Pre-lithiation method of silicon-based negative electrode material of lithium ion battery and product of pre-lithiation method

Abstract

The invention provides a pre-lithiation method for a silicon-based negative electrode material of a lithium ion battery. The pre-lithiation method comprises the following steps: (a) dissolving a first biphenyl derivative and a second biphenyl derivative in an organic solvent to form a mixed solution; (b) dissolving a lithium metal in the mixed solution to form a pre-lithiation solvent; and (c) soaking a silicon-based negative electrode material in the pre-lithiation solvent for a predetermined time to obtain a pre-lithiated silicon-based negative electrode material. The invention also provides the silicon-based negative electrode material prepared by the pre-lithiation method, a negative electrode of a lithium ion battery prepared by using the silicon-based negative electrode material, and the lithium ion battery.

Description

Technical Field

[0001] This disclosure relates to a method for pre-lithiation of silicon-based anode materials for lithium-ion batteries and the products thereof, and more particularly to a method for pre-lithiation of silicon-based anode materials using a mixture of two biphenyl derivatives and the products prepared by this method. Background Technology

[0002] The importance of lithium-ion batteries in various application fields such as 3C products and electric vehicles is increasing daily. Improving the energy density of single cells is one of the key development directions for lithium-ion batteries. Developing high-specific-capacity anode materials is one of the means to improve the energy density of lithium-ion cells. Currently, most lithium-ion batteries on the market use graphite as the anode material. However, with the increasing demand for portable and high-performance energy storage devices, graphite, with its theoretical capacity of only 372 mAh / g and drawbacks such as easy delamination and shedding of its layered structure during long cycles, can no longer meet the performance requirements of lithium-ion batteries.

[0003] Compared to graphite, silicon-based materials possess high specific capacity (~3750 mAh / g), effectively improving the energy density of lithium-ion batteries. They can also form binary alloys with lithium and have advantages such as low reactivity with organic solvents, abundant reserves, and low cost. Therefore, introducing silicon-based materials into the anode of lithium-ion batteries to increase their capacity is an effective way to improve battery energy density. However, during the first charge-discharge cycle, silicon-based anode materials undergo an irreversible reaction at the solid electrolyte interface, leading to low initial coulombic efficiency and consequently a loss of actual capacity in the lithium-ion battery.

[0004] To address this issue, pre-lithiation of silicon-based anode materials can compensate for additional lithium-ion losses before charge-discharge cycles, thereby improving lithium-ion battery capacity and cycle performance, and thus mitigating the low initial flux efficiency of silicon-based anode materials. However, insufficient pre-lithiation will fail to improve the low initial flux efficiency, while excessive pre-lithiation will lead to the formation of lithium dendrites during charge-discharge cycles, resulting in a decline in electrode electrochemical performance. Therefore, the lithium supply must be accurately controlled during pre-lithiation. Summary of the Invention

[0005] In view of this, in order to solve the problems existing in the pre-lithiation of silicon-based materials, this disclosure provides a simple and controllable chemical pre-lithiation method to rapidly and effectively pre-lithiate silicon-based materials, and also provides the product prepared by this method and the lithium-ion battery using the product as the negative electrode material.

[0006] The first part of this disclosure provides a method for pre-lithiation of a silicon-based anode material for lithium-ion batteries, comprising: (a) dissolving a first biphenyl derivative and a second biphenyl derivative in an organic solvent to form a mixed solution; (b) dissolving a lithium metal in the mixed solution to form a pre-lithiation solvent; and (c) immersing a silicon-based anode material in the pre-lithiation solvent for a predetermined time to obtain a pre-lithiated silicon-based anode material.

