Preparation method of a wide-temperature-range aqueous zinc battery electrolyte and its application and recycling

Abstract

The present invention provides a method for preparing an electrolyte for an aqueous zinc battery with a wide temperature range. By utilizing the characteristic that the amphiphilic anions of zinc ion salts can cause the aqueous phase and the hydrophobic ionic liquid to change from phase separation to mutual solubility, a hydrophobic ionic liquid is introduced into the aqueous electrolyte, greatly improving the thermal stability, chemical stability, and electrochemical stability window of the aqueous electrolyte. The ionic liquid also achieves a highly reversible and long-life zinc deposition / stripping cycle through the tip effect of the cation inhibition zinc deposition process, and inhibits the dissolution of transition metal elements from the zinc battery positive electrode, thereby improving the cyclic stability of the positive electrode. The electrolyte prepared by the present invention can be removed by simple heating and / or vacuum treatment to cause the zinc ion salt and the ionic liquid to spontaneously phase separate, thereby achieving rapid recovery of high-value components in the electrolyte. Aqueous zinc batteries containing the above-mentioned electrolyte have the advantages of long service life and a wide operating temperature range. At the same time, the electrolyte components are easy to recycle, and have important application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of aqueous batteries, and specifically relates to a method for preparing an electrolyte for an aqueous zinc battery with a wide temperature range and an aqueous zinc battery containing the electrolyte, and also relates to a method for recovering the electrolyte for an aqueous zinc battery with a wide temperature range. Background Art

[0002] Aqueous zinc batteries have high safety, low cost, high energy density (820mAh g -1 or 5855mAh cm -3 ), environmentally friendly, and other excellent properties show broad application prospects. However, aqueous zinc batteries face many challenges. When the battery is charged and discharged, hydrolysis reactions inevitably occur on the cathode and anode surfaces, resulting in severe corrosion of the zinc metal surface and shortened cycle life. In addition, practical applications require that the battery can operate in both low and high temperature environments. However, aqueous electrolytes have a narrow liquid range and are prone to crystallization in low temperature areas. At high temperatures, their reactivity with zinc metal increases, hindering their application in extreme temperatures.

[0003] For aqueous battery electrolytes, the freezing point or thermal stability of the electrolyte can be lowered by introducing a co-solvent. However, these organic co-solvents are often flammable, which not only compromises the safety of aqueous batteries but also increases production costs. Furthermore, green and sustainable development has always been a goal of social development. The development of recyclable electrolytes can reduce the environmental impact of batteries and resource consumption. However, for systems using co-solvents, achieving rapid separation of the three phases of water, zinc ion salt, and co-solvent is theoretically extremely difficult, and no relevant research has been reported.

[0004] Based on this, providing an easily recyclable, wide-temperature-range aqueous zinc battery electrolyte and its preparation method, so as to simultaneously broaden the operating temperature range of the aqueous zinc battery and solve the problem of electrolyte recyclability, will expand the application scope and prospects of aqueous zinc batteries, and is also a technical problem that urgently needs to be solved. Summary of the Invention

[0005] One of the objectives of the present invention is to provide an easily recyclable aqueous zinc battery electrolyte with a wide temperature range and a preparation method thereof.

[0006] A second object of the present invention is to provide an aqueous zinc battery with a wide operating temperature range, good cycle stability and easily recyclable electrolyte.

[0007] A third object of the present invention is to provide a simple and convenient method for recovering aqueous zinc battery electrolyte.

[0008] The technical solution adopted by the present invention to achieve one of the objectives is: to provide a method for preparing a wide-temperature-range aqueous zinc battery electrolyte, the preparation method comprising: adding zinc ion salt zinc trifluoromethanesulfonate (Zn(OTf)2) to a phase separation system composed of water and ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt (EmimFSI) to obtain a homogeneous wide-temperature-range aqueous zinc battery electrolyte (Zn(OTf)2-H2O / EmimFSI).

[0009] The overall concept of the present invention is as follows: providing an electrolyte for an aqueous zinc battery, the electrolyte comprising a ternary system consisting of a zinc ion salt containing amphoteric anions, water, and a hydrophobic ionic liquid. Taking advantage of the characteristic of the zinc ion salt's amphiphilic anions that can cause the aqueous phase and the hydrophobic ionic liquid to transition from phase separation to mutual solubility, a hydrophobic ionic liquid is introduced into the aqueous electrolyte. The ionic liquid can inhibit the tip effect of the zinc deposition process through its cations, achieving highly reversible and long-life zinc deposition / stripping cycles. Simultaneously, the ionic liquid can also inhibit the dissolution of transition metal elements from the zinc battery's positive electrode, improving the positive electrode's cyclic stability. Furthermore, the electrolyte exhibits the characteristic of salt-induced reversible phase separation and fusion, allowing the main components of the electrolyte to be easily separated and recovered.

