Anode materials and batteries

Abstract

The present application relates to an anode material and a battery, the anode material comprising primary particles including silicon crystal grains, wherein the average particle size of the silicon crystal grains measured at 25°C is M0 nm, the average particle size of the silicon crystal grains measured under conditions of heating to 1000°C under nitrogen gas protection, maintaining the temperature for 1 hour, and then naturally cooling to 25°C is M1 nm, and the crystalline instability of the anode material is F, where F = (M1 - M0) / M0, M1 > M0, and 0.01 ≤ F ≤ 500. The anode material provided herein can reduce the stress concentration problem that occurs in the primary particles including silicon crystal grains during the lithium release process, further improving the structural stability of the anode material and reducing the expansion rate of the material, thereby improving the electrochemical performance and cycle performance of the anode material.

Description

[Technical Field]

[0001] This application relates to the technical field of anode materials, and more particularly to anode materials and batteries. [Background technology]

[0002] Lithium ion batteries have advantages such as high energy density, high output power, long cycle life, and low environmental pollution, and are therefore widely used in electric vehicles and consumer electronics.

[0003] To improve the energy density of batteries, research and development of silicon anode materials, one of the key materials for lithium-ion batteries, is becoming increasingly mature. However, conventional silicon anode materials experience large volume expansion (>300%) during the lithium release process, which causes the silicon anode material to pulverize and fall off the current collector during charging and discharging. This leads to loss of electrical contact between the silicon particles and the current collector, resulting in reduced electrochemical performance, capacity fade, and poor cycling stability, making them difficult to commercialize.

[0004] Carbon coating can be used to improve the conductivity and cycling stability of silicon anode materials. However, the manufacturing process of conventional carbon coatings involves complicated steps, and simple carbon coatings cannot effectively improve the electrochemical performance of silicon carbon anodes.

[0005] Based on this, there is an urgent need to develop silicon-carbon anode materials with long cycle life and low expansion. Summary of the Invention [Problem to be solved by the invention]

[0006] The present application provides a negative electrode material and a battery that combine high initial coulombic efficiency, excellent cycle stability, and low expansion performance. [Means for solving the problem]

[0007] In a first aspect, the present disclosure provides an anode material, the anode material comprising a silicon matrix containing silicon crystal grains, wherein an average grain size of the silicon crystal grains measured at 25°C is M0 nm, an average grain size of the silicon crystal grains measured under conditions of heating to 1000°C under nitrogen gas protection, maintaining the temperature for 1 hour, and then naturally cooling to 25°C is M1 nm, and a crystalline instability of the anode material is F, where F=(M1-M0) / M0, M1>M0, and 0.01≦F≦500.

[0008] In a second aspect, the present disclosure provides a battery including the negative electrode material. [Effects of the Invention]

[0009] The technical solution of the present disclosure has at least the following beneficial effects:

[0010] The present disclosure achieves this by controlling the crystal instability of the negative electrode material to F, 0.01≦F≦500, thereby reducing the grain boundary surface energy of the silicon matrix, weakening the stress concentration phenomenon that occurs in the silicon matrix during the lithium release process, improving the electrochemical sintering phenomenon of the negative electrode material after lithium absorption, improving the structural stability of the silicon matrix during the lithiation process, reducing the expansion coefficient of the negative electrode material, and favoring the formation of a stable solid electrolyte film, thereby improving the electrochemical performance of the negative electrode material. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of the structure of a negative electrode material provided in one embodiment of the present application. [Figure 2] 1 is a flowchart of a method for manufacturing a negative electrode material provided in one embodiment of the present application. [Figure 3] 1 shows an XRD pattern of a silicon carbon composite negative electrode material in Example 1 of the present application. [Figure 4a] 1 is a scanning electron microscope image of the negative electrode material produced in Example 1. [Figure 4b]FIG. 2 is an internal cross-sectional view of the negative electrode material produced in Example 1. [Figure 5a] 1 is a transmission electron microscope image of the negative electrode material produced in Example 1. [Figure 5b] FIG. 2 is a partially enlarged transmission electron microscope image of the negative electrode material produced in Example 1. [Figure 6] 1 is a cycle performance curve of the negative electrode material produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] It should be noted that the following describes preferred embodiments of the present invention, and those skilled in the art may make some improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention.

[0013] Currently, the negative electrode material is one of the key materials that affect the charge and discharge performance of lithium-ion batteries, and research and development of high-capacity negative electrode materials is becoming increasingly mature in order to improve the energy density of batteries. However, these negative electrode materials undergo large volume expansion during the process of alloying with lithium, and the negative electrode material is pulverized and falls off the current collector during the charge and discharge process, resulting in loss of electrical contact between the negative electrode material and the current collector, which deteriorates the electrochemical performance of the battery, reduces capacity, and reduces cycle stability, making it difficult to use commercially.

[0014] In a first aspect, the present disclosure provides an anode material, the anode material comprising primary particles including silicon crystal grains, wherein the average grain size of the silicon crystal grains measured at 25°C is M0 nm, the average grain size of the silicon crystal grains measured under conditions of heating to 1000°C under nitrogen gas protection, maintaining the temperature for 1 hour, and then naturally cooling to 25°C is M1 nm, and the crystalline instability of the anode material is F, where F=(M1-M0) / M0, M1>M0, and 0.01≦F≦500.

[0015] In the above solution, the present disclosure controls the crystal instability of the negative electrode material to F, 0.01≦F≦500, thereby reducing the grain boundary surface energy of the silicon crystal grains, weakening the stress concentration phenomenon that occurs in the negative electrode material containing silicon crystal grains during the lithium release process, improving the electrochemical sintering phenomenon of the negative electrode material after lithium absorption, improving the structural stability of the negative electrode material containing silicon crystal grains during the lithiation process, reducing the expansion coefficient of the negative electrode material, and favoring the formation of a stable solid electrolyte film on the surface of the negative electrode material, thereby improving the electrochemical performance of the negative electrode material.

[0016] As used herein, the term "primary particle" refers to the smallest particle unit recognizable when observing a negative electrode active material with a scanning electron microscope, and in this application, a primary particle refers to a single polycrystalline silicon particle or a single single crystal silicon particle. Additionally, the term "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles.

[0017] In some embodiments, when the crystalline instability of the negative electrode material is F, F=(M1-M0) / M0, where 0.01≦F≦500, and specifically, F may be, for example, 0.01, 0.2, 0.5, 1, 5, 10, 20, 50, 80, 100, 200, 300, 400, or 500, or may be any other value within the above range, and is not limited thereto. The crystalline instability of silicon in the negative electrode material affects the structural stability of the entire negative electrode material after lithiation.

[0018] The smaller the crystalline instability value of the negative electrode material, the less likely the negative electrode material is to undergo crystal grain growth at high temperatures, and the greater the grain boundary energy of silicon in the negative electrode material. This makes it less likely that electrochemical sintering will occur in the silicon matrix during the lithiation process, effectively suppressing the stress concentration that occurs, ensuring the structural stability of the negative electrode material, reducing the expansion coefficient of the negative electrode material, and favoring the formation of a stable solid electrolyte film on the surface of the negative electrode material, thereby improving the electrochemical performance and cycle performance of the negative electrode material.

