Pre-lithiated silver-coated silicon-carbon material, method of making and use thereof

Abstract

This invention provides a pre-lithiated silver-plated silicon-carbon material, its preparation method, and its application. The preparation method includes: silicon particles, a silver source, a reducing agent, and a polymerization stabilizer are sequentially reacted and subjected to a first calcination to obtain a first product; the first product and a carbon matrix are sequentially mixed and subjected to a second calcination to obtain a second product; the second product and a pre-lithiating agent are sequentially mixed and subjected to a third calcination to obtain a third product; the third product is sequentially subjected to carbon coating and acid washing to obtain the pre-lithiated silver-plated silicon-carbon material. This invention is based on a strategy of silver coating combined with pre-lithiation. By coating silicon particles with silver and performing pre-lithiation treatment, it achieves the goal of optimizing the structure of silicon-carbon anode materials and improving their electrochemical performance. Ultimately, it significantly improves the structural stability and cycle life of the obtained pre-lithiated silver-plated silicon-carbon material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a pre-lithiated silver-plated silicon-carbon material, its preparation method, and its application. Background Technology

[0002] Silicon, due to its extremely high theoretical specific capacity (approximately 4200 mAh / g), is considered a key candidate for next-generation high-energy-density lithium-ion battery anode materials. However, silicon materials undergo significant volume changes (approximately 300%) during charge and discharge, leading to several major technical challenges that severely hinder its commercialization. Firstly, silicon-carbon particles fracture during cell cycling, and leakage of nano-silicon particles can easily cause negative reactions with the electrolyte. Secondly, silicon-carbon anodes suffer from low initial efficiency. Thirdly, silicon-carbon anodes exhibit poor high-rate charging performance, and their conductivity requires further improvement.

[0003] To address these issues, researchers have proposed a composite material concept that embeds silicon into a porous carbon matrix. This aims to utilize the elastic buffering effect of the carbon matrix to alleviate the stress caused by silicon volume changes, while simultaneously enhancing the overall conductivity of the material. Chemical vapor deposition (CVD) is a commonly used method for depositing silicon nanoparticles on a carbon matrix. However, this method also faces several challenges. On the one hand, although the carbon matrix can mitigate the volume effect to some extent, under high compaction density and high cycling rates, the buffering effect of the carbon matrix becomes limited, and silicon particles may still crack, leading to direct contact with the electrolyte and exacerbating side reactions. On the other hand, during CVD, the porous structure of the carbon framework easily adsorbs residual gases, affecting the uniform adsorption and reaction of subsequent silicon source gases, resulting in uneven distribution of silicon particles and further impacting the electrochemical performance of the material.

[0004] To address these issues, researchers have explored various strategies. For example, adding specific additives to improve the pore structure of the carbon framework and reduce gas adsorption; pre-mixing silicon and carbon using physical methods such as mechanical alloying or ball milling followed by high-temperature heat treatment to enhance interfacial bonding; and exploring novel carbon sources, such as biochar and graphene, to optimize carbon properties and improve overall material performance. However, these methods often only partially solve the problems or introduce additional production costs and complexities. A comprehensive solution that simultaneously addresses the issues of low conductivity, structural stability, and initial coulombic efficiency in silicon-carbon composites has yet to be found.

[0005] Therefore, how to provide a new method for preparing pre-lithiated silver-plated silicon-carbon materials and obtain pre-lithiated silver-plated silicon-carbon materials that can take into account both high electrochemical activity and long cycle stability is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to provide a pre-lithiated silver-plated silicon-carbon material, its preparation method and application, in order to solve the problem that silicon-carbon anode materials in the prior art are difficult to simultaneously possess high electrochemical activity and long cycle stability.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a pre-lithiated silver-plated silicon-carbon material, comprising: step S1, in which silicon particles, a silver source, a reducing agent, and a polymerization stabilizer are sequentially reacted and subjected to a first calcination to obtain a first product; step S2, in which the first product and a carbon matrix are sequentially mixed and subjected to a second calcination to obtain a second product; step S3, in which the second product and a pre-lithiating agent are sequentially mixed and subjected to a third calcination to obtain a third product; and step S4, in which the third product is sequentially subjected to carbon coating treatment and acid washing treatment to obtain the pre-lithiated silver-plated silicon-carbon material. The above preparation method, through a series of carefully designed steps, achieves the transformation from silicon particles to silver coating and then to a carbon matrix composite material. The resulting pre-lithiated silver-plated silicon-carbon material not only possesses excellent electronic conductivity and structural stability but also significantly improves the initial coulombic efficiency, reduces lithium loss during charge and discharge, and avoids the formation of lithium dendrites, thereby significantly improving the cycle performance and safety of lithium-ion batteries. In addition, the dual effects of silver coating and pre-lithiation help the material maintain high electrochemical activity, ensuring that the material can maintain good capacity retention and cycle stability even under high charge and discharge conditions.

[0008] Further, in step S1, the molar ratio of silicon particles, silver source, reducing agent, and stabilizer is 1:(0.8~20):(2~20):(0.001~0.002); and / or, the D50 of the silicon particles is 20nm~80nm; and / or, the silver source is silver nitrate and / or AgC2H3O2; and / or, the reducing agent is selected from one or more of triethanolamine, n-butylamine, ethylenediamine, and diethylamine; and / or, the stabilizer is selected from one or more of citric acid, oxalic acid, tartaric acid, and sodium ethylenediaminetetraacetate. The preferred molar ratios and the preferred types of raw materials enable the uniform deposition of the silver coating layer and the stable bonding of the nano-silicon particles.

