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. 2025 Aug 29;10(35):40009–40019. doi: 10.1021/acsomega.5c04122

Enhanced Interfacial Wettability and Retardancy of Cellulose Acetate/Ammonium Polyphosphate/Polyvinylidene Fluoride Ternary Composites Fabricated by One-Step Electrospinning

Weifu Sun †,*, Zhaoyin Ding §,∥, Hongyuan Wen ‡, Jiayu Zhao ⊥, Yuefeng Su ⊥, Jiali Qiu #,*
PMCID: PMC12423967  PMID: 40949246

Abstract

The cutting-edge development of lithium-ion batteries (LIBs) focuses on improving the security and cycle performance. The separator film plays an important role in cell performance and long-term service life, which requires both flame retardancy and mechanical strength. In this work, a one-step electrospinning technique has been adopted to prepare a novel polyvinylidene fluoride/cellulose acetate/ammonium polyphosphate membrane acting as a separator in the LIBs. The electrospinning conditions have been first optimized mainly by varying the concentration of precursor solution. The electrospun membranes have been characterized using scanning electron microscopy and infrared spectroscopy. The porosity, electrolyte uptake capability, the electrolyte wettability, thermal stability, and tensile properties have also been measured.

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1. Introduction

Due to the great demand for clean and sustainable energy, lithium-ion batteries (LIBs) have gained widespread attention as an energy storage solution. , However, the widespread adaptation of lithium-ion batteries for consumer products, electrified vehicles, and grid storage demands further enhancement in energy density, cycle life, and safety, all of which rely on the structural and physicochemical characteristics of cell components. The separator membrane is a key component in an electrochemical cell that is sandwiched between the positive and negative electrodes to prevent physical contact, while permitting ionic conduction through the electrolyte. Though it is an inactive component in a cell, the separator has a profound impact on the ionic transport, performance, cell life, and safety of the batteries. Notably, the separator, a pivotal and indispensable component in LIBs that primarily consists of a porous membrane material, warrants significant research attention.

The porosity and specific surface area of separator membranes are critical to the lithium-ion batteries (LIBs) for uptaking the electrolyte, and such membranes can be produced by the efficient approach of electrospinning. So far, a lot of membrane materials have been chosen from various types of high molecular polymers, including poly­(ether sulfone) (PES), poly m-phenyleneisophthalamide (PMIA), polyacrylonitrile (PAN), polysulfonamide (PSA), and polyimide (PI). Especially, there exist a lot of C–F chemical bonds within polyvinylidene fluoride (PVDF), thus endowing PVDF with a high dielectric constant and good chemical inertia. Therefore, it has attracted a lot of interest as an ideal electrolyte host in LIBs. Nevertheless, there are several disadvantageous shortcomings, such as a hydrophobic surface and high crystallinity, and all of these adverse defects result in low ionic conductivity and poor electrolyte retention.

As one of the promising secondary power sources, LIBs possess excellent characteristics, such as easy portability, stable cycling performance, and high energy density. Consequently, LIBs have gained successful prospects in different fields, including smart electronic devices, hybrid electric vehicles, and so on. However, LIBs still have serious challenges, and much work still needs to be done to overcome the shortcomings of higher energy density, prolonged life, and low cost. Besides, explosion and fire accidents arising from battery failure are frequently experienced in laptops and cell phones, and safety concerns have been raised. A lot of factors, such as high temperature exposure, penetration, and crash, can result in the failure of the membranes and subsequently the safety hazards of LIBs. Therefore, in order to prevent internal short circuits, it is required that the separator membrane should be resistant to high temperature and flame, in addition to an appropriate mechanical strength. On the other hand, superior electrolyte wettability and high porosity are the necessary preconditions for membranes, which can provide ionic channels for electrolytes. Currently, the commercialized separators mainly comprise of polyethylene (PE) and polypropylene (PP). Other high molecular weight polymers, such as polyolefin polymers, have an edge in mechanical property, cost control, and electrochemical property; nonetheless, their low thermal stability and poor wettability have seriously restricted their practical application.