[0019] As shown in FIG. 1, in some embodiments, the average particle diameter of the primary particles 11 is 1 nm to 100 nm. Specifically, for example, it may be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, or 100 nm, etc., and is not limited herein. In some embodiments, when the average particle diameter of the silicon crystallites measured under the condition of 25 °C is M0 nm, the negative electrode material satisfies 0.1 ≦ M0 ≦ 20. Specifically, for example, it may be 0.1 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, or 20 nm, etc., and is not limited herein.

[0020] In some embodiments, when the average particle diameter of the silicon crystallites measured under the condition that the negative electrode material is heated to 1000 °C at a heating rate of 5 °C / min under nitrogen gas protection, held at 1000 °C for 1 h, and then naturally cooled to 25 °C is M1 nm, 0.1 < M1 ≦ 50. Specifically, for example, it may be 0.11 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm, etc., and is not limited herein. Preferably, 1 ≦ M1 ≦ 30.

[0021] It should be understood that the average particle diameter of the silicon crystallites is less than or equal to the average particle diameter of the primary particles.

[0022] In some embodiments, as shown in FIG. 1, the negative electrode material includes secondary particles 13, and the secondary particles 13 include a matrix 12 and primary particles 11 dispersed in the matrix 12. In the secondary particles 13 of the negative electrode material, the primary particles 11 are dispersed in the matrix 12. The matrix has high conductivity and can improve the conductivity of the primary particles 11. Also, the matrix 12 itself has certain strength, and by wrapping the surface of the primary particles 11, the volume expansion of the silicon crystallites can be alleviated, thereby effectively alleviating the volume expansion of the negative electrode material containing the silicon crystallites.

[0023] In some embodiments, the negative electrode material includes secondary particles, the secondary particles including a substrate and primary particles dispersed in the substrate, the primary particles having pores, and at least some of the substrate being distributed within the pores of the primary particles. The primary particles including silicon crystal grains in this embodiment can mitigate their own volume expansion compared to primary particles without pores, and the negative electrode material in this embodiment has better expansion performance.

[0024] In some embodiments, the primary particles are made porous by forming holes in the surface of the silicon grains by an etching process such that at least a portion of the substrate is within the pores of the primary particles.

[0025] In some embodiments, some substrates further cover the surfaces of the secondary particles, which can further mitigate the volume expansion of the negative electrode material, effectively reduce side reactions between the primary particles and the electrolyte, and improve the structural stability of the negative electrode material, allowing the negative electrode material to have low expansion, high cycle stability, high rate capability, and high initial coulombic efficiency.

[0026] It is understood that the substrate comprises a carbon material and may be substituted with other materials having equivalent properties, such as non-carbon substrate materials comprising at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates.

[0027] It will be understood that any of the above-mentioned non-carbon substrates can function as a supporting skeleton, and compared to conventional conductive carbon substrates, the non-carbon substrates used in the present disclosure have higher strength and rigidity, which allows the anode material to have a higher compacted density during battery manufacturing, improving the structural stability of the anode material and reducing particle fracture and pulverization of the anode material, which is advantageous for improving the cycle performance of the anode material.

[0028] At the same time, non-carbon substrates have electronic insulating properties and therefore generally have good ionic conductivity, and can exert an effect similar to that of an artificial SEI film, reducing and delaying the subsequent formation of a natural SEI film, reducing direct contact between the negative electrode material and the electrolyte, and reducing the occurrence of side reactions.

[0029] Furthermore, non-carbon substrates have the advantage of lower cost compared to carbon substrates. Conventional carbon substrates require a complex pore formation process through activation, which results in relatively high energy consumption and environmental costs. By using a material that naturally has porous pores, such as porous ceramic, the complex pore formation process can be omitted, thereby reducing costs to 10% of the cost of porous carbon substrates, or even lower.

[0030] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitizable carbon. The primary particles 11 are dispersed in the carbon material, which can improve the electrical conductivity of the primary particles 11 and can effectively mitigate the volume expansion of the primary particles 11.

[0031] In some embodiments, the negative electrode material further includes a coating material 121 that coats at least a portion of the surface of the secondary particles 13, and the coating material includes at least one of an amorphous carbon material, a graphitizable carbon material, and a polymer.

[0032] In some embodiments, the coating material coats at least a portion of the surface of the secondary particles to form a coating layer, and the thickness of the coating layer is 5 nm to 500 nm.

[0033] It can be understood that by constructing a coating layer on the surface of the secondary particles, the coating layer can further mitigate the volume expansion of the negative electrode material; by using the coating layer to synergistically modify the secondary particles, the volume expansion of the primary particles can be effectively mitigated, ensuring that the negative electrode material has excellent electrical contact performance even after lithium absorption; and the surface coating layer can reduce the penetration of the electrolyte and reduce the contact between the electrolyte and the primary particles, further effectively reducing the side reactions between the primary particles and the electrolyte, and improving the structural stability of the negative electrode material.

[0034] In some embodiments, the coating material comprises a polymer, and illustratively the polymer may be at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0035] In some embodiments, the coating material includes a polymer, and the thickness of the coating layer formed by the coating material is 50 nm to 300 nm, specifically, for example, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm, or a range consisting of any two of these values, but is not limited thereto. If the thickness of the coating layer formed by the coating material is less than 50 nm, the volume expansion of the silicon material may cause the coating layer to crack, resulting in poor cycle performance. If the thickness of the coating layer formed by the coating material is more than 300 nm, the coating layer is too thick, making it difficult for lithium ions to penetrate inside, affecting capacity.

[0036] In some embodiments, the polymer comprises at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid. Preferably, the polymer is at least one of polypyrrole, polythiophene, polyaniline, and polyacetylene.

[0037] In some embodiments, the coating material includes a graphitizable carbon material, and the thickness of the coating layer formed by the coating material is 5 nm to 100 nm, specifically, for example, 5 nm, 10 nm, 30 nm, 50 nm, 70 nm, 80 nm, 90 nm, or 100 nm, or a range consisting of any two of these values, and is not limited thereto. It will be understood that, due to the high conductivity and strength of graphitizable carbon materials, controlling the thickness of the coating layer to within 5 nm to 100 nm can similarly achieve beneficial effects in improving cycle performance and capacity, despite the relatively small thickness.

[0038] In some embodiments, the coating material includes an amorphous carbon material, and the thickness of the coating layer formed by the coating material is 10 nm to 500 nm, which is advantageous for improving the lithium ion transport rate and preventing the electrolyte from contacting the silicon material, thereby preventing side reactions. Specifically, the thickness may be, for example, 10 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 450 nm, or 500 nm, or a range consisting of any two of these values, and is not limited here.

