Anode-free zinc metal battery with zwitterionic polymer as binder

Abstract

The present invention discloses a negative electrode-free zinc metal battery using a zwitterionic polymer as a binder. The negative electrode-free zinc metal battery is assembled from a positive electrode, a separator, a negative electrode current collector loaded with a zwitterionic polymer binder, and an electrolyte. The present invention uses a zwitterionic polymer binder as a negative electrode current collector, guides zinc ion deposition through the action of zwitterions, and the reversible hydrogen bonds and dynamic ionic bonds inside the polymer can buffer the volume change caused by zinc deposition, achieve uniform zinc deposition and high electroplating / stripping efficiency, and greatly improve the energy density and cycle performance of the negative electrode-free zinc metal battery.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc metal batteries without negative electrodes, and relates to a zinc metal battery without negative electrodes using a zwitterionic polymer as a binder. Background Art

[0002] In the post-lithium-ion era, rechargeable aqueous metal-ion batteries have broad application prospects as alternative energy storage devices due to their inherent green and safe characteristics. Aqueous zinc-ion batteries have high energy density among low-cost aqueous batteries, with a capacity of 840 mAh g -1 The theoretical capacity is 5850 mAh cm -3 The high volume capacity and other significant advantages of aqueous zinc-ion batteries are expected to be used in large-scale power storage systems. However, zinc anode problems such as zinc dendrites and side reactions seriously shorten the cycle life of aqueous zinc-ion batteries, and the aqueous zinc-ion batteries currently developed usually use thicker metal zinc anodes, which contain zinc that is more than tens of times the actual cycle amount, resulting in most materials being wasted. At the same time, the actual energy density of the battery is far lower than the theoretical value because the zinc utilization rate is far lower than the actual usage. Document 1 reports a negative-electrode-free zinc metal battery prepared by coating a carbon nano-nucleation layer on a copper foil by direct water treatment, but the assembled full battery has only 68.2% of the capacity retention rate after 80 cycles (Yunpei Zhu, Yi Cui, Husam N. Alshareef. Nano Letters, 2021, 21 (3): 1446-1453.), which limits its practical application. Therefore, it is necessary to develop a negative-electrode-free zinc metal battery with a high cycle life. Summary of the invention

[0003] The object of the present invention is to provide a negative electrode-free zinc metal battery using a zwitterionic polymer as a binder.

[0004] The technical solution to achieve the purpose of the present invention is:

[0005] The invention discloses a negative electrode-free zinc metal battery using a zwitterionic polymer as a binder, which is assembled from a positive electrode, a separator, a negative electrode current collector loaded with a zwitterionic polymer binder, and an electrolyte. The negative electrode current collector loaded with a zwitterionic polymer binder is prepared by the following steps: using N-methylpyrrolidone as a solvent, mixing and grinding a coating material and a zwitterionic polymer evenly, then coating the slurry evenly on the surface of the negative electrode current collector substrate, vacuum drying, and depositing zinc on the surface of the current collector coated with the coating material and the zwitterionic polymer by an electrodeposition method. The structural formula of the zwitterionic polymer is:

[0006] The positive electrode described in the present invention is a positive electrode conventionally used in zinc metal batteries without negative electrodes, such as sodium vanadate.

[0007] The diaphragm described in the present invention is a diaphragm commonly used in negative electrode-free zinc metal batteries, such as glass fiber.

[0008] The electrolyte described in the present invention is an electrolyte commonly used in negative electrode-free zinc metal batteries, such as zinc sulfate, zinc trifluoromethanesulfonate and zinc chloride.

[0009] The zwitterionic polymer of the invention is prepared by copolymerizing methacryloylethyl sulfobetaine, hydroxyethyl acrylate and methoxy polyethylene glycol acrylate in a molar ratio of 6:9:5 and is prepared by an existing method.

[0010] The negative electrode current collector substrate of the present invention is a current collector substrate conventionally used in the art, such as copper foil, aluminum foil, titanium foil, tin foil, etc.

[0011] Preferably, the coating material is selected from carbon black, carbon nanotubes or graphene. In a specific embodiment of the present invention, the coating material used is carbon black. When carbon black is used as the coating material, the mass ratio of carbon black to zwitterionic polymer is 7:3.

[0012] Preferably, the grinding time is more than 30 min.

[0013] Preferably, the vacuum drying temperature is 60±5° C., and the vacuum drying time is more than 36 hours.

[0014] Preferably, the specific method of the electrodeposition method is: in a two-electrode or three-electrode device, a current collector coated with a coating material and a zwitterionic polymer is used as a working electrode, zinc is used as a counter electrode, and metallic zinc is electrodeposited in a zinc salt solution by constant current charging or constant voltage charging.

[0015] Preferably, when constant current charging is adopted, the current density is 1 mA cm -2 , lasting for 2 to 6 hours.

