High-voltage electrolyte, lithium ion battery and preparation method

Abstract

The invention provides a high-voltage electrolyte, a lithium ion battery and a preparation method, and belongs to the technical field of lithium ion batteries. The high-voltage electrolyte is prepared from a basic electrolyte and HOB. And the HOB can effectively inhibit the decomposition reaction of the electrolyte in a high-voltage environment and prevent over-oxidation in the battery, so that the cycling stability of the battery is improved and the service life of the battery is prolonged. The HOB can also reduce the viscosity of the electrolyte and improve the diffusion coefficient of lithium ions, so that the transmission of the lithium ions in the electrolyte is smoother, the resistance of ion transmission is reduced, the stability of the battery electrolyte is improved, the battery performance is improved, and the charge-discharge capacity is optimized. After the HOB is added into the basic electrolyte, the first-circle discharge specific capacity of the battery is improved to 133.1-152.7 mAh / g, and the capacity retention ratio under the long cycle condition is improved to 62.7-75.1%.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries and relates to a high voltage electrolyte, a lithium ion battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries (LIBs) are secondary batteries that rely on the movement of lithium ions between the positive and negative electrodes to work. Lithium-ion batteries have the advantages of high energy density, high average output voltage, long cycle life, and good safety performance. Lithium-ion batteries are widely used in portable electronic devices due to their high energy density, and are increasingly used in electric vehicles and grid storage.

[0003] The electrolyte is a vital component in lithium-ion batteries, responsible for facilitating the movement of lithium ions between the anode and cathode during the charge and discharge process. At present, the commonly used electrolyte for lithium-ion batteries is a carbonate electrolyte, which is suitable for a standard voltage of about 4.2V. High-voltage lithium-ion batteries achieve higher energy density by operating at 4.5V or higher, which poses greater challenges to the stability and performance of the electrolyte. Under high-voltage conditions, carbonate electrolytes are prone to electrochemical decomposition, resulting in unstable chemical properties of the electrolyte. At the same time, the decomposition reaction of carbonate electrolytes will generate gases or harmful byproducts, causing increased internal pressure of the battery, capacity decay, and shortened cycle life. For example, ethylene carbonate in carbonate electrolytes is 4.5V vs Li + / Li and above, and the patent with publication number CN114520369A shows that this process will cause gas expansion and accelerate the decomposition of lithium salts, resulting in a battery capacity decay rate of more than 20% / 100 weeks. It may also cause structural changes or dissolution of the cathode material, affecting the cycle life and performance of the battery, which limits the performance and practical application of high-voltage lithium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a high voltage electrolyte, a lithium ion battery and a preparation method to solve the problem that the existing high voltage lithium ion battery has poor performance under high voltage.

[0005] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present application provides a high-voltage electrolyte, which includes a basic electrolyte and methyl 4-hydroxybenzoate (English name: Methyl 4-hydroxybenzoate; abbreviated as: HOB).

[0006] The basic electrolyte is composed of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC) and lithium salt, and is an existing carbonate electrolyte. In the basic electrolyte, the volume ratio of EMC, DEC and EC is 1:1:1, and the concentration of lithium salt in the basic electrolyte is 1 mol / L. The lithium salt includes one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, or lithium hexafluorophosphate.

[0007] HOB is an organic compound with antioxidant properties, which can effectively inhibit the decomposition reaction of the electrolyte under high voltage environment, prevent excessive oxidation in the battery, and thus improve the cycle stability and service life of the battery. HOB can also reduce the viscosity of the electrolyte, increase the diffusion coefficient of lithium ions, make the transmission of lithium ions in the electrolyte smoother, reduce the resistance of ion transmission, improve the stability of the battery electrolyte, improve battery performance, and optimize the charge and discharge capacity. After adding HOB to the basic electrolyte, the first cycle discharge capacity of the battery is increased to 133.1-152.7 mAh / g, and the capacity retention rate under long cycle conditions is increased to 62.7-75.1%.

[0008] In the present application, the amount of HOB added is 4-6% of the total volume of the high voltage electrolyte. Preferably, the amount of HOB added is 5% of the total volume of the high voltage electrolyte.