[0039] In some embodiments, the pore volume of the negative electrode material is less than or equal to 0.01 cm 3 / g~0.2cm 3 / g, which helps to alleviate volume expansion and make the structure more stable. The pore volume of the negative electrode material is 0.01 cm 3 If the pore volume of the negative electrode material is less than 0.2 cm / g, it is not favorable to alleviate the volume expansion. 3 If the pore volume is larger than 0.01 cm / g, the pore volume becomes too large, causing the structure to become unstable. 3 / g, 0.03cm 3 / g, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g, 0.13cm 3 / g, 0.15cm 3 / g, 0.18cm 3 / g or 0.2cm 3 / g, or a range consisting of any two of these values, and is not limited here.

[0040] In some embodiments, the powder tap density of the negative electrode material is 0.3 g / cm 3 ~1.3g / cm 3 Specifically, for example, 0.3 g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 1.0g / cm 3 , 1.3g / cm 3 Alternatively, the negative electrode material may have a powder tap density of 0.6 g / cm. 3 ~0.9g / cm 3 It is preferable that:

[0041] In some embodiments, the green density of the negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 For example, 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 or 1.8g / cm 3 , or a range consisting of any two of these values, and is not limited here. 3 If the density is less than 1.8 g / cm, the porosity of the final electrode sheet is high, which is likely to cause a decrease in the energy density of the battery, and the green density is likely to be less than 1.8 g / cm. 3 If the porosity is greater than 1.45 g / cm, the porosity is too low, which is unfavorable for the electrolyte to penetrate, resulting in a decrease in capacity. 3 ~1.75g / cm 3 It is preferable that:

[0042] In some embodiments, the median particle size of the negative electrode material is 0.5 μm to 26 μm. Optionally, the median particle size of the negative electrode material may be, for example, 0.5 μm, 1 μm, 3 μm, 4 μm, 5 μm, 7 μm, 10 μm, 13 μm, 15 μm, 20 μm, or 26 μm, or a range consisting of any two of these values, but is not limited thereto. Considering the green density and the volume expansion of the material itself, if the median particle size is too small, the green density will decrease, affecting capacity, while if the size is too large, the material will expand significantly, causing structural instability and resulting in reduced cycle performance. Furthermore, the median particle size of the negative electrode material is preferably 1 μm to 10 μm, and more preferably 3 μm to 7 μm.

[0043] The specific surface area of ​​the negative electrode material is 0.8m 2 / g~40m 2 Optionally, the specific surface area of ​​the negative electrode material is 0.8 m 2 / g, 1m 2 / g, 5m 2 / g, 8m 2 / g, 10m 2 / g, 15m 2 / g, 20m 2 / g, 25m 2 / g, 30m 2 / g, 35m 2 / g or 40m 2 / g, or a range consisting of any two of these values, and is not limited here. It should be understood that a specific surface area that is too large is likely to cause the formation of an SEI film, which will result in excessive consumption of irreversible lithium salts and a decrease in the initial coulomb efficiency of the battery. In consideration of the overall cost of the manufacturing process, it is recommended to set the specific surface area to 1 m 2 / g~20m 2 Control to / g.

[0044] In some embodiments, the mass content of carbon element in the negative electrode material is 5% to 80%. Specifically, it may be, for example, 5%, 8%, 10%, 15%, 20%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, or 80%, or a range consisting of any two of these values, but is not limited thereto. If the carbon content is too low, it is disadvantageous in improving conductivity and protecting the silicon material from contact with the electrolyte, while if the carbon content is too high, it will result in a decrease in capacity. The carbon in the negative electrode material is derived from the carbon material.

[0045] In some embodiments, the mass content of oxygen element in the negative electrode material is <15%. Specifically, it may be, for example, 5%, 6%, 8%, 10%, 12%, 13%, 14%, or 14.9%, or a range consisting of any two of these values, but is not limited thereto. It is understood that too high an oxygen element content can cause severe side reactions, resulting in the formation of irreversible silicates and a decrease in the first coulomb efficiency.

[0046] In some embodiments, the mass content of silicon in the negative electrode material is 40% to 80%, specifically, for example, 40%, 42%, 45%, 48%, 50%, 55%, 60%, 65%, 68%, 70%, or 80%, or a range consisting of any two of these values, but not limited thereto. It should be understood that if the silicon content in the negative electrode material is too low, the capacity will be low, and if the content is too high, the volume expansion of the material will be large and the cycle life will be poor.

[0047] The present disclosure further provides a method for manufacturing a negative electrode material, as shown in FIG. 2, the method includes the following steps:

[0048] In S10, a primary sintering process is performed on the mixture containing the silicon powder and the silicon fine powder to obtain an intermediate body.

[0049] In S20, the intermediate is subjected to a secondary sintering treatment, thereby causing the intermediate to undergo a disproportionation reaction to obtain a precursor, the primary particles of which include the precursor, and the anode material includes primary particles, wherein the primary particles include silicon crystal grains. The anode material has an average silicon crystal grain size measured at 25°C of M0 nm, and is heated to 1000°C under nitrogen gas protection, kept at that temperature for 1 hour, and then naturally cooled to 25°C. The average silicon crystal grain size measured under these conditions is M1 nm, and the crystalline instability of the anode material is F, where F=(M1-M0) / M0, M1>M0, and 0.01≦F≦500.

[0050] The method for producing an anode material provided in the present disclosure first performs a primary sintering process on a mixture of elemental silicon powder and silicon fine powder, allowing the elemental silicon to undergo a reduction reaction with silicon dioxide to form silicon oxide (silicon monoxide), and then performs a secondary sintering process on the silicon oxide, during which the silicon monoxide undergoes a disproportionation reaction. The presence of silicon dioxide can restrict the growth of silicon crystal grains, reduce the size of the generated silicon crystal grains, weaken the stress concentration that occurs during the lithiation process of the primary particles, improve the structural stability during the lithiation process of the primary particles, reduce the expansion rate of the anode material, and be beneficial to the formation of a stable solid electrolyte film, thereby improving the electrochemical performance of the anode material.

[0051] In some embodiments, the method for producing the negative electrode material further comprises the steps of:

[0052] In step S30, the precursor obtained in step S20 is etched in an etching solution to obtain primary particles. The anode material includes primary particles, where the primary particles include silicon crystal grains. The anode material has an average silicon crystal grain size of M0 nm measured at 25°C, heated to 1000°C under nitrogen gas protection, held at that temperature for 1 hour, and then naturally cooled to 25°C. The average silicon crystal grain size measured under these conditions is M1 nm. The crystalline instability of the anode material is F, where F = (M1 - M0) / M0, M1 > M0, and 0.01 ≦ F ≦ 500.

[0053] In some embodiments, the method for producing the negative electrode material further comprises the steps of:

[0054] In step S40, a first vapor-phase carbon source is used to perform vapor-phase carbon growth on the primary particles obtained in step S20 or step S30 to obtain secondary particles, and the negative electrode material includes the secondary particles.

[0055] It is understood that by directly performing vapor phase carbon growth on the precursor obtained in S20, the primary particles in the anode material are dispersed within and / or between the substrate particles, resulting in secondary particles. The dispersion of the substrate and the primary particles in the secondary particles of the anode material effectively improves the conductivity of the primary particles and more effectively mitigates the volumetric expansion of the primary particles. The location of a portion of the substrate on the surface of the secondary particles further mitigates the volumetric expansion of the anode material and effectively reduces side reactions between the primary particles and the electrolyte. This also improves the structural stability of the anode material, allowing it to have low expansion, high cycle stability, high rate capability, and high initial coulombic efficiency.