[0016] Preferably, when a constant voltage charging method is adopted, the voltage is 0.5V and the capacity is 2mAh to 6mAh.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The ion channels provided by zwitterionic polymers can significantly increase the zinc ion transfer rate. At the same time, the presence of sulfonic acid groups can reduce the zinc nucleation energy barrier, which is conducive to the uniform deposition of zinc ions.

[0019] (2) The reversible hydrogen bonds and dynamic ionic bonds inside the zwitterionic polymer buffer the volume change caused by zinc deposition, improving the cycle performance of the battery, so that the assembled full battery still has a capacity retention rate of 93.5% after 200 charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of the preparation of the zwitterionic polymer.

[0021] Figure 2 This is the infrared spectrum of zwitterionic polymer.

[0022] Figure 3 This is the SEM image of the copper@zwitterionic polymer negative electrode current collector prepared in Example 1.

[0023] Figure 4 This is the XPS graph of the Zn element in the copper@zwitterionic polymer negative electrode current collector prepared in Example 1.

[0024] Figure 5 This is the XPS graph of the Zn element in the titanium@zwitterionic polymer negative electrode current collector prepared in Example 2.

[0025] Figure 6 This is the XPS graph of the Zn element in the aluminum@zwitterionic polymer negative electrode current collector prepared in Example 3.

[0026] Figure 7 This is a comparison chart of the capacity-voltage curves of the negative electrode-free zinc metal battery prepared in Example 1 and Comparative Example 1.

[0027] Figure 8 This is a comparison chart of the cycle performance of the negative electrode-free zinc metal battery prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0028] The present invention will be further described below through specific embodiments and drawings.

[0029] The preparation of the zwitterionic polymer described in the present invention is based on the literature [Cheng Wang, Peng Chen, Yinan Wang, Tao Chen, Mingliang Liu, Mingchang Zhang, Yongsheng Fu, Jianqiang Xu, Jiajun Fu. Advanced Functional Materials, 2022, 32 (34): 2204451-2204462.], such as Figure 1 As shown, the specific steps are as follows: under an inert atmosphere, 2,2'-azobisisobutyronitrile is used as an initiator, methacryloylethyl sulfobetaine, hydroxyethyl acrylate and methoxypolyethylene glycol acrylate in a molar ratio of 6:9:5 are dissolved in trifluoroethanol, the mixed solution is reacted at 65°C for 48 hours, p-hydroxyanisole is added to terminate the reaction, the copolymer is added to ice ether for precipitation, and the obtained product is dried at 60°C under vacuum conditions for 24 hours to obtain a zwitterionic polymer.

[0030] Example 1

[0031] The preparation steps of the negative electrode-free zinc metal battery using a zwitterionic polymer as a binder are as follows:

[0032] (1) Carbon black and polymer were weighed in a mortar at a mass ratio of 7:3, and an appropriate amount of N-methylpyrrolidone was added and ground for 30 minutes. The slurry was evenly coated on the surface of the copper foil current collector substrate using a coater and dried at 60°C under vacuum for 36 hours.

[0033] (2) In a two-electrode device, the prepared current collector was used as the working electrode, metal zinc was used as the counter electrode and reference electrode, and a ZnSO4 solution with a concentration of 1 mol / L was used as the electrolyte at a flow rate of 1 mA cm -2 The battery was taken out after constant current charging at a current density of 10000 nm for 4 h, and the residual electrolyte on the surface was rinsed with deionized water, and then dried in a blast oven to obtain a negative electrode current collector with a copper foil as a matrix and loaded with a zwitterionic polymer binder.

[0034] (3) Sodium vanadate is used as the positive electrode, the negative electrode current collector prepared in step (2) is used as the negative electrode, 1 mol / L zinc trifluoromethanesulfonate is used as the electrolyte, and glass fiber is used as the separator to assemble a negative electrode-free zinc metal battery.

[0035] pass Figure 3 It can be seen that zinc metal is uniformly deposited on the surface coating of the current collector without dendrites and cracks.

[0036] pass Figure 4 It can be seen that the XPS analysis results show that the main component of the current collector coating is metallic zinc, and the content of the byproduct ZnO is very low, which proves that the present invention can promote the uniform deposition of zinc metal and effectively inhibit the generation of side reactions.

[0037] Example 2

[0038] This embodiment is basically the same as Embodiment 1, the only difference being that the current collector substrate used is titanium foil.

[0039] pass Figure 5 It can be seen that the XPS analysis results show that the main component of the current collector coating is metallic zinc, and the content of the byproduct ZnO is very low, which proves that the present invention can promote the uniform deposition of zinc metal and effectively inhibit the generation of side reactions.

[0040] Example 3

[0041] This embodiment is basically the same as Embodiment 1, the only difference being that the current collector substrate used is aluminum foil.

