Electrolyte capable of inhibiting lithium dendrites and battery

Abstract

The invention discloses an electrolyte capable of inhibiting lithium dendrites and a battery. The electrolyte is a mixed electrolyte formed by mixing lithium hexafluorophosphate and 5-sulfosalicylic acid in proportion; in the mixed electrolyte, the molar ratio of lithium hexafluorophosphate to 5-sulfosalicylic acid is 1: (2-6); the preparation method comprises the following steps: preparing a 5-sulfosalicylic acid solution; preparing a lithium hexafluorophosphate solution; and slowly adding the lithium hexafluorophosphate solution into the 5-sulfosalicylic acid solution, and uniformly stirring to obtain the mixed electrolyte Li-SA. The electrolyte provided by the invention can inhibit the growth of lithium dendrites and improve the electrochemical performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly relates to an electrolyte and a battery capable of suppressing lithium dendrites. Background Art

[0002] Lithium-ion batteries (LIBs) are currently the most maturely studied batteries widely used in various fields such as electric vehicles and electronic devices. However, during the charge and discharge process of lithium-ion batteries, there are serious parasitic side reactions and uncontrolled lithium dendrite growth, which easily cause battery short circuits and severely restrict the development of LIBs.

[0003] To solve these problems, researchers often adopt strategies related to anode and cathode material modification to slow down the uncontrolled lithium dendrite growth. For example, some researchers use highly conductive carbon materials containing abundant nitrogen sites and interfacial coatings rich in sulfonic acid groups to modify the electrode surface to promote the + desolvation process of Li, thereby enhancing the corrosion resistance of the electrode and the ability to inhibit dendrite growth. The research on electrolyte modification is also a new research direction to solve these problems, but the existing research results are still few and further research and exploration are needed. Summary of the Invention

[0004] The purpose of the present invention is to provide an electrolyte and a battery capable of suppressing lithium dendrites to solve the problem of lithium dendrite growth in lithium-ion batteries.

[0005] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0006] In the first aspect of the present application, an electrolyte capable of suppressing lithium dendrites is provided. The electrolyte is a mixed electrolyte formed by mixing lithium hexafluorophosphate and 5-sulfosalicylic acid in a certain proportion.

[0007] In the mixed electrolyte, the molar ratio of lithium hexafluorophosphate to 5-sulfosalicylic acid is 1:2 - 6.

[0008] In the second aspect of the present application, a preparation method of an electrolyte capable of suppressing lithium dendrites is provided, including the following steps:

[0009] Prepare a 5-sulfosalicylic acid solution;

[0010] Prepare a lithium hexafluorophosphate solution;

[0011] Slowly add the lithium hexafluorophosphate solution to the 5-sulfosalicylic acid solution and stir evenly to obtain the mixed electrolyte Li-SA.

[0012] To optimize the above technical solution, the specific measures taken also include:

[0013] The preparation method of the 5-sulfosalicylic acid solution is as follows: Dissolve 5-sulfosalicylic acid in deionized water to obtain a 5-sulfosalicylic acid solution; the concentration of the 5-sulfosalicylic acid solution is 1 - 1.5 mol / L -1 .

[0014] The preparation method of the lithium hexafluorophosphate solution is as follows: Dissolve phosphorus trifluoride in excess fluoroacetone, and react at a set heating temperature to generate lithium hexafluoropyruvate; dissolve lithium hexafluoropyruvate in excess water or alcohol solvent, add excess ammonium fluoride to generate lithium hexafluorophosphate; dissolve lithium hexafluorophosphate in a solvent to obtain a lithium hexafluorophosphate solution; the concentration of the lithium hexafluorophosphate solution is 2 - 4 mol / L -1 .

