Near-neutral zinc ion battery with 2V platform voltage

Abstract

The invention discloses a near-neutral zinc ion battery with 2V platform voltage, which comprises a positive electrode, a negative electrode and an electrolyte, the negative electrode is an indissolvable zinc compound, the electrolyte is soluble acetate without zinc ions, a layer of crowded micellar electrolyte is added between the positive electrode and the electrolyte, and the crowded micellar electrolyte is formed by mixing the positive electrode, the negative electrode and the electrolyte. The crowded micelle electrolyte is clay minerals or macromolecules rich in hydroxyl groups or amino groups. The zinc ion battery disclosed by the invention can realize a working voltage exceeding 2V under a nearly neutral aqueous electrolyte condition, the positive electrode of the zinc ion battery can be made of an existing common positive electrode material, and the matching applicability of the negative electrode and the electrolyte is wide, so that the zinc ion battery can be expanded to various zinc battery systems; for example, a mixed zinc-lithium ion system, a mixed zinc-sodium ion system or a zinc-iodine system and the like have a wide commercial application prospect.

Description

Technical Field

[0001] The present invention relates to a high-voltage aqueous zinc-ion battery under near-neutral electrolyte conditions and belongs to the field of high-voltage aqueous batteries. Technical Background

[0002] Aqueous batteries, such as lead-acid and nickel-based aqueous batteries, have been widely used in the field of energy storage. However, the electrolytes used in them are strongly acidic or alkaline, resulting in strong corrosiveness. Moreover, these batteries contain heavy metal elements such as lead and cadmium, which are not only highly toxic to the human body but also cause serious environmental pollution. These problems force us to develop a safer, non-toxic, and low-cost battery system. Aqueous zinc-ion batteries under near-neutral electrolyte conditions are expected to solve these problems due to their mild electrolyte conditions and environmental friendliness. However, such batteries often have disadvantages such as low energy density, mainly because of their low voltage plateau, generally less than 2V, which greatly limits their energy output. Currently, the reported voltage systems exceeding 2V generally use strong acid-base electrolytes or use ion exchange membranes to prepare decoupling devices. Such devices are not only troublesome to prepare but also have certain potential safety hazards during the experimental process. Other more efficient and simpler battery systems have not been reported yet.

[0003] Under near-neutral aqueous electrolyte conditions, there are mainly two challenges in achieving a high-voltage zinc-ion battery: Firstly, the selection of electrode materials under near-neutral electrolyte conditions is limited. Due to its mild neutral environment, the electrode reaction cannot be very intense, resulting in a relatively low absolute value of the electrode potential. Currently, the main type of negative electrode used in aqueous zinc-ion batteries is the zinc metal negative electrode, and the electrode potential of this type of negative electrode is only -0.76V (relative to the standard hydrogen electrode). If a 2V battery is to be constructed, the potential on the positive electrode side needs to exceed 1.24V, and such a high potential is almost impossible in a near-neutral electrolyte. Therefore, there is an urgent need to develop a new type of negative electrode with a lower electrode potential. Another key issue is that the electrochemical stability window of near-neutral electrolytes is narrow and there are compatibility problems with high-voltage positive and negative electrodes. The narrow electrochemical window often leads to side reactions such as hydrogen evolution and oxygen evolution. Currently, some solutions have been proposed by researchers to broaden the electrochemical stability window of neutral electrolytes, such as "water-in-salt" electrolytes, eutectic electrolytes, molecular crowding electrolytes, etc. However, this adjustment method treats the positive and negative electrode interfaces uniformly as the same, but in this high-voltage battery system, the requirements for the positive and negative electrode interfaces are often different, and a single electrolyte regulation cannot solve the contradictory problems between the two interfaces at the same time. Therefore, how to design an electrolyte to be compatible with both positive and negative electrode interfaces is also the key for a high-voltage aqueous zinc-ion battery to operate stably. Summary of the Invention

[0004] Aiming at the disadvantage of low voltage of near-neutral aqueous zinc-ion batteries, the purpose of the present invention is to provide a near-neutral zinc-ion battery with a 2V platform voltage, which can achieve a working voltage exceeding 2V in a near-neutral electrolyte.

[0005] In order to achieve the above technical purpose, the present invention adopts the following technical solutions:

[0006] A near-neutral zinc-ion battery with a 2V platform voltage, comprising a positive electrode, a negative electrode and an electrolyte. The negative electrode is a poorly soluble zinc compound, and the electrolyte is a soluble acetate without zinc ions. A layer of crowded micelle electrolyte is added between the positive electrode and the electrolyte, and the crowded micelle electrolyte is a clay mineral or a macromolecule rich in hydroxyl or amino groups.

