Silicon-based negative electrode material and preparation method thereof, negative electrode plate and battery
By forming a stable inorganic SEI film and nanoscale quartz phase through the synergistic reaction of lithium fluoride and lithium silicon, and combining an appropriate molar ratio and secondary sintering, the volume expansion and SEI film integrity issues of silicon-based anode materials are solved, thereby improving the energy density and cycle stability of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EVE ENERGY CO LTD
- Filing Date
- 2025-12-26
- Publication Date
- 2026-05-01
AI Technical Summary
During the charge and discharge process, silicon-based anode materials undergo volume expansion, leading to electrode structure pulverization and continuous SEI film rupture, which affects cycle life and irreversible loss of active lithium. Existing modification methods are difficult to balance volume expansion and SEI film integrity.
Lithium fluoride was used as a flux to work synergistically with silicon and lithium sources to generate a Li-Si-OF composite phase through high-temperature dissociation, forming a stable inorganic SEI film. During the sintering process, the melting point of the silicon source was reduced, promoting the formation of nanoscale quartz phase and dispersing volume expansion stress. Combined with an appropriate silicon-lithium molar ratio and a secondary sintering process, a porous network structure was constructed.
It effectively inhibits electrolyte decomposition, ensures the stability of the SEI film, reduces the volume expansion effect, improves the energy density and cycle stability of the negative electrode, and reduces the loss of active lithium.
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Abstract
Description
Silicon-based anode materials and their preparation methods, anode sheets, and batteries Technical Field
[0001] This application relates to the field of battery technology, specifically to a silicon-based anode material and its preparation method, anode sheet, and battery. Background Technology
[0002] Silicon-based anode materials possess ultra-high theoretical specific capacity, making them an important choice for anode materials in high-energy-density batteries. However, the dramatic volume expansion during charge and discharge of silicon-based anode materials can easily lead to electrode structure pulverization and continuous rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in irreversible loss of active lithium and reduced cycle life.
[0003] In related technologies, silicon-based anode materials are usually modified through element doping, carbon coating, and nanostructure design. However, these methods have limitations in terms of their singular modification effects, making it difficult to achieve both low volume expansion and good SEI film integrity in silicon-based anode materials. This severely restricts the industrial application of silicon-based anode materials. Summary of the Invention
[0004] This application provides a silicon-based anode material and its preparation method, anode sheet, and battery, aiming to provide a silicon-based anode material that takes into account both low volume expansion effect and SEI integrity, thereby improving the effective energy density of the anode sheet and the cycle stability of the silicon-based anode material.
[0005] In a first aspect, this application provides a silicon-based anode material obtained by sintering a precursor, the precursor including a silicon source, a lithium source and a flux; wherein the flux includes lithium fluoride, and the flux accounts for 1%-8% of the total mass of the silicon source and the flux.
[0006] By leveraging the synergistic effects of silicon sources, lithium sources, and fluxes, silicon-based anode materials with stable interfacial structures can be constructed. On one hand, lithium fluoride can dissociate into lithium ions and fluoride ions at high temperatures. Fluoride ions and the silicon source can react to form a Li-Si-OF composite phase. This composite phase preferentially decomposes during the first charge-discharge cycle, inducing the formation of an SEI film rich in inorganic substances such as lithium fluoride (LiF) and lithium oxide (Li₂O). Compared to traditional organic-dominated SEIs, inorganic SEIs exhibit higher mechanical strength and ionic conductivity, effectively inhibiting continuous electrolyte decomposition and ensuring the stability of the SEI film. Furthermore, LiF can synergistically interact with additives in the electrolyte to form a dense inner layer rich in LiF, reducing interfacial impedance and increasing the migration rate of lithium ions. On the other hand, lithium fluoride, as a flux, can lower the melting point of the silicon source during sintering, promoting the formation of dispersed nanoscale quartz phases on the silicon source surface. The quartz phase, acting as a rigid framework, can effectively disperse the stress generated by volume expansion, suppress the propagation of cracks at particle edges, and the dispersed quartz phase can separate the anode material particles into submicron-level units, limiting the expansion space of individual particles and reducing the overall volume change rate. By making the flux account for 1%-8% of the total mass of the silicon source and flux, the resulting silicon-based anode material can achieve both a low volume expansion effect and help ensure SEI integrity. In other words, the silicon-based anode material provided in this application can reduce the volume expansion effect while ensuring the integrity of the SEI film, reducing active lithium loss, improving the effective energy density of the anode sheet, and enhancing the cycle stability of the silicon-based anode material.