[0015] The solvent of the lithium hexafluorophosphate solution uses a mixed solution of ethylene carbonate and ethyl methyl carbonate

[0016] Further, the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3 - 5:5 - 7

[0017] Further, the set heating temperature is 60 - 80 °C

[0018] After the reaction to generate lithium hexafluoropyruvate, it is filtered, washed and dried to obtain a pure lithium hexafluorophosphate product, and the pure lithium hexafluorophosphate product is dissolved in a solvent to obtain a lithium hexafluorophosphate solution

[0019] The third aspect of the present application provides a battery containing the above electrolyte capable of inhibiting lithium dendrites

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows

[0021] The present invention proposes an electrolyte Li-SA, which can inhibit the growth of lithium dendrites on the anode of a lithium-ion battery. This electrolyte induces the deposition of Li + on the (110) crystal plane, regulates the solvation sheath structure to reduce the activity of its coordinated water, so that the activity of the coordinated water molecules in the primary solvation layer of Li + with Li-SA as the electrolyte significantly decreases. Thus, the occurrence of hydrogen evolution side reactions and the generation of by-products can be effectively reduced, and the migration of lithium ions in the electrolyte is optimized, improving the deposition uniformity, achieving the inhibition of the growth of lithium dendrites, enhancing the electrochemical performance of the lithium-ion battery. The lithium-ion battery assembled with Li-SA as the electrolyte exhibits excellent long-cycle stability and safety

[0022] In the mixed electrolyte of the present invention, the Li-SA complex ion itself has a large equilibrium constant, and the lithium salt in the electrolyte almost exists in the form of Li + This makes Li +The activity of the coordinated water molecules in the primary solvation layer decreases significantly, thus promoting the + desolvation process and further enhancing the corrosion resistance of the negative electrode and the ability to inhibit dendrite growth; in addition, the Li-SA electrolyte can also make the lithium deposition more uniform and dense, accelerate the ion and electron transport, and inhibit the growth of lithium dendrites; finally, the lithium-ion battery assembled with this mixed electrolyte can obtain a long and stable cycle life, effectively slowing down the hydrogen evolution side reaction near the electrode and inhibiting the growth of lithium dendrites.

[0023] In the solution of lithium hexafluorophosphate prepared in the solution of the present invention, the solvent is preferably a mixed solution of ethylene carbonate and ethyl methyl carbonate. The mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) comprehensively inhibits the nucleation and growth of lithium dendrites by synergistically optimizing the SEI film structure, improving the uniformity of lithium ion transport and inhibiting the interfacial side reaction. Therefore, it can synergistically inhibit the growth of lithium dendrites with the Li-SA complex ions in the electrolyte, thereby finally significantly improving the safety and cycle life of the lithium battery. Detailed implementation mode

[0024] The above content of the present invention will be further described in detail below in the form of specific implementation modes, but it should not be understood that the scope of the above subject matter of the present invention is limited to the following embodiments. All technologies implemented based on the above content of the present invention belong to the scope of the present invention.

[0025] The experimental methods used in the following examples are all conventional methods unless otherwise specified. The reagents, methods and equipment used are all conventional reagents, methods and equipment in the technical field unless otherwise specified.

[0026] The present invention provides an electrolyte that can inhibit lithium dendrites. The electrolyte is a mixed electrolyte formed by mixing lithium hexafluorophosphate and 5-sulfosalicylic acid in a ratio.

[0027] In the mixed electrolyte, the molar ratio of lithium hexafluorophosphate to 5-sulfosalicylic acid is 1:2 to 6.

[0028] In the mixed electrolyte of the present invention, the Li-SA complex ion itself has a large equilibrium constant (about 1×10 8.05 ), and almost all the lithium salts in the electrolyte exist in the form of Li + . This makes the activity of the coordinated water molecules in the primary solvation layer of Li + significantly decrease, thus promoting the + desolvation process and further enhancing the corrosion resistance of the negative electrode and the ability to inhibit dendrite growth; in addition, the Li-SA electrolyte of the present invention can also make the lithium deposition more uniform and dense, accelerate the ion and electron transport, and inhibit the growth of lithium dendrites;

[0029] The high dissociation degree of LiPF6 and the ionic coordination ability of 5-sulfosalicylic acid act synergistically to optimize the migration rate of lithium ions in the electrolyte and avoid local lithium deposition caused by transmission lag; this Li-SA electrolyte helps the electrode form more nucleation sites. During the electrochemical deposition process, nucleation sites are the starting points where metal ions begin to aggregate and eventually form a continuous metal layer. More nucleation sites can accommodate more Li + , thus accelerating the growth rate of the metal layer and improving the deposition uniformity, ultimately enhancing the performance of the lithium-ion battery;

[0030] Finally, the lithium-ion battery assembled with this mixed electrolyte can achieve a long and stable cycle life, effectively slowing down the hydrogen evolution side reaction near the electrode and inhibiting the growth of lithium dendrites.