Cellulose is abundant in nature and has a lot of advantageous properties, such as renewability, excellent biocompatibility properties, and low cost. , As a porous membrane material, cellulose acetate has a couple of advantages, including high selectivity, high water permeability, and facile processing. Hence, much attention has been devoted to cellulose acetate (CA) recently as a candidate alternative for LIB membranes because of their high decomposition temperature and good electrolyte uptake capabilities. Thus, the addition of CA is a promising approach to simultaneously improve the interfacial wettability and thermal stability of a pure PVDF membrane, but most of efforts have been devoted to the antifouling properties, waterproof, water remediation, etc. Furthermore, the addition of flame retardants can improve flame retardancy and consequent fire safety. Because of low emission of toxic substances, the halogen-free ammonium polyphosphate (APP) has received much attention in fabricating fire-proof coatings, , but attention has been mainly paid to improve thermal stability of electrodes or in the form of surface coatings on the separator with relatively weak adhesion force.

So far, little effort has been devoted to synergistically enhancing the interfacial wettability, mechanical property, and retardancy in the pursuit of the potential application for LIBs. Thus, in this work, by exploiting the advantageous properties of CA, PVDF, and APP, CA along with APP will be incorporated into the PVDF membrane by electrospinning in order to enhance the interfacial wettability and flame-resistant performance. First, composite membranes with different compositions have been fabricated using electrospinning using different precursor solutions. Then, the fabricated membranes were subjected to various characterizations. The morphology and porous microstructure and tensile mechanical properties will be characterized using SEM and a mechanical tester, respectively. The porosity, electrolyte uptake capability, electrolyte wettability, and thermal stability have been measured. Finally, batteries have been assembled to preliminarily explore storage performance and exhibit excellent electrochemical and cycle performance.

2. Experimental Section

2.1. Materials

PVDF, acetone, N,N-dimethylformamide (DMF), and n-butanol were all provided by Sigma-Aldrich. CA was provided by Shanghai Macklin reagent containing 39.5 wt % acetyl group and 4.0 wt % carboxyl group with a molecular weight of M w = 60,000. APP was provided by Meryer, Shanghai.

2.2. Preparation of Composite Membranes

  • (1)

    As shown in Figure , different concentrations (ranging from 10.0 wt %,14.3 wt %, 16.3 wt % to 18.2 wt %) of precursor solution containing PVDF, CA, and APP were prepared by completely dissolving it in the mixed solution of DMF and acetone with a ratio of 7:3, followed by vigorous stirring for 12 h at 40 °C until completely being dissolved.

  • (2)

    Next, the electrospinning processing will be carried out at 20 kV with a flow rate of 0.6 mL/h with a collecting distance of 15.5 cm. The resulting membranes will be subjected to drying in a vacuum oven at 80 °C.

1.

1

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Schematic illustration of the preparation process for the electrospun separator and the assembly of LIBs.

2.3. Characterizations

Scanning electron microscopy (SEM) was used to observe the morphologies of the separator membranes. Energy-dispersive X-ray spectroscopy (EDS) equipped with SEM was adopted for elemental analysis. Fourier transform infrared spectroscopy (FT-IR) is used to characterize the surface functional groups. Wettability between the separator and liquid electrolyte was evaluated by measuring contact angles using a video contact tester.

The mechanical properties of separator membranes were evaluated through tensile tests. The diaphragm was cut into a rectangle of 70 × 10 mm, and there were at least three parallel samples in each group. Then the thickness of each sample was measured by a vernier caliper. The tensile sample was fixed, and the standard distance was 50 mm. The tensile speed was 3 mm/min, and then, the breaking strength and elongation at break were obtained by calculating the obtained experimental data.

The electrospun membrane will be immersed in n-butanol for 1 h, and the porosity (P) of the membrane will be calculated by

P=mw−mdρbV×100% 1

where m d, m w, V, and ρb are the mass of the separator before and after being soaked in n-butanol, total volume of the separator, and density of n-butanol, respectively.

Electrolyte uptake (EU) was given by the following equation

EU=m−m0m0×100% 2

where m 0 and m, respectively, are the mass of the membrane before and after being immersed in an electrolyte.

Electrochemical impedance spectroscopy (EIS) will be performed to measure the ionic conductivity (σ) of each separator membrane and evaluate the interfacial stability of the separator membrane and lithium anodes. The conductivity was calculated by

σ=hRS 3

where S, h, and R are the effective contact area of the separator membrane, the thickness of the separator membrane, and bulk resistance, respectively.