[0009] Further, in step S1, the reaction is carried out by stirring for 10-120 minutes at a speed of 100-200 rpm; and / or, the holding temperature for the first calcination is 700-900℃ for 0.5-2.0 hours. The optimal conditions for stirring and the first calcination process described above are designed to solidify the silver coating and enhance the structural integrity of the material.

[0010] Further, in step S2, the weight ratio of the first product to the carbon matrix is ​​1:(4~5); and / or, the D50 of the carbon matrix is ​​10μm~20μm; and / or, the carbon matrix has a porous structure with a pore diameter of 20nm~100nm and a porosity of 50%~75%; and / or, the holding temperature for the second calcination is 600℃~900℃, and the holding time is 0.5h~2.0h. By further optimizing the weight ratio of the first product to the carbon matrix and the second calcination conditions in step S2, silver-coated silicon particles can be more effectively embedded into the porous carbon framework, forming a more structurally stable composite material.

[0011] Further, in step S3, the weight ratio of the second product to the pre-lithiation agent is 1:(0.1~0.2); and / or, the pre-lithiation agent is selected from one or more of LiOH, LiCl, LiH, Li2CO3, LiNO3, and LiF; and / or, the holding temperature of the third calcination is 600℃~1100℃, and the holding time is 6h~12h. The above-mentioned weight ratio of the second product to the pre-lithiation agent, combined with the third calcination, can more fully achieve pre-lithiation of the material, thereby better compensating for the consumption of lithium ions during the first charge and discharge cycle, significantly improving the coulombic efficiency of the material during the first charge and discharge cycle, and also reducing side reactions during cycling, further improving the electrochemical performance of the obtained material.

[0012] Furthermore, in step S4, the carbon-coated product obtained after carbon coating treatment includes a third product and a carbon layer coated on the surface of the third product; the carbon layer content is 1% to 6% based on the total weight of the carbon-coated product as 100%. The above-mentioned carbon coating treatment method and the preferred composition of the obtained product can further enhance the electronic conductivity and mechanical stability of the final composite material.

[0013] Further, in step S4, the washing solution used for acid pickling includes an acid pickling agent and an acid solution. The acid pickling agent is selected from one or more of Na2HPO4, Na2(COO)2, Li2HPO4, Li2(COO)2, NaF, and LiF, and the acid solution is selected from one or more of acetic acid, citric acid, formic acid, ascorbic acid, and phosphoric acid. In the washing solution, the concentration of the acid pickling agent is 3 g / L to 5 g / L, and the concentration of the acid solution is 10 g / L to 15 g / L. In the above preferred embodiment, the optimization of the type and mass concentration of the acid pickling agent can further optimize the surface state of the material while cleaning it, thereby improving the electrochemical activity of the resulting composite material. The optimization of the acid pickling conditions can better balance the requirements of cleaning effect and structural integrity, reduce possible material damage and excessive corrosion, and thus better maintain the microstructural stability and electrochemical activity of the obtained pre-lithiated silver-plated silicon-carbon material while removing residual impurities. In practical applications, the above preparation method also includes drying the product after acid pickling to obtain the pre-lithiated silver-plated silicon-carbon material product.

[0014] A second aspect of the present invention provides a pre-lithiated silver-plated silicon-carbon material, which is prepared by the above-described method for preparing pre-lithiated silver-plated silicon-carbon materials. Based on the microstructure optimization and performance regulation during the above-described preparation method, the obtained pre-lithiated silver-plated silicon-carbon material exhibits excellent electrochemical performance, such as improved initial coulombic efficiency, enhanced cycle stability, and improved fast-charging capability.

[0015] A third aspect of the present invention provides a negative electrode sheet comprising an active material layer including the aforementioned pre-lithiated silver-plated silicon-carbon material. By integrating the high-performance pre-lithiated silver-plated silicon-carbon material into the negative electrode sheet, the resulting negative electrode sheet exhibits higher electrical performance and longer cycle life, and can serve as an electrode assembly with high activity and stability to support the battery.

[0016] A fourth aspect of the present invention provides a lithium-ion battery comprising the aforementioned negative electrode sheet. Utilizing the high-performance pre-lithiated silver-plated silicon-carbon material in the negative electrode sheet, it exhibits excellent electronic conductivity and structural stability, and also prevents the formation of lithium dendrites during charge and discharge. Therefore, the lithium-ion battery in this configuration not only boasts higher initial efficiency but also demonstrates superior capacity retention and cycle stability under high-rate charge and discharge conditions.

[0017] By applying the technical solution of this invention, based on a strategy of silver coating combined with pre-lithiation, the structure of silicon-carbon anode materials is optimized and their electrochemical performance is improved through silver coating and pre-lithiation treatment of silicon particles. The silver coating layer not only enhances electronic conductivity and suppresses lithium dendrites but also effectively prevents side reactions between nano-silicon and the electrolyte. The pre-lithiation treatment further compensates for lithium ion consumption during the first cycle, optimizes SEI film formation, and ultimately significantly improves the structural stability and cycle life of the resulting pre-lithiated silver-plated silicon-carbon material. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0019] As described in the background section, existing silicon-carbon anode materials suffer from the problem of simultaneously possessing high electrochemical activity and long-term cycle stability. To address this technical problem, a first aspect of the present invention provides a method for preparing a pre-lithiated silver-plated silicon-carbon material, comprising: step S1, where silicon particles, a silver source, a reducing agent, and a polymerization stabilizer are sequentially reacted and subjected to a first calcination to obtain a first product; step S2, where the first product and a carbon matrix are sequentially mixed and subjected to a second calcination to obtain a second product; step S3, where the second product and a pre-lithiating agent are sequentially mixed and subjected to a third calcination to obtain a third product; and step S4, where the third product is sequentially subjected to carbon coating treatment and acid washing treatment to obtain the pre-lithiated silver-plated silicon-carbon material.

