Applications of lithium-ion battery electrolytes, lithium-ion batteries, and their compounds as electrolyte additives

Abstract

The application discloses application of a compound, 4-cyano-3-fluorophenyl boronic acid pinacol ester, as an electrolyte additive. The compound has a pinacol ester group, can be added to a lithium ion battery electrolyte as an electrolyte additive, can form a stable interface film on the surface of a positive electrode of the battery preferentially, slows down dissolution of metal ions of the positive electrode, and inhibits reduction deposition of the metal ions on a negative electrode. The compound alleviates side reactions at an electrode and electrolyte interface, and improves cycle stability of the battery. The application further discloses a lithium ion battery electrolyte containing 4-cyano-3-fluorophenyl boronic acid pinacol ester and a lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically relating to lithium-ion battery electrolytes, lithium-ion batteries, and the application of compounds as electrolyte additives. Background Technology

[0002] With the rapid development of electric vehicles and large-scale energy storage markets, higher demands are being placed on the energy density and cycle life of lithium-ion batteries. Using high-capacity nickel-rich cathodes (such as NCM811) and high-capacity silicon-carbon anodes (such as SiC450) is an effective way to improve battery energy density. However, when the battery operating voltage is increased to above 4.3V, traditional carbonate-based electrolytes undergo severe oxidative decomposition on the cathode side. The acidic decomposition products cause the cathode material structure to transform from a layered structure to a spinel or rock salt phase, resulting in cracks and the dissolution of transition metal ions. These dissolved transition metal ions migrate to the anode, damaging the solid electrolyte interphase (SEI) film and exacerbating the electrolyte's reductive decomposition, leading to irreversible consumption of active lithium and electrolyte.

[0003] Currently, mainstream lithium-ion battery electrolytes are generally formulated from lithium salt electrolyte, organic solvents, and functional additives in specific proportions. While additives are used in small quantities, they can specifically enhance the electrolyte's performance and have a crucial impact on the overall battery system. Existing technologies typically employ functional additives and continuously optimize the additive ratio to improve the electrode / electrolyte interface, thereby specifically enhancing the electrolyte's performance. Given the structural changes of the nickel-rich cathode under high voltage, developing a novel electrolyte additive to construct a stable electrode / electrolyte interface is particularly important. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium-ion battery electrolyte additive to construct a stable electrode / electrolyte interface.

[0005] According to a first aspect of the invention, the use of 4-cyano-3-fluorophenylboronic acid pinacol ester as an electrolyte additive is provided, particularly as an electrolyte additive for lithium-ion batteries.

[0006] The 4-cyano-3-fluorophenylboronic acid pinacol ester of the present invention contains a pinacol ester group and can be particularly used as an electrolyte additive to improve the cycle performance of lithium-ion batteries. Specifically, the 4-cyano-3-fluorophenylboronic acid pinacol ester can be added to the electrolyte of a lithium-ion battery as an electrolyte additive, preferentially forming a stable interfacial film on the surface of the positive electrode, slowing down the dissolution of positive electrode metal ions and inhibiting their reduction and deposition on the negative electrode. This alleviates side reactions at the electrode and electrolyte interface and improves the cycle stability of the battery.

[0007] The structural formula of pinacol ester of 4-cyano-3-fluorophenylboronic acid is: The CAS number is 870238-67-8.

[0008] According to a second aspect of the present invention, a lithium-ion battery electrolyte is provided, the raw materials of which include lithium salt, organic solvent and electrolyte additive, wherein the electrolyte additive is pinacol 4-cyano-3-fluorophenylboronic acid ester.

[0009] Among them, the mass fraction of 4-cyano-3-fluorophenylboronic acid pinacol ester in the lithium-ion battery electrolyte is 0.1%-5%, and the mass fraction of lithium salt in the lithium-ion battery electrolyte is 0.1%-15.0%.

[0010] When 4-cyano-3-fluorophenylboronic acid pinacol ester is added to the electrolyte of a lithium-ion battery, the para-substituted cyano group in the 4-cyano-3-fluorophenylboronic acid pinacol ester molecule can be firmly anchored to the transition metal site in the cobalt-rich region on the surface of the positive electrode active material through coordination, thus preventing Co ions from leaving the crystal lattice and entering the lithium-ion electrolyte from the source.

