Application of lithium-aromatic hydrocarbon compound in lithium battery pre-lithiation, pre-lithiation reagent, preparation method of pre-lithiation reagent, pre-lithiation electrolyte, lithium ion battery and pre-lithiation method of silicon-based negative electrode

Abstract

The invention belongs to the technical field of ion batteries, and particularly relates to application of a lithium-aromatic hydrocarbon compound in lithium battery pre-lithiation, a pre-lithiation reagent, a preparation method of the pre-lithiation reagent, a pre-lithiation electrolyte, a lithium ion battery and a pre-lithiation method of a silicon-based negative electrode. The invention provides an application of a lithium-aromatic hydrocarbon compound in lithium battery pre-lithiation, the lithium-aromatic hydrocarbon compound is 4, 4 '-dimethyl biphenyl lithium, and the preparation raw materials of the 4, 4'-dimethyl biphenyl lithium comprise 4, 4 '-dimethyl biphenyl and lithium elementary substance. 4, 4 '-dimethyl biphenyl lithium synthesized from 4, 4'-dimethyl biphenyl and lithium elementary substance is applied to lithium battery pre-lithiation, and shows excellent performance in the pre-lithiation process of a silicon-based negative electrode, so that the initial coulombic efficiency of the silicon-based negative electrode can be greatly improved, and the cycling stability is remarkably improved; powerful technical support and theoretical basis are provided for developing a high-energy-density lithium ion battery, and the commercial application process of a silicon-based negative electrode material is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion batteries, and specifically relates to the application of lithium-aromatic hydrocarbon complexes in the prelithiation of lithium batteries, prelithiation reagents and their preparation methods, prelithiation electrolytes, lithium-ion batteries, and prelithiation methods for silicon-based anodes. Background Art

[0002] During the electrochemical cycling process, significant electrolyte decomposition occurs on the surface of the silicon anode, followed by the formation of an irreversible solid electrolyte interface film (SEI). This film has a dual function: on the one hand, it acts as an ion conduction path to facilitate the transfer of Li + between the electrolyte and the silicon anode; on the other hand, as an electron blocking layer, it can effectively prevent electrons from migrating to the material surface, thereby curbing the continuous decomposition of the electrolyte. However, the formation of SEI irreversibly consumes electrolyte components and active lithium, resulting in a reduced initial Coulombic efficiency. In addition, the silicon anode undergoes significant volume changes (up to 300%) during charge and discharge, which can cause the rupture of SEI and prompt the continuous formation of new SEI. Each rupture of SEI triggers new electrolyte decomposition, and this process continuously consumes Li + and further exacerbates capacity decay. Compared with graphite anodes, these factors together lead to a significantly reduced initial Coulombic efficiency of silicon-based anodes.

[0003] As an effective solution, the prelithiation technology effectively compensates for the irreversible lithium loss during the first charge and discharge process by pre-supplying an active lithium source to the anode material. Prelithiation methods mainly include direct contact with lithium metal, electrochemical prelithiation, and chemical prelithiation, etc. Although direct contact with lithium metal is simple, it has safety and operation complexity issues. Although electrochemical prelithiation can precisely control the degree of prelithiation, its process is complex and time-consuming, making it difficult to be applied on a large scale. In contrast, chemical prelithiation has the advantages of simple operation and low cost by using reducing chemical reagents to react with the anode material.

[0004] Currently, chemical prelithiation reagents are mainly obtained by reacting aromatic hydrocarbon compounds with metallic lithium. However, when the current chemical prelithiation reagents are applied to the silicon-based anodes of lithium batteries, the initial Coulombic efficiency and cycle stability of the lithium batteries are still poor. Summary of the Invention

[0005] The object of the present invention is to provide an application of a lithium-aromatic hydrocarbon complex in the prelithiation of a lithium battery, a prelithiation reagent and its preparation method, a prelithiated electrolyte, a lithium-ion battery, and a method for prelithiating a silicon-based negative electrode. The prelithiation reagent provided by the present invention can not only significantly improve the initial Coulombic efficiency (first efficiency) of the silicon-based negative electrode, but also remarkably improve the cycle stability, providing strong technical support and theoretical basis for the development of high-energy-density lithium-ion batteries and promoting the commercial application process of silicon-based negative electrode materials.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides an application of a lithium-aromatic hydrocarbon complex in the prelithiation of a lithium battery. The lithium-aromatic hydrocarbon complex is lithium 4,4'-dimethylbiphenyl, and the raw materials for preparing lithium 4,4'-dimethylbiphenyl include 4,4'-dimethylbiphenyl (4,4'-DMBP) and lithium metal.

[0007] Preferably, the preparation method of lithium 4,4'-dimethylbiphenyl includes the following steps: Mix 4,4'-dimethylbiphenyl, 2-methyltetrahydrofuran (2-ME-THF) and lithium metal to obtain an organic solution of lithium 4,4'-dimethylbiphenyl.

[0008] The present invention provides a preparation method of a prelithiation reagent, including the following steps: Mix 4,4'-dimethylbiphenyl, 2-methyltetrahydrofuran and lithium metal to obtain the prelithiation reagent.

[0009] Preferably, the molar ratio of lithium metal to 4,4'-dimethylbiphenyl is 4:1.

[0010] The present invention provides a prelithiation reagent, which is prepared by the preparation method described in the above technical solution.

[0011] The present invention provides a prelithiated electrolyte, including a base electrolyte and the prelithiation reagent described in the above technical solution.

[0012] Preferably, the mass percentage of the prelithiation reagent in the base electrolyte is 1-3%; The base electrolyte includes lithium hexafluorophosphate, fluoroethylene carbonate and an organic solvent; the organic solvent includes ethylene carbonate and ethyl methyl carbonate; the molar concentration of lithium hexafluorophosphate in the base electrolyte is 1-1.5 mol / mL, and the volume percentage of fluoroethylene carbonate in the organic solvent is 1-10%.

[0013] The present invention provides a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, and the electrolyte is the prelithiated electrolyte described in the above technical solution.

[0014] Preferably, the negative electrode sheet includes a negative electrode current collector and a negative electrode material provided on the surface of the negative electrode current collector. The negative electrode material includes a negative electrode active component, and the negative electrode active component is a silicon-containing material; The positive electrode sheet includes a positive electrode current collector and a positive electrode material provided on the surface of the positive electrode current collector. The positive electrode material includes a positive electrode active component, and the positive electrode active component is lithium iron phosphate.

[0015] The present invention provides a pre-lithiation method for a silicon-based negative electrode, comprising the following steps: Mix the pre-lithiation reagent described in the above technical solution with a base electrolyte to obtain a pre-lithiated electrolyte; Prepare a lithium-ion battery using the pre-lithiated electrolyte and the silicon-based negative electrode.