[0007] In some embodiments, the silicon source includes at least one of elemental silicon and a silicon-oxygen material; wherein the molecular formula of the silicon-oxygen material is SiO2. x , 0 < x < 2; and / or, the lithium source includes at least one of lithium carbonate, lithium hydride, lithium nitrate, lithium hydroxide, lithium oxide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate.
[0008] Elemental silicon has a high lithiation capacity, which can improve energy density. Oxygen atoms in silicon-oxygen materials can form a Si-O-Si network structure. During charge and discharge, the oxygen buffer effect disperses stress and reduces volume expansion rate. In addition, silicon-oxygen materials can react with lithium to form quartz phases such as lithium oxide during the first charge and discharge, consuming some irreversible lithium and reducing capacity decay in subsequent cycles.
[0009] Lithium carbonate has low cost and high thermal stability, which can reduce lithium volatilization during sintering. Lithium hydride has high reactivity, promoting deep reactions between silicon and lithium, and its high lithium content can improve lithium replenishment. Lithium nitrate has excellent low-temperature performance and can modify the interface during sintering, increasing the specific surface area of silicon-based anode materials. Lithium hydroxide and lithium oxide can neutralize acidic byproducts generated during sintering and can provide oxygen atoms, regulating the oxygen content in silicon-based anode materials.
[0010] In some embodiments, the molar ratio of silicon in the silicon source to lithium in the lithium source is 1:(2-4.9).
[0011] By maintaining the molar ratio of silicon in the silicon source to lithium in the lithium source within the aforementioned range, lithiation effect can be guaranteed, capacity utilization can be improved, and the formation of inactive lithium compounds due to excess lithium can be prevented, thus avoiding capacity decay. Furthermore, within this molar ratio range, the silicon and lithium sources can form a suitable alloy phase, maintaining high capacity while controlling the volume expansion rate within a reasonable range, ensuring the overall performance of the silicon-based anode material.
[0012] Secondly, this application also provides a method for preparing a silicon-based anode material, comprising: providing a silicon source, a lithium source, and a flux; wherein the flux includes lithium fluoride, and the flux accounts for 1%-8% of the total mass percentage of the silicon source and the flux; and mixing the silicon source, the lithium source, and the flux and then sintering them to obtain the silicon-based anode material.
[0013] The method for preparing silicon-based anode materials provided in this application has all the beneficial effects of silicon-based anode materials as described above, and will not be repeated here.
[0014] In some embodiments, a silicon source, a lithium source, and a flux are mixed and then sintered to obtain a silicon-based anode material, including: mixing a silicon source and a flux, performing a first sintering to obtain a composite silicon source; and mixing the composite silicon source and a lithium source, performing a second sintering to obtain a silicon-based anode material.
[0015] By first sintering the silicon source and flux, the flux melts and coats the silicon source surface, forming a uniform flux layer. This provides a uniform reaction interface for the subsequent silicon-lithium reaction. A second sintering of the composite silicon and lithium sources accelerates lithium-ion diffusion and improves the efficiency of the silicon-lithium reaction. Furthermore, the two-stage sintering process constructs a porous network structure, enhancing cycle stability, suppressing side reactions during sintering, reducing the formation of inactive phases, and lowering production difficulty.
[0016] In some embodiments, a single sintering process includes sintering at a temperature of 600°C-900°C for 1-1.5 hours.
[0017] In some embodiments, secondary sintering includes sintering at a temperature of 500℃-800℃ for 3-4 hours.
[0018] Thirdly, this application also provides a negative electrode sheet, including a negative electrode active layer, the negative electrode active layer including the silicon-based negative electrode material as described above, and / or the silicon-based negative electrode material prepared by the method described above.
[0019] The negative electrode sheet provided in this application has all the beneficial effects of silicon-based negative electrode materials as described above, which will not be repeated here.
[0020] In some embodiments, the negative electrode active layer further includes a conductive agent and a binder; the mass ratio of silicon-based negative electrode material, conductive agent and binder is (45-55):(41-54):(1-4).
[0021] By keeping the ratio of silicon-based anode material, conductive agent, and binder within the above range, it is possible to improve capacity and energy density, and to make the anode sheet highly conductive while ensuring structural strength.
[0022] In some embodiments, the conductive agent includes at least one of graphite, Super P, and acetylene black; and / or, the binder includes at least one of polytetrafluoroethylene, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber.
