Negative electrode material, its manufacturing method, and lithium ion battery

Abstract

The present invention relates to the field of negative electrode materials, and provides a negative electrode material and a method for producing the same, and a lithium ion battery. [Solution] The negative electrode material has an aggregate containing an active material and a carbon material, has a porosity of 10% or less, and a target area ratio C of 15% or more. The target area ratio C is measured as follows: When an SEM cross section of a particle of the negative electrode material is divided into square regions A x B (both A and B are 1 μm or less) and the distribution of the active material in each region of a particle of a single negative electrode material is statistically analyzed, the number of regions where the distance between active materials is 10 nm to 300 nm is defined as N1, and the total number of regions where the distance between active materials is less than 10 nm and greater than 300 nm is defined as N2. The target area ratio X of a particle of a single negative electrode material is defined as X = N1 / N2, and C is the arithmetic mean of the X values ​​of any five particles of the negative electrode material. The negative electrode material according to the present invention can effectively suppress volume expansion of the negative electrode material and improve the cycle characteristics of a battery.

Description

[Technical field]

[0001] The present invention claims priority based on a Chinese patent application filed with the China Patent Office on September 3, 2021, bearing application number 2021110323875 and entitled "Negative electrode material and its manufacturing method, and lithium ion battery", the entire contents of which are incorporated herein by reference. The present invention relates to the technical field of anode materials, in particular to anode materials and their manufacturing methods, and lithium ion batteries. [Background technology]

[0002] Conventional lithium-ion batteries have the advantages of high energy density, high output, long cycle life, and less environmental pollution, and are therefore widely used in electric vehicles and consumer electronics. In order to increase the energy density of batteries, research and development of silicon-based anode materials is becoming mature. However, anode materials have a large volume expansion when releasing and absorbing lithium. In particular, silicon-based anode materials can have a volume expansion of more than 300% when releasing and absorbing lithium, which causes them to pulverize during charging and discharging and fall off from the current collector, resulting in the loss of electrical contact between the anode active material and the current collector, which leads to poor electrochemical properties, capacity attenuation, and reduced cycle stability, making them difficult to commercialize.

[0003] Therefore, suppressing the volume expansion of the negative electrode material and improving the cycle stability of the material are urgent issues to be solved. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above problems, the present invention provides a negative electrode material that can effectively suppress the volume expansion of the negative electrode material and improve the battery cycle characteristics, a manufacturing method thereof, and a lithium ion battery, and the manufacturing method can reduce manufacturing costs. [Means for solving the problem]

[0005] In a first aspect, a negative electrode material having an aggregate containing an active material and a carbon material, wherein the porosity is 10% or less and the target region ratio C obtained by the following measurement method is 15% or more. <Measurement method of target region ratio C> The SEM cross-section of the particles of the negative electrode material is divided into a region of A×B (both A and B are 1 μm or less), and when the distribution state of the active material in each of the regions of a single particle of the negative electrode material is statistically analyzed, the number of regions where the distance between the active materials is 10 nm to 300 nm is defined as N1, and the total number of regions where the distance between the active materials is less than 10 nm and greater than 300 nm is defined as N2. The target region ratio X of a single particle of the negative electrode material is defined as X = N1 / N2, and C is the arithmetic mean value of the X values of any five particles of the negative electrode material.

[0006] The negative electrode material of the present embodiment includes an active material and carbon material Fee and has an aggregate. The negative electrode material has a target region ratio C of 15% or more. By controlling the target region ratio C within this range, the interval between the active materials can be appropriately maintained, self-aggregation of the active materials can be effectively avoided, loss of electrical contact during the process of lithium release and absorption can be avoided, and it can contribute to the subsequent penetration of the carbon material, strengthen the bond between the active material and the carbon material, further improve the electrochemical properties of the material, the porosity of the aggregate is low, the electrolyte is also difficult to penetrate into the aggregate, and the aggregate structure contributes to protecting the internal active material particles, effectively suppressing the volume expansion of the negative electrode material, reducing the expansion rate, and improving the cycle characteristics of the battery.

[0007] In one embodiment, the active material contains at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, SiO x (0 < x < 2), Fe, Mg, Ti, Zn, Al, P, and Cu. In one embodiment, the active material has a median diameter of 1 nm to 500 nm. In one embodiment, the carbon material comprises at least one selected from the group consisting of amorphous carbon, crystalline carbon, and mesocarbon microbeads. In one embodiment, the mass ratio of the active material to the carbon material is (20-70):(10-80). In one embodiment, the aggregates further comprise a metal oxide. In one embodiment, the metal oxide is distributed among the active materials, and the carbon material is filled between the active materials and the metal oxide. In one embodiment, pores are present between the active material and the metal oxide, and the pores are filled with the carbon material.

[0008] In one embodiment, the metal oxide has the general formula: x O y (wherein 0.2≦y / x≦3; M includes at least one selected from the group consisting of Sn, Ge, Si, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn). In one embodiment, the metal oxide is in the form of flakes and / or strips. In one embodiment, the metal oxide has an aspect ratio greater than two. In one embodiment, the mass ratio of the metal oxide to the active material is (1-20:100). In one embodiment, the aggregate further comprises a conductivity enhancer. In one embodiment, the conductivity enhancer includes at least one selected from the group consisting of an alloy material and a conductive carbon. In one embodiment, the conductive carbon includes at least one selected from the group consisting of carbon nanotubes, carbon fibers, and graphite fibers.

[0009] In one embodiment, the conductivity enhancer has a conductivity of 10 2 S / m That's all. . In one embodiment, the electrical conductivity enhancer is in the form of flakes and / or strips and has an aspect ratio of 2-3,000. In one embodiment, the mass ratio of the conductivity improver to the active material is (0.1-10):100. In one embodiment, the conductivity enhancer has a tensile strength of 500 MPa or more. In one embodiment, the negative electrode material further comprises a carbon layer coating at least a portion of a surface of the aggregates. In one embodiment, the material of the carbon layer comprises amorphous carbon. In one embodiment, the carbon layer has a thickness of 10 nm to 1500 nm. In one embodiment, the negative electrode material has a median diameter of 0.5 μm to 30 μm.

[0010] In one embodiment, the negative electrode material has a specific surface area of ​​10 m 2 / g or less. In one embodiment, the negative electrode material has an indentation hardness of 50 Mpa or more. In one embodiment, the negative electrode material has a porosity of 10% or less. In one embodiment, the agglomerates have a density that satisfies the following relationship: The aggregate theoretical density and the aggregate Measurement density The difference is less than 5%.

[0011] In a second aspect, a step of mixing and thoroughly dispersing raw materials including an active material, a first carbon source, and a solvent, and then removing the solvent to produce a first precursor; A step of subjecting the first precursor to a primary heat treatment at 600° C. to 1200° C. to produce a second precursor; and a step of subjecting the two precursors to a densification treatment to obtain an aggregate.

[0012] In the above technical solution, by mixing a raw material containing an active material, a first carbon source, and a solvent and dispersing them sufficiently, the dispersion degree of the active material in the first precursor can be increased. Then, the obtained first precursor is subjected to a primary heat treatment at 600°C to 1200°C to obtain a second precursor. Further, the second precursor is densified. In the process of such densification treatment, the above-mentioned substances aggregate to form aggregates, thereby increasing the dispersion degree of the active material in the aggregates and reducing the porosity of the aggregates. The entire manufacturing process is simple, and the manufactured anode material can effectively suppress volume expansion, reduce the expansion rate, and improve the battery cycle characteristics.

[0013] In one embodiment, the active material includes at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, SiO x (0 < x < 2), Fe, Mg, Ti, Zn, Al, P, and Cu. In one embodiment, the first carbon source includes at least one selected from the group consisting of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt. In one embodiment, the mass ratio of the first carbon source to the active material is (5 - 40):100. In one embodiment, the solvent includes an organic solvent. In one embodiment, the organic solvent includes at least one selected from the group consisting of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerin, n-butanol, isobutanol, and pentanol.

[0014] In one embodiment , life Mix a raw material containing a substance, a first carbon source, and a solvent and disperse them sufficiently When , and further add an additive. In one embodiment, the additive includes at least one selected from the group consisting of a surfactant and a coupling agent In one embodiment, the surfactant comprises at least one selected from the group consisting of n-octadecanoic acid, lauric acid, polyacrylic acid, sodium dodecylbenzenesulfonate, n-eicosanoic acid, palmitic acid, tetradecanoic acid, undecylic acid, cetyltrimethylammonium bromide, and polyvinylpyrrolidone. In one embodiment, the coupling agent may be a silane coupling agent, and the silane coupling agent may be γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or γ-methacryloxypropyltrimethoxysilane. At least one selected from the group consisting of Includes.

[0015] In one embodiment, the mass ratio of the active material to the additive is (15-120):(1-10). In one embodiment , life The raw materials including the substance, the first carbon source, and the solvent are mixed and thoroughly dispersed. When Then, a metal oxide is further added. In one embodiment, the metal oxide has the general formula: x O y (wherein 0.2≦y / x≦3; M includes at least one selected from the group consisting of Sn, Ge, Si, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn). In one embodiment, the metal oxide is in the form of flakes and / or strips. In one embodiment, the metal oxide has an aspect ratio greater than two.

[0016] In one embodiment, the mass ratio of the metal oxide to the active material is (1-20:100). In one embodiment , life The raw materials including the substance, the first carbon source, and the solvent are mixed and thoroughly dispersed. When Then, a conductivity improver is further added. In one embodiment, the mass ratio of the conductivity improver to the active material is (0.1-10):100. In one embodiment, the conductivity enhancer includes at least one selected from the group consisting of an alloy material and a conductive carbon. In one embodiment, the conductive carbon includes at least one selected from the group consisting of carbon nanotubes, carbon fibers, and graphite fibers. In one embodiment, the conductivity enhancer has a conductivity of 10 2 S / m That's all. . In one embodiment, the conductivity enhancer is in the form of flakes and / or strips.