[0009] In a second aspect, the present application provides a method for preparing a high voltage electrolyte, the method comprising: S01: Ethyl methyl carbonate, diethyl carbonate and ethylene carbonate are mixed after removing water under an argon atmosphere, lithium salt is added, and stirred until completely dissolved to form a basic electrolyte.

[0010] EMC and DEC are respectively placed in a sealed container containing 3Å or 4Å molecular sieves, and then placed in a vacuum glove box to avoid lithium salt hydrolysis and solvent oxidation side reactions. Stand and remove water under argon atmosphere, water and oxygen content ≤0.1ppm at room temperature, so that the moisture content of EMC and DEC is ≤20ppm. Since EC has a high melting point and is solid at room temperature, it needs to be dehydrated at 70°C. Specifically, EC is placed in a sealed container containing 3Å or 4Å molecular sieves, and then placed in a vacuum glove box; stand and remove water under argon atmosphere, water and oxygen content ≤0.1ppm, and 70°C, so that the moisture content of EC is ≤20ppm.

[0011] The cooled EC was mixed evenly with EMC and DEC in a volume ratio of 1:1:1, lithium salt was added, and the mixture was shaken and mixed until completely dissolved to form a basic electrolyte with a lithium salt concentration of 1 mol / L.

[0012] S02: After adding methyl parahydroxybenzoate to the basic electrolyte, oscillate and mix to form a high voltage electrolyte.

[0013] Add HOB to the basic electrolyte, and make the amount of HOB added to be 4-6% of the total volume of the high-voltage electrolyte. Oscillate and mix evenly to form a high-voltage electrolyte, and seal and store for later use.

[0014] In a third aspect, the present application provides a lithium-ion battery, which includes the high-voltage electrolyte in the first aspect.

[0015] In a fourth aspect, the present application provides a method for preparing a lithium ion battery, the method comprising: S01: After mixing lithium iron phosphate, carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1, add N-methylpyrrolidone and stir evenly to form a viscous slurry.

[0016] The positive electrode active material lithium iron phosphate (English name: ferrous lithium phosphate; abbreviated: LFP), the conductive agent carbon black and the binder polyvinylidene fluoride (English name: polyvinylidene difluoride; abbreviated: PVDF) were mixed in a mass ratio of 8:1:1, and 42% of N-methylpyrrolidone (English name: N-Methylpyrrolidone; abbreviated: NMP) was added and stirred to form a uniform and viscous slurry. The viscosity of the viscous slurry is 6000 mPa·s‌ -1 The solid content is 58% to ensure uniform subsequent coating. The carbon black used in this application is Super-P.

[0017] S02: The viscous slurry is evenly coated on an aluminum foil current collector and vacuum dried to form a positive electrode sheet.

[0018] The viscous slurry was evenly coated on the aluminum foil current collector, placed in a vacuum drying oven, and dried at 80°C for 12 hours. After drying, the aluminum foil current collector was cut into a circular positive electrode sheet with a diameter of 14 mm, and the positive electrode sheet was weighed and placed in a glove box for use. The active material loading of each positive electrode sheet is about 3-4 mg / cm 2 .

[0019] S03: Mix graphite, carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1, evenly coat the mixture on a copper sheet, and vacuum dry the mixture to form a negative electrode sheet.

[0020] Graphite, carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and evenly coated on a copper sheet using a 100μm coater, and placed in a vacuum drying oven and dried at 80°C for 12 hours. After drying, the copper sheet was sliced ​​into a circular negative electrode sheet with a diameter of 14mm, and the negative electrode sheet was weighed and placed in a glove box for later use. The density of each negative electrode sheet is 3-4mg / cm 2 .

[0021] S04: placing the side of the positive electrode sheet coated with the viscous slurry on the negative electrode shell, placing a polypropylene separator, dripping the high-voltage electrolyte in the first aspect, and placing the negative electrode sheet, gasket, spring and positive electrode shell in sequence to form a lithium-ion battery.

[0022] In the glove box, the positive electrode sheet coated with the viscous slurry is placed on the negative electrode shell, and after placing the polypropylene separator, 100μL of high-voltage electrolyte is added, and then the negative electrode sheet, gasket and spring are placed in sequence, and the positive electrode shell is covered to form a lithium-ion battery. The lithium-ion battery is sealed and packaged using a button battery sealing machine.

