Aqueous battery electrolyte and preparation and application thereof

Abstract

The invention discloses an aqueous battery electrolyte as well as preparation and application thereof. The aqueous battery electrolyte comprises a solute, dimethyl phosphate and water, the solute is sodium salt or lithium salt, and the volume ratio of water to dimethyl phosphate is (0.1-3): (7-10). The preparation method comprises the following steps: uniformly mixing dimethyl phosphate with water to obtain a solution A; adding a solute into the solution A, and dissolving to obtain a solution B; and adjusting the pH value of the solution B to be neutral to obtain the aqueous battery electrolyte. The aqueous battery electrolyte prepared by the invention can be used for preparing aqueous lithium and sodium ion batteries. According to the invention, the electrochemical stability window of the pure water system electrolyte is effectively widened, the stable voltage window can reach 3V, and the decomposition of deionized water in the electrolyte is relieved; the aqueous electrolyte is simple in preparation method, low in price, good in safety and easy for industrial large-scale production; the aqueous battery adopting the electrolyte is long in cycle life and excellent in performance.

Description

Technical Field

[0001] The present invention relates to an aqueous electrolyte and a preparation method thereof, and in particular to an aqueous battery electrolyte and the preparation and application thereof. Background Art

[0002] The electrolyte mainly provides a medium for ion conduction, allowing ion transfer between the positive and negative electrodes of the battery, thereby completing the storage and release of charge. The advantage of aqueous battery electrolytes is that water is a relatively safe solvent. Compared with organic solvents, water has higher thermal and chemical stability, is non-flammable, and reduces the risk of thermal runaway of the battery. However, the electrochemical stability window of water is narrow, about 1.23V, which means that the operating voltage is lower when the battery is working; compared with organic electrolytes, the ionic conductivity of aqueous electrolytes is generally lower, which limits the electrochemical performance of the battery.

[0003] Phosphate compounds are usually used as flame retardant additives in non-aqueous electrolytes. For example, Chinese patent CN106953119A discloses a non-aqueous electrolyte that uses dimethyl methyl phosphate, trimethyl phosphate, etc. as flame retardant additives to prepare the non-aqueous electrolyte. However, these phosphate compounds do not have the function of widening the electrochemical stability window of aqueous electrolytes. Therefore, such substances are not used in the field of aqueous batteries to increase the operating voltage of batteries. How to effectively improve the electrochemical stability window of aqueous electrolytes has become a technical problem that needs to be solved in the process of improving the performance of aqueous batteries. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide an aqueous battery electrolyte to solve the problem of the narrow electrochemical stability window of existing aqueous electrolytes. Another purpose of the present invention is to propose a method for preparing an aqueous battery electrolyte to solve the problem of how to prepare an aqueous battery electrolyte. The third purpose of the present invention is to propose the use of an aqueous battery electrolyte in the preparation of aqueous lithium and sodium ion batteries to solve the problem of how to prepare aqueous lithium and sodium ion batteries.

[0005] Technical solution: The aqueous battery electrolyte described in the present invention comprises a solute, dimethyl phosphate and water, wherein the solute is a sodium salt or a lithium salt, and the volume ratio of water to dimethyl phosphate is 0.1-3:7-10.

[0006] The present invention improves the solvation structure of aqueous battery electrolyte by adding dimethyl phosphate as the second solvent to the traditional low-concentration aqueous electrolyte, broadens its operating voltage, inhibits hydrogen and oxygen evolution reactions, and selects matching positive and negative electrode materials to construct a wide-range aqueous full battery. The purpose is to ensure battery safety while increasing the operating voltage of the electrolyte and ensuring that the electrolyte has good ionic conductivity, thereby providing excellent electrochemical performance for the electrode material.

[0007] Preferably, the lithium salt is selected from one or more of lithium sulfate, lithium acetate, lithium nitrate, lithium chloride, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate; the sodium salt is selected from one or more of sodium sulfate, sodium acetate, sodium nitrate, sodium chloride, sodium tetrafluoroborate, and sodium trifluoromethanesulfonate.

[0008] Preferably, the final concentration of the solute is 0.5-10 mol / L.

