Synergistic effect assisted stable operation of aqueous zinc ion battery in low-temperature environment

Abstract

The invention discloses a low-temperature aqueous zinc ion battery electrolyte and application thereof in an aqueous ion battery, the electrolyte comprises a zinc salt and a solvent, and the solvent comprises water, methanol and tris (2-chloropropyl) phosphate (TCPP). The volume percent of the TCPP in the solvent is 0-40%. According to the invention, a proper amount of TCPP is added into the mixed solution of zinc salt and methanol to form the mixed electrolyte, so that the stability of the zinc negative electrode is effectively improved, the freezing point of the electrolyte is reduced, reversible zinc deposition dissolution at-40 DEG C is realized, and the cycle performance of the zinc ion battery at room temperature and low temperature is improved. The low-temperature rechargeable aqueous zinc ion battery provided by the invention can be kept in a liquid state at a low temperature, can be circulated for 1800 hours, and is high in coulombic efficiency and low in cost.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, and particularly to the preparation of an antifreeze electrolyte for an aqueous zinc-ion battery and the application of the battery. Background Art

[0002] With the development of fields such as intelligent electronic devices, electric vehicles, and large-scale energy storage, people have increasingly higher requirements for the energy density, fast charge and discharge performance, and safety performance of energy storage devices. Lithium-ion batteries have been widely used in various portable electronic devices due to their high energy density, excellent cycle stability, and high Coulomb efficiency. However, the shortage of lithium resources, high cost, and battery safety issues limit their large-scale application. In contrast, zinc resources are abundant, low-cost, highly safe, and have a high theoretical specific capacity (820 mAh g -1 ) Therefore, zinc-ion batteries have greater development prospects.

[0003] Aqueous zinc-ion batteries (AZIBs) are a new type of environmentally friendly battery, with advantages such as simple preparation process, non-toxic and low-cost battery materials, safe and environmentally friendly aqueous electrolytes, and relatively high energy density. Therefore, aqueous zinc-ion batteries are expected to be applied to large-scale energy storage power grid systems. However, most research on aqueous zinc-ion batteries is carried out at room temperature and cannot adapt to changing temperature conditions. In many regions, the temperature difference between day and night is large, or the average temperature in winter is below 0 °C, and even in more extreme low-temperature environments. The electrolyte inevitably freezes below zero degrees Celsius, resulting in a decrease in ionic conductivity, and problems such as poor contact are likely to occur at the electrode-electrolyte interface, exacerbating the deterioration of the performance of aqueous zinc-ion batteries and limiting the use of aqueous zinc-ion batteries in cold environments.

[0004] Water, as the main solvent in the aqueous electrolyte, its physical and chemical properties are mainly affected by the hydrogen bonds between water molecules. Adding organic solvents can change the hydrogen bond structure in the original system, effectively reduce the freezing point of the mixed solvent, and contribute to improving the low-temperature electrochemical performance of aqueous batteries. Currently, the organic additives applied to low-temperature electrolytes mainly include ethylene glycol (EG), dimethyl sulfoxide (DMSO), methanol (MeOH), acetonitrile (AN), and N-N-dimethylformamide (DMF), etc., to construct a water / organic mixed electrolyte. The challenges faced by low-temperature aqueous zinc-ion batteries include the increase in the freezing point of the aqueous electrolyte and the slow kinetics of zinc deposition and stripping reactions. The improved technical solution of this invention patent realizes the uniform deposition of the zinc anode, improves the cycle stability at low temperatures, and can stably cycle for more than 1800 hours at -40 °C. Summary of the Invention

[0005] The object of the present invention is to provide a general low-temperature AZIBs electrolyte and its application, to solve the problem that the freezing point of conventional AZIBs electrolytes is relatively high, resulting in the deterioration of the electrochemical performance of AZIBs at low temperatures. By adding an appropriate amount of TCPP to the mixed solution of zinc salt and methanol, reversible zinc deposition / dissolution at -40 °C is achieved, the cycle stability of the positive electrode material is improved, and thus the cycle performance of zinc-ion batteries at room temperature and low temperatures is improved.

