. PANI nanorods were prepared according to the previous literature (44). TFE (99.8%) and N-methyl-2-pyrrolidone (99.5%) were purchased from Aladdin. Single-walled carbon nanotubes (P3) were purchased from Carbon Solutions Inc. Polyvinylidene fluoride was purchased from SinopharmChemical Reagent Co., Ltd.

Preparation of LIAEs and PANI Cathode.

ZnCl₂ (4.089 g) and TFE were dispersed in deionized H₂O (1 g) under stirring to obtain LIAEs at different molar ratios. PANI, single-walled carbon nanotubes, and polyvinylidene fluoride were mixed with a weight ratio of 7: 2: 1 in N-methyl-2-pyrrolidone to achieve a slurry, which was then coated on a Ti foil. After vacuum drying at 60 °C for 24 h, the PANI cathode was obtained.

Characterizations and Electrochemical Measurements.

The size distribution of LIAEs was characterized via DLS (Malvern, ZetasizerNanoZS90). The viscosity and shear stress of LIAEs were measured by a rheometer (MCR302). The thermal properties of LIAEs were characterized using a differential scanning calorimeter (NETZSCH). The FTIR and Raman spectra of LIAEs were collected through Bruker Tensor II and a confocal Raman microscope (InVia Reflex) with a wavelength of 532 nm, respectively. The morphologies of materials were characterized via a scanning electron microscope (Phenom XL). CV curves of ZIBs were tested on an electrochemical workstation (CHI Instruments, CHI660E). Galvanostatic charge/discharge curves were recorded on a battery test system (LAND CT2001A). EIS curves were measured in the frequency range from 100 kHz to 100 mHz on an electrochemical workstation (Zahner, IM6ex). The sizes of PANI cathodes and Zn anodes are 1 × 1 cm². The loading and thickness of SWCNTs/PANI cathodes are 1 mg cm⁻² and 50 μm, respectively. The amount of electrolyte in a ZIB is 30 μL. The specific capacity of PANI cathodes was calculated based on the mass of the PANI.

Computational Methods.

The MESP mappings, binding energy and ionization energy calculations were performed using the DFT program DMol³ in Materials Studio. The physical wave functions were expanded in terms of numerical basis sets, DMol³/generalized gradient approximation (GGA)-Perdew–Burke–Ernzerhof (PBE)/Dual Numerical Polarization (DNP) (3.5) basis set. The core electrons were treated with DFT semicore pseudopotentials. The exchange-correlation energy was calculated with PBE GGA. A Fermi smearing of 0.005 Ha and a global orbital cutoff of 5.2 Å were employed. The convergence criteria for the geometric optimization and energy calculation were set as follows: a) a self-consistent field tolerance of 1.0 × 10⁻⁶ Ha atom⁻¹; b) an energy tolerance of 1.0 × 10⁻⁵ Ha atom⁻¹; c) a maximum force tolerance of 0.002 Ha Å⁻¹; and d) a maximum displacement tolerance of 0.005 Å. The MD simulations were made by gromacs 2019.1 using the OPLS-AA force field. Nose–Hoover and Berendsen method were used as the temperature and pressure coupling method, respectively. The electrostatic interactions used PME methods. A cutoff length of 1.0 nm was used in the calculation of electrostatic interactions. To make the density of the system reach a stable value, the NPT process was used to equilibrate the system under the conditions of 298.15 K and 1 atm for 30 ns. Then, 10-ns simulation in the NVT process at 298.15 K was used for data collection.

Supplementary Material

Appendix 01 (PDF)

Data, Materials, and Software Availability

All study data are included in the article and/or SI Appendix.