Negative electrode material and battery

Abstract

Provided in the present application are a negative electrode material and a battery. The negative electrode material contains silicon, and at least part of silicon is present in the form of crystalline-phase silicon. On the basis that the mass content of silicon in the negative electrode material is 100%, the mass content of the crystalline-phase silicon is A%, and the average size of silicon grains of the crystalline-phase silicon is B nm. The negative electrode material satisfies the following characteristics: 0.3≤A / B≤60, and 6≤A+B≤75. According to the negative electrode material and the battery provided in the present application, the negative electrode material can reach an ideal balance state between cycling performance, capacity exertion and rate capability.

Description

Anode materials and batteries Technical Field

[0001] The present application relates to the technical field of negative electrode materials, and in particular, to a negative electrode material and a battery. Background Art

[0002] Electric new energy vehicles are the future of the automotive market, and their core component is the lithium-ion battery. As the market develops, the demand for high-capacity batteries is increasing. Using new high-capacity cathode and anode materials is one of the key methods to increase battery energy density.

[0003] More and more new materials such as metals, oxides, and metal alloys are being used as active materials in negative electrode materials to continuously explore ways to improve the energy density of batteries. Silicon-based negative electrode materials, as one of the above-mentioned active materials, are generally considered to be the next generation of negative electrode materials. They have an ultra-high theoretical specific capacity (4200mAh / g) and a low delithiation potential (<0.5V). In addition, the voltage platform of silicon is slightly higher than that of graphite. After the battery is made and charged, it is difficult to cause surface lithium deposition, so it has better safety performance. However, silicon-based negative electrode materials have a severe volume expansion effect during the cycle process, and the negative electrode materials are easily pulverized and broken, resulting in rapid cycle decay of the battery.

[0004] To address this issue, conventional solutions in the industry include coating silicon-based anode materials, secondary granulation, and controlling silicon grain size. However, existing technical solutions often cause silicon-based anode materials to rapidly grow in size during heat treatment, leading to even greater volume expansion of elemental Si. Therefore, controlling the average size of silicon grains to reduce the volume expansion of the anode material and improve its cycling stability remains an urgent issue.

[0005] Summary of the Invention

[0006] The present application proposes a negative electrode material and a battery. By controlling the relationship between the mass ratio of crystalline silicon in the silicon-containing material and the average size of silicon grains, the volume expansion of the negative electrode material can be reduced and the cycle stability of the negative electrode material can be improved.

[0007] In a first aspect, the present application provides a negative electrode material, wherein the negative electrode material contains silicon, and the silicon is at least partially present in the form of crystalline silicon;

[0008] Taking the mass content of silicon element in the negative electrode material as 100%, the mass content of crystalline silicon is A%, and the average size of silicon grains of the crystalline silicon is B nm;

[0009] The negative electrode material satisfies the following characteristics: 0.3≤A / B≤60, and 6≤A+B≤75.

[0010] In some embodiments, the value of A ranges from 5 to 65.

[0011] In some embodiments, B≤7.

[0012] In some embodiments, the negative electrode material further includes oxygen, and the atomic ratio of oxygen to silicon in the negative electrode material is x, 0<x<2.2.

[0013] In some embodiments, the negative electrode material further includes oxygen, and the component containing oxygen and silicon in the negative electrode material includes at least one of silicon oxide and silicate.

[0014] In some embodiments, the negative electrode material further includes carbon elements, and the component containing carbon elements in the negative electrode material includes at least one of amorphous carbon, graphite, graphene, carbon nanotubes, and carbon fibers.

[0015] In some embodiments, the negative electrode material further includes a doping metal element, and the doping metal element is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr, and Zn.

[0016] In some embodiments, the doping metal element includes Mg, and the mass content of the Mg element in the negative electrode material is 3% to 25%; and / or B≤15.

[0017] In some embodiments, the doping metal element includes Li element, and the mass content of the Li element in the negative electrode material is 3% to 15%; and / or B≤10.

[0018] In some embodiments, the mass content of oxygen in the negative electrode material is 10% to 55%.

[0019] In some embodiments, the mass content of carbon in the negative electrode material is 1% to 40%.

[0020] In some embodiments, the mass content of silicon in the negative electrode material is 25% to 88%.

[0021] In some embodiments, at least a portion of the surface of the negative electrode material has a carbon layer.

[0022] In some embodiments, the particle size of the negative electrode material satisfies: D 20 -D 10 ≤4μm, D 90 -D 80 ≤8μm.

[0023] In some embodiments, the specific surface area of ​​the negative electrode material is 0.1 m 2 / g~25m 2 / g.

[0024] In some embodiments, the pH of the negative electrode material is 6-10.

[0025] In some embodiments, the true density of the negative electrode material is 2.0 g / cm 3 ~3.4g / cm 3 .

[0026] In a second aspect, the present application provides a battery comprising the negative electrode material described in the first aspect.

[0027] The technical solution of this application has at least the following beneficial effects:

[0028] The negative electrode material provided by the present application can reduce the lithium ion transmission impedance during charge and discharge, improve the solid-liquid interface stability of the negative electrode material and the electrolyte, and significantly improve the stability of the crystalline structure during long-term cycles by controlling the relationship between the mass ratio of crystalline silicon in the silicon element and the average size of silicon grains. Specifically, crystalline silicon is more stable than amorphous silicon in structure, and the peak intensity and peak position of crystalline silicon in the dQ / dV curve of the manufactured battery electrode change little during the cycle. However, the direction of expansion of crystalline silicon is selective, resulting in uneven expansion stress, which in turn causes the negative electrode particles to break, exposing the silicon interface to more electrolytes, triggering side reactions with the electrolyte, and causing SEI (Solid Electrolyte Interphase, solid electrolyte interface film) film continues to grow and thicken, resulting in deterioration of interface stability; the silicon element (single substance, compound) in the amorphous state can stabilize the overall structure of the negative electrode material particles and buffer expansion deformation, reduce the breakage of the negative electrode material particles and thus improve the interface stability. At the same time, the amorphous material is an isotropic material, there is no directional selectivity in lithium insertion, and the lithium ion transmission impedance is lower; the size of the silicon grains will also affect the stability of the negative electrode material. By regulating the mass proportion of crystalline silicon in the negative electrode material and the average size of the silicon grains, the effects of the two parameters of silicon grain size and the mass ratio between crystalline silicon and amorphous silicon on the electrochemical properties of the negative electrode material can be balanced, and at the same time, the negative electrode material can have the advantages of low lithium ion transmission impedance, high solid-liquid interface stability, and strong long-term cycle crystal phase structure stability, thereby greatly improving product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is a schematic flow chart of a method for preparing a negative electrode material provided in an embodiment of the present application.

[0030] FIG2 is a schematic diagram showing a battery in a discharged state.