[0006] To achieve the above object, the present invention adopts the following technical solutions: The electrolyte of a low-temperature aqueous zinc-ion battery mainly consists of a zinc salt, an organic solvent and water. The volume ratio of the organic solvent being methanol is 56%, and the volume ratio of TCPP is 0-40%.

[0007] Based on the above solution, preferably, the zinc salt is any one or a combination of at least two of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc phosphate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonyl)imide, zinc tetrafluoroborate, zinc hexafluorophosphate, zinc bis(oxalato)borate, and further preferably zinc sulfate.

[0008] Based on the above solution, the organic solvent additive is a flame retardant.

[0009] Based on the above solution, preferably, the flame retardant is tris(2-chloropropyl) phosphate.

[0010] The concentration of the electrolyte salt is 0.1 M to 17 M, where M is the volume concentration, that is, the ratio of the number of moles of the electrolyte salt to the volume of the solvent M: mol L -1 。

[0011] Based on the above solution, preferably, the volume percentage of methanol in the mixed electrolyte accounts for 56% of the solvent.

[0012] Based on the above solution, preferably, the zinc salt concentration is 0.1-2.5 mol L -1 (M), and further preferably 1 M.

[0013] Based on the above solution, preferably, the content of TCPP in the mixed electrolyte is 0-40%, and the low-temperature aqueous ion battery electrolyte is specifically OTf, TCPP0, TCPP5, TCPP10, TCPP20, TCPP40.

[0014] Based on the above solution, preferably, the zinc-ion battery is composed of a positive electrode, a membrane and a zinc negative electrode material. Among them, the positive electrode selects a zinc-ion insertion / extraction type material, and the manganese-based material is MnO2, Ca 0.28One or both of MnO2; the vanadium-based material is one or more of V2O5, V2O3, Zn2V2O7, and KV3O8; the membrane is a glass fiber membrane or a Celgard membrane; the zinc negative electrode is zinc foil or zinc powder.

[0015] The present invention also provides the application of a low-temperature aqueous ionic battery electrolyte in an aqueous ionic battery.

[0016] Innovation points: The functional electrolyte contains methanol and tris(2-chloropropyl) phosphate (TCPP), which enhances the stability of the zinc anode at low temperatures. Methanol tends to coordinate preferentially with Zn 2+ and participates in the primary solvation sheath of Zn 2+ The addition of TCPP further changes the Zn 2+ solvation structure, resulting in an increase in methanol molecules in the primary solvation sheath. In addition, TCPP has a tendency to adhere to the Zn anode due to its abundant chlorine atoms and ether bonds. Moreover, the chlorine atoms in TCPP can repel water molecules, and the adsorption on the Zn anode can limit the methanol molecules in the interface. More importantly, TCPP can also reduce the surface energy and limit the growth of deposited particles, thereby achieving compact, uniform, and fine deposition.

[0017] Advantages of the present invention: An innovative functional electrolyte is adopted, which can produce reversible deposition and uniform and fine zinc particles, greatly stabilizing the zinc anode and the Zn||Zn x V2O5·H2O full battery. The functional electrolyte can achieve a durable Zn||Zn symmetric battery, which can reach more than 1600 hours of room temperature cycling at 1 mA cm −2 and 1 mA h cm −2 Specifically, the battery using the TCPP20 electrolyte has a stable cycle life of more than 1800 hours below -40 °C, indicating that the zinc anode has good low-temperature stability. Description of the drawings

[0018] Figure 1 : Visualization photos of various electrolytes at 25 °C and -40 °C in Example 1.

[0019] Figure 2 : XRD patterns of zinc foil after cycling in various electrolytes in Example 2.

[0020] Figure 3 : SEM images of zinc foil after cycling in various electrolytes in Example 3.

[0021] Figure 4 : Electrochemical impedance diagrams of the Zn||Zn symmetric battery at room temperature in Example 4.

[0022] Figure 5 : Chronoamperometry curves of the Zn anode measured at -150 mV with OTf, TCPP0, and TCPP20 electrolytes in Example 5.

[0023] Figure 6 : Galvanostatic charge-discharge curves of the Zn||Zn symmetric cell at room temperature in Example 6.