[0009] The second aspect of the present invention discloses a method for preparing the aqueous battery electrolyte, comprising the following steps:

[0010] (1) mixing dimethyl phosphate and water to obtain solution A;

[0011] (2) adding the solute to solution A and dissolving it to obtain solution B;

[0012] (3) The pH value of solution B is adjusted to neutral to obtain an aqueous battery electrolyte.

[0013] Preferably, in step (1), the mixing temperature is 20-60° C. This temperature range can prevent the solvent from being overheated and causing serious volatilization.

[0014] Preferably, in step (3), the method for adjusting the pH value of solution B is: adding one or more of ammonia water, glacial acetic acid, ammonium oxalate, calcium hydroxide, and ammonium dihydrogen phosphate to solution B until the pH value of solution B is 6-8. The buffer can undergo hydrolysis and ionization in the electrolyte to balance the H + or OH - concentration, maintaining the pH of the solution.

[0015] The third aspect of the present invention discloses the use of the aqueous battery electrolyte in the preparation of aqueous lithium and sodium ion batteries, and the specific method comprises the following steps:

[0016] S1, mixing a positive electrode active material, a conductive agent, a binder and a solvent to prepare a positive electrode slurry, and coating the positive electrode slurry on a current collector to prepare a positive electrode sheet;

[0017] S2, mixing the negative electrode active material, the conductive agent, the binder and the solvent to prepare a negative electrode slurry, and coating the negative electrode slurry on the current collector to prepare a negative electrode sheet;

[0018] S3, assembling the aqueous battery electrolyte, positive electrode sheet, negative electrode sheet and separator into an aqueous lithium and sodium ion battery.

[0019] Preferably, in step S1, the positive electrode active material is one or more of lithium manganese oxide, lithium iron phosphate, sodium iron pyrophosphate, and Prussian blue, and the positive electrode active material loading is 1.0-2.0 mg cm -2In step S2, the negative electrode active material is one or more of sodium titanium phosphate, lithium titanate, and titanium niobate, and the loading amount of the negative electrode active material is 1.0-2.0 mg cm -2 .

[0020] In some embodiments, the conductive agent is conductive carbon black, the binder is polyvinylidene fluoride (PVDF), the positive electrode active material is LiMn2O4, and the solvent is N-methylpyrrolidone (NMP). LiMn2O4 is mixed with conductive carbon black and PVDF in a mass ratio of 8:1:1. The negative electrode active material is NaTi2(PO4)3, and NaTi2(PO4)3 is mixed with conductive carbon black and PVDF in a mass ratio of 8:1:1.

[0021] Preferably, in steps S1 and S2, the current collector is carbon paper; and in step S3, the separator is a glass fiber separator.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0023] (1) The present invention effectively broadens the electrochemical stability window of pure water electrolyte, and the stable voltage window can reach 3V, which alleviates the decomposition of deionized water in the electrolyte;

[0024] (2) The preparation method of the aqueous electrolyte in the present invention is simple, low-cost, safe, and easy to industrialize and mass-produce; the aqueous battery using the electrolyte has a long cycle life and excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The LSV curves of the electrolytes of Examples 1, 2, 3, 4 and Comparative Example 1;

[0026] Figure 2 The Tafel curves of the electrolytes of Examples 1, 2 and Comparative Example 1;

[0027] Figure 3 The charge and discharge curves of Example 2 and Comparative Example 1 at 0.2C;

[0028] Figure 4 The long cycle performance of Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0030] Example 1: A method for preparing an aqueous electrolyte is as follows:

[0031] (1) The volume ratio of water to dimethyl phosphate is 3:9. Dimethyl phosphate and water are stirred and mixed at 40° C. to obtain solution A;

[0032] (2) adding lithium trifluoromethanesulfonate to solution A so that the final concentration of lithium trifluoromethanesulfonate is 1 mol / L, and dissolving the lithium trifluoromethanesulfonate to obtain solution B;

[0033] (3) Aqueous ammonia is added to solution B until the pH value of solution B reaches 7 to obtain an aqueous battery electrolyte.