[0010] Among them, the zinc ion salt needs to contain an amphiphilic anion, have good solubility in water, and be insoluble in hydrophobic ionic liquids; at the same time, the hydrophobic ionic liquid needs to have the characteristics of zero vapor pressure, low viscosity and high ionic conductivity, and the ionic liquid is immiscible with water. After extensive research and exploration, the inventors found that the bis(fluorosulfonyl)imide (FSI) - ), bis(tri)fluoromethanesulfonimide (TFSI - ), hexafluorophosphate (PF6 - ) and cations such as imidazole, pyrrole, piperidine, quaternary ammonium, and quaternary phosphonium. Ultimately, they established a specific scheme using 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EmimFSI) as the hydrophobic ionic liquid and zinc trifluoromethanesulfonate (Zn(OTf)2) as the zinc ion salt. The resulting aqueous zinc battery electrolyte has been shown to significantly improve the thermal stability, chemical stability, and electrochemical stability window of the aqueous electrolyte.

[0011] Furthermore, in the phase separation system, the volume ratio of water to 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt is 1:5 to 1:2. Preferably, the volume ratio of water to 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt is 1:4.

[0012] Furthermore, the concentration of the zinc ion salt in the isotropic electrolyte is 0.3 to 2 mol / L. Preferably, the concentration of the zinc ion salt in the isotropic electrolyte is 0.5 to 1.5 mol / L. More preferably, the concentration of the zinc ion salt is 1 mol / L.

[0013] The electrolyte of the aqueous zinc battery obtained by the above preparation method can effectively broaden the working range of the aqueous zinc battery and can show good cycle stability under the working temperature conditions of -10 to 100°C.

[0014] The technical solution adopted by the present invention to achieve the second purpose is: to provide an aqueous zinc battery, which includes the wide-temperature-range aqueous zinc battery electrolyte prepared according to one of the purposes of the present invention.

[0015] The aqueous zinc battery provided by the present invention has the following two advantages: first, the use of a specific electrolyte, Zn(OTf)2-H2O / EmimFSI, can improve the service life of the zinc battery and expand its operating temperature range; second, the valuable components in the electrolyte can also be easily separated, recovered and reused through a simple processing process, reducing the battery's impact on the environment and resource consumption, and meeting the goal of green and sustainable development.

[0016] A third objective of the present invention is to provide a method for separating and recovering high-value ionic liquids and zinc ion salts in an electrolyte using a simple treatment process. The method comprises the following steps: removing water from the wide-temperature-range aqueous zinc battery electrolyte prepared in one of the objectives of the present invention by heating and / or vacuum treatment, causing the zinc ion salt and ionic liquid to separate, and then recovering them separately.

[0017] In the present invention, due to the non-volatility of the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EmimFSI), the zinc ion salt and the ionic liquid spontaneously phase separate after the water in the electrolyte is removed by simple heating and / or vacuum treatment, thereby achieving rapid recovery of high-value components in the electrolyte.

[0018] Preferably, the heating temperature is 50-80°C.

[0019] Preferably, the vacuum degree of the vacuum treatment is 100000-100Pa.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The wide-temperature-range aqueous zinc battery electrolyte and its preparation method provided by the present invention utilize the characteristic that the amphiphilic anions of zinc ion salts can make the aqueous phase and the hydrophobic ionic liquid change from phase separation to mutual solubility, and introduce a hydrophobic ionic liquid into the aqueous electrolyte, thereby greatly improving the thermal stability, chemical stability and electrochemical stability window of the aqueous electrolyte. At the same time, since the ionic liquid has the characteristics of non-volatility and non-flammability, the introduction of the ionic liquid will not sacrifice the safety of the aqueous battery.

[0022] (2) The wide temperature range aqueous zinc battery electrolyte provided by the present invention has the following characteristics: for the zinc negative electrode of the zinc battery, the cations of the ionic liquid can inhibit the uneven deposition of zinc, and the anions can participate in regulating the composition and uniformity of the solid electrolyte interface (SEI) on the zinc surface, thereby achieving a highly reversible and long-life zinc deposition / stripping cycle; for the positive electrode of the zinc battery, the introduction of the ionic liquid can inhibit the deposition and structural changes of the transition metal elements in the positive electrode, thereby improving the cycle stability of the positive electrode.