[0024] Figure 7 : Low-temperature (-40 °C) cycling stability of the Zn||Zn symmetric cell in various electrolytes in Example 7.

[0025] Figure 8 : CE curves of the Zn||Cu coin cell in Example 8. Detailed implementation mode

[0027] The following examples further illustrate the present invention rather than limiting the scope of the present invention.

[0028] Example 1.

[0029] Prepare an electrolyte (OTf) with 1 M zinc trifluoromethanesulfonate as the solvent.

[0030] Prepare a mixed electrolyte (TCPP0) with 1 M zinc trifluoromethanesulfonate, water, and methanol (56%) as solvents.

[0031] Prepare a mixed electrolyte with 1 M zinc trifluoromethanesulfonate, water, and methanol (56%) as solvents, and the addition amount of TCPP is 5% (TCPP5).

[0032] Prepare a mixed electrolyte with 1 M zinc trifluoromethanesulfonate, water, and methanol (56%) as solvents, and the addition amount of TCPP is 10% (TCPP10).

[0033] Prepare a mixed electrolyte with 1 M zinc trifluoromethanesulfonate, water, and methanol (56%) as solvents, and the addition amount of TCPP is 20% (TCPP20).

[0034] Prepare a mixed electrolyte with 1 M zinc trifluoromethanesulfonate, water, and methanol (56%) as solvents, and the addition amount of TCPP is 40% (TCPP40).

[0035] The antifreeze properties of different electrolytes were studied by visual experiments.

[0036] The test results are shown in Figure 1 . Except for the freezing of OTf, the other electrolytes after adding methanol do not freeze at -40 °C and show a clear and transparent solution state.

[0037] Example 2: The OTf, TCPP0, TCPP5, TCPP10, TCPP20, and TCPP40 electrolytes in Example 1.

[0038] Using a coin cell test, a Zn||Zn symmetric cell was assembled and the OTf, TCPP0, TCPP5, TCPP10, TCPP20, and TCPP40 electrolytes were used respectively. At 1 mA cm -2 , 1 mA cm -2 , a constant current charge-discharge test was carried out.

[0039] After 30 cycles of deposition, the zinc negative electrode was washed with deionized water, dried, and the surface of the zinc foil was analyzed by XRD. The test results are shown in Figure 2 . After cycling in OTf, a large amount of hydrogen evolution by-product Zn4SO4(OH)6·xH2O appeared on the surface of the zinc foil. However, no by-products appeared on the surface of the zinc foil after cycling in TCPP20. The above results indicate that in the TCPP20 mixed electrolyte, the hydrogen evolution corrosion of zinc is greatly inhibited.

[0040] Example 3: The zinc negative electrode after cycling the OTf, TCPP0, and TCPP20 electrolytes in Example 2.

[0041] The surface of the zinc foil was analyzed by SEM. The test results are shown in Figure 3 . In TCPP20, the zinc deposition was uniform and dense. In OTf and TCPP0, the zinc deposition was loose and there were a large number of irregular particles. It shows that the mixed electrolyte can significantly improve the zinc deposition morphology and thus inhibit the generation of zinc dendrites.

[0042] Example 4: The OTf, TCPP0, and TCPP20 electrolytes in Example 1.

[0043] Using a coin cell test, a Zn||Zn symmetric cell was assembled and the OTf, TCPP0, and TCPP20 electrolytes were used respectively. After standing for three hours, an electrochemical impedance test was carried out. The impedance values of the symmetric cells tested in OTf, TCPP0, and TCPP20 were 1200 Ω, 875 Ω, and 410 Ω respectively. It shows that the TCPP20 electrolyte improves the transport efficiency of zinc ions and is beneficial to improving the ion mobility on the surface of the zinc foil.

[0044] Example 5: The OTf, TCPP0, and TCPP20 electrolytes in Example 1.

[0045] The button cell test was adopted to assemble the Zn||Zn symmetric battery. OTf, TCPP0, and TCPP20 electrolytes were used respectively. After standing for three hours, the chronoamperometric current test of the Zn anode was carried out. The tests in OTf, TCPP0, and TCPP20 showed that zinc ions tended to three-dimensional diffusion in TCPP20. It shows that the TCPP20 electrolyte effectively inhibits the generation of zinc dendrites.

