Preparation method of lithium-silicon composite negative electrode, lithium-silicon composite negative electrode and all-solid-state lithium battery

Abstract

The invention belongs to the technical field of all-solid-state lithium batteries, and relates to a preparation method of a lithium-silicon composite negative electrode, the lithium-silicon composite negative electrode and an all-solid-state lithium battery. The preparation method of the lithium-silicon composite negative electrode comprises the following steps: generating a sulfide solid electrolyte coating layer on the surface of silicon powder in situ to obtain a silicon-based core-shell material; the passivated metal lithium powder and an FEC organic solvent are subjected to a contact reaction, a LiF protection layer is formed on the surface of the lithium powder in situ, and surface modified lithium powder is obtained; mixing the silicon-based core-shell material with the surface modified lithium powder, and carrying out heating treatment to realize lithium-silicon alloying, so as to obtain an alloyed product; and mixing the alloyed product, a conductive agent and a binder by a dry method, and carrying out calendaring molding to obtain the lithium-silicon composite negative electrode. The lithium-silicon composite negative electrode is obtained by constructing the core-shell structure and the multifunctional gradient interface layer step by step, and the electrochemical performance of the all-solid-state battery can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state lithium battery technology, and relates to a method for preparing a lithium-silicon composite anode, the lithium-silicon composite anode, and an all-solid-state lithium battery. Background Technology

[0002] With the rapid development of new energy vehicles and distributed energy storage, higher demands are being placed on the energy density and safety of lithium-ion batteries. Traditional liquid lithium-ion batteries pose safety risks, being susceptible to combustion and explosion due to external thermal or mechanical shocks. To address this issue, all-solid-state batteries offer enhanced safety due to their use of non-volatile, non-flowing, and non-flammable solid electrolytes.

[0003] Sulfide solid electrolytes (such as sulfide-germanium sulfide solid electrolytes, Li2S-P2S5 system sulfide solid electrolytes, etc.) have extremely high room temperature ionic conductivity (up to 10). -2 ~10 -3 The graphite anode has attracted widespread attention due to its high specific capacity (S / cm). However, its poor compatibility with high-capacity anode materials severely hinders the commercialization of sulfide all-solid-state batteries. While graphite anodes exhibit good stability, their theoretical specific capacity is only about 350 mAh / g, which cannot meet the high energy density requirements. Lithium metal anodes have a theoretical specific capacity as high as 3860 mAh / g, but they are prone to lithium dendrite formation during cycling, leading to battery short circuits, and exhibit severe side reactions at the interface with sulfide electrolytes, resulting in a surge in interface impedance. Silicon (Si) anode materials have a theoretical specific capacity as high as 4200 mAh / g (far exceeding that of graphite) and a low operating potential (0.4 V vs. Li⁺ / Li), making them highly promising high-capacity anode materials. However, silicon undergoes a huge volume change during lithiation / delithiation (expansion rate can reach over 300%), leading to the pulverization of active materials, damage to the conductive network, and severe mechanical stress between silicon and the solid electrolyte. This causes interfacial contact failure and a sharp capacity decay, with severe initial irreversible capacity loss (first-time efficiency is usually <80%), requiring additional lithium source compensation. In addition, there is chemical incompatibility between silicon and sulfide electrolytes, and side reactions lead to increased interfacial impedance and obstructed lithium-ion transport.

[0004] Existing silicon-based anode materials for sulfide all-solid-state batteries still suffer from the following problems: 1) When using micron-sized silicon powder as a raw material, it is difficult to simultaneously achieve high initial coulombic efficiency, low interfacial impedance, and excellent cycle stability; 2) Volume expansion and contraction of the silicon anode during charge and discharge lead to interfacial cracking and capacity decay; 3) Interfacial side reactions between silicon and the sulfide electrolyte severely affect battery performance; 4) Traditional wet electrode processes are not suitable for moisture-sensitive sulfide all-solid-state battery systems. Current attempts have attempted to alleviate these problems through nano-sizing, carbon coating, or pre-lithiation, but these methods still struggle to balance high initial efficiency, long cycle life, and process scalability in all-solid-state systems. Especially for lower-cost micron-sized silicon, its volume expansion stress is greater, and its interfacial stability is worse, often rendering conventional strategies ineffective. Therefore, an integrated solution that can simultaneously address bulk expansion, interfacial side reactions, and lithium loss is urgently needed. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for preparing a lithium-silicon composite anode, a lithium-silicon composite anode and an all-solid-state lithium battery. The lithium-silicon composite anode obtained by stepwise construction of a core-shell structure and a multifunctional gradient interface layer significantly improves the electrochemical performance of sulfide all-solid-state batteries.