[0007] Furthermore, the poorly soluble zinc compound of the present invention is selected from one of ZnC2O4·2H2O (zinc oxalate), Zn3(C6H5O7)2·2H2O (zinc citrate), 3Zn(OH)2·2ZnCO3 (basic zinc carbonate), Zn(OH)2 (zinc hydroxide), ZnF2 (zinc fluoride) and Zn3P2O8 (zinc phosphate). The poorly soluble zinc compound of the present invention has a lower electrode potential than the standard zinc electrode. During the charge and discharge process of the battery, it can undergo a conversion reaction with zinc metal. The electrode potential of this reaction depends on the solubility of the zinc compound. The smaller the solubility, the more obvious the decrease in its electrode potential, thereby increasing the working voltage of the battery.

[0008] Furthermore, the soluble acetate is selected from one of lithium acetate, sodium acetate and potassium acetate. The soluble acetate without zinc ions of the present invention has a cation without zinc ions and a relatively low binding energy between the anion and zinc ions, thus not affecting the conversion reaction of zinc salts. At the same time, the pH values of these electrolytes are weakly alkaline, which can effectively inhibit the hydrogen evolution side reaction of water.

[0009] The positive electrode of the present invention can adopt the existing commonly used positive electrode materials. For example, when it is a zinc-lithium mixed ion battery, the positive electrode material is lithium manganate, lithium cobaltate, lithium nickel cobalt manganate, etc.; when it is a zinc-sodium mixed ion battery, the positive electrode material is sodium vanadium phosphate, sodium fluorovanadate, sodium pyrophosphate vanadate, etc.; when it is a zinc-iodine battery, the positive electrode material is activated carbon, carbon cloth, etc.; the ions undergoing insertion / extraction reactions in these positive electrode materials have nothing to do with zinc ions.

[0010] Further, the clay mineral is selected from one of montmorillonite, meerschaum and kaolin; the macromolecule rich in hydroxyl or amino groups is selected from one of polyethylene glycol and polyacrylamide. Between the positive electrode and the electrolyte, the present invention also adds a layer of micellar electrolyte, which can fully inhibit the activity of water, thereby inhibiting the oxygen evolution side reaction, but does not affect the normal reaction process of the positive electrode, and finally realizes a working voltage exceeding 2V. The micellar electrolyte of the present invention is a kind of substance with strong binding effect on water molecules (such as the clay mineral or the macromolecule rich in hydroxyl or amino groups of the present invention, such as polyethylene glycol, polyacrylamide, etc.). These substances can inhibit the activity of water by restricting the liquid content to a lower level and converting the free water molecules in the liquid component into bound water molecules.

[0011] Taking lithium manganate as an example, in the high-voltage zinc-ion battery of the present invention, when the battery is charged, a trace amount of zinc ions are dissolved from the insoluble zinc compound, and then the zinc ions are reduced to zinc metal, while lithium ions are removed from the positive electrode lithium manganate; during discharge, vice versa. Since the electrode potential of the negative electrode is lower than that of the standard zinc electrode, and then combined with the positive electrode lithium manganate, a working voltage exceeding 2V can be achieved. At the same time, between the positive electrode and the liquid electrolyte, due to the presence of the micellar electrolyte, the oxygen evolution side reaction of water can be effectively inhibited, and the Coulomb efficiency and cycle life of the battery are improved.

[0012] The advantages of the present invention are as follows:

[0013] (1) The zinc-ion battery of the present invention can achieve a working voltage exceeding 2V under the condition of a nearly neutral aqueous electrolyte.

[0014] (2) For the zinc-ion battery of the present invention, the existing commonly used positive electrode materials can be used for the positive electrode, and the compatibility of the negative electrode and the electrolyte is wide, and can be extended to various zinc battery systems, such as a hybrid zinc-lithium ion system, a hybrid zinc-sodium ion system or a zinc-iodine system, etc. Description of the Drawings

[0015] Figure 1 It is a comparison chart of charge-discharge curves for Comparative Example 1, Comparative Example 2 and Example 1.

[0016] Figure 2 It is a cycle performance chart of Example 1 and Comparative Example 2. Figure 2 a is the cycle performance chart of Comparative Example 2. Figure 2 b is the cycle performance chart of Example 1.

[0017] Figure 3 It is an in-situ XRD change chart of the negative electrode during the reaction process of Example 1.

[0018] Figure 4 It is a chart of the in-situ XRD change process of the positive electrodes of Example 1 and Comparative Example 2.Figure 4 a is the in-situ XRD change process diagram of the positive electrode in Example 1, Figure 4 b is the in-situ XRD change process diagram of the positive electrode in Comparative Example 2.