[0016] The present invention provides an application of a lithium-aromatic hydrocarbon complex (LAC) in the pre-lithiation of a lithium battery. The lithium-aromatic hydrocarbon complex is lithium 4,4'-dimethylbiphenyl. The preparation raw materials of lithium 4,4'-dimethylbiphenyl include 4,4'-dimethylbiphenyl (4,4'-DMBP) and lithium metal. The present invention synthesizes lithium 4,4'-dimethylbiphenyl from 4,4'-dimethylbiphenyl and lithium metal and applies it in the pre-lithiation of a lithium battery, showing excellent performance in the pre-lithiation process of the silicon-based negative electrode, promoting the first efficiency and electrochemical performance of the silicon negative electrode.

[0017] The present invention provides a pre-lithiated electrolyte (4,4'-DMBP pre-lithiated electrolyte), comprising a base electrolyte and the pre-lithiation reagent described in the above technical solution. The present invention provides a pre-lithiation method for a silicon-based negative electrode, comprising the following steps: Mix the pre-lithiation reagent described in the above technical solution with a base electrolyte to obtain a pre-lithiated electrolyte; Prepare a lithium-ion battery using the pre-lithiated electrolyte and the silicon-based negative electrode. The present invention uses a method of adding a pre-lithiation reagent into the electrolyte to pre-lithiate a silicon-based negative electrode (Si negative electrode). The obtained pre-lithiated electrolyte electrode exhibits an excellent initial Coulomb efficiency of up to 93.84%, and presents a relatively high initial discharge capacity of 3588.1 mAh g -1 , and an excellent capacity retention rate of 79.35%.

[0018] The present invention provides a lithium-ion battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the electrolyte is the pre-lithiated electrolyte described in the above technical solution. When the positive active component is lithium iron phosphate, the initial Coulombic efficiency of the full cell assembled by matching LiFeO4 is also increased from 77.56% to 86.13%, and the capacity retention rate is increased from 50.40% to 72.56%. Further, through various characterization techniques such as XPS, SEM and CV, it is verified that the 4,4'-DMBP pre-lithiated electrolyte provided by the present invention changes the surface chemical composition and optimizes the structure of the silicon negative electrode.

[0019] The results show that when the pre-lithiation reagent provided by the present invention is added to the electrolyte, by virtue of its low reduction potential, effectively forming a stable SEI protective layer and optimizing the reaction kinetics of the negative electrode interface, not only the first efficiency of the silicon negative electrode is greatly improved, but also the cycle stability is significantly improved, providing strong technical support and theoretical basis for the development of high energy density lithium-ion batteries and promoting the commercial application process of silicon-based negative electrode materials. Description of the Drawings

[0020] Figure 1 are the first Coulombic efficiency and cycle performance of different pre-lithiated electrolytes; Figure 2 are the first Coulombic efficiency and cycle performance of pre-lithiated electrolytes with different addition amounts; Figure 3 are the first Coulombic efficiency and cycle performance of different methods; Figure 4 are the comparison of the first Coulombic efficiency and cycle performance of two electrolytes; Figure 5 are the charge-discharge curves of two electrolytes cycling 100 cycles at 0.5 A g -1 ; Figure 6 are the comparison of the rate performance of two electrolytes; Figure 7 are the comparison of the full cell electrochemical performance of two electrolytes; Figure 8 are the comparison of EIS and dQ / dV of two electrolytes; Figure 9 are the CV curves of two electrolytes cycling three cycles at a scan rate of 0.1 mV s -1 ; Figure 10 are the comparison of the Tafel tests of two electrolytes; Figure 11 are the TEM and SEM images of the electrode particles before and after cycling; Figure 12 are the SEM images of the electrode cross-section and surface before and after cycling; Figure 13Comparison of XPS spectra of two electrolyte electrodes after cycling. Detailed implementation manner

[0021] The present invention provides an application of a lithium-aromatic hydrocarbon complex in the prelithiation of a lithium battery. The lithium-aromatic hydrocarbon complex is lithium 4,4'-dimethylbiphenyl. The preparation raw materials of lithium 4,4'-dimethylbiphenyl include 4,4'-dimethylbiphenyl (4,4'-DMBP) and lithium metal.

[0022] In the present invention, the structure of lithium 4,4'-dimethylbiphenyl is shown in Formula 1: Formula 1.

[0023] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0024] In the present invention, lithium 4,4'-dimethylbiphenyl is preferably applied in the form of an organic solution of lithium 4,4'-dimethylbiphenyl.

[0025] In the present invention, the lithium metal is preferably a lithium sheet. The lithium metal is preferably a battery-grade lithium sheet.

[0026] In the present invention, the preparation method of lithium 4,4'-dimethylbiphenyl (i.e., the organic solution of lithium 4,4'-dimethylbiphenyl) preferably includes the following steps: Mix 4,4'-dimethylbiphenyl, 2-methyltetrahydrofuran (2-ME-THF) and lithium metal to obtain the organic solution of lithium 4,4'-dimethylbiphenyl. In the present invention, the molar ratio of the lithium metal to the 4,4'-dimethylbiphenyl is 4:1. The molar concentration of 4,4'-dimethylbiphenyl in the solution formed by 4,4'-dimethylbiphenyl and 2-ME-THF is preferably 0.5 - 1 mol / L. The mixing is preferably carried out under stirring conditions. The mixing preferably includes the following steps: stir and dissolve 4,4'-dimethylbiphenyl in 2-methyltetrahydrofuran to obtain a premixed solution; the molar concentration of 4,4'-dimethylbiphenyl in the premixed solution is 0.5 - 1 mol / L; stir and mix the premixed solution and the lithium metal. The stirring and dissolving is preferably carried out under magnetic stirring conditions. The stirring and mixing is preferably carried out under mechanical stirring conditions, and the time of the stirring and mixing is preferably 5 - 6 h. The temperature of the stirring and mixing is preferably room temperature (20 - 35 °C).

[0027] In the present invention, a salt-forming reaction occurs between the 4,4'-dimethylbiphenyl and the lithium metal. The reaction equation of the 4,4'-dimethylbiphenyl and the lithium metal is as follows: .

[0028] The present invention provides a preparation method of a prelithiation reagent, comprising the following steps: Mix 4,4'-dimethylbiphenyl, 2-methyltetrahydrofuran and lithium metal to obtain the prelithiation reagent.

[0029] In the present invention, the prelithiation reagent is an organic solution of the above-mentioned lithium 4,4'-dimethylbiphenyl. The preparation method of the prelithiation reagent is the same as that of the organic solution of lithium 4,4'-dimethylbiphenyl, which will not be elaborated herein.

[0030] The present invention provides a prelithiation reagent prepared by the preparation method described in the above technical solution.