[0006] The present invention employs the following technical solutions to achieve its objective: One aspect of the present invention provides a method for preparing a lithium-silicon composite anode, comprising the following steps: Silicon powder is mixed with a sulfide solid electrolyte precursor, and then ball-milled and heat-treated to generate a sulfide solid electrolyte coating layer in situ on the surface of the silicon powder, thus obtaining a silicon-based core-shell material. Passivated lithium metal powder is reacted with an organic solvent containing fluorinated ethylene carbonate (FEC) to form a lithium fluoride protective layer in situ on the surface of the lithium powder, thus obtaining surface-modified lithium powder. The silicon-based core-shell material is mixed with the surface-modified lithium powder and then subjected to heat treatment to achieve lithium-silicon alloying, thereby obtaining the alloyed product. The raw materials, including alloying products, conductive agents, and binders, are dry-mixed and rolled to obtain a lithium-silicon composite anode. The silicon powder is micron-sized, with a D50 of 0.5~10 μm.

[0007] Sulfide solid electrolyte precursors are the raw materials required to generate sulfide solid electrolytes.

[0008] Preferably, the sulfide solid electrolyte is one or more of the following: silver sulfide-germanium sulfide solid electrolyte and Li2S-P2S5 system sulfide solid electrolyte.

[0009] Further preferably, the sulfide solid electrolyte is a Li2S-P2S5 system sulfide solid electrolyte.

[0010] Further preferably, the sulfide solid electrolyte is Li7P3S. 11 .

[0011] Preferably, the thickness of the sulfide solid electrolyte coating layer is 10-20 nm. Within this range, the coating layer can effectively isolate the silicon from the side reactions of the external electrolyte and provide a continuous high-speed lithium-ion transport channel, significantly reducing the interface impedance. If the thickness is <10 nm, the protection is insufficient; if it is >20 nm, the ion diffusion path is too long, and the rate performance decreases.

[0012] The ball milling is carried out under an inert atmosphere. Preferably, the ball milling speed is 100~500 rpm and the ball milling time is 1.5~4.5 hours.

[0013] Preferably, the heat treatment is carried out in a vacuum or inert atmosphere, at a temperature of 200~290°C, for a time of 1~3 hours.

[0014] The D50 of passivated lithium metal powder is 5~100 μm.

[0015] Preferably, the concentration of fluoroethylene carbonate (FEC) in the organic solvent is 5-20 wt%, more preferably 12-18 wt%.

[0016] Preferably, the organic solvent is 1,3-dioxolane (DOL) and / or dimethoxyethane (DME). More preferably, it is a mixed solvent of 1,3-dioxolane and dimethoxyethane. Even more preferably, the volume ratio of 1,3-dioxolane to dimethoxyethane in the mixed solvent is 0.8~1.5:1. Under these conditions, FEC can be efficiently reduced on the lithium powder surface to form a dense and uniform LiF protective layer.

[0017] Preferably, the thickness of the formed lithium fluoride protective layer is 5-10 nm. LiF layers within this thickness range possess both high mechanical strength and moderate interfacial ionic conductivity, effectively suppressing lithium dendrite penetration and improving the operational stability of lithium powder in air.

[0018] The step of forming the lithium fluoride protective layer is carried out under an inert atmosphere.

[0019] Preferably, the mass ratio of silicon-based core-shell material to surface-modified lithium powder is 1:(0.13-0.18). This ratio is close to the ratio required for the complete alloying of silicon to form Li. 15 The stoichiometry of Si4 can accurately compensate for irreversible lithium loss in the first week, achieving high initial efficiency, while avoiding the risk of lithium plating caused by excessive lithium residue.

[0020] Preferably, during the lithium-silicon alloying process, the heat treatment temperature is 170~220℃, and the holding time is 1~3 hours. Within this process window, the lithium-silicon alloying reaction proceeds fully while avoiding excessive oxidation of the lithium powder.

[0021] Optionally, the conductive agent is one or more of Ketjen black, acetylene black, carbon nanotubes, graphene, carbon nanofibers, and vapor-grown carbon fibers. The binder is one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, and vinylidene fluoride-hexafluoropropylene copolymer.

[0022] The raw materials, including alloying products, conductive agents, and binders, are dry-mixed. Preferably, the mass ratio of alloying products, conductive agents, and binders is 100:1 to 10:1 to 5.

[0023] Preferably, the raw materials, including the alloying product, conductive agent, polyethylene oxide-lithium salt composite ionic conductor and binder, are dry-mixed.

