Negative electrode active material, negative electrode, and preparation methods and applications of negative electrode active material and negative electrode

Abstract

The invention relates to a negative electrode active material, a negative electrode and preparation methods and applications of the negative electrode active material and the negative electrode, the negative electrode active material contains first silicon-containing particles and first metal nanowires, the first silicon-containing particles and the first metal nanowires are connected through an alloy, the first metal nanowires comprise metal M, and the alloy phase comprises an M-Si alloy. The lithium ion battery prepared from the negative electrode plate containing the negative electrode active material disclosed by the invention can obtain a relatively low expansion rate, a relatively high capacity retention ratio and a relatively high first effect.

Description

Negative electrode active materials, negative electrodes, their preparation methods and applications Technical Field

[0001] This disclosure relates to the field of lithium-ion battery preparation, specifically to negative electrode active materials, negative electrodes, and their preparation methods and applications. Background Technology

[0002] Metallic materials possess excellent electrical conductivity, good ductility, and superior mechanical properties. Introducing metals into silicon-based materials can restrict silicon expansion and provide efficient electron transport pathways. However, existing methods for introducing metals into silicon-based materials are cumbersome or require high-temperature conditions, and the performance of the prepared materials urgently needs improvement. Summary of the Invention

[0003] The purpose of this disclosure is to provide negative electrode active materials, negative electrodes, methods for their preparation, and applications.

[0004] To achieve the above objectives, the first aspect of this disclosure provides a negative electrode active material containing first silicon-containing particles and first metal nanowires, wherein the first silicon-containing particles and the first metal nanowires are connected by an alloy phase, the first metal nanowires contain metal M, and the alloy phase contains an M-Si alloy.

[0005] Optionally, the diameter of the first metal nanowire is 10~80 nm and the length is 10~100 μm; the metal M is selected from one or more of Sn, Zn, Cu, Ag, In and Ga.

[0006] Optionally, the negative electrode active material further includes a second metal nanowire, which contains metal M; the diameter of the second metal nanowire is 10~80 nm and the length is 10~100 μm.

[0007] Optionally, the negative electrode active material further contains metal nanoparticles, which include metal nanoparticles and / or metal nanosheets; the metal nanoparticles include metal M', which is selected from one or more of Sn, Zn, Cu, Ag, In and Ga; optionally, at least a portion of the metal nanoparticles are connected to the first silicon-containing particles through an alloy phase, which comprises an M'-Si alloy.

[0008] Optionally, the metal nanoparticles have a particle size of 10-50 nm; the metal nanosheets have a thickness of 30-200 nm and a width of 1-10 μm.

[0009] Optionally, the first silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the first silicon-containing particles is 3~20μm, preferably 3~10μm; and the silicon content in the first silicon-containing particles is 40~60% by weight.

[0010] A second aspect of this disclosure provides a method for preparing a negative electrode active material, the method comprising: contacting a first silicon-containing particle with a first metal nanowire in a fourth solvent to form an alloy phase connecting the first silicon-containing particle and the first metal nanowire, thereby obtaining a slurry containing the negative electrode active material; wherein the first metal nanowire comprises a metal M, and the alloy phase comprises an M-Si alloy.

[0011] Optionally, the first metal nanowire is added in the form of a first dispersion; the method further includes: under vacuum conditions, stirring and mixing the mixture containing the first silicon-containing particles and the fourth solvent with the first dispersion for 30-90 minutes at a rotation speed of 200-1500 rpm to obtain a slurry containing the negative electrode active material; the first dispersion contains a first solvent, which includes one or more of water, N,N-dimethylformamide, N-methylpyrrolidone and ethanol.

[0012] Optionally, the diameter of the first metal nanowire is 10~80 nm and the length is 10~100 μm; the metal M is selected from one or more of Sn, Zn, Cu, Ag, In and Ga.

[0013] Optionally, the first silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the first silicon-containing particles is 3~20μm, preferably 3~10μm; and the silicon content in the first silicon-containing particles is 40~60% by weight.

[0014] Optionally, the method further includes: contacting the first silicon-containing particles with the metal nanoparticles in the fourth solvent to form an alloy phase connecting the first silicon-containing particles and the metal nanoparticles, wherein the metal nanoparticles include metal M', and the alloy phase comprises an M'-Si alloy; the metal nanoparticles include metal nanoparticles and / or metal nanosheets; M' is selected from one or more of Sn, Zn, Cu, Ag, In and Ga; the particle size of the metal nanoparticles is 10-50 nm; and the thickness of the metal nanosheets is 30-200 nm and the width is 1-10 μm.

[0015] Optionally, the metal nanoparticles are added in the form of a second dispersion containing a second solvent; the metal nanosheets are added in the form of a third dispersion containing a third solvent; the second solvent and the third solvent respectively include one or more of water, ethanol, N,N-dimethylformamide and N-methyl-2-pyrrolidone.

[0016] Optionally, the fourth solvent includes one or more of water, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethanol, acetone, and isopropanol.

[0017] The third aspect of this disclosure provides a negative electrode active material prepared using the method described in the second aspect of this disclosure.

[0018] The fourth aspect of this disclosure provides a negative electrode, the negative electrode comprising a current collector layer and an active material layer disposed on the current collector; the active material layer contains the negative electrode active material described in the first or third aspect of this disclosure.