[0056] In another embodiment, after removing excess silicon dioxide and other impurities by etching, silicon particles with holes, i.e., primary particles, are formed. Finally, vapor-phase carbon deposition is performed on the primary particles, allowing the substrate to grow and enter the pores of the silicon particles and at least a portion of the surface of the silicon particles, resulting in secondary particles. In the secondary particles of the negative electrode material, the substrate and the primary particles are dispersed together, which effectively improves the conductivity of the primary particles and more effectively reduces the volumetric expansion of the primary particles. The substrate is partially located on the surface of the secondary particles, which further reduces the volumetric expansion of the negative electrode material and effectively reduces side reactions between the primary particles and the electrolyte, improving the structural stability of the negative electrode material, allowing the negative electrode material to have low expansion, high cycle stability, high rate capability, and high initial coulombic efficiency.

[0057] The method for producing the negative electrode material provided herein not only improves the electrochemical performance of the material, but is also suitable for large-scale production, and the resulting negative electrode material can effectively improve the rate performance and cycle stability of lithium batteries.

[0058] The production method of the present invention will be specifically described below with reference to examples.

[0059] In step S10, a primary sintering process is performed on the mixture containing the silicon powder and the silicon fine powder to obtain an intermediate body.

[0060] In some embodiments, the mass content of oxygen element in the silicon fine powder is ≦5%, and specifically may be, for example, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, or 1%, or a range consisting of any two of these values, and is not limited thereto.

[0061] In some embodiments, the molar ratio of the silicon element powder to the silicon fine powder is 1:(0.9 to 1.1), and specifically may be, for example, 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.08, 1:1.09, or 1:1.1, or a range consisting of any two of these values, or of course, other values ​​within the above range, and are not limited here.

[0062] In some embodiments, step S10 may specifically include, for example, placing a mixture of silicon powder and silicon fine powder into a vacuum reaction chamber, evacuating the vacuum reaction chamber to a pressure of ≦10 Pa, and then performing a primary sintering process.

[0063] In some embodiments, the temperature of the primary sintering process is 1150°C to 1650°C, and specifically may be, for example, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, 1600°C, or 1650°C, or a range consisting of any two of these values, or of course, other values ​​within the above ranges, and are not limited here.

[0064] In some embodiments, the time for the primary sintering treatment is 3 hours to 12 hours, and specifically, for example, 3 hours, 4 hours, 6 hours, 8 hours, 9 hours, 10 hours, or 12 hours, or a range consisting of any two of these values, or of course, other values ​​within the above range, and are not limited here.

[0065] In some embodiments, the heating rate of the primary sintering treatment is 1°C / min to 20°C / min, and specifically may be, for example, 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, 15°C / min, or 20°C / min, or a range consisting of any two of these values, or of course, other values ​​within the above range, and are not limited here.

[0066] In some embodiments, the pressure of the primary sintering process is ≦10 Pa, and specifically may be, for example, 10 Pa, 9 Pa, 8 Pa, 7 Pa, 6 Pa, 5 Pa, 3 Pa, 2 Pa, or 1 Pa, or a range consisting of any two of these values, or of course, other values ​​within the above range, and are not limited thereto.

[0067] In step S20, the intermediate body is subjected to a secondary sintering treatment, which causes the intermediate body to undergo a disproportionation reaction to obtain a precursor.

[0068] In some embodiments, the temperature of the secondary sintering treatment is 200°C to 1050°C, and specifically may be, for example, 200°C, 300°C, 400°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 890°C, 900°C, 980°C, or 1050°C, or a range consisting of any two of these values, or of course, other values ​​within the above ranges, and are not limited here.

[0069] In some embodiments, the time for the secondary sintering treatment is 1 hour to 48 hours, and specifically, for example, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 15 hours, 20 hours, 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours, or a range consisting of any two of these values, or of course, other values ​​within the above range, and are not limited here.

[0070] In some embodiments, the heating rate of the secondary sintering treatment is 1°C / min to 30°C / min, and specifically may be, for example, 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min, 30°C / min, or a range consisting of any two of these values, and is not limited here.

[0071] In the present disclosure, by controlling the temperature, time, heating rate, etc. of the secondary sintering treatment, some intermediates can be disproportionated, and the general reaction formula is 2SiO = Si + SiO. The generated silicon dioxide restricts the growth of silicon crystal grains, so that small silicon crystal grains can be dispersed and distributed in the precursor, and can further form primary particles after the subsequent etching treatment.

[0072] In step S30, the precursor is put into an etching solution and etched to obtain primary particles.

[0073] It can be understood that the etching process can obtain primary particles with holes, and the substrate can then be easily inserted into the holes of the primary particles. Therefore, the primary particles of this embodiment can reduce their own volume expansion compared to primary particles without holes, and the negative electrode material manufactured by the manufacturing method of this embodiment of the present invention has better expansion performance.

[0074] In some embodiments, the mass ratio of the precursor to the etching solution is 1:(5 to 20), and specifically, for example, may be 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20, or a range consisting of any two of these values, or may be other values ​​within the above range, and is not limited here.

[0075] In some embodiments, the etching solution contains hydrofluoric acid, water, ethanol, and ammonium fluoride, where the mass ratio of hydrofluoric acid to water, ethanol, and ammonium fluoride is (6-24):3:1:(3-6), specifically, for example, 6:3:1:3, 10:3:1:3, 12:3:1:3, 15:3:1:3, 18:3:1:3, 20:3:1:3, 24:3:1:3, 6:3:1:5, 6:3:1:6, or a range consisting of any two of these values, or other values ​​within the above range, which are not limited herein. It is understood that the addition of ammonium fluoride can control the reaction rate, reduce oxidation of silicon particles due to local heat generation, reduce the formation of inactive silicon dioxide, and improve the specific capacity of the negative electrode material.

[0076] In some embodiments, the mass concentration of hydrofluoric acid is 37% to 50%, and specifically may be, for example, 37%, 39%, 40%, 42%, 45%, 46%, 48%, 50%, or a range consisting of any two of these values, or may be other values ​​within the above range, and is not limited thereto.

[0077] In some embodiments, the etching reaction time is 0.5 hours to 10 hours, and specifically may be, for example, 0.5 hours, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 9 hours, 10 hours, or a range consisting of any two of these values, and is not limited here.

[0078] In some embodiments, the temperature of the etching reaction is ≦40° C., and specifically may be, for example, 40° C., 38° C., 36° C., 35° C., 32° C., 30° C., 28° C., 25° C., 20° C., 15° C., or a range consisting of any two of these values, and of course, may be other values ​​within the above range, and are not limited thereto.

[0079] In some embodiments, the manufacturing method further comprises washing and drying the etching reaction product.

[0080] In some embodiments, the mass content of oxygen element in the silicon matrix is ​​<5%, and specifically may be, for example, 4.9%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, or a range consisting of any two of these values, or of course, other values ​​within the above range, and are not limited thereto.