[0023] Graphite provides long-range conductive pathways, facilitating rapid electron transport between silicon-based anode materials. Its layered structure also buffers the expansion stress of the silicon-based anode materials. Super P fills the gaps between silicon-based anode particles, forming a conductive network and reducing contact resistance. Acetylene black, with its high specific surface area and porous structure, can adsorb electrolyte to form conductive channels. Both Super P and acetylene black exhibit good flexibility, maintaining contact performance through deformation and reducing the breakage rate of the conductive network.
[0024] Polytetrafluoroethylene (PTFE) possesses high elasticity, providing adhesion while buffering the expansion stress of silicon-based anode materials. The carboxyl groups in polyacrylic acid form strong hydrogen bonds with the hydroxyl groups on the surface of the silicon-based anode material, ensuring adhesion. The linear molecular chains of sodium carboxymethyl cellulose encapsulate the silicon-based anode material and conductive agent particles, forming a physical barrier and reducing the recurrence of the SEI film. The flexible segments of styrene-butadiene rubber (SBR) improve the flexibility of the anode sheet.
[0025] Fourthly, embodiments of this application also provide a battery, including the negative electrode sheet as described above.
[0026] The battery provided in this application has all the beneficial effects of the silicon-based anode material as described above, which will not be repeated here.
[0027] In some embodiments, the battery further includes a positive electrode sheet, which comprises a positive electrode active material having the molecular formula Li. 1+x Co y Mn 2-(x+y) O4, 0<x≤0.33, 0<y≤0.1.
[0028] By using the molecular formula of the positive electrode active material as described above, the battery can meet the discharge capacity design requirements within a voltage range of 2.0V-3.3V. That is, the battery achieves a high capacity utilization rate within the 2.0V-3.3V range.
[0029] In some embodiments, the battery further includes an electrolyte; the electrolyte includes a lithium salt, a solvent, a first additive, and a second additive; wherein the first additive includes at least one of lithium bis(oxalato)borate, tris(trimethylsilyl)borate, 1,3,6-hexanetrionitrile, butadionitrile, and adiponitrile; and the second additive includes at least one of vinyl ethylene carbonate and lithium difluorophosphate.
[0030] The first additive inhibits the dissolution of transition metal ions such as manganese ions, while the second additive improves the flexibility of the generated SEI film and reduces SEI film rupture caused by the expansion of silicon-based anode materials. Through the synergistic effect of the first and second additives in the electrolyte, lithium ion consumption can be reduced, and the effective capacity utilization and cycle stability of the battery can be improved.
[0031] In some embodiments, the first additive has a mass percentage of 1%-5% in the electrolyte; and / or, the second additive has a mass percentage of 5%-10% in the electrolyte; and / or, the lithium salt has a concentration of 1 mol / L-2 mol / L in the electrolyte.
[0032] By maintaining the mass percentage of the first additive in the electrolyte within the aforementioned range, the inhibition effect on the dissolution of transition metal ions can be guaranteed, the cost of the first additive can be balanced, and the viscosity of the electrolyte can be kept within a suitable range. By maintaining the mass percentage of the second additive in the electrolyte within the aforementioned range, the mechanical strength of the SEI film can be improved, and the phenomenon of increased lithium-ion transport impedance caused by excessive SEI film thickness can be avoided. Low-temperature performance can also be improved. By maintaining the concentration of lithium salt in the electrolyte within the aforementioned range, the electrolyte can achieve both good ionic conductivity and stability. Detailed Implementation
[0033] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0034] This application provides a silicon-based anode material and its preparation method, an anode sheet, and a battery. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.
[0035] In a first aspect, embodiments of this application provide a silicon-based anode material obtained by sintering a precursor, the precursor including a silicon source, a lithium source and a flux; wherein the flux includes lithium fluoride, and the flux accounts for 1%-8% of the total mass percentage of the silicon source and the flux.