[0019] Optionally, the active material layer further contains second silicon-containing particles; the second silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the second silicon-containing particles is 3~20μm, preferably 3~10μm; the silicon content in the second silicon-containing particles is 40~60% by weight; optionally, in the active material layer, the total content of the first silicon-containing particles and the second silicon-containing particles is 60~90% by weight, and the content of active metal elements is 0.1~2% by weight; the active metal elements include one or more of Sn, Zn, Cu, Ag, In, and Ga.

[0020] Optionally, the active material layer further contains a second metal nanowire, the second metal nanowire comprising metal M; the diameter of the second metal nanowire is 10~80 nm and the length is 20~100 μm; optionally, the active material layer further contains metal nanoparticles, the metal nanoparticles including metal nanoparticles and / or metal nanosheets, the metal nanoparticles including metal M'; the particle size of the metal nanoparticles is 10~50 nm; the thickness of the metal nanosheets is 30~200 nm and the width is 1~10 μm.

[0021] Optionally, the active material layer further comprises a binder and a conductive agent; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, sodium polyacrylate, polyvinyl alcohol, and sodium carboxymethyl cellulose; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and graphene.

[0022] The fifth aspect of this disclosure provides a method for preparing a negative electrode, the method comprising: S1, preparing a slurry containing the negative electrode active material using the method described in the second aspect of this disclosure; S2, coating the slurry onto a current collector and then drying it.

[0023] Optionally, the negative electrode active material further comprises a second metal nanowire, the second metal nanowire comprising metal M; the diameter of the second metal nanowire is 10~80 nm and the length is 10~100 μm; optionally, the negative electrode active material further comprises metal nanoparticles, the metal nanoparticles comprising metal nanoparticles and / or metal nanosheets, the metal nanoparticles comprising metal M'; the particle size of the metal nanoparticles is 10~50 nm; the thickness of the metal nanosheets is 30~200 nm and the width is 1~10 μm.

[0024] Optionally, the first metal nanowire is added in the form of a first dispersion, which further contains a second metal nanowire; in the first dispersion, the total content of the first metal nanowire and the second metal nanowire is 1~10 mg / mL.

[0025] Optionally, the metal nanoparticles are added in the form of a second dispersion; in the second dispersion, the content of the metal nanoparticles is 1~10 mg / mL; the metal nanosheets are added in the form of a third dispersion; in the third dispersion, the content of the metal nanosheets is 1~10 mg / mL.

[0026] Optionally, the total weight of the first metal nanowire and the second metal nanowire is in the weight ratio of the metal nanoparticles to (1~10):1.

[0027] Optionally, the slurry further contains a second silicon-containing particle; the second silicon-containing particle includes one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the second silicon-containing particle is 3~20μm, preferably 3~10μm; the silicon content in the second silicon-containing particle is 40~60% by weight.

[0028] Optionally, the slurry further comprises a binder and a conductive agent; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, sodium polyacrylate, polyvinyl alcohol, and sodium carboxymethyl cellulose; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and graphene.

[0029] Optionally, based on the total weight of solids in the slurry, the total content of the first silicon-containing particles and the second silicon-containing particles is 60-90% by weight, and the content of active metal elements is 0.1-2% by weight; the active metal elements include one or more of Sn, Zn, Cu, Ag, In and Ga.

[0030] Optionally, in step S2, the thickness of the wet film coated on the current collector is 40~200μm; the drying temperature is 80~140℃ and the time is 1~10min.

[0031] Optionally, the method further includes: pre-lithiation treatment of the negative electrode obtained in step S2.

[0032] The sixth aspect of this disclosure provides a negative electrode prepared using the method described in the fifth aspect of this disclosure.

[0033] This disclosure provides a seventh aspect of a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode described in the fourth or sixth aspect.

[0034] Optionally, the electrolyte contains an ether solvent.

[0035] Through the above technical solution, the metal nanowires in the negative electrode active material of this disclosure are connected to silicon-containing particles through an alloy phase. The metal nanowires play a role in connecting and fixing the silicon-containing particles, forming a binding network on the outer layer of the silicon-containing particles, thereby suppressing the expansion of the silicon bulk and slowing down or hindering the breakage and pulverization of silicon-containing particles during cycling. In addition, the metal can construct a conductive network other than the conductive agent, which is beneficial to enhance the electrical connection between silicon-containing particles, reduce the generation of dead lithium and isolated lithium during cycling, and also provide a channel for efficient electron transport to the negative electrode, further improving battery performance. The method of this disclosure involves contacting and reacting silicon-containing particles and metal nanowires in a solvent to form an alloy phase connecting the two. This method is simple and prepares a composite negative electrode active material with a metal network binding silicon-based particles under mild conditions. Moreover, the preparation process avoids cumbersome steps such as high-temperature carbonization and post-processing, as well as the influence of high temperature on material performance.

[0036] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0037] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 is a SEM image of the negative electrode active material prepared in Example 1 of the present disclosure; Figure 2 is a SEM image of the negative electrode active material prepared in Example 1 of the present disclosure. Detailed Implementation

[0038] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0039] The first aspect of this disclosure provides a negative electrode active material, the negative electrode active material containing first silicon-containing particles and first metal nanowires, the first silicon-containing particles and the first metal nanowires being connected by an alloy phase, the first metal nanowires containing metal M, and the alloy phase containing an M-Si alloy.

[0040] In one embodiment of this disclosure, a first silicon-containing particle may form an alloy phase with one or more first metal nanowires, and a first metal nanowire may form an alloy phase with one or more first silicon-containing particles.