[0011] In some embodiments, the organic solvent has a mass fraction of 70.0%-90.0% in the lithium-ion battery electrolyte.

[0012] In some embodiments, the mass fraction of 4-cyano-3-fluorophenylboronic acid pinacol ester in the lithium-ion battery electrolyte is 0.1%-1%.

[0013] In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium tetrafluoro(oxalate) phosphate, lithium oxalate phosphate, lithium bis(oxalate) borate, lithium difluoro(oxalate) borate, lithium tetrafluoroborate, lithium difluoro(oxalate) imide, and lithium difluorosulfonylimide.

[0014] In some embodiments, the organic solvent is a cyclic carbonate or a linear carbonate. The cyclic carbonate is selected from at least one of ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, and propylene carbonate. The linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, and methyltrifluoroethyl carbonate.

[0015] According to a third aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and a lithium-ion battery electrolyte.

[0016] In some embodiments, the positive electrode sheet is prepared by the following steps: mixing a positive electrode active material, conductive carbon black, and a positive electrode binder, dispersing the resulting mixture in N-methyl-2-pyrrolidone (NMP), stirring to obtain a positive electrode paste, and then coating the positive electrode paste on a positive electrode current collector, followed by roll pressing and die cutting to obtain the positive electrode sheet; wherein, the mass ratio of the positive electrode active material, conductive carbon black, and positive electrode binder is 97:1.5:1.5.

[0017] In some embodiments, the positive electrode binder is polyvinylidene fluoride (PVDF).

[0018] In some embodiments, the positive electrode active material is a nickel-rich layered lithium transition metal oxide, with the general formula LiNi x Co y Mn z O2, where x + y + z = 1 and x ≥ 0.6. Preferably, the positive electrode active material is NCM811 (x = 0.8, y = 0.1, z = 0.1).

[0019] In some embodiments, the negative electrode sheet is prepared by the following steps: mixing a negative electrode active material, conductive carbon black, a negative electrode adhesive, and carboxymethyl cellulose, dispersing the resulting mixture in water to obtain a negative electrode paste, and then coating the negative electrode on both sides of a copper foil, drying and then performing roll pressing and die cutting to obtain the negative electrode sheet; where the mass ratio of the silicon-carbon material, conductive carbon black, negative electrode adhesive, and carboxymethyl cellulose is 94:1.5:3.0:1.5.

[0020] In some embodiments, the negative electrode active material is selected from at least one of silicon monoxide (SiO x , where 0 < x < 2), elemental silicon, and graphite.

[0021] In some embodiments, the negative electrode active material is a silicon-carbon material composed of silicon monoxide and graphite, where the mass fraction of silicon element in the silicon-carbon material is 7%.

[0022] The beneficial effects of the present invention are as follows: (1) The compound 4-cyano-3-fluorophenylboronic acid pinacol ester containing a pinacol ester group in the present invention can be used as an electrolyte additive, which can preferentially form a stable interfacial film on the surface of the battery positive electrode, slow down the dissolution of positive electrode metal ions, and inhibit their reduction and deposition on the negative electrode. It alleviates the side reactions at the electrode and electrolyte interface and improves the cycle stability of the battery.

[0023] (2) The cyano group substituted at the para position on the molecule of the compound containing a pinacol ester group can prevent Co ions from detaching from the lattice and entering the electrolyte through coordination. Description of the Drawings

[0024] Figure 1Cycle curves of the lithium-ion batteries prepared in Example 2 and Comparative Example 2 are shown. Figure 2 The rate performance graphs are for the lithium-ion batteries prepared in Example 2 and Comparative Example 2. Figure 3 Linear scan voltammetry graphs of the electrolytes prepared in Example 1 and Comparative Example 1; Figure 4 The content of Co deposited on the surface of the negative electrode after 400 cycles of the lithium-ion batteries prepared in Example 2 and Comparative Example 2; Figure 5 The lithium-ion migration rate during the entire charging and discharging process of the lithium-ion batteries prepared in Example 2 and Comparative Example 2 is shown. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0026] The silicon-carbon material in this invention is a mixture of silicon suboxide and graphite, wherein the mass percentage of silicon is 7 wt%.