[0031] The present invention also provides a method for preparing an electrolyte capable of inhibiting lithium dendrites, comprising the following steps:

[0032] (1) Prepare a 5-sulfosalicylic acid solution;

[0033] (2) Prepare a lithium hexafluorophosphate solution;

[0034] (3) Slowly add the lithium hexafluorophosphate solution to the 5-sulfosalicylic acid solution and stir evenly to obtain the mixed electrolyte Li-SA.

[0035] In some embodiments, the method of stirring evenly in step (3) uses magnetic stirring, and the rotation speed of the magnetic stirrer is set to 480 - 680 r / min.

[0036] In some embodiments, the method for preparing the 5-sulfosalicylic acid solution in step (1) is: dissolve 5-sulfosalicylic acid in deionized water to obtain a 5-sulfosalicylic acid solution; the concentration of the 5-sulfosalicylic acid solution is 1 - 1.5 mol / L -1 .

[0037] In some embodiments, the method for preparing the lithium hexafluorophosphate solution in step (2) is: dissolve phosphorus trifluoride in excess fluoroacetone and react at a set heating temperature to generate lithium hexafluoropyruvate; dissolve lithium hexafluoropyruvate in excess water or alcohol solvent, add excess ammonium fluoride to generate lithium hexafluorophosphate; dissolve lithium hexafluorophosphate in a solvent to obtain a lithium hexafluorophosphate solution; the concentration of the lithium hexafluorophosphate solution is 2 - 4 mol / L -1 .

[0038] In some embodiments, the solvent of the lithium hexafluorophosphate solution is a mixed solution of ethylene carbonate and ethyl methyl carbonate; ethylene carbonate (EC) has a high dielectric constant, which helps the dissociation of lithium salts and forms a stable SEI film on the negative electrode, while ethyl methyl carbonate (EMC), as a chain carbonate, has a low viscosity and good fluidity, which can improve the ion migration rate. The combination of the two balances conductivity and fluidity. At the same time, EC helps to form a stable SEI film, while EMC reduces the crystallization tendency of EC and enhances the low-temperature performance; in addition, the mixed solvent of EC and EMC cooperates synergistically in terms of electrochemical stability and temperature adaptability, providing support for the lithium dendrite growth inhibition effect of the Li-SA electrolyte.

[0039] Specifically, EC helps to generate a stable and dense solid electrolyte interface (SEI) film, effectively isolating the continuous reaction between the electrolyte and lithium metal, reducing the nucleation sites of lithium dendrites. The SEI film formed by EC has a low electronic conductivity, which can inhibit the non-uniform deposition of lithium ions in local areas and slow down the dendrite growth; the low-viscosity property of EMC can reduce the overall viscosity of the electrolyte, promote the uniform diffusion of lithium ions on the electrode surface, and avoid dendrite aggregation caused by too high local current density; the mixed solvent of EC and EMC can also adjust the composition of the SEI film, enhance its mechanical strength and flexibility, and inhibit the risk of dendrites penetrating the film layer during cycling; the low-temperature fluidity of EMC and the anti-crystallization property of EC act synergistically to avoid the hindrance of lithium ion transport caused by local solidification of the electrolyte in a low-temperature environment and reduce dendrite growth caused by uneven ion transport; the chemical stability of EC and EMC is combined to reduce the risk of oxidation and decomposition of the electrolyte under high voltage or high temperature conditions, and avoid the rupture of the SEI film and dendrite regeneration caused by gas generation from side reactions.

[0040] In some preferred embodiments, the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3-5:5-7; such a mixed ratio balances the viscosity and dielectric constant, thereby improving the overall performance.

[0041] In some embodiments, the heating temperature is set to 60-80 °C.