[0041] The disclosed metal nanowires form a binding network on the outer layer of silicon-containing particles and are connected to the silicon particles through an alloy to form an M-Si alloy. This restricts silicon expansion and slows down or hinders the breakage and pulverization of silicon particles during cycling. Furthermore, the metal nanowires can construct a conductive network in addition to the conductive agent, which is beneficial for enhancing the electrical connections between silicon-containing particles, reducing the generation of dead lithium and isolated lithium islands during cycling, and also providing a highly efficient electron transport channel for the negative electrode, further improving battery performance.

[0042] In one embodiment of this disclosure, the diameter of the first metal nanowire is 10-80 nm, preferably 10-70 nm; the length is 10-100 μm, preferably 30-80 μm; the first metal nanowire with the above structure is beneficial to forming a bound network, reducing the silicon expansion rate during battery use, and improving battery performance.

[0043] In one embodiment of this disclosure, the type of metal M is not particularly limited and can be any metal capable of forming an alloy with Si. In a further embodiment, the metal M is selected from one or more of Sn, Zn, Cu, Ag, In and Ga.

[0044] In one embodiment of this disclosure, the negative electrode active material further includes a second metal nanowire, the second metal nanowire comprising metal M; the diameter of the second metal nanowire is 10~80nm, preferably 10~70nm; and the length is 10~100μm, preferably 30~80μm.

[0045] To further reduce the expansion rate and improve battery performance, in one embodiment of this disclosure, the negative electrode active material also contains metal nanoparticles, which include metal nanoparticles and / or metal nanosheets. At least a portion of the metal nanoparticles are connected to the first silicon-containing particles through an alloy phase, which contains an M'-Si alloy.

[0046] In one embodiment of this disclosure, the metal nanoparticles include metal M'. The type of metal M' is not particularly limited and can be any type that can form an alloy with Si. In a further embodiment, M' is selected from one or more of Sn, Zn, Cu, Ag, In and Ga. Metal M' may be the same as or different from metal M, but preferably the same.

[0047] In a further embodiment, the particle size of the metal nanoparticles is 10~50nm; metal nanoparticles with the above structure are beneficial to forming a bound network, reducing the silicon expansion rate during battery use, and improving battery performance.

[0048] In a further embodiment, the metal nanosheet has a thickness of 30~200nm and a width of 1~10μm. The "width" refers to the maximum dimension of the metal nanosheet passing through the center in its sheet direction, and the "thickness" refers to the thickness of the metal nanosheet in the direction perpendicular to its sheet. Metal nanosheets with the above structure are beneficial for forming a bound network, reducing the silicon expansion rate during battery use, and improving battery performance.

[0049] In one embodiment of this disclosure, the first silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles, wherein the silicon-oxygen particles include silicon oxide particles (SiO2). x (x≤2), organosilicon oxygen particles.

[0050] In one embodiment of this disclosure, the average particle size of the first silicon-containing particles is 3~20μm, preferably 3~10μm. Silicon-containing particles with the above-mentioned size are beneficial to forming an alloy phase structure with nanowires, thereby limiting the expansion of the silicon bulk and reducing the expansion rate.

[0051] In one embodiment of this disclosure, the silicon content in the first silicon-containing particle is 40-60% by weight.

[0052] The second aspect of this disclosure provides a method for preparing a negative electrode active material, wherein a first silicon-containing particle and a first metal nanowire are contacted in a fourth solvent to form an alloy phase connecting the first silicon-containing particle and the first metal nanowire, thereby obtaining a slurry containing the negative electrode active material; the first metal nanowire comprises metal M, and the alloy phase comprises an M-Si alloy.

[0053] The method disclosed herein involves contacting silicon-containing particles with first metal nanowires to form an alloy phase, thereby maintaining good electrical connectivity between the silicon-containing particles, limiting the expansion of the silicon bulk, and reducing the formation of dead lithium and isolated lithium islands during cycling. The method of this disclosure is simple, preparing a silicon-based anode active material incorporating metal under mild conditions, avoiding cumbersome steps such as high-temperature carbonization and post-processing, as well as the impact of high temperatures on material properties.

[0054] In one embodiment of this disclosure, the first metal nanowires are added in the form of a first dispersion. The method further includes: under vacuum conditions, stirring and mixing the mixture containing the first silicon-containing particles and the fourth solvent with the first dispersion for 30-90 minutes, preferably 40-60 minutes, including but not limited to 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, or any combination thereof; the rotation speed is 200-1500 rpm, preferably 400-800 rpm, including but not limited to 200 rpm, 300 rpm, 400 rpm, 500 rpm, 800 rpm, 1200 rpm, 1500 rpm, or any combination thereof; obtaining a slurry containing the negative electrode active material; adding the first metal nanowires in the form of a dispersion and controlling the conditions can make the first metal nanowires uniformly distributed, avoid agglomeration, facilitate the formation of the alloy phase, and further reduce the expansion rate.

[0055] In one embodiment of this disclosure, the first dispersion contains a first solvent, which includes one or more of water, N,N-dimethylformamide, N-methylpyrrolidone, and ethanol.

[0056] In one embodiment of this disclosure, the method further includes: contacting the first silicon-containing particles with metal nanoparticles in the fourth solvent to form an alloy phase connecting the first silicon-containing particles and the metal nanoparticles, the metal nanoparticles comprising metal M', the alloy phase comprising an M'-Si alloy, wherein at least a portion of the metal nanoparticles form an alloy phase with the first silicon-containing particles.

[0057] In one embodiment of this disclosure, the metal nanoparticles are added in the form of a second dispersion containing a second solvent; the metal nanosheets are added in the form of a third dispersion containing a third solvent; the second solvent and the third solvent respectively include one or more of water, ethanol, N,N-dimethylformamide and N-methyl-2-pyrrolidone.