[0027] Example 1 This embodiment provides a method for preparing an electrolyte, including the following steps: In an argon-filled glove box, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7 to obtain a mixed solution (total volume of 50 mL). Then, 1 mol of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution and stirred until homogeneous. Finally, 0.3 wt% of the total weight of the electrolyte, pinacol 4-cyano-3-fluorophenylboronic acid, was added to the mixed solution and stirred until homogeneous to obtain the final product.

[0028] Comparative Example 1 This comparative example provides a method for preparing an electrolyte, comprising the following steps: In an argon-filled glove box, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3:7 to obtain a mixed solution (total volume of 50 mL). Then, 1 mol of lithium hexafluorophosphate (LiPF6) is slowly added to the mixed solution and stirred until homogeneous.

[0029] Example 2 This embodiment provides a method for preparing a lithium-ion battery, including the following steps: (1) Preparation of electrolyte: In a glove box filled with argon, ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:7 to obtain a mixed solution. Then, 1 mol of lithium hexafluorophosphate (LiPF6) is slowly added to the mixed solution and stirred evenly. 0.3 wt% of 4-cyano-3-fluorophenylboronic acid pinacol ester is added to the mixed solution and stirred evenly to obtain the electrolyte.

[0030] (2) Preparation of positive electrode sheet: NCM811 positive electrode active material, conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:1.5:1.5. The resulting mixture was then dispersed in 15 mL of N-methyl-2-pyrrolidone (NMP) and stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, dried, rolled and die-cut to obtain the positive electrode sheet.

[0031] (3) Preparation of negative electrode sheet: Silicon carbon material, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1.5:3.0:1.5. The resulting mixture was then dispersed in 15 mL of deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, dried, and then rolled and die-cut to obtain a negative electrode sheet.

[0032] (4) Assemble the CR2025 coin cell in an argon-filled glove box. First, place the positive electrode shell flat in the center of the worktable. Use tweezers to place the electrode plate in the center of the positive electrode shell. Then, drop 40 μL of electrolyte onto the electrode plate. Align and cover the electrode plate with a 19 mm diameter separator, ensuring that the electrode plate is in the center of the separator. Then, drop another 40 μL of electrolyte onto the separator. Next, place the negative electrode plate in the center above the separator and overlap it with the positive electrode plate below. Finally, place the gasket and spring on the negative electrode plate, then attach the negative electrode shell to the positive electrode shell. After pressing, seal the battery on a battery packaging machine. The separator model is Celgard 2500, the diameter of the positive electrode is 12 mm, and the diameter of the negative electrode is 14 mm. The amount of electrolyte added in step (1) of the coin cell is 80 μL.

[0033] Comparative Example 2 This comparative example provides a method for preparing a lithium-ion battery, including the following steps: (1) Preparation of electrolyte: In a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7 to obtain a mixed solution. Then, 1 mol of lithium hexafluorophosphate (LiPF6) is slowly added to the mixed solution and stirred evenly to obtain the electrolyte.

[0034] (2) Preparation of positive electrode sheet: NCM811 positive electrode active material, conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:1.5:1.5. The resulting mixture was then dispersed in 15 mL of N-methyl-2-pyrrolidone (NMP) and stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, dried, rolled and die-cut to obtain the positive electrode sheet.

[0035] (3) Preparation of negative electrode sheet: Silicon carbon material, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1.5:3.0:1.5. The resulting mixture was then dispersed in 15 mL of deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, dried, and then rolled and die-cut to obtain a negative electrode sheet.

