A functional electrolyte for an aqueous zinc-based battery and the battery

Abstract

The present invention discloses a functional electrolyte for an aqueous zinc-based battery and a battery. The electrolyte includes an electrolyte salt, a functional additive, and a solvent. The functional additive includes additive a, or further includes additive b. Additive a is one or more of acetates; additive b is one or more of electrolyte component decomposition promoters; the electrolyte salt is a zinc salt, and the concentration of the electrolyte salt is not higher than 4 mol / L. The electrolyte of the present invention can form a stable ion adsorption layer and a solid-state interface layer at the zinc negative electrode / electrolyte interface. Through the synergistic effect of the two, the side reactions of hydrogen evolution corrosion, the accumulation of by-products, and the uneven deposition of metallic zinc are alleviated, and the reaction reversibility, electrochemical stability, and cycle life of the zinc negative electrode of the aqueous zinc-based battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aqueous zinc-based batteries, and particularly relates to a functional electrolyte and a battery for an aqueous zinc-based battery. Background Art

[0002] In recent years, the well-developed lithium-ion batteries have dominated in electrochemical energy storage. However, the commercial lithium-ion batteries using organic electrolytes have poor safety, are prone to catch fire and explode during thermal runaway, and at the same time there are also problems such as high cost of lithium resources and uneven distribution of resources, which to a certain extent limit their large-scale energy storage applications. In recent years, aqueous zinc-based batteries have received extensive attention due to their high theoretical specific capacity, combined with the advantages of high safety and low cost of water-based electrolytes.

[0003] Currently, the electrolyte environment of zinc-based batteries widely studied is mostly weakly acidic. Therefore, during the deposition / dissolution process of the metal zinc anode, a side reaction of hydrogen evolution corrosion will occur, and at the same time, local alkalization will occur at the electrode / electrolyte interface, generating irreversible by-products on the surface of the zinc anode to passivate the electrode. As a result, there are problems of uneven deposition and zinc dendrites during the deposition / dissolution process of metal zinc, seriously affecting the coulombic efficiency and cycle life of aqueous zinc-based batteries.

[0004] In response to the above problems, researchers at home and abroad have proposed many improvement measures, including three-dimensional anodes or current collectors (CN114975847A, CN114883560A), artificial functional modification layers (CN114824229A, CN114613980A), separator modification (CN114709556A, CN114744367A), electrolyte additives (CN115149117A, CN115084636A), etc., which have alleviated the instability at the zinc anode / electrolyte interface to a certain extent and improved the cycle stability of aqueous batteries. The method of electrolyte additives can effectively regulate both the properties of the bulk electrolyte and the chemistry at the electrode / electrolyte interface, and a stable and uniform electrode / electrolyte interface layer is particularly important for achieving the cycle stability and deposition uniformity of the zinc anode during the repeated deposition / dissolution process. Therefore, reasonably designing the electrolyte components and controlling the composition and structure of the electrode / electrolyte interface layer are the key issues for realizing high-performance and high-stability zinc anodes. Summary of the Invention

[0005] The technical problem actually to be solved by the present invention is that in a zinc salt pure water-based electrolyte, the side reaction between the zinc negative electrode and the electrolyte is serious, which will form an unstable and uneven interfacial layer at the electrode / electrolyte interface, leading to the continuous deterioration of the electrolyte environment. On the other hand, it is more economically beneficial to effectively control the decomposition of electrolyte components at low salt concentrations. The present invention provides an acetate functional additive electrolyte and its application in zinc-based batteries. The present invention provides an application of a decomposition promoter additive combined with an acetate functional additive electrolyte at low salt concentrations in zinc-based batteries, which can significantly reduce the cost of the electrolyte and reduce the viscosity of the electrolyte.

[0006] The present invention provides a functional electrolyte for an aqueous zinc-based battery, which comprises an electrolyte salt, a functional additive and a solvent. Acetate is the main functional additive of the present invention, which can form an acetate anion adsorption layer at the zinc negative electrode / electrolyte interface, hinder the continuous side reaction of decomposable components and water molecules at the interface, inhibit the uncontrollable generation of by-products, form a stable solid electrolyte interface layer, and at the same time improve the deposition uniformity and Coulomb efficiency of metallic zinc. Further, a decomposition promoter and acetate (adsorbent) are compounded in a certain proportion to control the process of the decomposition reaction of the electrolyte at the zinc negative electrode interface. The composite additive can effectively promote the uniformity and reversibility of the reaction of the zinc negative electrode in the low-salt-concentration electrolyte, thereby significantly reducing the preparation cost of the electrolyte for the aqueous zinc-based battery.