[0046] Example 6: The OTF, TCPP0, TCPP5, TCPP10, TCPP20, and TCPP40 electrolytes in Example 1.

[0047] Six electrolytes were assembled into a Zn||Zn symmetric battery with a current density of 1 mA cm -2 , and a capacity of 1 mAh cm -2 as the test conditions, and the charge-discharge test was carried out at 25 °C.

[0048] The test results are shown in Figure 6 . At room temperature, compared with the traditional OTF electrolyte, the Zn||Zn symmetric battery using the TCPP20 mixed electrolyte has a significantly increased stable cycling time. It shows that due to the improvement of the zinc deposition morphology and the inhibition of hydrogen evolution corrosion by the Zn||Zn mixed electrolyte, the stability of the zinc negative electrode is greatly improved.

[0049] Example 7: The OTF, TCPP0, TCPP5, TCPP10, TCPP20, and TCPP40 electrolytes in Example 1 were used respectively to assemble a Zn||Zn symmetric battery with a current density of 1 mA cm -2 , and a capacity of 1 mAh cm -2 as the test conditions, and the charge-discharge test was carried out at -40 °C.

[0050] The test results are shown in Figure 7 . At -40 °C, the Zn||Zn symmetric battery using OTF could not operate normally after cycling for about 150 h. While the Zn||Zn symmetric battery using the TCPP20 mixed electrolyte could stably operate for more than 1800 h at -40 °C. It shows that the TCPP20 mixed electrolyte can achieve reversible zinc deposition and dissolution at -40 °C.

[0051] Example 8: The OTF and TCPP20 electrolytes in Example 1 were used. A Zn||Cu battery was assembled, and the current density was set to 2 mA cm -2 , and the areal capacity was 1 mAh cm -2。The reversibility of Zn stripping / plating increases with the increase of []. In particular, a high initial Coulombic efficiency (CE) of 97.5% is shown in TCPP20, an ultra-long cycle stability within 2100 cycles, and a high average CE of 99.8%. This indicates that Zn stripping / plating has good reversibility in TCPP20.

Claims

1. An electrolyte for a low-temperature aqueous zinc-ion battery, characterized in that, The electrolyte includes zinc salt and a solvent, and the solvent includes water, methanol and TCPP.

2. The electrolyte according to claim 1, wherein The volume ratio of the methanol in the solvent is 56%.

3. The electrolyte according to claim 2, characterized in that, The content of TCPP in the solvent is 0-40%.

4. The electrolyte according to claim 1, characterized in that, The zinc salt is any one or a combination of at least two of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc phosphate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethanesulfonyl)imide, zinc tetrafluoroborate, zinc hexafluorophosphate, and zinc bis(oxalato)borate.

5. The electrolyte according to claim 4, characterized in that, The zinc salt is zinc trifluoromethanesulfonate.

6. The electrolyte according to claim 1, wherein The concentration of the zinc salt in the electrolyte is 1 mol / L.

7. A water-based zinc-ion battery, characterized in that, The aqueous zinc ion battery includes the electrolyte according to any one of claims 1 to 6.

8. The zinc ion battery according to claim 7, wherein, The zinc-ion battery includes a positive electrode, a membrane, and a zinc negative electrode; the positive electrode is selected from zinc-ion insertion / extraction type materials, and the zinc-ion insertion / extraction type materials are one or a combination of manganese-based materials and vanadium-based materials; the manganese-based materials are one or both of MnO2 and Ca 0.28 One or two of MnO2; the vanadium-based materials are one or more of V2O5, V2O3, Zn2V2O7, and KV3O8; the membrane is a glass fiber membrane or a Celgard membrane; the zinc negative electrode is zinc foil or zinc powder.

9. The zinc ion battery according to claim 8, characterized in that, The positive electrode is Zn x V2O5·H2O (ZVO); the membrane is a glass fiber membrane; the zinc negative electrode is a zinc foil.

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