[0081] In some embodiments, the mass content of water in the primary particles is <1%, and specifically may be, for example, 0.99%, 0.9%, 0.8%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or a range consisting of any two of these values, and of course, may be other values ​​within the above range, and are not limited thereto.

[0082] In step S40, a first vapor-phase carbon source is used to perform vapor-phase carbon growth on the primary particles to obtain a negative electrode material.

[0083] It is understood that in the vapor phase carbon growth process, the first vapor phase carbon source enters the pores of the silicon particles and grows to form carbon material, some of which grows on the surface of the silicon particles.

[0084] In some embodiments, the temperature for vapor phase carbon growth is between 200°C and 1050°C, and specifically, the reaction temperature may be 200°C, 300°C, 400°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 890°C, 900°C, 980°C, 1050°C, or a range consisting of any two of these values. Preferably, the reaction temperature is between 700°C and 900°C.

[0085] In some embodiments, the incubation time for vapor phase carbon growth is 1 hour to 48 hours, and specifically may be, for example, 1 hour, 4 hours, 8 hours, 12 hours, 16 hours, 24 hours, 28 hours, 32 hours, 38 hours, 48 ​​hours, or a range consisting of any two of these values, and is not limited here.

[0086] In some embodiments, the first gas phase carbon source comprises at least one of acetylene, methane, ethylene, propane, toluene, cyclohexane, ethanol, ethylene, propylene, pyrrole, and acetonitrile.

[0087] In some embodiments, the flow rate of the first gaseous carbon source is 0.1 L / min to 10 L / min, and specifically may be, for example, 0.1 L / min, 0.4 L / min, 0.6 L / min, 0.8 L / min, 1.0 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 9 L / min, 10 L / min, or a range consisting of any two of these values, and is not limited here.

[0088] The present disclosure provides a method for controlling the time, temperature, and incubation time of vapor phase carbon growth to improve the reaction efficiency of vapor phase carbon growth, thereby growing and forming a carbon material within the pores of the silicon particles. The carbon material grown within the pores of the silicon particles can improve the conductivity of the anode material. The carbon material grown on the surface of the silicon particles can also form a carbon layer, which may be an amorphous carbon material, and further alleviate the volume expansion of the silicon particles, reduce direct contact between the silicon particles and the electrolyte, and improve the cycle performance of the anode material.

[0089] After step S40, the manufacturing method further includes a step of performing a surface coating treatment on the secondary particles using a coating material, where the coating material includes at least one of an amorphous carbon material, a graphitizable carbon material, and a polymer.

[0090] In some embodiments, the step of performing a surface coating treatment on the secondary particles with the coating material includes a step of spray-drying a mixed coating liquid containing the secondary particles and a polymer.

[0091] In some embodiments, the solid content of the secondary particles in the mixed coating liquid is 5% to 50%, and specifically may be, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of these values, and is not limited here.

[0092] In some embodiments, the coating mixture includes a polar solvent.

[0093] In some embodiments, the polar solvent comprises at least one of water, absolute ethanol, methanol, and isopropanol.

[0094] In some embodiments, the mass ratio of the secondary particles to the polymer is 10:(0.1 to 5), and specifically, for example, it may be 10:0.1, 10:1, 10:2, 10:3, 10:4, 10:5, or a range consisting of any two of these values, and is not limited here.

[0095] In some embodiments, the drying temperature for spray drying is 60°C to 200°C, and specifically may be, for example, 60°C, 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, or a range consisting of any two of these values.

[0096] In some embodiments, the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0097] In some embodiments, the polymer comprises at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0098] In some embodiments, the step of performing a surface coating treatment on the secondary particles with the coating material includes the steps of flowing a second gaseous carbon source onto the secondary particles and heating the second gaseous carbon source until it undergoes a pyrolysis reaction, thereby growing and forming the coating material on the surfaces of the secondary particles, wherein the coating material includes at least one of an amorphous carbon material and a graphitizable carbon material.

[0099] In some embodiments, the second gas phase carbon source comprises at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0100] In some embodiments, the heating rate of the pyrolysis reaction is 1°C / min to 20°C / min, and specifically may be, for example, 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, 15°C / min, 20°C / min, or a range consisting of any two of these values, and is not limited here.

[0101] In some embodiments, the temperature of the pyrolysis reaction is 600°C to 1000°C. Specifically, the reaction temperature may be 600°C, 650°C, 700°C, 750°C, 800°C, 890°C, 900°C, 960°C, 1000°C, or a range consisting of any two of these values. Through multiple experiments, the inventors have found that controlling the reaction temperature within the range of 600°C to 1000°C improves reaction efficiency and allows a uniform carbon layer to be formed on the surface of the secondary particles, and the carbon layer may be amorphous carbon. Preferably, the reaction temperature is 700°C to 900°C.

[0102] In some embodiments, the incubation time for the thermal decomposition reaction is 1 hour to 48 hours, and specifically may be, for example, 1 hour, 4 hours, 8 hours, 12 hours, 16 hours, 24 hours, 28 hours, 32 hours, 38 hours, 48 ​​hours, or a range consisting of any two of these values, and is not limited here.

[0103] In some embodiments, the concentration of the gas-phase carbon source is 0.1 L / min to 10 L / min, and specifically may be, for example, 0.1 L / min, 0.4 L / min, 0.6 L / min, 0.8 L / min, 1.0 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 9 L / min, 10 L / min, or a range consisting of any two of these values, and is not limited here.

[0104] In some embodiments, the pyrolysis reaction is carried out under a protective atmosphere.

[0105] In some embodiments, the protective atmosphere comprises at least one of helium, neon, argon, krypton, and xenon.

[0106] The present invention further provides a battery using the negative electrode material provided in the above-described embodiments of the present invention or the negative electrode material manufactured by the method for manufacturing the negative electrode material provided in the above-described embodiments of the present invention. The battery provided in the above-described embodiments of the present invention has advantages of high capacity, high initial coulombic efficiency, long cycle life, excellent rate performance, and low expansion. The battery may be a lithium ion battery, a sodium ion battery, a solid electrolyte battery, etc., but is not limited thereto.

[0107] The present invention will be further described below by dividing it into several examples. However, the present invention is not limited to the following specific examples. The present invention may be implemented by making appropriate modifications within the scope of the present invention.

[0108] Example 1 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.06 Pa, and then heated to 1250°C at a heating rate of 3°C / min. The pressure was maintained at 5 Pa and the mixture was kept at that temperature for 4 hours, after which an intermediate was obtained.

[0109] (2) The intermediate was placed in an atmospheric furnace and heated to 950°C at a heating rate of 3°C / min under the protection of an argon atmosphere, and then kept at that temperature for 5 hours before being cooled to obtain a precursor.

[0110] (3) 100 g of the precursor was dissolved in the prepared etching solution and allowed to undergo an etching reaction for 2 hours. The reaction temperature was maintained below 30°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 12:3:1:4. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0111] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 950°C at a heating rate of 3°C / min under the protection of an argon gas atmosphere. Then, acetylene gas was introduced at a rate of 0.5 L / min, so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. The temperature was maintained for 4 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0112] (5) 10 g of silicon carbon composite was dissolved in 100 g of anhydrous ethanol, and 1 g of polyacrylic acid was added. The mixture was mechanically stirred for 30 minutes, and then spray-dried at a drying temperature of 100°C to coat the surface of the silicon carbon composite with a polymer, yielding a negative electrode material.