[0017] In one embodiment, the electrical conductivity improver has an aspect ratio of 2-3,000. In one embodiment, the sufficient dispersion treatment method includes at least one selected from the group consisting of mechanical stirring, ultrasonic dispersion, and abrasive dispersion. In one embodiment , life The raw materials including the substance, the first carbon source and the solvent are mixed by a classifying mixing method. In one embodiment , life Mixing the raw materials including the active material, the first carbon source, and the solvent specifically includes mixing the active material and the solvent to form a first pre-mixture, mixing the first carbon source and the solvent to form a second pre-mixture, and mixing the first pre-mixture and the second pre-mixture. In one embodiment, the step of preparing the first precursor comprises mixing an active material, a first carbon source, and a solvent. Ingredients containing and then drying the mixture to obtain the first precursor. In one embodiment, the drying treatment is performed at a temperature of 40° C. to 600° C. for 1 hour to 15 hours.

[0018] In one embodiment, the densification process includes at least one selected from the group consisting of a fusion process, a kneading extrusion process, a compression molding process, an isostatic pressing process, and an immersion process. In one embodiment, the fusion process is mechanofusion. In one embodiment, the fusion machine used for the mechanofusion has a rotation speed of 300 r / min to 3000 r / min. In one embodiment, the fusion machine used for the mechanofusion has a blade gap width of 0.01 cm to 0.9 cm. In one embodiment, said mechanofusion is at least 0.5 hours in duration.

[0019] In one embodiment, the primary heat treatment has a duration of 1 hour to 10 hours. In one embodiment, a protective gas is passed through during the primary heat treatment. In one embodiment, the protective gas includes at least one selected from the group consisting of nitrogen gas, helium gas, neon gas, argon gas, and krypton gas. In one embodiment, the method further comprises coating the aggregates with carbon. In one embodiment, the carbon coating process includes mixing a second precursor with a second carbon source and performing a second heat treatment. In one embodiment, the mass ratio of the second precursor to the second carbon source is (30 to 100):(10 to 70). In one embodiment, the carbon coating process includes mixing the aggregates with a second carbon source and subjecting them to a secondary heat treatment.

[0020] In one embodiment, the second carbon source comprises at least one selected from the group consisting of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt. In one embodiment, the mass ratio of the aggregates to the second carbon source is (15-100):(10-70). In one embodiment, the secondary heat treatment is performed at a temperature of 600° C. to 1200° C. for 1 hour to 10 hours. In one embodiment, a protective gas is passed through during the secondary heat treatment. In one embodiment, the protective gas includes at least one selected from the group consisting of nitrogen gas, helium gas, neon gas, argon gas, and krypton gas.

[0021] In a third aspect, there is provided a lithium ion battery comprising the negative electrode material according to the first aspect, or the negative electrode material produced by the method according to the second aspect. Effect of the Invention

[0022] The technical solution of the present invention can achieve at least the following beneficial effects: The negative electrode material of this embodiment is a mixture of an active material and a carbon material. And The negative electrode material has a target area ratio C of 15% or more, and by being within this range, the distance between the active materials is appropriately maintained, self-aggregation of the active materials is effectively avoided, and loss of electrical contact during the process of releasing and absorbing lithium can be avoided, and the following carbon material can be penetrated, the bond between the active material and the carbon material can be strengthened, and the electrochemical properties of the material can be improved, the aggregate has a low porosity, and the electrolyte can hardly penetrate into the aggregate, and the aggregate structure contributes to protecting the active material particles inside, effectively suppressing the volume expansion of the negative electrode material, reducing the expansion rate, and improving the cycle properties of the battery.

[0023] Next, in the method for producing a negative electrode material according to the present invention, raw materials including an active material, a first carbon source, and a solvent are mixed and thoroughly dispersed, thereby increasing the degree of dispersion of the active material in a first precursor, and the obtained first precursor is subjected to a primary heat treatment to obtain a second precursor, which is then subjected to a densification treatment, and in the process of such densification treatment, the above-mentioned substances aggregate to form aggregates, thereby increasing the degree of dispersion of the active material in the aggregates and reducing the porosity of the aggregates, and the entire production process is simple, and the produced negative electrode material can effectively suppress volume expansion, reduce the expansion rate, and improve the battery cycle characteristics.

[0024] The manufacturing method of the present invention can be applied to large-scale production, and the manufactured negative electrode material can effectively improve the charge-discharge cycle stability of lithium batteries and effectively reduce the expansion rate of the negative electrode material. [Brief description of the drawings]

[0025] [Figure 1] 2 is a flowchart of a method for manufacturing a negative electrode material according to an embodiment of the present invention. [Diagram 2] 1 is a scanning electron microscope (SEM) photograph of the negative electrode material prepared in Example 1 of the present invention. [Diagram 3] 1 is an XRD chart of the negative electrode material produced in Example 1 of the present invention. [Figure 4] FIG. 2 is an initial charge / discharge curve diagram of the negative electrode material prepared in Example 1 of the present invention. [Diagram 5] FIG. 2 is a cycle characteristic curve diagram of the negative electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The following are preferred embodiments of the present invention, and it is understood that those skilled in the art can make some improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also within the protection scope of the present invention.

[0027] In one embodiment, the negative electrode material has an aggregate containing an active material and a carbon material, has a porosity of 10% or less, and has a target region proportion C obtained by the measurement method described below of 15% or more. <Measuring method for target area ratio C> When an SEM cross section of a particle of a negative electrode material is divided into square regions of A×B (both A and B are 1 μm or less) and the distribution state of active material in each region of a particle of a single negative electrode material is statistically analyzed, the number of regions where the distance between active materials is 10 nm to 300 nm is defined as N1, the total number of regions where the distance between active materials is less than 10 nm and more than 300 nm is defined as N2, the target region proportion X of a particle of a single negative electrode material is defined as X=N1 / N2, and C is the arithmetic mean value of the X values ​​of any five particles of a negative electrode material.

[0028] The number of regions in which active materials with a distance of 10 nm to 300 nm exist and active materials with a distance of less than 10 nm or more than 300 nm exist is added to N1.

[0029] The negative electrode material of this embodiment has an aggregate containing an active material and a carbon material. The negative electrode material has a target area ratio C of 15% or more. By being within this range, the interval between the active materials can be appropriately maintained, self-aggregation of the active material can be effectively avoided, and loss of electrical contact during the process of releasing and absorbing lithium can be avoided. In addition, the following penetration of the carbon material can be promoted, the bond between the active material and the carbon material can be strengthened, and the electrochemical properties of the material can be improved. The porosity of the aggregate is low, and the electrolyte is difficult to penetrate into the inside of the aggregate. The aggregate structure contributes to protecting the active material particles inside, effectively suppressing the volume expansion of the negative electrode material, reducing the expansion rate, and improving the cycle characteristics of the battery.

[0030] The negative electrode material has a porosity of 10% or less. In this case, the low porosity of the negative electrode material, i.e., the high density of the negative electrode material, contributes to improving the energy density of the composite material; on the other hand, even if the surface layer of the highly dense material is destroyed, the electrolyte is less likely to penetrate into the interior of the aggregate, which contributes to protecting the internal active material particles and reduces the probability of the electrolyte coming into contact with the active material, thereby contributing to the formation of a stable solid electrolyte film; further, the highly dense aggregate has high indentation hardness, which can eliminate the stress effect caused by expansion and improve the structural stability of the negative electrode material, effectively suppress the volume expansion of the negative electrode material, reduce its expansion rate, and improve the cycle characteristics of the battery.

[0031] In some embodiments, the porosity of the negative electrode material may be specifically 10%, 9%, 9.5%, 8%, 8.5%, 7.5%, 7%, 6.5%, 6% or 5%, etc., and of course, may be other values ​​within the above range, but are not limited thereto. It is understood that when the negative electrode material has a low porosity, i.e., a high density, it forms a stable solid electrolyte membrane and contributes to reducing the contact between the electrolyte and the active material. Preferably, the porosity of the negative electrode material is 3% or less.

[0032] In some embodiments, the indentation hardness of the negative electrode material is 50Mpa or more. Specifically, the indentation hardness of the negative electrode material may be 50MPa, 250MPa, 300MPa, 450MPa, 500MPa, 750MPa, 900MPa, 1150MPa, 1200MPa, 1250MPa, etc., and of course, may be other values ​​within the above range, but is not limited thereto. Since the negative electrode material has a strong rigidity, it has a high stability of particle structure and can resist a certain volume expansion stress, thereby reducing the expansion and improving the cycle stability of the battery. Preferably, the indentation hardness of the negative electrode material is 100Mpa or more, more preferably 200Mpa or more.

[0033] In some embodiments, the density of the aggregate satisfies the following relationship: theoretical density and aggregates Measurement density The difference between the density of the aggregate particles and theoretical density The closer and the smaller the difference, the fewer the pores inside the particles and the denser the particles become, which contributes to forming a stable solid electrolyte film and reducing the contact between the electrolyte and the active material.

[0034] Specifically, the density of the aggregate satisfies the following formula: ( ρ2 - ρ1 ) / ρ2≦5% (where ρ1 is the measured density of the aggregate and ρ2 is the theoretical density and ρ2 is the sum of the content (mass%) of each component in the aggregate multiplied by the theoretical density of each component.

[0035] In a specific example, when the aggregate contains an active material, a conductivity improver, and a carbon material, ρ2 is obtained by the following formula. ρ2 = content (mass %) of the active material in the aggregate of the active material × theoretical density of the active material + content (mass %) of the conductivity improver in the aggregate of the conductivity improver × theoretical density of the conductivity improver + content (mass %) of the carbon material in the aggregate of the carbon material × theoretical density of the carbon material

[0036] When the aggregate contains an active material, a metal oxide, a conductivity improver, and a carbon material, ρ2 is obtained by the following formula. ρ2 = content (mass %) of the active material in the aggregate of the active material × theoretical density of the active material + content (mass %) of the metal oxide in the aggregate of the metal oxide × theoretical density of the metal oxide + content (mass %) of the conductivity improver in the aggregate of the conductivity improver × theoretical density of the conductivity improver + content (mass %) of the carbon material in the aggregate of the carbon material × theoretical density of the carbon material

[0037] In some embodiments, the active material is a substance that reacts with lithium and can release and store lithium.

[0038] The active material further includes at least one selected from the group consisting of a simple metal, a metal oxide, and a metal alloy. Further, the metal further includes at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, Fe, Mg, Ti, Zn, Al, P, and Cu. The simple metal is a simple body of the above-described metals, the metal oxide is an oxide of the above-described metals, and the metal alloy is an alloy containing at least one of the above-described metals, for example, a silicon-lithium alloy and a silicon-magnesium alloy.