[0024] Preferably, the mass ratio of the alloying product, conductive agent, polyethylene oxide-lithium salt composite ionic conductor, and binder is 100:1~10:2~15:1~5.

[0025] Preferably, the polyethylene oxide-lithium salt composite ion conductor is a polyethylene oxide-lithium bis(fluorosulfonyl)imide (PEO-LiFSI) composite ion conductor and / or a polyethylene oxide-lithium bis(trifluoromethyl)sulfonylimide (PEO-LiTFSI).

[0026] Further preferably, the polyethylene oxide-lithium salt composite ion conductor is a polyethylene oxide-bis(fluorosulfonyl)imide lithium composite ion conductor.

[0027] Preferably, the dry mixing is carried out under an inert atmosphere.

[0028] Preferably, the calendering temperature is 70~100℃, and the thickness of the resulting negative electrode film is 50~80 μm. The negative electrode film has self-supporting properties and high density.

[0029] A second aspect of the present invention provides a lithium-silicon composite anode, which is prepared by the above-described preparation method.

[0030] A third aspect of the present invention provides an all-solid-state lithium battery comprising the above-described lithium-silicon composite anode.

[0031] The positive electrode, solid electrolyte membrane, and lithium-silicon composite negative electrode are assembled into an all-solid-state lithium battery under a high pressure of 100~300MPa. This pressure ensures atomic-level close contact between the electrode and the electrolyte and can effectively suppress the volume change of the silicon negative electrode during cycling, maintaining interface stability.

[0032] The principle behind the improved battery performance achieved by the lithium-silicon composite anode of this invention is as follows: This scheme employs a composite process of micron-sized silicon and sulfide solid electrolyte through ball milling and heat treatment to form a silicon-based core-shell material coated with sulfide solid electrolyte. The size effect of micron-sized silicon effectively alleviates the volume expansion stress during alloying, while the sulfide solid electrolyte provides up to 10 -3 The high-speed lithium-ion conduction channel, measured in S / cm, also functions as a buffer matrix to disperse stress and suppress silicon particle breakage during alloying. Furthermore, it acts as a chemical barrier, preventing direct contact between silicon and external sulfide electrolytes and reducing side reactions. Further, by reacting FEC solution with lithium metal powder, a LiF-rich artificial SEI film is pre-constructed on the lithium surface. This protective layer possesses high mechanical strength and chemical stability, effectively suppressing lithium dendrite growth and significantly improving the air stability of lithium metal during subsequent processing, providing a clean, low-impedance reaction interface in subsequent alloying. During electrode integration, pre-lithiation is achieved by stoichiometric incorporation of Li@FEC according to the stoichiometry of silicon alloying, compensating for the initial efficiency loss of the silicon anode. Combined with dry electrode technology, solvent damage to sensitive materials is avoided, while high-pressure rolling forms a dense, self-supporting electrode film. To optimize solid-solid interface contact, a polyethylene oxide-lithium salt composite was introduced. This composite flows and fills the gaps between rigid particles during hot pressing, establishing a continuous ion conduction network, thereby significantly reducing interfacial impedance. It also adapts to silicon volume changes during cycling, maintaining interfacial integrity. This invention constructs a three-tiered 'material-interface-electrode' system: ① a core-shell structure addresses silicon bulk expansion; ② a pre-passivation layer suppresses lithium dendrite formation; ③ the flexible polyethylene oxide-lithium salt composite compensates for volume changes, forming a multi-dimensional synergistic system that effectively improves solid-state battery performance.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) Commercial lithium powder is passed through liquid-phase passivation treatment by fluoroethylene carbonate to generate a composite protective layer dominated by lithium fluoride in situ. The newly generated LiF layer has high lithium-ion conductivity, excellent chemical stability and mechanical strength, which not only significantly improves the safety and storage stability of lithium powder in subsequent operations, but also provides a low impedance and high compatibility interface environment for lithium-silicon alloying reaction; and fluoroethylene carbonate is an irreplaceable modifier for forming the optimal LiF protective layer in the system of this invention.

[0034] (2) Pre-passivated lithium powder (Li@LiF) was used as the active lithium source to achieve precise and controllable in-situ alloying of silicon and lithium during low-temperature heat treatment, which compensated for the irreversible lithium loss during the first charge and discharge process of the silicon anode. Combined with a stable LiF / sulfide electrolyte interface, the continuous consumption of active lithium during cycling was effectively suppressed, resulting in a significant improvement in the first coulombic efficiency of the full cell, which is significantly better than that of unpre-lithiated or traditional pre-lithiated systems.

