Aqueous electrolyte for lithium-ion battery and its preparation method and use

Abstract

The present invention discloses a water-containing electrolyte for lithium-ion batteries, its preparation method and uses. In the present invention, water is added to a commercial electrolyte, and nano-diamond particles are introduced to prepare a mixed electrolyte of water and nano-diamond. The mixed electrolyte is introduced into a lithium-ion battery half-cell and full-cell. During the charge and discharge cycle process, the water-containing mixed electrolyte has a higher ionic conductivity and better separator wettability, which is beneficial to improving the lithium-ion transport ability. The synergistic effect of nano-diamond particles and water constructs a nano-diamond related solid electrolyte interface, providing abundant lithium-ion adsorption active sites, protecting the negative electrode such as graphite from peeling under the action of water, and improving the comprehensive performance of the battery such as capacity and rate performance. The preparation method of the present invention is simple, low-cost and environmentally friendly, and has good prospects for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery electrolytes, and relates to a method for containing a certain amount of water in the electrolyte and improving the comprehensive performance of the battery. Background Art

[0002] In recent years, the rapid development of advanced electric vehicles and various electronic products has put forward higher requirements for the energy density, cycle life and safety performance of lithium-ion batteries. The electrolyte in lithium batteries is usually water-containing or water-free, and most commercial lithium batteries are assembled from water-free electrolytes and graphite anodes. The mixing of trace water in commercial water-free electrolytes will cause hydrolysis of lithium salts, degradation of the solid electrolyte interface (SEI) and increased safety risks. In particular, the water in carbonate-based electrolytes reacts with lithium hexafluorophosphate to form corrosive hydrofluoric acid, which will reduce the performance of the electrolyte and cause its instability. At the same time, most commercial anodes use graphite materials, which are very sensitive to trace water in the electrolyte. The embedding of water molecules in the graphite anode will cause serious structural degradation of the graphite anode, resulting in rapid battery failure. During the entire production and transportation process of lithium batteries, a long-term dry storage environment needs to be provided, which will increase the product cost. Therefore, it is very necessary to evaluate the impact of water on the performance of lithium-ion batteries and study the possibility of using water to improve the performance of lithium-ion batteries.

[0003] Similar to the present invention is the patent application with the application number 202210909358.0 and the name "A water remover for carbonate organic solvents in lithium-ion battery electrolytes, its preparation method and application", which prepared a solid water remover. This water remover can efficiently remove water from the water-containing electrolyte, ensuring the purity of carbonate organic solvents in the lithium-ion electrolyte, and does not involve the actual functions and effects of water in the electrolyte to improve the capacity and rate performance of lithium-ion batteries.

[0004] Reports related to water-containing electrolytes all focus on designing to remove trace water, and there are almost no reports on improving the performance of lithium-ion batteries by increasing the concentration of trace water. Summary of the Invention

[0005] The present invention provides a method for preparing a mixed electrolyte of nanodiamond and water by introducing a high concentration of trace water with the assistance of nanodiamond, realizing the improvement of the capacity and cycle stability of lithium-ion batteries.

[0006] A water-containing electrolyte for a lithium-ion battery in the present invention is composed of a commercial electrolyte, nanodiamond particles and trace water. The concentration of the nanodiamond particles is 800 ppm, and the concentration of the trace water is 5000 ppm; the water is deionized water;

[0007] The particle size of the nanodiamond particles is 5-10 nm, and the nanodiamond particles are processed as follows:

[0008] 1) Add nanodiamond particles into the mixed acid solution prepared from concentrated sulfuric acid and concentrated hydrochloric acid, and heat at 180 °C for 20 min to remove the impurities on the surface of the diamond; the volume ratio of concentrated sulfuric acid to concentrated hydrochloric acid in the mixed acid solution is 1:1, and both concentrated sulfuric acid and concentrated hydrochloric acid are of commercial concentration.

[0009] 2) Perform surface oxygen termination treatment on the nanodiamond particles whose surface impurities have been removed in step 1).