[0042] After the reaction to generate lithium hexafluoropyruvate, it is filtered, washed, and dried to obtain a pure lithium hexafluorophosphate product, and the pure lithium hexafluorophosphate product is dissolved in a solvent to obtain a lithium hexafluorophosphate solution.

[0043] The present invention also provides a battery containing the electrolyte prepared by the above method that can inhibit lithium dendrites.

[0044] The battery of the present application can be prepared by using common preparation processes. The following are non-limiting examples:

[0045] Preparation of the negative electrode sheet: Coating the negative electrode slurry on the negative electrode current collector, drying, and rolling and compacting to obtain the negative electrode sheet;

[0046] Preparation of the positive electrode sheet: Coating the positive electrode slurry on the positive electrode current collector, drying, and rolling and compacting to obtain the positive electrode sheet;

[0047] Preparation of the electrolyte: Using the mixed electrolyte Li-SA prepared according to the above preparation method;

[0048] Preparation of the battery: Stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, winding or laminating to obtain the battery cell, placing it in the battery case, adding the mixed electrolyte Li-SA, and after encapsulation, standing, formation, and grading processes, obtaining the lithium-ion battery.

[0049] The addition amount of the mixed electrolyte Li-SA can be obtained by those skilled in the art through experience and experiments.

[0050] In some embodiments, the battery of the present application can be assembled into a battery module. The number of batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0051] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments:

[0052] It should be noted that there are no special restrictions on the purchasing manufacturers of all raw materials involved in the present invention. Exemplarily, they include: 5-sulfosalicylic acid, ethylene carbonate, ethyl methyl carbonate, purchased from the National Pharmaceutical Group; carbon black: grade SUPER P Li (TIMCAL, Switzerland), purchased from Guangdong Luwei New Materials Technology Co., Ltd.; aluminum foil: 12 μm thick, grade H18-1100, purchased from Shenzhen Honglei Metal Materials Co., Ltd.; positive electrode active material: lithium iron phosphate, DFD Nanotech DF5F; binder is polyvinylidene fluoride, grade KF7200 of Japan's Kureha, purchased from Shanghai Huahenghui New Materials Technology Co., Ltd.; copper foil: T2 purple copper foil, 8 μm thick, purchased from Shandong Huiya Metal Technology Co., Ltd.; battery case: model CR2032, purchased from Foshan Jiaying Battery Co., Ltd.; separator: PE film, 20 μm thick, purchased from Dongguan Xuecheng Plastic Products Co., Ltd.; lithium sheet: product number xk-li28, purchased from Changsha Xinkang New Materials Co., Ltd.; gasket: 304 stainless steel round sheet, purchased from Wenzhou Chenghang Fasteners Co., Ltd.; elastic sheet: product number 2032, purchased from Dongguan Meichang Spring Co., Ltd.

[0053] Example 1:

[0054] (1) Preparation of an electrolyte capable of inhibiting lithium dendrites, including the following processes:

[0055] Step S1: Preparation of 5-sulfosalicylic acid (SA) solution: Dissolve 500 g of 5-sulfosalicylic acid (C7H6O6S·2H2O) in 1000 mL of deionized water. After complete dissolution, a pink transparent solution is obtained, marked as SA solution. Finally, adjust the concentration to 1.5 mol L -1 ;

[0056] Step S2: Preparation of lithium hexafluorophosphate (LiPF6) solution: Dissolve 500 g of phosphorus trifluoride (PF3) in 5 kg of fluoroacetone (CF3COCH3) to react and form lithium hexafluoropyruvate (LiPF3(CF3CO2)); then dissolve 240 g of lithium hexafluoropyruvate in water, add 720 g of ammonium fluoride (NH4F), and react at an appropriate temperature to generate lithium hexafluorophosphate (LiPF6); after the reaction is completed, obtain pure lithium hexafluorophosphate through filtration, washing, and drying steps; subsequently, dissolve it in a mixed solution of ethylene carbonate and ethyl methyl carbonate with a volume ratio of 4:6, and finally prepare a 3 mol L -1 lithium hexafluorophosphate (LiPF6) solution;

[0057] Step S3: Preparation of Li-SA mixed electrolyte: Slowly add 80 mL of lithium hexafluorophosphate solution to 160 mL of SA solution (the molar ratio of lithium hexafluorophosphate to SA is 1:2); after magnetic stirring for a period of time, wait until the mixed solution is completely dissolved to obtain a yellow clear solution, marked as the Li-SA mixed electrolyte; finally, transfer it to a 100 ml volumetric flask and make up the volume to 100 ml of Li-SA.