[0023] The present invention has the following beneficial effects: The high-voltage electrolyte in this application is prepared using a basic electrolyte and HOB. HOB can effectively inhibit the decomposition reaction of the electrolyte under a high voltage environment, prevent excessive oxidation in the battery, and thereby improve the cycle stability and service life of the battery. HOB can also reduce the viscosity of the electrolyte, increase the diffusion coefficient of lithium ions, make the transmission of lithium ions in the electrolyte smoother, reduce the resistance to ion transmission, improve the stability of the battery electrolyte, improve battery performance, and optimize the charge and discharge capacity. After adding HOB to the basic electrolyte, the first-cycle discharge specific capacity of the battery is increased to 133.1-152.7 mAh / g, and the capacity retention rate under long-cycle conditions is increased to 62.7-75.1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a test diagram of the 2C rate current cycling performance of the lithium ion battery prepared in Comparative Example 1 of the present application at a cut-off voltage of 4.5V; Figure 2 This is a test diagram of the 2C rate current cycling performance of the lithium-ion battery prepared in Example 4 of the present application at a cut-off voltage of 4.5V; Figure 3 The charge and discharge curves of the lithium-ion batteries prepared in Example 4 and Comparative Example 1 of the present application during the first cycle; Figure 4 The charge and discharge curves of the lithium-ion batteries prepared in Example 4 and Comparative Example 1 of the present application at the 100th cycle; Figure 5 CV curve diagram of the lithium-ion battery prepared in Comparative Example 1 of the present application; Figure 6 CV curve diagram of the lithium-ion battery prepared in Example 4 of the present application; Figure 7 The battery impedance diagram of the lithium ion battery prepared in Example 4 and Comparative Example 1 of the present application after 100 cycles; Figure 8 Z' and Z' of the lithium ion battery prepared in Example 4 and Comparative Example 1 after 100 cycles ω -1 / 2 Relationship diagram. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0026] Example 1 An embodiment of the present application provides a high-voltage electrolyte, which includes a basic electrolyte and HOB with a volume ratio of 5%, wherein the basic electrolyte includes EMC, DEC, EC with a volume ratio of 1:1:1 and lithium hexafluorophosphate with a concentration of 1 mol / L in the basic electrolyte.

[0027] The preparation method of the high voltage electrolyte comprises: S101: EMC and DEC are placed in sealed containers containing 3Å molecular sieves, respectively, and then placed in a vacuum glove box. Stand and remove water under argon atmosphere, water and oxygen content of 0.05ppm at room temperature, so that the moisture content of EMC and DEC is ≤20ppm. EC is placed in a sealed container containing 3Å molecular sieves, and then placed in a vacuum glove box; stand and remove water under argon atmosphere, water and oxygen content of 0.05ppm, and 70°C, so that the moisture content of EC is ≤20ppm. The cooled EC is evenly mixed with EMC and DEC in a volume ratio of 1:1:1, lithium hexafluorophosphate is added, and the mixture is shaken until completely dissolved to form a basic electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0028] S102: Add 5% by volume of HOB to the basic electrolyte, oscillate and mix evenly to form a high voltage electrolyte.

[0029] Example 2 An embodiment of the present application provides a high-voltage electrolyte, which includes a basic electrolyte and HOB with a volume ratio of 4%, wherein the basic electrolyte includes EMC, DEC, EC with a volume ratio of 1:1:1 and lithium hexafluorophosphate with a concentration of 1 mol / L in the basic electrolyte.

[0030] The preparation method of the high voltage electrolyte comprises: S201: EMC and DEC are placed in sealed containers containing 4Å molecular sieves, respectively, and then placed in a vacuum glove box. Stand and remove water in an argon atmosphere at room temperature with a water and oxygen content of 0.1ppm, so that the moisture content of EMC and DEC is ≤20ppm. EC is placed in a sealed container containing 4Å molecular sieves, and then placed in a vacuum glove box; stand and remove water in an argon atmosphere at 70°C with a water and oxygen content of 0.1ppm, so that the moisture content of EC is ≤20ppm. The cooled EC is mixed with EMC and DEC in a volume ratio of 1:1:1, lithium hexafluorophosphate is added, and the mixture is shaken until it is completely dissolved to form a basic electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0031] S202: Add 4% by volume of HOB to the basic electrolyte, oscillate and mix evenly to form a high voltage electrolyte.