[0023] (3) The wide-temperature-range aqueous zinc battery electrolyte provided by the present invention has a hydrophobic ionic liquid with the characteristic of being non-volatile. After the water in the electrolyte is removed by simple heating and / or vacuum treatment, the zinc ion salt will spontaneously phase separate from the ionic liquid, thereby realizing the rapid recovery of high-value components in the electrolyte.

[0024] (4) The aqueous zinc battery provided by the present invention adopts an electrolyte composed of a ternary system consisting of a zinc ion salt containing amphoteric anions, water and a hydrophobic ionic liquid. This electrolyte can not only improve the service life of the zinc battery and expand its operating temperature range, but also the valuable components in the electrolyte can be easily separated, recovered and reused through a simple processing process. It is suitable for industrial production and has important application potential in the field of large-scale aqueous energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Digital photographs showing the process of spontaneous separation and dissolution of Zn(OTf)2 and EmimFSI by dehydration / addition of water to prepare a 1 mol / L Zn(OTf)2-H2O / EmimFSI (v / v = ~1 / 4) electrolyte using an amphiphilic anion-containing zinc ion salt Zn(OTf)2 in Example 1 of the present invention;

[0026] Figure 2 These are digital photos of zinc foils immersed in the electrolytes prepared in Example 1 and Comparative Example 1, respectively; (a) is placed at room temperature for 24 hours; (b) is placed at 80°C for 1 hour;

[0027] Figure 3 Comparison of cycle life results of Zn||Zn batteries made with the electrolytes prepared in Example 1 of the present invention and Comparative Example 1;

[0028] Figure 4 Comparison of the coulombic efficiency results of Zn||Cu batteries made using the electrolytes prepared in Example 1 of the present invention and Comparative Example 1;

[0029] Figure 5 The Zn prepared by using the electrolyte prepared in Example 1 and Comparative Example 1 of the present invention 0.25 Comparison of cycling performance of V2O5·nH2O||Cu batteries at 30℃;

[0030] Figure 6 The Zn prepared by the electrolyte prepared in Example 1 and Comparative Example 1 of the present invention 0.25 Comparison of cycling performance of V2O5·nH2O||Cu batteries at 60℃;

[0031] Figure 7 The Zn prepared by using the electrolyte prepared in Example 1 and Comparative Example 1 of the present invention 0.25 V2O5·nH2O||Cu battery at -10~100℃(0.05~0.2A g -1 ) Comparison of cycle performance in different temperature ranges;

[0032] Figure 8 X-ray diffraction spectrum of the solid product obtained by dehydrating and filtering the electrolyte prepared in Example 1 of the present invention and Zn(OTf)2;

[0033] Figure 9 This is an infrared spectrum of the solid product and liquid product obtained by dehydration and filtration separation of the electrolyte prepared in Example 1 of the present invention, as well as the original Zn(OTf)2 and EmimFSI. DETAILED DESCRIPTION

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0036] The present invention will be further described below with reference to specific examples, but they are not intended to limit the present invention.

[0037] Example 1

[0038] This example provides a method for preparing an easily recyclable, wide-temperature-threshold aqueous zinc battery electrolyte. Its composition is as follows: zinc trifluoromethanesulfonate (Zn(OTf)2), water, and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt (EmimFSI). In a phase separation system with a volume ratio of 1:4 between water and EmimFSI, Zn(OTf)2 is added to prepare a 1 mol / L (mol / L) homogeneous electrolyte 1mol / L Zn(OTf)2-H2O / EmimFSI (v / v=1 / 4). The preparation process is as follows: Figure 1 shown.

[0039] Example 2

[0040] This example provides a method for preparing an easily recyclable, wide-temperature-threshold aqueous zinc battery electrolyte. Its composition is as follows: zinc trifluoromethanesulfonate (Zn(OTf)2), water, and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EmimFSI). In a phase-separated system of water and EmimFSI (1:2 by volume), zinc salt Zn(OTf)2 is added to create a homogeneous electrolyte with a concentration of 1.5 mol / L.

[0041] Example 3

[0042] This example provides a method for preparing an easily recyclable, wide-temperature-threshold aqueous zinc battery electrolyte. The electrolyte consists of zinc trifluoromethanesulfonate (Zn(OTf)2), water, and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EmimFSI). Zn(OTf)2 is added to a phase-separated system with a 1:5 volume ratio of water to EmimFSI to create a 0.5 mol / L homogeneous electrolyte.

[0043] Comparative Example 1

[0044] Prepare the benchmark electrolyte 3 mol / L Zn(OTf)2-H2O.