[0010] The commercially available electrolyte is preferably LiPF6 electrolyte, and the volume ratio of the solvents EC:DMC = 1:1.

[0011] A preparation method of a water-containing electrolyte for a lithium-ion battery is as follows:

[0012] 1) Add nanodiamond particles into the mixed acid solution prepared from concentrated sulfuric acid and concentrated hydrochloric acid, and heat at 180 °C for 20 min to remove the impurities on the surface of the diamond; the particle size of the nanodiamond particles is 5 - 10 nm, the volume ratio of concentrated sulfuric acid to concentrated hydrochloric acid in the mixed acid solution is 1:1, and both concentrated sulfuric acid and concentrated hydrochloric acid are of commercial concentration.

[0013] 2) Perform surface oxygen termination treatment on the nanodiamond particles whose surface impurities have been removed in step 1);

[0014] 3) Add the nanodiamonds obtained in step 2) and deionized water into the commercially available electrolyte, and perform ultrasonic treatment for 15 min under argon protection to obtain a mixed electrolyte of trace water and nanodiamonds; the concentration of nanodiamond particles in the mixed electrolyte is 800 ppm, and the concentration of trace water is 5000 ppm.

[0015] The surface oxygen termination treatment is carried out under ultraviolet light irradiation in the atmospheric environment for 5 - 30 s.

[0016] The use of a water-containing electrolyte for a lithium-ion battery in the preparation of a lithium-ion battery half-cell is as follows:

[0017] 1) Mix the graphite negative electrode with a conductive aid (carbon black), grind it under the action of a binder polyvinylidene fluoride (PVDF), and add a solvent 1-methyl-2-pyrrolidone (NMP) and stir with a magnetic stirrer until it becomes a viscous fluid; the proportions of graphite, conductive aid and binder are 80 wt%, 10 wt% and 10 wt% respectively;

[0018] 2) Coat the viscous fluid on a copper foil current collector and dry it at 120 °C; finally, compact and cut it into a circular electrode (diameter 12 mm) to prepare the graphite negative electrode of the lithium-ion battery, and the loading mass is about 4 mg cm -2 ;

[0019] 3) Under an anhydrous and anaerobic condition, using metallic lithium as the counter electrode, graphite as the negative electrode, and dropping 80 μL of a mixed electrolyte of trace water and nanodiamond to assemble a lithium-ion half cell.

[0020] Use of a water-containing electrolyte for a lithium-ion battery in the preparation of a lithium-ion battery full cell. The specific process is as follows:

[0021] 1) Using lithium iron phosphate (LFP) as the positive electrode of the full cell, mixing lithium iron phosphate powder with a conductive agent acetylene black, grinding under the action of a binder polyvinylidene fluoride (PVDF), and adding a solvent 1-methyl-2-pyrrolidone (NMP) until it is stirred into a viscous fluid by a magnetic stirrer; the proportions of lithium iron phosphate, conductive agent, and binder are 80 wt%, 10 wt%, and 10 wt% respectively;

[0022] 2) Coating the viscous fluid on an aluminum foil and drying it under vacuum at 120 °C for 12 hours; finally stamping it into a disk (diameter 12 mm) with a loading mass of 6 - 8 mg cm -2 .

[0023] 3) Under an anhydrous and anaerobic condition, using LFP as the positive electrode and graphite as the negative electrode, dropping 80 μL of a mixed electrolyte of trace water and nanodiamond to assemble a lithium-ion full cell.

