A three-dimensional zinc / zinc oxalate anode material, its preparation method and application

Abstract

This invention belongs to the field of aqueous secondary batteries, specifically relating to a three-dimensional zinc / zinc oxalate anode material, its preparation method, and its application. The three-dimensional zinc / zinc oxalate anode material includes a zinc metal substrate and a three-dimensional protective layer. The zinc metal substrate is a commercially available zinc metal foil, and the three-dimensional protective layer is a zinc oxalate interface material formed in situ by the displacement reaction of the zinc metal substrate with an oxalic acid solution. This invention uses low-temperature ultrasound as the reaction condition to deposit zinc oxalate on the surface of the zinc metal foil, forming a tightly bonded and uniform three-dimensional protective interface in situ. Its specific surface area is more than 10 times larger than that of the original zinc metal foil, effectively reducing local current density to suppress dendrite growth. Simultaneously, the dense zinc oxalate protective layer isolates the active zinc from the aqueous electrolyte to suppress corrosion and hydrogen evolution side reactions, thereby improving the cycle performance of the zinc metal anode in aqueous secondary batteries.

Description

Technical Field

[0001] This invention belongs to the field of aqueous secondary batteries, specifically relating to a three-dimensional zinc / zinc oxalate anode material, its preparation method, and its application. Background Technology

[0002] Aqueous zinc secondary batteries possess characteristics such as high safety, low cost, and environmental friendliness, and are expected to be applied in large-scale energy storage and smart grids. This is due to the high theoretical specific capacity of metallic zinc (820 mAh·g). -1 Zinc metal is an ideal negative electrode material for aqueous batteries due to its characteristics such as high oxidation-reduction potential (-0.76V, relative to the standard hydrogen electrode). However, side reactions between zinc metal and aqueous electrolyte during battery charging and discharging, as well as dendrite problems caused by uneven deposition / dissolution of zinc metal at the negative electrode, reduce the reversibility of the zinc negative electrode, leading to a decrease in battery cycle life. Summary of the Invention

[0003] The main objective of this invention is to solve the problems of dendrite growth and corrosion hydrogen evolution side reactions that occur in zinc metal anodes during charging and discharging, improve the electrochemical reversibility of zinc metal anodes, and thus improve the cycle life of aqueous zinc secondary batteries.

[0004] A method for preparing a three-dimensional zinc / zinc oxalate anode material includes the following steps:

[0005] S1. Add H2C2O4 to 250-1000 mL of deionized water and stir magnetically at room temperature to dissolve it and form a clear and transparent oxalic acid solution.

[0006] S2. The zinc foil is ultrasonically cleaned in ethanol and deionized water in sequence.

[0007] S3. Add the cleaned zinc metal foil to the solution obtained in S1, and after ultrasonic treatment, obtain zinc metal foil coated with zinc oxalate.

[0008] S4. After the zinc metal foil coated with zinc oxalate is subjected to ultrasonic treatment again, it is ultrasonically cleaned in ethanol and deionized water for 1 to 60 minutes, and then dried to obtain the three-dimensional zinc / zinc oxalate anode material.

[0009] Furthermore, in S1, the concentration of the oxalic acid solution is 10. -3 ~10 -1 g / mL.

[0010] Furthermore, in S2, the thickness of the zinc foil is 0.01–1 mm, and the surface area is 1–1000 cm². 2 The ultrasonic treatment time is 1 to 60 minutes.

[0011] Furthermore, in S3, the temperature conditions for ultrasonic treatment are -5 to 0℃, the power conditions are 100 to 300W, and the time conditions are 5 to 120min.

[0012] Furthermore, in S4, the specific operation of ultrasonic treatment is as follows: the zinc metal foil coated with zinc oxalate is ultrasonically cleaned in ethanol and deionized water for 1 to 60 minutes.

[0013] Furthermore, in S4, the drying temperature is 40–100°C and the time is 8–24 h.

[0014] The three-dimensional zinc / zinc oxalate anode material prepared by the above method.

[0015] Furthermore, the three-dimensional zinc / zinc oxalate anode material includes a substrate material and a three-dimensional protective layer, wherein the thickness of the substrate material is 0.01–1 mm and the surface area is 1–1000 cm². 2 The three-dimensional protective layer is made of zinc oxalate and has a thickness of 2–20 μm.