[0020] This invention, based on a silver-coating combined with pre-lithiation strategy, solves the key problems of poor conductivity, particle cracking during cycling, and low initial coulombic efficiency in existing silicon-carbon anode materials by silver-coating silicon particles and performing pre-lithiation treatment. Specifically, in the above preparation process:

[0021] In step S1, silicon particles, acting as the core of the active material, react with a silver source, a reducing agent, and a stabilizer under specified conditions. During this process, silver ions (Ag...) +Under the action of a reducing agent, silver ions are reduced to silver atoms (Ag) and deposited on the surface of silicon particles at the nanoscale. The reducing agent provides electrons to reduce silver ions to metallic silver, forming a thin silver coating layer. The stabilizer helps optimize the reaction rate of this process, preventing the formation of excessively large or irregular agglomerates of silver during deposition, ensuring the uniformity and density of the silver coating layer. The silver coating layer formed in this process can effectively reduce the lithium nucleation barrier, promote more uniform deposition of lithium ions on the silicon surface, thereby avoiding the formation of lithium dendrites and improving the safety of the final pre-lithiated silver-plated silicon-carbon material during use. Then, in step S2, the first product obtained in step S1 (silver-coated silicon particles) is mixed and calcined with the carbon matrix in a second step, thereby promoting the diffusion of silicon atoms into the micropores of the carbon framework to form a tight bond, and solidifying the silver coating layer to further enhance the stability of the silver layer and the bonding strength between the silver layer and the silicon particles. During this process, the silver coating layer and the carbon matrix may interact, which helps reduce interparticle voids and enhance the mechanical strength of the material. Simultaneously, the synergistic effect of silver and carbon significantly improves the electronic conductivity of the final pre-lithiated silver-plated silicon-carbon material. Further, in step S3, the second product (silver-coated silicon-carbon composite material) is mixed with the pre-lithiating agent again and calcined. During this process, the lithium ions released from the decomposition of the pre-lithiating agent can uniformly penetrate into the material system under the synergistic effect of the silver coating layer and the carbon skeleton. This not only improves the coulombic efficiency of the resulting anode material but also optimizes the composition and stability of the SEI film during application, reducing additional lithium loss during cycling. Finally, in step S4, the pre-lithiated third product undergoes additional carbon coating treatment, further enhancing its electronic conductivity network and mechanical stability, and isolating silicon particles from direct contact with the electrolyte. Subsequent acid washing removes any residual metallic silver or other impurities from the material surface, clearing the pathway and ensuring seamless lithium ion transport.

[0022] In summary, the above-described preparation method, through a series of carefully designed steps, achieves the transformation from silicon particles to silver coating and then to a carbon-based composite material. The resulting pre-lithiated silver-plated silicon-carbon material not only possesses excellent electronic conductivity and structural stability but also significantly improves the initial coulombic efficiency, reduces lithium loss during charge and discharge, and avoids the formation of lithium dendrites, thereby significantly enhancing the cycle performance and safety of lithium-ion batteries. Furthermore, the combined effects of silver coating and pre-lithiation help the material maintain high electrochemical activity, ensuring that even under high-rate charge and discharge conditions, the material can maintain good capacity retention and cycle stability.

[0023] In step S1, to more precisely control the thickness and uniformity of the formed silver coating layer, thereby significantly improving the conductivity and reactivity of the final pre-lithiated silver-plated silicon-carbon material, the preferred molar ratio of silicon particles, silver source, reducing agent, and stabilizer is 1:(0.8~20):(2~20):(0.001~0.002). Based on this preferred scheme, the formed silver coating layer will not be too thick or too thin, ensuring that the silver-coated silicon particles in the final composite material maintain good conductivity and structural stability, without hindering lithium-ion transport due to excessive silver layer thickness or losing its protective and conductive effects due to excessively thin silver layer. Simultaneously, an appropriate ratio of reducing agent and stabilizer promotes a more stable reaction, reduces silver particle agglomeration or premature crystallization, thereby further improving the uniformity and density of the formed silver layer, ultimately significantly optimizing the overall performance of the resulting composite material. To further optimize the morphology and structure of the first product, the following are preferred for each raw material in this step: the D50 of the silicon particles is 20 nm to 80 nm; and / or the silver source is silver nitrate and / or AgC2H3O2, preferably silver nitrate with higher solubility; and / or the reducing agent is selected from one or more of triethanolamine, n-butylamine, ethylenediamine and diethylamine; and / or the stabilizer is selected from one or more of citric acid, oxalic acid, tartaric acid and sodium ethylenediaminetetraacetate.