[0007] The present invention solves the key technical problems at the zinc negative electrode / electrolyte interface in the zinc-based battery through the following technical solutions.

[0008] The present invention provides a novel and low-cost aqueous functional electrolyte, which comprises an electrolyte salt, a functional additive and a solvent; the functional additive is additive a, or additive b can also be added; the concentration of the electrolyte salt in the electrolyte is not higher than 4 mol / L (usually 0.1~4 mol / L), the additive a is acetate, and the additive b is an electrolyte component decomposition promoter.

[0009] In the present invention, the acetate is mainly one or more of ammonium acetate (NH4Ac), sodium acetate (NaAc), potassium acetate (KAc), zinc acetate (Zn(Ac)2), manganese acetate (Mn(Ac)2), preferably NH4Ac and Mn(Ac)2. Among them, as an additive (Zn(Ac)2 is not used as the main salt of the electrolyte.

[0010] In the present invention, the concentration of acetate in the electrolyte is not higher than 3 mol / L (usually 0.01 mol / L~3 mol / L), preferably 0.6 mol / L.

[0011] In the present invention, the component decomposition promoter is trimethylethylammonium trifluoromethanesulfonate (Me3EtNOTF), tetraethylammonium trifluoromethanesulfonate (Et4NOTF), lithium bis(trifluoromethanesulfonimide) (LiTFSI), sodium bis(trifluoromethanesulfonimide) (NaTFSI), lithium trifluoromethanesulfonate (LiOTF), sodium trifluoromethanesulfonate (NaOTF), lithium bis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide (NaFSI), preferably tetraethylammonium trifluoromethanesulfonate.

[0012] In the present invention, the concentration of the electrolyte component decomposition promoter is not higher than 1 mol (usually 0.01 mol / L - 1 mol / L), preferably 0.1 mol / L.

[0013] In the present invention, the electrolyte salt can be conventional in the art and can be one or more of zinc sulfate (ZnSO4), zinc trifluoromethanesulfonate (Zn(OTF)2), zinc bis(trifluoromethanesulfonimide) (Zn(TFSI)2), zinc perchlorate (Zn(ClO4)2), zinc acetate (Zn(Ac)2), zinc chloride (ZnCl2). Preferably, they are Zn(OTF)2, Zn(TFSI)2, Zn(ClO4)2.

[0014] In the present invention, the zinc negative electrode can be a zinc sheet, zinc powder or a zinc-based alloy material.

[0015] In the present invention, the additive can be used alone or in combination with other additives.

[0016] In the present invention, the aqueous zinc-based battery can be an aqueous zinc-ion battery, a zinc-air battery or a zinc-based flow battery.

[0017] On the basis of not violating the common knowledge in the art, the above preferred conditions can be arbitrarily combined to obtain various preferred examples of the present invention for different batteries.

[0018] The functional electrolyte of the present invention has the following main advantages:

[0019] (1) The acetate additive can form an anion adsorption layer at the zinc negative electrode / electrolyte interface, significantly reducing the possibility of continuous decomposition of the electrolyte components at the interface and forming a stable solid electrolyte protection layer. The adsorption layer and the solid electrolyte layer act together to improve the Coulombic efficiency, deposition uniformity and cycle stability of metallic zinc.