[0031] The present invention provides a prelithiated electrolyte, comprising a base electrolyte and the prelithiation reagent described in the above technical solution.

[0032] In the present invention, the prelithiation reagent is preferably used in the form of the above-mentioned organic solution of lithium 4,4'-dimethylbiphenyl.

[0033] In the present invention, the base electrolyte preferably comprises lithium hexafluorophosphate, fluoroethylene carbonate and an organic solvent. The organic solvent preferably comprises ethylene carbonate (EC) and ethyl methyl carbonate (EMC). The volume ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) is preferably 3:7. The molar concentration of lithium hexafluorophosphate in the base electrolyte is preferably 1-1.5 mol / mL, and the molar amount of lithium hexafluorophosphate to the volume of the organic solvent in the examples is preferably 1.2 mol:1 mL. The volume percentage of fluoroethylene carbonate in the organic solvent is preferably 1-10%, and can be 10% in the examples.

[0034] In the present invention, the preparation method of the base electrolyte preferably comprises the following steps: Stir and dissolve lithium hexafluorophosphate in an organic solvent, and then add the fluoroethylene carbonate and continue to stir and mix to obtain the base electrolyte. The stirring and dissolving is carried out under the condition of magnetic stirring, and the time of the stirring and dissolving is preferably 15-20 min. The time of the continuous stirring and mixing is preferably 6-8 h; the temperature is preferably room temperature (20-35 °C). The rotation speed of the stirring and dissolving is preferably 60-150 r / min -1 . The rotation speed of the stirring and mixing is preferably 60-150 r min -1 . The base electrolyte is preferably prepared in a glove box with a water and oxygen value ≤ 0.1 ppm.

[0035] In the present invention, the mass percentage of the prelithiation reagent in the base electrolyte is preferably 1-3%, and can be 1%, 2% or 3% in the examples.

[0036] The present invention provides a method for preparing the prelithiated electrolyte described in the above technical solution, preferably including the following steps: adding the prelithiation reagent to the base electrolyte. The addition is preferably dropwise addition or batch addition. The addition is preferably carried out under stirring conditions. After the addition of the prelithiation reagent, stirring is preferably continued for 2 to 4 h.

[0037] The present invention provides a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the electrolyte is the prelithiated electrolyte described in the above technical solution.

[0038] In the present invention, the positive electrode sheet preferably includes a positive electrode current collector and a positive electrode material provided on the surface of the positive electrode current collector. The positive electrode material includes a positive electrode active component, and the positive electrode active component is lithium iron phosphate (LiFeO4, abbreviated as LFP). In the present invention, the positive electrode current collector is preferably an aluminum foil current collector, and the positive electrode material preferably further includes a binder and a conductive agent. The binder is preferably polyvinylidene fluoride (PVDF). The conductive agent is preferably Super P. The mass ratio of the positive electrode active component, the conductive agent, and the binder is preferably 8:1:1. The shape of the positive electrode sheet is preferably a circular sheet, and the diameter of the circular sheet is preferably 13 mm.

[0039] In the present invention, the method for preparing the positive electrode sheet preferably includes the following steps: mixing the positive electrode active component, the binder, the conductive agent, and an organic solvent, and then performing stirring and defoaming to obtain a positive electrode slurry; coating the positive electrode slurry on the surface of the positive electrode current collector, and then successively performing first drying, blanking, and second drying to obtain the positive electrode sheet. The organic solvent is preferably N-methylpyrrolidone (NMP). The stirring and defoaming are preferably carried out in a stirring and defoaming machine. The rotation speed of the stirring and defoaming is preferably 1000 to 1500 r min -1 , and the time is preferably 20 to 25 min. The coating is preferably carried out using a doctor blade. The first drying is preferably carried out in a vacuum drying oven, and the temperature of the first drying is preferably 75 to 80 °C; the time is preferably 12 to 24 h. The second drying is preferably carried out in a vacuum drying oven, and the temperature of the second drying is preferably 100 to 110 °C; the time is preferably 4 to 6 h.

[0040] In the present invention, the negative electrode sheet preferably comprises a negative electrode current collector and a negative electrode material provided on the surface of the negative electrode current collector. The negative electrode material comprises a negative electrode active component, and the negative electrode active component is a silicon-containing material. The silicon-containing material is preferably a silicon material, and the silicon material is preferably a nano-silicon material (Si). In the present invention, the negative electrode current collector is preferably a copper foil current collector. The purity of the silicon material is preferably ≥99%, more preferably ≥99.9%, and is 99.99% in the examples. The negative electrode material preferably further comprises a binder and a conductive agent. The binder is preferably polyacrylic acid (PAA). The conductive agent is preferably SuperP. The mass ratio of the negative electrode active component, the binder, and the conductive agent is preferably 8:1:1. In the present invention, the loading amount of the negative electrode active component in the negative electrode material on the negative electrode sheet is preferably 1 mg cm -2 . The shape of the negative electrode sheet is preferably a disc, and the diameter of the disc is preferably 14 mm.

[0041] In the present invention, the method for preparing the negative electrode sheet preferably comprises the following steps: mixing the negative electrode active component, the binder, the conductive agent, and water, followed by stirring and defoaming to obtain a negative electrode slurry; coating the negative electrode slurry on the surface of the negative electrode current collector, and then successively drying and cutting to obtain the negative electrode sheet. The water is preferably deionized water. The mixing preferably comprises: grinding the negative electrode active component, the binder, and the conductive agent and then mixing with water. The stirring and defoaming are preferably carried out in a stirring and defoaming machine. The rotation speed of the stirring and defoaming is preferably 1000~1500 r min -1 , and the time is preferably 20~25 min. The coating is preferably carried out using a doctor blade, and the specification of the doctor blade is 80 μm. The drying is preferably carried out in an electrothermal blast drying oven, the drying temperature is preferably 65~70 °C; the time is preferably 12~24 h. The negative electrode sheet of the lithium-ion battery is stored in a drying tank.

[0042] The lithium-ion battery provided by the present invention uses LFP as the positive electrode active component material and Si as the negative electrode active component material, and the capacity ratio (N / P ratio) of the negative electrode sheet to the positive electrode sheet is preferably about 1.2.

[0043] The present invention provides a method for prelithiation of a silicon-based negative electrode, comprising the following steps: Mixing the prelithiation reagent described in the above technical solution with a base electrolyte to obtain a prelithiated electrolyte; Preparing a lithium-ion battery using the prelithiated electrolyte and the silicon-based negative electrode.

[0044] The present invention mixes the prelithiation reagent described in the above technical solution with a base electrolyte to obtain a prelithiated electrolyte. In the present invention, the preparation method of the prelithiated electrolyte is the same as above and will not be described herein again.