CR2025 coin-type half batteries were assembled in a glovebox filled with argon gas (H2O: < 0.1 ppm and 02 < 0.1 ppm). Li metal was used as the counter electrode, cellulose acetate/ammonium polyphosphate/polyvinylidene fluoride ternary composites fabricated by a one-step electrospinning technique were used as the separator, and 1 M LiPF6 dissolved in an ethylene carbonate (EC)/dimethyl carbonate (DMC) mixture (1/1 v/v) was used as the electrolyte. The cathode paste consisted of the active cathode material (80 wt %), electrically conductive additive (acetylene black, 10 wt %), and a binder (PVDF, 10 wt %). Then, the paste was coated onto the aluminum foil and dried at 60 °C for 12 h. The average loading of the cathode is about 2 mg/cm2. LiFePO4 and lithium were used as cathodes and anodes, respectively. The diameters of the anode and cathode are 11.9 and 15 mm, respectively, and the diameter of the separator is about 19 mm. Then, the cycling performance and charge/discharge profiles of the assembled cells have been tested at room temperature using a LAND system.

In this work, seven different precursor solutions have been prepared and then used to electrospin different membranes. The different formulations, including the different initial concentrations and different chemical compositions, are summarized in Table .

1. Separator Membranes Electrospun from Different Formulations .

  concentration PVDF (g) CA (g) APP (g)
#1 10.0 wt % 3.60 0.40  
#2 14.3 wt % 4.05 0.45  
#3 16.3 wt % 6.30 0.70  
#4 18.2 wt % 7.20 0.80  
#5 10.0 wt % 4.00    
#6 10.0 wt % 3.24 0.36 0.40
#7 10.0 wt %   4.00  
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a

Note: The ratio of PVDF to CA is 9:1.

3. Results and Discussion

The performance of separators is sensitively dependent upon the quality and chemical composition of the electrospun membrane. In this work, the quality of the electrospun membrane is first mainly optimized by varying the initial concentration of the precursor solution. Then, attention has been paid to the effect of different chemical compositions of electrospun membranes on the morphology, tensile property, porosity, and electrolyte uptake.

3.1. Effect of the Initial Concentration of the Precursor Solution

3.1.1. Morphology Characterization

The highly porous structure would facilitate the adsorption and penetration of the organic electrolyte, thereby improving the cycle stability and rate performance of batteries. SEM is a useful approach to characterize the morphology of the PVDF/CA polymer membranes electrospun from different initial concentrations of 10.0, 14.3, 16.3, and 18.2 wt %, as shown in Figure . It can be observed that the fiber electrospun from 10.0 wt % gives a relatively uniform diameter and almost bead-free morphology, whereas the other three cases give rise to a wide distribution of diameters. Thus, the initial concentration of 10.0 wt % polymer precursor solution will be employed next.

2.

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SEM images of PVDF/CA polymer membranes electrospun from different initial concentrations of (a) 10.0 wt %, (b) 14.3 wt %, (c) 16.3 wt %, and (d) 18.2 wt %.

3.1.2. Tensile Test

Since the mechanical properties are vital to battery safety, in this work, the mechanical properties of the different electrospun membranes have been subjected to tensile loading. The stress–strain curves have been calculated and listed in Figure and the effect of initial concentration of precursor solutions and the effect of different formulations have been demonstrated. As observed from Figure b, the tensile strength corresponding to 10.0, 14.3, 16.3, and 18.2 wt % are 8.13, 7.15, 6.52, and 7.07 MPa, respectively. In other words, 10.0 and 14.3 wt % deliver comparable tensile strength.

3.

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(a) Stress–strain curves and (b) tensile strength of membranes electrospun from different concentrations of 10.0%, 14.3%, 16.3%, and 18.2%.

3.1.3. Porosity and Electrolyte Uptake

Electrospinning is an industrially viable technique for the fabrication of LIB separators due to the unique property (high porosity, interconnected pore structure, electrolyte uptake, ionic conductivity, etc.) of electrospun separators. , It is known that porosity has an important role to play in the electrolyte uptake (EU) performance of polymer membranes. A porous structure can be generated by interlaying fibers in the electrospun membranes. As observed from Figure , the porosities of PVDF/CA composite membranes corresponding to different initial concentrations of 10.0, 14.3, 16.3, and 18.2 wt % are 61.74%, 74.09%, 50.26%, and 41.15%. The corresponding EU values are 124.00%, 130.77%, 73.33%, and 51.62%, respectively. It can be concluded that 10.0 and 14.3 wt % give comparable porosity and EU capability.