[0036] (4) Assemble the CR2025 button cell in an argon-filled glove box. The separator is Celgard 2500, the positive electrode diameter is 12 mm, and the negative electrode diameter is 14 mm. First, place the positive electrode shell flat in the center of the worktable. Use tweezers to place the electrode sheet in the center of the positive electrode shell. Then, drop 40 μL of electrolyte onto the electrode sheet. Align and cover the electrode sheet with the 19 mm diameter separator, ensuring that the electrode sheet is in the center of the separator. Then, drop another 40 μL of electrolyte onto the separator. Next, place the negative electrode sheet in the center above the separator and overlap it with the positive electrode sheet below. Finally, place the gasket and spring sheet on the negative electrode sheet, and then attach the negative electrode shell to the positive electrode shell. After pressing, seal the battery on the battery packaging machine. The separator is Celgard 2500, the positive electrode diameter is 12 mm, and the negative electrode diameter is 14 mm. The amount of electrolyte added in step (1) of the button cell is 80 microliters.

[0037] The electrochemical performance of the electrolytes of Example 1 and Comparative Example 1, and the CR2025 coin cells prepared in Example 2 and Comparative Example 2 are then tested.

[0038] I. Electrochemical Performance Testing 1. Battery cycle test The tests were conducted on the Xinwei testing system at a temperature of 25°C. All batteries were tested in constant current discharge (CC) mode. The cutoff voltages for charging and discharging were 2.8 V and 4.3 V, respectively. The batteries were cycled at a charge / discharge rate of 0.1 / 0.5C. The capacity retention rate was calculated after 400 charge / discharge cycles.

[0039] The formula for calculating the capacity retention rate at the 400th cycle is as follows: Capacity retention rate at 400th cycle (%) = (Discharge capacity at 400th cycle / Discharge capacity at first cycle) × 100%.

[0040] 2. Ratio Performance Test Rate performance testing is a core experimental method for evaluating high-power lithium-ion batteries. Through stepped rate charge-discharge cycles, it quantifies the capacity retention and voltage plateau stability of the battery at different current densities, reflecting the battery's ion transport kinetics. Rate performance testing was also conducted on the Xinwei battery system. CR2025 coin cells were sequentially subjected to constant current charge-discharge cycles of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 3 C, each cycle lasting 5 times. To verify capacity recovery, a 0.5 C rate cycle was then performed to evaluate the reversibility of the electrode structure after high-rate cycling.

[0041] 3. Linear sweep voltammetry test To verify the effect of the increased HOMO level of the additive 4-cyano-3-fluorophenylboronic acid pinacol ester on its oxidation behavior, linear sweep voltammetry (LSV) tests were performed on the electrolytes prepared in Example 1 and Comparative Example 1, respectively. Linear sweep voltammetry is a commonly used steady-state electrochemical testing technique, widely applied to evaluate the electrochemical stability of electrolytes. Its testing principle involves starting the coin cell with different electrolytes at the open-circuit potential and linearly increasing the applied voltage at a constant scan rate, while continuously recording the current response at the electrodes. When the voltage rises above the oxidation decomposition potential of the electrolyte, an electrochemical oxidation reaction occurs on the electrode surface, generating a current, which is reflected in the LSV curve as a sharp increase in current.

[0042] 4. Inductively Coupled Plasma Emission Spectroscopy Test Co ions dissolved from the NCM811 cathode material during cycling can penetrate the separator and deposit on the anode surface, damaging the SEI film and catalyzing electrolyte decomposition. To verify the complexing effect of the additive 4-cyano-3-fluorophenylborate pinacol ester on Co ions, a CR2025 coin cell was disassembled after 400 cycles, and the anode sheet was dissolved and subjected to inductively coupled plasma atomic emission spectrometry (ICP-OES). The amount of Co ion deposition on the silicon-carbon anode surface after cycling was quantitatively detected using an Agilent 720ES ICP-OES spectrometer.

[0043] The sample preparation process is as follows: CR2025 coin cells that have undergone 400 cycles were disassembled under argon protection. The silicon-carbon negative electrode was removed, cleaned with dimethyl carbonate to remove residual electrolyte, and dried. A quantitative sample was weighed and dissolved in dilute nitric acid for testing. By comparing the differences in Co deposition concentration in different electrolyte systems, the effect of the additive 4-cyano-3-fluorophenylboronic acid pinacol ester on inhibiting Co ion dissolution was quantitatively evaluated.