[0031] FIG3 is a comparison chart of the cycle performance of the negative electrode materials provided in Example 1 and Comparative Example 1 of the present application.

[0032] FIG4 a is a first schematic diagram of the software interface state of the negative electrode material during XRD testing of the embodiment involved in the present application.

[0033] FIG4 b is a second schematic diagram of the software interface state of the negative electrode material during XRD testing of the embodiment involved in this application.

[0034] FIG4 c is a third schematic diagram of the software interface state during XRD testing of the negative electrode material according to the embodiment of the present application.

[0035] FIG4 d is a fourth schematic diagram of the software interface status during XRD testing of the negative electrode material according to the embodiment of the present application.

[0036] FIG4e is a fifth schematic diagram of the software interface state of the negative electrode material during XRD testing of the embodiment involved in this application. DETAILED DESCRIPTION

[0037] The following is a preferred implementation of the embodiment of the present invention. It should be noted that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the embodiment of the present invention. These improvements and modifications are also considered to be within the scope of protection of the embodiment of the present invention.

[0038] Specifically, the present application provides a negative electrode material, the negative electrode material contains silicon, and the silicon is at least partially present in the form of crystalline silicon;

[0039] Through XRD (X-Ray Diffraction) test analysis, taking the mass content of silicon element in the negative electrode material as 100%, the mass content of crystalline silicon is A%, the average size of silicon grains is Bnm, and it satisfies 0.3≤A / B≤60, 6≤A+B≤75.

[0040] In the above scheme, by controlling the relationship between the mass ratio of crystalline silicon in silicon elements and the average size of silicon grains, it is possible to reduce the lithium ion transmission impedance during charge and discharge, improve the solid-liquid interface stability of the negative electrode material and the electrolyte, and significantly improve the stability of the crystalline structure during long-term cycles. Specifically, crystalline silicon is more stable than amorphous silicon. The peak intensity and peak position of crystalline silicon in the dQ / dV curve of the manufactured battery electrode change little during the cycle. However, the direction of expansion of crystalline silicon is selective, resulting in uneven expansion stress, which in turn causes the negative electrode particles to break, exposing the silicon interface to more electrolytes, triggering side reactions with the electrolyte, and causing SEI (Solid Electrolyte Interphase, solid electrolyte interface film) film continues to grow and thicken, resulting in deterioration of interface stability; the silicon element (single substance, compound) in the amorphous state can stabilize the overall structure of the negative electrode material particles and buffer expansion deformation, reduce the breakage of the negative electrode material particles and thus improve the interface stability. At the same time, the amorphous material is an isotropic material, there is no directional selectivity in lithium insertion, and the lithium ion transmission impedance is lower; the size of the silicon grains will also affect the stability of the negative electrode material. By regulating the mass proportion of crystalline silicon in the negative electrode material and the average size of the silicon grains, the effects of the two parameters of silicon grain size and the mass ratio between crystalline silicon and amorphous silicon on the electrochemical properties of the negative electrode material can be balanced, and at the same time, the negative electrode material can have the advantages of low lithium ion transmission impedance, high solid-liquid interface stability, and strong long-term cycle crystal phase structure stability, thereby greatly improving product performance.

[0041] Specifically, the specific value of A / B is, for example, 0.3, 0.5, 1, 5, 10, 15, 20, 25, 35, 40, 55 or 60, and the specific value of A+B is, for example, 6, 8, 10, 15, 20, 25, 35, 40, 45, 50, 55, 60, 65, 70 or 75, etc., which are not limited here. The present application balances the volume expansion and long cycle stability of the negative electrode material by controlling the values ​​of A / B and A+B, that is, controlling the relationship between the two parameters of silicon grain size and the mass ratio between crystalline silicon and amorphous silicon.

[0042] In some embodiments, taking the mass content of silicon in the negative electrode material as 100%, the mass content of crystalline silicon is A%, and the value range of A is 5 to 65. The value range of A can specifically be 5, 11, 21, 26, 31, 40, 50, 59, 61 or 65, etc., which is not limited here. It can be understood that when the mass content of crystalline silicon in the silicon element is too low, the amorphous component in the silicon element is too high and the reaction activity is high. During the charge and discharge process, electrochemical sintering is easily caused under the action of the applied voltage, causing the average size of the silicon grains to increase sharply. The drastic structural changes and the uncontrollable size of the silicon grains lead to the deterioration of the product cycle performance; when the mass content of crystalline silicon in the silicon element is too high, the charge and discharge polarization is aggravated, which leads to a decrease in product capacity, while reducing the rate performance and low temperature performance of the product. Therefore, controlling the mass content of crystalline silicon between 5% and 65% is beneficial to suppressing the volume expansion effect of the negative electrode material and improving the cycle performance of the negative electrode material.

[0043] In some embodiments, the silicon grain size of the crystalline silicon is Bnm, and B≤7; the average size of the silicon grains can specifically be 7nm, 6.5nm, 6.0nm, 5.9nm, 5.5nm, 5.0nm, 4.5nm, 4.0nm, 3.5nm, 3nm, 2.5nm, 2nm, 1nm, etc., which are not limited here. It can be understood that when the average size of the silicon grains is too large, the expansion stress generated by the silicon grains during the lithium insertion process is uneven, which can easily cause the negative electrode material particles to break and lose electrochemical activity, thereby reducing the product cycle performance. Therefore, controlling the average size of the silicon grains within the above range is conducive to improving the uniformity of the expansion stress of the negative electrode material particles, reducing the breakage of the negative electrode material particles, and allowing the negative electrode material to achieve an ideal balance in cycle performance, capacity utilization and rate performance, thereby obtaining the best comprehensive performance.

[0044] Combined with the above content, it can be seen that the effects of the crystalline silicon mass ratio and the silicon grain size on the performance of the final negative electrode material have a mutually repairing effect. For example, when the silicon grain size is smaller, that is, B is smaller, it is beneficial to the structural stability of the negative electrode particles, and can alleviate the negative effect of the crystalline silicon mass ratio being too high, that is, A being larger, on product performance; when the crystalline silicon mass ratio is relatively low, that is, A is smaller, it can provide more amorphous phase structures to buffer the stress unevenness caused by the large silicon grain size, that is, B being too large. Therefore, in order to pursue more ideal product performance, in addition to limiting the values ​​of A and B respectively, it is more important to establish the relationship between A and B. Through research, it was found that when the relationship between A and B satisfies 0.3≤A / B≤60, 6≤A+B≤75, the crystalline silicon mass ratio and the silicon grain size achieve the best balance, and the performance of the negative electrode material is optimized.