[0058] In one specific embodiment of this disclosure, the method includes: under vacuum conditions, contacting a mixture containing first silicon-containing particles and a fourth solvent, a first dispersion containing first metal nanowires, an optional second dispersion containing metal nanoparticles, and an optional third dispersion containing metal nanosheets; the first dispersion, the second dispersion, and the third dispersion are added sequentially at intervals, without any specific limitation on the order of addition.

[0059] According to one embodiment of this disclosure, after adding the second or third dispersion, the mixture is stirred and mixed under vacuum for 10 to 60 minutes, preferably 20 to 40 minutes, including but not limited to 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, or any combination thereof; the rotation speed is 800 to 3000 rpm, preferably 1200 to 1800 rpm, including but not limited to 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or any combination thereof.

[0060] In one embodiment of this disclosure, the fourth solvent includes one or more of water, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethanol, acetone, and isopropanol.

[0061] In one embodiment of this disclosure, the slurry containing the negative electrode active material further contains a second metal nanowire. The second metal nanowire and the first metal nanowire are added simultaneously through a first dispersion. The first metal nanowire and the second metal nanowire may be of the same or different types, preferably the same.

[0062] The third aspect of this disclosure provides a negative electrode active material prepared using the method described in the second aspect of this disclosure.

[0063] The negative electrode active material described in the third aspect of this disclosure has the same characteristics as the negative electrode active material described in the first aspect of this disclosure, and will not be described again here.

[0064] The fourth aspect of this disclosure provides a negative electrode, the negative electrode comprising a current collector layer and an active material layer disposed on the current collector; the active material layer contains the negative electrode active material described in the first or third aspect of this disclosure.

[0065] In one embodiment of this disclosure, the active material layer further comprises second silicon-containing particles; the second silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the second silicon-containing particles are silicon-containing particles that have not formed an alloy phase, wherein the silicon-oxygen particles include silicon oxide particles (SiO2). x(x≤2), organosilicon oxygen particles.

[0066] In one embodiment of this disclosure, the average particle size of the second silicon-containing particles is 3-20 μm, preferably 3-10 μm; the silicon content in the second silicon-containing particles is 40-60% by weight.

[0067] In one embodiment of this disclosure, the total content of the first silicon-containing particles and the second silicon-containing particles in the active material layer is 60-90% by weight, including but not limited to 60% by weight, 65% by weight, 70% by weight, 73% by weight, 80% by weight, 85% by weight, 88% by weight, 90% by weight, or any combination thereof; the content of the active metal element is 0.1-2% by weight, including but not limited to 0.1% by weight, 0.5% by weight, 0.8% by weight, 1.0% by weight, 1.2% by weight, 1.5% by weight, 1.8% by weight, 2% by weight, or any combination thereof; the active metal element includes one or more of Sn, Zn, Cu, Ag, In, and Ga, and the active metal element is a metal element in metal nanowires and metal nanoparticles; limiting the content of silicon-containing particles and active metal within the above range can reduce the expansion rate while taking into account electron transport performance, thereby improving battery performance.

[0068] In one embodiment of this disclosure, the active material layer further contains a second metal nanowire.

[0069] In one embodiment of this disclosure, the active material layer further contains metal nanoparticles.

[0070] In one embodiment of this disclosure, the active material layer further comprises a binder and a conductive agent; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, sodium polyacrylate, polyvinyl alcohol, and sodium carboxymethyl cellulose; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and graphene.

[0071] In one embodiment of this disclosure, the current collector layer includes one or more of aluminum foil current collectors, copper foil current collectors, and carbon-coated copper foil, and the thickness of the current collector layer is 6~10μm.

[0072] In one embodiment of this disclosure, a first active material layer and a second active material layer are respectively provided on both sides of the current collector layer. The thickness and composition of the first active material layer and the second active material layer may be the same or different, but preferably the same.

[0073] The fifth aspect of this disclosure provides a method for preparing a negative electrode, the method comprising: S1, preparing a slurry containing the negative electrode active material using the method described in the second aspect of this disclosure; S2, coating the slurry onto a current collector and then drying it.

[0074] In one embodiment of this disclosure, the slurry further comprises a binder and a conductive agent; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, sodium polyacrylate, polyvinyl alcohol, and sodium carboxymethyl cellulose; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and graphene. The amounts of binder, conductive agent, and fourth solvent are conventional in the art. For example, the weight ratio of the total weight of the first silicon-containing particles and the second silicon-containing particles, the binder, the conductive agent, and the fourth solvent is 1:(0.05~0.2):(0.001~0.02):(0.2~0.4).

[0075] In one embodiment of this disclosure, the slurry further contains second silicon-containing particles.

[0076] In one embodiment of this disclosure, the first silicon-containing particle and the second silicon-containing particle are added simultaneously, and the first silicon-containing particle and the second silicon-containing particle can be the same substance.

[0077] In one embodiment of this disclosure, based on the total weight of solids in the slurry, the total content of the first silicon-containing particles and the second silicon-containing particles is 60-90% by weight, including but not limited to 60% by weight, 65% by weight, 70% by weight, 73% by weight, 80% by weight, 85% by weight, 88% by weight, 90% by weight, or any combination thereof; the content of active metal elements is 0.1-2% by weight, including but not limited to 0.1% by weight, 0.5% by weight, 0.8% by weight, 1.0% by weight, 1.2% by weight, 1.5% by weight, 1.8% by weight, 2% by weight, or any combination thereof; "total weight of solids in the slurry" includes the total weight of binder, conductive agent, first silicon-containing particles, first metal nanowires, optional second silicon-containing particles, optional second metal nanowires, and optional metal nanoparticles.

