Negative electrode material and battery

Abstract

Provided in the present application are a negative electrode material and a battery. The negative electrode material comprises a silicon-based active substance and a carbon material located on at least part of the surface of the silicon-based active substance, and the silicon-based active substance comprises silicon, a silicon oxide and a metal M compound; the negative electrode material is subjected to a Lab color difference test, so as to obtain the brightness L, the red-green chromaticity a and the yellow-blue chromaticity b of the negative electrode material, wherein 15≤L≤35, -2≤a≤5, and -2≤b≤5; in an XRD pattern of the negative electrode material, the full width at half maximum of the strongest characteristic peak of the metal M compound in the negative electrode material is FWHM(M), and the full width at half maximum of the characteristic peak of a silicon (111) plane is FWHM(si), wherein 0.2<FWHM(M) / FWHM(si)<0.8. The negative electrode material provided in the present application can improve the initial Coulombic efficiency and cycle stability of the negative electrode material, and reduce the expansion efficiency of the negative electrode material.

Description

Anode materials and batteries

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411850203.X, filed on December 16, 2024, entitled “Anode Material and Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of negative electrode material technology, specifically to negative electrode materials and batteries. Background Technology

[0004] Electrified new energy vehicles represent the future direction 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, and adopting novel high-specific-capacity positive and negative electrode materials is one of the important methods to improve battery energy density.

[0005] More and more new materials such as metals, oxides, and metal alloys are being used as active materials in anode materials to continuously explore various ways to improve battery energy density. Taking silicon-based anode materials as an example, silicon-based anode materials, as one of the aforementioned active materials, are widely considered the next generation of anode materials. Their ultra-high theoretical specific capacity (4200 mAh / g) and low lithium depletion potential (<0.5V), along with silicon's slightly higher voltage plateau than graphite, making it less prone to surface lithium plating during charging and offering better safety performance, have made them highly praised. However, silicon anodes suffer from severe volume expansion during cycling, leading to material pulverization and breakage, and rapid battery degradation. As a high-specific-capacity anode material, silicon-oxygen materials have received considerable attention in recent years. Silicon-oxygen materials have a specific capacity exceeding 2000 mAh / g, but compared to graphite materials, they have lower initial coulombic efficiency, poorer cycle performance, and lower rate performance. Summary of the Invention

[0006] This application proposes a negative electrode material and a battery that can comprehensively improve the initial coulombic efficiency, cycle performance and rate performance of the negative electrode material.

[0007] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material comprising silicon, silicon oxide, and a metal M compound;

[0008] Lab color difference test was performed on the negative electrode material to obtain the brightness L, red-green hue a, and yellow-blue hue b of the negative electrode material, wherein 15≤L≤35, -2≤a≤5, and -2≤b≤5;

[0009] In the XRD pattern of the negative electrode material, the full width at half maximum (FWHM) of the strongest characteristic peak in the metal M compound of the negative electrode material is 0.5 WHM. (M) The full width at half maximum (FWHM) of the characteristic peaks on the silicon (111) surface is 1000 ppm. (Si) 0.2 < FWHM (M) / FWHM (Si) <0.8.

[0010] In a second aspect, this application provides a battery comprising the negative electrode material as described in the first aspect.

[0011] The technical solution of this application has at least the following beneficial effects:

[0012] The negative electrode material provided in this application includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. In this application, through color difference testing, the brightness L, red-green hue a, and yellow-blue hue b of the negative electrode material satisfy the following relationships: 15 ≤ L ≤ 35, -2 ≤ a ≤ 5, -2 ≤ b ≤ 5. Due to the color difference between the carbon material and silicon, silicon oxide, and metal M compounds, when the carbon material completely coats the silicon-based active material, the brightness L of the negative electrode material decreases; when there is too little carbon material on the surface of the silicon-based active material, the a and b values ​​of the negative electrode material are too high. This application controls the color difference parameters of the negative electrode material and coordinates with the control of FWHM (Fluorescent White-Green Mixture). (M) / FWHM (Si) A value in the range of 0.2 to 0.8 can adjust the mass content of the metal M compound, the silicon grain size, and the phase segregation, thereby enhancing the interfacial stability between the anode material and the electrolyte, improving the initial coulombic efficiency and specific capacity of the anode material, and reducing the expansion efficiency of the anode material. FWHM (M) / FWHM (Si) An excessively large value indicates a large silicon grain size, resulting in poor cycle rate performance of the anode material. (FWHM) (M) / FWHM (Si) If the value is too small, it indicates that the mass content of metal M compound in the negative electrode material is low. Since metal M compound is inert, under the synergistic effect of appropriate amount of metal M compound and carbon material, it can reduce the side reaction between silicon-based active material (especially silicon and silicon oxide) and electrolyte, reduce the consumption of active lithium ions, enhance the interfacial stability between negative electrode material and electrolyte, improve the first coulombic efficiency and specific capacity of negative electrode material, and reduce the expansion efficiency of negative electrode material. Attached Figure Description

[0013] Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application. Detailed Implementation

[0014] To better illustrate this application and facilitate understanding of its technical solutions, the following detailed description is provided. However, the following embodiments are merely simplified examples and do not represent or limit the scope of protection of this application. The scope of protection of this application is determined by the claims.