[0045] After obtaining the prelithiated electrolyte, the present invention uses the prelithiated electrolyte and a silicon-based negative electrode to prepare a lithium-ion battery. The present invention has no special requirements for the preparation method of the lithium-ion battery.

[0046] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0047] The raw materials and reagents used in the following examples are shown in Table 1: Table 1 Raw materials and reagents used in the examples

[0048] Example 1 This example provides the preparation of 4,4'-DMBP prelithiated electrolyte: (1) Preparation of the baseline electrolyte: Use a micropipette to accurately measure ethylene carbonate (EC) and ethyl methyl carbonate (EMC) according to a volume ratio of 3:7. Measure 300 μL of EC and 700 μL of EMC respectively, and add the two into a clean small glass bottle. Use a magnetic stirrer to stir at a low speed for 10 minutes under the condition of 150 rmin -1 to ensure uniform mixing of the solvents. Weigh 0.1823 g of lithium hexafluorophosphate (LiPF6), add it to the obtained mixed solvent, and stir while adding (150 r min -1 ), and continue to stir for 15 minutes until LiPF6 is completely dissolved and the solution is clear and transparent. Then add 100 μL of fluoroethylene carbonate (FEC), and continue to stir for 6 h to complete the preparation. The entire preparation process is completed in a glove box environment with a water oxygen value lower than 0.1 ppm.

[0049] (2) Preparation of the prelithiation reagent: Prepare a 4,4'-DMBP / 2-MeTHF solution with a molar concentration of 1 mol / L of 4,4'-DMBP (the concentration of 4,4'-DMBP is 1 mol / L, and the solvent is 2-MeTHF): Weigh 0.1822 g of 4,4'-DMBP and dissolve it in 1 mL of anhydrous 2-methyltetrahydrofuran (2-ME-THF). Use a magnetic stirrer to stir at a low speed until it is completely dissolved and the solution is clear and transparent. Then add 0.0280 g of battery-grade lithium foil (molar ratio Li:4,4'-DMBP = 4:1), and mechanically stir for 6 h to obtain the prelithiation reagent (i.e., 4,4'-DMBP prelithiation reagent). The same operation can be used to prepare lithium-aromatic hydrocarbon complex (LAC) reagents with the same concentration but different aromatic hydrocarbon molecules.

[0050] (3) Preparation of 4,4'-DMBP prelithiated electrolyte: 0.024 g of prelithiation reagent was added dropwise to 1 mL of Baseline solution (with a mass of 1.2 g) (the added mass ratio was 2%, that is, the mass percentage of the added prelithiation reagent in the Baseline solution was 2%). After mechanical stirring for 4 h, a prelithiated electrolyte was obtained. The same operation can be used to prepare prelithiated electrolytes with different addition amounts.

[0051] Example 2: This example provides the preparation of a silicon electrode: In this example, polyacrylic acid (PAA) was used as the binder, and Super P was selected as the conductive agent. According to the mass ratio of the active material (silicon nanoparticles), binder, and conductive agent of 8:1:1, precise weighing was carried out. After being thoroughly ground until uniform, it was transferred to a stirring and degassing container. Subsequently, an appropriate amount of deionized water was added as a solvent, and then the container was placed in an AD-680 type stirring and degassing machine and stirred at a speed of 1500 r min -1 for 20 minutes to obtain a uniformly mixed slurry. Then, the slurry was uniformly coated on one side of a copper foil current collector using an 80 μm scraper. After coating, the electrode was placed in an electrothermal blast drying oven at 70 °C and dried for 12 h to remove moisture. Finally, the electrode sheet was cut into 14 mm circular pieces, weighed, and stored in a drying tank. The active material loading of the electrode sheet was approximately 1 mg cm -2 .

[0052] Example 3: This example provides a method for assembling a half-cell: In this example, a CR2032 type button battery was assembled. The electrode prepared in Example 2 was used as the electrode of the half-cell, a lithium sheet with a diameter of 15.4 mm was used as the negative electrode, porous polypropylene was selected as the separator, and the 4,4'-DMBP prelithiated electrolyte prepared in Example 1 was used. During assembly, 50 μL of the electrolyte was dropped on each side of the separator. The entire battery assembly process was completed in an argon-protected glove box to ensure an oxygen-free and water-free environment. The specific assembly process of the CR2032 type button half-cell is as follows: First, the negative electrode case, shrapnel, gasket, lithium metal sheet, separator, electrode sheet, and gasket were sequentially placed, and finally the positive electrode case was covered. Then, a pressure of 50 MPa was applied to the battery using a battery encapsulation machine for sealing and encapsulation to ensure the battery was prepared well. The assembled half-cell was left standing at room temperature for 24 h, and then tested and evaluated using a LAND battery test system under normal temperature conditions.

[0053] Example 4: This example provides the assembly of a full cell: The cathode material of this embodiment is lithium iron phosphate (LiFeO4, abbreviated as LFP). LFP, conductive additive (SuperP), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone (NMP) is added as a solvent and placed in a stirring and degassing box. After sealing, it is put into an AD-680 stirring and degassing machine and homogenized at a high speed of 1500 r min -1 at a rate of 20 minutes. The slurry is evenly coated on one side of the aluminum foil current collector using a scraper, and then processed in a vacuum drying oven at 80 °C for 12 h. The dried electrode sheet is punched into a circular sheet with a diameter of 13 mm and further dried in a vacuum oven at 110 °C for 6 h to completely remove the residual solvent. Using LFP as the cathode active component material and Si material as the anode active component material, the capacity ratio of the anode to the cathode (N / P ratio) is adjusted to be close to a value of 1.2. The assembly sequence of the full cell is as follows: negative electrode shell, shrapnel, gasket, Si electrode sheet, separator, LFP electrode sheet, gasket, positive electrode shell. 50 μL of 4,4'-DMBP prelithiation electrolyte is dropped on both sides of the separator. It is sealed under a pressure of 50 MPa using a battery encapsulation machine to prepare a CR2032 type button battery. All assembly steps are completed inside an argon-protected glove box, and the water and oxygen content inside the box is strictly controlled below 0.1 ppm. After the encapsulated battery is left standing at room temperature for 30 h, the electrochemical performance is evaluated using a LAND battery test system.

[0054] Examples and effect data (1) Screening of prelithiation solvents and exploration of key parameters In order to explore the optimal conditions for improving the first Coulombic efficiency of the silicon anode by the prelithiation electrolyte, two factors that affect the preparation of the prelithiation electrolyte in this invention are experimentally explored: the selection of aromatic hydrocarbon molecules in the prelithiation reagent and the addition amount of the prelithiation reagent. At the same time, the effects of using the prelithiation reagent by different methods on the first efficiency improvement and cycle stability of the silicon anode are explored.