[0007] In some embodiments of the first part of this disclosure, the first biphenyl derivative and the second biphenyl derivative are any two of biphenyl, biphenyl, their methyl-substituted derivatives, their ethyl-substituted derivatives, their propyl-substituted derivatives, or their hydroxy-substituted derivatives. For example, the first biphenyl derivative can be any one of biphenyl, biphenyl, their methyl-substituted derivatives, their ethyl-substituted derivatives, their propyl-substituted derivatives, or their hydroxy-substituted derivatives, and the second biphenyl derivative can be any one of biphenyl, biphenyl, their methyl-substituted derivatives, their ethyl-substituted derivatives, their propyl-substituted derivatives, or their hydroxy-substituted derivatives.

[0008] In some embodiments of the first part of this disclosure, the first biphenyl derivative and the second biphenyl derivative are any two of biphenyl, dimethylbiphenyl, tetramethylbiphenyl, diethylbiphenyl, or dihydroxybiphenyl, or dipropylbiphenyl. For example, the first biphenyl derivative can be any one of biphenyl, dimethylbiphenyl, tetramethylbiphenyl, diethylbiphenyl, or dihydroxybiphenyl, or dipropylbiphenyl, and the second biphenyl derivative can be any one of biphenyl, dimethylbiphenyl, tetramethylbiphenyl, diethylbiphenyl, or dihydroxybiphenyl, or dipropylbiphenyl.

[0009] In some embodiments of the first part of this disclosure, the dimethylbiphenyl may be 2,2'-dimethylbiphenyl, 2,3'-dimethylbiphenyl, 2,4'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 3,4'-dimethylbiphenyl, or 4,4'-dimethylbiphenyl.

[0010] In some embodiments of the first part of this disclosure, the tetramethylbiphenyl may be 2,2',6,6'-tetramethylbiphenyl, 2,3,3',5'-tetramethylbiphenyl, 2,3,4,5-tetramethylbiphenyl, 2,3,5,6-tetramethylbiphenyl, 2,3,6,7-tetramethylbiphenyl, 2,4,5,7-tetramethylbiphenyl, 3,3',4,4'-tetramethylbiphenyl, or 3,3',5,5'-tetramethylbiphenyl.

[0011] In some embodiments of the first part of this disclosure, the diethylbiphenyl may be 2,2'-diethylbiphenyl, 2,3'-diethylbiphenyl, 2,4'-diethylbiphenyl, 3,3'-diethylbiphenyl, 3,4'-diethylbiphenyl, or 4,4'-diethylbiphenyl.

[0012] In some embodiments of the first part of this disclosure, the dihydroxybiphenyl may be 2,2'-dihydroxybiphenyl, 2,3'-dihydroxybiphenyl, 2,4'-dihydroxybiphenyl, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, or 4,4'-dihydroxybiphenyl.

[0013] In some embodiments of the first part of this disclosure, the dipropylbiphenyl may be 2,2'-dipropylbiphenyl, 2,3'-dipropylbiphenyl, 2,4'-dipropylbiphenyl, 3,3'-dipropylbiphenyl, 3,4'-dipropylbiphenyl, or 4,4'-dipropylbiphenyl.

[0014] In some embodiments of the first part of this disclosure, the first biphenyl derivative and the second biphenyl derivative are biphenyl, 3,3'-dimethylbiphenyl, 4,4'-dimethylbiphenyl, 3,3',4,4'-tetramethylbiphenyl, 4,4'-dihydroxybiphenyl, or 4,4'-diisopropylbiphenyl.

[0015] In some embodiments of the first part of this disclosure, the first biphenyl derivative and the second biphenyl derivative are 4,4'-dimethylbiphenyl and 4,4'-diethylbiphenyl.

[0016] In some embodiments of the first part of this disclosure, the first biphenyl derivative and the second biphenyl derivative are mixed in a molar ratio of 1 to 4:1, and preferably, the first biphenyl derivative and the second biphenyl derivative are mixed in a molar ratio of 1 to 2:1.

[0017] The second part of this disclosure provides a silicon-based anode material, wherein the silicon-based anode material is prepared by the pre-lithiation method for lithium-ion battery silicon-based anode materials as described above.

[0018] The third part of this disclosure provides a negative electrode for a lithium-ion battery, comprising the pre-lithiated silicon-based negative electrode material as described above.