[0035] (3) A multi-level gradient composite structure was constructed, consisting of "Si core – rigid fast ion channel of sulfide solid electrolyte – LiF stable interface layer – flexible filling phase of polyethylene oxide-lithium salt composite". This structure has high ionic conductivity, strong interfacial bonding force and adaptive volume change capability: the sulfide solid electrolyte coating layer provides a fast lithium-ion transport path and constrains silicon expansion; the LiF layer suppresses side reactions; the flexible phase of polyethylene oxide-lithium salt composite fills the interparticle gaps, maintaining a continuous ion / electron network inside the dry electrode, thereby effectively alleviating the problems of pulverization and contact failure of silicon-based materials during cycling.

[0036] (4) By in-situ ball milling and heat treatment on the surface of silicon powder to generate a sulfide solid electrolyte coating layer, a dense and uniform core-shell structure is formed, which effectively isolates the direct contact between silicon and external electrolyte and greatly reduces interfacial side reactions. At the same time, the coating layer maintains structural integrity during the silicon volume expansion process, prevents rapid capacity decay caused by interface rupture, and significantly improves the long-cycle stability of the battery.

[0037] (5) The dry electrode forming process adopted does not require organic solvents, thus avoiding problems such as uneven distribution of binder and uncontrollable pore structure in traditional wet coating. Combined with the synergistic effect of conductive agent, polyethylene oxide-lithium salt complex and binder, an electron / ion dual continuous conduction network is realized, further reducing the internal resistance of the electrode.

[0038] (6) The homogeneous lithium silicon phase formed by in-situ alloying significantly improves the conductivity of the negative electrode body; at the same time, a low-impedance solid-solid interface is formed between the alloying product and the sulfide electrolyte, which effectively solves the common interface kinetic hysteresis problem in all-solid batteries.

[0039] (7) This invention obtains a lithium-silicon composite anode by constructing a core-shell structure and a multifunctional gradient interface layer in steps, which can significantly improve the electrochemical performance of sulfide all-solid-state batteries. Moreover, when using low-cost micron-sized silicon as raw material, it can also achieve high initial coulombic efficiency (≥89%), low interfacial impedance and excellent cycle stability, and is compatible with dry electrode processes, meeting the needs of industrialization. Detailed Implementation

[0040] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two or more types, and can be two, three, four, five, or more.

[0041] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention.

[0042] In the following examples and comparative examples: The polyoxyethylene oxide-lithium bis(fluorosulfonyl)imide (PEO-LiFSI) composite was prepared by the following method: Polyoxyethylene oxide (PEO) with a molecular weight of 600,000 and lithium bis(fluorosulfonyl)imide (LiFSI) were mixed in a manner with EO((-CH2CH2O-) repeating units and Li + Weigh the mixture at a molar ratio of 18:1, dissolve it in anhydrous acetonitrile, stir magnetically at 60°C for 12 hours, then vacuum dry at 60°C for 24 hours, and grind it into powder for later use.

[0043] The polyoxyethylene-lithium bis(trifluoromethanesulfonyl)imide (PEO-LiTFSI) composite was prepared by the following method: Polyoxyethylene (PEO) with a molecular weight of 600,000 was mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a manner that followed the EO((-CH2CH2O-) repeating unit and Li + Weigh the mixture at a molar ratio of 18:1, dissolve it in anhydrous acetonitrile, stir magnetically at 60°C for 12 hours, then vacuum dry at 60°C for 24 hours, and grind it into powder for later use.

[0044] Example 1 The method for preparing the lithium-silicon composite anode provided in this embodiment is as follows: (1) Preparation of silicon-based core-shell materials: Micron-sized silicon powder (D50 = 2 μm, purity ≥ 99%), lithium sulfide (Li₂S), and phosphorus pentasulfide (P₂S₅) were mixed at a mass ratio of 1.0:0.38:1.0 and placed in a planetary ball mill jar (ZrO₂ grinding balls, ball-to-powder ratio 20:1). The mixture was ball-milled at 400 rpm for 3 hours under argon protection. The resulting powder was then vacuum heat-treated at 250°C for 2 hours to allow the Li₂S and P₂S₅ to react in situ, forming Li₇P₃S. 11 The sulfide coating is uniformly coated onto the surface of silicon particles to obtain a silicon-based core-shell material; the thickness of the sulfide coating layer is approximately 15 nm.