[0042] pass Figure 6It can be seen that the XPS analysis results show that the main component of the current collector coating is metallic zinc, and the content of the byproduct ZnO is very low, which proves that the present invention can promote the uniform deposition of zinc metal and effectively inhibit the generation of side reactions.

[0043] Comparative Example 1

[0044] This comparative example is basically the same as Example 2, the only difference being that the binder used is PVDF.

[0045] Figure 7 The figure is a comparison of the capacity-voltage curves of the negative electrode-free zinc metal battery prepared in Example 1 and Comparative Example 1. As shown in the figure, the nucleation overpotential of the battery using commercial PVDF as a binder is relatively large, about 51mV, while the nucleation overpotential of the battery using a zwitterionic polymer as a binder is only 29mV, indicating that the zwitterionic polymer can reduce the zinc ion nucleation overpotential, which is conducive to the uniform deposition of zinc ions.

[0046] Figure 8 The negative electrode-free zinc metal battery prepared in Example 1 and Comparative Example 1 is 1Ag -1 As shown in the figure, the capacity of the full battery using commercial PVDF as a binder begins to decay rapidly after 70 charge / discharge cycles. This is because the zinc deposited on the current collector using PVDF as a binder is mostly dead zinc, and the dendrite growth is serious, and the available zinc is very limited. Therefore, as the available zinc supply is insufficient, the capacity drops sharply. The capacity of the full battery using zwitterionic polymer as a binder is stably maintained at 320mAh g -1 About, and still has a capacity retention rate of 93.5% after 200 charge and discharge cycles. This is mainly due to the amphiphilic ionic groups in the zwitterionic polymer. Since the inherent zwitterionic groups on the sulfobetaine chain can provide separated ion migration channels for positive and negative ions for large ion transport, a higher rate capacity is generated, which greatly promotes the transport of electrolyte ions. At the same time, the negatively charged sulfonic acid groups can combine with zinc ions, reducing the barrier of zinc nucleation and electroplating / stripping on the surface of the nucleation layer, which is conducive to promoting uniform zinc plating and inhibiting side reactions.

[0047] In summary, the present invention uses a zwitterionic polymer binder and utilizes the action of zwitterions to guide the deposition of zinc ions. The reversible hydrogen bonds and dynamic ionic bonds inside the polymer can buffer the volume changes caused by zinc deposition, ultimately achieving uniform zinc deposition and high electroplating / stripping efficiency, greatly improving the energy density and cycle performance of negative electrode-free zinc metal batteries.

Claims

1. A negative electrode-free zinc metal battery using a zwitterionic polymer as a binder, characterized in that: The invention is assembled from a positive electrode, a separator, a negative electrode current collector loaded with a zwitterionic polymer binder and an electrolyte. The negative electrode current collector loaded with a zwitterionic polymer binder is prepared by the following steps: using N-methylpyrrolidone as a solvent, mixing and grinding a coating material and a zwitterionic polymer evenly, then coating the slurry evenly on the surface of the negative electrode current collector substrate, vacuum drying, and depositing zinc on the surface of the current collector coated with the coating material and the zwitterionic polymer by an electrodeposition method. The zwitterionic polymer has a structural formula of , the coating material is selected from carbon black, carbon nanotubes or graphene.

2. The negative electrode-free zinc metal battery according to claim 1, characterized in that: The positive electrode is sodium vanadate, the diaphragm is glass fiber, and the electrolyte is zinc sulfate, zinc trifluoromethanesulfonate or zinc chloride.

3. The negative electrode-free zinc metal battery according to claim 1, characterized in that: The negative electrode current collector substrate is copper foil, aluminum foil, titanium foil or tin foil.

4. The negative electrode-free zinc metal battery according to claim 3, characterized in that: The mass ratio of carbon black to zwitterionic polymer is 7:

3.

5. The negative electrode-free zinc metal battery according to claim 1, characterized in that: The grinding time is more than 30 minutes.

6. The negative electrode-free zinc metal battery according to claim 1, characterized in that: The vacuum drying temperature is 60±5 ℃ and the vacuum drying time is more than 36 hours.

7. The negative electrode-free zinc metal battery according to claim 1, characterized in that: The specific method of the electrodeposition method is: in a two-electrode or three-electrode device, a current collector coated with a coating material and a zwitterionic polymer is used as a working electrode, zinc is used as a counter electrode, and metallic zinc is electrodeposited in a zinc salt solution by constant current charging or constant voltage charging.

8. The negative electrode-free zinc metal battery according to claim 1, characterized in that: When constant current charging is adopted, the current density is 1 mA cm -2 , lasting for 2~6 hours.

9. The negative electrode-free zinc metal battery according to claim 1, characterized in that: When using constant voltage charging, the voltage is 0.5 V and the capacity is 2 mAh~6 mAh.

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