[0045] In some embodiments, the negative electrode material further includes oxygen, and the components containing oxygen and silicon in the negative electrode material include but are not limited to at least one of silicon oxide and silicate. Silicon oxide can be represented by the general formula SiO y (0<y≤2). Specifically, SiO y Specifically, it can be SiO 0.1 、SiO 0.2 、SiO 0.3 、SiO 0.4 、SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 , SiO2, etc., are not limited here. Silicon oxide can be a material formed by dispersing silicon particles in SiO2; or it can be a material having a tetrahedral structural unit, wherein the silicon atom is located at the center of the tetrahedral structural unit, and silicon atoms and / or oxygen atoms are located at the four vertices of the tetrahedral structural unit.

[0046] In some embodiments, the overall atomic ratio of oxygen to silicon in the negative electrode material is x (0<x<2.2), where x can be 0.1, 0.2, 0.5, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 1.9, 2.1, 2.185, etc., or other values ​​within the above range.

[0047] It can be understood that the silicon-containing component in the negative electrode material contains at least one of elemental silicon, silicon alloy, silicon oxide and silicate. The elemental silicon can be amorphous silicon and / or crystalline silicon, and the silicon alloy can be silicon-lithium alloy, silicon-magnesium alloy, silicon-nickel alloy, etc.

[0048] In some embodiments, the mass content of oxygen element in the negative electrode material is 10% to 55%, specifically 10%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 55%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0049] In some embodiments, the negative electrode material further includes a doped metal element, and the doped metal element is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr and Zn. In the element distribution spectrum obtained by scanning the SEM (Scanning Electron Microscope) section of the negative electrode material particles using X-rays, the distribution surface of Si, O and the doped metal element is in a uniform dispersion state. In the negative electrode material, Si, O and the doped metal element are evenly distributed in the particles, which can effectively reduce the infiltration of air and other components into the interior of the particles and cause the active components to fail. The structure and properties will not deteriorate during long-term storage, and it is very suitable for use in lithium-ion batteries. The uniformly dispersed distribution state of the metal elements is conducive to the expansion and contraction of the negative electrode material at all locations during the lithium insertion and deintercalation process. There will be no stress weak points caused by excessive local expansion. The doped metal can also improve the conductivity of the negative electrode material and enhance the structural strength of the negative electrode material, thereby making the material performance better. It can be understood that in the negative electrode material of the present application, at least part of the doped metal elements exist in the form of silicates.

[0050] In some embodiments, the doped metal element includes Mg element, and the mass content of Mg element in the negative electrode material is 3% to 25%, specifically 3%, 5%, 8%, 10%, 12%, 14%, 18%, 20%, 23%, 24% or 25%, etc., or other values ​​within the above range.

[0051] In some embodiments, when the doping metal element includes Mg, the crystalline silicon in the negative electrode material has a grain size of B nm, where B ≤ 15. The average size of the silicon grains can be, for example, 15 nm, 12 nm, 10 nm, 9 nm, 7 nm, 6.0 nm, 5.5 nm, 5.0 nm, 4.5 nm, 4.0 nm, 3 nm, 2 nm, or 1 nm, without limitation. It will be appreciated that when the metal M is magnesium, the negative electrode material can include MgSiO3 and Mg2SiO4, which can reduce the size of the Si crystallites and thus reduce material expansion.

[0052] In some embodiments, the doped metal element includes Li element, and the mass content of Li element in the negative electrode material is 3% to 15%, specifically 3%, 5%, 8%, 9%, 10%, 12%, 13%, 14% or 15%, etc., or other values ​​within the above range.

[0053] In some embodiments, when the doped metal element includes lithium, the crystalline silicon in the negative electrode material has a grain size of B nm, where B ≤ 10. The average size of the silicon grains can be, for example, 10 nm, 9 nm, 7 nm, 6.0 nm, 5.5 nm, 5.0 nm, 4.5 nm, 4.0 nm, 3 nm, 2 nm, 1 nm, and the like, without limitation. It is understood that at least a portion of the lithium element exists in the form of lithium silicate. In this case, the silicon grain size in the negative electrode material is ≤ 10 nm, which facilitates the dispersed distribution of the silicon grains, effectively reducing silicon volume expansion and improving cycle performance.

[0054] In some embodiments, the negative electrode material further comprises carbon, and the carbon-containing component in the negative electrode material comprises at least one of amorphous carbon, graphite, graphene, carbon nanotubes, and carbon fibers. Amorphous carbon may be soft carbon and / or hard carbon, and graphite may be artificial graphite and / or natural graphite. It is understood that the carbon-containing component can improve the conductivity of the silicon-based active material. Graphite is a material with high conductivity, low volume expansion, high initial efficiency, and stable cycle performance.

[0055] In some embodiments, at least a portion of the surface of the negative electrode material has a carbon layer. It is understood that the carbon layer on the surface of the negative electrode material can reduce the breakage of material particles caused by repeated formation of the SEI film, thereby improving the cycle performance of the negative electrode material and reducing the volume expansion caused by the formation of the SEI film.

[0056] In some embodiments, the active material (silicon and / or silicon oxide, etc.) is dispersed in a carbon material containing carbon elements. The carbon material constructs a conductive network for the active material, overcoming the shortcomings of the active material (such as silicon and / or silicon oxide, etc.) having poor conductivity, which is beneficial to the capacity of silicon oxide and cycle stability. In some embodiments, the mass content of the carbon element in the negative electrode material is 1% to 40%, specifically 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 28%, 35% or 40%, etc., and of course other values ​​within the above range can also be used, which is not limited here.

[0057] In some embodiments, the silicon content of the negative electrode material is 25% to 88% by mass, and specifically can be 25%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, 85%, or 88%, etc., and of course other values ​​within the above range are also possible, and are not limited here. Preferably, the silicon content of the negative electrode material is 40% to 60% by mass.

[0058] In some embodiments, in the negative electrode material, the active material and the carbon material containing carbon elements are dispersed with each other in the form of particles.

[0059] In some embodiments, the pH value of the negative electrode material is 6-10, specifically 6, 7, 8, 8.5, 9, 9.5 or 10, etc., which are not limited here. Preferably, the pH value of the negative electrode material is 7-10.

[0060] In some embodiments, the specific surface area of ​​the negative electrode material is 0.1 m 2 / g~25m 2 / g, specifically 0.1m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g, 3.6m 2 / g, 4.0m 2 / g、5m 2 / g, 5.5m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g、8.5m 2 / g, 10.0m 2 / g, 12.0m 2 / g, 15.0m 2 / g, 18.0m 2 / g or 25m 2 / g, but is not limited to the listed values, and other values ​​not listed in this range are also applicable. It can be understood that the smaller the specific surface area, the better. Too large a specific surface area is likely to lead to the formation of SEI film, consume too much irreversible lithium salt, and reduce the initial efficiency of the battery. Taking into account the cost of the preparation process, preferably, the specific surface area of ​​the negative electrode material is 1m 2 / g~10m 2 / g.