4.

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Effect of the concentration of the polymer precursor on (a) porosity and (b) electrolyte uptake (Lithium hexafluorophosphate, LiPF6) of PVDF/CA composite membranes.

The porosity and electrolyte uptake (liquid absorption) capacity are closely correlated, and the trends as a function of concentration are consistent with each other. This can be explained by the pore size and density of fiber formed from electrospinning, as shown in the SEM images in Figure . When the concentration is low, the pore size is relatively large, but with increasing concentration, a uniform and dense fiber can be formed, and more electrolyte molecules can be arrested and maintained without leaking. However, when the concentration becomes high, aggregation of fibers can be observed and the formed fiber becomes nonuniform, which is not in favor of arresting liquid molecules. Therefore, there exists one optimal concentration of electrospinning solution to form uniform and dense fibers to absorb electrolyte molecules.

3.2. Effect of Different Chemical Compositions

3.2.1. Morphology Characterization

The morphology of the electrospun membranes of different chemical compositions has been characterized using SEM. The SEM images of pure PVDF, CA, PVDF/CA, and PVDF/CA/APP membranes and the corresponding histograms of fiber diameter are shown in Figure a–d, respectively. It is observed that all the membranes are composed of relatively uniform nanofibers, most of which are in the range of 200–700 nm. For instance, the electrospun PVDF nanofibers have a wide diameter scope ranging from 150 to 900 nm, whereas the diameter of electrospun CA nanofibers ranges from 100 to 750 nm. After the addition of CA into PVDF, the diameter of electrospun PVDF/CA nanofibers ranges from 150 to 900 nm. After the further addition of APP into the PVDF/CA precursor solution, the diameter of electrospun nanofibers becomes slightly smaller and ranges from 150 to 600 nm. The average diameter of fibers for these membranes is around 400 nm. It is known that nanosized fibers usually have a large surface area, and the interlaying nanofibers can generate a lot of pores. Thus, all of these pores are beneficial for the uptake of the liquid electrolyte when the membrane is soaked in liquid electrolyte.

5.

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SEM images and histograms of the fiber diameter from different electrospun polymer membranes of (a) pure PVDF, (b) pure CA, (c) PVDF/CA, and (d) PVDF/CA/APP.

3.2.2. FT-IR Analysis

The FT-IR spectra of pure PVDF, PVDF/CA, PVDF/CA/APP, and pure CA have been characterized and are shown in Figure . It can be observed that the characteristic peaks located at 1402 and 1170 cm–1 are ascribed to the vibration bands of C–H in –CH2– and C–F, respectively. This indicates the presence of PVDF. The peaks located at 1231 and 1752 cm–1 could be attributed to the stretching vibration of C–O and CO of CA, respectively. In the PVDF/CA/APP spectrum, the absorption bands at 1058, 966, and 496 cm–1 were ascribed to PO4 of APP. All of these spectrum data have indicated that the APP has been successfully introduced into the composite membranes through electrospinning techniques.

6.

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FT-IR spectra of pure PVDF, CA, PVDF/CA, and PVDF/CA/APP membranes.

3.2.3. Tensile Test

The stress–strain curves of different membranes after being subjected to tensile loadings are shown in Figure a. With the increase of strain, the stress increases gradually.

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Stress–strain curves and tensile strength of membranes under the condition of different formulations (a,b).

As observed from Figure b, compared with the study of Chen Yue et al., we increased the thickness of the membrane to improve the accuracy of the stretching experiment, the tensile strength corresponding to pure PVDF, PVDF/CA, PVDF/CA/APP, and pure CA are 10.29, 8.13, 8.52, and 7.49 MPa, respectively. In other words, pure PVDF delivers the highest tensile strength, whereas pure CA gives the worst tensile strength; the PVDF/CA lies in between PVDF and CA. The further addition of APP into PVDF/CA composite membrane can slightly improve the mechanical strength.