[0019] Part IV of this disclosure provides a lithium-ion battery including a negative electrode, wherein the negative electrode uses a pre-lithiated silicon-based negative electrode material as described above.

[0020] This disclosure provides a simple and controllable chemical pre-lithiation method for silicon-based materials. Unlike prior art methods that use a single biphenyl derivative, this method involves dissolving two biphenyl derivatives in a specific ratio in an organic solvent, followed by dissolving lithium metal in the solvent. This results in a lithium-biphenyl complex with a lower redox potential, which is more conducive to rapid and efficient pre-lithiation through simple immersion of the silicon-based anode material. The product obtained by this pre-lithiation method can effectively improve the low initial coulombic efficiency of lithium-ion batteries, and because it can form strong CF bonds, it is more conducive to the formation of a more stable SEI layer, thereby significantly improving the cycle stability of lithium-ion batteries. Attached Figure Description

[0021] This disclosure will be better understood when the following detailed description is read in conjunction with the accompanying drawings, in which:

[0022] Figure 1 This is a flowchart of a pre-lithiation method for a silicon-based anode material for a lithium-ion battery according to an embodiment of this disclosure.

[0023] Figure 2A and Figure 2B These are XPS analysis data graphs of un-lithiated and pre-lithiated silicon-carbon anode materials according to one embodiment of this disclosure. The horizontal axis represents binding energy (eV), and the vertical axis represents intensity (au).

[0024] Figure 3 It is Figure 2A and Figure 2B XPS analysis data of unlithiated and prelithiated silicon-carbon anode materials after one charge-discharge cycle. (a) and (b) represent unlithiated silicon-carbon anode materials; (c) and (d) represent prelithiated silicon-carbon anode materials. The horizontal axis represents binding energy (eV); the vertical axis represents intensity (au).

[0025] Figure 4 These are XPS analysis data graphs of a pre-lithiated silicon-carbon anode material according to an embodiment of this disclosure. (a) and (b) represent pre-lithiated silicon-carbon anode materials prepared by mixing dimethylbiphenyl and diethylbiphenyl in a 1:1 ratio; (c) and (d) represent pre-lithiated silicon-carbon anode materials prepared by mixing dimethylbiphenyl and diethylbiphenyl in a 2:1 ratio; and (e) and (f) represent pre-lithiated silicon-carbon anode materials prepared by mixing dimethylbiphenyl and diethylbiphenyl in a 3:1 ratio. The horizontal axis represents binding energy (eV), and the vertical axis represents intensity (au). Detailed Implementation

[0026] The following description contains specific information about the illustrative embodiments in this disclosure. The accompanying drawings and detailed descriptions in this disclosure are only for illustrative embodiments. However, this disclosure is not limited to these illustrative embodiments. Other variations and embodiments of this disclosure will be recognized by those skilled in the art.

[0027] The terms "at least one embodiment," "one embodiment," "multiple embodiments," "different embodiments," "some embodiments," and "this embodiment" indicate that the embodiments described herein may include specific features, components, or characteristics. However, not every possible embodiment of this disclosure must include specific features, components, or characteristics. Furthermore, the repeated use of the phrases "in one embodiment" and "in this embodiment" does not necessarily refer to the same embodiment, although they may be identical. Moreover, the use of phrases such as "embodiment" in connection with "this disclosure" does not imply that all embodiments of this disclosure must include specific features, components, or characteristics, and should be understood as "at least some embodiments of this disclosure" including the stated specific features, components, or characteristics.

[0028] The terms "first" and "second," etc., used in this disclosure and the aforementioned drawings are used to distinguish different objects and not to describe a specific order. Furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps is not limited to the steps listed, but may optionally include steps not listed, or may optionally include other steps inherent to those processes, methods, products, or apparatus.