[0055] Different aromatic hydrocarbon molecules react with battery-grade lithium sheets in 2-MeTHF to form different LAC reagents. This invention selects three different aromatic hydrocarbon molecules, biphenyl (BP), 4-methylbiphenyl (4-MBP), and 4,4'-dimethylbiphenyl (4,4'-DMBP). Under the condition of keeping other conditions unchanged, three prelithiation electrolytes, BP, 4-MBP, and 4,4'-DMBP, are prepared according to the experimental operation of Example 1 and experimentally explored. In order to explore the improvement effect of the prelithiation electrolytes prepared from different aromatic hydrocarbon molecules on the first efficiency of the Si anode, half-cell tests are carried out on the above prelithiation electrolytes, and the experimental data are as Figure 1 shown, Figure 1are the initial Coulombic efficiency and cycling performance of different prelithiated electrolytes. All cells were activated for 3 cycles at a current density of 0.1 A g -1 . Figure 1 Figure (a) in -1 shows the first charge-discharge curves of different prelithiated electrolytes tested at 0.1 A g

[0056] As Figure 1 shown in Figure (a), the first discharge specific capacities of the four electrolytes Baseline, BP, 4-MBP, and 4,4'-DMBP are 3260.8 mAh g -1 , 3465.2 mAh g -1 , 3552.2 mAh g -1 and 3588.1 mAh g -1 respectively, and the corresponding charge specific capacities are 2961.1 mAh g -1 , 316.09 mAh g -1 , 3271.4 mAh g -1 and 3367.1 mAh g -1 respectively. Their corresponding initial Coulombic efficiencies (ICE) are 90.81%, 91.45%, 92.10%, and 93.84%. It can be found that compared with the Baseline electrolyte, the ICE of the electrolytes added with different prelithiation reagents has all increased, and the ICE of the 4,4'-DMBP electrolyte has increased the most significantly, by 3.03%. In addition, the discharge capacities of the electrolytes added with different prelithiation reagents have all increased. It is worth noting that after cycling 100 times at 0.5 A g -1 , the 4,4'-DMBP electrolyte still shows significant cycling stability, with a capacity retention rate of 79.35%, which is significantly higher than 53.21% of the Baseline electrolyte, 61.05% of the BP electrolyte, and 65.04% of the 4-MBP electrolyte ( Figure 1 Figure (b) in

[0057] The reason why 4,4'-DMBP is superior to unsubstituted BP and 4-MBP with only a methyl group at the 4-position in terms of improving the first-cycle efficiency and capacity retention rate of silicon anodes is mainly attributed to the two methyl groups introduced at the 4,4'-positions in its molecular structure, which not only have an electron-donating effect but also introduce an appropriate steric hindrance effect. As a result, the redox potential of the overall molecule is significantly reduced to below 0.2 V. This low potential endows it with stronger reducing ability, enabling it to more effectively reduce the active sites on the surface of silicon materials and promote the formation of a uniform and dense SEI protective layer when pre-lithiating with silicon-oxygen anodes. Thus, it can compensate for the lithium consumed due to SEI formation and other side reactions during the first cycle to the greatest extent, while effectively inhibiting the structural damage and electrolyte side reactions caused by volume expansion of the silicon anode during cycling. In contrast, 4-MBP only has a methyl group introduced on one side, so its effect of reducing the redox potential is weaker, and its electronic effect and stereoregulatory ability are not as obvious as those of 4,4'-DMBP. Unsubstituted BP lacks a regulatory group, has a relatively high potential, and insufficient pre-lithiation activity, resulting in mediocre effects in improving the initial efficiency and capacity retention rate of silicon anodes.

[0058] The 4,4'-DMBP pre-lithiation reagent is an excellent pre-lithiation reagent with extremely strong reducing ability, which can improve the ICE and cycling stability of silicon anode materials during cycling.

[0059] In this invention, the addition amount of the 4,4'-DMBP pre-lithiation reagent was explored, and the effects of three different addition amounts of 1 wt%, 2 wt%, and 3 wt% on the performance of silicon-based electrodes were systematically studied, and a comprehensive electrochemical performance evaluation was carried out. Figure 2 The first Coulombic efficiency and cycling performance of pre-lithiated electrolytes with different addition amounts. Figure 2 As shown in (a) of [reference], the first-cycle charge-discharge curves of the three addition amounts are presented. The first-cycle discharge specific capacities of the addition amounts of 1 wt%, 2 wt%, and 3 wt% are 3530.2 mAh g -1 、3588.1 mAh g -1 and 3755.5 mAh g -1 , respectively, and the corresponding charge specific capacities are 3257.4 mAh g -1 、3367.1 mAh g -1 and 3451.5 mAh g -1 , respectively. Their corresponding ICEs are 92.27%, 93.84%, and 91.91%. It can be found that the first efficiency of the 2 wt% 4,4'-DMBP pre-lithiation reagent is improved most significantly, and the capacity retention rate after 100 cycles is also significantly higher than those of the addition amounts of 1 wt% and 3 wt% ( Figure 2 In (b) of [reference] is the cycling performance of pre-lithiated electrolytes with different addition amounts).

[0060] Different usage methods of prelithiation reagents will have different effects on the electrochemical performance of silicon anode materials. Currently, there are mainly two common usage methods: one is to directly add prelithiation reagents to the electrolyte as adopted above; another prelithiation method is to immerse the prepared silicon electrode into the prelithiation reagent, keep it for a period of time to fully react, and then wash it with 2-MeTHF ( Figure 3 the 4,4'-DMBP-immersion group in Figure 3 ). To explore the effects of the two methods on the initial Coulomb efficiency (ICE) and cycling stability of silicon anodes, half-cell tests were carried out using the 4,4'-DMBP prelithiation reagent with the above two methods. Figure 3 Figure (a) in Figure 3 shows the comparison of the first charge-discharge curves of the two methods. It can be seen that the open-circuit voltage of the addition method is 1.372 V, and the initial Coulomb efficiency is 93.84%. While the open-circuit voltage of the immersion method significantly drops to 0.435 V, and the initial Coulomb efficiency is significantly increased to 98.77%. This is because when the silicon electrode is directly immersed in the 4,4'-DMBP prelithiation reagent, a large amount of lithium ions can be rapidly obtained on the electrode surface in a short time. The lithium ions can be rapidly embedded into the electrode material in a short time, resulting in a higher lithium ion concentration on the electrode surface. Thus, it can more effectively compensate for the irreversible loss during the first charge-discharge process, thereby reducing the open-circuit voltage and increasing the initial Coulomb efficiency. However, the immersion method will show obvious capacity decay after 20 cycles, and the capacity decays to 0 after 60 cycles. While the addition method still has a capacity retention rate of 79.35% after 100 cycles, showing excellent cycling stability ( Figure (b) in

[0061] shows the cycling performance of different methods). Although the electrode infiltration method can quickly supplement lithium ions, due to the fact that lithium ions are mainly concentrated on the electrode surface, it may lead to local excessive lithium deposition and form an uneven SEI film. This uneven SEI film is prone to cause side reactions and affect the long-term cycling stability of the battery. When the 4,4'-DMBP prelithiation reagent is added to the electrolyte, the lithium ions can be evenly dispersed in the entire electrolyte system. This is conducive to constructing a more uniform and dense SEI film. At the same time, during the charge-discharge process of the battery, the lithium ions will gradually be released from the electrolyte and embedded into the silicon anode material, rather than being deposited on the electrode surface in a large amount at one time, thus achieving a uniform prelithiation effect.

