Negative active material, preparation method of negative active material and lithium ion battery

Abstract

The invention relates to a negative electrode active material, a preparation method of the negative electrode active material and a lithium ion battery. The negative electrode active material is used for the lithium ion battery, the negative electrode active material comprises a silicon-carbon compound, the silicon-carbon compound comprises silicon particles and porous fiber carbon nets, and the silicon particles are located between the porous fiber carbon nets to form a sandwich structure; carbon nanotubes and amorphous carbon are embedded in the porous fiber carbon net, and the thickness of the porous fiber carbon net is 20-500 nm. The porous fiber carbon net of the silicon-carbon compound is formed through a melt-blowing method, the prepared silicon-carbon compound is uniform and controllable in particle size and higher in compression resistance, tensile strength, electric conductivity and heat conductivity, and the expansion, cycle life and low-temperature rate performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The invention discloses a negative electrode active material for a lithium ion battery, a method for preparing the negative electrode active material, and a lithium ion battery comprising the negative electrode active material. Background Art

[0002] Lithium-ion batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc. As lithium-ion batteries have made great progress, higher requirements are placed on the performance of lithium-ion batteries. In order to improve the energy density of lithium-ion batteries, the industry is currently considering the use of silicon-based negative electrode active materials. However, although silicon-based materials have a higher gram capacity, they have a large expansion, which seriously affects the cycle performance of the battery.

[0003] In order to solve this problem, the expansion of silicon materials is improved through micro-manufacturing (micro-machining) of active materials, the introduction of inert substrates and the use of surface treatment. At present, carbon materials using conventional liquid phase coating technology often have the problem of uneven coating. If the coating layer is too thick, it will hinder the migration of lithium ions; if the coating layer is too thin, it may lead to insufficient conductivity and compressive resistance at the defect. Or the carbon skeleton structure is formed by HF etching, but there are many processes, high and complex operation requirements, and increased costs. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a negative electrode active material, a preparation method of the negative electrode active material and a lithium ion battery, wherein the negative electrode active material exhibits improved cycle life characteristics and improved compression, tension and low expansion characteristics.

[0005] In the first aspect, the present invention provides a negative electrode active material for a lithium-ion battery, comprising a silicon-carbon composite, wherein the silicon-carbon composite comprises silicon particles and a porous fibrous carbon mesh, and the silicon particles are located between the porous fibrous carbon mesh to form a sandwich structure; and the porous fibrous carbon mesh is embedded with carbon nanotubes and amorphous carbon, and the thickness of the porous fibrous carbon mesh is 20nm to 500nm.

[0006] In some embodiments, the porous fibrous carbon web is formed by meltblowing.

[0007] In some embodiments, the average particle size of the silicon-carbon composite is 2 μm to 60 μm, preferably 5 μm to 15 μm.

[0008] In some embodiments, the average particle size of the silicon particles is 5 nm to 5000 nm, preferably 10 nm to 500 nm.

[0009] In some embodiments, the thickness of the porous fibrous carbon net is 30 nm to 200 nm; or / and the pore size of the network pores of the porous fibrous carbon net is 30 nm to 200 nm, preferably 50 nm to 160 nm.

[0010] In some embodiments, the porous fibrous carbon mesh further has a graphene layer on its surface, and the thickness of the graphene layer is 1 nm to 10 nm, preferably 2 nm to 5 nm.

[0011] In some embodiments, the negative electrode active material further comprises at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microbeads, or silicon oxide.

[0012] In a second aspect, the present invention provides a method for preparing a negative electrode active material for a lithium ion battery, wherein the negative electrode active material comprises a silicon-carbon composite, and the formation of the silicon-carbon composite comprises the following steps:

[0013] S1. Mixing and stirring the polymer material and the carbon nanotubes in a molten state at a mass ratio of 1:1 to 80 to obtain a mixed slurry;

[0014] S2, spraying the mixed slurry onto the surface of a web-forming roller having a concave-convex shape by a melt-blowing method to form a first porous fiber web;

[0015] S3, when the first porous fiber web is not completely cooled, spraying silicon particles uniformly on the first porous fiber web to form a second porous fiber web;

[0016] S4, continuing to use the melt-blowing method to evenly spray the mixed slurry in S1 onto the second porous fiber web to form a third porous fiber web;

[0017] S5. Place the third porous fiber mesh into a carbonization furnace for high-temperature sintering and carbonization to form a silicon-carbon composite, wherein the silicon-carbon composite includes silicon particles and a porous fiber carbon mesh, and the silicon particles are located between the porous fiber carbon meshes to form a sandwich structure; and the porous fiber carbon mesh is embedded with carbon nanotubes and amorphous carbon, and the thickness of the porous fiber carbon mesh is 20nm to 500nm.

[0018] In some embodiments, in S1, the polymer fiber includes one or more of acrylic resin, polymethyl methacrylate, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethylstyrene, alginate, carboxymethyl cellulose, glucose, or phenolic resin.

[0019] In some embodiments, in S2, the mixed slurry is sprayed on the concave and convex surface of the web-forming roller through a horizontal spinneret by a melt-blowing method; or / and in S3, the silicon particles are evenly sprayed on the first porous fiber web from top to bottom by a melt-blowing method through a vertical spinneret; or / and in S4, the mixed slurry is evenly sprayed on the second porous fiber web from top to bottom by a melt-blowing method.

[0020] In some embodiments, in S5, it also includes placing the third porous fiber web in a carbonization furnace for high-temperature sintering and carbonization, and then growing graphene to obtain the silicon-carbon composite having graphene on the surface.

[0021] In some embodiments, the high-temperature sintering carbonization and graphene growth conditions in S5 can be as follows: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 600°C to 1200°C, and the temperature is kept for 0.5h to 3h to carbonize the polymer material; then hydrogen and carbon source gas are added and kept at high temperature for 1h to 5h to grow graphene.

[0022] In a third aspect, the present invention provides a lithium ion battery, a negative electrode, a positive electrode, an electrolyte and a separator;

[0023] The negative electrode comprises the negative electrode active material according to the first aspect, or comprises the negative electrode active material obtained according to the preparation method according to the second aspect;

[0024] The positive electrode includes a positive electrode active material.

[0025] In some embodiments, the electrolyte includes at least two of lithium difluorophosphate, vinyl sulfate, vinylene carbonate, succinonitrile, 1,3,6-hexanetrinitrile, and glyceroltrinitrile.