[0039] In some embodiments, the active material includes at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, SiO x (0 < x < 2), Fe, Mg, Ti, Zn, Al, P, and Cu.

[0040] In some embodiments, the active material is a particle, and has a median diameter of 1 nm to 500 nm. Specifically, it may be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm, and of course, it may be other values ​​within the above range, and is not limited thereto. As a result of repeated tests, it was found that the nano-order active material has a high surface energy, is easily aggregated during charging and discharging, has a high structural strength of the particles, and can suppress the volume expansion of silicon. However, the nano-order silicon-based active material particles have a high surface energy, and are easily aggregated during charging and discharging. The active material has a too small particle diameter, and the manufacturing cost is high. Preferably, the active material has a median diameter of 1 nm to 200 nm, more preferably 1 nm to 100 nm.

[0041] In some embodiments, the carbon material comprises at least one selected from the group consisting of amorphous carbon, crystalline carbon, and mesocarbon microbeads. In some embodiments, the mass ratio of the active material to the carbon material is (20-70):(10-80). Specifically, it may be 20:10, 20:20, 20:30, 20:50, 20:60, 20:80, 40:10, 40:50, 40:80, 50:70, 50:80, etc. Of course, it may be other values ​​within the above range and is not limited to these. In some embodiments, the aggregate further comprises a metal oxide, which combines the metal oxide with the active material to reduce expansion of the active material, improve long term cycling performance, and increase the indentation hardness of the aggregate.

[0042] In some embodiments, the aggregates have metal oxide distributed among the active materials, with the carbon material packed between the active materials and the metal oxide. Specifically, there are voids between the active material and the metal oxide, and the voids are filled with a carbon material. It is understood that the void structure formed by the active material and the metal oxide overlapping and agglomerating allows the carbon material to fill the voids, improving the structural stability of the aggregate, resisting a certain volume expansion stress, and reducing the expansion.

[0043] In some embodiments, the metal oxide has the general formula: x O y (wherein 0.2≦y / x≦3; M includes at least one selected from the group consisting of Sn, Ge, Si, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn). Specifically, the metal oxide may be SiO, GeO2, SnO2, ZnO, TiO2, Fe3O4, MgO, SiO2, CuO, or the like. The selected metal oxide has a lower volume expansion rate during lithium absorption than the active material, and therefore, by combining the metal oxide with the active material, it is possible to reduce the expansion of the active material and improve the long-term cycle performance.

[0044] In some embodiments, the metal oxide is in the form of flakes and / or strips.

[0045] In some embodiments, the metal oxide has an aspect ratio greater than 2. When the metal oxide is strip-shaped, the aspect ratio is specifically the ratio of particle length to particle diameter, and when the metal oxide is flake-shaped, the aspect ratio is specifically the ratio of the length to width of the flake-shaped metal oxide. Specifically, the aspect ratio of the metal oxide may be 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 12, 15, 17, 18, or 22, etc., and of course, may be other values ​​within the above range, but is not limited thereto. As a result of repeated testing, it has been found that when the aspect ratio of the metal oxide is greater than 2, the physical bonding strength between the metal oxide and the active material is improved, thereby further mitigating the volume expansion change of the active material and improving the cycle characteristics.

[0046] In some embodiments, the mass ratio of the metal oxide to the active material is (1-20):100. Specifically, the mass ratio of the metal oxide to the active material may be 1:100, 1.5:100, 2:100, 3:100, 4.5:100, 5:100, 6:100, 7:100, 8:100, 9:100, etc. Of course, other values ​​within the above range may also be used, and are not limited thereto. If the content of the metal oxide is too high, the initial efficiency of the material will decrease, and if the content of the metal oxide is too low, the rigidity of the aggregate structure will decrease, and the cycle stability of the particles will decrease.

[0047] In some embodiments, the aggregate further comprises a conductivity enhancer.

[0048] In some embodiments, the tensile strength of the conductivity enhancer is 500 MPa or more, and the degree of dispersion N of the conductivity enhancer in the negative electrode material is 1 or more. The degree of dispersion N is measured by dividing the SEM cross section of the particle of the negative electrode material into square regions of A×B (both A and B are 1 μm or less), and statistically calculating the distribution of the conductivity enhancer in each region of the particle of a single negative electrode material. The number of regions where the distance between the conductivity enhancers is less than 10 nm is Na, and the number of regions where the distance between the conductivity enhancers is 10 nm or more is Nb. The degree of dispersion C of the conductivity enhancer in the particle of a single negative electrode material is defined as C=Nb / Na, and N is the arithmetic average value of the C values ​​of any five particles of the negative electrode material. The uniform dispersion of the conductivity enhancer can effectively improve the transport of the carrier inside the aggregate and increase the conductivity of the aggregate. The conductivity enhancer can effectively improve the structural stability of the aggregate, strengthen the structural strength of the aggregate, avoid stress changes due to the expansion of the active material, and maintain the structural stability of the aggregate, thereby improving the cycle stability of the material and reducing the expansion rate. By controlling the tensile strength of the conductivity enhancer within the range of 500 MPa or more, the conductivity enhancer has excellent mechanical properties and can reinforce the stability of the material by acting as a structural support. By controlling the minimum distance between the conductivity enhancers, the active material can be filled between the conductivity enhancers and the conductivity enhancer can reinforce the stability of the material by acting as a structural support, thereby buffering the volumetric expansion change of the active material and improving the cycle characteristics.

[0049] The conductivity enhancer may have a tensile strength of 500 MPa, 800 MPa, 1 Gpa, 5 Gpa, 10 Gpa, 25 Gpa, 30 Gpa, 45 Gpa, or 50 Gpa, or of course, other values ​​within the above ranges, but are not limited thereto.

[0050] The conductivity enhancer is distributed within and / or on the surface of the aggregates.

[0051] In some embodiments, the conductivity enhancer is distributed among the active materials, and the carbon material is filled between the active materials and the conductivity enhancer. It is understood that distributing the conductivity enhancer among the active materials can increase the conductivity of the active materials and improve the transport of carriers within the active materials.

[0052] In some embodiments, the carbon material and the conductivity improver overlap and aggregate to form voids, and the voids are filled with the active material. It is understood that the carbon material and the conductivity improver form a void structure, which allows the active material to fill the voids and increase the structural strength of the aggregate, and that such a void structure can resist stress changes caused by the expansion of the active material and maintain the structural stability of the aggregate.

[0053] In some embodiments, the electrical conductivity enhancer further comprises at least one selected from the group consisting of an alloy material and an electrically conductive carbon. Of course, it is understood that any electrically conductive material having a tensile strength of 500 MPa or more can be used as the electrical conductivity enhancer.

[0054] In some embodiments, the conductive carbon comprises at least one selected from the group consisting of carbon nanotubes, carbon fibers, and graphite fibers. In some embodiments, the alloy material has a conductivity of 10 2 S / m That's all. , an alloy with a tensile strength of 500 MPa or more.

[0055] In some embodiments, the alloy material comprises at least one selected from the group consisting of a silicon alloy, an aluminum alloy, a copper alloy, an aluminum alloy, and a lithium alloy. Further, the silicon alloy comprises at least one selected from the group consisting of a nickel silicon alloy, an iron silicon alloy, a copper silicon alloy, a silicon manganese alloy, and an aluminum silicon alloy.

[0056] In some embodiments, the conductivity enhancer has a conductivity of 10 2 S / m That's all.Specifically, the conductivity improver has a conductivity of 100 S / m, 10 3 S / m, 10 4 S / m, 10 5 S / m, 10 8 S / m, etc. The conductivity enhancer within this range can effectively improve the transport of the carrier inside the aggregate and improve the conductivity of the aggregate.

[0057] In some embodiments, the conductivity enhancer is in the form of flakes and / or strips.

[0058] In some embodiments, the conductivity enhancer has an aspect ratio of 2 to 3000. When the conductivity enhancer is strip-shaped, the aspect ratio is specifically the ratio of the particle length to the particle diameter, and the particle diameter refers to the maximum linear distance between both points on the cross-sectional edge of the strip-shaped conductivity enhancer that intersects with the length direction of the strip-shaped conductivity enhancer; Conductivity enhancer When the conductive improver is flaky, the aspect ratio is specifically the ratio of the length to the width of the conductive improver in the form of flakes. Specifically, the aspect ratio of the conductive improver may be 2, 30, 46, 150, 360, 670, 800, 900, 1500, 2000, or 3000, etc., and of course, may be other values ​​within the above range, but is not limited thereto. Through repeated testing, it has been found that the conductive improver having an aspect ratio within this range has excellent mechanical properties and can reinforce the stability of the material as a structural support, thereby buffering the volume expansion change of the active material and improving the cycle characteristics.

[0059] In some embodiments, the conductivity improver has a tensile strength of 500 MPa or more. If the conductivity improver has a tensile strength that is too low, it is difficult to resist stress changes caused by the expansion of the active material, and it is difficult to maintain the structural stability of the aggregate, which is disadvantageous in improving the cycle characteristics of the material. Specifically, the conductivity improver may have a tensile strength of 500 Mpa, 520 Mpa, 550 Mpa, 580 Mpa, 600 Mpa, 650 Mpa, 700 Mpa, 750 Mpa, or 800 Mpa, etc., and of course, may have other values ​​within the above range, but are not limited thereto. As a result of repeated testing, it was found that the conductivity improver has excellent mechanical properties and can reinforce the stability of the material as a structural support by controlling the tensile strength within the above range, thereby buffering the volume expansion changes of the active material and improving the cycle characteristics.

[0060] In some embodiments, the mass ratio of the conductivity improver to the active material is (0.1 to 10):100. Specifically, it may be 0.1:100, 0.5:100, 0.8:100, 1:100, 2:100, 3:100, 5:100, 6:100, 7:100, 8:100, 10:100, etc. Of course, it may be other values ​​within the above range and is not limited to these.