[0029] This disclosure provides a simple and controllable chemical pre-lithiation method for silicon-based materials. Unlike prior art that uses a single biphenyl derivative, this disclosure dissolves two biphenyl derivatives in an organic solvent in a specific ratio, then dissolves lithium metal in the solvent, and finally immerses the silicon-based anode material in the mixed solution for several minutes before washing it with the organic solvent to complete the pre-lithiation.

[0030] Pre-lithiation of silicon-based anode materials involves covering the surface separating the active material layer and the current collector with a thin SEI layer, while simultaneously embedding lithium within the silicon particles. Before assembling a lithium-ion battery, this SEI layer reduces the consumption of available lithium within the material and isolates organic solvents from the internal components. Furthermore, the pre-lithiated silicon-based anode material contains lithium-intercalated compounds, which reduces the consumption of available lithium during charge and discharge, thereby improving the initial coulombic efficiency of the silicon-based anode material. This ensures increased energy density and improved cycle stability in lithium-ion battery applications.

[0031] The present disclosure will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] Figure 1 This is a flowchart of a pre-lithiation method 100 for a silicon-based anode material for a lithium-ion battery according to an embodiment of this disclosure. Because there are various ways to perform the pre-lithiation method 100, therefore... Figure 1 The pre-lithiation method 100 shown is merely an example. Figure 1 Each step shown in the diagram may represent one or more processes, methods, or subroutines being performed, and additional steps may be added between each step without causing the essence of the pre-lithiation method 100 to deviate from the scope of the technical solution of the pre-lithiation method 100.

[0033] This disclosure provides a method for pre-lithiation of a silicon-based anode material for lithium-ion batteries, comprising: (a) dissolving a first biphenyl derivative and a second biphenyl derivative in an organic solvent to form a mixed solution; (b) dissolving a lithium metal in the mixed solution to form a pre-lithiation solvent; and (c) immersing a silicon-based anode material in the pre-lithiation solvent for a predetermined time to obtain a pre-lithiated silicon-based anode material.

[0034] In the pre-lithiation method for silicon-based anode materials for lithium-ion batteries disclosed herein, two biphenyl derivatives in a specific ratio are dissolved in an organic solvent and then combined with subsequently added lithium metal to form a lithium-biphenyl complex. Pre-lithiation can then be performed by simply immersing the silicon-based anode material. This pre-lithiation method for silicon-based anode materials for lithium-ion batteries can accurately control the lithium supply during the pre-lithiation process, thereby effectively improving the low initial coulombic efficiency of the silicon-based anode material and forming a more stable SEI layer.

[0035] In some embodiments, the first biphenyl derivative and the second biphenyl derivative can be any two of biphenyl, bipolyphenyl, its methyl-substituted derivative, its ethyl-substituted derivative, its propyl-substituted derivative, or its hydroxy-substituted derivative. In some embodiments, the first biphenyl derivative and the second biphenyl derivative are preferably any two of biphenyl, dimethylbiphenyl, tetramethylbiphenyl, diethylbiphenyl, or dihydroxybiphenyl, dipropylbiphenyl. In some embodiments, the first biphenyl derivative and the second biphenyl derivative are preferably dimethylbiphenyl and diethylbiphenyl. In some embodiments, the first biphenyl derivative or the second biphenyl derivative is preferably 4,4'-dimethylbiphenyl or 4,4'-diethylbiphenyl.

[0036] The redox potential (RPo) of chemical pre-lithiation reagents, relative to the RPo of silicon-based materials, significantly affects the effectiveness of pre-lithiation of silicon-based materials. For example, biphenyl has an RPo of 0.33 V. When a lithium-biphenyl complex is used as a chemical pre-lithiation reagent, it is higher than the RPo of silicon-based materials (~0.2 V). Therefore, the lithium-biphenyl complex can only form an SEI layer on the surface of silicon-based anode material particles and will not intercalate lithium into the bulk silicon phase inside the particles. However, by introducing different functional groups into biphenyl, its RPo can be lower than that of silicon-based materials. For example, introducing methyl or ethyl groups can reduce it to 0.19 V and 0.13 V, respectively, making it a potential compound for effective reducing agents. Furthermore, different biphenyl derivatives have different reducing abilities. Therefore, by controlling the mixing ratio of biphenyl derivatives with different functional groups, a pre-lithiation solution for silicon anodes can be prepared.