[0016] The above-mentioned three-dimensional zinc / zinc oxalate anode material is used in the preparation of aqueous secondary batteries.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. The preparation method of the three-dimensional zinc / zinc oxalate anode material of the present invention involves depositing a uniform and stable zinc oxalate protective layer in situ on the surface of zinc metal foil through a simple low-temperature water bath ultrasonic displacement reaction method. By manipulating the low-temperature reaction conditions, the displacement reaction rate between oxalic acid and different crystal planes of zinc metal foil can be controlled. Different crystal planes of zinc metal are etched at different rates by oxalic acid, thereby forming an electrode structure with a three-dimensional interface.

[0019] 2. The three-dimensional zinc / zinc oxalate anode material prepared by the present invention has a three-dimensional interface structure in its zinc oxalate protective layer, resulting in a large electrochemical surface area of ​​the electrode. Compared with the original zinc metal foil electrode, its specific surface area is increased by more than 10 times, which can effectively reduce the local current density during battery cycling and thus inhibit dendrite growth.

[0020] 3. The three-dimensional zinc / zinc oxalate anode material prepared by the present invention has a dense zinc oxalate protective layer that is tightly bonded to the zinc metal foil, which can effectively isolate the zinc anode from the aqueous electrolyte, thereby avoiding direct contact between the active zinc metal and water molecules, thus inhibiting the hydrogen evolution corrosion side reaction and improving the cycle stability and electrochemical performance of the battery.

[0021] 4. When the three-dimensional zinc / zinc oxalate anode material prepared using the present invention is applied to an aqueous zinc secondary battery, the resulting battery has a long cycle life and stable performance. Other advantages and features of the present invention will be partly reflected in the following description and specific embodiments. Attached Figure Description

[0022] Figure 1 This is a SEM image of the three-dimensional zinc electrode of Comparative Example 1 of the present invention.

[0023] Figure 2 The symmetrical cell assembled with a three-dimensional zinc electrode as shown in Comparative Example 1 of this invention operates at 10 mA·cm⁻¹. -2 10mAh·cm -2 Overpotential diagram under test conditions.

[0024] Figure 3 SEM image of the two-dimensional zinc / zinc oxalate electrode of Comparative Example 2 of this invention.

[0025] Figure 4 The symmetrical cell assembled with a two-dimensional zinc / zinc oxalate electrode as Comparative Example 2 of this invention operates at 10 mA·cm⁻¹. -2 10mAh·cm -2 Overpotential diagram under test conditions.

[0026] Figure 5 This is a SEM image of the zinc metal foil electrode of Embodiment 1 of the present invention.

[0027] Figure 6 ab are SEM images of the surface and cross-section of the three-dimensional zinc / zinc oxalate anode material of Example 1 of the present invention, respectively.

[0028] Figure 7 The electrochemical impedance spectroscopy of the three-dimensional zinc / zinc oxalate anode material and the original zinc metal foil electrode in Example 1 of this invention is shown.

[0029] Figure 8 The symmetrical cell assembled with the original zinc foil electrode of Embodiment 1 of the present invention operates at 1 mA·cm⁻¹. -2 0.5mAh·cm -2 Overpotential diagram under test conditions.

[0030] Figure 9 The symmetrical battery assembled using the three-dimensional zinc / zinc oxalate anode material of Example 1 of this invention operates at 1 mA·cm⁻¹. -2 0.5mAh·cm -2 Overpotential diagram under test conditions.

[0031] Figure 10 The symmetrical cell assembled with the original zinc foil electrode of Embodiment 1 of the present invention operates at 10 mA·cm⁻¹. -2 10mAh·cm-2 Overpotential diagram under test conditions.

[0032] Figure 11 The symmetrical battery assembled using the three-dimensional zinc / zinc oxalate anode material of Example 1 of this invention operates at 10 mA·cm⁻¹. -2 10mAh·cm -2 Overpotential diagram under test conditions. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through specific embodiments. The specific embodiments described in detail herein are merely illustrative of the invention and are not intended to limit its scope.