[0019] Figure 5 are the charge-discharge curves of the electrolyte with different anions in combination with the zinc oxalate negative electrode in Example 2 and Comparative Example 3.

[0020] Figure 6 are the charge-discharge curve diagrams of Example 1, Example 3 and Example 4. Detailed implementation manners

[0021] The following examples further elaborate on the content of the present invention; however, the protection scope of the claims of the present invention is not limited by the examples.

[0022] Comparative Example 1

[0023] Using zinc metal as the negative electrode, the electrolyte uses 1 mol L -1 zinc sulfate and 1 mol L -1 lithium sulfate as the mixed electrolyte, and using lithium manganate as the positive electrode, a button battery is assembled.

[0024] Comparative Example 2

[0025] First, prepare a slurry by mixing zinc oxalate and PVDF in a mass ratio of 9:1, coat it on a zinc foil current collector, and use it as the negative electrode. The electrolyte uses a lithium acetate electrolyte, and its preparation method is to mix lithium acetate and water in a ratio of 2 g:5 mL. Use lithium manganate as the positive electrode and assemble a button battery.

[0026] Example 1

[0027] First, prepare a slurry by mixing zinc oxalate and PVDF in a mass ratio of 9:1, coat it on a zinc foil current collector, and use it as the negative electrode. The electrolyte uses a lithium acetate electrolyte, and its preparation method is to mix lithium acetate and water in a ratio of 2 g:5 mL. Use lithium manganate as the positive electrode, and add a pressed montmorillonite sheet as a crowded micelle electrolyte in the positive electrode and the liquid electrolyte, and assemble a button battery. Its electrochemical performance measurement and mechanism characterization are shown in the figure:

[0028] Figure 1Shows the charge-discharge curves of Comparative Example 1, Comparative Example 2, and Example 1. As can be seen from the figure, the voltage platforms of Comparative Example 1 are mainly around 1.85 V and 1.7 V, and the highest voltage window only reaches about 2 V. After replacing the zinc negative electrode with a zinc oxalate negative electrode, the voltage platforms are significantly improved, showing discharge voltage platforms around 2.05 V and 1.9 V, and the voltage exceeds 2 V. However, the capacity during the charging process is significantly higher than that during the discharging process, indicating that a serious oxygen evolution side reaction occurs at the positive electrode at this time, resulting in a severely low Coulombic efficiency. After adding a layer of crowded micelle electrolyte to the positive electrode and the electrolyte, not only can the high-voltage property be maintained, but the Coulombic efficiency of charge-discharge is also increased to nearly 100%.

[0029] Figure 2 Shows the cycling performance graphs of Comparative Example 2 and Example 1. As can be seen from the figure, the cycling performance of Comparative Example 2 is poor, which is caused by the oxygen evolution side reaction. After adding the crowded micelle electrolyte, the cycling stability of Example 1 is significantly improved, indicating that the crowded micelle electrolyte plays a key role in cycling stability.

[0030] Figure 3 Shows the XRD changes of the negative electrode during the reaction. As can be seen from the figure, during the charging process, the peaks of zinc oxalate gradually decrease, while the peaks of zinc metal gradually increase, which means that the reaction mechanism during the charging process is the gradual transformation of zinc oxalate into zinc metal. The discharging process shows the opposite phenomenon to the charging process, indicating that the conversion reaction between zinc oxalate and zinc metal is reversible.

[0031] Figure 4 Shows the XRD change process of the positive electrodes of Example 1 and Comparative Example 2. As can be seen from the figure, after adding the crowded micelle electrolyte, the peak position of the lithium manganese oxide positive electrode can shift from 44.0° to 44.9°, indicating that the lithium manganese oxide in Example 1 can be fully charged and discharged, and the discharging process also shows good reversibility. For the lithium manganese oxide positive electrode in Comparative Example 2, its peak position can only shift from 44.0° to 44.5°. The main reason is that under high-voltage conditions, the oxygen evolution reaction also participates in the competition for electrons, resulting in the inability of lithium manganese oxide to normally release lithium ions.

[0032] Example 2

[0033] First, prepare a slurry of zinc oxalate and PVDF in a mass ratio of 9:1, coat it on a zinc foil current collector, and use it as the negative electrode. The electrolyte uses a lithium acetate electrolyte, which is prepared by mixing lithium acetate and water in a ratio of 2 g:5 mL. The positive electrode uses lithium iron phosphate. In the positive electrode and the liquid electrolyte, add a pressed montmorillonite sheet as the crowded micelle electrolyte to assemble a button battery.