[0037] Controlling the reduction capability is crucial for the pre-lithiation process. If the lithiation process is too fast and uneven, it will cause uneven internal stress distribution when lithium ions are inserted into the material, making the material prone to cracking and resulting in a decrease in charge capacity. In addition, if the lithiation process is too fast and excessive lithium is inserted into the material, phenomena such as lithium dendrites may occur, causing a short circuit in the battery. However, if the lithiation process is too slow, not only will the pre-lithiation process fail to achieve the expected goal of inserting sufficient lithium into the material, but the extended immersion time of the negative electrode to achieve sufficient lithium will cause the negative electrode to expand significantly, thereby increasing the thickness of the finished battery and causing battery deformation and assembly difficulties.

[0038] Therefore, in the pre-lithiation method for silicon-based anode materials for lithium-ion batteries disclosed herein, a biphenyl derivative composed in a specific ratio can yield a pre-lithiation reagent with a low redox potential. Furthermore, adjusting the mixing ratio of dimethylbiphenyl and diethylbiphenyl to select an appropriate reaction rate and soaking time is essential for the pre-lithiation treatment of the anode material. Based on test results, a pre-lithiation solution using a 1–4:1 molar ratio of dimethylbiphenyl to diethylbiphenyl can control the lithium supply during the pre-lithiation process, thereby enabling rapid and efficient pre-lithiation of the silicon-based material and achieving optimal electrochemical performance.

[0039] In some embodiments, the first biphenyl derivative and the second biphenyl derivative may be a mixture of dimethylbiphenyl and diethylbiphenyl in a molar ratio of 1 to 4:1. In some embodiments, the first biphenyl derivative and the second biphenyl derivative are preferably a mixture of dimethylbiphenyl and diethylbiphenyl in a molar ratio of 1 to 2:1. In some embodiments, the first biphenyl derivative and the second biphenyl derivative are preferably a mixture of dimethylbiphenyl and diethylbiphenyl in a molar ratio of 2:1.

[0040] In some embodiments, the organic solvent may be an ether or furan solution, such as tetrahydrofuran, 1,2-dimethoxyethane, butyl methyl ether, 2-methyltetrahydrofuran, or diethylene glycol dimethyl ether. In some embodiments, the mixture of the first biphenyl derivative and the second biphenyl derivative may be mixed with the organic solvent to form a mixed solution with a concentration of 0.2–1 M (mol / L), preferably 0.5 M. For example, the first biphenyl derivative and the second biphenyl derivative may be mixed to a total molar amount of 5 mmol and then added to 10 mL of organic solvent to prepare a 0.5 M mixed solution.

[0041] In some embodiments, the lithium metal may be any one or more of lithium powder, lithium foil, lithium sheets, or lithium blocks. In some embodiments, the mixed solution (comprising a mixture of a first biphenyl derivative, a second biphenyl derivative, and the organic solvent) and the lithium metal may be mixed with the mixture of the first biphenyl derivative and the second biphenyl derivative at a molar ratio of 1 to 4:1 to form the pre-lithiation solvent, preferably 1.15:1. The addition of excess lithium is primarily to ensure sufficient lithium to react with the biphenyl derivative to form the pre-lithiation solvent.

[0042] In some embodiments, the silicon-based anode material can be pure silicon, silicon-carbon, silicon-oxygen, or any combination of two or more thereof. Examples include silicon oxide (SiOx), graphite / silicon composites (Graphite / Si), silicon nanoparticles, silicon oxide / carbon composites (SiOx / C), or silene derived from calcium disilicide (CaSi2).