[0036] By leveraging the synergistic effects of silicon sources, lithium sources, and fluxes, silicon-based anode materials with stable interfacial structures can be constructed. On one hand, lithium fluoride can dissociate into lithium ions and fluoride ions at high temperatures. Fluoride ions and the silicon source can react to form a Li-Si-OF composite phase. This composite phase preferentially decomposes during the first charge-discharge cycle, inducing the formation of an SEI film rich in inorganic substances such as lithium fluoride (LiF) and lithium oxide (Li₂O). Compared to traditional organic-dominated SEIs, inorganic SEIs exhibit higher mechanical strength and ionic conductivity, effectively inhibiting continuous electrolyte decomposition and ensuring the stability of the SEI film. Furthermore, LiF can synergistically interact with additives in the electrolyte to form a dense inner layer rich in LiF, reducing interfacial impedance and increasing the migration rate of lithium ions. On the other hand, lithium fluoride, as a flux, can lower the melting point of the silicon source during sintering, promoting the formation of dispersed nanoscale quartz phases on the silicon source surface. The quartz phase, acting as a rigid framework, can effectively disperse the stress generated by volume expansion, suppress the propagation of cracks at particle edges, and the dispersed quartz phase can separate the anode material particles into submicron-level units, limiting the expansion space of individual particles and reducing the overall volume change rate. By making the flux account for 1%-8% of the total mass of the silicon source and flux, the resulting silicon-based anode material can achieve both a low volume expansion effect and help ensure SEI integrity. In other words, the silicon-based anode material provided in this application can reduce the volume expansion effect while ensuring the integrity of the SEI film, reducing active lithium loss, improving the effective energy density of the anode sheet, and enhancing the cycle stability of the silicon-based anode material.
[0037] By keeping the flux addition ratio within the above range, the melting temperature of the silicon source can be reduced, the melting temperatures of the silicon source and lithium source can be matched, the sintering effect can be improved, and side reactions during the sintering process can be reduced, the formation of inactive phases can be reduced, and the performance of silicon-based anode materials can be guaranteed.
[0038] For example, the mass percentage of flux in the total amount of silicon source and flux can be 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%.
[0039] In some embodiments, the silicon source includes at least one of elemental silicon and a silicon-oxygen material; wherein the molecular formula of the silicon-oxygen material is SiO2. x , 0 < x < 2.
[0040] Elemental silicon has a high lithiation capacity, which can improve energy density. Oxygen atoms in silicon-oxygen materials can form a Si-O-Si network structure. During charge and discharge, the oxygen buffer effect disperses stress and reduces volume expansion rate. In addition, silicon-oxygen materials can react with lithium to form quartz phases such as lithium oxide during the first charge and discharge, consuming some irreversible lithium and reducing capacity decay in subsequent cycles.
[0041] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydride, lithium nitrate, lithium hydroxide, lithium oxide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate.
[0042] Lithium carbonate has low cost and high thermal stability, which can reduce lithium volatilization during sintering. Lithium hydride has high reactivity, promoting deep reactions between silicon and lithium, and its high lithium content can improve lithium replenishment. Lithium nitrate has excellent low-temperature performance and can modify the interface during sintering, increasing the specific surface area of silicon-based anode materials. Lithium hydroxide and lithium oxide can neutralize acidic byproducts generated during sintering and can provide oxygen atoms, regulating the oxygen content in silicon-based anode materials.
[0043] In some embodiments, the molar ratio of silicon in the silicon source to lithium in the lithium source is 1:(2-4.9).
[0044] By maintaining the molar ratio of silicon in the silicon source to lithium in the lithium source within the aforementioned range, lithiation effect can be guaranteed, capacity utilization can be improved, and the formation of inactive lithium compounds due to excess lithium can be prevented, thus avoiding capacity decay. Furthermore, within this molar ratio range, the silicon and lithium sources can form a suitable alloy phase, maintaining high capacity while controlling the volume expansion rate within a reasonable range, ensuring the overall performance of the silicon-based anode material.
[0045] For example, the molar ratio of silicon in the silicon source to lithium in the lithium source can be 1:2.2, 1:2.5, 1:2.7, 1:3, 1:3.2, 1:3.5, 1:3.7, 1:4, 1:4.2, 1:4.4, 1:4.7 or 1:4.9.
[0046] Secondly, embodiments of this application also provide a method for preparing a silicon-based anode material, comprising: providing a silicon source, a lithium source, and a flux; wherein the flux includes lithium fluoride, and the flux accounts for 1%-8% of the total mass percentage of the silicon source and the flux; and mixing the silicon source, the lithium source, and the flux and then sintering them to obtain the silicon-based anode material.
[0047] The method for preparing silicon-based anode materials provided in this application has all the beneficial effects of silicon-based anode materials as described above, and will not be repeated here.