[0034] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation scheme are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0035] Comparative Example 1

[0036] The preparation method of three-dimensional zinc metal anode material includes the following steps:

[0037] (1) Add 10 mL of concentrated hydrochloric acid to 1000 mL of deionized water and stir for 20 min at room temperature to form a clear and transparent solution;

[0038] (2) Cut a commercial zinc foil with a length of 5cm, a width of 5cm and a thickness of 0.1mm, and place it in ethanol and deionized water for ultrasonic cleaning for 20min each. Then place the cleaned zinc foil in a 60℃ oven to dry for later use.

[0039] (3) After immersing the zinc metal foil in hydrochloric acid solution, place it in a low-temperature ice-water bath at a temperature of -5℃ and subject it to an ultrasonic reaction with a power of 300W for 30 minutes to obtain a three-dimensional zinc metal anode material.

[0040] The scanning electron microscope (SEM) images of the three-dimensional zinc metal electrode surface in this comparative example are shown below. Figure 1 As shown, the three-dimensional structure that appears on its surface due to selective etching can be seen.

[0041] Symmetrical battery assembly: Three-dimensional zinc metal foil was cut into circular pieces with a diameter of 11 mm to make aqueous zinc secondary battery electrodes; two three-dimensional zinc electrodes were used as positive and negative electrodes respectively, glass fiber membrane was used as separator, and 2.0M ZnSO4 solution was used as electrolyte to assemble a CR2025 type symmetric battery.

[0042] The CR2025 symmetrical cell prepared above was subjected to a 10 mA / cm² temperature range. 2 and 10mAh / cm2 Under the conditions of continuous cyclic testing, the results are as follows: Figure 2 As shown, the symmetrical battery exhibits polarization after 40 hours of cycling, with the overpotential increasing from 100mV to 150mV. After 80 hours of cycling, the battery overpotential increases to 200mV, resulting in battery failure.

[0043] Comparative Example 2

[0044] The preparation method of two-dimensional zinc / zinc oxalate anode material includes the following steps:

[0045] (1) Add 14g of C2H2O4·2H2O to 1000mL of deionized water and stir at room temperature for 20min to dissolve it, so as to obtain a concentration of 10 -2 Zinc oxalate solution at a concentration of g / mL;

[0046] (2) Cut a commercial zinc foil with a length of 5cm, a width of 5cm and a thickness of 0.1mm, and place it in ethanol and deionized water for ultrasonic cleaning for 20min each. Then place the cleaned zinc foil in a 60℃ oven to dry for later use.

[0047] (3) After immersing the zinc metal foil in oxalic acid solution, place it in a high-temperature water bath at 40°C and stir for 30 minutes to grow a uniform white zinc oxalate protective layer on the zinc metal foil in situ, thus obtaining a two-dimensional zinc / zinc oxalate metal foil.

[0048] The scanning electron microscope (SEM) images of the two-dimensional zinc metal anode surface in this comparative example are shown below. Figure 3 As shown, due to the high reaction temperature, the selectivity of inorganic acid for etching the zinc metal crystal surface is weakened, thus only a two-dimensional interface structure can be formed, and the specific surface area does not increase significantly. Symmetrical cell assembly: Two-dimensional zinc / zinc oxalate metal foil was cut into circular pieces with a diameter of 11 mm to make aqueous zinc secondary battery electrodes; two two-dimensional zinc / zinc oxalate electrodes were used as the positive and negative electrodes, respectively, with a glass fiber membrane as the separator and a 2.0 M ZnSO4 solution as the electrolyte, to assemble a CR2025 type symmetric cell.

[0049] The CR2025 symmetrical cell prepared above was subjected to a 10 mA / cm² temperature range. 2 and 10mAh / cm 2 Under the conditions of continuous cyclic testing, the results are as follows: Figure 4 As shown, the overpotential of the symmetrical battery increases from 100mV to 200mV after 30 hours of cycling, and increases to 1.5V after another 41 hours of cycling, leading to battery failure.

[0050] Example 1

[0051] A method for preparing a three-dimensional zinc / zinc oxalate anode material includes the following steps:

[0052] (1) Add 14g of C2H2O4·2H2O to 1000mL of deionized water and stir at room temperature for 20min to dissolve it, so as to obtain a concentration of 10 -2 oxalic acid solution at a concentration of g / mL;

[0053] (2) Cut a piece of original commercial zinc foil with a length of 5cm, a width of 5cm and a thickness of 0.1mm. Place it in ethanol and deionized water for ultrasonic cleaning for 20min each. Then place the cleaned zinc foil in a 60℃ oven to dry for later use.