[0061] The negative electrode material further comprises a carbon layer coated on at least a portion of the surface of the aggregate, and preferably the carbon layer is distributed on the surface of the aggregate. In some embodiments, the carbon layer comprises amorphous carbon. In some embodiments, the carbon layer has a thickness of 10 nm to 1500 nm. It is understood that the carbon layer covering the surface of the aggregate can reduce the contact between the active material and the electrolyte, reduce the generation of a passivation film, and improve the reversible capacity of the battery.

[0062] Specifically, the thickness of the carbon layer may be 10nm, 50nm, 180nm, 200nm, 350nm, 400nm, 550nm, 700nm, 850nm, 900nm, 1050nm, 1200nm or 1500nm, etc., and of course, may be other values ​​within the above range, but are not limited thereto. If the carbon layer is too thick, the proportion of carbon is too high, which is disadvantageous for obtaining a composite material with a high specific capacity, and if the carbon layer is too thin, it is disadvantageous for increasing the conductivity of the negative electrode material, and the suppression performance against the volume expansion of the material is weak, which deteriorates the long-term cycle performance. Preferably, the thickness of the carbon layer is 50nm to 800nm, more preferably, 100nm to 500nm.

[0063] In some embodiments, the negative electrode material in which the surface of the aggregate is coated with a carbon layer has a porosity of 10% or less and an indentation hardness of 50 MPa or more. By maintaining the porosity and indentation hardness of the entire negative electrode material within the above ranges, the performance of the negative electrode material can be further improved.

[0064] In some embodiments, the median diameter of the negative electrode material is 0.5 μm to 30 μm. Specifically, it may be 0.5 μm, 1 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, etc., and of course, it may be other values ​​within the above range, and is not limited thereto. It is understood that controlling the median diameter of the negative electrode material within the above range contributes to improving the cycle characteristics of the negative electrode material.

[0065] In some embodiments, the specific surface area of ​​the negative electrode material is greater than 10 m 2 / g or less. 2 / g, 8m 2 / g, 7m 2 / g, 5m 2 / g, 3m 2 / g, 2m 2 / g, 1m 2 / g or 0.5m 2 / g, etc., and of course, may be other values ​​within the above range, but are not limited thereto. It is understood that controlling the specific surface area of ​​the negative electrode material within the above range contributes to suppressing volume expansion and contributes to improving the cycle characteristics of the negative electrode material.

[0066] The negative electrode materials of the above embodiments Features can be arbitrarily combined as long as they are not mutually contradictory. For example, the indentation hardness, porosity and density of the aggregate are combined to define the aggregate.

[0067] In another aspect, as shown in FIG. A step S10 of mixing raw materials including an active material, a first carbon source, and a solvent, sufficiently dispersing the raw materials, and then removing the solvent to produce a first precursor; A step S20 of subjecting the first precursor to a primary heat treatment at 600° C. to 1200° C. to produce a second precursor; and a step S30 of densifying the second precursor to obtain an aggregate.

[0068] In the manufacturing method of this embodiment, raw materials including an active material, a first carbon source, and a solvent are mixed and thoroughly dispersed, thereby increasing the degree of dispersion of the active material in the first precursor, and the first precursor is subjected to a primary heat treatment at 600°C to 1200°C to obtain a second precursor, which is then subjected to a densification treatment. During this densification treatment, the above-mentioned substances aggregate to form aggregates, thereby increasing the degree of dispersion of the active material in the aggregates and reducing the porosity of the aggregates. The entire manufacturing process is simple, and the manufactured negative electrode material can effectively suppress volume expansion, reduce the expansion rate, and improve the battery cycle characteristics.

[0069] The production method of the present invention will be specifically described below with reference to examples. In step S10, raw materials including an active material, a first carbon source, and a solvent are mixed and thoroughly dispersed, and then the solvent is removed to produce a first precursor.

[0070] In some embodiments, the step of mixing a raw material containing an active material, a first carbon source, and a solvent adopts a classification mixing method. Specifically, the active material and the solvent may be mixed to form a first preliminary mixture, the first carbon source and the solvent may be mixed to form a second preliminary mixture, and then the first preliminary mixture and the second preliminary mixture may be mixed to achieve classification mixing. According to the specific components of the active material, the first carbon source, and the solvent, by selecting an appropriate classification mixing operation in accordance with the principle of classification mixing so as to sufficiently disperse the active material, the target region ratio C in the negative electrode material finally becomes 15% or more.

[0071] In some embodiments, the sufficient dispersion treatment method includes at least one selected from the group consisting of mechanical stirring, ultrasonic dispersion, and abrasive dispersion. Of course, the sufficient dispersion is not limited to the above methods, and it is understood that any method that can sufficiently disperse the active material may be used as long as the target region ratio C in the negative electrode material finally becomes 15% or more.

[0072] In some embodiments, the active material is a substance that can react with lithium and release / absorb lithium.

[0073] The active material further includes at least one selected from the group consisting of a simple metal, a metal oxide, and a metal alloy. Further, the metal further includes at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, Fe, Mg, Ti, Zn, Al, P, and Cu.

[0074] In some embodiments, the active material includes at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, SiO x (0 < x < 2), Fe, Mg, Ti, Zn, Al, P, and Cu.

[0075] In some embodiments, the active material may be an elemental metal such as the above, and more specifically, may be Si, Sn, Ge, or Al. In some embodiments, the active material may be an alloy of at least two of the above metals, such as a silicon-lithium alloy or a silicon-magnesium alloy. In some embodiments, the active material may be an oxide of the above metal, such as silicon monoxide. The active material may include at least two selected from the group consisting of an elemental metal, a metal alloy, and a metal oxide.

[0076] In some embodiments, the active material is a particle, and has a median diameter of 1 nm to 500 nm. Specifically, the active material may be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm, and may of course be other values ​​within the above range, but is not limited thereto. As a result of repeated tests, it has been found that nano-order active materials have high particle structural strength and can suppress the expansion of the active material particle volume. However, nano-order active material particles have a large surface energy, so they tend to aggregate during charging and discharging, and the active material has a too small particle diameter, resulting in high manufacturing costs. Preferably, the active material has a median diameter of 1 nm to 200 nm, more preferably 1 nm to 100 nm.

[0077] In some embodiments, the first carbon source comprises at least one selected from the group consisting of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

[0078] In some embodiments, the solvent comprises an organic solvent, the organic solvent comprising at least one selected from the group consisting of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerin, n-butanol, isobutanol, and pentanol.

[0079] In some embodiments, an additive is further added during the process of mixing and thoroughly dispersing the raw material including the active material, the first carbon source and the solvent, which can effectively enhance the connection stability between the active material and the first carbon source, thereby forming a strong system and reducing the expansion rate of the pole piece.

[0080] In some embodiments, the mass ratio of the first carbon source to the active material is (5-40):100, and may be specifically 5:100, 10:100, 15:100, 20:100, 25:100, 30:100, 35:100, 38:100, 40:100, etc. The mass ratio of the first carbon source to the active material should not be too high, i.e., the content of the first carbon source should not be too high, which is disadvantageous to the formation of a precursor with high porosity and affects subsequent processing.

[0081] In some embodiments, the additive comprises at least one selected from the group consisting of a surfactant and a coupling agent.

[0082] The surfactant includes at least one selected from the group consisting of n-octadecanoic acid, lauric acid, polyacrylic acid, sodium dodecylbenzenesulfonate, n-eicosanoic acid, palmitic acid, tetradecanoic acid, undecylic acid, cetyltrimethylammonium bromide, and polyvinylpyrrolidone.

[0083] The coupling agent may be a silane coupling agent, and examples of the silane coupling agent include γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane. and γ-Methacryloxypropyltrimethoxysilane At least one selected from the group consisting of Includes.

[0084] In some embodiments, the raw materials including the active material, the additive, the first carbon source, and the solvent are mixed and thoroughly dispersed. When Then, a conductivity improver is further added. In some embodiments, the conductivity enhancer further comprises at least one selected from the group consisting of an alloy material and conductive carbon. In some embodiments, the conductive carbon comprises at least one selected from the group consisting of carbon nanotubes, carbon fibers, and graphite fibers. In some embodiments, the conductivity enhancer has a conductivity of 10 2 S / m That's all. ,Specifically, 100S / m, 10 3 S / m, 10 4 S / m, 10 5 S / m, or 10 8 It may be S / m, etc. In some embodiments, the conductivity enhancer is in the form of flakes and / or strips.

[0085] In some embodiments, the aspect ratio of the conductivity enhancer is 2 to 3000. When the conductivity enhancer is strip-shaped, the aspect ratio is specifically the ratio of particle length to particle diameter, where the particle diameter refers to the maximum linear distance between both points on the cross-sectional edge of the strip-shaped conductivity enhancer that intersects the length direction, and when the conductivity enhancer is flake-shaped, the aspect ratio is specifically the ratio of the length to the width of the flake-shaped conductivity enhancer. Specifically, the aspect ratio of the conductivity enhancer may be 2, 30, 46, 150, 360, 670, 800, 900, 1500, 2000, or 3000, etc., and of course, may be other values ​​within the above range, but is not limited thereto. As a result of repeated tests, it has been found that a conductivity enhancer having an aspect ratio within this range has excellent mechanical properties and can reinforce the stability of the material as a structural support, thereby buffering the volume expansion change of the active material and improving the cycle characteristics.

[0086] In some embodiments, the mass ratio of the conductivity improver to the active material is (0.1 to 10): 100. Specifically, the mass ratio of the conductivity improver to the active material may be 0.1:100, 0.5:100, 1:100, 2:100, 2.6:100, 3:100, 3.5:100, 4:100, 4.8:100, 6:100, 7:100, 8.5:100, or 10:100, etc. Of course, other values ​​within the above range may also be used, and are not limited thereto.

[0087] In some embodiments, the raw materials including the active material, the additive, the first carbon source, and the solvent are mixed and thoroughly dispersed. When Then, a metal oxide is further added. In some embodiments, the metal oxide has the general formula: x O y (wherein 0.2≦y / x≦3; M includes at least one selected from the group consisting of Sn, Ge, Si, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn). In some embodiments, the metal oxide is in the form of flakes and / or strips. In some embodiments, the aspect ratio of the metal oxide is greater than two.