[0043] In some embodiments, the silicon-based anode material is simply immersed in the pre-lithiation solvent for a predetermined time, and then the remaining pre-lithiation solution on the silicon-based anode material is washed with the organic solvent without any added solvent, and further pre-lithiation reaction is stopped. This completes the pre-lithiation process, and a pre-lithiated silicon-based anode material with excellent performance can be obtained quickly. In some embodiments, the predetermined time can be 10 to 60 minutes, for example: 2 minutes, 5 minutes, 10 minutes, 30 minutes, or 60 minutes, preferably 10 to 50 minutes, more preferably 20 to 40 minutes, and most preferably 30 minutes. Generally, the longer the immersion time, the higher the degree of pre-lithiation. In some embodiments, the temperature at which the silicon-based anode material is simply immersed in the pre-lithiation solvent can be room temperature, for example, 25°C to 30°C. In some embodiments, when the active material in a single electrode composed of silicon-based anode material weighs about 0.8 to 1 mg, the amount of pre-lithiation solvent used can range from 0.5 to 1 mL, preferably 1 mL.

[0044] This disclosure further provides a silicon-based anode material, wherein the silicon-based anode material is prepared by the aforementioned pre-lithiation method for silicon-based anode materials in lithium-ion batteries.

[0045] This disclosure further provides a negative electrode for a lithium-ion battery, including a silicon-based negative electrode material prepared by the aforementioned pre-lithiation method.

[0046] This disclosure further provides a lithium-ion battery, including a negative electrode, wherein the negative electrode is prepared using a silicon-based negative electrode material prepared by the aforementioned pre-lithiation method.

[0047] The present disclosure is further described below through several sets of embodiments (i.e., Embodiment 1 to Embodiment 2), but the present disclosure is not limited to these embodiments. Example 1

[0048] Dimethylbiphenyl and diethylbiphenyl were mixed in a 1:1 molar ratio and dissolved in 1,2-dimethoxyethane to prepare a 0.5M solution. The solution was stirred until completely dissolved, and then lithium metal was dissolved in the solution in a 2:1 molar ratio. The mixture was stirred continuously at room temperature for 1 hour to form a blue-green lithium-aromatic hydrocarbon complex (LAC) solution, which is the pre-lithiation solvent disclosed herein. For example, dimethylbiphenyl and diethylbiphenyl were mixed in a 1:1 molar ratio to a total molar amount of 5 mmol, dissolved in 10 mL of 1,2-dimethoxyethane, and 69.4 mg of lithium metal was added. The silicon-carbon anode material was then immersed in 1 mL of this pre-lithiation solvent and allowed to react at room temperature for 30 minutes to obtain the pre-lithiated silicon-carbon anode material disclosed herein. An unlithiated silicon-carbon anode material was used as a comparative example.

[0049] Next, X-ray photoelectron spectroscopy (XPS) was used to analyze the silicon-carbon anode materials before and after lithiation. The results are as follows: Figure 2A and 2B As shown, similar C peaks attributable to Si-C, CC, and COC bonds can be observed in both unlithiated and prelithiated silicon-carbon anode materials; however, CO32- is observed only in prelithiated silicon-carbon anode materials. 2 The peak is attributed to the formation of Li2CO3 bonds. It is worth noting that the LixSiy peak, which is attributed to lithium intercalation in the silicon-carbon anode material, was also observed only in the pre-lithiated silicon-carbon anode material. Therefore, this result indicates that the pre-lithiation method has indeed been successfully performed.

[0050] Furthermore, to observe the SEI layer formed during the pre-lithiation process of silicon-based anode materials, the aforementioned unlithiated and prelithiated silicon-carbon anode materials were paired with lithium sheets to form a half-cell, and after one charge-discharge cycle, XPS analysis was performed. The results are as follows: Figure 3 As shown in the figure. The charge / discharge conditions were as follows: constant current discharge at a current density of 200 mA / g to 0.01 V, followed by charging at the same current density of 200 mA / g to 1.5 V, and then constant voltage charging to maintain the negative electrode material at 1.5 V to ensure complete delithiation and maintain its material structure containing SEI. The results show that LiF peaks attributable to SEI formation can be observed in both cases. However, the silicon-carbon negative electrode material after pre-lithiation treatment has a significantly stronger CF peak, which is conducive to the formation of a more stable SEI layer.