[0034] Example 2: A method for preparing an aqueous electrolyte is as follows:

[0035] (1) The volume ratio of water to dimethyl phosphate is 1:9. Dimethyl phosphate and water are stirred and mixed at 20° C. to obtain solution A;

[0036] (2) adding lithium trifluoromethanesulfonate to solution A so that the final concentration of lithium trifluoromethanesulfonate is 0.5 mol / L, and dissolving the lithium trifluoromethanesulfonate to obtain solution B;

[0037] (3) Aqueous ammonia is added to solution B until the pH value of solution B reaches 8 to obtain an aqueous battery electrolyte.

[0038] Example 3: A method for preparing an aqueous electrolyte is as follows:

[0039] (1) The volume ratio of water to dimethyl phosphate is 2:8. Dimethyl phosphate and water are stirred and mixed at 60° C. to obtain solution A;

[0040] (2) adding lithium trifluoromethanesulfonate to solution A so that the final concentration of lithium trifluoromethanesulfonate is 2 mol / L, and dissolving the lithium trifluoromethanesulfonate to obtain solution B;

[0041] (3) Aqueous ammonia was added to solution B until the pH value of solution B reached 7.5 to obtain an aqueous battery electrolyte.

[0042] Embodiment 4: A method for preparing an aqueous electrolyte is as follows:

[0043] (1) The volume ratio of water to dimethyl phosphate is 3:7. Dimethyl phosphate and water are stirred and mixed at 45° C. to obtain solution A;

[0044] (2) adding lithium trifluoromethanesulfonate to solution A so that the final concentration of lithium trifluoromethanesulfonate is 1.5 mol / L, and dissolving the lithium trifluoromethanesulfonate to obtain solution B;

[0045] (3) Add ammonium dihydrogen phosphate to solution B until the pH value of solution B reaches 6 to obtain an aqueous battery electrolyte.

[0046] Example 5: A method for preparing an aqueous electrolyte is as follows:

[0047] (1) The volume ratio of water to dimethyl phosphate is 1:9. Dimethyl phosphate and water are stirred and mixed at 30° C. to obtain solution A;

[0048] (2) adding sodium trifluoromethanesulfonate to solution A so that the final concentration of sodium trifluoromethanesulfonate is 1 mol / L, and dissolving the solution to obtain solution B;

[0049] (3) Ammonium oxalate is added to solution B until the pH value of solution B reaches 6.5 to obtain an aqueous battery electrolyte.

[0050] Example 6: A method for preparing an aqueous electrolyte is as follows:

[0051] (1) The volume ratio of water to dimethyl phosphate is 1:8. Dimethyl phosphate and water are stirred and mixed at 50° C. to obtain solution A;

[0052] (2) adding sodium trifluoromethanesulfonate to solution A so that the final concentration of sodium trifluoromethanesulfonate is 1 mol / L, and dissolving the solution to obtain solution B;

[0053] (3) Aqueous ammonia was added to solution B until the pH value of solution B reached 7.5 to obtain an aqueous battery electrolyte.

[0054] Example 7: A method for preparing an aqueous electrolyte is as follows:

[0055] (1) The volume ratio of water to dimethyl phosphate is 2.5:8.5. Dimethyl phosphate and water are stirred and mixed at 35° C. to obtain solution A;

[0056] (2) adding sodium trifluoromethanesulfonate to solution A so that the final concentration of sodium trifluoromethanesulfonate is 0.5 mol / L, and dissolving the solution to obtain solution B;

[0057] (3) Aqueous ammonia is added to solution B until the pH value of solution B reaches 7 to obtain an aqueous battery electrolyte.

[0058] Embodiment 8: A method for preparing an aqueous electrolyte is as follows:

[0059] (1) The volume ratio of water to dimethyl phosphate is 3:8. Dimethyl phosphate and water are stirred and mixed at 60° C. to obtain solution A;

[0060] (2) adding sodium trifluoromethanesulfonate to solution A so that the final concentration of sodium trifluoromethanesulfonate is 1 mol / L, and dissolving the solution to obtain solution B;

[0061] (3) Aqueous ammonia is added to solution B until the pH value of solution B reaches 7 to obtain an aqueous battery electrolyte.