[0058] (2) A battery with an electrolyte capable of inhibiting lithium dendrites, and its preparation process includes the following steps:

[0059] Step one: Preparation of the negative electrode sheet: Mix graphite, styrene-butadiene rubber, carboxymethyl cellulose, conductive agent, and pure water evenly to obtain a negative electrode slurry (the mass ratio of graphite, styrene-butadiene rubber, carboxymethyl cellulose, conductive agent, and pure water is 94.6:1.2:1.8:2.4:1.88), coat the negative electrode slurry on a copper foil, bake at 130 °C for 12 h, and roll and compact to obtain a negative electrode sheet (the compacted density is 1.38 g / cc);

[0060] Step two: Preparation of the positive electrode sheet: Mix the ternary active material NCM811, conductive agent, polyvinylidene fluoride, and N-methylpyrrolidone evenly to obtain a positive electrode slurry (the mass ratio of the ternary active material NCM811, conductive agent, polyvinylidene fluoride, and N-methylpyrrolidone is 92:4:4:2.13); coat the positive electrode slurry on a carbon-coated current collector, bake at 130 °C for 12 h, and roll and compact to obtain a positive electrode sheet (the compacted density is 2.8 g / cc);

[0061] Step 3: Preparation of the electrolyte: The electrolyte prepared by the preparation method of step (1).

[0062] Step 4: Preparation of the battery: Using a PE film as the separator, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, winding them to obtain an electrode core, placing it in a battery case, adding the electrolyte, and after processes of encapsulation, standing, formation, and grading, a lithium-ion battery is obtained.

[0063] Example 2:

[0064] Compared with Example 1, in step S3 of Example 2, 53 mL of lithium hexafluorophosphate solution was slowly added to 160 mL of SA solution (the molar ratio of lithium hexafluorophosphate to SA was 1:3), and other steps were the same as those in Example 1.

[0065] Example 3:

[0066] Compared with Example 1, in step S3 of Example 2, 40 mL of lithium hexafluorophosphate solution was slowly added to 160 mL of SA solution (the molar ratio of lithium hexafluorophosphate to SA was 1:4), and other steps were the same as those in Example 1.

[0067] Example 4:

[0068] Compared with Example 1, in step S3 of Example 2, 32 mL of lithium hexafluorophosphate solution was slowly added to 160 mL of SA solution (the molar ratio of lithium hexafluorophosphate to SA was 1:5), and other steps were the same as those in Example 1.

[0069] Example 5:

[0070] Compared with Example 1, in step S3 of Example 2, 26 mL of lithium hexafluorophosphate solution was slowly added to 160 mL of SA solution (the molar ratio of lithium hexafluorophosphate to SA was 1:6), and other steps were the same as those in Example 1.

[0071] Comparative Example 1:

[0072] Compared with Example 1, in step S3 of Comparative Example 1, 160 mL of lithium hexafluorophosphate solution was slowly added to 160 mL of SA solution (the molar ratio of lithium hexafluorophosphate to SA was 1:1), and other steps were the same as those in Example 1.

[0073] Comparative Example 2:

[0074] Compared with Example 1, in step S3 of Comparative Example 1, no SA solution was added, and other steps were the same as those in Example 1.

[0075] Comparative Example 3:

[0076] Compared with Example 1, in Comparative Example 3, the solvent for preparing lithium hexafluorophosphate is not a mixed solution of ethylene carbonate and ethyl methyl carbonate, but the same amount of ethylene glycol dimethyl ether, and other steps are the same as those in Example 1.