[0026] In some embodiments, based on 100 parts by mass of the electrolyte, if the lithium difluorophosphate is included, the content of the lithium difluorophosphate is 0.01 to 0.5 parts by mass; if the vinyl sulfate is included, the content of the vinyl sulfate is 0.01 to 0.5 parts by mass; if the vinylene carbonate is included, the content of the vinylene carbonate is 0.01 to 0.5 parts by mass; if the succinonitrile is included, the content of the succinonitrile is 0.7 to 5.5 parts by mass; if the 1,3,6-hexanetrinitrile is included, the content of the 1,3,6-hexanetrinitrile is 0.8 to 3.2 parts by mass; if the glycerol trinitrile is included, the content of the glycerol trinitrile is 0.1 to 2.8 parts by mass.

[0027] Other embodiments of the invention are included in the detailed description below.

[0028] The beneficial effects of the present invention are: when the negative electrode active material of the present invention is used in a lithium ion battery, it can show improved cycle life characteristics and improved compression, tension and low expansion characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0030] Figure 1 It is a schematic diagram of the three-dimensional structure of the silicon-carbon complex in the negative electrode active material of the present invention.

[0031] Figure 2 It is a schematic diagram of the side structure of the silicon-carbon composite in the negative electrode active material of the present invention.

[0032] Figure 3 It is a schematic structural diagram of the side surface of the web-forming roller in the preparation equipment of the present invention.

[0033] Figure 4 It is a parameter schematic diagram of the boss on the web-forming roller of the present invention.

[0034] Figure 5 It is a schematic flow chart of the spray coating process in the preparation method of the present invention. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below. However, these embodiments are exemplary, the present invention is not limited thereto, and the present invention is defined by the scope of the claims.

[0036] Silicon-carbon composite

[0037] The negative electrode active material for a lithium ion battery according to an embodiment of the present invention includes a silicon-carbon composite, such as Figure 1 and Figure 2 As shown, the silicon-carbon composite includes silicon particles 100 and a porous fibrous carbon mesh 200, and the silicon particles 100 are located between the porous fibrous carbon mesh 200 to form a sandwich structure, and the porous fibrous carbon mesh is embedded with carbon nanotubes and amorphous carbon, and the thickness of the porous fibrous carbon mesh 200 is 20nm to 500nm.

[0038] The porous fiber carbon mesh structure formed by the melt-blowing method in the present invention not only strengthens the compressive and tensile properties of the matrix and maintains the stability of the material structure, but also effectively inhibits the damage to the material caused by the expansion effect of silicon nanoparticles and prevents the repeated formation of SEI film caused by silicon powder. When used as a negative electrode, it has higher conductivity, thereby reducing the amount of conductive agent in the subsequent negative electrode material, which helps to improve the capacity density of the battery negative electrode; more effectively meet and improve the gram capacity of the silicon-carbon negative electrode, while meeting the requirements of the first efficiency, cycle performance, electrode cycle expansion performance, safety performance and rate performance of the lithium battery.

[0039] In the present invention, the thickness of the porous fibrous carbon net is 20nm to 500nm. When the thickness of the porous fibrous carbon net is greater than 500nm, for example, at the micrometer level, the defect of expansion can be increased. In particular, when the thickness of the porous fibrous carbon net is in the range of 30nm to 200nm, improved cycle life characteristics and improved expansion suppression effects can be obtained.

[0040] In the present invention, the average particle size of the silicon particles may be nanometer size, and the average particle size of the silicon particles may be 5nm to 500nm. When the average particle size of the silicon particles is larger than the nanometer size, for example, at the micrometer level, the defects of the expanded silicon particles may be increased. In particular, when the average particle size of the silicon particles is in the range of 10nm to 300nm, improved cycle life characteristics and improved expansion suppression effects may be obtained. In the present invention, the average particle size of the silicon-carbon composite is 2μm to 60μm, preferably 5μm to 15μm. Improved cycle life characteristics and improved expansion suppression effects may be obtained.

[0041] The above average particle size is measured as follows:

[0042] The average particle size D1 of silicon particles is calculated as follows. First, a SEM image of silicon particles is taken using a SEM manufactured by Hitachi High-Technologies Corporation. Then, using image analysis software, 10 silicon particles are randomly selected from the SET image and the area of ​​each of these silicon particles is calculated (the area of ​​the silicon particles when viewed from one direction on the SEM image). Next, assuming that the silicon particles are spherical, the particle size is calculated using the following formula:

[0043] R=2×(S / π) 1 / 2

[0044] Here, S is the area of ​​the silicon particle when observing from one direction.

[0045] The processing for determining the particle diameter of the silicon particles is performed on 10 SEM images, and the particle diameters of the obtained (10×10) silicon particles are simply averaged (arithmetic mean) to determine the average particle diameter D1 of the silicon particles.

[0046] In addition, the average particle size of the silicon-carbon composite was determined in the same manner.

[0047] In the present invention, the pore size of the network pores of the porous fibrous carbon net is 30 nm to 200 nm, preferably 50 nm to 160 nm. Improved cycle life characteristics and improved expansion suppression effect can be obtained.

[0048] In the present invention, the surface of the porous fiber carbon mesh also has a graphene layer, and the thickness of the graphene layer is 1nm to 10nm, preferably 2nm to 5nm. Graphene and carbon nanotubes have high strength and flexibility, including the gaps inside the hollow tubular structure of carbon nanotubes, which provide necessary buffer space, rebound support and elastic space for the expansion and contraction of silicon particles, strengthen the material's compression and tensile properties, maintain the stability of the material structure, and improve the first effect and cycle life. Its high thermal conductivity helps to reduce the temperature of the battery during the charging and discharging process, thereby improving safety.

[0049] In the present invention, the negative electrode active material further comprises at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, or silicon oxide. The above materials and the silicon-carbon composite are used as active materials at the same time, which can further obtain improved cycle life characteristics and improved expansion inhibition effect.

[0050] Silicon-carbon composite preparation

[0051] See also Figures 3 to 5 As shown, a silicon-carbon composite manufacturing device is provided, which includes a web-forming roller 1, a horizontal spinneret 2, a silicon particle nozzle 3, a vertical spinneret 4 and a winder 5.