[0088] In some embodiments, the mass ratio of the metal oxide to the active material is (1-20):100. Specifically, the mass ratio of the metal oxide to the active material may be 1:100, 1.5:100, 2:100, 3:100, 4.5:100, 5:100, 6:100, 7:100, 8:100, 10:100, 15:100, 20:100, etc. Of course, other values ​​within the above range may also be used, and are not limited thereto. If the content of the metal oxide is too high, the initial efficiency of the material will decrease, and if the content of the metal oxide is too low, the rigidity of the aggregate structure will decrease, and the cycle stability of the negative electrode material will decrease.

[0089] In some embodiments, the sufficient dispersion treatment includes at least one selected from the group consisting of mechanical stirring, ultrasonic dispersion, and grinding dispersion. Preferably, grinding dispersion is adopted so that the active material can be dispersed, the active material can be prevented from agglomerating, and the active material can be dispersed into relatively small nanoparticles. Preferably, a wet ball mill is adopted, and the dispersion time in the wet ball mill can be 0.5h to 10h. By grinding sufficiently, the components can be mixed more uniformly, and the particle size of the active material particles can be 1nm to 500nm.

[0090] In some embodiments, the raw materials including the active material, the first carbon source, and the solvent are mixed and thoroughly dispersed, and then the solvent is removed to obtain the first precursor. The method for removing the solvent includes a drying process.

[0091] In some embodiments, the temperature of the drying process is 40°C to 600°C, specifically, 40°C, 50°C, 80°C, 100°C, 120°C, 250°C, 380°C, 400°C, 500°C, 580°C, or 600°C, etc., the time of the drying process is 1h to 15h, specifically, 1h, 3h, 5h, 7h, 9h, 10h, 12h, or 15h, etc., and the drying process method may be, for example, oven drying, freeze drying, stirring evaporation to dryness, spray drying, etc., and in this embodiment, the solvent in the precursor solution can be removed as much as possible by the drying process.

[0092] The first precursor after drying may be dispersed, and the dispersion may be a grinding dispersion, and the dispersion time is 0.5h to 9h, specifically, 0.5h, 1.5h, 2.5h, 3.5h, 4.5h, 5.5h, 7.5h or 9h, etc., and in this embodiment, the particle size after dispersion is controlled by grinding dispersion.

[0093] In some embodiments, a second carbon source may be added in the step of dispersing the dried first precursor, and the mass ratio of the first precursor to the second carbon source is (10 to 80): 10. After dispersion, secondary drying is performed to obtain a carbon-coated first precursor. In step S20, the first precursor is subjected to a primary heat treatment to produce a second precursor.

[0094] In some embodiments, the primary heat treatment regime may be, for example, vacuum sintering, hot press sintering, or pressureless sintering. In some embodiments, the temperature of the first heat treatment is 600°C to 1200°C, such as 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, etc. Preferably, the temperature of the first heat treatment is 600°C to 1000°C. In some embodiments, the time for the primary heat treatment may be from 1 h to 10 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0095] The temperature rise rate during the heat treatment is 1° C. / min to 30° C. / min, and specifically may be 1° C. / min, 5° C. / min, 10° C. / min, 15° C. / min, 20° C. / min, 25° C. / min, 30° C. / min, etc. For example, the temperature rise rate during the heat treatment is preferably 1° C. / min to 15° C. / min. A protective gas is passed through during the heat treatment, and the protective gas includes at least one gas selected from the group consisting of nitrogen gas, helium gas, neon gas, argon gas, and krypton gas.

[0096] In step S30, the second precursor is densified to obtain an aggregate, the porosity of which is 10% or less. In some embodiments, the densification process comprises at least one selected from the group consisting of a fusion process, a kneading / extrusion process, a compression molding process, an isostatic pressing process, and a dipping process.

[0097] In some embodiments, the fusion process is mechanofusion. The precursor is fused to improve the indentation hardness of the negative electrode material, and a single heat treatment can enhance the stability of the particle structure, improve the connection stability between the active material and the first carbon source, and reduce the porosity. Of course, in other embodiments, the densification process can be performed by methods other than those mentioned above, such as compression molding, isostatic pressing, immersion, etc., as long as the porosity of the aggregate can be reduced to 10% or less.

[0098] In some embodiments, the indentation hardness of the aggregate is 50 MPa or more, specifically, 50 MPa, 250 MPa, 300 MPa, 450 MPa, 500 MPa, 750 MPa, 900 MPa, 1150 MPa, 1200 MPa, 1250 MPa, etc., and of course, other values ​​within the above range are also possible, but are not limited thereto. Since the aggregate has a strong rigidity, the stability of the particle structure is high and it can resist a certain volume expansion stress, thereby reducing the expansion and improving the cycle stability of the battery. Preferably, the indentation hardness of the aggregate is 100 Mpa or more, more preferably 200 Mpa or more.

[0099] In some embodiments, the porosity of the final negative electrode material is 10% or less, and the indentation hardness of the negative electrode material is 50 MPa or more, in which case the porosity of the aggregate and the indentation hardness of the final carbon coating layer are determined according to the condition of the final carbon coating layer. Indentation hardness By controlling the porosity and Indentation hardness can reach the target value.

[0100] In some embodiments, during fusing, the rotation speed of the fusing machine is 300 r / min to 3000 r / min, specifically, 300 r / min, 1000 r / min, 1500 r / min, 2000 r / min, 2500 r / min, or 3000 r / min, etc.; the blade gap width is 0.01 cm to 0.9 cm, specifically, 0.01 cm, 0.05 cm, 0.1 cm, 0.15 cm, 0.2 cm, 0.25 cm, 0.3 cm, 0.5 cm, or 0.9 cm, etc.; and the fusing time is at least 0.5 h, specifically, 0.5 h, 0.8 h, 0.9 h, 1.0 h, 1.5 h, or 2 h, etc., but is not limited thereto.

[0101] In step S40, the aggregates are coated with carbon to obtain a negative electrode material.

[0102] The negative electrode material of the present embodiment may not be carbon-coated, in which case step S40 may be omitted. In some embodiments, the carbon-coating process includes mixing the aggregates with a second carbon source and performing a secondary heat treatment to form a carbon layer on the surface of the aggregates.

[0103] In some embodiments, the second carbon source comprises at least one selected from the group consisting of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

[0104] In some embodiments, the mass ratio of the aggregate to the second carbon source is (20-100):(10-120), specifically, 100:25, 100:35, 100:45, 100:55, 100:65, etc., and of course may be other values ​​within the above range, but is not limited thereto.

[0105] In some embodiments, the aggregates may be carbon coated in other ways, specifically, the carbon coating process includes mixing a second precursor with a second carbon source and performing a secondary heat treatment to form a carbon layer on the surface of the second precursor. In some embodiments, the mass ratio of the second precursor to the second carbon source is (30-100):(10-70). The mass ratio of the second precursor to the second carbon source may be, but is not limited to, 50:25, 100:20, 100:35, 100:45, 100:55, 100:65, etc., and of course, other values ​​within the above range.

[0106] In some embodiments, the temperature of the secondary heat treatment is 600°C to 1200°C, such as 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, etc. Preferably, the temperature of the secondary heat treatment is 600°C to 1000°C. In some embodiments, the time for the secondary heat treatment is 1 h to 10 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0107] In some embodiments, the temperature rise rate during the secondary heat treatment is 1° C. / min to 30° C. / min, and specifically may be 1° C. / min, 5° C. / min, 10° C. / min, 15° C. / min, 20° C. / min, 25° C. / min, 30° C. / min, etc. For example, the temperature rise rate during the secondary heat treatment is preferably 1° C. / min to 15° C. / min. In some embodiments, the secondary heat A protective gas is passed through during the treatment, and the protective gas includes at least one gas selected from the group consisting of nitrogen gas, helium gas, neon gas, argon gas, and krypton gas.

[0108] In some embodiments, the mixing method is magnetic stirring, mechanical stirring, ultrasonic dispersion, and / or It may also include abrasive dispersions. The negative electrode material of this embodiment does not need to be carbon-coated, and is not limited to the above two types of carbon-coating methods. In some embodiments, after the secondary heat treatment, at least one selected from the group consisting of pulverization, sieving, and demagnetization is further performed, and preferably, after the secondary heat treatment, pulverization, sieving, and demagnetization are further performed in this order. In some embodiments , machine Select from mechanical grinders, airflow grinders, and cryogenic grinders. Grinding .

[0109] In some embodiments , solid Any one selected from a fixed sieve, drum screen, resonant sieve, roller sieve, vibrating sieve, and chain grizzly. Sieving The mesh number for sieving is 500 mesh or more, and specifically, the mesh number for sieving may be 500 mesh, 600 mesh, 700 mesh, 800 mesh, etc., and controlling the particle size of the negative electrode material within the above range contributes to improving the cycle characteristics of the negative electrode material.

[0110] In some embodiments, the demagnetizing device is any one selected from a permanent magnet drum type magnetic separator, an electromagnetic separator, and a pulsating high gradient magnetic separator, and the demagnetizing is for finally controlling the magnetic material content of the negative electrode material, so as to avoid the discharge effect of the magnetic material on the lithium ion battery and the impact on the safety of the battery during use.

[0111] The present invention further provides a lithium ion battery having the above negative electrode material. EXAMPLES

[0112] The present invention will be further described below with reference to several examples. However, the present invention is not limited to the following specific examples. The present invention can be modified appropriately without departing from the spirit of the present invention. The method for measuring the target area ratio C is as follows. When an SEM cross section of a particle of a negative electrode material is divided into square regions of A×B (both A and B are 1 μm or less) and the distribution state of active material in each region of a particle of a single negative electrode material is statistically analyzed, the number of regions where the distance between active materials is 10 nm to 300 nm is defined as N1, the total number of regions where the distance between active materials is less than 10 nm and more than 300 nm is defined as N2, the target region proportion X of a particle of a single negative electrode material is defined as X=N1 / N2, and C is the arithmetic mean value of the X values ​​of any five particles of a negative electrode material.