[0024] Furthermore, in step S1, the reaction is preferably carried out by stirring for 10-120 minutes at a speed of 100-200 rpm, thereby promoting more thorough contact between the reactants, facilitating the formation of a more uniform silver coating layer, and further improving the consistency and stability of the overall structure of the final composite material. Regarding the product obtained from the above reaction, before the first calcination, step S1 preferably includes a washing process for the product obtained from the reaction, using ethanol at a temperature of 40-60°C as the washing solution. This washing process can remove residual silver precursors, byproducts, and impurities that may affect subsequent reactions, thereby improving the cleanliness and reactivity of the surface of the obtained first product. The preferred holding temperature for the first calcination is 700℃~900℃, and the holding time is 0.5h~2h. This promotes a stronger bond between the formed silver coating layer and silicon particles, forming a more stable silver-silicon interface. This further improves the mechanical strength and conductivity of the obtained first product, providing raw materials with better morphology for subsequent carbon matrix composite and pre-lithiation steps, ultimately resulting in a pre-lithiation silver-plated silicon-carbon material with superior overall performance.

[0025] In step S2, to form a more ideal silver-coated nano-silicon composite carbon structure and better maintain the electron transport and structural integrity of the carbon matrix, the weight ratio of the first product to the carbon matrix is ​​preferably 1:(4~5). Within this weight ratio range, the carbon matrix can provide sufficient space and structural support for the silicon particles, while more effectively optimizing the overall conductivity and mechanical stability of the resulting composite material. Complementarily, the holding temperature for the second calcination is preferably 600℃~900℃, and the holding time is preferably 0.5h~2.0h, to further optimize the alloying tendency of silver and silicon, which is beneficial for forming a more stable interface structure under the support of the carbon matrix, and better suppresses material cracking caused by volume effects during subsequent cycling.

[0026] In several typical implementations, in order to provide a more suitable embedding environment for nanoscale silicon particles and to more significantly optimize the migration and recombination of silicon atoms, the D50 of the carbon matrix used is preferably 10 μm to 20 μm; and / or, the carbon matrix is ​​a porous structure with a pore diameter of 20 nm to 100 nm and a porosity of 50% to 75%.

[0027] Further, in step S3, the preferred weight ratio of the second product to the pre-lithiating agent is 1:(0.1~0.2); simultaneously, the preferred holding temperature for the third calcination is 600℃~1100℃, and the holding time is 6h~12h. In the above preferred embodiment, the pre-lithiating agent is present to compensate for the lithium consumed in the formation of the SEI film during the first charge-discharge process of the obtained pre-lithiated silver-plated silicon-carbon material, thereby improving the first charge-discharge coulombic efficiency of the material. However, if the amount of pre-lithiating agent is too large, it may lead to lithium-ion supersaturation, affecting the microstructure of the material and subsequent electrochemical reactions; conversely, if the amount of pre-lithiating agent is too small, it cannot fully compensate for the lithium consumed in the formation of the SEI film, reducing the electrochemical activity and first coulombic efficiency of the material. Based on this, the above-mentioned dosage ratio is preferred, thereby providing the appropriate amount of lithium-ion intercalation while better reducing the phenomenon of lithium-ion supersaturation, thereby further improving the structural stability and consistency of the finally obtained pre-lithiated silver-plated silicon-carbon material. Correspondingly, the optimal conditions for the third calcination, as described above, promote a more thorough decomposition of the pre-lithiation agent, releasing more lithium ions and distributing them more uniformly and fully within the material structure (in subsequent applications, the formation of the SEI film is better optimized with the support of the silver coating layer and porous carbon framework). This significantly reduces the electrochemical inhomogeneity caused by lithium ion enrichment, ultimately further improving the overall performance of the obtained pre-lithiated silver-plated silicon-carbon material. Furthermore, the pre-lithiation agent preferably used is selected from one or more of LiOH, LiCl, LiH, Li2CO3, LiNO3, and LiF.

[0028] In practical applications, to further reduce the introduction of impurities and improve the structural stability of the final composite material, it is preferable that the first, second, and third calcinations are all carried out in a protective atmosphere, and the protective atmosphere is selected from one or more of nitrogen, helium, and argon. Furthermore, the mixing process in each step of the above preparation method can employ one or more of shear mixing, fusion machine mixing, or ball milling mixing methods.

[0029] For the carbon coating process in step S4, the preferred method is one or more of gas phase coating, solid phase coating, and liquid phase coating. Meanwhile, the carbon-coated product obtained after the carbon coating process preferably includes a third product and a carbon layer coated on the surface of the third product; the carbon layer content is 1% to 6% based on 100% of the total weight of the carbon-coated product, so as to coat the surface of the third product with a more suitable thickness (5nm to 10nm), and a thin and uniform carbon layer, which does not affect the normal diffusion of lithium ions and can more significantly improve the electronic conductivity of the final pre-lithiated silver-plated silicon-carbon material.

[0030] In practical applications, the preferred carbon coating treatment method is selected from one or more of gas-phase coating, solid-phase coating, and liquid-phase coating (the carbon source can be acetylene, carbon black, carbon nanotubes, glucose, citric acid, polyvinyl alcohol, and other commonly used carbon source types in the art). More preferably, the carbon coating treatment method is gas-phase coating, which includes: placing the third product in a vapor deposition apparatus, introducing a carbon source at a flow rate of 500±100 mL / min and a protective gas at a flow rate of 1000±200 mL / min into the apparatus, heating to 800±100℃, and carbonizing for 1 h to 3 h to obtain the carbon-coated product. The carbon source used for gas-phase coating can be acetylene.