[0078] In one embodiment of this disclosure, the negative electrode active material further comprises a second metal nanowire.

[0079] In one embodiment of this disclosure, the negative electrode active material further comprises metal nanoparticles.

[0080] In one embodiment of this disclosure, both the first metal nanowire and the second metal nanowire are added through a first dispersion, and the first metal nanowire and the second metal nanowire can be the same substance.

[0081] In one embodiment of this disclosure, the first metal nanowire is added in the form of a first dispersion, the first dispersion further containing a second metal nanowire; in the first dispersion, the total content of the first metal nanowire and the second metal nanowire is 1~10 mg / mL, including but not limited to 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, or any combination thereof.

[0082] In one embodiment of this disclosure, the weight ratio of the total weight of the first metal nanowire and the second metal nanowire to the weight of the metal nanoparticle is (1~10):1, including but not limited to 1:1, 2:1, 3:1, 3.5:1, 5:1, 6:1, 8:1, and 10:1.

[0083] In one embodiment of this disclosure, the metal nanoparticles are added in the form of a second dispersion; in the second dispersion, the content of the metal nanoparticles is 1~10 mg / mL, including but not limited to 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, or any combination thereof, and the above content includes the total content of metal nanoparticles that are connected to the first silicon-containing particles through the alloy phase and those that have not formed the alloy phase.

[0084] According to one embodiment of this disclosure, the metal nanosheets are added in the form of a third dispersion; in the third dispersion, the content of the metal nanosheets is 1~10 mg / mL, including but not limited to 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, or any combination thereof, or any combination thereof, or any combination thereof, or any combination thereof, and the above content includes the total content of metal nanosheets connected to the first silicon-containing particles by the alloy phase and those that have not formed the alloy phase.

[0085] In one specific embodiment of this disclosure, step S1 includes: sequentially adding a first dispersion, an optional second dispersion, and an optional third dispersion to a fourth dispersion containing a binder, a conductive agent, a fourth solvent, first silicon-containing particles, and an optional second silicon-containing particle to obtain a slurry containing a negative electrode active material; the method for preparing the mixture containing the binder, conductive agent, fourth solvent, first silicon-containing particles, and an optional second silicon-containing particle is conventional in the art; the second dispersion and the third dispersion contain metal nanoparticles and metal nanosheets, respectively, and there is no specific limitation on the order of addition of the first dispersion, the second dispersion, and the third dispersion.

[0086] In one embodiment of this disclosure, in step S2, the thickness of the wet film coated on the current collector is 40~200μm. The above thickness can avoid the negative impact of excessive active material layer thickness on electrode performance, and can also ensure that the electrode has good performance. The drying treatment temperature is 80~140℃ and the time is 1~10min.

[0087] In one embodiment of this disclosure, the method of applying slurry to the current collector in step S2 is conventional in the art, including scraping, electrostatic spraying, etc.

[0088] In one embodiment of this disclosure, step S2 includes: applying slurry to both sides of the current collector and then drying it; the thickness of the wet film on both sides may be the same or different.

[0089] In one embodiment of this disclosure, the negative electrode obtained in step S2 is pre-lithiated, for example, by using lithium foil or lithium powder. Pre-lithiation can promote the formation and distribution of the M-Si alloy phase, and lithium can form an alloy phase with silicon particles, metal nanowires, and metal nanoparticles, further improving the performance of the negative electrode sheet. The thickness of the lithium foil can be 5~20μm. This disclosure does not impose specific limitations on the conditions and steps of pre-lithiation.

[0090] The sixth aspect of this disclosure provides a negative electrode prepared using the method described in the fifth aspect of this disclosure.

[0091] The negative electrode described in the sixth aspect of this disclosure has the same characteristics as the negative electrode described in the fourth aspect of this disclosure, and will not be repeated here.

[0092] The seventh aspect of this disclosure provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode described in the fourth or sixth aspect of this disclosure.

[0093] In one embodiment of this disclosure, the electrolyte contains an ether solvent, which may include one or more of fluorinated ethers and non-fluorinated ethers, preferably including ethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl ethyl ether, tetrafluoroethyl-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2- One or more of the following: trifluoroethyl ether, difluoromethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1,1,2,3,3,3-pentafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether and bis(2,2-difluoroethyl) ether (BDE).

[0094] In one embodiment of this disclosure, the lithium salt in the electrolyte includes one or more of LiPF6, LiN(SO2F)2, LiN(CF3SO2)2, LiCF3SO3, LiC(CF3SO2)3, LiB(C2O4)2, Li2Al(CSO3Cl4), LiP(C6H4O2)3, LiPF3(C2F5)3, LiN(CF3SO2)2, and LiN(SiC3H9)2.

[0095] In one embodiment of this disclosure, the positive electrode includes layered oxides, phosphate-based polyanionic materials, etc.

[0096] The present invention will be described in detail below through embodiments, but is not limited to the following embodiments.

[0097] Unless otherwise specified, all reagents used in the following examples and comparative examples were commercially available.

[0098] The total content of the first and second silicon-containing particles and the content of active metal elements in the active material layer are the same as those in the slurry composition.