[0048] In some embodiments, a silicon source, a lithium source, and a flux are mixed and then sintered to obtain a silicon-based anode material, including: mixing a silicon source and a flux, performing a first sintering to obtain a composite silicon source; and mixing the composite silicon source and a lithium source, performing a second sintering to obtain a silicon-based anode material.
[0049] By first sintering the silicon source and flux, the flux melts and coats the silicon source surface, forming a uniform flux layer. This provides a uniform reaction interface for the subsequent silicon-lithium reaction. A second sintering of the composite silicon and lithium sources accelerates lithium-ion diffusion and improves the efficiency of the silicon-lithium reaction. Furthermore, the two-stage sintering process constructs a porous network structure, enhancing cycle stability, suppressing side reactions during sintering, reducing the formation of inactive phases, and lowering production difficulty.
[0050] In some embodiments, a single sintering process includes sintering at a temperature of 600°C-900°C for 1-1.5 hours.
[0051] By performing a single sintering process at a temperature of 600℃-900℃, the flux can be fully melted and uniformly coated on the surface of the silicon source, and the occurrence of side reactions can be suppressed.
[0052] For example, the sintering temperature for a single sintering can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃, and the sintering time can be 1h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h.
[0053] In some embodiments, secondary sintering includes sintering at a temperature of 500℃-800℃ for 3-4 hours.
[0054] By performing secondary sintering at temperatures of 500℃-800℃, the diffusion rate of the lithium source can be accelerated, the reaction efficiency can be improved, and a porous structure can be formed.
[0055] For example, the sintering temperature of the secondary sintering can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, and the sintering time can be 3h, 3.2h, 3.5h, 3.7h or 4h.
[0056] Thirdly, embodiments of this application also provide a negative electrode sheet, including a negative electrode active layer, the negative electrode active layer including the silicon-based negative electrode material as described above, and / or the silicon-based negative electrode material prepared by the method described above.
[0057] The negative electrode sheet provided in this application has all the beneficial effects of silicon-based negative electrode materials as described above, which will not be repeated here.
[0058] In some embodiments, the negative electrode active layer further includes a conductive agent and a binder; the mass ratio of silicon-based negative electrode material, conductive agent and binder is (45-55):(41-54):(1-4).
[0059] By keeping the ratio of silicon-based anode material, conductive agent, and binder within the above range, it is possible to improve capacity and energy density, and to make the anode sheet highly conductive while ensuring structural strength.
[0060] In some embodiments, the conductive agent includes at least one of graphite, Super P, and acetylene black.
[0061] Graphite provides long-range conductive pathways, facilitating rapid electron transport between silicon-based anode materials. Its layered structure also buffers the expansion stress of the silicon-based anode materials. Super P fills the gaps between silicon-based anode particles, forming a conductive network and reducing contact resistance. Acetylene black, with its high specific surface area and porous structure, can adsorb electrolyte to form conductive channels. Both Super P and acetylene black exhibit good flexibility, maintaining contact performance through deformation and reducing the breakage rate of the conductive network.
[0062] In some embodiments, the adhesive includes at least one of polytetrafluoroethylene, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber.
[0063] Polytetrafluoroethylene (PTFE) possesses high elasticity, providing adhesion while buffering the expansion stress of silicon-based anode materials. The carboxyl groups in polyacrylic acid form strong hydrogen bonds with the hydroxyl groups on the surface of the silicon-based anode material, ensuring adhesion. The linear molecular chains of sodium carboxymethyl cellulose encapsulate the silicon-based anode material and conductive agent particles, forming a physical barrier and reducing the recurrence of the SEI film. The flexible segments of styrene-butadiene rubber (SBR) improve the flexibility of the anode sheet.
[0064] For example, this application also provides a method for preparing a negative electrode sheet, comprising: mixing a silicon-based negative electrode material, a conductive agent and a binder to form a mixture; and forming a negative electrode active layer by using a dry process to obtain a negative electrode sheet.
[0065] The method for preparing the negative electrode sheet provided in this application has all the beneficial effects of silicon-based negative electrode materials as described above, which will not be repeated here. In addition, the negative electrode sheet is prepared by a dry process, which reduces material costs and production costs, and enables the silicon-based negative electrode material, conductive agent, and binder in the negative electrode active layer to be more tightly bonded, thus ensuring the performance of the negative electrode sheet.
[0066] In some embodiments, forming a negative electrode active layer by a dry process of the mixture includes: shearing the mixture to form a sheared mixture; and forming a film of the sheared mixture at a temperature of 20°C-60°C to form a negative electrode active layer.