[0054] (3) After immersing the zinc foil in oxalic acid solution, place it in a low-temperature ice-water bath at -5°C and subject it to ultrasonic treatment at 300W for 30 minutes to allow a uniform white zinc oxalate protective layer to grow in situ on the zinc foil, thus obtaining a three-dimensional zinc / zinc oxalate anode material. The obtained three-dimensional zinc / zinc oxalate anode material is then sliced ​​using a slicer into pieces with a diameter of 11mm (surface area of ​​0.94985cm²). -2 The circular pieces are used as electrode plates;

[0055] Scanning electrode images of the zinc metal foil from step (2) and the three-dimensional zinc / zinc oxalate anode material in this embodiment were obtained respectively, and the results are as follows: Figure 5-6 As shown, it can be seen that Figure 5 The images show scanning electron microscope (SEM) images of the original zinc foil surface, which exhibits a relatively flat two-dimensional surface structure, while the three-dimensional zinc / zinc oxalate anode material surface is shown in the following images. Figure 6 a, its surface is covered with a uniformly distributed zinc oxalate protective layer, and its cross-sectional scanning electron microscope image is as follows. Figure 6 b. It can be seen that the interface between zinc metal and zinc oxalate protective layer has a three-dimensional structure, and the thickness of zinc oxalate protective layer is 4-6μm.

[0056] Using the zinc foil from step (2) as a comparative experiment, the specific surface area of ​​the three-dimensional zinc / zinc oxalate anode material prepared in this embodiment was characterized by EIS testing. The electrochemical impedance spectroscopy was measured under open-circuit voltage conditions, and the results are as follows: Figure 7 As shown, the double-layer capacitance of the three-dimensional zinc / zinc oxalate anode material prepared in this embodiment is 41.3 μF cm⁻¹. -2 Compared to the original zinc foil electrode's double-layer capacitance (3.5 μF cm⁻¹), -2 The surface area of ​​the three-dimensional zinc / zinc oxalate anode material is increased by 11.8 times, which indicates that the surface area of ​​the three-dimensional zinc / zinc oxalate anode material is larger than that of the original zinc foil.

[0057] Symmetrical cells were assembled using zinc metal foil as the negative electrode material and the three-dimensional zinc / zinc oxalate negative electrode material prepared in this embodiment as the electrode material, respectively:

[0058] Zinc metal foil was cut into 11mm diameter discs to form an aqueous zinc secondary battery electrode. Two zinc metal foils were used as the positive and negative electrodes, respectively, with a glass fiber membrane as the separator and a 2.0M ZnSO4 solution as the electrolyte, to assemble a CR2025 type symmetrical battery.

[0059] The three-dimensional zinc / zinc oxalate anode material prepared in this embodiment was cut into circular pieces with a diameter of 11 mm to form an aqueous zinc secondary battery electrode. Two pieces of three-dimensional zinc / zinc oxalate anode material were used as the positive and negative electrodes, respectively, with a glass fiber membrane as the separator and a 2.0 M ZnSO4 solution as the electrolyte, to assemble a CR2025 type symmetrical battery.

[0060] The two CR2025 symmetrical cells prepared above were subjected to an A / cm test at 1 mA / cm. 2 and 0.5mAh / cm 2 or 10mA / cm 2 and 10mAh / cm 2 Under the conditions of continuous cyclic testing, the results are as follows: Figure 8-11 As shown, at 1 mA / cm 2 and 0.5mAh / cm 2 Under certain conditions, the symmetrical cell assembled with zinc foil exhibited an overpotential of approximately 35 mV during cycling. Furthermore, the overpotential of the symmetrical cell increased to 60 mV after 60 hours of cycling, and exceeded 500 mV after 80 hours. In contrast, the symmetrical cell assembled with a three-dimensional zinc / zinc oxalate electrode exhibited a lower overpotential (approximately 20 mV) and could cycle stably for 2000 hours. At 10 mA / cm², the overpotential was lower. 2 and 10mAh / cm 2 Under the given conditions, the symmetrical battery assembled from zinc foil exhibited an overpotential of approximately 250 mV during cycling and experienced a short circuit after 10 hours of cycling, while the battery assembled from three-dimensional zinc / zinc oxalate electrodes exhibited an overpotential of only 100 mV and was able to cycle stably for 100 hours.