[0052] The web forming roller 1 has a concavoconvex surface 11, the concavoconvex surface 11 has bosses 12 arranged in a queue, the bosses 12 are in a truncated cone shape, the bosses 12 in two adjacent rows are arranged in a staggered manner, the two rows of bosses 12 separated by one row are arranged in parallel, and the center distance L is 20 μm to 70 μm, the diameter D of the bosses 12 is 10 μm to 30 μm, and the height H is 10 μm to 60 μm;

[0053] Horizontal spinneret 2: located on one side of the web-forming roller 1 and horizontally facing the web-forming roller 1;

[0054] Silicon particle nozzle 3: arranged above the web-forming roller 1 and vertically facing the web-forming roller;

[0055] Winding machine 5: arranged at the other side of the web forming roller 1 and having a feeding end 52;

[0056] The vertical spinneret 4 is arranged above the feed end 52 and vertically faces the feed end 52 .

[0057] In one embodiment, the specific preparation method of the silicon-carbon composite is as follows:

[0058] S1. Mixing and stirring the polymer material and the carbon nanotubes in a molten state at a mass ratio of 1:1 to 80 to obtain a mixed slurry;

[0059] The polymer material is not particularly limited. For example, it includes one or more of acrylic resin, polymethyl methacrylate, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethylstyrene, alginic acid, carboxymethyl cellulose, glucose, or phenolic resin. These readily available and inexpensive raw materials are preferred, which can significantly reduce the manufacturing cost.

[0060] S2, using a melt-blowing method to spray the mixed slurry onto the concave and convex surface of the web-forming roller 1 through a horizontal spinneret 2 to form a first porous fiber web; the diameter of the carbon nanotube-containing polymer fiber sprayed by the horizontal spinneret 2 is 0.005nm-0.5μm;

[0061] S3, when the first porous fiber web is not completely cooled, spraying silicon particles uniformly on the first porous fiber web from top to bottom to form a second porous fiber web;

[0062] S4, continue to use the melt-blowing method to evenly spray the mixed slurry in S1 on the second porous fiber web from top to bottom through the vertical spinneret 4 to form a third porous fiber web, and roll up the third porous fiber web after cooling; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret 4 is 0.005-0.5 μm;

[0063] S5. Place the rolled third porous fiber web into a carbonization furnace for high-temperature sintering and carbonization to form a silicon-carbon composite, wherein the silicon-carbon composite includes silicon particles and a porous fiber carbon web, and the silicon particles are located between the porous fiber carbon webs to form a sandwich structure; and the porous fiber carbon web is embedded with carbon nanotubes and amorphous carbon, and the thickness of the porous fiber carbon web is 20nm to 500nm.

[0064] Preferably, in S5, the third porous fiber web is placed in a carbonization furnace for high-temperature sintering and carbonization, and then graphene is grown to obtain a silicon-carbon composite with graphene on the surface. The specific conditions may be as follows: first, argon is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 600°C to 1200°C, and the temperature is kept for 0.5h to 3h to carbonize the polymer material; then hydrogen and carbon source gas are added and kept at high temperature for 1h to 5h to grow graphene.

[0065] The carbon source gas includes at least one of methane, ethane, propane, ethylene, acetylene and ethanol.

[0066] Compared with the traditional liquid phase grinding and coating technology, the method of the present invention has the following advantages:

[0067] 1) The melt-blowing method and the concave-convex roller combined coating method are adopted to avoid the etching step of HF and other acids, and the thickness of the fiber carbon mesh skeleton is uniform and controllable, the pore size and porosity of the fiber carbon mesh are controllable, the pores between the silicon particle core and the silicon carbon composite material are controllable, the particle size of the silicon carbon composite material is uniform, and the network structure is more conducive to the shuttle of lithium ions;

[0068] 2) By precisely controlling the thickness of the sprayed fiber web and the size of the concave and convex shapes on the web-forming roller, the mass ratio of silicon to carbon can be effectively adjusted between 80:20 and 95:5 to meet the design requirements of long-life, low-temperature, fast-rate charging and high-gram capacity materials;

[0069] 3) During the sintering process, a package fixed bed is used instead of the traditional powder fluidized bed or rotary kiln, which has lower requirements on equipment and process, while ensuring high product consistency, high efficiency, high production capacity, low energy consumption and low cost.

[0070] Lithium-ion battery

[0071] Another embodiment of the present invention provides a lithium ion battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; an electrolyte and a separator.

[0072] In the positive electrode active material layer, the positive electrode active material may be a compound capable of inserting and extracting lithium (lithiated inserting compound), and in particular one or more composite oxides of a metal selected from cobalt, manganese, nickel and a combination thereof and lithium. More specifically, a compound represented by one of the following chemical formulas may be used.

[0073] Li a A 1-b X b D 2 (0.90≤a≤1.8,0≤b≤0.5);

[0074] Li a A 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);

[0075] Li a E 1-b X b O 2-c D c (0≤b≤0.5,0≤c≤0.05);

[0076] Li a E 2-b X b O 4-c Dc (0≤b≤0.5,0≤c≤0.05);

[0077] Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α≤2);

[0078] Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0≤α<2);

[0079] Li a Ni 1-b-c Co b X c O 2-α T 2 (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0≤α<2);

[0080] Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0≤α≤2);

[0081] Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0≤α<2);

[0082] Li a Ni 1-b-c Mr b X c O 2-α T 2 (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0≤α<2);

[0083] Li a Ni b HAVE BEEN c G d O 2(0.90≤a≤1.8.0≤b≤0.9.0≤c≤0.5.0.001≤d≤0.1);

[0084] The a Nor b Co c Mn d G e O 2 (0.90≤a≤1.8.0≤b≤0.9.0≤c≤0.5.0≤d≤0.5.0.001≤e≤0.1);

[0085] The a NiG b O 2 (0.90≤a≤1.8,0.001≤b≤0.1)Li a CoG b O 2 (0.90≤a≤1.8,0.001≤b≤0.1);

[0086] The a Mn 1-b G b O 2 (0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn 2 G b O 4 (0.90≤a≤1.8,0.001≤b≤0.1);

[0087] The a Mn 1-g G g MONTH 4 (0.90≤a≤1.8.0≤g≤0.5);QO 2 ;QS 2 ;LiQS 2 ;V 2 O 5 ;LiV 2 O 5 ;LiZO 2 ;

[0088] LiNiVO 4 ;The (3-f) J 2 (MONTH 4 ) 3 (0≤f≤2);Li (3-f) Fe 2 (MONTH 4 ) 3 (0≤f≤2);Li a FePO4 (0.90≤a≤1.8).