[0077] Battery assembly instructions:

[0078] Lithium iron phosphate, polyvinylidene fluoride, conductive agent and N-methylpyrrolidone are mixed evenly to obtain a positive electrode material slurry (the composition of the positive electrode slurry is: 95% lithium iron phosphate, 2% polyvinylidene fluoride, 3% conductive agent, and N-methylpyrrolidone as the solvent, with a total solid content of 50%); the positive electrode material slurry is coated on the surface of an aluminum foil current collector, vacuum dried at 120 °C for 12 h, and roll-compacted to obtain a positive electrode sheet; graphite, styrene-butadiene rubber, carboxymethyl cellulose, conductive agent and pure water are mixed evenly to obtain a negative electrode slurry (the mass ratio of graphite, styrene-butadiene rubber, carboxymethyl cellulose, conductive agent and pure water is 94.6:1.2:1.8:2.4:1.88), the negative electrode slurry is coated on copper foil, baked at 130 °C for 12 h, and roll-compacted to obtain a negative electrode sheet (the compaction density is 1.38 g / cc); the electrolytes used are the electrolytes prepared in the examples and comparative examples respectively; in an inert gas atmosphere, a button battery is assembled in the order of battery case - placing the positive electrode sheet - dropping the electrolyte - placing the separator - dropping the electrolyte - placing the negative electrode sheet - placing the gasket spring piece - battery case.

[0079] The button battery is subjected to corresponding cycle life tests and stability tests using a Wuhan Blue Electric test system (CT3002A). Specifically, a constant current charge-discharge test method is adopted, and cycle tests are carried out at different current densities (0.1, 0.5, 2, 4 A g -1 ) with the voltage cut-off range set to 1.8 - 4.1 V.

[0080] Cycle life: Start the test equipment and start the constant current charge-discharge test; Charge test: Under the specified test ambient temperature, the battery is initially charged until the specified charge cut-off voltage is reached; Discharge test: The battery is discharged at the specified discharge current until the specified discharge cut-off voltage is reached; Cycle test: According to the above steps, the battery is subjected to multiple charge-discharge cycle tests; The number of cycles is usually set to 3000 cycles.

[0081] Cycle capacity retention rate: During the cycle test, the corresponding charge / discharge capacity of each cycle is recorded; The specific calculation formula is: Capacity retention rate = (termination capacity / initial capacity) × 100%; Initial capacity: Refers to the rated capacity of the battery during the test process (i.e., the first charge-discharge cycle); Termination capacity: Refers to the remaining capacity of the battery at the end of a certain specific cycle after a certain number of charge-discharge cycles.

[0082] Conductivity test: This is done using a dedicated conductivity meter. A conductivity meter typically consists of a pair of electrodes spaced a fixed distance apart. When the electrodes are inserted into the solution being tested, a certain resistance is generated between the electrodes, depending on the solution's conductivity. The meter calculates the conductivity based on this resistance.

[0083] The test results are shown in Table 1 and Table 2:

[0084] Table 1

[0085]

[0086]

[0087] Table 2

[0088]

[0089] According to the data in the above table, we can clearly draw the following conclusions:

[0090] 1. Compared with Comparative Example 2, the battery performance of Examples 1-5 is significantly improved, not only having a longer cycle life, but also improving the capacity retention rate. The Li-SA electrolyte in the present invention can make the Li + It can reach the electrode surface in a shorter time, thus promoting a faster and more uniform deposition process and helping the electrode to form more nucleation points and accommodate more Li + , accelerating the growth rate of the metal layer and improving the uniformity of deposition, ultimately improving the performance of lithium-ion batteries.

[0091] 2. In Examples 1-5, it can be clearly found that the lithium ion battery corresponding to Example 2 has the best performance. Therefore, it can be concluded that the optimal molar ratio of lithium hexafluorophosphate to SA is 1:3; however, as the ratio increases, the performance of the lithium ion battery gradually decreases. This is because as the SA solution increases to a certain proportion, the proportion of solvent water molecules in the electrolyte increases, the viscosity increases, the conductivity decreases, and the solubility of the lithium salt decreases, ultimately leading to a decrease in battery performance. The conductivity data of the corresponding examples and comparative examples are shown in Table 2.