[0051] These results show that pre-lithiation of silicon-based anode materials using the method provided in this disclosure can not only effectively form an SEI layer on the surface of silicon-based anode material particles, but also reliably intercalate lithium into the particles of silicon-based materials. Example 2

[0052] To compare the effect of pre-lithiation with different proportions of biphenyl derivatives on the resulting silicon-based anode materials, dimethylbiphenyl and diethylbiphenyl were mixed in molar ratios of 1:1, 2:1, 3:1, and 4:1, respectively, and dissolved in 1,2-dimethoxyethane to prepare a 0.5M solution. After complete dissolution, lithium metal was dissolved in the solution at a 2:1 molar ratio, and the mixture was stirred continuously at room temperature for 1 hour to form a blue-green LAC solution, which is the pre-lithiation solvent disclosed herein. For example, dimethylbiphenyl and diethylbiphenyl were mixed in molar ratios of 1:1, 2:1, 3:1, and 4:1 to a total molar amount of 5 mmol, dissolved in 10 mL of 1,2-dimethoxyethane, and 69.4 mg of lithium metal was added. The silicon-carbon anode material was then immersed in 1 mL of this pre-lithiation solvent and allowed to react at room temperature for 30 minutes, resulting in four silicon-carbon anode materials pre-lithiated with different proportions of biphenyl derivatives. The unlithiated silicon-carbon anode material was used as a comparative example.

[0053] Next, the four pre-lithiated silicon-carbon anode materials were subjected to one charge-discharge cycle, and then analyzed using XPS. The results are as follows: Figure 4 As shown, CO3 generated attributable to Li2CO3 bonds can be observed in all of them. 2 All of them have LiF peaks attributable to SEI generation, with the strongest CF peak observed in the system with a 2:1 mixing ratio, which is conducive to the formation of a more stable SEI layer.

[0054] In addition, the aforementioned four pre-lithiated silicon-carbon anode materials were also prepared into lithium-ion batteries for electrochemical testing. The specific method for preparing the lithium-ion batteries is as follows: First, the pre-lithiated silicon-carbon anode material was uniformly mixed with a conductive agent and a binder in a specific ratio to prepare an anode slurry. Then, the slurry was uniformly mixed by micro-ball milling and coated onto copper foil (current collector) with a scraper. It was then placed in a vacuum oven and dried under vacuum at 80°C for 1 hour. After drying, it was cut into 12mm electrode sheets using a pressing machine. Finally, the lithium sheet was used as the counter electrode to obtain a coin-type lithium-ion battery.

[0055] In some embodiments, the conductive agent can be Super P carbon black, multi-walled carbon nanotubes (MWCNTs), acetylene black, or Ketjin black; in this embodiment, multi-walled carbon nanotubes are used. In some embodiments, the adhesive can be a mixture of sodium carboxymethyl cellulose (NaCMC), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), or LA133 adhesive; in this embodiment, polyacrylic acid is used. In some embodiments, the mixing ratio of the pre-lithiated silicon carbon anode material, conductive agent, and adhesive can be 8:1:1, 7:2:1, 6:2:2, or 7:1.5:1.5. The ratio of the pre-lithiated silicon carbon anode material, conductive agent, and adhesive can be adjusted as needed and can be any combination of the above ratios; in this embodiment, a mixing ratio of 7:1.5:1.5 is used.

[0056] The results of the electrochemical tests are shown in Table 1 below. It can be observed that the lithium-ion batteries made from the four pre-lithiated silicon-carbon anode materials can significantly improve the problem of low initial coulombic efficiency, and the product made from a 2:1 mixture of dimethylbiphenyl and diethylbiphenyl has the best performance. Table 1

[0057] These results show that pre-lithiation of silicon-based anode materials using the method disclosed herein can not only effectively improve the low initial coulombic efficiency of lithium-ion batteries, but also form strong CF bonds, which is conducive to the formation of a more stable SEI layer, thereby improving the cycle stability of lithium-ion batteries.