[0089] In the chemical formula, A is selected from Ni, Co, Mn and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from O, F, S, P and combinations thereof; E is selected from Co, Mn and combinations thereof. T is selected from F, S, P and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; Q is selected from Ti, Mo, Mn and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu and combinations thereof.

[0090] The compound may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from the group consisting of: an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating may be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. By using these elements in the compound, the coating may be provided in a manner that has no adverse effect on the performance of the positive active material. For example, the method may include any coating method, such as spraying, dipping, etc., but since it is well known in the relevant art, it is not described in more detail.

[0091] In the positive electrode, the content of the positive electrode active material may be 90 wt % to 98 wt % based on the total weight of the positive electrode active material layer.

[0092] In an embodiment of the present invention, the positive electrode active material layer may further include a binder and a conductive material. Here, the binder and the conductive material may be included in an amount of 1 wt % to 5 wt % based on the total amount of the positive electrode active material layer.

[0093] The binder improves the bonding performance of the positive electrode active material particles to each other and to the current collector, and examples thereof may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0094] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change, and examples of the conductive material may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0095] The current collector may be aluminum foil, nickel foil or a combination thereof, but is not limited thereto.

[0096] The negative electrode includes a current collector and a negative electrode active material layer disposed on the current collector and including a negative electrode active material.

[0097] In the negative active material layer, the negative active material may be included in an amount of 95 wt % to 99 wt % based on the total weight of the negative active material layer.

[0098] In an embodiment of the present invention, the negative electrode active material layer includes a binder and an optional conductive material. In the negative electrode active material layer, the content of the binder may be 1wt% to 5wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes 90wt% to 98wt% of the negative electrode active material, 1wt% to 5wt% of the binder, and 1wt% to 5wt% of the conductive material.

[0099] The binder improves the binding performance between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder may be a non-aqueous binder, an aqueous binder or a combination thereof.

[0100] The non-aqueous binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0101] The aqueous binder can be styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene-propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, polyacrylic acid or a combination thereof.

[0102] When an aqueous binder is used as a negative electrode binder, a cellulose compound may be further used as a thickener to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or an alkali metal salt thereof. The alkali metal may be Na, K or Li. The thickener may be included in an amount of 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0103] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change, and examples of the conductive material may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0104] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0105] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0106] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0107] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent.

[0108] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. In addition, alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include: nitriles, such as R-CN (wherein R is a hydrocarbon group having a linear, branched or cyclic structure of C2 to C20, and may include a double bond, an aromatic ring or an ether bond), etc.; amides, such as dimethylformamide, etc.; dioxolanes, such as 1,3-dioxolane, etc.; cyclopentane sulfone, etc.

[0109] The organic solvent may be used alone or in a mixture, and when the organic solvent is used in a mixture, the mixture ratio may be controlled according to desired battery performance.

[0110] The carbonate-based solvent may include a mixture with a cyclic carbonate and a linear (chain) carbonate. The cyclic carbonate and the linear carbonate are mixed together in a mass ratio of 1:1 to 1:9, which may provide enhanced electrolyte performance.

[0111] In some embodiments, when the electrolyte includes at least two of lithium difluorophosphate, vinyl sulfate, vinylene carbonate, succinonitrile, 1,3,6-hexanetrinitrile, and glyceroltrinitrile, the cycle life characteristics and low expansion characteristics of the silicon-carbon composite of the present invention can be further improved.

[0112] In some embodiments, based on 100 parts by mass of the electrolyte, the content of the lithium difluorophosphate is 0.01 to 0.5 parts by mass; or the content of the vinyl sulfate is 0.01 to 0.5 parts by mass; or the content of the vinylene carbonate is 0.01 to 0.5 parts by mass; or the content of the succinonitrile is 0.7 to 5.5 parts by mass; or the content of the 1,3,6-hexanetrinitrile is 0.8 to 3.2 parts by mass; or the content of the glycerol trinitrile is 0.1 to 2.8 parts by mass.

[0113] Examples of the electrolyte salt include LiPF 6 、LiSbF 6 、LiAsF 6 、LiN(SO 2 C 2 F 5 ) 2 、Li(CF 3 SO 2 ) 2 N、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N(Lithium bis(fluorosulfonyl)imide: LiFSI), LiC 4 F 9 SO 3 、LiClO 4 、LiAlO 2 、LiAlCl 4 and LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2)(wherein x and y are natural numbers, such as integers of 1 to 20.) The lithium salt may be used at a concentration in the range of about 0.1 M to about 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to appropriate or optimal electrolyte conductivity and viscosity.

[0114] The separator may be a porous substrate; or may be a composite porous substrate.

[0115] The porous substrate may be a substrate including pores, and lithium ions may move through the pores. The porous substrate may, for example, include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer thereof (such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator).

[0116] The composite porous substrate may have a form including a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functions, the functional layer may be, for example, at least one selected from a heat-resistant layer and a bonding layer. For example, the heat-resistant layer may include a heat-resistant resin and may optionally include a filler.

[0117] In some embodiments, the tie layer may include a binder resin and, optionally, a filler.

[0118] The filler may be an organic filler and / or an inorganic filler.

[0119] The form of the lithium ion battery is not particularly limited, and various conventionally known forms of batteries such as a cylindrical type, a flat wound rectangular type, a stacked rectangular type, a coin type, a flat wound stacked type, and a stacked laminated type can be employed.

[0120] Example

[0121] The following combination Figures 1 to 4 The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0122] [1] Preparation of silicon-carbon composites

[0123] Example 1-1

[0124] S1: 1 g of polytetrafluoroethylene, 3 g of polyacrylic acid, 6 g of polypropylene and 10 g of carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0125] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 10 μm, and the height H is 10 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.1 μm;

[0126] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 5 nm, 80 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0127] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0128] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 600°C, and the temperature is kept for 0.5h to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 2μm, the thickness of the porous fiber carbon mesh is 20nm, and the pore size of the network pores is 200nm.

[0129] Example 1-2

[0130] S1: 1 g of polymethyl methacrylate, 4 g of polystyrene, 2 g of polyvinyl methyl ether, 3 g of phenolic resin and 800 g of carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0131] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 70 μm, the diameter D of the boss 12 is 30 μm, and the height H is 60 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.2 μm;

[0132] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 500 nm, 15000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0133] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.2 μm;

[0134] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 1200°C, and the temperature is kept for 3 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 60μm, the thickness of the porous fiber carbon mesh is 500nm, and the pore size of the network pores is 30nm.