3.2.4. Porosity and Electrolyte Uptake

The effect of different chemical compositions of electrospun membranes on the porosity and EU has been explored, and the results have been displayed in Figure . It can be observed that both the porosity and EU follow the order of PVDF/CA/APP > PVDF/CA > CA > PVDF. The porosity values of pure PVDF, pure CA, PVDF/CA, and PVDF/CA/APP are 41.16%, 55.41%, 61.74%, and 73.50%, respectively. Meanwhile, the EU values corresponding to pure PVDF, pure CA, PVDF/CA, and PVDF/CA/APP are 101.86%, 129.17%, 131.06%, and 135.37%, respectively. After the addition of APP into PVDF/CA membrane, both the porosity and EU have significantly increased. PVDF/CA/APP composite membrane delivers the highest porosity and EU, indicating that the addition of CA and APP favors the generation of a porous structure and the uptake of electrolyte.

8.

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Effect of different compositions of the polymer precursor on (a) porosity and (b) electrolyte uptake (lithium hexafluorophosphate, LiPF6) of pure PVDF, PVDF/CA, PVDF/CA/APP, and pure CA membranes.

The wettability of each membrane has an important role to play in the electrolyte uptake and also the interfacial impedance between different layers of cells. Figure a–d shows the measured contact angle results for different membranes. It demonstrates that the contact angles of pure PVDF and pure CA are estimated to be 28.6° and 23.9°, respectively, while those of composite membranes PVDF/CA and PVDF/CA/APP are 23.0° and 36.9°, respectively. Compared to pure PVDF, the addition of CA indeed improves the wettability between the electrolyte and composite membranes.

9.

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Contact angles of electrospun membranes: (a) PVDF, (b) PVDF/CA, (c) PVDF/CA/APP, and (d) CA.

3.2.5. Thermal Property and Flame Retardancy

The thermal properties of pure PVDF, CA, PVDF/CA, and PVDF/CA/APP membranes are assessed using DSC, as shown in Figure . The melting temperatures of pure PVDF and pure CA are about 153.5 and 295.3 °C, respectively. As for PVDF/CA membranes, two endothermic peaks appear at 156.5 and 295.5 °C, corresponding to melting temperature (T m) values of PVDF and CA, respectively. As for the PVDF/CA/APP membrane, the first peak has shifted to 158.9 °C, indicating the improved thermal stability.

10.

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DSC curves of different membranes of PVDF, PVDF/CA, PVDF/CA/APP, and CA.

To evaluate the effect of the addition of APP on the flame resistance of composite membranes, the membranes were ignited by a direct lighter flame (Figure ). The membranes of pure PVDF, CA, and PVDF/CA have been readily ignited and almost burned out in 2 s. In contrast, the addition of APP can make it difficult to ignite, the PVDF/CA/APP still keeps the shape integrity after being subjected to 2 s of direct lighter flame, indicating the improved flame retardancy of the composite membrane because of APP.

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Digital photographs demonstrating the flame resistance of pure PVDF, PVDF/CA, pure CA, and PVDF/CA/APP membranes.

3.2.6. Battery Performance

The AC impedance spectra of cells assembled from different membranes of PVDF, CA, PVDF/CA, and PVDF/CA/APP membranes acting as separators are shown in Figure . Since the intercept on the X-axis corresponds to the bulk resistance, as shown in Figure a, PVDF gives the highest bulk resistance, followed by pure CA and PVDF/CA. The further addition of APP leads to the lowest bulk resistance. The bulk resistances of pure CA, PVDF, PVDF/CA, and PVDF/CA/APP are approximately estimated to be 20.0, 70, 12, and 8.3 Ω, respectively. The thicknesses of pure CA, PVDF, PVDF/CA, and PVDF/CA/APP are estimated to be about 120, 60, 40, and 70 μm, respectively. The effective contact area was estimated from the diameter of the separator of 19 mm. Then, the conductivity was calculated according to eq . Therefore, the ionic conductivity of pure CA, PVDF, PVDF/CA, and PVDF/CA/APP is estimated to be 5.29 × 10–3, 7.56 × 10–4, 2.94 × 10–3, and 7.44 × 10–3 S/m, respectively. The PVDF/CA/APP delivers the highest ionic conductivity.

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AC impedance spectra of cells assembled from PVDF, CA, PVDF/CA, and PVDF/CA/APP acting as separators. (a) is the highlight of (b).