[0067] By shearing the mixture, the binder can be fiberized. The fiberized binder can encapsulate the silicon-based anode material, forming a three-dimensional network structure that enhances mechanical strength and conductivity. Under temperature conditions of 20℃-160℃, the binder easily forms fibers, maintaining good contact between the silicon-based anode material and the conductive agent, stabilizing the anode sheet structure, and ensuring its structural integrity.
[0068] For example, the film-forming temperature can be 20°C, 40°C, or 60°C.
[0069] Fourthly, this application also provides a battery, including the negative electrode sheet as described above.
[0070] The battery provided in this application has all the beneficial effects of the silicon-based anode material as described above, which will not be repeated here.
[0071] In some embodiments, the battery further includes a positive electrode sheet, which comprises a positive electrode active material having the molecular formula Li. 1+x Co y Mn 2-(x+y) O4, 0<x≤0.33, 0<y≤0.1.
[0072] By using the molecular formula of the positive electrode active material as described above, the battery can meet the discharge capacity design requirements within a voltage range of 2.0V-3.3V. That is, the battery achieves a high capacity utilization rate within the 2.0V-3.3V range.
[0073] In some embodiments, the battery further includes an electrolyte; the electrolyte includes a lithium salt, a solvent, a first additive, and a second additive. The first additive includes at least one selected from lithium bis(oxalato)borate, tris(trimethylsilyl)borate, 1,3,6-hexanetrionitrile, butadionitrile, and adiponitrile; the second additive includes at least one selected from vinyl ethylene carbonate and lithium difluorophosphate.
[0074] The first additive inhibits the dissolution of transition metal ions such as manganese ions, while the second additive improves the flexibility of the generated SEI film and reduces SEI film rupture caused by the expansion of silicon-based anode materials. Through the synergistic effect of the first and second additives in the electrolyte, lithium ion consumption can be reduced, and the effective capacity utilization and cycle stability of the battery can be improved.
[0075] In some embodiments, the first additive has a mass percentage of 1%-5% in the electrolyte.
[0076] By ensuring that the mass percentage of the first additive in the electrolyte is within the aforementioned range, the inhibition effect on the dissolution of transition metal ions can be guaranteed, the cost of the first additive can be balanced, and the viscosity of the electrolyte can be kept within a suitable range.
[0077] For example, the mass percentage of the first additive in the electrolyte can be 1%, 2%, 3%, 4%, or 5%. In some embodiments, the mass percentage of the second additive in the electrolyte is 5%-10%.
[0078] By ensuring that the mass percentage of the second additive in the electrolyte is within the aforementioned range, the mechanical strength of the SEI film can be improved, and the phenomenon of increased lithium-ion transport impedance caused by excessive SEI film thickness can be avoided. It can also improve low-temperature performance.
[0079] For example, the mass percentage of the second additive in the electrolyte can be 5%, 6%, 7%, 8%, 9%, or 10%.
[0080] In some embodiments, the concentration of lithium salt in the electrolyte is 1 mol / L to 2 mol / L.
[0081] By keeping the concentration of lithium salt in the electrolyte within the above range, the electrolyte can achieve both good ionic conductivity and stability.
[0082] For example, the concentration of lithium salt in the electrolyte can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2 mol / L.
[0083] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.
[0084] The fluoride ions in lithium bisfluorosulfonylimide (LiFSI) possess strong charge-withdrawing ability, weakening the coordination effect between cations and anions in lithium salts, thus enhancing ionic activity and improving electrolyte conductivity. LiFSI also exhibits high thermal stability, a wide electrochemical window, and strong hydrolysis resistance, and can inhibit lithium dendrite growth. Lithium hexafluorophosphate (LiPF6) has high ionic conductivity, a wide electrochemical window, and can promote SEI film formation.
[0085] In some embodiments, the solvent includes at least one of ethylene carbonate, ethyl methyl carbonate, fluoroethylene carbonate, and ethyl propionate.
[0086] Ethylene carbonate (EC) possesses a high dielectric constant, which promotes lithium salt dissociation and improves the ionic conductivity of the electrolyte. Furthermore, the reduction products of EC contribute to the formation of a stable solid electrolyte interfacial film on the electrode surface, enhancing electrode interfacial stability. Ethyl methyl carbonate (EMC) exhibits low viscosity and a low melting point, reducing the viscosity of the electrolyte system and improving the low-temperature performance of the battery. Ethyl propionate (EP) also possesses low melting point and low viscosity, improving the low-temperature performance of the electrolyte. Fluorinated ethylene carbonate (FEC) can be preferentially reduced on the negative electrode surface to form a dense LiF-containing SEI film, enhancing interfacial stability, improving the electrochemical performance of the electrolyte, enhancing environmental adaptability, and improving safety.