[0024] Advantages of the present invention:

[0025] The present invention uses nanodiamond particles and deionized water to prepare a mixed electrolyte of trace water and nanodiamond; the ionic conductivity of this electrolyte and its wettability to a polypropylene separator are both improved; the synergistic effect of nanodiamond and water constructs a nanodiamond solid electrolyte interface (SEI) on the surface of the graphite negative electrode; using the mixed electrolyte of trace water and nanodiamond to prepare a high-performance lithium-ion battery, solving the limitations of the preparation and use conditions of commercial lithium batteries (anhydrous and dry environment), and at the same time solving problems such as low specific capacity and low capacity retention rate of the graphite negative electrode. The nanodiamond solid electrolyte interface not only has high hardness, can inhibit the growth of lithium dendrites and the volume expansion of the negative electrode material, but also is conducive to promoting the solid-phase diffusion of lithium ions and providing a large number of active sites for the rapid adsorption / desorption of lithium ions. The preparation method of the mixed electrolyte of trace water and nanodiamond of the present invention has the advantages of simple process, low cost, and easy implementation, and is expected to be mass-produced in the future. Description of the drawings

[0026] Figure 1 It is the wettability diagram of samples 1, 2, and 3 for the polypropylene separator in Example 1.

[0027] Figure 2 It is the ionic conductivity diagram of samples 1, 2, and 3 in Example 1.

[0028] Figure 3Electrochemical performance comparison chart of batteries 1, 2, and 3 in Example 2 (0.1Ag -1 ).

[0029] Figure 4 Electrochemical performance comparison chart of batteries 1, 2, and 3 in Example 2 (1Ag -1 ).

[0030] Figure 5 Electrochemical performance comparison chart of batteries 1, 2, and 3 in Example 2 (variable magnification).

[0031] Figure 6 Composition content chart of samples 4, 5, and 6 in Example 4.

[0032] Figure 7 Transmission electron microscope image of sample 6 in Example 4.

[0033] Figure 8 Electrochemical performance comparison chart of batteries 4, 5, and 6 in Example 5 (0.1Ag -1 ).

[0034] Figure 9 Electrochemical performance comparison chart of batteries 7, 8, and 9 in Example 6 (0.1Ag -1 ).

[0035] Figure 10 Electrochemical performance comparison chart of batteries 10, 11, and 12 in Example 7 (0.1Ag -1 ). Detailed implementation mode

[0036] The following further describes the present application in detail in conjunction with the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present application and do not limit it in any way.

[0037] Example 1: Preparation of trace water and nanodiamond mixed electrolyte

[0038] 1) Take 10 mL of concentrated hydrochloric acid (commercially available mass percentage concentration of 37%) and concentrated sulfuric acid (commercially available mass percentage concentration of 98.3%) solutions respectively, and prepare a mixed acid solution with a volume ratio of 1:1;

[0039] 2) Add 0.1 g - 0.3 g of nanodiamond particles with a particle size of 5 - 10 nm to the above mixed acid solution, and heat at 180 °C for 20 min to remove the surface impurities of the diamond;

[0040] 3) Treat the acid-treated nanodiamond particles in step 2) under ultraviolet light irradiation in the atmospheric environment for 5 - 30 s;

[0041] 4) Preparation of electrolyte sample:

[0042] a. Denote 100 mL of commercial LiPF6 electrolyte (with a volume ratio of EC to DMC of 1:1) as Sample 1.

[0043] b. Add a certain amount of deionized water to 100 mL of commercial LiPF6 electrolyte (the same as Sample 1) to prepare an aqueous electrolyte with a water concentration of 5000 ppm, denoted as Sample 2.

[0044] c. Take 0.08 g of the treated nanodiamond particles and add them to the electrolyte with the same components as Sample 2, and ultrasonically treat for 15 min under argon protection to obtain a trace water and nanodiamond mixed electrolyte with a diamond concentration of 800 ppm and a water concentration of 5000 ppm, denoted as Sample 3.

[0045] Example 2: Fabrication of Lithium-Ion Half-Cell

[0046] 1) The negative electrode of the lithium-ion battery is composed of 80 wt% graphite, 10 wt% binder (polyvinylidene fluoride, PVDF), and 10 wt% acetylene black.

[0047] 2) Add a certain amount of 1-methyl-2-pyrrolidone (NMP, solvent) to the mixed negative electrode and stir for 6 h until the mixture becomes a viscous fluid.

[0048] 3) Coat the fluid slurry on the copper foil and dry it under vacuum at 120 °C for 12 hours.