[0044] 5. Constant current intermittent titration test Intermittent galvanostatic titration is a classic electrochemical method for studying the diffusion kinetics of lithium ions in electrode materials. Using a Newway battery system, a series of constant current pulses are applied to the battery, followed by disconnection to allow for relaxation, enabling lithium ions to diffuse sufficiently within the active material to reach equilibrium. Potential changes are recorded throughout the process. By analyzing the potential response during the pulse-relaxation cycle and applying Fick's second law, the lithium ion diffusion coefficient under different charge states can be calculated, reflecting the ionic conductivity of lithium ions in the bulk phase of the active material.

[0045] II. Test Results Figure 1 This is a cycle curve obtained from battery cycle testing. From... Figure 1 It can be seen that the lithium-ion battery (Example 2) including the electrolyte additive 4-cyano-3-fluorophenylboronic acid pinacol ester exhibits better cycle performance than the lithium-ion battery of Comparative Example 2. The lithium-ion battery prepared in Example 2 has an initial discharge specific capacity of 193 mAh / g and a capacity retention rate of 70% after 400 cycles. In contrast, the lithium-ion battery of Comparative Example 2 has a capacity retention rate of only about 51% after 400 cycles under the same conditions. This indicates that the additive of the present invention significantly improves the long-term cycle stability of the lithium-ion battery. This may be because 4-cyano-3-fluorophenylboronic acid pinacol ester, as an additive, can form a protective film on the positive electrode during the first charge, which can inhibit the continued reduction and decomposition of solvent components on the positive electrode material, reduce the consumption of lithium source in the electrolyte, and thus achieve excellent long-term cycle performance.

[0046] The results of the rate performance test are shown below. Figure 2 .Depend on Figure 2 As shown in the rate performance graph, the specific capacity of the electrolyte in Comparative Example 1 at different current densities is significantly lower than that of the electrolyte in Example 1. The electrolyte in Example 1 can recover to a high specific capacity of 173.7 mAh / g after experiencing a high current of 3 C. In contrast, the electrolyte in Comparative Example 1 only has a specific capacity of 158.2 mAh / g when recovering to 0.5 C after experiencing a high current of 3 C. This indicates that the presence of the additive 4-cyano-3-fluorophenylboronic acid pinacol ester can generate a denser interfacial film at the positive electrode, preventing the electrode material from being damaged by impact at high currents and ensuring the stability of the electrode structure. This is manifested in the strong capacity reversibility of the lithium-ion battery with 4-cyano-3-fluorophenylboronic acid pinacol ester added at high current densities.

[0047] The results of the linear sweep voltammetry test are shown below. Figure 3 .Depend on Figure 3The linear sweep voltammetry results show that the oxidation onset potential of the electrolyte in Comparative Example 1 is 4.03 V. This indicates that the current in the electrolyte of Comparative Example 1 begins to rise significantly at 4.03 V, marking the start of oxidative decomposition of the carbonate solvent in the electrolyte. When 4-cyano-3-fluorophenylboronic acid pinacol ester is added to the electrolyte, the oxidation onset potential is advanced to 3.80 V, which is about 0.23 V lower than that of the electrolyte in Comparative Example 1. This experimental result confirms that 4-cyano-3-fluorophenylboronic acid pinacol ester has a higher HOMO energy level, which means that its outer electrons have higher energy and are more likely to lose electrons to undergo oxidation reactions, thus exhibiting an oxidation current response at a lower potential. Therefore, the preferential oxidation of the electrolyte in Example 1 starting at 3.80 V is a manifestation of the function of 4-cyano-3-fluorophenylboronic acid pinacol ester as a sacrificial additive for positive electrode film formation.

[0048] The content of Co deposited on the surface of the silicon-carbon anode after 400 cycles was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Figure 4 .Depend on Figure 4 It can be seen that after 400 cycles of the electrolyte in Comparative Example 1, the Co ion content dissolved from the NCM811 positive electrode and deposited on the silicon-carbon negative electrode was 0.0597 ppm, while after 400 cycles of the electrolyte in Example 2, the Co ion content dissolved from the NCM811 and deposited on the silicon-carbon negative electrode was 0.0225 ppm. It is evident that the Co ion content deposited on the silicon-carbon negative electrode by the lithium-ion battery in Comparative Example 2 after 400 cycles was much higher than that of the lithium-ion battery in Example 2. This can be attributed to the fact that the para-substituted cyano group in the 4-cyano-3-fluorophenylboronic acid pinacol ester molecule can be firmly anchored to the transition metal site in the cobalt-rich region of the NCM811 surface through coordination, preventing Co ions from escaping the crystal lattice and entering the electrolyte from the source, resulting in a significant reduction in the Co ion content deposited on the negative electrode.