[0135] Examples 1-3

[0136] S1: 2 g polyethylene, 3 g carboxymethyl cellulose alginate, 5 g methyl gluconate resin and 500 g carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0137] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 50 μm, the diameter D of the boss 12 is 20 μm, and the height H is 40 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.1 μm;

[0138] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 10 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0139] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0140] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 800°C, and the temperature is kept for 2.5 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 5μm, the thickness of the porous fiber carbon mesh is 30nm, and the pore size of the network pores is 50nm.

[0141] Examples 1-4

[0142] S1: 1 g polystyrene, 1.5 g alginate, 2.5 g glucose and 250 g carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0143] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 50 μm, the diameter D of the boss 12 is 20 μm, and the height H is 40 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.1 μm;

[0144] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 30 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0145] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0146] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 800°C, and the temperature is kept for 2.5 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 8μm, the thickness of the porous fiber carbon mesh is 70nm, and the pore size of the network pores is 80nm.

[0147] Examples 1-5

[0148] S1: 2.2 g of polyethylene, 3.3 g of alginic acid, 5.5 g of phenolic resin and 550 g of carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0149] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 20 μm, and the height H is 10 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.05 μm;

[0150] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 100 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0151] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.05 μm;

[0152] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 800°C, and the temperature is kept for 2.5 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 10μm, the thickness of the porous fiber carbon mesh is 100nm, and the pore size of the network pores is 90nm.

[0153] Examples 1-6

[0154] S1: 1.2 g polymethylstyrene, 1.8 g polypropylene alginate, 3 g glucose and 300 g carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0155] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 20 μm, and the height H is 10 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.1 μm;

[0156] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 200 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0157] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0158] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 800°C, and the temperature is kept for 2.5 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 12μm, the thickness of the porous fiber carbon mesh is 150nm, and the pore size of the network pores is 120nm.

[0159] Examples 1-7

[0160] S1: 2 g polyethylene, 3 g alginate, 5 g glucose and 500 g carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0161] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 50 μm, the diameter D of the boss 12 is 20 μm, and the height H is 40 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.1 μm;

[0162] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 300 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0163] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0164] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 800°C, and the temperature is kept for 2.5 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 15μm, the thickness of the porous fiber carbon mesh is 200nm, and the pore size of the network pores is 160nm.

[0165] Example 1-8 Adding Graphene

[0166] S1: 2.2 g of polyethylene, 3.3 g of alginic acid, 5.5 g of phenolic resin and 550 g of carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0167] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 20 μm, and the height H is 10 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.05 μm;

[0168] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 100 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0169] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.05 μm;

[0170] S5: placing the sandwich fiber mesh into a carbonization furnace for high-temperature sintering and carbonization: first, introducing argon gas to replace the system air in the carbonization furnace with an oxygen-free environment, and then raising the temperature from room temperature to 800° C., and keeping the temperature for 2.5 hours to carbonize the polymer material.

[0171] S6: Then hydrogen and methane were added and kept at high temperature for 3 hours to grow graphene. After the growth was completed, the methane was turned off and the temperature was cooled to room temperature in an argon and hydrogen atmosphere. Then, the mixture was crushed and sieved to obtain a silicon-carbon composite: the average particle size was 8.9μm, the thickness of the porous fiber carbon network was 96nm, the pore size of the network pores was 102nm, and the thickness of the graphene layer was 2nm.

[0172] Example 1-9 with graphene

[0173] S1: 1.2 g polymethylstyrene, 1.8 g polypropylene alginate, 3 g glucose and 300 g carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0174] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 20 μm, and the height H is 10 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.2 μm;

[0175] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 200 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0176] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0177] S5: placing the sandwich fiber mesh into a carbonization furnace for high-temperature sintering and carbonization: first, introducing argon gas to replace the system air in the carbonization furnace with an oxygen-free environment, and then raising the temperature from room temperature to 800° C., and keeping the temperature for 2.5 hours to carbonize the polymer material.

[0178] S6: Then hydrogen and methane were added and kept at high temperature for 5 hours to grow graphene. After the growth was completed, the methane was turned off and the temperature was cooled to room temperature in an argon and hydrogen atmosphere. Then, the mixture was crushed and sieved to obtain a silicon-carbon composite: the average particle size was 9.2μm, the thickness of the porous fiber carbon network was 106nm, the pore size of the network pores was 120nm, and the thickness of the graphene layer was 3nm.

[0179] Example 1-10 Graphene Addition

[0180] S1: 2 g polyethylene, 3 g alginate, 5 g glucose and 500 g carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0181] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 50 μm, the diameter D of the boss 12 is 20 μm, and the height H is 40 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.08 μm;

[0182] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 300 nm, 5000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0183] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0184] S5: placing the sandwich fiber mesh into a carbonization furnace for high-temperature sintering and carbonization: first, introducing argon gas to replace the system air in the carbonization furnace with an oxygen-free environment, and then raising the temperature from room temperature to 800° C., and keeping the temperature for 2.5 hours to carbonize the polymer material.

[0185] S6: Then hydrogen and ethane were added and kept at high temperature for 4 hours to grow graphene. After the growth was completed, the ethane was turned off and the temperature was cooled to room temperature in an atmosphere of argon and hydrogen. Then, the mixture was crushed and sieved to obtain a silicon-carbon composite: the average particle size was 11.4μm, the thickness of the porous fiber carbon network was 89nm, the pore size of the network pores was 135nm, and the thickness of the graphene layer was 5nm.

[0186] Comparative Example 1-1 without carbon nanotubes

[0187] S1: 1 g of polytetrafluoroethylene, 3 g of polyacrylic acid, and 6 g of polypropylene were mixed and stirred at 350° C. to obtain a mixed slurry;

[0188] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 10 μm, and the height H is 10 μm; the polymer fibers are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the polymer fibers sprayed by the horizontal spinneret is 0.1 μm;

[0189] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 5 nm, 80 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0190] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.1 μm;

[0191] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 600°C, and the temperature is kept for 0.5h to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 2.8μm, the thickness of the porous fiber carbon mesh is 18nm, and the pore size of the network pores is 168nm.