[0087] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.
[0088] Example 1 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 hour to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 3%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:3.2, and the lithium source is lithium carbonate.
[0089] Example 2 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 hour to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 1%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x(2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:2, and the lithium source is lithium carbonate.
[0090] Example 3 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 hour to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 8%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:4.9, and the lithium source is lithium carbonate.
[0091] Example 4 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 hour to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 5%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:3.2, and the lithium source is lithium carbonate.
[0092] Example 5: Silicon-oxygen materials, lithium fluoride and lithium source were mixed and then sintered at 750°C for 3 hours to obtain silicon-based anode materials.
[0093] The lithium fluoride content in the total lithium fluoride and silicon-oxygen materials is 3% by mass. The molar ratio of silicon in the silicon source to lithium in the lithium source is 1:3.2. The silicon-oxygen material is a commercially available silicon-oxygen material (SiO2). x The lithium source is lithium carbonate.
[0094] Example 6 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 hour to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 3%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:1.8, and the lithium source is lithium carbonate.
[0095] Example 7 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 hour to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 3%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2).x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:4.5, and the lithium source is lithium carbonate.
[0096] Comparative Example 1: A silicon source and a lithium source were mixed and then sintered at 650℃ for 4 hours to obtain a silicon-based anode material. The molar ratio of silicon in the silicon source to lithium in the lithium source was 1:3.2, and the silicon-oxygen material was a commercially available silicon-oxygen material (SiO₂). x The lithium source is lithium carbonate.
[0097] Comparative Example 2 (1) Lithium fluoride was added to a silicon-oxygen material, and then sintered at 750°C for 1 h to obtain a silicon-based anode material; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 3%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x ).
[0098] Comparative Example 3 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 h to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 0.8%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:1.8, and the lithium source is lithium carbonate.
[0099] Comparative Example 4 (1) Lithium fluoride was added to a silicon-oxygen material, and then pre-sintered at 750°C for 1 h to obtain a composite silicon source; wherein, the mass percentage of lithium fluoride in the total amount of lithium fluoride and silicon-oxygen material was 8.5%, and the silicon-oxygen material was a commercial silicon-oxygen material (SiO2). x (2) Mix the composite silicon source and the lithium source, and then sinter at 650°C for 3.5 h to obtain a silicon-based anode material; wherein the molar ratio of silicon in the composite silicon source and lithium in the lithium source is 1:1.8, and the lithium source is lithium carbonate.
[0100] The silicon-based anode materials from Examples 1-7 and Comparative Examples 1-4 were mixed with conductive agents and binders in a mass ratio of 50:48:2, and then anode sheets were prepared by a dry film deposition process. Different anode sheets were then assembled with cathode sheets, separators, and electrolytes to form CR2016 batteries. The assembled batteries were subjected to charge-discharge performance evaluation and cycle performance testing. The test voltage range was 2.0V-3.3V, and the current was 0.1C. The test results are shown in Table 1.
[0101] The positive electrode sheet is prepared by a dry process using a mixture of positive electrode active material, graphite, and polytetrafluoroethylene in a mass ratio of 90:8:2. The molecular formula of the positive electrode active material is Li. 1.2 Co 0.01 Mn 0.79 O4. The separator is a PP (polypropylene) separator. The electrolyte includes lithium salts, solvents, and additives. The lithium salts include lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. The concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.8M, and the concentration of lithium hexafluorophosphate in the electrolyte is 0.2M. The solvent contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and ethyl propionate (EP) in a mass ratio of 30:50:10:10. The additives include tris(trimethylsilane)phosphate (TMSP), adiponitrile (ADN), and vinyl sulfate (DTD). The mass percentage of TMSP in the electrolyte is 1%, ADN is 2%, and DTD is 1%.
[0102] Table 1. Comparison of battery performance tests in different embodiments and comparative examples.