Besides, the interface impedance between the anode and electrolyte is critical to the battery performance. It is known that the X-axis intercept of the semiarc is considered the interface impedance. As observed from Figure b, the interfacial resistances for pure PVDF, CA, and PVDF/CA membranes are 1149.0, 1006.6, and 1088.6 Ω, respectively, whereas composite membrane of PVDF/CA/APP delivers an estimated value of 333.6 Ω only. The decrease in interface impedance facilitates the extraction speed of lithium ions from the electrode surface and is beneficial to the rate performance and discharge capacity. Since the thicknesses of pure CA, PVDF, PVDF/CA, and PVDF/CA/APP are estimated to be about 120, 60, 40, and 70 μm, respectively. The interfacial impedance of pure CA with the largest thickness of 120 μm gives rise to 1006.6 Ω, which is lower than that of PVDF (1149 Ω) with a relatively smaller thickness of 60 μm. This indicates that the better the interfacial wettability, the lower the interfacial impedance. The reduction in the interfacial impedance should be the joint contribution of the thickness decrease and improved interfacial wettability arising from the incorporation of CA.

The charge/discharge curves of cells with PVDF/CA and PVDF/CA/APP have been preliminarily explored at first, 20th, and 50th cycles are shown in Figure a,b. It can be observed that the initial discharge capacities of the cells with PVDF/CA and PVDF/CA/APP membranes reached 131.0 mA h g–1 and 126.0 mA h g–1, respectively. After 50 cycles, the Coulombic efficiencies of both membranes are still comparable to each other and approach 100% as shown in Figure c. Moreover, the discharge capacity of the cell with PVDF/CA/APP decreases slightly to 105.8 mA h g–1 with capacity retention of 84.0%, as shown in Figure d. However, this capacity retention value is still acceptable. This may be associated with the high rate of 1.0 C applied in carrying out the charge/discharge profiles. The capacity normally decreases with an increase in the applied rate.

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Charge/discharge curves for cells in the potential range of 2.0 V–4.6 V at a 1.0 C rate under room temperature conditions. (a) PVDF/CA and (b) PVDF/CA/APP membrane; cycling performance of the LiFePO4/membrane/Li cells at 1.0 C rate. (c) PVDF/CA and (d) PVDF/CA/APP membrane.

4. Conclusions

In this work, different membranes, including PVDF, PVDF/CA, PVDF/CA/APP, and pure CA, have been successfully electrospun by optimizing the initial concentrations of polymer precursor solution. Their properties, including contact angle, porosity, EU, tensile properties, and flame retardancy, have been further characterized. Finally, cells containing different PVDF, PVDF/CA, PVDF/CA/APP, and pure CA electrospun membranes acting as separators have been assembled, and their battery performance has been characterized.

  • (1)

    The results show that 10.0 and 14.3 wt % give better and comparable porosity and EU capability than other concentrations. Moreover, 10.0 wt % polymer precursor solution can lead to fibers with uniform diameter and almost bead-free morphology and delivers a slightly higher tensile strength.

  • (2)

    The results also show that PVDF/CA/APP composite membrane indeed exhibits the highest porosity and EU, indicating that the addition of CA and APP favors the generation of a porous structure and the uptake of electrolyte. The addition of APP not only significantly enhances the flame retardancy, but also improves the thermal stability and tensile strength as compared to PVDF/CA.

  • (3)

    Moreover, PVDF/CA/APP composite membrane exhibits improved interfacial impedance, thus facilitating the detaching speed of lithium ions from the electrode surface and improving the discharge capacity.

Acknowledgments

The authors acknowledge the financial support from the National Natural Science Foundation of China (grant no. 12372348), Taishan Scholars Program, Natural Science Foundation of Chongqing for Distinguished Young Scholars (CSTB2022NSCQ-JQX0011), National Key R&D Program of China (grant no. 2023YFB4202900 and 2020YFA0711800), State Key Laboratory of Explosion Science & Technology (YPJH20-6, YBKT23-02), BIT-BRFFR Joint Research Program (BITBLR2020018), and Beijing Institute of Technology Research Fund and BIT Research and Innovation Promoting Project (grant no. 2022YCXZ023).

Prof. Weifu Sun conceived the idea and designed the experiments, performed the data analysis, and was in charge of the paper refining. Zhaoyin Ding performed part of the experiments. Jiali Qiu was in charge of paper drafting, the setting of electrospinning experimental conditions, and the experimental design, including compositions of precursor, part of the experiments, and Jiayu Zhao and Yuefeng Su supervised the battery assembly experiments. Hongyuan Wen was in charge of the paper refining and data analysis. All the authors guarantee that the above information is reliable and correct. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

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