[0113] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0114] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0115] FIG. 3 shows the XRD pattern of the negative electrode material in this example. As can be seen from the XRD pattern in FIG. 3, the three strong peaks at 28.4°, 47.3°, and 56.1° correspond to the three strong peaks of silicon (JCPDS No. 27-1402). There are essentially no impurity phases. Calculations based on the Scherrer equation yield a silicon crystal grain size of 3.5 nm.

[0116] 4a and 4b are a scanning electron microscope image and an internal cross-sectional view of the negative electrode material prepared in Example 1, respectively. As shown in FIGS. 4a and 4b, the surface of the negative electrode material has a dense carbon coating layer.

[0117] FIG. 5a is a transmission electron microscope image of the negative electrode material in this example, and FIG. 5b is an enlarged view of a portion of the transmission electron microscope image of the negative electrode material in this example. As shown in FIGS. 5a and 5b, the primary particles inside the negative electrode material are uniformly distributed in the carbon substrate.

[0118] FIG. 6 shows the cycle performance curve of the negative electrode material in this example. As shown in FIG. 6, the negative electrode material had excellent cycle performance, with a capacity retention rate of 93.8% after 50 cycles under a current of 0.25 C.

[0119] Example 2 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.03 Pa, and then heated to 1250°C at a heating rate of 1°C / min. The pressure was maintained at 3 Pa and the mixture was kept at this temperature for 6 hours, after which an intermediate was obtained.

[0120] (2) The intermediate was placed in an atmospheric furnace and heated to 750°C at a rate of 1°C / min under the protection of an argon atmosphere, and then kept at this temperature for 12 hours before being cooled to obtain a precursor.

[0121] (3) 100 g of precursor was dissolved in the prepared etching solution and allowed to undergo an etching reaction for 2 hours. The reaction temperature was maintained below 30°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 12:3:1:4. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0122] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 750°C at a heating rate of 3°C / min under the protection of an argon gas atmosphere. Then, propane gas was introduced at a rate of 4.5 L / min, so that the volume ratio of argon gas to propane in the rotary atmosphere furnace was 9:1. The temperature was maintained for 4 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0123] (5) 10 g of silicon carbon composite was placed in a rotary atmosphere furnace and heated to 600°C at a heating rate of 1°C / min under the protection of an argon gas atmosphere. Then, propane gas was introduced at a rate of 0.2 L / min, so that the volume ratio of argon gas to propane in the rotary atmosphere furnace was 9:1. After keeping the temperature for 6 hours, the propane gas was shut off and the material was cooled to obtain a negative electrode material.

[0124] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0125] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0126] Example 3 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.01 Pa, and then heated to 1150°C at a heating rate of 1°C / min. The pressure was maintained at 2 Pa and the mixture was kept at that temperature for 8 hours, after which an intermediate was obtained.

[0127] (2) The intermediate was placed in an atmospheric furnace and heated to 650°C at a rate of 1°C / min under the protection of an argon gas atmosphere, and then kept at this temperature for 12 hours before being cooled to obtain a precursor.

[0128] (3) 100 g of the precursor was dissolved in 100 g of the prepared etching solution and allowed to undergo an etching reaction for 2 hours. The reaction temperature was maintained below 20°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 6:3:1:3. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0129] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 650°C at a heating rate of 3°C / min under the protection of an argon gas atmosphere. Then, propane gas was introduced at a rate of 5.5 L / min, so that the volume ratio of argon gas to propane in the rotary atmosphere furnace was 9:1. The temperature was maintained for 8 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0130] (5) 10 g of silicon carbon composite was dissolved in 100 g of anhydrous ethanol, and 1 g of polyacrylic acid was added. The mixture was mechanically stirred for 30 minutes, and then spray-dried at a drying temperature of 110°C to coat the surface of the silicon carbon composite with a polymer, yielding a negative electrode material.

[0131] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0132] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0133] Example 4 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.075 Pa, and then heated to 1650°C at a heating rate of 10°C / min. The pressure was maintained at 9 Pa and the mixture was kept at that temperature for 8 hours, after which an intermediate was obtained.

[0134] (2) The intermediate was placed in an atmospheric furnace and heated to 1050°C at a temperature increase rate of 30°C / min under the protection of an argon gas atmosphere, and then kept at that temperature for 12 hours before being cooled to obtain a precursor.

[0135] (3) 100 g of the precursor was dissolved in 100 g of the prepared etching solution and allowed to undergo an etching reaction for 2 hours. The reaction temperature was maintained below 20°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 6:3:1:3. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0136] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 950°C at a heating rate of 5°C / min under the protection of an argon gas atmosphere. Then, propane gas was introduced at a rate of 2 L / min, so that the volume ratio of argon gas to propane in the rotary atmosphere furnace was 9:1. The temperature was maintained for 8 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0137] (5) 100 g of the silicon carbon composite was placed in a rotary atmosphere furnace and heated to 950°C at a heating rate of 10°C / min under the protection of an argon gas atmosphere. Then, acetylene gas was introduced at a rate of 4 L / min, so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 6 hours, the acetylene gas was shut off and the material was cooled to obtain the negative electrode material.

[0138] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0139] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0140] Example 5 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.075 Pa, and then heated to 1650°C at a heating rate of 10°C / min. The pressure was maintained at 9 Pa and the mixture was kept at that temperature for 8 hours, after which an intermediate was obtained.

[0141] (2) The intermediate was placed in an atmospheric furnace and heated to 1000°C at a heating rate of 30°C / min under the protection of an argon gas atmosphere, and then kept at that temperature for 12 hours before being cooled to obtain a precursor.

[0142] (3) 100 g of the precursor was dissolved in 100 g of the prepared etching solution and allowed to undergo an etching reaction for 2 hours. The reaction temperature was maintained below 20°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 6:3:1:3. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0143] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 1000°C at a heating rate of 5°C / min under the protection of an argon gas atmosphere. Then, propane gas was introduced at a rate of 2 L / min, so that the volume ratio of argon gas to propane in the rotary atmosphere furnace was 9:1. The temperature was maintained for 8 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0144] (5) 100 g of silicon carbon composite was taken and placed in a rotary atmosphere furnace. Under the protection of an argon gas atmosphere, it was heated to 1000°C at a heating rate of 10°C / min. Then, acetylene gas was flowed at 4 L / min so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 6 hours, the acetylene gas was shut off and the material was cooled to obtain a negative electrode material.

[0145] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0146] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0147] Example 6 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.075 Pa, and then heated to 1550°C at a heating rate of 10°C / min. The pressure was maintained at 9 Pa and the mixture was kept at that temperature for 7 hours, after which an intermediate was obtained.

[0148] (2) The intermediate was placed in an atmospheric furnace and heated to 600°C at a rate of 1°C / min under the protection of an argon gas atmosphere, and then kept at this temperature for 24 hours before being cooled to obtain a precursor.