[0061] In some embodiments, the true density of the negative electrode material is 2.0 g / cm 3 ~3.4g / cm 3 , specifically 2.0 g / cm 3 , 2.2g / cm 3 , 2.4g / cm 3 , 2.6g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3.0g / cm 3 、3.2g / cm 3 or 3.4m 2 / g, and other values ​​not listed in this numerical range are also applicable. Controlling the true density within the above range is beneficial to improving the energy density and rate performance of the negative electrode material.

[0062] In some embodiments, the particle size of the negative electrode material satisfies: D 20 -D 10 ≤4μm, D 90 -D 80 ≤8μm; D 20 -D 10 Specifically, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3.5μm, or 4μm, etc. 90 -D 80 Specifically, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3.5μm, 5μm, 5.5μm, 6μm, 6.5μm or 8μm, etc., which are not limited here. It can be understood that when the particle size of the negative electrode material deviates from the above range, it means that the overall particle size distribution of the product shifts towards the direction of large particle size. Large particle size particles are more fragile in long cycles and are more likely to break and deactivate, affecting the electrochemical performance of the product; when D 20 -D 10 Does not meet the requirements and D 90 -D 80 When these requirements are met, the overall particle size distribution of the product shifts toward smaller particles. Smaller particles have a larger specific surface area, resulting in higher reactivity with the electrolyte and less likely to form a stable SEI, which affects the product's long-term cycling performance and high-temperature storage performance. Therefore, controlling the particle size of the negative electrode material within the above range is beneficial for improving the negative electrode material's rate performance, long-term cycling stability, and high-temperature storage performance.

[0063] The present application also provides a method for preparing a negative electrode material, as shown in FIG1 , the method comprises the following steps S10 to S20:

[0064] S10, heating and vaporizing a raw material mixture containing silicon and oxygen in a vacuum state, transporting the resulting vapor into a plasma flow for plasma reaction, and condensing to obtain a precursor;

[0065] S20, carbon-coating the precursor, and heat-treating the carbon-coated product at 800° C. to 1100° C. to obtain a negative electrode material. The negative electrode material comprises a silicon content of 100% by mass, a crystalline silicon content of A% by mass, an average silicon grain size of B nm, and the conditions 0.3 ≤ A / B ≤ 60, and 6 ≤ A + B ≤ 75 are satisfied.

[0066] The present application provides a method for preparing a negative electrode material. The vapor formed after the raw material mixture is heated and gasified is transported to a plasma flow for a plasma reaction. The plasma has the characteristics of low temperature and high energy level. The precursor vapor condenses and settles in the plasma to generate uniformly distributed silicon microcrystalline seeds without affecting the overall amorphous state of the substance. When such seeds exist in the precursor, the silicon grain size in the aforementioned S20 process can be promoted to grow rapidly, and the excessive heat treatment time can be reduced to reduce the loss of control of the mass ratio of crystalline silicon. The plasma condensation process is used to obtain seeds, and high-temperature heat treatment is used to regulate the crystallization state. The two aspects of the two actions simultaneously act to achieve 0.3≤A / B≤60, 6≤A+B≤75, that is, by controlling the relationship between the mass ratio of crystalline silicon in the silicon element and the average size of the silicon grains, the negative electrode material obtains the best comprehensive performance.

[0067] The following is a detailed introduction to this plan:

[0068] S10, heating and vaporizing a raw material mixture containing silicon and oxygen elements in a vacuum state to form vapor, transporting it into a plasma flow for plasma reaction, and condensing it to obtain a precursor.

[0069] In some embodiments, the raw material mixture includes Si, SiO z A mixture of SiO2 and SiO y At least one of a mixture of Si and Si, and a mixture of Si and SiO2, wherein 0<z<2.

[0070] In some embodiments, the raw material mixture further includes a doping metal element, and the doping metal element is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr and Zn; the doping metal element can be added to the raw material mixture in the form of a metal element, a metal oxide, etc.

[0071] In some embodiments, the doping metal element is selected from Mg and / or Li.

[0072] In some embodiments, the pressure in the vacuum state is 1.333×10 -1 Pa~1.333×10 -6 Pa, specifically 1.333×10 -1 Pa, 1.333×10 -2 Pa, 1.333×10 -3 Pa, 1.333×10 -4 Pa, 1.333×10 -5 Pa or 1.333×10 - 6 Pa et al., not limited here.

[0073] In some embodiments, the temperature of heating and gasification is 1000° C. to 1800° C., specifically 1000° C., 1050° C., 1100° C., 1200° C., 1250° C., 1300° C., 1350° C., 1400° C., 1500° C., 1600° C., 1700° C., or 1800° C. It will be understood that the above temperature is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0074] In some embodiments, the gas source of the plasma flow includes at least one of argon, hydrogen, neon, and helium.

[0075] In some embodiments, the radio frequency power of the plasma generating device is 10kW to 100kW, specifically 10kW, 20kW, 30kW, 40kW, 50kW, 60kW, 70kW, 80kW, 90kW, 100kW, etc., which is not limited here.

[0076] In some embodiments, the raw material mixture further includes a doping metal element, the doping metal includes Li, and the molar ratio of Si to Li in the raw material mixture is (1 to 50):1, specifically 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 40:1 or 50:1, etc., which is not limited here.

[0077] In some embodiments, the raw material mixture further includes a doping metal element, the doping metal includes Mg, and the molar ratio of Si to Mg in the raw material mixture is (5-50):1, specifically 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 40:1 or 50:1, etc., which is not limited here.

[0078] In some embodiments, the cooling is performed using a protective gas, and the protective gas includes at least one of nitrogen, argon, neon, krypton, and helium.

[0079] In some embodiments, the method further comprises crushing the condensed precursor so that the particle size D of the precursor is 50 0.1μm~25μm. The particle size D of the precursor 50 Specifically, it can be 0.1μm, 0.3μm, 0.4μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 6μm, 10μm, 12μm, 15μm, 20μm or 25μm, etc., which is not limited here.

[0080] S20, carbon-coating the precursor, and heat-treating the carbon-coated product at 800° C. to 1100° C. to obtain a negative electrode material.

[0081] In one embodiment, the carbon coating treatment is at least one of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating. In this application, the carbon coating treatment is low temperature coating (below 800°C), which can effectively inhibit the increase of silicon grain size.

[0082] Specifically, the carbon coating treatment step specifically includes: heating the precursor obtained by the cooling treatment, introducing a protective gas and a carbon source gas, and thermally cracking the carbon source gas to obtain a carbon-coated product.

[0083] In some embodiments, the carbon source gas used for vapor-phase carbon coating comprises hydrocarbons.

[0084] In some embodiments, the carbon source gas includes at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone, and benzene.