[0034] Comparative Example 3

[0035] First, zinc oxalate and PVDF are prepared into a slurry in a mass ratio of 9:1, which is coated on a zinc foil current collector and used as the negative electrode. The electrolyte is a lithium sulfate electrolyte, which is prepared by mixing lithium sulfate and water in a ratio of 2g:5mL. The positive electrode is lithium iron phosphate. In the positive electrode and the liquid electrolyte, a compacted montmorillonite sheet is added as a crowded micelle electrolyte to assemble a button battery.

[0036] Figure 5 The charge-discharge curves of the zinc oxalate negative electrode with different anionic electrolytes in Example 2 and Comparative Example 3 are shown. It can be seen that there are obvious differences in the charge-discharge curves. In the lithium sulfate electrolyte, the polarization voltage is significantly higher than that in the lithium acetate electrolyte. This is mainly because the binding energies of different anions with zinc ions are different. The binding energy of sulfate ions with zinc ions is large, which will affect the conversion reaction between zinc oxalate and zinc metal, resulting in an increase in the polarization voltage. In addition, acetate ions are weak acid radicals, and the pH value of its electrolyte is higher than that of the sulfate electrolyte, which can more effectively inhibit the hydrogen evolution side reaction and is beneficial to the reversible progress of the conversion reaction between zinc oxalate and zinc metal.

[0037] Example 3

[0038] First, zinc fluoride and PVDF are prepared into a slurry in a mass ratio of 9:1, which is coated on a zinc foil current collector and used as the negative electrode. The electrolyte is a lithium acetate electrolyte, which is prepared by mixing lithium acetate and water in a ratio of 2g:5mL. The positive electrode is lithium manganate. In the positive electrode and the liquid electrolyte, a compacted montmorillonite sheet is added as a crowded micelle electrolyte to assemble a button battery.

[0039] Example 4

[0040] First, basic zinc carbonate and PVDF are prepared into a slurry in a mass ratio of 9:1, which is coated on a zinc foil current collector and used as the negative electrode. The electrolyte is a lithium acetate electrolyte, which is prepared by mixing lithium acetate and water in a ratio of 2g:5mL. The positive electrode is lithium manganate. In the positive electrode and the liquid electrolyte, a compacted montmorillonite sheet is added as a crowded micelle electrolyte to assemble a button battery.

[0041] Figure 6 The charge-discharge curves of Example 1, Example 3, and Example 4 are shown. As can be seen from the figure, under this battery design, different zinc ion compounds can be used as the negative electrode and can all undergo reversible cycling. However, each zinc ion compound negative electrode has a different effect on voltage improvement, which is mainly related to the solubility of the zinc ion compound. The smaller the solubility of the zinc ion compound, the higher the corresponding battery voltage improvement.

Claims

1. A near-neutral zinc-ion battery with a platform voltage of 2V, characterized in that: It includes a positive electrode, a negative electrode and an electrolyte. The negative electrode is a poorly soluble zinc compound, and the electrolyte is a soluble acetate without zinc ions. A layer of crowded micelle electrolyte is added between the positive electrode and the electrolyte. The crowded micelle electrolyte is a clay mineral or a macromolecule rich in hydroxyl groups or amine groups.

2. The near-neutral zinc-ion battery according to claim 1, wherein: The poorly soluble zinc compound is selected from one of zinc oxalate, zinc citrate, basic zinc carbonate, zinc hydroxide, zinc fluoride and zinc phosphate.

3. The near-neutral zinc-ion battery according to claim 1, characterized in that: The soluble acetate is selected from one of lithium acetate, sodium acetate and potassium acetate.

4. The near-neutral zinc-ion battery according to claim 1, wherein: The clay mineral is selected from one of montmorillonite, meerschaum and kaolin.

5. The near-neutral zinc ion battery according to claim 1, wherein: The macromolecule rich in hydroxyl groups or amine groups is selected from one of polyethylene glycol and polyacrylamide.

6. The near-neutral zinc-ion battery according to any one of claims 1-5, characterized in that: When the near-neutral zinc ion battery is a zinc-lithium mixed ion battery, the positive electrode material is lithium manganate, lithium cobaltate or lithium nickel cobalt manganate.

7. The near-neutral zinc-ion battery according to any one of claims 1-5, characterized in that: When the near-neutral zinc ion battery is a zinc-sodium mixed ion battery, the positive electrode material is sodium vanadium phosphate, sodium fluorovanadate or sodium pyrophosphate vanadate.

8. The near-neutral zinc-ion battery according to any one of claims 1-5, characterized in that: When the near-neutral zinc ion battery is a zinc-iodine battery, the positive electrode material is activated carbon or carbon cloth.

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