[0045] (2) Preparation of surface-modified lithium powder: Commercial passivated lithium powder (mainly composed of Li₂CO₃, D50 = 20 μm) was added to a mixed solution of DOL and DME (volume ratio of DOL to DME 1:1) containing 10 wt% fluoroethylene carbonate (FEC), with the mass ratio of the mixed solution to lithium powder controlled at 12:1. The mixture was ultrasonically treated for 30 minutes in an argon-atmosphere glove box (H₂O and O₂ concentrations both below 0.1 ppm) to reduce FEC in situ on the lithium powder surface, forming a lithium fluoride (LiF) protective layer. After the reaction, the mixture was filtered and rapidly washed once with anhydrous DME, then vacuum dried at 60°C for 2 hours to obtain surface-modified lithium powder; the LiF layer thickness was approximately 7 nm.

[0046] (3) Lithium-silicon alloying: The silicon-based core-shell material obtained in step (1) and the surface-modified lithium powder obtained in step (2) were mixed at a mass ratio of 1:0.15 and placed in a three-dimensional mixer. The mixture was stirred at 15 rpm for 45 minutes to achieve uniform low-shear mixing. The mixed powder was then transferred to a vacuum drying oven and kept at 190 °C for 2 hours to complete the lithium-silicon alloying reaction and obtain the alloyed product.

[0047] (4) Negative electrode film forming: The alloyed product obtained in step (3), vapor-grown carbon fiber (VGCF) conductive agent, PEO-LiFSI and polytetrafluoroethylene binder are dry-mixed in a mass ratio of 100:3:7:2. After the mixture is uniform, it is rolled into a self-supporting negative electrode film at 85°C using a roller press, and the film thickness is controlled to be 65 μm.

[0048] Example 2 The preparation method of the lithium-silicon composite anode provided in Example 2 differs from that in Example 1 only in that the FEC concentration in the mixed solution of step (2) of Example 2 is 5 wt%, while the rest is the same as in Example 1. The thickness of the LiF layer was measured to be 5 nm.

[0049] Example 3 The preparation method of the lithium-silicon composite anode provided in Example 3 differs from that in Example 1 only in that the FEC concentration in the mixed solution of step (2) in Example 3 is 20 wt%, while the rest is the same as in Example 1. The thickness of the LiF layer was measured to be 10 nm.

[0050] Example 4 The preparation method of the lithium-silicon composite anode provided in Example 4 differs from that in Example 1 only in that the ball milling time in step (1) of Example 4 is 2 hours, while the rest is the same as in Example 1. The measured Li7P3S... 11 The coating thickness is 11 nm.

[0051] Example 5 The preparation method of the lithium-silicon composite anode provided in Example 5 differs from that in Example 1 only in that the ball milling time in step (1) of Example 5 is 4 hours, while the rest is the same as in Example 1. The measured Li7P3S... 11 The coating thickness is 20 nm.

[0052] Example 6 The difference between the preparation method of the lithium-silicon composite anode provided in Example 6 and Example 1 is that in step (3) of Example 6, the silicon-based core-shell material and the surface-modified lithium powder are mixed at a mass ratio of 1:0.13, and the rest is the same as in Example 1.

[0053] Example 7 The difference between the preparation method of the lithium-silicon composite anode provided in Example 7 and Example 1 is that in step (3) of Example 7, the silicon-based core-shell material and the surface-modified lithium powder are mixed at a mass ratio of 1:0.18, and the rest is the same as in Example 1.

[0054] Example 8 The preparation method of the lithium-silicon composite anode provided in Example 8 differs from that in Example 1 only in that, in step (1) of Example 8, micron-sized silicon powder, Li2S, and P2S5 are mixed in a mass ratio of 1.0:0.25:1.0, and the vacuum heat treatment temperature is 230℃. The rest is the same as in Example 1. The measured Li7P3S... 11 The coating layer is 12 nm thick.

[0055] Example 9 The preparation method of the lithium-silicon composite anode provided in Example 9 differs from that in Example 1 only in that, in step (1) of Example 9, micron-sized silicon powder, Li2S, and P2S5 are mixed in a mass ratio of 1.0:0.5:1.0, and the vacuum heat treatment temperature is 230℃. The rest is the same as in Example 1. The measured Li7P3S... 11 The coating layer is 18nm.

[0056] Example 10 The preparation method of the lithium-silicon composite anode provided in Example 10 differs from that in Example 1 only in that, in step (1) of Example 10, micron-sized silicon powder, Li2S, P2S5, and LiCl are mixed, with a mass ratio of micron-sized silicon powder to Li2S of 1.0:0.3 and a mass ratio of Li2S, P2S5, and LiCl of 1.0:1.0:0.12. The rest is the same as in Example 1. The thickness of the Li6PS5Cl coating layer was measured to be 15 nm.