[0049] 4) Cut the copper foil into small disc-shaped pieces (diameter 12 mm) and control the loading density of the electrode at 4 mg cm -2 .

[0050] 5) In an anhydrous and anaerobic environment, assemble a CR-2025 type button battery with a lithium metal sheet as the positive electrode and graphite as the negative electrode, and drop 80 μL of Sample 1, Sample 2, and Sample 3 electrolytes into each battery respectively.

[0051] 6) Weigh the mass of the electrode sheet before assembly to calculate subsequent specific capacity parameters, etc.

[0052] 7) Denote the lithium-ion half-cells prepared using Sample 1, Sample 2, and Sample 3 as Battery 1, Battery 2, and Battery 3 respectively.

[0053] Example 3: Fabrication of Lithium-Ion Full-Cell

[0054] 1) The positive electrode of the lithium-ion full-cell is composed of 80 wt% lithium iron phosphate, 10 wt% binder (polyvinylidene fluoride, PVDF), and 10 wt% acetylene black.

[0055] 2) Add a certain amount of 1-methyl-2-pyrrolidone (NMP, solvent) to the mixed cathode and stir for 6 h until the mixture becomes a viscous fluid.

[0056] 3) Coat the fluid slurry on a copper foil and dry it under vacuum at 120 °C for 12 h.

[0057] 4) Cut the copper foil into small disc-shaped pieces (diameter 12 mm) and control the loading density of the electrode at 6 - 8 mg cm -2 .

[0058] 5) In an anhydrous and anaerobic environment, assemble CR-2025 type button cells with lithium iron phosphate as the cathode and the graphite electrode prepared in Example 2 as the anode, and drop 80 μL of electrolyte of Sample 1, Sample 2, and Sample 3 into each cell respectively.

[0059] 6) Weigh the mass of the electrode sheet before assembly to calculate subsequent specific capacity parameters, etc.

[0060] 7) Label the lithium-ion full cells prepared using Sample 1, Sample 2, and Sample 3 as Cell 4, Cell 5, and Cell 6 respectively.

[0061] Example 4: Testing of lithium-ion half cells

[0062] Test the electrochemical performance of Cells 1, 2, and 3 in a BlueTEC test system. At 25 °C, discharge at a certain rate to 0.01 V; after discharge, let the cell stand for 3 minutes: then charge at a certain rate to 3 V, after charging, let the cell stand for 3 minutes and then discharge at the same constant rate to 0.01 V; after the cell is discharged, let it stand for 3 minutes and then charge under the same conditions. After the test is completed, take out the negative active materials in Cells 1, 2, and 3 and label them as Sample 4, Sample 5, and Sample 6 respectively.

[0063] Example 5: Testing of lithium-ion full cells

[0064] Test the electrochemical performance of Cells 4, 5, and 6 in a BlueTEC test system. At 25 °C, charge at a certain rate to 3.9 V; after charging, let the cell stand for 3 minutes: then discharge at a certain rate to 2.5 V, after discharge, let the cell stand for 3 minutes and then charge at the same constant rate to 3.9 V; after the cell is charged, let it stand for 3 minutes and then discharge under the same conditions.

[0065] Example 6: Testing of lithium-ion half cells at different trace water concentrations

[0066] The production steps of the lithium-ion half-cell in Example 2 were followed. The difference was that the electrolytes used were samples 1 with 10 ppm, 2000 ppm, and 3000 ppm of trace water added respectively. The lithium-ion half-cells thus prepared were labeled as Battery 7, Battery 8, and Battery 9 respectively.

[0067] Example 7: Testing of Lithium-Ion Half-Cells with Different ND Contents

[0068] The production steps of the lithium-ion half-cell in Example 2 were followed. The difference was that the electrolytes used had ND contents of 200 ppm, 400 ppm, and 1000 ppm in sample 3 respectively. The lithium-ion half-cells thus prepared were labeled as Battery 10, Battery 11, and Battery 12 respectively.