[0099] Example 1 uses the following steps to prepare the negative electrode and lithium-ion battery: Step (1), silicon carbon material (purchased from a reagent website, average particle size of 6 μm, silicon content of 50% by weight) is added to polyacrylic acid (PAA) as a binder and stirred at 500 rpm; then single-walled carbon nanotubes (SWCNT) and conductive graphite are added as conductive agents and stirred at 1500 rpm for 90 min; then deionized water is added and stirred continuously for 360 min; the weight ratio of silicon carbon material, binder, conductive agent and water is 1:0.15:0.02:0.25; Step (2), the first dispersion of DMF (N,N-dimethylformamide) (concentration 1 mg / mL) containing silver nanowires (purchased from Aladdin, purity 99.5% by weight, diameter 10~30 nm, length 80 μm) is added to the mixture in step (1) and stirred continuously at 200 rpm under vacuum for 30 min. min, a slurry containing the negative electrode active material is obtained, the slurry containing the negative electrode active material of this disclosure; based on the total weight of solids in the slurry, the total content of silicon carbon particles is 85% by weight, and the content of active metal element Ag is 0.5% by weight; step (3), the slurry obtained in step (2) is coated on both sides of the copper current collector (thickness 8μm), the wet film thickness is 100μm respectively, and then dried at 120℃ for 5min; the electrode obtained after drying is subjected to SEM test, which is the SEM test image of the negative electrode active material, the results are listed in Figures 1 and 2, where Figure 2 is an enlarged image. According to Figures 1 and 2, it can be seen that the negative electrode active material of this disclosure contains connected silicon-containing particles and metal nanowires; step (4), the electrode obtained in step (3) is coated with 10 After pressing μm lithium foil, a negative electrode sheet is obtained, which is numbered L-AS; in step (5), the L-AS electrode sheet obtained in step (4) is stacked alternately with ternary NCM622, and the positive and negative electrodes are separated by a separator. The bare cell is placed in an aluminum-plastic film and injected with electrolyte (solvent: 60% by weight of methyl ethyl carbonate (EMC) + 20% by weight of diethyl carbonate (DEC) + 20% by weight of fluoroethylene carbonate (FEC), and the content of lithium salt LiPF6 is 15% by weight). The amount of electrolyte injected is 3 g / Ah. After injection, vacuum sealing is performed. The sealed cell is left to stand at 45 ℃ for 48 h to allow the electrolyte to fully wet it, and a lithium-ion battery is obtained. The parameters of the electrode sheet are listed in Table 1.

[0100] Example 2 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery, with the difference being: In step (2), a second dispersion of DMF (N,N-dimethylformamide) with silver nanoparticles (purchased from Aladdin, purity 99.5%, weight 0.1%, particle size 10~20nm) (concentration 1 mg / mL) is added to the mixture in step (1), and stirred and dispersed at 800 rpm for 40 min under vacuum; a first dispersion of DMF (N,N-dimethylformamide) with silver nanowires (purchased from Aladdin, purity 99.5%, diameter 10~30 nm, length 80 μm) (concentration 1 mg / mL) is added to the mixture obtained by the above stirring and dispersion, and stirred at 200 rpm for 30 min under vacuum. After min, a slurry containing the negative electrode active material was obtained. The slurry contained the negative electrode active material of this disclosure. Based on the total weight of solids in the slurry, the total content of silicon carbon particles was 85% by weight, the content of active metal elements was 0.5% by weight, and the weight ratio of silver nanowires to silver nanoparticles was 4:1. The parameters of the negative electrode are listed in Table 1. SEM testing of the negative electrode active material showed that the negative electrode active material of this disclosure contains connected silicon-containing particles and metal nanowires.

[0101] Example 3 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery, the difference being that the silver nanowires are replaced with an equal weight of copper nanowires (purchased from Aladdin, purity 99% by weight, diameter 30 nm, length 80 μm). The parameters of the negative electrode are listed in Table 1. SEM testing of the negative electrode active material shows that the negative electrode active material disclosed in this invention contains connected silicon-containing particles and metal nanowires.

[0102] Example 4 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery, except that the silver nanowires are replaced with an equal weight of zinc nanowires (purchased from Aladdin, 99% by weight, 30 nm in diameter and 80 μm in length). The parameters of the negative electrode are listed in Table 1. SEM testing of the negative electrode active material shows that the negative electrode active material disclosed in this invention contains connected silicon particles and metal nanowires.

[0103] Example 5 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery, the difference being that the average particle size of the silicon-carbon material is 3 μm, and the parameters of the negative electrode are listed in Table 1; SEM testing of the negative electrode active material shows that the negative electrode active material disclosed herein contains connected silicon-containing particles and metal nanowires.

[0104] Example 6 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery, the difference being that the silver nanowires have a diameter of 80 nm and a length of 100 μm. The parameters of the negative electrode are listed in Table 1. SEM testing of the negative electrode active material shows that the negative electrode active material disclosed in this invention contains connected silicon-containing particles and metal nanowires.

[0105] Example 7 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery. The difference is that in step (2), the amount of raw materials is adjusted. Based on the total weight of solids in the slurry, the total content of silicon carbon particles is 85% by weight, and the content of active metal elements is 0.1% by weight. The parameters of the negative electrode are listed in Table 1. SEM test of the negative electrode active material shows that the negative electrode active material disclosed in this invention contains connected silicon particles and metal nanowires.

[0106] Example 8 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery. The difference is that in step (2), the amount of raw materials is adjusted. Based on the total weight of solids in the slurry, the total content of silicon carbon particles is 90% by weight, and the content of active metal elements is 0.5% by weight. The parameters of the negative electrode are listed in Table 1. SEM test of the negative electrode active material shows that the negative electrode active material disclosed in this invention contains connected silicon-containing particles and metal nanowires.