[0057] Example 11 The preparation method of the lithium-silicon composite anode provided in Example 11 differs from that in Example 1 only in that: in step (4) of Example 11, the PEO-LiFSI ion conductor is not added, that is, the alloy product obtained in step (3), VGCF conductive agent and polytetrafluoroethylene binder are dry-mixed in a mass ratio of 100:3:2. The rest is the same as in Example 1.

[0058] Example 12 The preparation method of the lithium-silicon composite anode provided in Example 12 differs from that in Example 1 only in that, in step (4) of Example 12, PEO-LiTFSI is added instead of PEO-LiFSI. The rest is the same as in Example 1.

[0059] Example 13 The preparation method of the lithium-silicon composite anode provided in Example 13 differs from that in Example 1 only in that: in step (2) of Example 13, only DOL is used as the organic solvent, that is, passivated lithium powder is added to a solution of DOL containing 10 wt% FEC. The rest is the same as in Example 1.

[0060] Example 14 The method for preparing the lithium-silicon composite anode provided in Example 14 differs from that in Example 1 only in that: in step (2) of Example 14, only DME is used as the organic solvent, that is, passivated lithium powder is added to a solution of DME containing 10 wt% FEC. The rest is the same as in Example 1.

[0061] Comparative Example 1 The only difference between the preparation method of the lithium-silicon composite anode provided in Comparative Example 1 and Example 1 is that the silicon powder in Comparative Example 1 was not coated; instead, the uncoated micron-sized silicon powder was directly mixed with the surface-modified lithium powder. Everything else was the same as in Example 1.

[0062] Comparative Example 2 The only difference between the preparation method of the lithium-silicon composite anode provided in Comparative Example 2 and Example 1 is that the lithium powder in Comparative Example 2 does not form a LiF layer; instead, the silicon-based core-shell material is directly mixed with commercially passivated lithium powder. Everything else is the same as in Example 1.

[0063] Comparative Example 3 The negative electrode film preparation method provided in Comparative Example 3 is as follows: The silicon-based core-shell material (prepared according to step (1) of Example 1), VGCF conductive agent, PEO-LiFSI and polytetrafluoroethylene binder were dry-mixed in a mass ratio of 100:3:7:2. After the mixture was uniform, it was rolled into a self-supporting negative electrode film at 85°C by a roller press, and the film thickness was controlled to be 65 μm.

[0064] Comparative Example 4 The preparation method of the lithium-silicon composite anode provided in Comparative Example 4 differs from that in Example 1 only in that the FEC concentration in the mixed solution of step (2) of Comparative Example 4 is 2 wt%, while the rest is the same as in Example 1. The thickness of the LiF layer was measured to be 3 nm.

[0065] Comparative Example 5 The preparation method of the lithium-silicon composite anode provided in Comparative Example 5 differs from that in Example 1 only in that the FEC concentration in the mixed solution of step (2) of Comparative Example 5 is 25 wt%, while the rest is the same as in Example 1. The thickness of the LiF layer was measured to be 15 nm.

[0066] Comparative Example 6 The preparation method of the lithium-silicon composite anode provided in Comparative Example 6 differs from that in Example 1 only in that the ball milling time in step (1) of Comparative Example 6 is 1 hour, while the rest is the same as in Example 1. The measured Li7P3S... 11 The coating thickness is 8 nm.

[0067] Comparative Example 7 The preparation method of the lithium-silicon composite anode provided in Comparative Example 7 differs from that in Example 1 only in that the ball milling time in step (1) of Comparative Example 7 is 5 hours, while the rest is the same as in Example 1. The measured Li7P3S... 11 The coating thickness is 25 nm.

[0068] Comparative Example 8 The difference between the preparation method of the lithium-silicon composite anode provided in Comparative Example 8 and Example 1 is that in step (3) of Comparative Example 8, the silicon-based core-shell material and the surface-modified lithium powder are mixed at a mass ratio of 1:0.1, and the rest is the same as in Example 1.

[0069] Comparative Example 9 The difference between the preparation method of the lithium-silicon composite anode provided in Comparative Example 9 and Example 1 is that in step (3) of Comparative Example 9, the silicon-based core-shell material and the surface-modified lithium powder are mixed at a mass ratio of 1:0.25, and the rest is the same as in Example 1.