[0085] In some embodiments, the chemical vapor deposition apparatus includes at least one of a rotary chemical vapor deposition reactor, a plasma enhanced chemical vapor deposition reactor, a chemical vapor deposition tube furnace, and a fluidized bed. Specifically, the chemical vapor deposition apparatus is at least one of a rotary furnace and a box furnace.

[0086] In some embodiments, the thermal cracking temperature is 600°C-800°C, and the thermal cracking time is 2h-20h. The thermal cracking temperature can be 600°C, 620°C, 650°C, 680°C, 700°C, 750°C, or 800°C, etc., without limitation herein. The thermal cracking time can be 2h, 3h, 4h, 6h, 8h, 10h, 12h, 15h, or 20h, etc., without limitation herein.

[0087] In some embodiments, the carbon source gas is introduced under a protective gas.

[0088] In some embodiments, the protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0089] In some embodiments, the carbon coating step specifically includes: carbonizing a mixture obtained by mixing the precursor obtained by the cooling treatment with a solid carbon source to obtain a negative electrode material.

[0090] In some embodiments, the solid carbon source comprises at least one of sugars, esters, hydrocarbons, organic acids, and polymers. Specifically, the solid carbon source may be at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin, and phenolic resin.

[0091] In some embodiments, the cooling product and the carbon source can be mixed by VC mixing, fusion, ball milling, three-dimensional mixing, fluidized bed mixing, etc.

[0092] In some embodiments, the mass ratio of the solid carbon source to the precursor is 5:(5-95).

[0093] In some embodiments, the carbonization temperature is 500°C-800°C, and the carbonization time is 2 hours-20 hours. The carbonization temperature can be 500°C, 530°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, 750°C, or 800°C, etc., without limitation herein. The thermal cracking time can be 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, or 20 hours, etc., without limitation herein.

[0094] In some embodiments, the equipment used for solid-phase carbon coating is at least one of a rotary kiln, a box furnace, a roller kiln, a tunnel kiln, and a push plate kiln.

[0095] In some embodiments, the protective gas may be at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0096] The liquid phase carbon coating process specifically involves uniformly mixing the cooled product with a carbon source, then placing it in a furnace, introducing a protective gas, and heat treating the mixture to cause the carbon source to crack and coat the surface of the cooled product.

[0097] In some embodiments, the carbon source used for liquid carbon coating is an organic carbon source, specifically low-temperature liquid asphalt, furfuryl alcohol, glycidyl methacrylate, triethylene glycol dimethacrylate, etc.

[0098] In some embodiments, the protective gas may be at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0099] In some embodiments, the carbon-coated product is placed at 800° C. to 1100° C. for heat treatment, and the heat treatment holding time is 0.5 h to 18 h to obtain a negative electrode material.

[0100] In some embodiments, the temperature of the heat treatment may be 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C or 1100°C, etc., which is not limited here.

[0101] In some embodiments, the holding time of the heat treatment is 0.5h to 18h, specifically 0.5h, 1h, 2h, 3h, 4h, 6h, 8h, 10h, 12h, 16h or 18h, etc., which are not limited here. Preferably, the holding time of the heat treatment is 3h to 8h. The maximum temperature treatment holding time during heat treatment is defined as the time when the temperature measured by the heat treatment equipment reaches the maximum temperature of the heat treatment within the range of ±10°C. The text related to high temperature heat treatment time in the following text refers to this concept and will not be repeated. The embodiment of the present invention also provides a lithium ion battery, which uses the negative electrode material provided by the above embodiment of the present invention or the negative electrode material prepared by the preparation method of the negative electrode material provided by the above embodiment of the present invention. The lithium ion battery provided by the embodiment of the present invention has the advantages of excellent rate performance and low expansion.

[0102] One embodiment of the present application provides a secondary battery (such as a lithium-ion battery, a sodium-ion battery, etc.), comprising a housing, an electrode assembly, and an electrolyte / electrolyte. The electrode assembly and the electrolyte / electrolyte are both located within the housing.

[0103] The outer shell can be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), such as a soft-pack battery. In other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0104] Figure 2 shows a schematic diagram of a battery in a discharged state, i.e., during operation. As shown, the electrode assembly includes a positive electrode sheet 110, a negative electrode sheet 120, and a separator 130, with the separator being disposed between the positive and negative electrode sheets. The electrode assembly can be a laminated structure, in which the positive electrode sheets, separators, and negative electrode sheets are alternately stacked in sequence. In other embodiments, the electrode assembly can also be a wound structure, in which the positive electrode sheets, separators, and negative electrode sheets are stacked in sequence and then wound.

[0105] positive electrode

[0106] The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 provided on at least one surface of the positive electrode current collector. The positive electrode current collector can be made of aluminum foil or nickel foil, etc., or it can be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and the polymer substrate. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes a compound that can reversibly embed and deintercalate metal ions. In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide, a sodium transition metal composite oxide, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0107] negative electrode

[0108] The negative electrode sheet 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector. It can also be any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0109] During battery operation, that is, when the battery is in a discharged state, the metal ions 140 (eg, lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the separator 130 via the electrolyte / electrolyte, and are embedded in the lattice of the positive electrode material.

[0110] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes the metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the isolation membrane through the electrolyte / electrolyte, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing the metal ions to be embedded in the lattice of the negative electrode material.

[0111] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve discharge and charging processes over thousands of cycles.

[0112] Test method:

[0113] 1) Particle size of negative electrode material:

[0114] The particle size test method refers to GB / T 19077-2016. It can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0115] 2) Test method for specific surface area of ​​negative electrode material:

[0116] At constant temperature and low temperature, after measuring the adsorption amount of gas on the solid surface at different relative pressures, the monolayer adsorption amount of the sample is obtained based on the Brownauer-Ettel-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0117] 3) pH test of negative electrode material:

[0118] Take 10g of negative electrode material, add 10g of water, stir for 30min, and then measure the pH value using a pH meter.

[0119] 4) Test of the mass content of carbon element in negative electrode material:

[0120] The mass content of amorphous carbon was determined by thermogravimetric analysis.

[0121] 5) Test of the mass content of oxygen in the negative electrode material:

[0122] Use an oxygen, nitrogen and hydrogen analyzer to test the oxygen content.

[0123] 6) Test method for the mass content of doped metal elements in negative electrode materials:

[0124] The negative electrode material was calcined at 750°C in an oxygen-containing atmosphere to constant weight. It was then dissolved in a mixed acid consisting of concentrated HF, concentrated HCl, and concentrated HNO3 until the solution no longer produced bubbles. The mixed acid was then doubled in volume. When the solution remained bubble-free, solid-state separation was performed to obtain the negative electrode material digest. The mass content of the doped metal elements in the digestion solution was determined using inductively coupled plasma atomic emission spectrometry.