[0031] In step S4, preferably, the washing solution used for the pickling treatment includes a pickling agent and an acid solution. The pickling agent is selected from one or more of Na2HPO4, Na2(COO)2, Li2HPO4, Li2(COO)2, NaF, and LiF. The acid solution is selected from one or more of acetic acid (CH3COOH), citric acid (C6H8O7), formic acid (HCOOH), ascorbic acid (vitamin C, C6H8O6), and phosphoric acid (H3PO4). The concentration of the pickling agent in the washing solution is 3 g / L to 5 g / L, and the concentration of the acid solution is 10 g / L to 15 g / L. Preferably, the pickling treatment includes immersing the third product after carbon coating treatment in the washing solution at 25±2℃ and stirring for 1 h to 3 h. In the above preferred embodiment, the selection of the type and mass concentration of the pickling agent can further optimize the surface state of the material while cleaning the material surface, thereby improving the electrochemical activity of the resulting composite material. Optimizing the pickling conditions can better maintain the microstructural stability and electrochemical activity of the obtained pre-lithiated silver-plated silicon-carbon material while removing residual impurities. In several more typical embodiments, the pickling solution used above contains 12±1 g / L acetic acid and 4±0.5 g / L LiH2PO4, thereby better balancing the requirements of cleaning effect and structural integrity, reducing possible material damage and excessive corrosion, and ultimately obtaining a pre-lithiated silver-plated silicon-carbon material with a more stable structure and higher electrochemical activity.

[0032] A second aspect of this invention provides a pre-lithiated silver-plated silicon-carbon material, which is prepared by the aforementioned method for preparing pre-lithiated silver-plated silicon-carbon materials. Based on the microstructure optimization and performance regulation during the preparation process, the obtained pre-lithiated silver-plated silicon-carbon material exhibits excellent electrochemical performance, such as improved initial coulombic efficiency, enhanced cycle stability, and improved fast-charging capability. It should be noted that due to the complex structural formation and compositional changes during the preparation process, and the limitations of the material field and existing testing and characterization methods, it is difficult to perform a comprehensive quantitative characterization of the complex microstructure of the obtained pre-lithiated silver-plated silicon-carbon material. However, performance test results show that the pre-lithiated silver-plated silicon-carbon material obtained by this invention possesses a superior microstructure and exhibits higher electrochemical activity and cycle stability in application.

[0033] A third aspect of the present invention provides a negative electrode sheet comprising an active material layer including the aforementioned pre-lithiated silver-plated silicon-carbon material. By integrating the high-performance pre-lithiated silver-plated silicon-carbon material into the negative electrode sheet, the resulting negative electrode sheet exhibits higher electrical performance and longer cycle life, and can serve as an electrode assembly with high activity and stability to support the battery.

[0034] A fourth aspect of the present invention provides a lithium-ion battery comprising the aforementioned negative electrode sheet. Utilizing the high-performance pre-lithiated silver-plated silicon-carbon material in the negative electrode sheet, it exhibits excellent electronic conductivity and structural stability, and also prevents the formation of lithium dendrites during charge and discharge. Therefore, the lithium-ion battery in this configuration not only boasts higher initial efficiency but also demonstrates superior capacity retention and cycle stability under high-rate charge and discharge conditions.

[0035] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Example 1

[0038] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0039] (1) Coating with nano-silicon particles: Nano-sized silicon powder with a D50 particle size of 50 nm was dispersed in ethanol, and then silver nitrate, ethylenediamine reducing agent, and citric acid stabilizer were added to the solution simultaneously. The mixture was stirred at 150 rpm for 30 min. During the above process, the molar ratio of silicon particles, silver nitrate, reducing agent, and stabilizer was controlled at 1:10:12:0.0015 to adjust the coverage and thickness of silver on the surface of silicon particles. Afterward, the product was washed with ethanol at 50 °C to remove residual silver precursor. After filtration, it was dried in a vacuum oven at 80 °C for 12 h. The resulting silver-coated silicon particles were then calcined in a tube furnace at 800 °C with argon for 1 h to perform high-temperature curing treatment on the coating interface, resulting in the first product.

[0040] (2) The first product obtained is mixed with porous carbon material (D50 particle size of 15μm, pore diameter of 70nm~90nm, porosity of 60%) at a weight ratio of 1:4.5, and then calcined at 750℃ for 1.5h in an inert atmosphere. Silicon atoms migrate into the microporous structure of porous carbon through surface diffusion force to obtain the second product.

[0041] (3) The obtained second product and the pre-lithiation agent LiOH were mixed at a weight ratio of 1:0.15 and calcined at 850°C for 9 hours in an inert atmosphere to obtain the pre-lithiation silver-coated silicon-carbon precursor material, i.e. the third product.

[0042] (4) Carbon coating of the third product with acetylene as the carbon source. The carbon source used for carbon coating is acetylene. The specific process is as follows: the third product is placed in a CVD device, and argon gas (inert gas, flow rate 1000 mL / min) and acetylene gas (carbon source, flow rate 500 mL / min) are introduced. The temperature is raised to 800℃ and carbonized for 2 hours. Acetylene is decomposed at high temperature to generate amorphous carbon, which is uniformly deposited on the surface of the third product to form a carbon coating layer with a thickness of 5~10 nm (which accounts for 5% of the total weight of the coated product). The carbon layer further inhibits the direct contact between the electrolyte and Si, while enhancing the interparticle conductivity and improving the cycle stability of the pre-lithiation material. Afterwards, acid washing is performed at 25℃ for 2 hours using an acetic acid solution of LiH2PO4 (where the mass concentration of acetic acid is 12.0 g / L and the mass concentration of Na2HPO4 is 4 g / L).