[0070] Comparative Example 10 The preparation method of the lithium-silicon composite anode provided in Comparative Example 10 differs from that in Example 1 only in that, in step (1) of Comparative Example 10, micron-sized silicon powder, Li2S, and P2S5 are mixed in a mass ratio of 1.0:0.2:1.0, while the rest is the same as in Example 1. The measured Li7P3S... 11 The coating layer is 9nm.

[0071] Comparative Example 11 The preparation method of the lithium-silicon composite anode provided in Comparative Example 11 differs from that in Example 1 only in that, in step (1) of Comparative Example 11, micron-sized silicon powder, Li2S, and P2S5 are mixed in a mass ratio of 1.0:0.6:1.0, while the rest is the same as in Example 1. The measured Li7P3S... 11 The coating layer is 21nm.

[0072] Comparative Example 12 The only difference between the preparation method of the lithium-silicon composite anode provided in Comparative Example 12 and Example 1 is the preparation method of the surface-modified lithium powder. The specific preparation method of the surface-modified lithium powder in Comparative Example 12 is as follows: Commercial passivated lithium powder (mainly composed of Li₂CO₃, D50 = 20 μm) was added to a mixed solution of DOL and DME (volume ratio of DOL to DME 1:1) containing 12 wt% difluoroethylene carbonate (DFEC), with the mass ratio of the mixed solution to lithium powder controlled at 12:1. The mixture was ultrasonically treated for 35 minutes in an argon-atmosphere glove box (H₂O and O₂ concentrations both below 0.1 ppm) to reduce DFEC in situ on the lithium powder surface, forming a lithium fluoride (LiF) protective layer. After the reaction, the mixture was filtered and rapidly washed once with anhydrous DME, then vacuum dried at 60°C for 2 hours to obtain surface-modified lithium powder; the LiF layer thickness was approximately 7 nm.

[0073] Everything else is the same as in Example 1.

[0074] Comparative Example 13 The only difference between the preparation method of the lithium-silicon composite anode provided in Comparative Example 13 and Example 1 is the preparation method of the surface-modified lithium powder. The specific preparation method of the surface-modified lithium powder in Comparative Example 13 is as follows: Commercially passivated lithium powder (mainly composed of Li₂CO₃, D50 = 20 μm) was immersed in a mixed solution containing 20 wt% 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (DOL and DME, volume ratio 1:1), with the mass ratio of the mixed solution to lithium powder controlled at 12:1. The mixture was ultrasonically treated for 15 minutes in an argon-atmosphere glove box (H₂O and O₂ concentrations both below 0.1 ppm) to generate a lithium fluoride (LiF) protective layer in situ on the lithium powder surface. After the reaction, the mixture was filtered and rapidly washed once with anhydrous DME, then vacuum dried at 60 °C for 2 hours to obtain surface-modified lithium powder; the LiF layer thickness was approximately 7 nm.

[0075] All-solid-state battery assembly and testing: Cathode: NCM811 (LiNiO3-coated) 0.8 Co 0.1 Mn 0.1O2) is used as the positive electrode active material, and is mixed with Li6PS5Cl solid electrolyte and VGCF in a mass ratio of 70:20:10 and pressed into a positive electrode sheet.

[0076] Solid electrolyte membrane: Li6PS5Cl powder was cold-pressed into a dense ceramic sheet with a thickness of 80 μm at 300 MPa; Stacking and Packaging: The negative electrode film, Li6PS5Cl solid electrolyte separator, and positive electrode sheet of the examples and comparative examples are stacked in sequence and cold-pressed stepwise under a pressure of 200 MPa to ensure tight contact at the interface; then the stacked sheets are installed into a CR2032 button cell case and an external holding pressure of 20 MPa is applied to assemble an all-solid-state lithium battery.

[0077] The batteries prepared in the examples and comparative examples were charged and discharged at 0.1C for the first cycle and then cycled at 0.5C for 200 cycles. The battery performance data are shown in Table 1.

[0078]

[0079] By comparing Examples 1-3 with Comparative Examples 4-5, it can be seen that the concentration of FEC affects the final thickness of the LiF protective layer. When the thickness of the LiF protective layer is controlled at 5~10 nm, the prepared LiF protective layer exhibits better performance adaptability.

[0080] The comparisons of Examples 1, 4-5, 8-9, and Comparative Examples 6-7 and 10-11 show that the ball milling time and the amount of Li2S added affect the Li7P3S content. 11 The thickness of the coating layer will affect Li7P3S 11 By controlling the coating thickness to 10~20nm, the overall performance of the prepared anode material is better.