[0125] 7) Test method for average size of silicon grains in negative electrode materials:

[0126] The negative electrode material was tested using a TD3600 X-ray diffraction analysis instrument produced by Dandong Tongda. The data was processed using X'Pert HighScore Plus software. The parameters in the Strip K-Alpha2 project were set as follows: K-A1 / K-A2 Intensity ratio was 0.5, and wavelength ratio corr was 0. After completing Strip K-Alpha2 smoothing, the smooth degree parameter used was 1. After the software's automatic peak search function was used, the angle value range was set to 27.5-29.5. After using automatic fitting, the half-maximum width and peak position of the Si characteristic peak around 28° were read from the Peak List and substituted into the Scherrer formula to calculate the average size of the silicon grains.

[0127] 8) Test method for the mass content of crystalline silicon in negative electrode materials

[0128] 4.5 g of the negative electrode material of each embodiment and comparative example was taken and mixed evenly with 0.5 g of magnesium oxide (analytical grade) sealed and preserved to ensure no deterioration. The sample was accurately sampled to 0.1 mg and manually ground using an agate mortar. It was necessary to grind the magnesium oxide powder with a slight effort to break up any small fragments that might exist. The grinding time was recommended to be 15-20 min, with no white powder visible visually. There was no upper limit on the time. The test was performed using an X-ray diffraction analysis device model TD3600 produced by Dandong Tongda, and the test parameters were as follows:

[0129] The X-ray diffraction (XRD) data were processed using Jade 6.0 software. The data processing workflow and parameter settings are as follows. Right-click the BG icon in the main toolbar. Set the background parameters as shown in Figure 4a and click "Apply." The resulting red dot represents the set background point.

[0130] Click the BE button in the middle toolbar to delete or add background points on the graph. On the graph, left-click to add background points and right-click to delete background points. Delete all background points above the background line to minimize the background line. Click "Remove" in the Background Parameter Settings dialog box to remove the background.

[0131] Set the smoothing parameters as shown in Figure 4b to complete the smoothing operation. Then set the peak search parameters as shown in Figure 4c, click "Apply", select all the check boxes on the left, and click "OK".

[0132] As shown in Figure 4d, in the above phase analysis window, right click on the upper toolbar icon, and click on the possible elements in the pop-up periodic table. After selecting the possible elements in the above periodic table, click "OK". Click on the toolbar icon, then only the phases related to the selected element will remain in the phase analysis window, making it convenient for phase retrieval and analysis.

[0133] In the phase analysis window shown in Figure 4e, select the appropriate PDF card based on the sample conditions, elemental composition, peak matching degree and other factors. Click the check box in front of the selected card to select it.

[0134] Note: Phase selection principle

[0135] Under the condition that other factors are the same, give priority to cards with low FOM values ​​and J values ​​of C or +. Be sure to choose cards with RIR values, otherwise quantitative calculations cannot be performed.

[0136] When processing the same data multiple times, testing the same sample multiple times, or testing the same series of samples multiple times, try to choose the same PDF card. Even if you cannot choose the same PDF card, you must choose cards with the same or similar RIR values ​​to ensure the consistency of the calculation results.

[0137] If you can't find a known card in the window list, enter the card number in the input window and press Enter. The corresponding card will be added to the window list. After the crystal phase is determined, return to the main window of the software. For different phases, select the appropriate angle range for fitting. Generally, only the strongest peak of a phase needs to be fitted. However, if the peak to be fitted overlaps with other peaks, the overlapping peaks should be fitted together to ensure reasonable peak separation.

[0138] After selecting the range, right-click icon, and click the "Refine" button three times in the pop-up dialog box. Once the strongest peaks of all phases are fitted, proceed to the next step.

[0139] Click the "Option" button in the taskbar and select "Easy Quantitative Analysis" in the drop-down box. In the quantitative calculation window that pops up, first select the internal standard phase to be added, fill in the amount of internal standard added (mass percentage) and check the "Internal Standard" checkbox.

[0140] Next, examine each phase one by one, paying attention to the peak checkboxes (marked by angles) on the left side of the window (as shown above). For each phase, select only the strongest peak (or other peaks selected for calculation), leaving all other peaks unchecked to avoid calculation errors. Click the "Calc RIR" button in the toolbar above the window, followed by the "Calc Wt%" button, to complete the calculation. Then, click the "Show Graph" button to display the results.

[0141] Wherein, “Wt(n)%” represents the mass percentage content of each crystalline phase after deducting the internal standard, and reads the mass percentage content of the Si phase; “Others+Amorphous” represents the sum of the contents of unidentified crystalline phases and amorphous phases, which represents the amorphous phase content in this method.

[0142] The number in the brackets after each crystalline phase content value represents the calculation error. This method requires that the error value does not exceed 10% of the corresponding crystalline phase content value (except for amorphous phase and low-content crystalline phase).

[0143] Repeated calculation: Since the fitting operation is greatly affected by human factors, which also has a great influence on the final calculation results, each sample is calculated three times according to the above steps, and the relative standard deviation (RSD) of the three calculations is required to be ≤10% to reduce the influence of human factors. After manually deducting the background, smoothing the curve, patrolling the peak to confirm the crystal phase, and fitting the data, the strongest peak of each phase is used as the standard for calculation to obtain the composition ratio of all crystal phases and amorphous phases. Then, the proportion of silicon crystal phase in the total sample is confirmed as above, and the percentage is converted to a decimal count and set as M Si .

[0144] Calculation method of mass ratio of crystalline silicon The carbon content of the negative electrode materials of each embodiment and comparative example was tested using the aforementioned test method, and the decimals were counted and set as M C The oxygen content of the negative electrode materials of each embodiment and comparative example was tested using the aforementioned test method, with decimal counts set as M OThe total content of each metal element in the negative electrode materials of each embodiment and comparative example was tested using the above test method, and the decimals were counted as M. M In summary, the mass ratio of crystalline silicon = M Si / (1-M C -M O -M M ).

[0145] 9) Cycle performance and rate test

[0146] The prepared negative electrode material was mixed with graphite (artificial graphite S360 series) in a ratio of 10:90, and then mixed with sodium carboxymethyl cellulose CMC, binder styrene-butadiene rubber SBR, conductive agent Super-P, and conductive agent KS-6 in a mass ratio of 92:2:2:4 to form a slurry, which was coated on copper foil and vacuum dried and rolled to prepare a negative electrode sheet; the counter electrode was a lithium sheet, and a 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte and a Celgard2400 separator were assembled into a button battery.

[0147] Cycling performance testing uses a constant current charge and discharge experiment at 30mA, with the charge and discharge voltage limited to 0-1.5V. Testing is performed using the LAND battery testing system from Wuhan Jinnuo Electronics Co., Ltd. At room temperature, button cells are cycled at 0.1C, 0.2C, and 0.5C for one cycle each, followed by 47 cycles at 1C. The capacity at the 50th cycle is divided by the capacity at the first cycle to determine the product's 50-cycle capacity retention rate. The 0.1C capacity divided by the 1C capacity is used to evaluate the product's rate performance.