[0032] Example 3 An embodiment of the present application provides a high-voltage electrolyte, which includes a basic electrolyte and HOB with a volume ratio of 6%, wherein the basic electrolyte includes EMC, DEC, EC with a volume ratio of 1:1:1 and lithium hexafluorophosphate with a concentration of 1 mol / L in the basic electrolyte.

[0033] The preparation method of the high voltage electrolyte comprises: S301: EMC and DEC are placed in sealed containers containing 4Å molecular sieves, respectively, and then placed in a vacuum glove box. Stand and remove water in an argon atmosphere at room temperature with a water and oxygen content of 0.07ppm, so that the moisture content of EMC and DEC is ≤20ppm. EC is placed in a sealed container containing 4Å molecular sieves, and then placed in a vacuum glove box; stand and remove water in an argon atmosphere at a water and oxygen content of 0.07ppm and 70°C, so that the moisture content of EC is ≤20ppm. The cooled EC is mixed with EMC and DEC in a volume ratio of 1:1:1, lithium hexafluorophosphate is added, and the mixture is shaken until it is completely dissolved to form a basic electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0034] S302: Add 6% by volume of HOB to the basic electrolyte, oscillate and mix evenly to form a high voltage electrolyte.

[0035] Example 4 The present invention provides a lithium-ion battery, and the preparation method of the lithium-ion battery includes: S401: After mixing the positive electrode active material LFP, the conductive agent Super-P and the binder PVDF in a mass ratio of 8:1:1, NMP is added and stirred to form a uniform and viscous slurry.

[0036] S402: The viscous slurry is evenly coated on the aluminum foil current collector, placed in a vacuum drying oven, and dried at 80°C for 12 hours. After drying, the aluminum foil current collector is cut into a circular positive electrode sheet with a diameter of 14 mm, and the positive electrode sheet is weighed so that the active material loading of each positive electrode sheet is about 3.6 mg / cm 2 , put it in the glove box for later use.

[0037] S403: Graphite, carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and evenly coated on a copper sheet using a 100μm coater, and placed in a vacuum drying oven and dried at 80°C for 12 hours. After drying, the copper sheet was sliced ​​into a circular negative electrode sheet with a diameter of 14 mm, and the negative electrode sheet was weighed so that the density of each negative electrode sheet was 3.5 mg / cm 2 , put it in the glove box for later use.

[0038] S404: In a glove box, place the side of the positive electrode sheet coated with the viscous slurry on the negative electrode shell, place a polypropylene separator, drop 100 μL of the high-voltage electrolyte prepared in Example 1, and then place the negative electrode sheet, gasket and spring in sequence, cover the positive electrode shell to form a lithium-ion battery. Use a button battery sealing machine to seal and package the lithium-ion battery.

[0039] Example 5 The present invention provides a lithium-ion battery, and the preparation method of the lithium-ion battery includes: S501: After mixing the positive electrode active material LFP, the conductive agent Super-P and the binder PVDF in a mass ratio of 8:1:1, NMP is added and stirred to form a uniform and viscous slurry.

[0040] S502: The viscous slurry is evenly coated on the aluminum foil current collector, placed in a vacuum drying oven, and dried at 80°C for 12 hours. After drying, the aluminum foil current collector is cut into a circular positive electrode sheet with a diameter of 14 mm, and the positive electrode sheet is weighed so that the active material loading of each positive electrode sheet is about 4 mg / cm 2 , put it in the glove box for later use.

[0041] S503: Graphite, carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and evenly coated on a copper sheet using a 100μm coater, and placed in a vacuum drying oven and dried at 80°C for 12 hours. After drying, the copper sheet was sliced ​​into a circular negative electrode sheet with a diameter of 14 mm, and the negative electrode sheet was weighed so that the density of each negative electrode sheet was 4 mg / cm 2 , put it in the glove box for later use.

[0042] S504: In a glove box, place the side of the positive electrode sheet coated with the viscous slurry on the negative electrode shell, place a polypropylene separator, drop 100 μL of the high-voltage electrolyte prepared in Example 2, and then place the negative electrode sheet, gasket and spring in sequence, cover the positive electrode shell to form a lithium-ion battery. Use a button battery sealing machine to seal and package the lithium-ion battery.