[0107] Comparative Example 1 uses the method of Example 1 to prepare a negative electrode and a lithium-ion battery. The difference is that the first dispersion containing silver nanowires is not added in step (2). The weight ratio of silicon carbon material, binder, conductive agent and water is 1:0.15:0.02:0.25. The parameters of the negative electrode are listed in Table 1.

[0108] Test Example: Electrode Conductivity Test: The conductivity of the electrode was tested using a small pressure resistance meter from Yuaneng Technology at a test pressure of 25 MPa. The electrode was placed on the test bench for testing. Six potentials were measured for each electrode, and the test time for each potential was 20 seconds. After all six points were measured, the average value of the six points was recorded as the conductivity of the electrode, with the unit being S / cm.

[0109] First-time efficiency test: The lithium-ion battery prepared in the example was subjected to step-by-step lithium insertion at the negative electrode at a rate of 0.2 C to 0.05 C under the condition of 25 ℃ (room temperature), with a cutoff voltage of 0.005 V, and left to stand for 10 min; then lithium was removed at a rate of 0.1 C, with a cutoff voltage of 1.5 V; First-time efficiency (%) = Lithium removal capacity / Lithium insertion capacity × 100%.

[0110] Cell thickness expansion test: Under 25 ℃ (room temperature) conditions, the lithium-ion battery is charged at a constant current rate of 1 C with a cutoff voltage of 4.2 V. After standing for 10 min, it is charged at a constant voltage until the current is ≤0.1 C and then stopped. After standing for 10 min, it is discharged at a constant current rate of 1 C with a cutoff voltage of 2.2 V and then stood for 10 min. This process is recorded as the first cycle. The above process is repeated for 300 cycles. The electrode thickness before and after 300 cycles is measured with a micrometer. Cell thickness expansion rate (%) = (thickness after cycle - thickness before cycle) / thickness before cycle × 100%.

[0111] Cyclic performance test: At 25 ℃ (room temperature), the lithium-ion battery was charged at a constant current rate of 0.5 C, with a cutoff voltage of 4.2 V. After resting for 10 min, constant voltage charging was performed until the current ≤ 0.05 C, at which point charging was stopped, and the battery was allowed to rest for 10 min. Then, it was discharged at a constant current rate of 0.5 C, with a cutoff voltage of 2.2 V, and allowed to rest for 10 min. This process was recorded as the first cycle, and the discharge capacity was recorded as the first discharge capacity. This process was repeated for 300 cycles, and the discharge capacity was recorded for each cycle. Cycle retention rate (%) = (300th cycle discharge capacity / first discharge capacity) × 100%.

[0112] The test parameters are listed in Table 1.

[0113] Table 1

[0114] Based on the above data, it can be seen that the method disclosed herein can prepare silicon-based anode active materials with introduced metals under relatively mild conditions, and make them into anode sheets for use in lithium-ion batteries, thereby obtaining lower expansion rate, higher capacity retention rate, first-time efficiency and conductivity.

[0115] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0116] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0117] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A negative electrode active material, characterized in that, The negative electrode active material contains first silicon-containing particles and first metal nanowires. The first silicon-containing particles and the first metal nanowires are connected by an alloy phase. The first metal nanowires contain metal M, and the alloy phase contains an M-Si alloy.

2. The negative electrode active material according to claim 1, wherein, The diameter of the first metal nanowire is 10~80nm and the length is 10~100μm; the metal M is selected from one or more of Sn, Zn, Cu, Ag, In and Ga.

3. The negative electrode active material according to claim 1, wherein, The negative electrode active material further includes a second metal nanowire, which contains metal M; the diameter of the second metal nanowire is 10~80nm and the length is 10~100μm.

4. The negative electrode active material according to claim 1, wherein, The negative electrode active material also contains metal nanoparticles, which include metal nanoparticles and / or metal nanosheets; the metal nanoparticles include metal M', which is selected from one or more of Sn, Zn, Cu, Ag, In and Ga; optionally, at least a portion of the metal nanoparticles are connected to the first silicon-containing particles through an alloy phase, which comprises an M'-Si alloy.

5. The negative electrode active material according to claim 4, wherein, The metal nanoparticles have a particle size of 10-50 nm; the metal nanosheets have a thickness of 30-200 nm and a width of 1-10 μm.

6. The negative electrode active material according to claim 1, wherein, The first silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the first silicon-containing particles is 3~20μm, preferably 3~10μm; the silicon content in the first silicon-containing particles is 40~60% by weight.

7. A method for preparing a negative electrode active material, characterized in that, The method includes: contacting a first silicon-containing particle with a first metal nanowire in a fourth solvent to form an alloy phase connecting the first silicon-containing particle and the first metal nanowire, thereby obtaining a slurry containing the negative electrode active material; the first metal nanowire comprises metal M, and the alloy phase comprises an M-Si alloy.

8. The method according to claim 7, wherein, The first metal nanowire is added in the form of a first dispersion; the method further includes: under vacuum conditions, stirring and mixing the mixture containing the first silicon-containing particles and the fourth solvent with the first dispersion for 30-90 minutes at a speed of 200-1500 rpm to obtain a slurry containing the negative electrode active material; the first dispersion contains a first solvent, which includes one or more of water, N,N-dimethylformamide, N-methylpyrrolidone and ethanol.

9. The method according to claim 7, wherein, The diameter of the first metal nanowire is 10~80nm and the length is 10~100μm; the metal M is selected from one or more of Sn, Zn, Cu, Ag, In and Ga.