[0148] The negative electrode materials prepared in each embodiment and comparative example were used as negative electrode precursors. The mass ratio of precursor, conductive agent (Super-P) and binder (CMC+SBR) in the electrode sheet coating was 92:4:4. The counter electrode was a lithium sheet. A 1 mol / L LiPF6 / EC+DMC+EMC (v / v=1:1:1) electrolyte and Celgard2400 separator were used to assemble button cells. The first cycle charge and discharge test was carried out using this battery. The charge and discharge system was

[0149] Charging: 0.1C to 10mV CC, 0.02C to 5mV CC; Discharging: 0.1C to 1.5V CC.

[0150] The following further describes the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0151] Example 1

[0152] A method for preparing a negative electrode material comprises the following steps:

[0153] (1) Take a mixture of silicon and silicon dioxide, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1100 ° C to form vapor; in the vacuum deposition chamber, helium is used to generate plasma flow at a radio frequency power of 30kW, and the vapor is transported to the plasma flow for plasma reaction. The condensed and collected solids are crushed to D 50 =12μm precursor.

[0154] (2) The precursor was carbon-coated at 700°C for 6 hours using a CVD method, and the carbon-coated product was heat-treated at 1100°C for 1 hour to obtain a negative electrode material.

[0155] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2). Parameters of the negative electrode material are detailed in Table 1.

[0156] Example 2

[0157] A method for preparing a negative electrode material comprises the following steps:

[0158] (1) Take a mixture of silicon, silicon dioxide and magnesium oxide, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1100 ° C, vapor is formed by gasification, and a plasma flow is generated in a vacuum deposition chamber using helium at a radio frequency power of 30 kW. The vapor is transported into the plasma flow for plasma reaction, and the solid collected by condensation is crushed to D 50 =12μm precursor.

[0159] (2) The precursor was carbon-coated at 700°C for 6 hours using a CVD method, and the carbon-coated product was heat-treated at 900°C for 1 hour to obtain a negative electrode material.

[0160] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), magnesium silicate, the parameters of the negative electrode material are shown in Table 1.

[0161] Example 3

[0162] A method for preparing a negative electrode material comprises the following steps:

[0163] (1) Take a mixture of silicon, silicon dioxide and magnesium metal, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4Pa, heated to 1100 ° C, vapor is formed, and a plasma flow is generated in a vacuum deposition chamber using helium at a radio frequency power of 20 kW. The vapor is transported into the plasma flow for plasma reaction, and the solid collected by condensation is crushed to D 50 =12μm precursor.

[0164] (2) The precursor was carbon-coated at 700°C for 6 hours using a CVD method, and the carbon-coated product was heat-treated at 920°C for 2 hours to obtain a negative electrode material.

[0165] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), magnesium silicate, and other parameters of the negative electrode material are shown in Table 1.

[0166] Example 4

[0167] A method for preparing a negative electrode material comprises the following steps:

[0168] (1) Take a mixture of silicon, silicon dioxide and metallic lithium, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1300℃, vapor is formed, and helium is used in the vacuum deposition chamber to generate plasma flow at 20kW RF power. The vapor is transported into the plasma flow for plasma reaction, and the solid collected by condensation is crushed to D 50 =6μm precursor.

[0169] (2) The precursor was carbon-coated at 700°C for 6 hours using a CVD method, and the carbon-coated product was heat-treated at 950°C for 1 hour to obtain a negative electrode material.

[0170] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), lithium silicate, and other parameters of the negative electrode material are shown in Table 1.

[0171] Example 5

[0172] A method for preparing a negative electrode material comprises the following steps:

[0173] (1) Take a mixture of silicon and silicon dioxide, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1200 ° C gasification to form vapor, in the vacuum deposition chamber using helium at RF power of 90kW to generate plasma flow, the vapor is transported to the plasma flow for plasma reaction, condensed and collected solid crushed to D 50 =5μm precursor.

[0174] (2) The precursor was carbon-coated at 800°C for 6 hours using a CVD method, and the carbon-coated product was heat-treated at 1000°C for 8 hours to obtain a negative electrode material.

[0175] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), other parameters of the negative electrode material are shown in Table 1.

[0176] Example 6

[0177] The difference from Example 1 is that the carbon-coated product is heat-treated at 1100° C. for 18 hours.

[0178] Example 7

[0179] The difference from Example 1 is that the carbon-coated product is heat-treated at 800° C. for 2 hours.

[0180] Example 8

[0181] The difference from Example 1 is that the particle size of the negative electrode material is D20-D10=5.1 μm, and D90-D80=9.5 μm.

[0182] Example 9

[0183] The difference from Example 1 is that the carbon coating reaction temperature of the CVD method in step (2) is 800°C, and the carbon-coated product is heat-treated at 1000°C for 18 hours.

[0184] Example 10

[0185] The difference from Example 1 is that the radio frequency power used to excite the plasma in step (1) is 100 kW, the firing temperature in step (2) is 1100° C., and the firing time is 0.5 hours.

[0186] Example 11

[0187] The difference from Example 1 is that the radio frequency power used to excite the plasma in step (1) is 10 kW, the firing temperature in step (2) is 800° C., and the firing time is 10 hours.

[0188] Comparative Example 1

[0189] A method for preparing a negative electrode material comprises the following steps:

[0190] (1) Take a mixture of silicon and silicon dioxide, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1200℃, vaporized to form steam, condensed and collected solids crushed to D 50 =5μm composite.

[0191] (2) The composite was carbon-coated at 800°C using a CVD method, and the carbon-coated product was heat-treated at 1000°C for 8 hours to obtain a negative electrode material.

[0192] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), the parameters of the negative electrode material are shown in Table 1.

[0193] Comparative Example 2

[0194] A method for preparing a negative electrode material comprises the following steps:

[0195] (1) Take a mixture of silicon and silicon dioxide, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1200 ° C, using neon gas in a vacuum deposition chamber at a radio frequency power of 5kW to generate a plasma flow, the vapor is transported into the plasma flow for plasma reaction, and the condensed and collected solids are crushed to D 50 =5μm composite.

[0196] (2) The composite was carbon-coated at 900°C using a CVD method, and the carbon-coated product was heat-treated at 1200°C for 20 hours to obtain a negative electrode material.

[0197] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), other parameters of the negative electrode material are shown in Table 1.

[0198] Comparative Example 3

[0199] A method for preparing a negative electrode material comprises the following steps:

[0200] (1) Take a mixture of silicon and silicon dioxide, place it in a reaction chamber, and evacuate it to a vacuum degree of less than 1*10 -4 Pa, heated to 1200℃, vaporized to form steam, condensed and collected solids crushed to D 50 =5μm composite.