[0043] Example 6 The present invention provides a lithium-ion battery, and the preparation method of the lithium-ion battery includes: S601: After mixing the positive electrode active material LFP, the conductive agent Super-P and the binder PVDF in a mass ratio of 8:1:1, NMP is added and stirred to form a uniform and viscous slurry.

[0044] S602: The viscous slurry is evenly coated on the aluminum foil current collector, placed in a vacuum drying oven, and dried at 80°C for 12 hours. After drying, the aluminum foil current collector is cut into circular positive electrode sheets with a diameter of 14 mm, and the positive electrode sheets are weighed so that the active material loading of each positive electrode sheet is about 3 mg / cm 2 , put it in the glove box for later use.

[0045] S603: Graphite, carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and evenly coated on a copper sheet using a 100μm coater, and placed in a vacuum drying oven and dried at 80°C for 12 hours. After drying, the copper sheet was sliced ​​into a circular negative electrode sheet with a diameter of 14 mm, and the negative electrode sheet was weighed so that the density of each negative electrode sheet was 3 mg / cm 2 , put it in the glove box for later use.

[0046] S604: In a glove box, place the side of the positive electrode sheet coated with the viscous slurry on the negative electrode shell, place a polypropylene separator, drop 100 μL of the high-voltage electrolyte prepared in Example 3, and then place the negative electrode sheet, gasket and spring in sequence, cover the positive electrode shell to form a lithium-ion battery. Use a button battery sealing machine to seal and package the lithium-ion battery.

[0047] Comparative Example 1 The comparative example of the present application provides a lithium ion battery, and the preparation method of the lithium ion battery comprises: D101: After mixing the positive electrode active material LFP, the conductive agent Super-P and the binder PVDF in a mass ratio of 8:1:1, NMP was added and stirred to form a uniform and viscous slurry.

[0048] D102: The viscous slurry was evenly coated on the aluminum foil current collector, placed in a vacuum drying oven, and dried at 80°C for 12 hours. After drying, the aluminum foil current collector was cut into circular positive electrode sheets with a diameter of 14 mm, and the positive electrode sheets were weighed so that the active material loading of each positive electrode sheet was about 3.6 mg / cm 2 , put it in the glove box for later use.

[0049] D103: Graphite, carbon black and PVDF were mixed evenly in a mass ratio of 8:1:1, and evenly coated on a copper sheet using a 100μm coater, and placed in a vacuum drying oven and dried at 80°C for 12 hours. After drying, the copper sheet was sliced ​​into a circular negative electrode sheet with a diameter of 14 mm, and the negative electrode sheet was weighed so that the density of each negative electrode sheet was 3.5 mg / cm 2 , put it in the glove box for later use.

[0050] D104: In a glove box, place the side of the positive electrode sheet coated with the viscous slurry on the negative electrode shell, place a polypropylene separator, add 100μL of basic electrolyte, and then place the negative electrode sheet, gasket and shrapnel in sequence, and cover the positive electrode shell to form a lithium-ion battery. Use a button battery sealing machine to seal and package the lithium-ion battery.

[0051] After the lithium ion batteries prepared in Example 4 and Comparative Example 1 were left to stand for 12 hours, cycle performance test, constant current charge and discharge performance test, cyclic voltammetry curve test and electrochemical impedance test were performed respectively, wherein the lithium ion battery prepared in Example 4 was marked as LEDEHOB, and the lithium ion battery prepared in Comparative Example 1 was marked as LEDE. The specific test contents are as follows: 1. Cycle performance test The lithium ion batteries prepared in Example 4 and Comparative Example 1 were subjected to current cycle charge and discharge at room temperature, 2C rate, and a cut-off voltage of 4.5V to obtain the attached Figure 1 , 2 .

[0052] By the attached Figure 1 It can be seen that the first discharge capacity of the lithium-ion battery LEDE prepared in Comparative Example 1 is 133.1 mAh / g; as the number of cycles increases, when the number of cycles reaches 140, its discharge capacity decreases to 89.4 mAh / g, and the capacity retention rate is 67.2%. In addition, after the start of the cycle, the battery capacity is maintained at about 150 mAh / g, and the battery capacity decays significantly after the cycle reaches 100 times.