10. The method according to claim 7, wherein, The first silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the first silicon-containing particles is 3~20μm, preferably 3~10μm; the silicon content in the first silicon-containing particles is 40~60% by weight.

11. The method according to claim 7, wherein, The method further includes: contacting the first silicon-containing particles with metal nanoparticles in the fourth solvent to form an alloy phase connecting the first silicon-containing particles and the metal nanoparticles, wherein the metal nanoparticles include metal M', and the alloy phase comprises an M'-Si alloy; the metal nanoparticles include metal nanoparticles and / or metal nanosheets; M' is selected from one or more of Sn, Zn, Cu, Ag, In and Ga; the particle size of the metal nanoparticles is 10-50 nm; and the thickness of the metal nanosheets is 30-200 nm and the width is 1-10 μm.

12. The method according to claim 11, wherein, The metal nanoparticles are added in the form of a second dispersion containing a second solvent; the metal nanosheets are added in the form of a third dispersion containing a third solvent; the second solvent and the third solvent respectively include one or more of water, ethanol, N,N-dimethylformamide and N-methyl-2-pyrrolidone.

13. The method according to claim 7, wherein, The fourth solvent includes one or more of water, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethanol, acetone, and isopropanol.

14. The negative electrode active material prepared by the method according to any one of claims 7 to 13.

15. A negative electrode, the negative electrode comprising a current collector layer and an active material layer disposed on the current collector; characterized in that, The active material layer contains the negative electrode active material as described in any one of claims 1 to 6 and 14.

16. The negative electrode according to claim 15, wherein, The active material layer further contains second silicon-containing particles; the second silicon-containing particles include one or more of elemental silicon particles, silicon-oxygen particles, and silicon-carbon particles; the average particle size of the second silicon-containing particles is 3~20μm, preferably 3~10μm; the silicon content in the second silicon-containing particles is 40~60% by weight; optionally, in the active material layer, the total content of the first silicon-containing particles and the second silicon-containing particles is 60~90% by weight, and the content of active metal elements is 0.1~2% by weight; the active metal elements include one or more of Sn, Zn, Cu, Ag, In, and Ga.

17. The negative electrode according to claim 15, wherein, The active material layer further contains a second metal nanowire, which comprises metal M; the diameter of the second metal nanowire is 10-80 nm and the length is 20-100 μm; optionally, the active material layer further contains metal nanoparticles, which include metal nanoparticles and / or metal nanosheets, and the metal nanoparticles include metal M'; the particle size of the metal nanoparticles is 10-50 nm; the thickness of the metal nanosheets is 30-200 nm and the width is 1-10 μm.

18. The negative electrode according to claim 15, wherein, The active material layer also contains a binder and a conductive agent; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, sodium polyacrylate, polyvinyl alcohol, and sodium carboxymethyl cellulose; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and graphene.

19. A method for preparing a negative electrode, characterized in that, The method includes: S1, preparing a slurry containing the negative electrode active material using the method described in any one of claims 7 to 13; S2, coating the slurry onto a current collector and then drying it.

20. The method according to claim 19, wherein, The negative electrode active material further comprises a second metal nanowire, which contains metal M; the diameter of the second metal nanowire is 10~80 nm and the length is 10~100 μm; optionally, the negative electrode active material further comprises metal nanoparticles, which include metal nanoparticles and / or metal nanosheets, and the metal nanoparticles include metal M'; the particle size of the metal nanoparticles is 10~50 nm; the thickness of the metal nanosheets is 30~200 nm and the width is 1~10 μm.

21. The method according to claim 20, wherein, The first metal nanowire is added in the form of a first dispersion, which also contains a second metal nanowire; the total content of the first metal nanowire and the second metal nanowire in the first dispersion is 1~10 mg / mL.

22. The method according to claim 20, wherein, The metal nanoparticles are added in the form of a second dispersion; in the second dispersion, the content of the metal nanoparticles is 1~10 mg / mL; the metal nanosheets are added in the form of a third dispersion; in the third dispersion, the content of the metal nanosheets is 1~10 mg / mL.

23. The method according to claim 20, wherein, The total weight ratio of the first metal nanowire and the second metal nanowire to the weight of the metal nanoparticle is (1~10):

1.

24. The method according to claim 19, wherein, The slurry also contains a second silicon-containing particle; the second silicon-containing particle includes one or more of elemental silicon particles, silicon-oxygen particles and silicon-carbon particles; the average particle size of the second silicon-containing particle is 3~20μm, preferably 3~10μm; the silicon content in the second silicon-containing particle is 40~60% by weight.

25. The method according to claim 19, wherein, The slurry also contains a binder and a conductive agent; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, sodium polyacrylate, polyvinyl alcohol, and sodium carboxymethyl cellulose; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and graphene.

26. The method according to claim 25, wherein, Based on the total weight of solids in the slurry, the total content of the first silicon-containing particles and the second silicon-containing particles is 60-90% by weight, and the content of active metal elements is 0.1-2% by weight; the active metal elements include one or more of Sn, Zn, Cu, Ag, In and Ga.

27. The method according to claim 19, wherein, In step S2, the thickness of the wet film coated on the current collector is 40~200 μm; the drying temperature is 80~140℃ and the time is 1~10 min.

28. The method according to claim 19, wherein, The method further includes: pre-lithiation treatment of the negative electrode obtained in step S2.

29. The negative electrode prepared by the method according to any one of claims 19 to 28.

30. A lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The negative electrode is the negative electrode according to any one of claims 15-18 and 29.

31. The lithium-ion battery according to claim 30, wherein, The electrolyte contains ether solvents.

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