[0149] (3) 100 g of the precursor was dissolved in 100 g of the prepared etching solution and allowed to undergo an etching reaction for 2 hours. The reaction temperature was maintained below 20°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 6:3:1:3. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0150] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 600°C at a heating rate of 5°C / min under the protection of an argon gas atmosphere. Then, 3 L / min of propane gas was introduced to make the volume ratio of argon gas to propane in the rotary atmosphere furnace 9:1. The temperature was maintained for 8 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0151] (5) 100 g of silicon carbon composite was taken and placed in a rotary atmosphere furnace. Under the protection of an argon gas atmosphere, it was heated to 600°C at a heating rate of 1°C / min, and then acetylene gas was flowed at 4 L / min so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 6 hours, the acetylene gas was shut off and the material was cooled to obtain a negative electrode material.

[0152] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0153] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0154] Example 7 (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:1, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.06 Pa, and then heated to 1250°C at a heating rate of 10°C / min. The pressure was maintained at 5 Pa and the mixture was kept at that temperature for 6 hours, after which an intermediate was obtained.

[0155] (2) The intermediate was placed in an atmospheric furnace and heated to 700°C at a rate of 1°C / min under the protection of an argon gas atmosphere, and then kept at this temperature for 18 hours before being cooled to obtain a precursor.

[0156] (3) 100 g of the precursor was dissolved in 100 g of the prepared etching solution and allowed to undergo an etching reaction for 4 hours. The reaction temperature was maintained below 20°C throughout the entire etching process. The etching solution used was a mixed solution of hydrofluoric acid, water, ethanol, and ammonium fluoride in a mass ratio of 6:3:1:3. After the reaction was completed, the mixture was centrifuged and dried to obtain primary particles.

[0157] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 700°C at a heating rate of 5°C / min under the protection of an argon gas atmosphere. Then, acetylene gas was introduced at a rate of 2 L / min, so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. The temperature was maintained for 12 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0158] (5) 100 g of the silicon carbon composite was placed in a rotary atmosphere furnace and heated to 700°C at a temperature increase rate of 1°C / min under the protection of an argon gas atmosphere. Then, acetylene gas was introduced at a rate of 4 L / min, so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the acetylene gas was shut off and the material was cooled to obtain the negative electrode material.

[0159] The negative electrode material produced in this example includes secondary particles and a coating material located on at least a portion of the surface of the secondary particles, the coating material being a polymer, the secondary particles including a carbon material and primary particles dispersed with each other, and the primary particles including a plurality of silicon crystal grains.

[0160] Other parameters of the negative electrode material in this example are shown in detail in Table 1.

[0161] Example 8 The differences from the first embodiment are as follows.

[0162] (1) Silicon powder and silicon fine powder (SiO2) were mixed uniformly in a molar ratio of 1:0.9, then placed in a vacuum high-temperature sintering furnace. The vacuum high-temperature sintering furnace was evacuated to 0.06 Pa, and then heated to 1250°C at a heating rate of 3°C / min. The pressure was maintained at 5 Pa and the mixture was kept at that temperature for 4 hours, after which an intermediate was obtained.

[0163] Example 9 The differences from the first embodiment are as follows.

[0164] (4) 500 g of silicon particles were placed in a rotary atmosphere furnace and heated to 950°C at a temperature increase rate of 3°C / min under the protection of an argon gas atmosphere. Then, acetylene gas was introduced at a rate of 0.5 L / min, so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. The mixture was kept at this temperature for 8 hours, and then cooled to obtain the negative electrode material.

[0165] Example 10 The differences from the first embodiment are as follows.

[0166] Step (3) was not performed.

[0167] (Comparative Example 1) (1) Silicon powder and magnesium powder were uniformly mixed in a 1:1 mass ratio, then placed in a sintering furnace. Argon gas was introduced at a rate of 1 L / min, and the mixture was heated to 650°C at a rate of 3°C / min. The mixture was then kept at this temperature for 4 hours, yielding a reaction product.

[0168] (2) The reaction product was added to 1 mol / L hydrochloric acid. After mechanical stirring for 2 hours, it was centrifuged, washed with water, and dried to obtain a silicon precursor.

[0169] (3) 500 g of silicon precursor was placed in a rotary atmosphere furnace and heated to 950°C at a heating rate of 3°C / min under the protection of an argon gas atmosphere. Then, acetylene gas was introduced at a rate of 0.5 L / min, so that the volume ratio of argon gas to acetylene in the rotary atmosphere furnace was 9:1. The temperature was maintained for 4 hours, and then the material was cooled to obtain a silicon-carbon composite.

[0170] (4) 10 g of silicon carbon composite was dissolved in 100 g of anhydrous ethanol, and 1 g of polyacrylic acid was added. The mixture was mechanically stirred for 30 minutes, and then spray-dried at a drying temperature of 100°C to coat the surface of the silicon carbon composite with a polymer, yielding a negative electrode material.

[0171] (Comparative Example 2) The differences from the first embodiment are as follows.

[0172] Without carrying out steps (1) and (2) to prepare a precursor, 100 g of elemental silicon powder was directly taken and subjected to step (3) and subsequent reactions.

[0173] (Performance test) 1) Median particle size of negative electrode material: The test method for the median particle size of negative electrode materials is based on GB / T19077-2016, and is measured using a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd. in the UK. In the volume-based distribution, the diameter with a cumulative frequency of 50% is defined as D50, the diameter with a cumulative frequency of 90% is defined as D90, and the diameter with a cumulative frequency of 10% is defined as D10.

[0174] 2) Test method for specific surface area of ​​negative electrode material: The equipment used was the TriStar3000&3020 fully automatic specific surface area and pore size analysis instrument from Micromeritics Instrument Ltd. in the United States, which complies with the Chinese national standard GB / T19587-2017. It measures the gas adsorption amount on solid surfaces at different relative pressures under constant and low temperatures, and then calculates the monolayer adsorption amount of the sample based on the Brunauer-Emmett-Teller adsorption theory and its equation (BET equation), thereby calculating the specific surface area of ​​the material.

[0175] 3) Test method for tap density: The tap density of the powder is measured using a DAT-6-220 powder tap density meter from Quantachrome Instruments, USA, and is tested according to the Chinese national standard GB / T5162-2006 / ISO3953:1993 by weighing a certain amount of sample and vibrating it 3000 times at 300 times / min.

[0176] 4) Oxygen and carbon content test method: The oxygen content is measured using a Nicolet Is10 Fourier infrared spectrometer from ThermoFisher, USA, and the carbon layer content is measured using thermogravimetric analysis.

[0177] 5) SEM test: Scanning electron microscopy characterization is carried out with a Hitachi S4800 field emission electron microscope from Japan, with an operating voltage of 200 kV to observe the structure of the anode material and calibrate the thickness of the coating layer.

[0178] 6) Test method for average size of primary particles: The average particle size is measured using an E3500 ion milling machine and an S4800 field emission electron microscope from Hitachi, Japan.