[0069] Effect Verification

[0070] 1. Contact Angle Test:

[0071] The contact angle test results between sample 1, sample 2, and sample 3 and the polypropylene separator (PP separator) are as Figure 1 shown. It can be seen from the figure that the contact angles between sample 2 and sample 3 with high water concentration and the PP separator are 27.1°, lower than that of the anhydrous sample 1 (35.1°). Therefore, the trace water in the electrolyte is beneficial to improving its wettability to the separator, promoting the uniform distribution of lithium-ion flux, and providing more pathways for lithium-ion transport.

[0072] 2. Ionic Conductivity Test

[0073] The ionic conductivity test results of sample 1, sample 2, and sample 3 are as Figure 2 shown. The ionic conductivities of sample 2 and sample 3 with high water concentration are about 10.5 mS cm -1 , significantly higher than that of sample 1 with low water concentration (8.2 mS cm -1 ). High ionic conductivity helps to improve the transport ability of lithium ions between electrodes, thus improving the rate performance of the battery.

[0074] 3. Charge-Discharge Performance Test of Lithium-Ion Half-Cells

[0075] The electrochemical performance test results of Battery 1, Battery 2, and Battery 3 at a current density of 0.1 A g -1 are as Figure 3 shown. It can be seen from the figure that the initial discharge capacity of Battery 1 is 455 mA h g -1 , and the capacity remains at 365 mAh g -1 after 100 cycles. The initial discharge capacity of Battery 2 is 6500 mA h g -1 , and it drops to 5 mA h g -1 after 10 cycles., the capacity loss is close to 99%. The initial discharge capacity of Battery 3 is 1850 mA h g -1 , and it remains at 900 mA h g after 100 cycles -1 . It can be seen that the capacity of Battery 3 is much higher than that of Battery 1 and Battery 2

[0076] The results of the electrochemical performance test at a current density of 1 A g -1 are as follows Figure 4 . The initial discharge capacity of Battery 1 is 150 mA h g -1 , and it remains at 55 mA h g after 1000 cycles -1 . The initial discharge capacity of Battery 2 is 250 mA h g -1 , and it decreases to 2 mA h g after 30 cycles -1 . The initial discharge capacity of Battery 3 is 605 mA h g -1 , and it remains at 350 mA h g after 1000 cycles -1 . It can be seen that after 1000 long cycles, the capacity of Battery 3 is almost 4 times that of Battery 1

[0077] Variable rate discharge, set to 0.1 A g -1 , 0.5 A g -1 , 1 A g -1 , 2 A g -1 and 5 A g -1 in turn. The charge reversible specific capacity tests are carried out on Battery 1, Battery 2 and Battery 3, as Figure 5 shown. Battery 3 shows better rate performance. At 0.1 A g -1 , 0.5 A g -1 , 1 A g -1 , 2 A g -1 and 5 A g -1 current densities, the capacities are 1000, 625, 390, 240 and 150 mA h g -1 respectively, and the capacity in each rate test stage is higher than that of Battery 1. The capacity of Battery 2 is almost zero after a few cycles. When the current density decreases from 5 A g -1 to 0.1 A g -1 , the capacity of Battery 3 recovers to 950 mA h g -1 , and the capacity retention rate is 95%, indicating that the trace water and nanodiamond mixed electrolyte has significant repeatability and stability

[0078] 4. Composition content characterization of Sample 4, Sample 5 and Sample 6

[0079] Figure 6The compositional analysis of Samples 4, 5, and 6 is presented. The corresponding histograms indicate that the content of LiF in Sample 4 is greater than that of Li x PF y , and the content of Li2CO3 is relatively low. In Sample 5, the content of Li x PF y is as high as 60%, which indicates that the water in the electrolyte induces the enrichment of Li x PF y in the SEI. However, for Sample 6, the content of LiF is significantly higher than that of Li x PF y , and the content of Li2CO3 exceeds 40%. Importantly, LiF and Li2CO3 are key components for stabilizing the SEI layer, which can enhance the passivation function of the SEI layer, improve the interfacial transport ability of lithium ions, and thus improve the rate performance and cycle stability of lithium-ion batteries.