[0062] Comparative Example 1: The rest is the same as Example 1, except that:

[0063] In step (1), no dimethyl phosphate is added, and deionized water is directly mixed with lithium trifluoromethanesulfonate to obtain solution B.

[0064] Comparative Example 2: The rest is the same as Example 1, except that:

[0065] Different aqueous electrolytes were prepared as samples by replacing lithium trifluoromethanesulfonate with any one of sodium sulfate, sodium tetrafluoroborate, sodium acetate, lithium nitrate, lithium chloride, and lithium tetrafluoroborate.

[0066] Comparative Example 3: The rest is the same as Example 1, except that:

[0067] Taking the volume ratio of water to dimethyl phosphate as a variable, different aqueous electrolytes were prepared as samples.

[0068] Comparative Example 4: The rest is the same as Example 1, except that:

[0069] Different aqueous electrolytes were prepared as samples by replacing dimethyl phosphate with any one of dimethyl methyl phosphate, dimethyl (3,3-difluoro-2-oxoheptyl) phosphate, trimethyl phosphate, and triethyl phosphate.

[0070] In order to test the performance of the electrolyte sample, the voltage window test of the electrolyte was carried out. The test conditions were: the voltage scanning window was (2~2)V, and the voltage scanning rate was 10mV / s. The results are as follows:

[0071] Table 1 Voltage window test results of different electrolytes

[0072]

[0073]

[0074] In the results of Table 1, the stable voltage window of Comparative Example 1 is significantly narrower than that of Example 1, indicating that the addition of dimethyl phosphate can effectively solve the problem of narrow stable voltage window in pure aqueous electrolyte samples. After replacing a variety of different solutes in Comparative Example 2, the stable voltage window is greatly reduced compared with Example 1, indicating that dimethyl phosphate relies on trifluoromethanesulfonate to improve the performance of aqueous electrolytes. When the type of solute changes, dimethyl phosphate cannot widen the stable voltage window of aqueous electrolytes. Comparative Example 3 shows that the volume ratio of water to dimethyl phosphate is more important for dimethyl phosphate to play a role. When the water content in the aqueous electrolyte is too much or too little, the effect of dimethyl phosphate will be greatly reduced, and the stable voltage window of the aqueous electrolyte cannot be effectively improved. The test results of the 0.1:10 group of samples in Comparative Example 3 are comparable to those of Comparative Example 1, indicating that dimethyl phosphate cannot expand the stable voltage window under anhydrous conditions, and dimethyl phosphate can only play a role in expanding the stable voltage window in an aqueous electrolyte system. In Comparative Example 4, when dimethyl phosphate is replaced by other types of phosphate compounds, the electrochemical stability window of the electrolyte sample is equivalent to that of the pure water electrolyte sample, indicating that most types of phosphate compounds do not have the function of widening the electrochemical stability window of the water electrolyte. Therefore, the present invention can effectively widen the voltage window of the electrolyte and provide a wider voltage reaction range for the water battery.

[0075] The electrolyte samples prepared in Examples 1-8 and Comparative Examples 1-4 were assembled into batteries with the positive electrode, the negative electrode and the separator for subsequent performance testing. The preparation method of the batteries is as follows:

[0076] Positive electrode preparation: LiMn2O4, conductive carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP solution was added to the mixed slurry, which was then evenly coated on the carbon paper current collector to obtain a positive electrode sheet. The active material loading was 1.5 mg cm -2 .

[0077] Negative electrode preparation: NaTi2(PO4)3, conductive carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP solution was added to the mixed slurry, which was then evenly coated on the carbon paper current collector to obtain the negative electrode sheet. The active material loading was 1.5 g cm -2 .

[0078] Preparation of glass fiber diaphragm: Cut GF-glass fiber into 18 mm discs and set aside.

[0079] In the following embodiments, the battery performance test adopts the blue electric test system, and the assembled battery includes:

[0080] LiMn2O4 / / NaTi2(PO4)3 full battery: The positive and negative electrodes are prepared as above, the glass fiber is the separator, the electrolyte is the electrolyte obtained in Examples 1, 2, 3, 4 and Comparative Example 1, and the LiMn2O4 / / NaTi2(PO4)3 full battery is assembled in a 2025 button battery shell at room temperature. The test voltage range is 1.0~2.0V, and the results are as follows Figure 1 shown.