[0020] (2) By promoting the decomposition of the composite component promoter and combining the action of the anion adsorption layer, it can effectively promote the formation of a stable steady-state electrolyte interface on the zinc negative electrode in an electrolyte with a low salt concentration, further inhibit the occurrence of side reactions at the interface, improve the Coulomb efficiency, synergistically promote the uniform deposition of metallic zinc, inhibit the growth of zinc dendrites, and significantly reduce the preparation cost of the electrolyte. Description of the Drawings

[0021] Figure 1 Schematic diagram of the principle of the electrolyte of the present invention;

[0022] Figure 2 Results of the double-layer capacitance test for Examples 1, 4, 5, 6 and Comparative Example 1 of the present invention;

[0023] Figure 3 Cycling performance test of the Zn-Cu half-cell of the electrolytes of Examples 1, 2, 3 and Comparative Example 1 of the present invention;

[0024] Figure 4 Cycling performance test of the Zn-Cu half-cell of the electrolytes of Examples 1, 4, 5 and 6 of the present invention;

[0025] Figure 5 Cycling performance test of the Zn-Cu half-cell of the electrolytes of Example 7 and Comparative Example 2 of the present invention;

[0026] Figure 6 Cycling performance test of the Zn-Cu half-cell of the electrolytes of Example 8 and Comparative Example 3 of the present invention;

[0027] Figure 7 Cycling performance test of the Zn-Cu half-cell of the electrolytes of Examples 9, 10, 11 and Comparative Example 4 of the present invention;

[0028] Figure 8 Cycling performance test of the Zn-Cu half-cell of the electrolytes of Examples 11 and 12 of the present invention;

[0029] Figure 9 Voltage-time curve of the Zn-Zn symmetric cell of the electrolytes of Examples 1, 4, 5, 6 and Comparative Example 1 of the present invention at 2 mA cm -2 , 2 mAh cm -2 (zinc utilization rate: 11.4%) under the test conditions;

[0030] Figure 10 Voltage-time curve of the Zn-Zn symmetric cell of the electrolytes of Examples 1, 4, 5, 6 and Comparative Example 1 of the present invention at 5 mA cm -2 , 5 mAh cm -2Voltage-time curve under the test conditions (zinc utilization rate: 28.7%);

[0031] Figure 11 Voltage-time curves of the Zn-Zn symmetric cells with the electrolytes of Example 9, Example 11 and Comparative Example 4 of the present invention at 2 mA cm -2 , 2 mAh cm -2 (zinc utilization rate: 11.4%);

[0032] Figure 12 Voltage-time curves of the Zn-Zn symmetric cells with the electrolytes of Example 9, Example 11 and Comparative Example 4 of the present invention at 5 mA cm -2 , 5 mAh cm -2 (zinc utilization rate: 28.7%); Detailed implementation manners

[0033] The present invention will be further illustrated by way of examples below, but the implementation manners of the present invention are not limited thereto. For the experimental methods without specific conditions indicated in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0034] In the table, " / " indicates that the battery cannot cycle 50 times.

[0035] In the following examples, unless otherwise specified, the battery test temperature is 25 °C.

[0036] Examples and comparative examples

[0037] Taking Example 1 as an example, the preparation process of the zinc-based battery electrolyte is as follows: 3 mol / L Zn(OTF)2 and 0.6 mol / L NH4Ac are successively added to ultrapure water. After the solution is mixed evenly, it is left for more than 12 hours, and the supernatant is taken for use.

[0038] The electrolyte formulations of the zinc-based batteries in each example and comparative example are shown in Table 1 below.

[0039] Table 1

[0040]

[0041] The above electrolyte formulations of the examples and comparative examples are applied to Zn-Cu half cells and Zn-Zn symmetric cells.

[0042] Comparative Example 1 and Examples 1-3 explored the effect of NH4Ac concentration on the electrochemical performance; Examples 1 and 4-6 explored the effect of the type of acetate cation on the electrochemical performance; Comparative Examples 2-3 and Examples 7-8 explored the effect of ammonium acetate additive on the electrochemical performance after the change of zinc salt type; Examples 1 and 9 explored the effect of zinc salt concentration on the electrochemical performance; Comparative Example 4 and Examples 9-10 explored the effect of additive type on the electrochemical performance at low salt concentration; Examples 11-12 explored the synergistic effect of different concentrations of additives on the electrochemical performance at low salt concentration.

[0043] Effect analysis

[0044] In the present invention, the evaluation methods for battery performance are all carried out in accordance with industry standards.