[0192] Comparative Example 1-2

[0193] S1: 1 g of polytetrafluoroethylene, 3 g of polyacrylic acid, 6 g of polypropylene and 10 g of carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0194] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 20 μm, the diameter D of the boss 12 is 10 μm, and the height H is 10 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.05 μm;

[0195] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 5 nm, 80 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0196] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.05 μm;

[0197] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 600°C, and the temperature is kept for 0.5h to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 1.6μm, the thickness of the porous fiber carbon mesh is 16nm, and the pore size of the network pores is 220nm.

[0198] Comparative Examples 1-3

[0199] S1: 1 g of polymethyl methacrylate, 4 g of polystyrene, 2 g of polyvinyl methyl ether, 3 g of phenolic resin and 800 g of carbon nanotubes were mixed and stirred at 350° C. to obtain a mixed slurry;

[0200] S2: The mixed slurry is sprayed onto a web-forming roller with a concave-convex shape through a horizontal spinneret by melt-blowing method, wherein the center distance L of the web-forming roller is 70 μm, the diameter D of the boss 12 is 30 μm, and the height H is 60 μm; the polymer fibers containing carbon nanotubes are bonded on the concave-convex surface and woven into a first porous fiber web with a concave-convex shape; the diameter of the carbon nanotube polymer fibers sprayed by the horizontal spinneret is 0.3 μm;

[0201] S3: When the first porous fiber web is not completely cooled, silicon particles (average particle size of 500 nm, 15000 g) are uniformly sprayed on the first porous fiber web from top to bottom, so that the silicon particles are bonded in the pits of the first porous fiber web to form a second porous fiber web;

[0202] S4: spraying the mixed slurry evenly on the second porous fiber net again through the vertical spinneret, so that the silicon particles are sandwiched in the porous fiber carbon net, and after cooling, a sandwich third porous fiber net is obtained; the diameter of the carbon nanotube polymer fiber sprayed by the vertical spinneret is 0.3 μm;

[0203] S5: The sandwich fiber mesh is placed in a carbonization furnace for high-temperature sintering and carbonization: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 1500°C, and the temperature is kept for 3 hours to carbonize the polymer material, and then the temperature is lowered to room temperature in an argon and hydrogen atmosphere, and then crushed and sieved to obtain a silicon-carbon composite: the average particle size is 45μm, the thickness of the porous fiber carbon mesh is 550nm, and the pore size of the network pores is 25nm.

[0204] Comparative Examples 1-4

[0205] With reference to the preparation method of lithium-ion battery silicon-carbon negative electrode material in CN111952558A, the silicon-carbon material obtained by the liquid phase synthesis method in Example 1 is used as the material for Comparative Example 4 of the present invention.

[0206] The following references CN111952558A Example 1

[0207] (1) Add 100 ml of methyl silicate to 400 ml of methanol solution, stir for 30 min, then drop 50 ml of dilute hydrochloric acid solution into the solution, keep stirring, and continue the reaction for 1 h. After the hydrolysis of methyl silicate is completed, add 50 ml of ammonia water (concentration is 20%) and continue stirring for 2 h to obtain nano-SiO 2 Hydrogel solution.

[0208] (2) Add 50 ml of formaldehyde and 30 g of resorcinol to the above solution, then add 50 ml of ammonia water (concentration of 20%), keep stirring and react for 3 hours. Use centrifugation to obtain slurry, then wash the slurry with deionized water and ethanol twice, and then dry it in an oven at 80°C to obtain phenolic resin-coated SiO 2 Nanoparticle Precursors.

[0209] (3) The obtained precursor is placed in a tubular furnace, and reacted at 800°C for 6 hours under nitrogen protection, with a heating rate of 5°C / min, to finally obtain a lithium-ion battery silicon-carbon negative electrode material.

[0210] [2] Manufacturing of lithium-ion batteries

[0211] Preparation of positive electrode sheets: lithium cobalt oxide, conductive agent conductive carbon black Super-P, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone are stirred and mixed evenly in a weight ratio of 97:2:1 to obtain a positive electrode active film layer slurry with a solid content of 73%; then the positive electrode active film layer slurry is evenly coated on an aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0212] Preparation of negative electrode sheets: artificial graphite and the silicon-carbon materials obtained in all the above embodiments and comparative examples (mass ratio 90:10), conductive agent conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water at a weight ratio of 98:0.5:1.5, and mixed evenly to prepare a negative electrode active film layer slurry; the negative electrode slurry is evenly coated on a copper foil, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0213] Isolation film: Polypropylene film is used as the isolation film.

[0214] Preparation of electrolyte: In an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm), mix the organic solvents ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) in a mass ratio of 2:1.5:2.5, and add 12.5% ​​LiPF 6 The lithium salt is dissolved in an organic solvent, and then 7% fluoroethylene carbonate, 3% 1,3-propane sultone, and additive A are added to obtain an electrolyte. Additive A is selected from at least two of lithium difluorophosphate, vinyl sulfate, vinylene carbonate, succinonitrile, 1,3,6-hexane trinitrile, and glycerol trinitrile.

[0215] The electrolyte additives A used in the following batteries are as follows:

[0216] Electrolyte code Component A (parts by mass) EL-1 Lithium difluorophosphate (0.2), Succinonitrile (3.2) EL-2 Lithium difluorophosphate (0.4), 1,3,6-hexanetrinitrile (1.8) EL-3 Vinyl carbonate (0.2), vinyl sulfate (0.5) EL-4 Vinyl sulfate (0.1), succinonitrile (3.2) EL-5 Lithium difluorophosphate (0.01), succinonitrile (1.3), glycerol trinitrile (1.8) EL-0 none

[0217] Preparation of wound structure battery cell: The negative electrode sheet prepared above is wound together with the positive electrode sheet and the separator to form a wound structure battery cell (referred to as wound core).

[0218] Preparation of lithium-ion battery: The prepared wound structure battery cell is hot-pressed and shaped, then packaged with aluminum-plastic film, baked to remove moisture, and then injected with electrolyte, and the obtained battery cell is converted into a lithium-ion battery.

[0219] [Examples 2-1 to 2-10]

[0220] Lithium ion batteries were prepared using the silicon-carbon composites of Examples 1-1 to 1-10, respectively, and EL-0 was used as an electrolyte. Evaluation was performed under the following conditions.

[0221] [Examples 2-11 to 2-21]

[0222] In Example 2-11, a lithium ion battery was prepared in the same manner as in Example 2-1 except that EL-1 was used as the electrolyte instead of EL-0.