[0080] 5. Transmission Electron Microscopy (TEM) Characterization of Sample 6

[0081] Figure 7 The TEM images of Sample 6 after charge-discharge cycling are presented. A dense SEI is formed on the surface of the graphite anode, with a thickness of approximately 150 nm. A large number of nanodiamond particles are dispersed in the SEI matrix. A considerable density of nanodiamond particles can inhibit the intercalation of water molecules into the graphite anode, protect the stability of the anode structure, and can provide more lithium-ion storage and adsorption sites, shortening the lithium-ion transport distance, and achieving high capacity and excellent rate performance of the battery.

[0082] 6. Charge-Discharge Performance Test of Lithium-Ion Full Battery

[0083] At a current density of 0.1 A g -1 , the results of the full battery electrochemical performance test are as Figure 8 shown. It can be seen from the figure that for Battery 5, the initial discharge and charge capacities are 200 mA h g -1 and 202 mA h g -1 , respectively. However, after only 10 cycles, its performance seriously deteriorates and degrades. The initial discharge and charge capacities of Battery 6 are 180 mA h g -1 and 178 mA h g -1 , respectively. After 50 cycles, it remains at 168 mA h g -1 , with a capacity retention rate of 95% and a Coulomb efficiency close to 100%, showing good cycle stability. At the same time, the capacity of Battery 6 is significantly higher than that of Battery 4 (98 mA h g -1 ).

[0084] 7. Test of Lithium-Ion Half Battery at Different Trace Water Concentrations

[0085] At a current density of 0.1 A g -1 , the test results of lithium-ion half-cells with different trace water concentrations are as Figure 9 shown. The capacities of Cells 7, 8, and 9 are close after 50 cycles, but Cell 7 shows better cycling stability. This indicates that without nanodiamond, water in the electrolyte has a negative impact on battery performance.

[0086] 8. Test of lithium-ion half-cells with different nanodiamond contents

[0087] At a current density of 0.1 A g -1 , the test results of lithium-ion half-cells based on 5000 ppm water and different nanodiamond contents are as Figure 10 shown. The capacities of Cells 10 (200 ppm), 11 (400 ppm), and 12 (1000 ppm) after 50 cycles are 20 mAh g -1 , 450 mAh g -1 and 850 mA h g -1 , respectively. Among them, the capacity of Cell 12 is close to that of Cell 3 (900 mA h g -1 ).

[0088] To further verify the effect of the present invention, in addition to the above embodiments, the present invention also uses an electrolyte of LiClO4 (volume ratio of EC and DMC is 1:1) to replace the commercial LiPF6 (volume ratio of EC and DMC is 1:1) used in Embodiments 1 to 7. After verification, the two have the same verification effect, and it can be inferred that the method of the present invention also has the same or similar effect in other commercial electrolytes.

Claims

1. An aqueous electrolyte for a lithium-ion battery, characterized in that, The electrolyte is composed of commercial electrolyte, nanodiamond particles and trace water. The concentration of nanodiamond particles is 800 ppm, and the concentration of trace water is 5000 ppm. The water is deionized water. The commercial electrolyte is LiClO4 electrolyte or LiPF6 electrolyte, and the solvent volume ratio of EC:DMC = 1:

1. The particle size of the nanodiamond particles is 5 - 10 nm, and the nanodiamond particles are processed as follows: 1) Add the nanodiamond particles into a mixed acid solution prepared from concentrated sulfuric acid and concentrated hydrochloric acid, and heat at 180 °C for 20 min to remove the impurities on the diamond surface. The volume ratio of concentrated sulfuric acid to concentrated hydrochloric acid in the mixed acid solution is 1:

1. The concentrated sulfuric acid is of a commercially available 98.3 wt% concentration, and the concentrated hydrochloric acid is of a commercially available 37 wt% concentration. 2) Perform surface oxygen termination treatment on the nanodiamond particles whose surface impurities have been removed in step 1).

2. The aqueous electrolyte for a lithium-ion battery according to claim 1, wherein The commercial electrolyte is LiPF6 electrolyte, and the solvent volume ratio of EC:DMC = 1:

1.