[0081] The comparison of Examples 1, 6-7 and Comparative Examples 8-9 shows that the silicon-lithium mass ratio has a significant impact on the electrochemical performance of the anode material. When the silicon-lithium mass ratio is 1:0.13~0.18, the battery assembled with the prepared anode exhibits better electrochemical performance.

[0082] A comparison of Example 1 and Examples 11-12 shows that adding a polyethylene oxide-lithium salt composite ion conductor during the preparation of the negative electrode can bring better performance, with the PEO-LiFSI composite ion conductor performing better than the PEO-LiTFSI composite ion conductor.

[0083] A comparison of Example 1 with Examples 13-14 shows that when the organic solvent is a mixture of 1,3-dioxolane and dimethoxyethane, it has a slight effect on the overall performance of the battery (including the first discharge specific capacity, the first cycle coulombic efficiency, and the cycle performance).

[0084] A comparison of Example 1 and Comparative Examples 12-13 shows that, compared with difluoroethylene carbonate and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, the LiF layer formed by using fluoroethylene carbonate (FEC) as a modifier has better overall performance.

[0085] The data from the embodiments and comparative examples of this invention fully demonstrate that by constructing a silicon-based core-shell material coated with a sulfide solid electrolyte (preferably with a coating thickness of 10-20 nm) and LiF surface-modified lithium powder (preferably with a LiF layer thickness of 5-10 nm), and pre-alloying them at an optimized mass ratio (1:0.13-0.18), the three components work synergistically to successfully prepare a high-performance anode. This design, especially through the pre-alloying process, fundamentally improves the first-cycle coulombic efficiency (reaching 89.3% in Example 1) and significantly reduces the interfacial impedance (Rct of 40.2 Ω), thereby endowing the all-solid-state battery with excellent cycle stability (83.5% capacity retention after 200 cycles). Furthermore, the data proves that fluoroethylene carbonate (FEC) is an irreplaceable modifier for forming the optimal LiF protective layer, exhibiting excellent performance.

[0086] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0087] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0088] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing a lithium-silicon composite anode, characterized in that, Includes the following steps: Silicon powder is mixed with a sulfide solid electrolyte precursor, and then ball-milled and heat-treated to generate a sulfide solid electrolyte coating layer in situ on the surface of the silicon powder, thus obtaining a silicon-based core-shell material. Passivated lithium metal powder is reacted with an organic solvent containing fluorinated ethylene carbonate to form a lithium fluoride protective layer in situ on the surface of the lithium powder, thus obtaining surface-modified lithium powder. The silicon-based core-shell material is mixed with the surface-modified lithium powder and then subjected to heat treatment to achieve lithium-silicon alloying, thereby obtaining the alloyed product. The raw materials, including alloying products, conductive agents and binders, are dry-mixed and rolled to obtain lithium-silicon composite anodes.

2. The preparation method according to claim 1, characterized in that, The thickness of the sulfide solid electrolyte coating layer is 10~20 nm; The thickness of the lithium fluoride protective layer is 5~10 nm; The mass ratio of the silicon-based core-shell material to the surface-modified lithium powder is 1:(0.13-0.18).

3. The preparation method according to claim 1, characterized in that, The sulfide solid electrolyte precursor is the raw material required to generate the sulfide solid electrolyte, and the sulfide solid electrolyte is one or more of the following: silver sulfide-germanium ore type sulfide solid electrolyte and Li2S-P2S5 system sulfide solid electrolyte. The organic solvent is 1,3-dioxolane and / or dimethoxyethane.

4. The preparation method according to claim 3, characterized in that, The sulfide solid electrolyte is Li7P3S. 11 .

5. The preparation method according to claim 1 or 3, characterized in that, The organic solvent is a mixed solvent of 1,3-dioxolane and dimethoxyethane, with a volume ratio of 1,3-dioxolane to dimethoxyethane of 0.8 to 1.5:

1.

6. The preparation method according to claim 1, characterized in that, The concentration of fluoroethylene carbonate in organic solvents is 5-20 wt%.

7. The preparation method according to claim 1, characterized in that, The raw materials, including alloying products, conductive agents, polyethylene oxide-lithium salt composite ionic conductors, and binders, are dry-mixed.

8. The preparation method according to claim 7, characterized in that, The polyethylene oxide-lithium salt composite ion conductor is a polyethylene oxide-bis(fluorosulfonyl)imide lithium composite ion conductor and / or a polyethylene oxide-bis(trifluoromethyl)sulfonylimide lithium.

9. A lithium-silicon composite anode, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 8.

10. An all-solid-state lithium battery, characterized in that, It includes the lithium-silicon composite anode as described in claim 9.

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