[0113] Example 1 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Silicon powder with a median diameter of 100 nm, alkylphenol ethoxylate (APEO) and phenol resin are added to an ethylene glycol solution in a mass ratio of 50:3.6:16.4, and ultrasonically dispersed for 60 minutes to obtain a dispersion solution. The dispersion solution is then placed in a ball mill and polished and dispersed for 6 hours to obtain a first precursor solution, which is then freeze-dried to produce the first precursor. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 890°C for the first heat treatment, and the temperature is kept for 4 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 400 r / min and a blade gap width of 0.8 cm, and mechanofused for 2 h to obtain an aggregate. (4) The aggregates and sucrose are mixed in a mass ratio of 80:89. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 850°C. After keeping the temperature for 4 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0114] The negative electrode material prepared in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 64.6:35.4. The median diameter of the negative electrode material is 13.2 μm and the specific surface area is 3.5 m 2 / g and the average thickness of the carbon layer is 350 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 15%. The porosity of the anode material is 2.0%, as measured by testing the particles of the anode material by mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 155 MPa on average. Fig. 2 is a scanning electron microscope (SEM) photograph of the negative electrode material produced in Example 1 of the present invention, and Fig. 3 is an XRD chart of the negative electrode material produced in Example 1 of the present invention. As shown in Fig. 3, there is a peak position of silicon in the negative electrode material.

[0115] Example 2 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Silicon powder with a median diameter of 40 nm, γ-aminopropyltriethoxysilane and phenolic resin are added to an ethylene glycol solution in a mass ratio of 60:2.6:17.4, and ultrasonically dispersed for 60 minutes to obtain a dispersion solution. The dispersion solution is then placed in a ball mill and polished and dispersed for 6 hours to obtain a first precursor solution, which is then freeze-dried to produce the first precursor. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 850°C for the first heat treatment, and the temperature is kept for 4 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 600 r / min and a blade gap width of 0.7 cm, and fused for 1.5 h to obtain an aggregate. (4) The aggregates and asphalt are mixed in a mass ratio of 70:64. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 850°C. After keeping the temperature for 4 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0116] The negative electrode material prepared in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 61.6:38.4. The median diameter of the negative electrode material is 12.2 μm and the specific surface area is 3.1 m 2 / g and the average thickness of the carbon layer is 380 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 35%. The porosity of the anode material is 1.6%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 231 MPa on average.

[0117] Example 3 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Silicon powder with a median diameter of 30 nm, sodium dodecylbenzenesulfonate and citric acid are added to an ethylene glycol solution in a mass ratio of 45:4.6:14.4, and ultrasonically dispersed for 40 minutes to obtain a dispersion solution. The dispersion solution is then placed in a ball mill and polished and dispersed for 6 hours. 1. A precursor solution is obtained, which is then freeze-dried. 1. A precursor is prepared. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 800°C for the first heat treatment, and the temperature is maintained for 4 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 400 r / min and a blade gap width of 0.6 cm, and fused for 2.5 h to obtain an aggregate. (4) The aggregates and asphalt are mixed in a mass ratio of 40:54. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 850°C. After keeping the temperature for 2 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0118] The negative electrode material prepared in this embodiment has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 57.1:42.9. The median diameter of the negative electrode material is 10.2 μm and the specific surface area is 2.1 m 2 / g and the average thickness of the carbon layer is 580 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 45%. The porosity of the anode material is 2.3%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 123 MPa on average.

[0119] Example 4 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Add silicon powder with a median diameter of 80 nm, undecylic acid and fructose in a mass ratio of 40:2.6:7.4 to a butanol solution, ultrasonically disperse for 60 minutes to obtain a dispersion solution, and then put the dispersion solution into a ball mill and grind and disperse for 8 hours to obtain a first precursor solution, which is then spray-dried to produce the first precursor. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 820°C for the first heat treatment, and the temperature is kept for 4 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 480 r / min and a blade gap width of 0.6 cm, and fused for 3 h to obtain an aggregate. (4) The aggregates and phenolic resin are mixed in a mass ratio of 38:63. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 880°C. After keeping the temperature for 2 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0120] The negative electrode material prepared in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 49.4:50.6. The median diameter of the negative electrode material is 10.5 μm and the specific surface area is 2.0 m 2 / g and the average thickness of the carbon layer is 680 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 52%. The porosity of the anode material is 3.1%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 301 MPa on average.

[0121] Example 5 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Silicon powder with a median diameter of 40 nm, γ-methacryloxypropyltrimethoxysilane and asphalt are added to a butanol solution in a mass ratio of 46:4.5:13.5, and ultrasonically dispersed for 60 minutes to obtain a dispersion solution. The dispersion solution is then placed in a ball mill and ground and dispersed for 4 hours to obtain a first precursor solution, which is then spray-dried to produce the first precursor. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 720°C for the first heat treatment, and the temperature is kept for 3 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 580 r / min and a blade gap width of 0.5 cm, and fused for 2 h to obtain an aggregate. (4) The aggregates and phenolic resin are mixed in a mass ratio of 58:63. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 880°C. After keeping the temperature for 2 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0122] The negative electrode material prepared in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 47.2:52.8. The median diameter of the negative electrode material is 13.5 μm and the specific surface area is 1.9 m 2 / g and the average thickness of the carbon layer is 850 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 38%. The porosity of the anode material is 2.4%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 266 MPa on average.

[0123] Example 6 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Ge powder with a median diameter of 40 nm, n-octadecanoic acid and glucose are added to a propanol solution in a mass ratio of 46:4.5:9.5, and ultrasonically dispersed for 80 minutes to obtain a dispersion solution. The dispersion solution is then placed in a ball mill and polished and dispersed for 4 hours to obtain a first precursor solution, which is then spray-dried to produce the first precursor. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 790°C for the first heat treatment, and the temperature is kept for 3 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 540 r / min and a blade gap width of 0.8 cm, and fused for 2 h to obtain an aggregate. (4) The aggregates and phenolic resin are mixed in a mass ratio of 88:70. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 980°C. After keeping the temperature for 2 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0124] The negative electrode material prepared in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nano Ge powder and a carbon material in a mass ratio of 70.8:29.2. The median diameter of the negative electrode material is 14.5 μm and the specific surface area is 4.9 m 2 / g and the average thickness of the carbon layer is 310 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 65%. The porosity of the anode material is 2.8%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 89 MPa on average.

[0125] Example 7 The method for producing the negative electrode material of this embodiment includes the following steps. (1) Sn powder with a median diameter of 80 nm, cetyltrimethylammonium bromide and phenolic resin are added to an ethanol solution in a mass ratio of 66:4.5:15.5, and ultrasonically dispersed for 90 minutes to obtain a dispersion solution. The dispersion solution is then placed in a ball mill and polished and dispersed for 5 hours to obtain a first precursor solution, which is then spray-dried to produce the first precursor. (2) The first precursor is placed in a heat treatment furnace, nitrogen gas is introduced, and the temperature is raised to 890°C for the first heat treatment, and the temperature is kept for 2 hours to produce the second precursor. (3) The second precursor is placed in a fusion machine with a rotation speed of 640 r / min and a blade gap width of 0.8 cm, and fused for 4 h to obtain an aggregate. (4) The aggregates and asphalt are mixed in a mass ratio of 100:75. The mixed material is then placed in a high-temperature box furnace, nitrogen gas is introduced, and secondary heat treatment is performed at 920°C. After keeping the temperature for 2 hours, the material is crushed and sieved through a 500 mesh sieve to obtain the negative electrode material.

[0126] The negative electrode material manufactured in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nano Sn powder and a carbon material in a mass ratio of 63.5:36.5. The median diameter of the negative electrode material is 11.5 μm and the specific surface area is 3.1 m 2 / g and the average thickness of the carbon layer is 350 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 75%. The porosity of the anode material is 1.4%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 117 MPa on average.

[0127] Example 8 Example 8 is the same as Example 1 except for the following two points. In step (1), a liquid in which silicon powder having a median diameter of 100 nm is dispersed in an ethylene glycol solution and a liquid in which an alkylphenol ethoxylate and a phenol resin are dispersed in an ethylene glycol solution are mixed in a stirring state, and ultrasonically dispersed for 10 minutes to obtain a dispersion solution, and the dispersion solution is then put into a ball mill and ground and dispersed for 6 hours to obtain a first precursor solution, which is then freeze-dried to produce a first precursor; In step (2), the temperature of the first heat treatment is 1200°C.

[0128] The negative electrode material prepared in this example has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 64.6:35.4. The median diameter of the negative electrode material is 14.8 μm and the specific surface area is 3.7 m 2 / g and the average thickness of the carbon layer is 400 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 78%. The porosity of the anode material is 2.6%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 167 MPa on average.

[0129] Example 9 Example 9 is the same as Example 1, except that the temperature of the secondary heat treatment in step (4) is 600°C. The negative electrode material produced in this example has an agglomerate and a carbon layer covering the surface of the agglomerate, and the agglomerate contains silicon powder and carbon material in a mass ratio of 64.6:35.8. The median diameter of the negative electrode material is 13.8 μm and the specific surface area is 3.1 m 2 / g and the average thickness of the carbon layer is 420 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 40%. The porosity of the anode material is 3.5%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 133 MPa on average.

[0130] Example 10 In Example 10, step (4 )of This embodiment is the same as the first embodiment except that the above-mentioned is not performed. The negative electrode material prepared in this example has aggregates containing silicon powder and carbon material in a mass ratio of 64.1:32.8. The median diameter of the negative electrode material is 14.5 μm and the specific surface area is 3.8 m 2 / g and the average thickness of the carbon layer is 380 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 26%. The porosity of the anode material is 6.7%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 59 MPa on average.

[0131] Example 11 In Example 11, a negative electrode material is produced in the same manner as in Example 1, except that no alkylphenol ethoxylate is added as an additive in step (1). The negative electrode material prepared in this embodiment has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 64.8:35.2. The median diameter of the negative electrode material is 13.8 μm and the specific surface area is 3.9 m 2 / g and the average thickness of the carbon layer is 360 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 16%. The porosity of the anode material is 9.6%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 95 MPa on average.

[0132] Example 12 In Example 12, a negative electrode material is produced in the same manner as in Example 1, except that in step (1), metal oxide (SiO) is further added so that the mass ratio of SiO to silicon powder is 5:100. The negative electrode material produced in this example has an aggregate and a carbon layer covering the surface of the aggregate. The aggregate is made of nanosilicon powder. , SiO and a carbon material, the mass ratio of the silicon powder, SiO, and the carbon material being 63.8:4.5:31.7. The median diameter of the negative electrode material is 11.8 μm and the specific surface area is 3.5 m 2 / g and the average thickness of the carbon layer is 320 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 18%. The porosity of the anode material is 2.5%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is an average of 195 MPa.