[0043] The specific pickling method is as follows: ① Prepare the pickling agent: Dissolve 2g of pickling agent LiH2PO4 in 500g of deionized water, and adjust the pH to about 4 with acetic acid to obtain the above pickling solution; ② Take 50g of carbon-coated material and put it into the above pickling agent and stir to pickle for 2 hours to remove residual lithium salts (such as Li2CO3, LiOH) and by-products on the surface; ③ Rinse with a large amount of deionized water until neutral, dry in a vacuum oven at 80℃ for 6 hours, and finally pass through a 100-mesh sieve to remove agglomerated particles to obtain the pre-lithium silver-coated silicon carbon material product.

[0044] Example 2

[0045] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0046] (1) Coating with nano-silicon particles: Nano-sized silicon powder with a D50 particle size of 20 nm was dispersed in ethanol, and then silver nitrate, n-butylamine reducing agent, and oxalic acid stabilizer were added to the solution simultaneously. The mixture was stirred at 200 rpm for 5 min. During the above process, the molar ratio of silicon particles, silver nitrate, reducing agent, and stabilizer was controlled at 1:0.8:2:0.001 to adjust the coverage and thickness of silver on the surface of silicon particles. Afterward, the product was washed with ethanol at 40 °C to remove residual silver precursor. After filtration, it was dried in a vacuum oven at 80 °C for 12 h. The resulting silver-coated silicon particles were then calcined in a tube furnace at 700 °C with argon for 0.5 h to perform high-temperature curing treatment on the coating interface, resulting in the first product.

[0047] (2) The first product obtained was mixed with porous carbon material (consistent with Example 1) at a weight ratio of 1:4 and calcined at 600°C for 2.0 h in an inert atmosphere. Silicon atoms migrated into the microporous structure of porous carbon through surface diffusion force to obtain the second product.

[0048] (3) The obtained second product was mixed with the pre-lithiation agent LiCl at a weight ratio of 1:0.1 and calcined at 600°C for 12 h in an inert atmosphere to obtain the pre-lithiation silver-coated silicon-carbon precursor material, i.e. the third product.

[0049] (4) Refer to Example 1.

[0050] Example 3

[0051] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0052] (1) Coating with nano-silicon particles: Nano-sized silicon powder with a D50 particle size of 80 nm was dispersed in ethanol, and then silver nitrate, ethylenediamine reducing agent, and tartaric acid stabilizer were added to the solution simultaneously. The mixture was stirred at 100 rpm for 120 min. During the above process, the molar ratio of silicon particles, silver nitrate, reducing agent, and stabilizer was controlled at 1:20:20:0.002 to adjust the coverage and thickness of silver on the surface of silicon particles. Afterward, the product was washed with ethanol at 60 °C to remove residual silver precursor. After filtration, it was dried in a vacuum oven at 80 °C for 12 h. The resulting silver-coated silicon particles were then calcined in a tube furnace at 900 °C with argon for 2 h to perform high-temperature curing treatment on the coating interface, resulting in the first product.

[0053] (2) The first product obtained is mixed with porous carbon material (consistent with Example 1) at a weight ratio of 1:5, and then calcined at 900°C for 0.5 h in an inert atmosphere. Silicon atoms migrate into the microporous structure of porous carbon through surface diffusion force to obtain the second product.

[0054] (3) The obtained second product is mixed with the pre-lithiation agent Li2CO3 at a weight ratio of 1:0.2 and calcined at 1100℃ for 6 hours in an inert atmosphere to obtain the pre-lithiation silver-coated silicon-carbon precursor material, i.e. the third product.

[0055] (4) Refer to Example 1.

[0056] Example 4

[0057] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0058] The only difference between this embodiment and Embodiment 1 is that in step (1), the molar ratio of silicon particles, silver source, reducing agent and stabilizer is changed to 1:0.5:30:0.003; and the calcination holding temperature in this step is changed to 600℃.

[0059] Example 5

[0060] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0061] The only difference between this embodiment and Embodiment 1 is that in step (1), the molar ratio of silicon particles, silver source, reducing agent and stabilizer is changed to 1:25:1:0.0005; and the calcination holding temperature in this step is changed to 1000℃.

[0062] Example 6

[0063] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0064] The only difference between this embodiment and embodiment 1 is that in step (2), the weight ratio of the first product to the carbon matrix is ​​changed to 1:3, and the calcination holding temperature in this step is changed to 500°C and the holding time is changed to 3h.

[0065] Example 7

[0066] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0067] The only difference between this embodiment and embodiment 1 is that in step (3), the weight ratio of the second product to the pre-lithiating agent is changed to 1:0.3, and the calcination holding temperature in this step is changed to 1200℃ and the holding time is changed to 5h.

[0068] Example 8

[0069] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0070] The only difference between this embodiment and embodiment 1 is that in step (3), the weight ratio of the second product to the pre-lithiating agent is changed to 1:0.05, and the calcination holding temperature in this step is changed to 500°C and the holding time is changed to 15h.

[0071] Example 9

[0072] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0073] The only difference between this embodiment and embodiment 1 is that the flow rate of acetylene is changed during the carbon coating process in step (4) so ​​that the weight ratio of the carbon layer in the obtained carbon coating product is changed to 0.5%.