[0061] The three-dimensional zinc / zinc oxalate anode material prepared in this embodiment can be used to prepare aqueous zinc secondary battery anodes, and can be used in symmetrical, button, pouch, and three-electrode battery systems.

[0062] Example 2

[0063] A method for preparing a three-dimensional zinc / zinc oxalate anode material includes the following steps:

[0064] (1) Add 1.4 g of C2H2O4·2H2O to 1000 mL of deionized water and stir at room temperature for 100 min to dissolve it, so as to obtain a concentration of 10 -3 Zinc oxalate solution at a concentration of g / mL;

[0065] (2) Cut a commercial zinc foil with a length of 10cm, a width of 10cm and a thickness of 0.05mm, and place it in ethanol and deionized water for ultrasonic cleaning for 20min each. Then place the cleaned zinc foil in a 60℃ oven to dry for later use.

[0066] (3) After immersing the zinc metal foil in oxalic acid solution, place it in a low-temperature ice-water bath at -5℃ and subject it to an ultrasonic reaction with a power of 200W for 5 minutes to grow a uniform white zinc oxalate protective layer on the zinc metal foil in situ, thus obtaining a three-dimensional zinc / zinc oxalate metal foil.

[0067] Symmetrical cell assembly: Three-dimensional zinc / zinc oxalate metal foil was cut into circular pieces with a diameter of 15 mm to make aqueous zinc secondary battery electrodes; two three-dimensional zinc / oxalate electrodes were used as positive and negative electrodes respectively, glass fiber membrane was used as separator, and 2.0M ZnSO4 solution was used as electrolyte to assemble a CR2025 type symmetric cell.

[0068] Symmetrical cell testing: Cyclic performance was tested under normal temperature conditions at 2 mA·cm⁻¹. -2 0.5mAh·cm -2 Under continuous cycle testing conditions, the symmetrical cell exhibited an overpotential of approximately 30 mV and maintained this overpotential for 500 hours.

[0069] Full cell assembly: A three-dimensional zinc / zinc oxalate anode material is used as the anode, a copper foil-loaded MnO2 is used as the cathode, a glass fiber membrane is used as the separator, and a 2.0M ZnSO4+0.1M MnSO4 solution is used as the electrolyte to assemble a three-dimensional zinc / zinc oxalate|MnO2 full cell.

[0070] Full battery test: Under normal temperature conditions, within a voltage range of 1.0–1.8V, at 100mA·g -1 Charge-discharge tests were conducted at a constant current density. After 100 cycles, the three-dimensional zinc / zinc oxalate|MnO2 full cell exhibited a capacity retention of 85.6% and a high coulombic efficiency of 99.5%. Using the zinc foil from step (2) as the negative electrode, the original zinc foil|MnO2 full cell was assembled. The test results showed that the original zinc foil|MnO2 had a cycle stability of 32.9% and a coulombic efficiency of 98.5%, which were significantly inferior to those of the three-dimensional zinc / zinc oxalate|MnO2 full cell.

[0071] Example 3

[0072] A method for preparing a three-dimensional zinc / zinc oxalate anode material includes the following steps:

[0073] (1) Add 14g of C2H2O4·2H2O to 1000mL of deionized water and stir for 100min at room temperature to dissolve it, so as to obtain a concentration of 10 -1 Zinc oxalate solution at a concentration of g / mL;

[0074] (2) Cut a commercial zinc foil with a length of 10cm, a width of 10cm and a thickness of 0.05mm, and place it in ethanol and deionized water for ultrasonic cleaning for 20min each. Then place the cleaned zinc foil in a 60℃ oven to dry for later use.

[0075] (3) After immersing the zinc metal foil in oxalic acid solution, place it in a low-temperature ice-water bath at 0°C and subject it to an ultrasonic reaction with a power of 300W for 60 minutes to grow a uniform white zinc oxalate protective layer on the zinc metal foil in situ, thus obtaining a three-dimensional zinc / zinc oxalate metal foil.