[0133] Example 13 In Example 13, a negative electrode material is produced in the same manner as in Example 1, except that in step (1), a conductivity improver (single-walled carbon nanotubes) having a tensile strength of 59 GPa is further added so that the mass ratio of single-walled carbon nanotubes to silicon powder is 1.5:100. The negative electrode material produced in this example has an aggregate and a carbon layer covering the surface of the aggregate. The aggregate is made of nanosilicon powder. , single-walled carbon nanotubes and a carbon material, the mass ratio of the silicon powder, the single-walled carbon nanotubes and the carbon material being 64.8:1.1:34.1. The median diameter of the negative electrode material is 10.4 μm and the specific surface area is 2.1 m 2 / g and the average thickness of the carbon layer is 360 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 18.8%. The porosity of the anode material is 2.9%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 175 MPa on average.

[0134] Comparative Example 1 In Comparative Example 1, a negative electrode material is produced in the same manner as in Example 1, except that the polishing and dispersing treatment is not carried out in step (1). Books Comparative Example The negative electrode material produced in the above has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 60.8:38.2 to each other. The median diameter of the negative electrode material is 10.4 μm and the specific surface area is 4.6 m 2 / g and the average thickness of the carbon layer is 320 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 2%. The porosity of the anode material is 6.8%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 48 MPa on average.

[0135] Comparative Example 2 In Comparative Example 2, a negative electrode material is produced in the same manner as in Example 1, except that no fusion treatment is performed in step (3). Books Comparative Example The negative electrode material produced in the above has an aggregate and a carbon layer covering the surface of the aggregate, and the aggregate contains nanosilicon powder and carbon material in a mass ratio of 76.2:35.2. The median diameter of the negative electrode material is 21.6 μm and the specific surface area is 6.9 m 2 / g and the average thickness of the carbon layer is 680 nm. The target area ratio C in the negative electrode material measured by the above-mentioned method for measuring the target area ratio C is 6%. The porosity of the anode material is 13.9%, as measured by testing the particles of the anode material with mercury intrusion porosimetry. The indentation hardness of the negative electrode material, measured by testing particles of the negative electrode material with a nanoindenter, is 44 MPa on average.

[0136] Measurement method (1) Button battery testing The electrochemical cycle performance is measured by the following method. Defeat The electrode material, conductive agent, and adhesive are dissolved in a solvent in a mass ratio of 94:1:5, mixed, and applied to a copper foil collector, then vacuum dried to produce a negative electrode sheet. The ternary positive electrode sheet, which was manufactured using conventional mature technology, was manufactured using 1mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v / v The electrolyte (H0:1:1), Celgard 2400 separator, and case are assembled into a button-type lithium-ion battery using conventional manufacturing techniques. The initial thickness H0 of the lithium-ion battery pole pieces is measured with a micrometer. The charge / discharge test of the lithium-ion battery is performed using a LAND battery measurement system from WuhanLANDelectronics Co., Ltd. (original Chinese: Wuhan Jinnuo Electronics Co., Ltd.) at room temperature, with a constant current charge / discharge of 0.2C, and the charge / discharge voltage is set to 2.75-4.2V, to obtain the initial reversible capacity, first cycle charge capacity, and first cycle discharge capacity. Initial Coulombic efficiency = first cycle discharge capacity / first cycle charge capacity After 50 cycles, the thickness H1 of the lithium-ion battery pole piece was measured with a micrometer, and the expansion rate after 50 cycles was calculated as (H1-H0) / H0×100%. Repeat 100 cycles, record the discharge capacity as the remaining capacity of the lithium-ion battery, and capacity retention rate = remaining capacity / First reversible Capacity x 100%.

[0137] (2) Measurement of the porosity of aggregates The porosity is measured by mercury intrusion porosimetry. The arithmetic mean value of the porosity measured at least three times is used as the measurement result.

[0138] (3) Measurement of median diameter In the present invention, the physical meaning of the median diameter is the particle diameter. Volumetric basisIt is the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and is measured by a Malvern particle size analyzer. Malvern particle size analyzers use the phenomenon of light scattering by particles, and comprehensively convert the particle size distribution of the measured particles based on the distribution of scattered light energy.

[0139] (4) Indentation hardness measurement An indentation hardness test is performed using a nanoindenter with a load of 0.6 N and an indentation depth of 0.5 μm to measure the indentation hardness.

[0140] (5) Measured density of negative electrode material An empty bottle is weighed out to a mass m, and filled with distilled water. The bottle is then weighed out to a mass m1. The bottle is then washed and dried, a certain amount of negative electrode material is added to the pycnometer, the total mass at this point is recorded as m2, and distilled water is then added to fill the pycnometer, the mass m3 is weighed out, and the volume V1 of the pycnometer is calculated as V1 = (m1 - m) / ρ 水 (ρ 水 is the density of distilled water.) and calculate the volume V2 of the negative electrode material as V2 = V1- ( m3 - m2 ) / ρ 水 and the measured density ρ2 of the negative electrode material is ρ2 = ( m2 -m) / V2 and calculate.

[0141] (6) Measurement of specific surface area The specific surface area of ​​the negative electrode material is measured using a specific surface area measuring device manufactured by Micromeritics.

[0142] (7) Measurement of tensile strength The tensile strength of the conductivity enhancer is measured using a tensile tester. The above performance measurement results are shown in the table below.

[0143] Table 1 Performance comparison results [Table 1]

[0144] Fig. 4 is a diagram showing the initial charge-discharge curve of the negative electrode material prepared in Example 1 of the present invention. As shown in Fig. 4, the negative electrode material prepared in Example 1 has a high initial charge-discharge capacity and a high initial efficiency, which is because the negative electrode material can properly maintain the distance between the active materials, effectively avoid the self-aggregation of the active materials, avoid the loss of electrical contact during the process of releasing and absorbing lithium, strengthen the bond between the active materials and the carbon material, and further improve the electrochemical properties of the negative electrode material.

[0145] Fig. 5 is a cycle characteristic curve diagram of the negative electrode material produced in Example 1 of the present invention. As shown in Fig. 5, the negative electrode material has excellent cycle characteristics, with a 100 cycle capacity retention rate of 93.1%. This is because the aggregate has a low porosity, and the electrolyte is unlikely to penetrate into the aggregate, and the aggregate structure contributes to protecting the active material particles inside, effectively suppressing the volume expansion of the negative electrode material, reducing the expansion rate, and improving the cycle characteristics of the battery.

[0146] As shown in Table 1, the negative electrode materials produced in Examples 1 to 10 have aggregates containing active material and carbon material, and the spacing between the active material in the aggregates is controlled to ensure the dispersion of the active material, thereby avoiding the tendency of the active material to aggregate and ensuring a smooth carrier transport path inside the aggregate. The soft aggregation of particles can be avoided, the spacing between the active materials can be properly maintained, which also contributes to the penetration of the subsequent carbon material, increases the binding force between the active material and the carbon material, and further improves the electrochemical properties of the material. The porosity of the aggregates is low, and the electrolyte is difficult to penetrate into the aggregates. The aggregate structure contributes to protecting the active material particles inside, effectively suppressing the volume expansion of the negative electrode material, reducing the expansion rate, and improving the cycle characteristics of the battery.

[0147] Here, in the production of the negative electrode material of Example 8, the primary heat treatment temperature is too high, so that a small amount of inactive SiC material is generated, and the reversible capacity and initial coulombic efficiency of the negative electrode material are reduced.

[0148] In the preparation of the negative electrode material of Example 9, the secondary heat treatment temperature was too low, so that the carbon source coated on the surface of the aggregate was incompletely carbonized, resulting in a decrease in the conductivity of the negative electrode material and a decrease in the initial coulombic efficiency of the negative electrode material.

[0149] In the negative electrode material of Example 10, the surface of the aggregate is not coated with carbon during production, and no carbon layer is formed, so that the electrical conductivity of the negative electrode material is reduced, and the initial coulombic efficiency is reduced.

[0150] Since no additives were added during the production of the negative electrode material of Example 11, the active material particles and the carbon material were not tightly connected, the structural stability of the resulting aggregates was reduced, and the buffering and suppressing effect against expansion was weakened.

[0151] The negative electrode material of Example 12 is produced by classifying and mixing the active material, the additive, the first carbon source, and the solvent. When The further addition of metal oxide increases the rigidity of the aggregate structure, improving the cycling stability of the particles and reducing the expansion rate of the pole pieces after cycling.

[0152] In the preparation of the negative electrode material of Example 13, a conductive enhancer is further added in the step of classifying and mixing the active material, additive, first carbon source and solvent, which can effectively improve the transport of carrier inside the aggregate, increase the conductivity of the aggregate, and improve the initial Coulombic efficiency of the negative electrode material. In addition, the conductive enhancer can effectively improve the structural stability of the aggregate, improve the cycle stability of the particles, and reduce the expansion rate of the pole piece after cycling.

[0153] In the production of the negative electrode material of Comparative Example 1, the raw materials were not ground and dispersed in step (1), which reduced the mixing uniformity of the active material and carbon material. As a result, the active material was not sufficiently dispersed in the raw materials. As a result, the distance between adjacent active materials in the agglomerates of the negative electrode material was obviously reduced, the dispersion degree of the active material was reduced, and the active material tended to aggregate. As a result, the carrier transport pathways inside the agglomerates were easily clogged, and the electrochemical properties of the material were reduced.

[0154] In the production of the negative electrode material of Comparative Example 2, since the precursor is not fused in step (2), the overall structure tends to be loose, the connection stability between the active material and the carbon material is low, and the number of voids between the active material and the carbon material increases, which reduces the structural strength of the aggregate. Indentation hardness The stress change caused by the expansion of the active material is hardly tolerated, and the expansion rate is improved.

[0155] As described above, the present invention has been disclosed with reference to the preferred embodiments, but these are not intended to limit the scope of the claims. Those skilled in the art may make various possible modifications and variations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be limited only by the scope of the claims.