[0053] By the attached Figure 2It can be seen that the initial discharge capacity of the lithium-ion battery LEDEHOB prepared in Example 4 is 152.7 mAh / g; as the number of cycles increases, when the number of cycles reaches 140, its discharge capacity decreases to 114.7 mAh / g, and the capacity retention rate is 75.1%. In addition, after the cycle starts, the battery capacity is basically maintained at about 150 mAh / g.

[0054] It can be seen that compared with the lithium-ion battery without HOB, the lithium-ion battery with HOB added in the embodiment of the present application has a greatly improved charge and discharge specific capacity at a cut-off voltage of 4.5V, and the coulombic efficiency is stable at about 98%, and the capacity retention rate is 75.1%, showing very stable high-voltage electrochemical performance.

[0055] 2. Constant current charge and discharge performance test The lithium ion batteries prepared in Example 4 and Comparative Example 1 were subjected to current cyclic charge and discharge at room temperature and 2C rate with a charge and discharge range of 3-4.5V, and their charge and discharge curves were measured at the 1st cycle and the 100th cycle to obtain the attached Figure 3 , 4 .

[0056] By the attached Figure 3 , 4 It can be seen that during the first cycle, there is a certain gap between the charge and discharge specific capacities of the two groups of batteries. With the increase in the number of charge and discharge cycles, when the current cycles to 100 times, the specific capacities of the two groups of batteries are significantly lower and the gap is more obvious, and the battery charge and discharge specific capacity of the lithium-ion battery LEDEHOB is better than the battery charge and discharge specific capacity of the lithium-ion battery LEDE. This is because the phenolic hydroxyl group in HOB gives it antioxidant ability, which can be oxidized on the positive electrode surface before the electrolyte solvent, forming a dense protective film, inhibiting the decomposition of the electrolyte, and effectively protecting the positive electrode. In addition, the polarity of the ester group also optimizes the solvation structure of lithium ions, thereby improving the electrolyte ion mobility and reducing the internal resistance of the battery, thereby more efficiently utilizing the active material, so that the battery has a higher charge and discharge specific capacity at high voltage.

[0057] 3. Cyclic voltammetry curve test The lithium ion batteries prepared in Example 4 and Comparative Example 1 were tested for current-voltage relationship by cyclic voltammetry at room temperature, charge and discharge voltage of 3-4.5V, and 1Mv / s. Figure 5 , 6 The CV curve diagram is shown.

[0058] By the attached Figure 5 , 6It can be seen that the potential difference between the first oxidation peak and the reduction peak of the lithium ion battery LEDE prepared in Comparative Example 1 is 0.73 V, and the potential difference between the first oxidation peak and the reduction peak of the lithium ion battery LEDEHOB prepared in Example 4 is 0.702 V, the oxidation-reduction peak potential difference ΔEp is reduced, and the reversibility of the reaction is improved. At the same time, in the lithium ion battery LEDEHOB prepared in Example 4, the addition of HOB increases the oxidation peak potential, which indicates that the hydroxyl and ester groups in HOB may adjust the Li⁺ solvation structure by complexing Li⁺, promote the lithium ion desolvation process, and improve the reaction kinetics. In addition, relative to the lithium ion battery LEDE, the peak current of the CV curve of the lithium ion battery LEDEHOB increases, but the shape of the CV curve does not change much. This is because HOB, as an additive, increases the ionic conductivity of the electrolyte by reducing the viscosity of the LEDE electrolyte, making the transmission of lithium ions in the electrolyte smoother, reducing the resistance to ion transmission, and thus leading to an increase in peak current.

[0059] 4. Electrochemical impedance test In the present embodiment, the impedance response of the system to the AC power supply is measured to obtain information about the electrochemical process of the lithium-ion battery prepared in Example 4 and Comparative Example 1. Specifically, on a CHI660E electrochemical workstation, at 0.01-10 5 The EIS test of LFP / graphite battery after 100 cycles was carried out in the frequency range of Hz. Figure 7 , 8 .