[0201] (2) The composite was carbon-coated at 700°C by CVD method, and the carbon-coated product was heat-treated at 400°C for 24 hours to obtain a negative electrode material;

[0202] The negative electrode material of this embodiment includes an active material core and a carbon layer. The active material core includes Si, SiO x (0<x≤2), the parameters of the negative electrode material are shown in Table 1.

[0203] Comparative Example 4

[0204] The difference from Example 1 is that the carbon-coated product is heat-treated at 1400° C. for 8 hours.

[0205] The performance tests were performed on the negative electrode materials obtained in the examples and comparative examples. The results of the above performance tests are shown in Table 1:

[0206] Table 1. Summary of performance test results

[0207] The data in Table 1 show that by controlling the relationship between the mass ratio of crystalline silicon in the silicon element and the average size of silicon grains, significant improvements can be achieved in lithium-ion transfer impedance, solid-liquid interface stability, and long-term cyclic crystalline phase structural stability. Specifically, crystalline silicon is more structurally stable than amorphous materials, with less variation in dQ / dV peak intensity and position during cycling. However, crystalline silicon has a selective expansion direction, resulting in uneven expansion stress, which in turn causes anode particle fragmentation, exposing the silicon interface more, triggering side reactions with the electrolyte, causing the SEI film to grow and thicken, and deteriorating interfacial stability. The presence of silicon in the amorphous state (elemental or compound) stabilizes the overall structure of the anode particles and buffers expansion deformation, reducing particle fragmentation and improving interfacial stability. Furthermore, amorphous materials are isotropic, with no directional selectivity in lithium insertion, resulting in lower lithium-ion transfer impedance. In summary, by controlling the mass ratio of crystalline silicon and the average size of silicon grains, low lithium-ion transfer impedance, high solid-liquid interface stability, and strong long-term cyclic crystalline phase structural stability can be achieved in anode products, significantly improving the overall performance of the product.

[0208] The mass content of crystalline silicon in Example 7 is lower than that in Example 1. This is because the temperature of the carbonized coating product is relatively low and the time is too short during the heat treatment process. Therefore, a part of the silicon element does not form crystalline silicon, which causes a slight decrease in the cycle performance of the negative electrode material.

[0209] The negative electrode material prepared in Example 8 has a particle size deviation from D 20 -D 10 ≤4μm, D 90 -D 80 In the range of ≤8μm, the particle size distribution of the negative electrode material shifts toward larger particle sizes as a whole. Large-size particles are more fragile and more likely to break and deactivate during long cycles, affecting the electrochemical performance of the product. Therefore, the cycle performance of the negative electrode material decreases slightly.

[0210] During the preparation of the composite in Comparative Example 1, steam was not input into the plasma flow for plasma reaction. After the inducing effect of the seed crystal was lost, the mass content of crystalline silicon decreased significantly. As shown in Figure 3, compared with Example 1, although the first-cycle reversible capacity of the negative electrode material increased, its cycle performance decreased significantly, and the rate performance also decreased.

[0211] In Comparative Example 2, the heat treatment temperature is too high and the treatment time is too long, resulting in a significant increase in the mass content of crystalline silicon beyond the expected range. The size of the silicon particles will also increase, resulting in an imbalance in the ratio of amorphous silicon and crystalline silicon, which can easily lead to excessive local expansion stress in the negative electrode material, resulting in a decrease in the rate performance and cycle performance of the negative electrode material.

[0212] In Comparative Example 3, plasma was not used to manufacture seed crystals and the carbonization temperature was too low. After a long period of carbonization, the silicon grains were difficult to grow, causing the mass content of crystalline silicon to increase significantly beyond the expected range, causing A / B to exceed the required range, resulting in deterioration of product performance.

[0213] In Comparative Example 4, the carbonization temperature of the semi-finished product containing seed crystals was too high, resulting in rapid growth of silicon grains. Although the mass content of crystalline silicon did not exceed expectations, the product expansion stress was still out of control, leading to performance degradation.

[0214] Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the claims. Any person skilled in the art may make several possible changes and modifications without departing from the concept of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined by the claims of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material contains silicon, and the silicon is at least partially present in the form of crystalline silicon; Taking the mass content of silicon element in the negative electrode material as 100%, the mass content of crystalline silicon is A%, and the average size of silicon grains of the crystalline silicon is B nm; The negative electrode material meets the following characteristics: 0.3≤A / B≤60, and 6≤A+B≤75.

2. The negative electrode material according to claim 1, characterized in that The value range of A is 5 to 65.

3. The negative electrode material according to claim 1, characterized in that B≤7。 4. The negative electrode material according to claim 1, characterized in that Meet at least one of the following characteristics: (1) The negative electrode material further includes an oxygen element, and the atomic ratio of the oxygen element to the silicon element in the negative electrode material is x, 0<x<2.2; (2) The negative electrode material further includes oxygen, and the component containing the oxygen and silicon in the negative electrode material includes at least one of silicon oxide and silicate; (3) The negative electrode material further includes carbon element, and the component containing the carbon element in the negative electrode material includes at least one of amorphous carbon, graphite, graphene, carbon nanotubes and carbon fibers.

5. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a doped metal element, and the doped metal element is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr and Zn.

6. The negative electrode material according to claim 5, characterized in that The doped metal element includes Mg element, and the mass content of the Mg element in the negative electrode material is 3% to 25%; and / or, B≤15.

7. The negative electrode material according to claim 5, characterized in that The doped metal element comprises Li element, and the mass content of Li element in the negative electrode material is 3% to 15%; and / or, B≤10.

8. The negative electrode material according to claim 1, characterized in that Meet at least one of the following characteristics: (1) The mass content of oxygen in the negative electrode material is 10% to 55%; (2) The mass content of carbon in the negative electrode material is 1% to 40%; (3) The mass content of silicon in the negative electrode material is 25% to 88%.

9. The negative electrode material according to any one of claims 1 to 8, characterized in that At least a portion of the surface of the negative electrode material has a carbon layer.

10. The negative electrode material according to any one of claims 1 to 8, characterized in that Meet at least one of the following characteristics: (1) The specific surface area of ​​the negative electrode material is 0.1 m 2 / g~25m 2 / g; (2) The true density of the negative electrode material is 2.0 g / cm 3 ~3.4g / cm 3 .

11. The negative electrode material according to any one of claims 1 to 8, characterized in that The particle size of the negative electrode material satisfies: D 20 -D 10 ≤4μm, D 90 -D 80 ≤8μm.

12. The negative electrode material according to any one of claims 1 to 8, characterized in that Take 10 g of the negative electrode material, add 10 g of water, stir for 30 min, and measure the pH value using a pH meter calibrated with a standard solution. The pH value of the negative electrode material is 6-10.

13. A battery, characterized in that: The negative electrode material comprises the negative electrode material as claimed in any one of claims 1 to 12.

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