[0062] (2)Electrochemical Characterization of 4,4'-DMBP Prelithiated Electrolyte Comparison of the cycling performance, initial Coulombic efficiency, and open-circuit voltage between the Baseline electrolyte and the 4,4'-DMBP prelithiated electrolyte is as Figure 4 shown, Figure 4 For the comparison of the initial Coulombic efficiency and cycling performance of the two electrolytes, Figure 4 (a) in it is the initial charge-discharge curves of the Baseline and 4,4'-DMBP prelithiated electrolytes (denoted as 4,4'-DMBP in the figure) at 0.1 A g -1 -1, Figure 4 (b) in it is the cycling performance of the Baseline and 4,4'-DMBP at 0.5 A g -1 -1. In the voltage range of 0.01 - 2 V, the initial Coulombic efficiency of the Baseline electrolyte is 90.81%, and the open-circuit voltage is 2.2058 V. At a current density of 0.5 A g -1 -1, the capacity retention rate after 100 cycles is only 53.21%. While for the 4,4'-DMBP prelithiated electrolyte, the initial Coulombic efficiency is 93.84%, the open-circuit voltage is 1.3724 V, and the capacity retention rate reaches 79.35% after 100 cycles. It can be seen that the initial Coulombic efficiency of the 4,4'-DMBP prelithiated electrolyte is increased by 3.03% compared with the Baseline electrolyte, the open-circuit voltage is reduced by 0.8334 V, and the capacity retention rate is increased by 26.14%.

[0063] The reason why the 4,4'-DMBP prelithiated electrolyte provided by the present invention exhibits such excellent initial discharge capacity and capacity retention rate is that the Baseline electrolyte does not contain a prelithiation reagent, so it cannot effectively compensate for the lithium ions consumed by the formation of SEI during the first charge-discharge process of the silicon negative electrode, which results in a relatively low initial Coulombic efficiency of the silicon negative electrode. The addition of the 4,4'-DMBP prelithiation reagent can pre-embed lithium ions into the silicon negative electrode, enabling the electrolyte to compensate for this part of lithium loss through the chemical prelithiation process, thereby improving the initial efficiency of the silicon negative electrode and reducing the open-circuit voltage. At the same time, it can also provide additional lithium ions for the silicon negative electrode during the charge-discharge process, enabling more lithium ions to participate in the electrochemical reaction. By compensating for the irreversible lithium loss, the discharge capacity and capacity retention rate of the silicon negative electrode are effectively improved.

[0064] Figure 5 For the Baseline electrolyte and the 4,4'-DMBP prelithiated electrolyte in the voltage range of 0.01 - 2 V, the evolution of the charge-discharge curves during 100 cycles at a current density of 0.5 A g -1 -1. Figure 5 (a) in it is the Baseline charge-discharge curve,Figure 5 In (b), it is the charge-discharge curve of 4,4'-DMBP. The voltage plateau of the Baseline electrolyte gradually disappears as the number of cycles increases, and at the same time, the capacity decays rapidly. However, for the 4,4'-DMBP pre-lithiated electrolyte, the capacity shows no obvious decay, and the change in the voltage plateau is also small, proving that the 4,4'-DMBP pre-lithiated electrolyte can improve its stability.

[0065] To further analyze the electrochemical performance of the pre-lithiated electrolyte, charge and discharge rate tests were carried out on the Baseline electrolyte and the 4,4'-DMBP pre-lithiated electrolyte. As Figure 6 shown, Figure 6 it is the comparison of the rate performance of the two electrolytes. Five charge-discharge cycles were carried out at current densities of 0.1 A g -1 , 0.2 A g -1 , 0.5 A g -1 , 1.0 A g -1 and 2.0 A g -1 . The average reversible discharge capacities of 4,4'-DMBP are 3604.6 mAh g -1 , 3500.4 mAh g -1 , 3148.7 mAh g -1 , 2748.4 mAh g -1 and 2188.2 mAh g -1 in sequence. It is worth noting that once the current density is restored from 2.0 A g -1 to 0.1 A g -1 , its average reversible discharge capacity can be restored to 3536.8 mAh g -1 , indicating that the 4,4'-DMBP pre-lithiated electrolyte has good reversibility.

[0066] To further evaluate the application effect of the 4,4'-DMBP pre-lithiated electrolyte in the full cell, the electrochemical performances of the Si|Baseline|LFP and Si|4,4'-DMBP|LFP full cells were assembled and evaluated according to the experimental operation of Example 4. Figure 7 It is the comparison of the electrochemical performances of the two electrolytes in the full cell. Figure 7 In (a), it is the initial charge-discharge curves of the Baseline and 4,4'-DMBP full cells at 0.1 C. Figure 7 In (b), it is the cycling performance of the Baseline and 4,4'-DMBP full cells at 0.33 C. The corresponding voltage range and N / P ratio are set to 2.2~4.0 V and 1.20 respectively. Figure 7 In (a), it shows that at 0.1 C (1 C = 160 A g -1) First charge-discharge curves at a current density. The initial Coulombic efficiency of Si|4,4'-DMBP|LFP is 86.13%, and that of Si|Baseline|LFP is 77.56%. By comparison, it can be found that the initial efficiency has increased by 8.57%. In addition, the cycling performance of Si|Baseline|LFP and Si|4,4'-DMBP|LFP batteries at a current density of 0.33 C was compared ( Figure 7 as shown in (b) of

[0067] ). After 50 cycles, the capacity retention rate of Si|4,4'-DMBP|LFP is 72.56%. The capacity of Si|Baseline|LFP decays rapidly, and the capacity retention rate after 50 cycles is only 50.40%. In contrast, the capacity retention rate has increased by 22.16%. The 4,4'-DMBP prelithiated electrolyte also shows excellent initial Coulombic efficiency and cycling stability in the full cell. Figure 8 For the comparison of EIS and dQ / dV of the two electrolytes, Figure 8 in (a) and (b) of Figure 8 are the EIS and equivalent circuit before cycling, respectively, and Figure 8 in (c) of ct is the dQ / dV of the second cycle. As shown in (a) of SEI Figure 8 ct Figure 8 ct Figure 8 Figure 8 Figure 8