[0045] The secondary battery using the electrolyte of the present invention was subjected to charge and discharge performance tests. Unless otherwise specified, the separator used in the present invention is a glass fiber separator, assembled into a CR2032 button battery, the charging cut-off voltage of the Zn-Cu half-cell is 0.6 V, and at 1 mA cm -2 、1 mAh cm -2 conditions, the reversibility test of metal zinc deposition / dissolution was carried out, and the average Coulomb efficiency and cycle life were compared; the Zn-Zn symmetric cells were respectively at 2 mA cm -2 、2 mAh cm -2 (zinc utilization rate: 11.4%) and 5 mA cm -2 、5 mAhcm -2 (zinc utilization rate: 28.7%) of the current density and areal capacity to compare the long cycle performance.

[0046] According to Figure 2 It can be obtained that compared with Comparative Example 1, the electrolytes prepared in Examples 1 and 4-6 of the present invention can effectively reduce the double-layer capacitance of the battery, indicating that there is an acetate anion adsorption layer on the surface of the zinc negative electrode. Therefore, the electrolyte of the present invention can effectively reduce the possibility of decomposition of electrolyte components at the interface.

[0047] Electrochemical performance of Zn-Cu half-cell:

[0048] According to Figure 3In Examples 1-3 and Comparative Example 1 of the present invention, ammonium acetate additives with different concentrations were applied to the Zn-Cu half-cell. In Examples 1, 2, and 3, the average Coulombic efficiency in the first 50 cycles could be significantly improved, reaching 99.11%, 99.18%, and 98.89% respectively. Among them, Example 1 had the highest average Coulombic efficiency and the longest cycle life after 50 cycles, which were 99.87% and 2378 h respectively; the average Coulombic efficiency of Comparative Example 1 in the first 50 cycles was 71.39%, and it could only cycle for 76 h. Therefore, the acetate concentration of the electrolyte of the present invention is preferably 0.6 mol / L, which can significantly improve the reversibility of metal zinc deposition / dissolution and the cycle life.

[0049] According to Figure 4 In Examples 1, 4-6 of the present invention, acetate additives with the same concentration but different cation species were applied to the Zn-Cu half-cell. Examples 1, 4, 5, and 6 all showed high Coulombic efficiency and long cycle life. The average Coulombic efficiencies after 50 cycles were 99.87%, 99.87%, 99.89%, and 99.91% respectively, and the cycle lives were 2378 h, 1724 h, 1860 h, and 2380 h respectively. It shows that the acetate anion in the acetate additive used in the present invention plays a dominant role in significantly improving the reversibility of metal zinc deposition / dissolution and the cycle life, and the electrolyte prepared by the present invention has universality in the selectivity of acetate cations.

[0050] According to Figure 5 and Figure 6 In Examples 7, 8, Comparative Example 2, and Comparative Example 3 of the present invention, different zinc salt species and 0.6 mol / L ammonium acetate electrolytes were applied to the Zn-Cu half-cell. The average Coulombic efficiencies of Examples 7 and 8 in the first 50 cycles were 99.33% and 98.91% respectively, the average Coulombic efficiencies after 50 cycles were 99.84% and 99.31% respectively, and the cycle lives were 1502 h and 780 h respectively; the average Coulombic efficiencies of Comparative Example 2 and Comparative Example 3 in the first 50 cycles were only 77.54% and 83.89% respectively, and the cycle lives were only 92 h and 84 h respectively. It shows that the electrolyte prepared by the present invention has universality in the selectivity of zinc salt species, so cheaper zinc salts can be selected to further reduce the cost of the electrolyte.

[0051] According to Figure 7From Examples 9-11 and Comparative Example 4, it can be concluded that the Zn-Cu half-cell containing both acetate and decomposition promoter at low salt concentration has more excellent cycling performance. The average Coulombic efficiency of Example 11 after 50 cycles is 99.74%, and the cycle life is 1704 h; the average Coulombic efficiencies of Example 9 and Example 10 after 50 cycles are only 99.52% and 95.27% respectively; the average Coulombic efficiency of the first 50 cycles of Comparative Example 4 is only 71.92%, and the cycle life is only 90 h. It shows that the acetate additive and decomposition promoter used in the present invention can synergistically improve the zinc anode / electrolyte interface, and improve the reversibility and cycle life of metal zinc deposition / dissolution at low salt concentration.