[0045] Comparative Example 2

[0046] In water and N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt (Pyr 14 The addition of Zn(OTf)2 to the phase separation system with a FSI volume ratio of 1:4 cannot form a uniform, single-phase electrolyte.

[0047] Performance Testing

[0048] (1) Stability test

[0049] Two zinc foils were immersed in 1 mol / L Zn(OTf)2-H2O / EmimFSI (v / v=1 / 4) prepared in Example 1 and 3 mol / L Zn(OTf)2-H2O, the reference electrolyte prepared in Comparative Example 1, respectively. The foils were sealed and allowed to stand at room temperature and high temperature, and the changes on the zinc surface were observed. The results are as follows: Figure 2 (a) and 2(b).

[0050] Depend on Figure 2 It can be seen that the electrolyte prepared by the present invention has excellent stability to metallic zinc. The electrolyte does not react significantly with zinc either at room temperature or at a high temperature of 80°C. In contrast, the benchmark electrolyte 3 mol / L Zn(OTf)2-H2O configured in comparison ratio 1 reacts violently with the zinc foil either at room temperature or at a high temperature of 80°C, resulting in obvious corrosion and the generation of a large number of bubbles.

[0051] (2) Electrochemical testing

[0052] Using 1.0, 1.5 and 0.5 mol / L Zn(OTf)2-H2O / EmimFSI (v / v=1 / 2) prepared in Examples 1, 2 and 3 as electrolytes, aqueous zinc ion symmetric batteries, aqueous zinc ion asymmetric batteries and aqueous zinc ion full batteries were prepared and electrochemical performance tests were performed. At the same time, three batteries were prepared in the same way using the benchmark electrolyte 3 mol / L Zn(OTf)2-H2O prepared in Comparative Example 1 as a control group, as follows:

[0053] (1) High-purity zinc foil was used as the positive and negative electrodes, respectively, and Zn(OTf)2-H2O / EmimFSI with different concentrations prepared in Examples 1-3 and 3 mol / L Zn(OTf)2-H2O prepared in Comparative Example 1 were used as electrolytes. Glass fiber was used as the separator to assemble a button aqueous zinc ion symmetric battery (Zn||Zn battery). The test conditions were: current density of 1 mA cm -2 The deposition / stripping time for a single cycle is 1 hour / 1 hour. The cycle life of the aqueous zinc ion symmetric battery Zn||Zn prepared in each embodiment and comparative example is shown in Table 1 below:

[0054] Table 1

[0055] Cycle life of aqueous zinc ion symmetric battery Zn||Zn Example 1 680h Example 2 280h Example 3 210h Comparative Example 1 128h Comparative Example 2 The battery is not working

[0056] As can be seen from the table above, compared to the aqueous zinc ion symmetric battery prepared in Comparative Example 1 using 3 mol / L Zn(OTf)2-H2O as the electrolyte, the aqueous zinc ion symmetric batteries Zn||Zn prepared in Examples 1-3 of the present invention using Zn(OTf)2-H2O / EmimFSI as the electrolyte have significantly improved cycle life. Among them, the symmetric battery prepared in Example 1 using 1 mol / L Zn(OTf)2-H2O / EmimFSI (v / v = 1 / 4) as the electrolyte has the highest cycle life of 680 hours.

[0057] (2) A button aqueous zinc ion asymmetric battery (Zn||Cu battery) was assembled using copper foil and zinc foil as the positive and negative electrodes, 1 mol / L Zn(OTf)2-H2O / EmimFSI (v / v = 1 / 4) as the electrolyte, and glass fiber as the separator. The test conditions were: current density of 1 mA cm -2 , single cycle deposition 1h, stripping cut-off voltage is 0.8V (for Zn / Zn 2+ ).

[0058] (3) Using zinc vanadate electrode (Zn 0.25 V2O5·nH2O, carbon nanotubes and bacterial cellulose were mixed in a mass ratio of 7:2:1 and filtered) and zinc foil were used as positive and negative electrodes, respectively. 1 mol / L Zn(OTf)2-H2O / EmimFSI (v / v=1 / 4) was used as electrolyte and glass fiber was used as separator to assemble the button aqueous zinc ion full battery (Zn 0.25 V2O5·nH2O||Zn battery), the test conditions are: working current density 0.1A g -1 (Based on the positive electrode), the operating voltage range is 0.5~1.4V, and the test temperature is 30℃. The electrochemical test results are as follows Figure 3-5 shown.