[0179] 7) Test method for average grain size of silicon crystal grains: The XRD pattern of the sample was measured using a TD-3600 X-ray diffractometer manufactured by Dandong Tongda Co., Ltd., China. The half-width of the diffraction peak of the sample and the corresponding Bragg angle were obtained using Jade software. The average grain size of the silicon crystal grains was calculated using the Scherrer equation D=Kγ / Bcosθ, and the obtained average grain size was used to represent the average grain size of the crystal grains.

[0180] 8) Coating thickness test method: The material is cut using a Hitachi E3500 ion milling machine and a Hitachi S4800 field emission electron microscope from Japan, and the thickness of the particle modification layer and the protective layer is measured by SEM.

[0181] The negative electrode materials produced in Examples 1 to 9 and Comparative Example 1 through the above tests correspond to sample numbers S1 to S9 and R1, and the performance parameters of the negative electrode materials are shown in Table 1.

[0182] [Table 1]

[0183] 10) Electrochemical testing: The negative electrode material was prepared as a slurry of sodium carboxymethylcellulose, styrene butadiene rubber, conductive graphite (KS-6), and carbon black (SP) in a ratio of 92:2:2:2:2, respectively. This slurry was then uniformly applied to copper foil and dried to form a negative electrode sheet. A coin-type battery was then assembled in a glove box under an argon gas atmosphere. A polypropylene microporous membrane was used as the separator, 1 mol / L lithium hexafluorophosphate was used as the electrolyte (the solvent was a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate), and a metallic lithium sheet was used as the counter electrode.

[0184] The above 10 groups of batteries were subjected to a discharge specific capacity test using the LANDEN CT2001A battery test system, and the ratio of the amount of electricity discharged for one hour to the battery capacity was taken as the discharge specific capacity.

[0185] The above 10 batteries were subjected to an initial coulombic efficiency test using the LANDEN CT2001A battery test system, with the charge / discharge current set to 0.05C to measure the initial coulombic efficiency.

[0186] The above 10 groups of batteries were subjected to a 100-cycle test using the LANDEN CT2001A battery test system, with the charge / discharge current set at 0.2C. After 100 cycles, the post-cycle battery capacity and post-cycle capacity retention rate were calculated.

[0187] The capacity retention rate after 100 cycles at 0.2 C was calculated as follows: discharge capacity at 100th cycle / discharge capacity at 1st cycle*100%. The results are shown in Table 2.

[0188] [Table 2]

[0189] As shown in Table 2, the anode materials prepared in Examples 1 to 10 have a crystal instability of F, 0.01≦F≦500, which reduces the grain boundary surface energy of the silicon crystal grains. This reduces the stress concentration that occurs in the anode material containing silicon crystal grains during the lithium release process, improves the electrochemical sintering of the anode material after lithium absorption, improves the structural stability of the anode material during the lithiation process, reduces the expansion rate of the anode material, and is favorable for the formation of a stable solid electrolyte film, thereby improving the electrochemical performance of the anode material. Furthermore, the carbon material and primary particles are dispersed within the secondary particles of the anode material, which effectively improves the conductivity of the primary particles and effectively reduces the volumetric expansion of the anode material containing silicon crystal grains. The location of a portion of the carbon material on the surface of the secondary particles further reduces the volumetric expansion of the anode material, effectively reducing side reactions between the silicon crystal grains and the electrolyte. This also improves the structural stability of the anode material, allowing the anode material to have low expansion, high cycle stability, high rate capability, and high initial coulombic efficiency.

[0190] In the manufacturing process of the anode material of Comparative Example 1, the crystal instability F of the anode material is too large, which means that the size of the silicon crystal grains is too small and electrochemical sintering is likely to occur on the surface of the silicon crystal grains. After sintering, the silicon crystal grains grow, which causes large local stress in the anode material after lithium release, leading to increased instability of the entire structure, which causes a decrease in the cycle performance and capacity of the anode material, and poor electrochemical performance of the anode material.

Claims

1. An anode material, the anode material including primary particles including silicon crystal grains, The average grain size of the silicon crystal grains measured under the condition of 25° C. is defined as M 0 The average grain size of the silicon crystal grains measured under the conditions of heating to 1000°C under nitrogen gas protection, keeping the temperature for 1 hour, and then naturally cooling to 25°C is defined as M nm. 1 nm and the crystalline instability of the negative electrode material is F, F = (M 1 -M 0 ) / M 0 , M 1 >M 0 , 0.01≦F≦500; Anode material.

2. The negative electrode material is (1) The average grain size of silicon crystal grains measured under the conditions of heating to 1000°C at a rate of 5°C / min under nitrogen gas protection, keeping the temperature for 1 hour, and then naturally cooling to 25°C is M 1 nm, 0.1 < M 1 ≦50; (2) The average grain size of silicon crystal grains measured under the condition of 25°C is M 0 nm, 0.1≦M 0 and satisfying at least one of the following characteristics: The negative electrode material according to claim 1 .

3. The average particle size of the primary particles is 1 nm to 100 nm. The negative electrode material according to claim 1 .

4. The negative electrode material includes secondary particles, and the secondary particles include a substrate and the primary particles dispersed in the substrate. The negative electrode material according to claim 1 .

5. the primary particles have pores, and at least a portion of the substrate is distributed within the pores of the primary particles; The negative electrode material according to claim 4 .

6. the substrate comprises a carbon material, the carbon material comprising at least one of amorphous carbon and graphitizable carbon; The negative electrode material according to claim 4 .

7. the negative electrode material further includes a coating material located on at least a portion of a surface of the secondary particles, the coating material including at least one of an amorphous carbon material, a graphitizable carbon material, and a polymer; The negative electrode material according to claim 4 .

8. The coating material is (1) A polymer is included, and the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid; (2) A coating layer formed by the coating material contains a polymer and has a thickness of 50 nm to 300 nm; (3) A coating layer formed by a graphitizable carbon material has a thickness of 5 nm to 100 nm; (4) The coating layer contains an amorphous carbon material, and the thickness of the coating layer formed by the coating material is 10 nm to 500 nm. The negative electrode material according to claim 7.

9. The negative electrode material is (1) The mass content of carbon element in the negative electrode material is 5% to 80%; (2) The mass content of oxygen element in the negative electrode material is less than 15%; (3) The mass content of silicon element in the negative electrode material is 40% to 80%. The negative electrode material according to any one of claims 1 to 8.

10. The pore volume of the negative electrode material is 0.01 cm 3 / g~0.2cm 3 / g, The negative electrode material according to any one of claims 1 to 8.

11. The median particle size of the negative electrode material is 0.5 μm to 26 μm. The negative electrode material according to any one of claims 1 to 8.

12. The specific surface area of ​​the negative electrode material is 0.8 m 2 / g~40m 2 / g, The negative electrode material according to any one of claims 1 to 8.

13. The powder tap density of the negative electrode material is 0.3 g / cm 3 ~1.3g / cm 3 That is, The negative electrode material according to claim 1 .

14. The green density of the negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 That is, The negative electrode material according to claim 1 .

15. The negative electrode material according to any one of claims 1 to 14, battery.

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