[0060] By the attached Figure 7 , 8 It can be seen that the impedance of the lithium-ion battery LEDE is about 126.7Ω, and the impedance of the lithium-ion battery LEDEHOB is 121Ω, which indicates that the addition of HOB can reduce the impedance of the battery. This may be because the -COOCH3 ester group of HOB is polar and can partially participate in the solvation process of lithium ions, reducing the binding energy between lithium ions and EC and DEC solvent molecules. This optimized solvation structure reduces the migration resistance of Li⁺ in the electrolyte, thereby improving the ionic conductivity and reducing the impedance of the battery. This conjecture is confirmed by the relationship between the diffusion coefficient and the Warburg factor σ, which is given by the following formula: (1) (2) In the formula, R and T represent the gas constant and temperature respectively, A represents the electrode area, n represents the number of transferred electrons, F represents the Faraday constant, C represents the guest ion concentration, σ represents the Warburg factor, and R ct and R1 represent the charge transfer resistance and ohmic resistance respectively. Figure 8As shown, the electrode σ of the lithium-ion battery LEDE is larger than that of the electrode of the lithium-ion battery LEDEHOB, which indicates that the addition of HOB can reduce σ, increase the diffusion coefficient, and is beneficial to the improvement of battery performance.

[0061] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A high voltage electrolyte, characterized in that: The invention comprises a basic electrolyte and methyl parahydroxybenzoate, wherein the basic electrolyte consists of ethyl methyl carbonate, diethyl carbonate, ethylene carbonate and lithium salt.

2. The high voltage electrolyte according to claim 1, characterized in that: The added amount of the methyl parahydroxybenzoate is 4-6% of the total volume of the high voltage electrolyte.

3. The high voltage electrolyte according to claim 1, characterized in that: The concentration of the lithium salt in the basic electrolyte is 1 mol / L.

4. The high voltage electrolyte according to claim 1, characterized in that: The volume ratio of the ethyl methyl carbonate, diethyl carbonate and ethylene carbonate is 1:1:

1.

5. The high voltage electrolyte according to claim 1, characterized in that: The lithium salt includes one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, or lithium hexafluorophosphate.

6. A method for preparing a high voltage electrolyte according to any one of claims 1 to 5, characterized in that: include: Ethyl methyl carbonate, diethyl carbonate and ethylene carbonate are mixed after removing water under an argon atmosphere, lithium salt is added, and stirred until completely dissolved to form a basic electrolyte; After methyl p-hydroxybenzoate is added to the basic electrolyte, the mixture is shaken and mixed to form a high-voltage electrolyte.

7. The method for preparing a high voltage electrolyte according to claim 6, characterized in that: The preparation of the basic electrolyte comprises: Ethyl methyl carbonate and diethyl carbonate are respectively placed in sealed containers containing molecular sieves, and allowed to stand and dehydrate under argon atmosphere and room temperature conditions with a water and oxygen content of ≤0.1ppm, so that the water content of ethyl methyl carbonate and diethyl carbonate is ≤20ppm; Put ethylene carbonate into a sealed container containing molecular sieves, and stand to remove water under the conditions of argon atmosphere, water and oxygen content ≤ 0.1 ppm, and 70° C., so that the water content of ethylene carbonate is ≤ 20 ppm; The ethyl methyl carbonate, diethyl carbonate and ethylene carbonate after dehydration are mixed, lithium salt is added, and stirred until completely dissolved to form a basic electrolyte.

8. A lithium ion battery, characterized in that: The invention comprises the high voltage electrolyte as claimed in any one of claims 1 to 5.

9. A method for preparing a lithium ion battery according to claim 8, characterized in that: include: After lithium iron phosphate, carbon black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, N-methylpyrrolidone is added and stirred evenly to form a viscous slurry; The viscous slurry is evenly coated on an aluminum foil current collector and vacuum dried to form a positive electrode sheet; Graphite, carbon black and polyvinylidene fluoride are mixed evenly in a mass ratio of 8:1:1, evenly coated on a copper sheet, and vacuum dried to form a negative electrode sheet; The positive electrode sheet coated with the viscous slurry is placed on the negative electrode shell, a polypropylene separator is placed, and the high-voltage electrolyte according to any one of claims 1 to 5 is dripped, and the negative electrode sheet, gasket, spring and positive electrode shell are placed in sequence to form a lithium-ion battery.

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