[0223] In Examples 2-12 to 2-16, lithium ion batteries were prepared in the same manner as in Example 2-4 except that EL-1 to EL-5 were used as electrolytes instead of EL-0.

[0224] In Examples 2-17 to 2-21, lithium ion batteries were prepared in the same manner as in Example 2-8 except that EL-1 to EL-5 were used as electrolytes instead of EL-0.

[0225] [Comparative Examples 2-1 to 2-4]

[0226] Lithium ion batteries were prepared using the silicon-carbon composites in Comparative Examples 1-1 to 1-4, respectively, and EL-0 was used as the electrolyte.

[0227] [3] Battery performance test

[0228] <Low temperature rate characteristics>

[0229] After the lithium-ion batteries prepared in the examples and comparative examples were injected with electrolyte, they were left to stand at a temperature of 25°C for 5 hours. Next, they were charged at a temperature of 25°C and 0.2C with a constant current method until the battery cell voltage reached 3.8V, and then aged at a temperature of 60°C for 12 hours. Then, they were discharged at a temperature of 25°C and 0.2C with a constant current method until the battery cell voltage reached 3.0V. After that, CC-CV charging was performed at a constant current of 0.2C (the upper limit of the battery cell voltage was 4.5V; the 0.2C charge and discharge was repeated three times.

[0230] Next, at a temperature of 25°C, a constant current charge and discharge of 0.2C is performed between the battery cell voltage of 4.5-3.0V, and the discharge capacity at this time is defined as C0. After that, the battery is charged at a constant current CC-CV of 0.2C in the same manner, and discharged to 3.0V at a constant current of 0.5C at a temperature of -20°C, and the discharge capacity at this time is defined as C1. Then, as a rate characteristic, the capacity retention rate represented by ΔC = (C1 / C0) × 100 (%) is calculated and evaluated according to the following criteria. The larger the value of the capacity retention rate ΔC, the higher the discharge capacity at a high current in a low temperature environment, and the lower the internal resistance.

[0231] A+: Capacity retention rate ΔC is above 85%;

[0232] A: The capacity retention rate ΔC is greater than 80% and less than 85%;

[0233] B: The capacity retention rate ΔC is greater than 70% and less than 80%;

[0234] C: Capacity retention rate ΔC is 60% or more and less than 70%;

[0235] D: The capacity retention rate ΔC is greater than 50% and less than 60%;

[0236] E: The capacity retention rate ΔC is less than 50%.

[0237] <Swelling suppression>

[0238] At a temperature of 25°C, the manufactured lithium-ion battery was left to stand for 5 hours with the electrodes immersed in the electrolyte. Next, at a temperature of 25°C, the stationary lithium-ion battery was charged to a battery voltage of 3.8V using a constant current method at a rate of 0.2C. Then, at a temperature of 60°C, the charged lithium-ion battery was aged for 12 hours. Next, at a temperature of 25°C, the aged lithium-ion battery was discharged to a battery voltage of 3.0V using a constant current method at a rate of 0.2C. Then, the lithium-ion battery that had been discharged was disassembled, and the value of the thickness of the entire negative electrode minus the thickness of the current collector was measured, which was used as the thickness of the negative electrode before cycling (d0).

[0239] Next, the lithium-ion battery is assembled again, and the assembled lithium-ion battery is charged and discharged for 500 cycles at a battery voltage of 4.5V to 3.0V and a charge and discharge rate of 1C at a temperature of 25°C. Finally, the lithium-ion battery after 50 cycles is charged at a rate of 1C at a temperature of 25°C. Then, the charged lithium-ion battery is disassembled, the negative electrode is taken out, and the value of the thickness of the entire negative electrode minus the thickness of the current collector is measured, which is taken as the thickness of the negative electrode after the cycle (d1). Then, the rate of change of the thickness d1 of the negative electrode after the cycle relative to the thickness d0 of the negative electrode before the cycle is calculated, and it is taken as the expansion of the negative electrode after the cycle = {(d1-d0) / d0}×100(%), and evaluated according to the following criteria. The smaller the expansion of the negative electrode after the cycle, the longer the life of the lithium-ion battery, that is, the negative electrode composite material layer can maintain its structure even if the charge and discharge cycle is repeated.

[0240] A+: The expansion of the negative electrode after cycling is less than 10%;

[0241] A: The expansion of the negative electrode after cycling is greater than 10% and less than 15%;

[0242] B: The expansion of the negative electrode after cycling is greater than 15% and less than 20%;

[0243] C: The expansion of the negative electrode after cycling is greater than 20% and less than 30%;

[0244] D: The expansion of the negative electrode after cycling is greater than 30% and less than 40%;

[0245] E: The expansion of the negative electrode after the cycle is 40% or more.

[0246] <Cyclic Characteristics>

[0247] After the prepared lithium-ion battery was injected with electrolyte, it was left to stand at 25°C for 5 hours. Next, it was charged to a battery voltage of 3.8V at a constant current method of 0.2C at a temperature of 25°C, and then aged at 60°C for 12 hours. Then, it was discharged to a battery voltage of 3.0V at a constant current method of 0.2C at a temperature of 25°C. Then, CC-CV charging (upper limit of battery voltage 4.5V) was performed at a constant current method of 0.2C, and CC discharge was performed to 3.0V at a constant current method of 0.2C.

[0248] Then, at a temperature of 25°C, 800 cycles of charge and discharge operation were performed at a battery voltage of 4.5-3.0V and a charge and discharge rate of 1.0C. Then, the capacity of the first cycle, i.e., the initial discharge capacity X1, and the discharge capacity X2 of the 800th cycle were measured, and the capacity change rate shown by ΔC=(X2 / X1)×100(%) was obtained, and the evaluation was performed according to the following criteria. The larger the value of the capacity change rate ΔC, the better the cycle characteristics.

[0249] A+: ΔC is more than 90%;

[0250] A: ΔC is 85% or more and less than 90%;

[0251] B: ΔC is 80% or more and less than 85%;

[0252] C: ΔC is 75% or more and less than 80%;

[0253] D: ΔC is 70% or more and less than 75%;

[0254] E: ΔC is less than 70%.