[0058] In summary, unlike methods using a single biphenyl derivative, the pre-lithiation method for silicon-based materials disclosed herein involves dissolving two biphenyl derivatives in an organic solvent at a specific ratio to form a complex with lithium metal, resulting in a lower redox potential. This approach facilitates rapid and efficient pre-lithiation through simple immersion of the silicon-based anode material. The product obtained using this pre-lithiation method effectively improves the low initial coulombic efficiency of lithium-ion batteries, and the formation of strong CF bonds further promotes the formation of a more stable SEI layer, thereby significantly improving the cycle stability of lithium-ion batteries.

[0059] Based on the above description, it is evident that various techniques can be used to implement the concepts described in this application without departing from the scope of these concepts. Furthermore, although the concepts have been described with specific reference to certain embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the scope of these concepts. Thus, the described embodiments are to be considered illustrative rather than restrictive in all respects. Moreover, it should be understood that this application is not limited to the specific embodiments described above, but many rearrangements, modifications, and substitutions can be made without departing from the scope of this disclosure.

Claims

1. A method of pre-lithiation of a silicon-based anode material for lithium-ion batteries, comprising: (a) dissolving a first biphenyl derivative and a second biphenyl derivative in an organic solvent to form a mixed solution; (b) dissolving a lithium metal in the mixed solution to form a pre-lithiation solvent; and (c) soaking a silicon-based anode material in the pre-lithiation solvent for a predetermined time to obtain a pre-lithiated silicon-based anode material.

2. The method of pre-lithiation of a lithium-ion battery silicon-based anode material according to claim 1, characterized in that, The first biphenyl derivative is selected from any one of biphenyl, bitolyl, a methyl-substituted derivative thereof, an ethyl-substituted derivative thereof, a propyl-substituted derivative thereof, or a hydroxyl-substituted derivative thereof; and the second biphenyl derivative is selected from any one of biphenyl, bitolyl, a methyl-substituted derivative thereof, an ethyl-substituted derivative thereof, a propyl-substituted derivative thereof, or a hydroxyl-substituted derivative thereof.

3. The method of pre-lithiation of a lithium-ion battery silicon-based anode material according to claim 2, characterized in that, The first biphenyl derivative is any one of biphenyl, dimethyl biphenyl, tetramethyl biphenyl, diethyl biphenyl, or dihydroxy biphenyl, dipropyl biphenyl; and the second biphenyl derivative is any one of biphenyl, dimethyl biphenyl, tetramethyl biphenyl, diethyl biphenyl, or dihydroxy biphenyl, dipropyl biphenyl.

4. The method of pre-lithiation of a lithium-ion battery silicon-based anode material according to claim 3, characterized in that, The first biphenyl derivative is dimethyl biphenyl, and the second biphenyl derivative is diethyl biphenyl.

5. The method of pre-lithiation of a lithium-ion battery silicon-based anode material according to claim 4, characterized in that, The first biphenyl derivative is 4,4’-dimethyl biphenyl, and the second biphenyl derivative is 4,4’-diethyl biphenyl.

6. The method of pre-lithiation of a lithium-ion battery silicon-based anode material according to any one of claims 2 to 5, characterized in that, The first biphenyl derivative and the second biphenyl derivative are mixed at a molar ratio of 1-4:

1.

7. The method of pre-lithiation of a lithium-ion battery silicon-based anode material according to any one of claims 2 to 5, characterized in that, The first biphenyl derivative and the second biphenyl derivative are mixed at a molar ratio of 1-2:

1.

8. A silicon-based anode material, wherein the silicon-based anode material is prepared by the pre-lithiation method of a lithium ion battery silicon-based anode material according to any one of claims 1-5.

9. An anode of a lithium ion battery, comprising the silicon-based anode material according to claim 8.

10. A lithium ion battery, comprising the anode according to claim 9.

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