[0059] Depend on Figure 3-5 It can be seen that the aqueous zinc ion symmetrical battery using the electrolyte prepared in Example 1 of the present invention has a -2 , cycle life is 680h; the stable coulombic efficiency of the asymmetric Zn||Cu battery exceeds 99%, and the number of cycles exceeds 220 times; Zn 0.25 The capacity retention rate of the V2O5·nH2O||Zn battery after 500 cycles is 87.7%.

[0060] In contrast, the aqueous zinc ion symmetric battery using the benchmark electrolyte 3 mol / L Zn(OTf)2-H2O configured in Comparative Example 1 has a high -2 , the cycle life is 128h; the number of asymmetric Zn||Cu batteries is less than 40 times; Zn 0.25 The capacity retention rate of the V2O5·nH2O||Zn battery after 500 cycles is 54.4%.

[0061] (3) Cyclic stability test at different temperatures

[0062] Zinc vanadate electrode (Zn 0.25V2O5·nH2O, carbon nanotubes and bacterial cellulose were mixed in a mass ratio of 7:2:1 and filtered) and zinc foil were used as the positive and negative electrodes, respectively. The 1 mol / L Zn(OTf)2-H2O / EmimFSI (v / v=1 / 4) prepared in Example 1 was used as the electrolyte, and glass fiber was used as the separator to assemble a button aqueous zinc ion full battery. At the same time, the reference electrolyte 3 mol / L Zn(OTf)2-H2O configured in Comparative Example 1 was used to prepare an aqueous zinc ion full battery in the same manner as the control group. Cyclic stability tests were carried out under different temperature conditions. The test conditions were: operating voltage range 0.5~1.4V, test temperature 60℃ (1A g -1 ) Constant temperature and -10~100℃(0.05~0.2A g -1 ) Stepwise temperature increase, each temperature cycle 10 or 15 times. The cycle stability test results at different temperatures are as follows Figure 6 and Figure 7 shown.

[0063] Depend on Figure 6 and Figure 7 It can be seen that the Zn 0.25 V2O5·nH2O||Zn battery at 60℃(1A g -1 ) test conditions, the capacity retention rate after 400 cycles was 85.3%, and it showed good cycle stability in the temperature range of -10 to 100°C.

[0064] In contrast, the Zn 0.25 V2O5·nH2O||Zn battery at 60℃(1A g -1 ) Under the test conditions, the capacity retention rate after 500 cycles is only 18.3%, and it cannot be stably cycled when the temperature exceeds 60℃ or is below 0℃.

[0065] (IV) Recycling performance test

[0066] The electrolyte prepared in Example 1 was placed in a vacuum oven at 60°C for 24 hours to remove moisture. Zn(OTf)2 was precipitated from EmimFSI. The ionic liquid EmimFSI was then separated from Zn(OTf)2 by simple filtration. Figure 8 and Figure 9 The composition analysis results of the separated products show that there are only trace amounts of residual impurities in the separated EmimFSI and Zn(OTf)2.

[0067] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A method for preparing a wide temperature range aqueous zinc battery electrolyte, characterized in that: In a phase separation system consisting of water and ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, zinc ion salt zinc trifluoromethanesulfonate is added and mixed to obtain a homogeneous wide-temperature range aqueous zinc battery electrolyte.

2. The preparation method according to claim 1, characterized in that In the phase separation system, the volume ratio of water to 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt is 1:5 to 1:

2.

3. The preparation method according to claim 2, characterized in that In the phase separation system, the volume ratio of water to 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt is 1:

4.

4. The preparation method according to claim 1, characterized in that In the wide temperature range aqueous zinc battery electrolyte, the concentration of zinc ion salt is 0.3 to 2 mol / L.

5. The preparation method according to claim 4, characterized in that In the wide temperature range aqueous zinc battery electrolyte, the concentration of zinc ion salt is 0.5 to 1.5 mol / L.

6. A wide temperature range aqueous zinc battery electrolyte, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5, the wide-temperature-range aqueous zinc battery electrolyte has an operating temperature range of -10 to 100°C.

7. An aqueous zinc battery, characterized in that: It comprises the wide temperature range aqueous zinc battery electrolyte according to claim 6.

8. A method for recovering electrolytes for wide temperature range aqueous zinc batteries according to claim 6, characterized in that: Water in the wide temperature range aqueous zinc battery electrolyte is removed by heating and / or vacuum treatment, so that the zinc ion salt and the ionic liquid are phase separated and then recovered separately.

9. The recycling method according to claim 8, characterized in that: The heating temperature is 50-80° C., and the heating time is 30-60 minutes.

10. The recycling method according to claim 8, characterized in that: The vacuum degree of the vacuum treatment is 100000~100Pa.

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