[0103] As can be seen from the comparison of Examples 1-7 and Comparative Examples 1-2 in Table 1, the batteries prepared using the silicon-based anode materials of Examples 1-7 of this application all have high capacity retention rates. This is mainly because the examples of this application, by adding lithium fluoride as a flux in the precursor, enable the silicon-based anode material to have a low volume expansion effect and help ensure the integrity of the SEI film, thereby improving cycle stability and ensuring a high capacity retention rate. As can be seen from the comparison of Examples 1-7 and Comparative Examples 3-4 in Table 1, the examples of this application, by setting the mass percentage of lithium fluoride in the total amount of silicon source and lithium fluoride to 1%-8%, can reduce negative reactions during sintering, improve the sintering effect, and thus improve the first-cycle discharge capacity and capacity retention rate of the prepared batteries.
[0104] A comparison of Examples 1 and 5 shows that a porous network structure can be constructed through two sintering processes, which enhances cycle stability and ensures a high capacity retention rate.
[0105] The foregoing has provided a detailed description of a silicon-based anode material, its preparation method, anode sheet, and battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A silicon-based anode material, characterized in that, The precursor is obtained by sintering a precursor, which includes a silicon source, a lithium source, and a flux; wherein the flux includes lithium fluoride, and the flux accounts for 1%-8% of the total mass of the silicon source and the flux.
2. The silicon-based anode material according to claim 1, characterized in that, The silicon source includes at least one of elemental silicon and silicon-oxygen materials; wherein the molecular formula of the silicon-oxygen material is SiO2. x , 0 < x < 2; and / or, the lithium source includes at least one of lithium carbonate, lithium hydride, lithium nitrate, lithium hydroxide, lithium oxide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate.
3. The silicon-based anode material according to claim 1 or 2, characterized in that, The molar ratio of silicon in the silicon source to lithium in the lithium source is 1:(2-4.9).
4. A method for preparing a silicon-based anode material, characterized in that, include: The system provides a silicon source, a lithium source, and a flux; wherein the flux includes lithium fluoride, and the flux accounts for 1%-8% of the total mass of the silicon source and the flux. The silicon source, the lithium source, and the flux are mixed and then sintered to obtain a silicon-based anode material.
5. The method for preparing the silicon-based anode material according to claim 4, characterized in that, The step of mixing the silicon source, the lithium source, and the flux and then sintering them to obtain a silicon-based anode material includes: mixing the silicon source and the flux and performing a first sintering to obtain a composite silicon source; and mixing the composite silicon source and the lithium source and performing a second sintering to obtain the silicon-based anode material.
6. The method for preparing the silicon-based anode material according to claim 5, characterized in that, The first sintering includes sintering at a temperature of 600℃-900℃ for 1h-1.5h.
7. The method for preparing the silicon-based anode material according to claim 5, characterized in that, The secondary sintering includes sintering at a temperature of 500℃-800℃ for 3-4 hours.
8. A negative electrode sheet, characterized in that, It includes a negative electrode active layer, wherein the negative electrode active layer comprises a silicon-based negative electrode material as described in any one of claims 1-3, and / or a silicon-based negative electrode material prepared by the method described in any one of claims 4-7.
9. The negative electrode sheet according to claim 8, characterized in that, The negative electrode active layer further includes a conductive agent and a binder; the mass ratio of the silicon-based negative electrode material, the conductive agent and the binder is (45-55):(41-54):(1-4).
10. The negative electrode sheet according to claim 9, characterized in that, The conductive agent includes at least one of graphite, Super P, KS-6 and acetylene black; and / or, the binder includes at least one of polytetrafluoroethylene, polyacrylic acid, sodium carboxymethyl cellulose and styrene-butadiene rubber.
11. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 8-10.
12. The battery according to claim 11, characterized in that, The battery further includes a positive electrode sheet, which comprises a positive electrode active material having the molecular formula Li. 1+x Co y Mn 2-(x+y) O4, 0<x≤0.33, 0<y≤0.
1.
13. The battery according to claim 11, characterized in that, The battery further includes an electrolyte; the electrolyte includes a lithium salt, a solvent, a first additive, and a second additive; wherein the first additive includes at least one of lithium bis(oxalato)borate, tris(trimethylsilyl)borate, 1,3,6-hexanetrionitrile, butadionitrile, and adiponitrile; and the second additive includes at least one of vinyl ethylene carbonate and lithium difluorophosphate.
14. The battery according to claim 13, characterized in that, The first additive has a mass percentage of 1%-5% in the electrolyte; and / or, the second additive has a mass percentage of 5%-10% in the electrolyte; And / or, the concentration of the lithium salt in the electrolyte is 1 mol / L-2 mol / L.