Claims

1. A negative electrode material having an aggregate containing an active material and a carbon material, A negative electrode material having a porosity of 10% or less and a target region ratio C obtained by the following measurement method of 15% or more. <Method of Measuring Target Area Ratio C> When an SEM cross section of a particle of the negative electrode material is divided into square regions of A×B (both A and B are 1 μm or less) and a distribution state of the active material in each of the regions of a single particle of the negative electrode material is statistically analyzed, the number of regions in which the distance between the active materials is 10 nm to 300 nm is defined as N1, the total number of regions in which the distance between the active materials is less than 10 nm and greater than 300 nm is defined as N2, a target region ratio X of a single particle of the negative electrode material is defined as X=N1 / N2, and C is the arithmetic average value of the X values ​​of any five particles of the negative electrode material.

2. The negative electrode material of claim 1 , wherein the aggregates further comprise a metal oxide.

3. The negative electrode material of claim 1 , wherein the aggregate further comprises a conductivity enhancer.

4. The negative electrode material according to claim 2, which satisfies at least one of the following (1) to (6): (1) the metal oxide is distributed among the active materials, and the carbon material is filled between the active materials and the metal oxide; (2) There are pores between the active material and the metal oxide, and the pores are filled with the carbon material; (3) The metal oxide is represented by the general formula: M ｘ O ｙ (wherein 0.2≦y / x≦3; M includes at least one selected from the group consisting of Sn, Ge, Si, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn); (4) The metal oxide is in the form of flakes and / or strips; (5) The metal oxide has an aspect ratio of greater than 2; (6) The mass ratio of the metal oxide to the active material is (1-20):

100.

5. The negative electrode material according to claim 3, which satisfies at least one of the following (1) to (6): (1) The electrical conductivity improver further includes at least one selected from the group consisting of an alloy material and a conductive carbon; (2) The conductive carbon includes at least one selected from the group consisting of carbon nanotubes, carbon fibers, and graphite fibers; (3) The conductivity improver has a conductivity of 10 ２ S / m or more; (4) The electrical conductivity improver is in a flake and / or strip shape and has an aspect ratio of 2 to 3000; (5) The mass ratio of the electrical conductivity improver to the active material is (0.1 to 10):100; (6) The electrical conductivity improver has a tensile strength of 500 MPa or more.

6. The negative electrode material according to claim 1, which satisfies at least one of the following (1) to (4): (1) The active material is Li, Na, K, Sn, Ge, Si, SiO ｘ (0<x<2), including at least one selected from the group consisting of Fe, Mg, Ti, Zn, Al, P, and Cu; (2) The active material has a median diameter of 1 nm to 500 nm; (3) The carbon material includes at least one selected from the group consisting of amorphous carbon, crystalline carbon, and mesocarbon microbeads; (4) The mass ratio of the active material to the carbon material is (20 to 70):(10 to 80).

7. The negative electrode material according to claim 1, which satisfies at least one of the following (1) to (8): (1) the negative electrode material further comprises a carbon layer covering at least a portion of a surface of the aggregate; (2) the material of the carbon layer includes amorphous carbon; (3) the carbon layer has a thickness of 10 nm to 1500 nm; (4) The negative electrode material has a median diameter of 0.5 μm to 30 μm; (5) The negative electrode material has a specific surface area of ​​10 m ２ / g or less; (6) The negative electrode material has an indentation hardness of 50 MPa or more; (7) The negative electrode material has a porosity of 10% or less; (8) The agglomerates satisfy a density relationship in which the difference between theoretical density and measured density is 5% or less.

8. A step of mixing raw materials including an active material, a first carbon source, and a solvent, dispersing the mixture by ultrasonic dispersion and polishing, and then removing the solvent to produce a first precursor; A step of subjecting the first precursor to a primary heat treatment at 600° C. to 1200° C. to produce a second precursor; and a step of subjecting the second precursor to a densification treatment to obtain an aggregate.

9. The method according to claim 8, wherein at least one of the following (1) to (22) is satisfied: (1) The active material includes at least one selected from the group consisting of Li, Na, K, Sn, Ge, Si, SiOx (0<x<2), Fe, Mg, Ti, Zn, Al, P, and Cu; (2) The first carbon source includes at least one selected from the group consisting of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenol resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt; (3) the mass ratio of the first carbon source to the active material is (5 to 40):100; (4) The solvent comprises an organic solvent; (5) The organic solvent includes at least one selected from the group consisting of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerin, n-butanol, isobutanol, and pentanol; (6) When the raw materials including the active material, the first carbon source, and the solvent are mixed and dispersed, an additive is further added; (7) When the raw materials including the active material, the first carbon source, and the solvent are mixed and dispersed, an additive including at least one selected from the group consisting of a surfactant and a coupling agent is further added; (8) When mixing and dispersing raw materials including an active material, a first carbon source, and a solvent, an additive including a surfactant including at least one selected from the group consisting of n-octadecanoic acid, lauric acid, polyacrylic acid, sodium dodecylbenzenesulfonate, n-eicosanoic acid, palmitic acid, tetradecanoic acid, undecylic acid, cetyltrimethylammonium bromide, and polyvinylpyrrolidone is further added; (9) When the raw materials including the active material, the first carbon source, and the solvent are mixed and dispersed, an additive including a coupling agent including a silane coupling agent including at least one selected from the group consisting of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane is further added; (10) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, an additive is further added so that the mass ratio of the active material to the additive is (15 to 120):(1 to 10); (11) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, a metal oxide is further added; (12) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, a compound represented by the general formula: M ｘ O ｙ (wherein 0.2≦y / x≦3; M includes at least one selected from the group consisting of Sn, Ge, Si, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn); (13) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, a flake-shaped and / or strip-shaped metal oxide is further added; (14) When a raw material including an active material, a first carbon source, and a solvent is mixed and dispersed, a metal oxide having an aspect ratio of more than 2 is further added; (15) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, a metal oxide is further added so that the mass ratio of the metal oxide to the active material is (1 to 20):100; (16) When the raw materials including the active material, the first carbon source, and the solvent are mixed and dispersed, a conductivity improver is further added; (17) When a raw material containing an active material, a first carbon source, and a solvent is mixed and dispersed, a conductivity improver is further added so that the mass ratio of the conductivity improver to the active material is (0.1 to 10):100; (18) When a raw material including an active material, a first carbon source, and a solvent is mixed and dispersed, a conductivity improver including at least one selected from the group consisting of an alloy material and conductive carbon is further added; (19) When a raw material including an active material, a first carbon source, and a solvent is mixed and dispersed, a conductivity improver is further added, and the conductive carbon includes at least one selected from the group consisting of carbon nanotubes, carbon fibers, and graphite fibers; (20) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, the electrical conductivity is 10 ２ further adding a conductivity improver having a conductivity of S / m or more; (21) When the raw materials including the active material, the first carbon source, and the solvent are mixed and dispersed, a flake-shaped and / or strip-shaped electrical conductivity improver is further added; (22) When raw materials including an active material, a first carbon source, and a solvent are mixed and dispersed, a conductivity improver having an aspect ratio of 2 to 3,000 is further added.

10. The method according to claim 8, wherein at least one of the following (1) to (5) is satisfied: (1) The dispersion treatment method includes at least one selected from the group consisting of mechanical stirring, ultrasonic dispersion, and abrasive dispersion; (2) When mixing raw materials including an active material, a first carbon source, and a solvent, a classification mixing method is adopted; (3) when mixing raw materials including an active material, a first carbon source, and a solvent, the active material and the solvent are mixed to form a first pre-mixture, the first carbon source and the solvent are mixed to form a second pre-mixture, and the first pre-mixture and the second pre-mixture are mixed; (4) The step of producing the first precursor includes mixing and dispersing raw materials including an active material, a first carbon source, and a solvent, and then drying the mixture to obtain the first precursor; (5) The step of producing the first precursor includes mixing and dispersing an active material, a first carbon source, and a solvent, and then drying the mixture at 40° C. to 600° C. for 1 h to 15 h to obtain the first precursor.

11. The method according to claim 8, wherein at least one of the following (1) to (8) is satisfied: (1) The densification treatment includes at least one selected from the group consisting of a fusion treatment, a kneading / extrusion treatment, a compression molding treatment, a hydrostatic pressing treatment, and a dipping treatment; (2) The densification process includes a fusion process which is mechanofusion; (3) The densification treatment includes a fusion treatment, which is mechanofusion, and the rotation speed of the fusion machine used for the mechanofusion is 300 r / min to 3000 r / min; (4) The densification process includes a fusion process which is mechanofusion, and the fusion machine used for the mechanofusion has a blade gap width of 0.01 cm to 0.9 cm; (5) the densification treatment includes a fusion treatment which is mechanofusion, the mechanofusion having a duration of at least 0.5 h; (6) The first heat treatment has a duration of 1h to 10h; (7) A protective gas is passed through during the primary heat treatment; (8) During the primary heat treatment, a protective gas containing at least one gas selected from the group consisting of nitrogen gas, helium gas, neon gas, argon gas, and krypton gas is passed through.

12. The method according to claim 8, wherein at least one of the following (1) to (3) is satisfied: (1) The method further comprises subjecting the aggregate to a carbon coating treatment; (2) The method further includes carbon-coating the aggregate, the carbon-coating treatment including a step of mixing a second precursor and a second carbon source and performing a secondary heat treatment; (3) The production method further includes subjecting the aggregate to a carbon coating treatment, and the carbon coating treatment includes a step of mixing the aggregate with a second carbon source and subjecting the mixture to a secondary heat treatment.

13. The method according to claim 12, characterized in that at least one of the following (1) to (6) is satisfied: (1) the mass ratio of the second precursor to the second carbon source is (30 to 100):(10 to 70); (2) the second carbon source includes at least one selected from sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt; (3) the mass ratio of the aggregate to the second carbon source is (20 to 100):(10 to 120); (4) The secondary heat treatment is performed at a temperature of 600° C. to 1200° C. for 1 h to 10 h; (5) A protective gas is passed through during the secondary heat treatment; (6) During the secondary heat treatment, a protective gas containing at least one gas selected from the group consisting of nitrogen gas, helium gas, neon gas, argon gas, and krypton gas is passed through.

14. A lithium ion battery comprising the negative electrode material according to any one of claims 1 to 7.

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