[0052] According to Figure 8 From Example 11 and Example 12, it can be concluded that the Zn-Cu half-cell can have good cycling performance at low concentration of decomposition promoter. Example 11 and Example 12 have similar average Coulombic efficiencies before and after 50 cycles, and the cycle lives are 1704 h and 1912 h respectively. It shows that the low-concentration decomposition promoter used in the present invention can effectively improve the reversibility and cycle life of metal zinc deposition / dissolution, and thus can save costs.

[0053] Electrochemical performance of Zn-Zn symmetric battery:

[0054] As Figure 9 shown, under the conditions of 2 mA cm -2 , 2 mAh cm -2 , the functional electrolytes in Example 1 and Examples 4-6 can stably cycle for more than 900 h compared with the unmodified electrolyte in Comparative Example 1, effectively improving the cycle life of the zinc anode, and the electrolytes prepared in the present invention have universality in the selectivity of acetate cations.

[0055] As Figure 10 shown, under 5 mA cm -2 , 5 mAh cm -2 , the functional electrolytes in Example 1 and Examples 4-6 can effectively improve the cycle life of the zinc anode at high current density and high areal capacity compared with the unmodified electrolyte in Comparative Example 1. Among them, the cycle life of Example 6 exceeds 1500 h, and the electrolytes prepared in the present invention have universality in the selectivity of acetate cations.

[0056] As Figure 11 shown, under the conditions of 2 mA cm -2 , 2 mAh cm -2Under such circumstances, compared with the unmodified electrolyte in Comparative Example 4, the functional electrolytes in Example 9 and Example 11 can significantly improve the cycle life of the zinc anode. Among them, the cycle life of Example 11 exceeds 600 h, indicating that the acetate additive and decomposition promoter used in the present invention can synergistically improve the zinc anode / electrolyte interface and increase the cycle life of metallic zinc at low salt concentrations.

[0057] As Figure 12 shown, at 5 mA cm -2 , 5 mAh cm -2 under, compared with the unmodified electrolyte in Comparative Example 4, the functional electrolytes in Example 9 and Example 11 can significantly improve the cycle life of the zinc anode at high current density and high areal capacity. Among them, the cycle life of Example 11 exceeds 450 h, indicating that the acetate additive and decomposition promoter used in the present invention can synergistically improve the zinc anode / electrolyte interface chemistry and increase the cycle life of metallic zinc at low salt concentrations.

[0058] Cycling performance of Zn-Cu half cells

[0059]

Claims

1. A functional electrolyte for an aqueous zinc-based battery, characterized in that, The electrolyte comprises an electrolyte salt, a functional additive and a solvent. The functional additive includes additive a and also includes additive b, which is used to form an ion adsorption layer and a solid-state interface layer between the zinc negative electrode and the electrolyte; additive a is an acetate salt, which is one or more of ammonium acetate, sodium acetate, potassium acetate, and manganese acetate; additive b is an electrolyte component decomposition promoter, which is one or more of trimethylethylammonium trifluoromethanesulfonate, tetraethylammonium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonimide), sodium bis(trifluoromethanesulfonimide), lithium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium bis(fluorosulfonyl)imide; the solvent is ultrapure water, the concentration of the electrolyte salt is less than 4 mol / L, the concentration of additive a is not higher than 3 mol / L, and the concentration of additive b is not higher than 1 mol / L.

2. The functional electrolyte according to claim 1, wherein The electrolyte salt is one or more of zinc sulfate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonimide), zinc perchlorate, zinc acetate, and zinc chloride.

3. The functional electrolyte according to claim 1, wherein The concentration of the electrolyte salt is 2 - 3 mol / L.

4. The functional electrolyte according to claim 1, wherein The concentration of additive a is 0.5 - 1 mol / L.

5. The preparation method of the functional electrolyte according to any one of claims 1-4, characterized in that, The specific steps include: dissolving the electrolyte salt and the functional additive in an aqueous solvent, and mixing evenly to obtain a clear and transparent aqueous solution, namely the functional electrolyte for an aqueous zinc-based battery.

6. A water-based zinc-based battery, characterized in that, Using the functional electrolyte according to any one of claims 1 to 4, the battery is an aqueous zinc-ion battery, a zinc-air battery or a zinc-based flow battery.

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