[0074] Example 10

[0075] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0076] The only difference between this embodiment and embodiment 1 is that the carbonization insulation temperature is changed to 1000℃ during the carbonization treatment in step (4).

[0077] Example 11

[0078] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0079] The only difference between this embodiment and embodiment 1 is that in step (4), the mass concentration of acetic acid in the acetic acid solution used for pickling is changed to 5 g / L, and the mass concentration of Li2HPO4 pickling agent is changed to 10 g / L.

[0080] Example 12

[0081] A method for preparing a pre-lithiated silver-plated silicon-carbon material:

[0082] The only difference between this embodiment and embodiment 1 is that in step (4), the mass concentration of acetic acid in the acetic acid solution used for pickling is changed to 20 g / L, and the mass concentration of Li2HPO4 pickling agent is changed to 1 g / L.

[0083] Comparative Example 1

[0084] Preparation of a negative electrode material:

[0085] The only difference between this comparative example and Example 1 is that step (1) was not performed. Instead, the raw material nano-silicon particles were directly used as the first product and subsequent steps were performed to finally obtain the negative electrode material sample.

[0086] Comparative Example 2

[0087] Preparation of a negative electrode material:

[0088] The only difference between this comparative example and Example 1 is that step (3) was not performed; instead, the second product was directly coated with carbon and acid-washed to obtain the negative electrode material sample.

[0089] Comparative Example 3

[0090] Preparation of a negative electrode material:

[0091] The only difference between this comparative example and Example 1 is that the third product obtained in step (3) is directly used as the final negative electrode material sample.

[0092] Battery sample preparation and testing methods:

[0093] Using N-methylpyrrolidone as a solvent, commercially available 8-series ternary materials as positive electrode active materials are uniformly mixed with polyvinylidene fluoride and carbon nanotube conductive paste in a mass ratio of 97%:1.5%:1.5% to prepare a positive electrode paste. The positive electrode sheet is then prepared by coating, drying, rolling and slitting.

[0094] Using deionized water as a solvent, the silicon-carbon composite material prepared in the above examples and comparative examples was used as the negative electrode active material. It was uniformly mixed with graphite, polyacrylic acid and conductive carbon black in a mass ratio of 19%:76%:3%:2%. Then, the negative electrode material samples obtained in the above examples and comparative examples were prepared into negative electrode sheets by coating, drying, rolling and slitting.

[0095] Lithium hexafluorophosphate (LiPF6) was used as the lithium salt, and a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) was used as the solvent, with a volume ratio of DMC:EMC:EC = 3:1:1. Then, 2% (mass ratio) of vinylene carbonate (VC) and 3% (mass ratio) of ethylene ethylene carbonate (VEC) were added to the electrolyte. The total lithium salt concentration was controlled at 1 mol / L to serve as the electrolyte.

[0096] A 9μm thick polyethylene (PE) base film was coated with 3μm thick ceramic on both sides as a separator, and the battery samples corresponding to the various embodiments and comparative examples were assembled.

[0097] Test conditions:

[0098] 1. First efficiency: Under normal temperature and pressure conditions, the first efficiency of each battery sample can be obtained by performing capacity testing at 0.33C (charging: charging the battery at 0.33C with constant current and constant voltage to 4.35V, with a cutoff current of 0.05C; discharging: discharging at 0.33C to 2.5V).

[0099] 2. Rate performance at 2C and 3C: Each battery sample was charged to 4.35V at a constant current and constant voltage of 0.33C, with a cutoff current of 0.05C. Then, it was discharged to 2.5V at 0.33C, 2C, and 3C respectively. The discharge capacity at 0.33C was taken as the initial capacity, and the ratio of the discharge capacity at other rates to the initial capacity was taken as the discharge capacity retention rate, which was used to evaluate the rate performance of each battery sample.

[0100] 3. Cyclic performance: Each battery sample was charged at 0.5C with constant current and constant voltage to 4.35V, and the cutoff current was 0.05C; Discharge: Discharged at 1C to 2.5V, with the first discharge capacity as the initial capacity, and the ratio of the discharge capacity of the 500th cycle to the initial capacity as the cycle capacity retention rate, which is used to evaluate the cycle performance of each battery sample.

[0101] The results of the above tests are shown in Table 1.

[0102] Table 1. Electrical performance test results of each battery sample

[0103]

[0104] As can be seen from the above description, compared with the comparative examples, the embodiments of the present invention are based on a silver coating combined with pre-lithiation strategy. By coating silicon particles with silver and performing pre-lithiation treatment, the structure of silicon-carbon anode materials is optimized and their electrochemical performance is improved. The structural stability and cycle life of the resulting pre-lithiated silver-plated silicon-carbon material are significantly improved, ultimately optimizing the various performance characteristics of the battery in which it is located.

[0105] Specifically, in each embodiment:

[0106] Comparing Examples 4 and 5 with Example 1, it can be seen that in step S1, the preferred molar ratio of silicon particles, silver source, reducing agent and stabilizer, as well as the preferred calcination conditions in this step, can promote more sufficient contact between the above reactants, promote the formation of a more uniform silver coating layer, thereby more accurately controlling the thickness and uniformity of the formed silver coating layer, and further improving the consistency and stability of the overall structure of the final composite material.