[0068] , the Baseline electrolyte shows only a semicircle in the high-frequency region, corresponding to the charge transfer resistance R ct = 217.5 Ω. In contrast, the EIS spectrum of the 4,4'-DMBP prelithiated electrolyte shows two semicircles in the high-frequency region, corresponding to the solid electrolyte interface film impedance (R SEI ) and the charge transfer impedance (R ct = 146.4 Ω). This phenomenon directly confirms that the 4,4'-DMBP prelithiation reagent participates in the chemical prelithiation process and forms a stable SEI film on the electrode surface. The lower R ct value indicates that the electrode has faster charge transfer kinetics, which is beneficial to reducing electrode polarization, making the working potential of the silicon anode closer to its kinetic potential, and thus promoting the reversible lithium-ion insertion / extraction process. Similarly, the differential capacity curves (dQ / dV) of the second cycle of the Baseline electrolyte and the 4,4'-DMBP prelithiated electrolyte can also prove that chemical prelithiation reduces polarization ( Figure 8 as shown in (b) of

[0068] ). Compared with the Baseline electrolyte, the peak separation potential of the 4,4'-DMBP prelithiated electrolyte is reduced by 19 mV, indicating that 4,4'-DMBP effectively reduces the electrochemical polarization.The kinetic behaviors of the Baseline electrolyte and the 4,4'-DMBP prelithiated electrolyte were investigated using cyclic voltammetry and Tafel tests. Figure 9 are the cyclic voltammetry (CV) curves of the Baseline electrolyte and the 4,4'-DMBP prelithiated electrolyte in the voltage range of 0.01 - 2 V at a scan rate of 0.1 mV s -1 after three cycles. Figure 9 In (a) is the result of the Baseline electrolyte, Figure 9 and in (b) is the result of the 4,4'-DMBP prelithiated electrolyte. The Baseline electrolyte has reduction peaks related to SEI formation near 0.728 V and 0.981 V ( Figure 9 in (a)), while the CV curve of the 4,4'-DMBP prelithiated electrolyte ( Figure 9 in (b)) does not show an SEI formation peak during the negative scan, indicating that a stable interfacial layer has been pre-formed during the prelithiation process. This phenomenon is consistent with the EIS results. It should be noted that no abnormal redox peaks appear in the CV curves of both electrolytes, indicating that the 4,4'-DMBP prelithiation process only participates in the formation of the SEI film and does not affect the intrinsic lithium storage mechanism of the silicon material. Only silicon participates in the redox reaction in the prelithiated electrode, and no other side reactions occur. The reduction of side reactions reduces the concentration polarization and electrochemical polarization on the electrode surface, further promoting the charge transfer efficiency. Similarly, the Tafel test results of the Baseline electrolyte and the 4,4'-DMBP prelithiated electrolyte can also confirm the improvement of the charge transfer efficiency ( Figure 10 Comparison of Tafel tests for the two electrolytes). The 4,4'-DMBP prelithiated electrolyte has a significantly higher exchange current density than the Baseline electrolyte, which proves that the charge transfer kinetics at the electrode / electrolyte interface has been significantly improved.

[0069] (3) Investigation of the Si electrode after cycling in the 4,4'-DMBP prelithiated electrolyte The morphological differences of the Si electrodes in the Baseline electrolyte battery and the 4,4'-DMBP prelithiated electrolyte battery before and after cycling were observed, as Figure 11 shown. Figure 11 are the TEM and SEM images of the electrode particles before and after cycling. Figure 11 In (a) and (d) are the TEM and SEM of the Si particles before cycling, Figure 11 in (b) and (e) are the TEM and SEM of the Baseline electrode particles after cycling, Figure 11 and in (c) and (f) are the TEM and SEM of the 4,4'-DMBP electrode particles after cycling.

[0070] Figure 11 Figures (a), (b), and (c) respectively show the TEM test results of the electrodes of pristine silicon particles, Baseline electrolyte, and 4,4'-DMBP pre-lithiated electrolyte after 100 cycles at a current density of 0.5 A g -1 . It was found that compared with the TEM of pristine silicon particles, the Baseline electrode presented an amorphous flocculent structure after 100 cycles, and intact silicon particles could not be observed ( Figure 11 Figure (b)), which was due to the huge volume expansion of silicon particles during cycling, resulting in more fresh surfaces being exposed, thereby causing the decay of cycling performance. On the contrary, as shown in Figure 11 Figure (c), due to the formation of a uniform and dense SEI film during the chemical pre-lithiation process of 4,4'-DMBP, this SEI film, as a protective layer, can effectively relieve the mechanical stress caused by volume expansion during the charge and discharge process of the silicon negative electrode, and effectively alleviate the cracking or pulverization of silicon particles. Intact particle morphology could still be observed even after 100 cycles.

[0071] To further explore the beneficial effect of 4,4'-DMBP on the structural stability of the silicon negative electrode, SEM tests were carried out on the nano-silicon particles loaded on the cycled electrode sheets. Figure 11 Figure (d) in Figure 11 shows the SEM of Si particles before cycling, and Figure 11 Figures (e) and (f) in Figure 11 show the results after cycling. The results showed that compared with the SEM image of silicon particles before cycling, obvious cracking and pulverization appeared on the surface of the particles of the Baseline electrode after 100 cycles (

[0072] Figure 12 Figure (e)), while the particles of the 4,4'-DMBP electrode could still maintain an intact morphology ( -1 Figure (f)), which was consistent with the TEM test results. It further demonstrated that the presence of 4,4'-DMBP provided an effective buffering effect for the volume expansion of Si particles, endowing the electrode with excellent long-cycle stability. Figure 12 Figures (a) and (d) in Figure 12 show the cross-section and surface SEM of the Si electrode before cycling, and Figure 12 Figures (b) and (e) in Figure 12In (b), the volume expansion is up to 117% after 100 cycles. On the contrary, the volume expansion of the 4,4'-DMBP electrode is significantly reduced ( Figure 12 in (c)), proving that the addition of the 4,4'-DMBP prelithiation reagent endows the silicon anode with good structural stability. The excellent electrochemical performance is attributed to the fact that 4,4'-DMBP can promote the formation of a uniform and dense SEI film, thus well buffering the volume change of the silicon anode during cycling, while supplementing active lithium ions, making the lithium intercalation process of the silicon anode more stable and significantly reducing the overall expansion. Through the SEM characterization of the surfaces of the two electrodes ( Figure 12 in (d), (e) and (f)), it can be observed that after 100 cycles, the surface of the Baseline electrode presents cracks similar to a turtle shell ( Figure 12 in (e)), while the surface of the 4,4'-DMBP electrode maintains a complete morphology without obvious large cracks ( Figure 12 in (f)), further proving that 4,4'-DMBP can promote the good structural stability of the silicon anode.