3. The preparation method of the water-containing electrolyte for the lithium-ion battery according to claim 1, wherein The specific steps of this method are as follows: 1) Add the nanodiamond particles into a mixed acid solution prepared from concentrated sulfuric acid and concentrated hydrochloric acid, and heat at 180 °C for 20 min to remove the impurities on the diamond surface. The particle size of the nanodiamond particles is 5 - 10 nm. The volume ratio of concentrated sulfuric acid to concentrated hydrochloric acid in the mixed acid solution is 1:

1. The concentrated sulfuric acid is of a commercially available 98.3 wt% concentration, and the concentrated hydrochloric acid is of a commercially available 37 wt% concentration. 2) Perform surface oxygen termination treatment on the nanodiamond particles whose surface impurities have been removed in step 1). 3) Add the nanodiamond obtained in step 2) and deionized water into the commercial electrolyte, and perform ultrasonic treatment for 15 min under argon protection to obtain a mixed electrolyte of trace water and nanodiamond. The concentration of nanodiamond particles in the mixed electrolyte is 800 ppm, and the concentration of trace water is 5000 ppm. The commercial electrolyte is LiClO4 electrolyte or LiPF6 electrolyte, and the solvent volume ratio of EC:DMC = 1:

1.

4. The preparation method of the aqueous electrolyte for a lithium-ion battery according to claim 3, characterized in that, The surface oxygen termination treatment is carried out under ultraviolet light irradiation in the atmospheric environment for 5 s - 30 s.

5. Use of the aqueous electrolyte for lithium-ion batteries according to claim 1 for preparing a lithium-ion half cell, characterized in that, The specific process of preparing a lithium-ion half-cell is as follows: 1) Mix the graphite negative electrode with a conductive additive, grind it under the action of a binder, add a solvent, and stir it into a viscous fluid with a magnetic stirrer. The proportions of graphite, conductive additive and binder are 80 wt%, 10 wt% and 10 wt% respectively. 2) Apply the viscous fluid to the copper foil current collector and dry it at 120 °C; finally, compact and cut it into circular electrodes to obtain the graphite negative electrode of the lithium-ion battery, with a loading mass of 4 mg cm -2 ; 3) Under anhydrous and anaerobic conditions, use metallic lithium as the counter electrode, and drop 80 μL of the mixed electrolyte of trace water and nanodiamond onto the negative electrode obtained in step 2) to assemble a lithium-ion half-cell.

6. Use of the aqueous electrolyte for lithium-ion batteries according to claim 5 for preparing a lithium-ion half cell, characterized in that, The conductive additive is carbon black, the binder is polyvinylidene fluoride, and the solvent is 1-methyl-2-pyrrolidone.

7. Use of the aqueous electrolyte for lithium-ion batteries as claimed in claim 1 for preparing a lithium-ion full cell, characterized in that, The specific process of preparing a lithium-ion full-cell is as follows: 1) Use lithium iron phosphate as the positive electrode of the full cell. Mix the lithium iron phosphate powder with a conductive additive, grind it under the action of a binder, add a solvent, and stir it into a viscous fluid with a magnetic stirrer. The proportions of lithium iron phosphate, conductive additive and binder are 80 wt%, 10 wt% and 10 wt% respectively. 2) Coat the viscous fluid on the aluminum foil and dry it under vacuum at 120 °C for 12 hours; finally, stamp it into a disk with a loading mass of 6 - 8 mg cm -2 ; 3) Under anhydrous and anaerobic conditions, using the positive electrode obtained in step 2) and graphite as the negative electrode, 80 μL of a mixed electrolyte of trace water and nanodiamond was dropped to assemble a lithium-ion full battery.

8. Use of the aqueous electrolyte for lithium-ion batteries according to claim 7 in the preparation of a lithium-ion full cell, characterized in that, The conductive agent is acetylene black, the binder is polyvinylidene fluoride, and the solvent is 1-methyl-2-pyrrolidone.

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