[0049] The results of the constant current intermittent titration test are as follows: Figure 5 As shown, from Figure 5 It can be seen that the electrolyte with added 4-cyano-3-fluorophenylboronic acid pinacol ester exhibits superior lithium-ion transport performance compared to the electrolyte in Comparative Example 2 throughout the entire charge-discharge cycle. Regardless of whether the voltage increases during charging or decreases during discharging, the lithium-ion diffusion coefficient of the battery with added 4-cyano-3-fluorophenylboronic acid pinacol ester is higher than that of the comparative example. Specifically, the average lithium-ion diffusion coefficient of the battery containing the lithium-ion battery electrolyte of Comparative Example 2 during the complete cycle is 7.92 × 10⁻⁶. -8 cm 2 / s, while the average lithium-ion diffusion coefficient of the battery containing the lithium-ion battery electrolyte of Example 2 was 1.02 × 10⁻⁶ during a complete cycle. -7 cm 2 / s, an increase of approximately 28.8%, indicating that the CEI film formed by adding 4-cyano-3-fluorophenylboronic acid pinacol ester optimizes the transport kinetics of lithium ions at the cathode interface and has a higher lithium ion mobility coefficient.

[0050] In summary, the 4-cyano-3-fluorophenylboronic acid pinacol ester of this invention, as an electrolyte additive, can preferentially form a stable interfacial film on the surface of the battery's positive electrode, slowing down the dissolution of positive electrode metal ions and inhibiting their reduction and deposition on the negative electrode. This alleviates side reactions at the electrode and electrolyte interface and improves the battery's cycle stability.

[0051] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

Application of 1,4-cyano-3-fluorophenylboronic acid pinacol ester as an electrolyte additive.

2. A lithium-ion battery electrolyte, characterized in that, The raw materials include lithium salt, organic solvent and pinacol 4-cyano-3-fluorophenylboronic acid; The mass fraction of 4-cyano-3-fluorophenylboronic acid pinacol ester in the lithium-ion battery electrolyte is 0.1%-5%, the mass fraction of lithium salt in the lithium-ion battery electrolyte is 0.1%-15.0%, and the mass fraction of organic solvent in the lithium-ion battery electrolyte is 70.0%-90.0%.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that, The mass fraction of 4-cyano-3-fluorophenylboronic acid pinacol ester in lithium-ion battery electrolyte is 0.1%-1%.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium tetrafluoro(oxalate) phosphate, lithium oxalate phosphate, lithium bis(oxalate) borate, lithium difluoro(oxalate) borate, lithium tetrafluoroborate, lithium difluoro(oxalate) imide, and lithium difluoro(oxalate) imide.

5. The lithium-ion battery electrolyte according to claim 2, characterized in that, The organic solvent is a cyclic carbonate or a linear carbonate.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that, Cyclic carbonates are selected from at least one of ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, and propylene carbonate; linear carbonates are selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, and methyl trifluoroethyl carbonate.

7. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the lithium-ion battery electrolyte as described in any one of claims 2 to 6.

8. The lithium-ion battery according to claim 7, characterized in that, The general formula for the positive electrode active material used in the positive electrode sheet is LiNi. x Co y Mn z O2, where x+y+z=1 and x≥0.

6.

9. The lithium-ion battery according to claim 7, characterized in that, The negative electrode active material used in the negative electrode sheet is selected from at least one of silicon suboxide, elemental silicon, and graphite.

10. The lithium-ion battery according to claim 7, characterized in that, The negative electrode active material used in the negative electrode sheet is a silicon-carbon material composed of silicon suboxide and graphite.

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