[0073] To explore the role of 4,4'-DMBP in the formation of the SEI film, X-ray photoelectron spectroscopy (XPS) test analysis was carried out on the electrodes that had undergone 100 cycles at a current density of 0.5 A g -1 . Figure 13 Figure shows the comparison of the XPS spectra of the Baseline electrolyte electrode and the 4,4'-DMBP prelithiated electrolyte electrode after cycling. Figure 13 In (a) is C 1s, Figure 13 in (b) is Li 1s, Figure 13 in (c) is F 1s. As shown in the C 1s spectrum in (a) of Figure 13 , in addition to the C−C peak at 284.8 eV, the signals at 286.3 and 288.4 eV are respectively related to C-O and C=O bonding, which is attributed to the presence of the sodium polyacrylate binder and the surface functional groups on the electrode. By comparison, it can be found that after 100 cycles, an additional C-C* peak appears at 283.9 eV in the 4,4'-DMBP electrode, indicating a rich electron state. It shows that electrons of 4,4'-DMBP transfer from the aromatic anion radical to the Si anode material and participate in the formation of the SEI film, which enhances the stability of the SEI film. LiF is one of the important components in the SEI film and has good mechanical stability. By comparison Figure 13In (b), it can be found that the LiF content in the 4,4'-DMBP electrode increases significantly. Its high mechanical strength can prevent the decomposition of the electrolyte and adapt to the repeated volume changes of the Si negative electrode. At the same time, although LiF is an ion-insulating layer, the formation of a nanoscale heterojunction between LiF and other inorganic components can meet the ionic conductivity requirements of the SEI film. And Li x PO y F z is an unstable by-product that easily triggers further side reactions, leading to the thickening of the SEI film and the degradation of battery performance.

[0074] Comparative analysis reveals that the peak area ratio of Li x PO y F z in the 4,4'-DMBP electrode decreases significantly, indicating that 4,4'-DMBP significantly improves the stability of the SEI film, thereby extending the cycle life of the battery. In addition, the comparative results show that the peak area ratio of Li2CO3 in 4,4'-DMBP increases significantly. The presence of Li2CO3 can improve the stability and ionic conductivity of the SEI film, reduce the irreversible loss of lithium ions, and thus improve the initial efficiency and cycle stability of the battery. It should be noted that comparative analysis also shows that the organic content in the 4,4'-DMBP electrode increases significantly. These organolithium compounds have certain flexibility and stability, and can form a uniform and elastic coating on the electrode surface. They can not only effectively buffer the volume changes of the silicon negative electrode during charge and discharge, but also improve the lithium ion transmission environment, making the insertion and extraction of lithium ions more uniform, and further enhancing the battery stability. Figure 13 The F spectral comparison results in (c) of Figure 13 are consistent with the spectral results in (b) of

[0075] This further proves that the SEI formed on the 4,4'-DMBP electrode has a balanced organic and inorganic composition, indicating that the addition of 4,4'-DMBP significantly improves the composition and properties of the SEI film, thereby enhancing the initial Coulombic efficiency and cycle stability of the battery. -1, and an excellent capacity retention rate of 79.35%. By matching the LiFeO4 to assemble the full cell, the initial Coulombic efficiency also increased from 77.56% to 86.13%, and the capacity retention rate increased from 50.40% to 72.56%. Further, through various characterization techniques such as XPS, SEM, and CV, the surface chemical composition changes and structural optimization of the silicon anode by the 4,4'-DMBP prelithiated electrolyte were verified. The research results of the present invention show that the prelithiation reagent prepared by 4,4'-DMBP is added to the electrolyte. With its low reduction potential, effectively forming a stable SEI protective layer, and optimizing the negative electrode interface reaction kinetics, it not only significantly improves the first efficiency of the silicon anode but also remarkably improves the cycle stability, providing strong technical support and theoretical basis for the development of high-energy-density lithium-ion batteries and promoting the commercial application process of silicon-based anode materials.

[0076] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, not all of them. Other embodiments can be obtained based on these embodiments without creative efforts, and these embodiments all belong to the protection scope of the present invention.

Claims

1. Application of a lithium-aromatic hydrocarbon complex in prelithiation of a lithium battery, characterized in that, The lithium-aromatic hydrocarbon complex is lithium 4,4'-dimethylbiphenyl, and the raw materials for preparing lithium 4,4'-dimethylbiphenyl include 4,4'-dimethylbiphenyl and lithium metal.

2. The application according to claim 1, characterized in that The preparation method of the lithium 4,4'-dimethylbiphenyl includes the following steps: Mix 4,4'-dimethylbiphenyl, 2-methyltetrahydrofuran and lithium metal for reaction to obtain an organic solution of the lithium 4,4'-dimethylbiphenyl.

3. A preparation method of a prelithiation reagent, characterized in that, It includes the following steps: Mix 4,4'-dimethylbiphenyl, 2-methyltetrahydrofuran and lithium metal to obtain the pre-lithiation reagent.

4. The preparation method according to claim 3, characterized in that, The molar ratio of the lithium metal to the 4,4'-dimethylbiphenyl is 4:

1.

5. A prelithiation reagent, characterized in that, The pre-lithiation reagent is prepared by the preparation method described in claim 3 or 4.

6. A prelithiated electrolyte, characterized in that, It includes a base electrolyte and the pre-lithiation reagent described in claim 5.

7. The prelithiated electrolyte according to claim 6, wherein The mass percentage of the pre-lithiation reagent in the base electrolyte is 1-3%; The base electrolyte includes lithium hexafluorophosphate, fluorinated ethylene carbonate and an organic solvent; the organic solvent includes ethylene carbonate and ethyl methyl carbonate; the molar concentration of lithium hexafluorophosphate in the base electrolyte is 1-1.5 mol / mL, and the volume percentage of the fluorinated ethylene carbonate in the organic solvent is 1-10%.

8. A lithium-ion battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, characterized in that, The electrolyte is the pre-lithiated electrolyte described in claim 6 or 7.

9. The lithium-ion battery according to claim 8, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode material provided on the surface of the negative electrode current collector. The negative electrode material includes a negative electrode active component, and the negative electrode active component is a silicon-containing material; The positive electrode sheet includes a positive electrode current collector and a positive electrode material provided on the surface of the positive electrode current collector. The positive electrode material includes a positive electrode active component, and the positive electrode active component is lithium iron phosphate.

10. A prelithiation method for a silicon-based negative electrode, characterized in that, It includes the following steps: Mix the pre-lithiation reagent described in claim 5 with the base electrolyte to obtain a pre-lithiated electrolyte; Use the pre-lithiated electrolyte and a silicon-based negative electrode to prepare a lithium-ion battery.

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