[0107] Comparing Examples 6 and 7 with Example 1, it can be seen that in step S2, the preferred weight ratio of the first product to the carbon matrix, as well as the preferred calcination conditions in this step, can form a more ideal silver-coated nano-silicon composite carbon structure, better maintain the electron transport and structural integrity of the carbon matrix, and further optimize the alloying tendency of silver and silicon. This is beneficial for forming a more stable interface structure under the support of the carbon matrix, and better suppresses material cracking caused by volume effects in subsequent cycling processes.

[0108] Comparing Example 8 with Example 1, it can be seen that in step S3, the preferred weight ratio of the second product to the pre-lithiating agent, as well as the preferred calcination conditions in this step, can better reduce the supersaturation of lithium ions while providing the appropriate amount of lithium ion insertion. At the same time, it can also promote the more thorough decomposition of the pre-lithiating agent, release more lithium ions, and distribute them more evenly and fully in the material structure, significantly reducing the electrochemical inhomogeneity caused by lithium ion enrichment, thereby further improving the structural stability and consistency of the final pre-lithiated silver-plated silicon-carbon material.

[0109] Comparing Examples 9 and 10 with Example 1, it can be seen that the preferred carbon coating conditions in step S4 can coat the surface of the third product with a carbon layer of more suitable thickness, which is thin and uniform. This does not affect the normal diffusion of lithium ions and can significantly improve the electronic conductivity of the final pre-lithiated silver-plated silicon-carbon material.

[0110] Comparing Examples 11 and 12 with Example 1, it can be seen that in step S4, the preferred type of washing solution used for acid pickling can further optimize the surface state of the material while cleaning the material surface, thereby improving the electrochemical activity of the resulting composite material.

[0111] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0112] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a pre-lithiated silver-plated silicon-carbon material, characterized in that, include: In step S1, silicon particles, a silver source, a reducing agent, and a stabilizer are sequentially reacted and subjected to a first calcination to obtain a first product; the molar ratio of the silicon particles, the silver source, the reducing agent, and the stabilizer is 1:(0.8~20):(2~20):(0.001~0.002); the silver source is silver nitrate and / or AgC2H3O2; the stabilizer is selected from one or more of citric acid, oxalic acid, tartaric acid, and sodium ethylenediaminetetraacetate; the first product is silver-coated silicon particles. In step S2, the first product and the carbon matrix are sequentially mixed and then calcined. The first product migrates into the porous structure of the carbon matrix through surface diffusion to obtain the second product. The carbon matrix has a porous structure with a pore diameter of 20 nm to 100 nm and a porosity of 50% to 75%. Step S3: The second product and the pre-lithiation agent are mixed sequentially and then calcined in a third step to obtain the third product; Step S4: The third product is subjected to carbon coating treatment and acid washing treatment in sequence to obtain the pre-lithiated silver-plated silicon-carbon material; the carbon-coated product obtained by the carbon coating treatment includes the third product and a carbon layer coated on the surface of the third product.

2. The method for preparing pre-lithiated silver-plated silicon-carbon material according to claim 1, characterized in that, In step S1 The D50 of the silicon particles is 20nm~80nm; and / or, The reducing agent is selected from one or more of triethanolamine, n-butylamine, ethylenediamine, and diethylamine.

3. The method for preparing pre-lithiated silver-plated silicon-carbon material according to claim 1, characterized in that, In step S1 The reaction is carried out by stirring for 10 to 120 minutes at a speed of 100 to 200 rpm; and / or, The holding temperature for the first calcination is 700℃~900℃, and the holding time is 0.5h~2.0h.

4. The method for preparing the pre-lithiated silver-plated silicon-carbon material according to any one of claims 1 to 3, characterized in that, In step S2 The weight ratio of the first product to the carbon matrix is ​​1:(4~5); and / or, The carbon matrix has a D50 of 10 μm to 20 μm; and / or, The second calcination is held at a temperature of 600℃ to 900℃ for a duration of 0.5h to 2.0h.

5. The method for preparing the pre-lithiated silver-plated silicon-carbon material according to any one of claims 1 to 3, characterized in that, In step S3 The weight ratio of the second product to the pre-lithiating agent is 1:(0.1~0.2); and / or, The pre-lithiation agent is selected from one or more of LiOH, LiCl, LiH, Li2CO3, LiNO3, and LiF; and / or, The holding temperature for the third calcination is 600℃~1100℃, and the holding time is 6h~12h.

6. The method for preparing the pre-lithiated silver-plated silicon-carbon material according to any one of claims 1 to 3, characterized in that, In step S4, the carbon layer content is 1% to 6% based on the total weight of the carbon-coated product as 100%.

7. The method for preparing the pre-lithiated silver-plated silicon-carbon material according to any one of claims 1 to 3, characterized in that, In step S4 The pickling solution used in the pickling process includes a pickling agent and an acid solution. The pickling agent is selected from one or more of Na2HPO4, Na2(COO)2, Li2HPO4, Li2(COO)2, NaF, and LiF. The acid solution is selected from one or more of acetic acid, citric acid, formic acid, ascorbic acid, and phosphoric acid. The concentration of the pickling agent in the washing solution is 3g / L to 5g / L, and the concentration of the acid solution is 10g / L to 15g / L.

8. A pre-lithiated silver-plated silicon-carbon material, characterized in that, The pre-lithiated silver-plated silicon-carbon material is prepared by the method for preparing pre-lithiated silver-plated silicon-carbon material according to any one of claims 1 to 7.

9. A negative electrode sheet, comprising an active material layer, characterized in that, The active material layer includes the pre-lithiated silver-plated silicon-carbon material as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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