[0255] The battery performance test is shown in Table 1:

[0256] [Table 1]

[0257]

[0258]

[0259] The present invention forms a silicon-carbon composite with a "sandwich" structure by melt-blowing method. The thickness of the porous fiber carbon network is within a specific range, which not only strengthens the compressive and tensile properties of the matrix and maintains the stability of the material structure, but also enables the lithium-ion battery using the composite to achieve unexpectedly low expansion, low-temperature rate and cycle life.

[0260] The inventors have also found that, in particular, in the following situations, further improved effects are obtained:

[0261] 1) The thickness of the porous fiber carbon network is 30nm to 200nm, which can further inhibit the expansion;

[0262] 2) The mesh pores of the porous fiber carbon mesh are 50nm to 160nm, which can further inhibit expansion;

[0263] 3) When the porous fiber carbon mesh also has a graphene layer on its surface, the low-temperature magnification is further improved;

[0264] 4) When the electrolyte system includes at least two of lithium difluorophosphate, vinyl sulfate, vinylene carbonate, succinonitrile, 1,3,6-hexanetrinitrile, and glyceroltrinitrile, the low expansion, low temperature rate and cycle life characteristics are further significantly improved.

[0265] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the main purpose of the present invention, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A negative electrode active material, characterized in that: including silicon-carbon composites; The silicon-carbon composite includes silicon particles and a porous fiber carbon mesh, and the silicon particles are located between the porous fiber carbon mesh to form a sandwich structure; and the porous fiber carbon mesh is embedded with carbon nanotubes and amorphous carbon, and the thickness of the porous fiber carbon mesh is 20nm to 500nm.

2. The negative electrode active material according to claim 1, characterized in that: The porous fibrous carbon web is formed by melt-blowing.

3. The negative electrode active material according to claim 1, characterized in that: The average particle size of the silicon-carbon composite is 2 μm to 60 μm, preferably 5 μm to 15 μm.

4. The negative electrode active material according to claim 1, characterized in that: The average particle size of the silicon particles is 5 nm to 500 nm, preferably 10 nm to 300 nm.

5. The negative electrode active material according to claim 1, characterized in that: The thickness of the porous fibrous carbon net is 30 nm to 200 nm; or / and the pore size of the network pores of the porous fibrous carbon net is 30 nm to 200 nm, preferably 50 nm to 160 nm.

6. The negative electrode active material according to claim 1, characterized in that: The surface of the porous fiber carbon net also has a graphene layer, and the thickness of the graphene layer is 1nm to 10nm, preferably 2nm to 5nm.

7. The negative electrode active material according to claim 1, characterized in that: The negative electrode active material further comprises at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microbeads or silicon oxide.

8. A method for preparing a negative electrode active material, wherein the negative electrode active material comprises a silicon-carbon composite, and the formation of the silicon-carbon composite comprises the following steps: S1. Mixing and stirring the polymer material and the carbon nanotubes in a molten state at a mass ratio of 1:1 to 80 to obtain a mixed slurry; S2, spraying the mixed slurry onto the surface of a web-forming roller having a concave-convex shape by a melt-blowing method to form a first porous fiber web; S3, when the first porous fiber web is not completely cooled, spraying silicon particles uniformly on the first porous fiber web to form a second porous fiber web; S4, continuing to use the melt-blowing method to evenly spray the mixed slurry in S1 onto the second porous fiber web to form a third porous fiber web; S5, placing the third porous fiber mesh into a carbonization furnace for high-temperature sintering and carbonization to form a silicon-carbon composite, The silicon-carbon composite includes silicon particles and a porous fiber carbon mesh, and the silicon particles are located between the porous fiber carbon mesh to form a sandwich structure; and the porous fiber carbon mesh is embedded with carbon nanotubes and amorphous carbon, and the thickness of the porous fiber carbon mesh is 20nm to 500nm.

9. The method for preparing the negative electrode active material according to claim 8, characterized in that: In S1, the polymer material includes one or more of acrylic resin, polymethyl methacrylate, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethylstyrene, alginic acid, carboxymethyl cellulose, glucose, or phenolic resin.

10. The method for preparing the negative electrode active material according to claim 8, characterized in that: In S2, the mixed slurry is sprayed onto the concave and convex surface of the web-forming roller through a horizontal spinneret by melt-blowing; or / and In S3, the silicon particles are uniformly sprayed on the first porous fiber web by spraying from top to bottom; or / and In S4, the mixed slurry is evenly sprayed on the second porous fiber web from top to bottom through a vertical spinneret by melt-blowing.

11. The method for preparing the negative electrode active material according to claim 8, characterized in that: The step S5 further includes placing the third porous fiber web in a carbonization furnace for high-temperature sintering and carbonization, and then growing graphene to obtain a silicon-carbon composite having graphene on the surface.

12. The method for preparing the negative electrode active material according to claim 11, characterized in that: In S5, the high-temperature sintering carbonization and graphene growth conditions can be as follows: first, argon gas is introduced to replace the system air in the carbonization furnace with an oxygen-free environment, and then the temperature is raised from room temperature to 600°C to 1200°C, and the temperature is kept for 0.5h to 3h to carbonize the polymer material; then hydrogen and carbon source gas are added and kept at high temperature for 1h to 5h to grow graphene.

13. A lithium ion battery, characterized in that: It includes a negative electrode, a positive electrode, an electrolyte and a separator; The negative electrode comprises the negative electrode active material according to any one of claims 1 to 7, or comprises the negative electrode active material obtained by the preparation method according to any one of claims 8 to 12; The positive electrode includes a positive electrode active material.

14. The lithium ion battery according to claim 13, characterized in that: The electrolyte includes at least two of lithium difluorophosphate, vinyl sulfate, vinylene carbonate, succinonitrile, 1,3,6-hexanetrinitrile, and glyceroltrinitrile.

15. The lithium ion battery according to claim 14, characterized in that: Based on 100 parts by mass of the electrolyte, if the lithium difluorophosphate is included, the content of the lithium difluorophosphate is 0.01 to 0.5 parts by mass; If the vinyl sulfate is included, the content of the vinyl sulfate is 0.01 to 0.5 parts by mass; If the vinylene carbonate is included, the content of the vinylene carbonate is 0.01 to 0.5 parts by mass; If the succinonitrile is included, the content of the succinonitrile is 0.7 to 5.5 parts by mass; If the 1,3,6-hexane trinitrile is included, the content of the 1,3,6-hexane trinitrile is 0.8 to 3.2 parts by mass; If the glycerol trinitrile is included, the content of the glycerol trinitrile is 0.1 to 2.8 parts by mass.

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