[0076] Symmetrical cell assembly: Three-dimensional zinc / zinc oxalate metal foil was cut into circular pieces with a diameter of 15 mm to make aqueous zinc secondary battery electrodes; two three-dimensional zinc / oxalate electrodes were used as positive and negative electrodes respectively, glass fiber membrane was used as separator, and 2.0M ZnSO4 solution was used as electrolyte to assemble a CR2025 type symmetric cell.

[0077] Symmetrical cell testing: Cyclic performance was tested under normal temperature conditions at 2 mA·cm⁻¹. -2 0.5mAh·cm -2 Under continuous cycle testing conditions, the symmetrical cell exhibited an overpotential of approximately 32 mV and maintained this overpotential for 550 hours.

[0078] Full cell assembly: A three-dimensional zinc / zinc oxalate anode material is used as the anode, a copper foil-loaded MnO2 is used as the cathode, a glass fiber membrane is used as the separator, and a 2.0M ZnSO4+0.1M MnSO4 solution is used as the electrolyte to assemble a three-dimensional zinc / zinc oxalate|MnO2 full cell.

[0079] Full battery test: Under normal temperature conditions, within a voltage range of 1.0–1.8V, at 100mA·g -1 Charge-discharge tests were conducted at a constant current density. After 100 cycles, the three-dimensional zinc / zinc oxalate|MnO2 full cell exhibited a capacity retention of 87.3% and a high coulombic efficiency of 99.1%. Using the zinc foil from step (2) as the negative electrode, the original zinc foil|MnO2 full cell was assembled. The test results showed that the original zinc foil|MnO2 had a cycle stability of 32.9% and a coulombic efficiency of 98.5%, which were significantly inferior to those of the three-dimensional zinc / zinc oxalate|MnO2 full cell.

[0080] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional zinc / zinc oxalate anode material, characterized in that, Includes the following steps: S1. Add H2C2O4 to 250-1000 mL of deionized water and stir magnetically at room temperature to dissolve it and form a clear and transparent oxalic acid solution. S2. The zinc foil is ultrasonically cleaned in ethanol and deionized water in sequence. S3. Add the cleaned zinc metal foil to the solution obtained in S1, and after ultrasonic treatment, obtain zinc metal foil coated with zinc oxalate; wherein, the temperature conditions for ultrasonic treatment are -5~0℃, the power conditions are 100~300W, and the time conditions are 5~120min. S4. After the zinc metal foil coated with zinc oxalate is ultrasonically treated again, it is ultrasonically cleaned in ethanol and deionized water for 1 to 60 minutes, and then dried. The drying temperature is 40 to 100℃ and the time is 8 to 24 hours to obtain the three-dimensional zinc / zinc oxalate anode material.

2. The method for preparing the three-dimensional zinc / zinc oxalate anode material according to claim 1, characterized in that, In S1, the concentration of the oxalic acid solution was 10 -3 ~ 10 -1 g / mL.

3. The method for preparing the three-dimensional zinc / zinc oxalate anode material according to claim 1, characterized in that, In S2, the thickness of the zinc metal foil is 0.01-1 mm, the surface area is 1-1000 cm 2 , and the time condition for ultrasonic treatment is 1-60 min.

4. The method for preparing the three-dimensional zinc / zinc oxalate anode material according to claim 1, characterized in that, The specific procedure for ultrasonic treatment is as follows: zinc foil coated with zinc oxalate is ultrasonically cleaned in ethanol and deionized water for 1 to 60 minutes.

5. The three-dimensional zinc / zinc oxalate anode material prepared by the preparation method according to any one of claims 1-4.

6. The three-dimensional zinc / zinc oxalate anode material according to claim 5, characterized in that, The three-dimensional zinc / zinc oxalate anode material includes a substrate material and a three-dimensional protective layer. The substrate material has a thickness of 0.01–1 mm and a surface area of ​​1–1000 cm². 2 The three-dimensional protective layer is made of zinc oxalate and has a thickness of 2–20 μm.

7. The application of the three-dimensional zinc / zinc oxalate anode material as described in claim 6 in the preparation of aqueous secondary batteries.

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