[0081] In order to illustrate the superiority of the corrosion voltage and corrosion current of the electrolyte of the present invention, the Tafel curve test was carried out in a three-electrode system with carbon paper as the current collector for Example 1, Example 2 and Comparative Example 1. Figure 2 As shown, the corrosion potential of Example 1 is 0.12V, and the corrosion potential of Example 2 is 0.07V, both higher than -0.03V of Comparative Example 1. Similarly, the corrosion currents of Examples 1 and 2 are lower than that of Comparative Example 1, which improves the corrosion inhibition ability of the aqueous battery current collector.

[0082] In order to demonstrate the improvement of battery performance by the electrolyte of the present invention, electrochemical performance tests were conducted on Example 2 and Comparative Example 1. Figure 3 As shown, the discharge capacity of Example 2 at 0.2C is 42.2 mAh g -1 , Comparative Example 1 is 38.5 mAh g -1 .like Figure 4 As shown, the battery was charged and discharged at 1C. After 1160 cycles, the specific capacity of Example 2 remained at 32.9 mAh g -1 , while the specific capacity of comparative example 1 decayed to 5.5 mAh g after 980 cycles. -1 Therefore, the electrolyte provided by the present invention can maintain the battery specific capacity while greatly extending the cycle life of the battery.

Claims

1. An aqueous battery electrolyte, characterized in that: The method comprises a solute, dimethyl phosphate and water, wherein the solute is a sodium salt or a lithium salt, and the volume ratio of the water to the dimethyl phosphate is 0.1-3:7-10.

2. The aqueous battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium sulfate, lithium acetate, lithium nitrate, lithium chloride, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate; the sodium salt is selected from one or more of sodium sulfate, sodium acetate, sodium nitrate, sodium chloride, sodium tetrafluoroborate, and sodium trifluoromethanesulfonate.

3. The aqueous battery electrolyte according to claim 1, characterized in that: The final concentration of the solute is 0.5-10 mol / L.

4. The method for preparing an aqueous battery electrolyte according to any one of claims 1 to 3, characterized in that: The steps include: (1) mixing dimethyl phosphate and water to obtain solution A; (2) adding the solute to solution A and dissolving it to obtain solution B; (3) The pH value of solution B is adjusted to neutral to obtain an aqueous battery electrolyte.

5. The method for preparing an aqueous battery electrolyte according to claim 4, characterized in that: In step (1), the mixing temperature is between 20°C and 60°C.

6. The method for preparing an aqueous battery electrolyte according to claim 4, characterized in that: In step (3), the method for adjusting the pH value of solution B is: adding one or more of ammonia water, glacial acetic acid, ammonium oxalate, calcium hydroxide, and diammonium phosphate to solution B until the pH value of solution B is 6-8.

7. Use of the aqueous battery electrolyte according to any one of claims 1 to 3 in the preparation of aqueous lithium-ion and sodium-ion batteries.

8. The use according to claim 7, characterized in that: The steps include: S1, mixing a positive electrode active material, a conductive agent, a binder and a solvent to prepare a positive electrode slurry, and coating the positive electrode slurry on a current collector to prepare a positive electrode sheet; S2, mixing the negative electrode active material, the conductive agent, the binder and the solvent to prepare a negative electrode slurry, and coating the negative electrode slurry on the current collector to prepare a negative electrode sheet; S3, assembling the aqueous battery electrolyte, positive electrode sheet, negative electrode sheet and separator into an aqueous lithium and sodium ion battery.

9. The use according to claim 8, characterized in that: In step S1, the positive electrode active material is one or more of lithium manganese oxide, lithium iron phosphate, sodium iron pyrophosphate, and Prussian blue, and the positive electrode active material loading is 1.0-2.0 mg cm -2 In step S2, the negative electrode active material is one or more of sodium titanium phosphate, lithium titanate, and titanium niobate, and the loading amount of the negative electrode active material is 1.0-2.0 mg cm -2 .

10. The use according to claim 8, characterized in that: In steps S1 and S2, the current collector is carbon paper; in step S3, the separator is a glass fiber separator.

Images