[0092] 3. In Comparative Example 1, when the solution was prepared according to a molar ratio of lithium hexafluorophosphate to SA of 1:1, obvious precipitation was found, which resulted in the inability to assemble the subsequent battery. This was mainly due to the generation of irreversible side reaction products during the reaction between the two, and the failure of the complexation reaction between ions.

[0093] 4. Comparative Example 3 The solvent of lithium hexafluorophosphate did not use a mixed solution of ethylene carbonate and ethyl methyl carbonate, but used dimethoxyethane. The assembled lithium-ion battery had poor cycle stability and capacity retention rate, resulting in serious irreversible capacity loss and poor electrochemical stability. This is because the electrolyte composed of ether solvents will undergo violent oxidative decomposition in the battery voltage range of 3 - 4.1V, making it difficult to form a stable and reliable electrode / electrolyte interface and difficult to match the high-voltage cathode material, so it cannot be effectively applied to the electrolyte system of this patent.

[0094] The above are only the preferred embodiments of the present invention, and do not impose any formal restrictions on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, any simple modifications, equivalent replacements, and improvements made to the above embodiments shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. An electrolyte capable of suppressing lithium dendrites, characterized in that: The electrolyte described is a mixed electrolyte formed by mixing lithium hexafluorophosphate and 5-sulfosalicylic acid in a certain proportion.

2. The electrolyte capable of suppressing lithium dendrites according to claim 1, wherein: In the described mixed electrolyte, the molar ratio of lithium hexafluorophosphate to 5-sulfosalicylic acid is 1:2 - 6.

3. A preparation method of an electrolyte capable of suppressing lithium dendrites, characterized in that, It includes the following steps: Prepare a 5-sulfosalicylic acid solution; Prepare a lithium hexafluorophosphate solution; Slowly add the lithium hexafluorophosphate solution to the 5-sulfosalicylic acid solution and stir evenly to obtain the mixed electrolyte Li-SA.

4. The electrolyte capable of suppressing lithium dendrites according to claim 3, characterized in that: The preparation method of the 5-sulfosalicylic acid solution is as follows: Dissolve 5-sulfosalicylic acid in deionized water to obtain a 5-sulfosalicylic acid solution; the concentration of the 5-sulfosalicylic acid solution is 1 to 1.5 mol / L -1 .

5. The electrolyte capable of suppressing lithium dendrites according to claim 3, wherein: The preparation method of the lithium hexafluorophosphate solution is as follows: Phosphorus trifluoride is dissolved in excessive fluoroacetone, and the reaction is carried out at a set heating temperature to generate lithium hexafluoropyruvate; Lithium hexafluoropyruvate is dissolved in excessive water or alcohol solvent, and excessive ammonium fluoride is added to generate lithium hexafluorophosphate; Lithium hexafluorophosphate is dissolved in a solvent to obtain a lithium hexafluorophosphate solution; The concentration of the lithium hexafluorophosphate solution is 2-4 mol / L -1 .

6. The electrolyte capable of suppressing lithium dendrites according to claim 5, wherein: For dissolving lithium hexafluorophosphate in a solvent, the solvent of the lithium hexafluorophosphate solution uses a mixed solution of ethylene carbonate and ethyl methyl carbonate.

7. The electrolyte capable of suppressing lithium dendrites according to claim 6, wherein: The volume ratio of the ethylene carbonate to the ethyl methyl carbonate is 3 - 5:5 - 7.

8. The electrolyte capable of suppressing lithium dendrites according to claim 5, wherein: Set the heating temperature to 60 - 80 °C.

9. The electrolyte capable of suppressing lithium dendrites according to claim 5, characterized in that: After reacting to generate lithium hexafluoropyruvate, it is filtered, washed, and dried to obtain a pure lithium hexafluorophosphate product, and the pure lithium hexafluorophosphate product is dissolved in a solvent to obtain a lithium hexafluorophosphate solution.

10. A battery, characterized in that: An electrolyte containing the electrolyte described in claim 1 or 2 or prepared by the method described in any one of claims 3 - 9, which can inhibit lithium dendrites.

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