[0015] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0016] In a first aspect, this application provides a negative electrode material, which includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The silicon-based active material includes silicon, silicon oxide, and a metal M compound.

[0017] Lab color difference test was performed on the negative electrode material to obtain the brightness L, red-green hue a, and yellow-blue hue b of the negative electrode material, where 15≤L≤35, -2≤a≤5, and -2≤b≤5.

[0018] In the XRD pattern of the anode material, the full width at half maximum (FWHM) of the strongest characteristic peak in the metal M compound is _____. (M) The full width at half maximum (FWHM) of the characteristic peaks on the silicon (111) surface is 1000 ppm. (Si) 0.2 < FWHM (M) / FWHM (Si) <0.8.

[0019] The negative electrode material provided in this application includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. In this application, through color difference testing, the brightness L, red-green hue a, and yellow-blue hue b of the negative electrode material satisfy the following relationships: 15≤L≤35, -2≤a≤5, -2≤b≤5. Due to the color difference between the carbon material and silicon, silicon oxide, and metal M compounds, when the carbon material completely coats the silicon-based active material, the brightness L of the negative electrode material decreases; when there is too little carbon material on the surface of the silicon-based active material, the a and b values ​​of the negative electrode material are too high. This application controls the color difference parameters of the negative electrode material and coordinates with the control of FWHM (Fluorescent White-Green Mixture). (M) / FWHM (Si) A value in the range of 0.2 to 0.8 can adjust the mass content of the metal M compound, the silicon grain size, and the phase segregation, thereby enhancing the interfacial stability between the anode material and the electrolyte, improving the initial coulombic efficiency and specific capacity of the anode material, and reducing the expansion efficiency of the anode material. FWHM (M) / FWHM (Si)An excessively high value indicates high crystallinity and large grain size of silicon in the anode material, resulting in poor cycle rate performance. (FWHM) (M) / FWHM (Si) If the value is too small, it indicates that the mass content of metal M compound in the negative electrode material is low. Since metal M compound is inert, under the synergistic effect of appropriate amount of metal M compound and carbon material, it can reduce the side reaction between silicon-based active material (especially silicon and silicon oxide) and electrolyte, reduce the consumption of active lithium ions, enhance the interfacial stability between negative electrode material and electrolyte, improve the first coulombic efficiency and specific capacity of negative electrode material, and reduce the expansion efficiency of negative electrode material.

[0020] It should be noted that there is a significant color difference between silicon-based active materials and carbon materials. The color of metal M compound is bluish-green, silicon oxide is yellowish-brown, and carbon materials are black. When there is too much carbon material on the surface of the silicon-based active material, the brightness and red-green hue (a) and yellow-blue hue (b) measured by the color difference model are significantly affected by the carbon material. Conversely, when there is too little carbon material on the surface of the silicon-based active material, the red-green hue (a) and yellow-blue hue (b) measured by the color difference model are significantly affected by the silicon-based active material. Furthermore, the results of the color difference model are related to the state of the carbon material on the surface of the negative electrode material. Moreover, the type and physicochemical properties of the carbon material on the surface of the silicon-based active material also affect the color difference data. Specifically, carbon materials include those with sp... 2 Carbon atoms with hybrid orbitals and sp 3 Carbon atoms with hybrid orbitals, when sp orbitals are present in carbon materials 3 When the molar proportion of hybridized carbon atoms is relatively high and the carbon material is mainly composed of disordered carbon, the color of the carbon material tends to be grayish, and the overall brightness of the anode material will increase. When the carbon material contains sp... 3 When the molar proportion of hybrid carbon is small and the carbon material is mainly composed of disordered carbon, the carbon material tends to be black, and the brightness of the negative electrode material will decrease. Therefore, after silicon-based active materials are coated with carbon materials, the brightness of the negative electrode material will also change, and the red-green hue a and yellow-blue hue b will also change accordingly.

[0021] In some implementations, the negative electrode material I D / I G Within the range of 0.4 to 3.0, I D / I G Specifically, the values ​​can be 0.4, 0.43, 0.5, 0.72, 0.8, 1.0, 1.2, 1.22, 1.29, 1.39, 1.5, 1.55, 1.69, 2.0, 2.08, 2.3, 2.5, 2.8, 2.97, or 3.0, etc., or other values ​​within the above range; no limitation is imposed here. Where I... D with I G They can represent having sp respectively3 Carbon atoms with hybrid orbitals and sp 2 The number of carbon atoms in the hybrid orbitals. When sp in the anode material 2 When the molar percentage of hybridized carbon atoms is relatively high, I D / I G The ratio is also relatively small. Conversely, when the sp in the negative electrode material is larger... 3 When the molar percentage of hybridized carbon atoms is relatively high, I D / I G The ratio increases. In this application, the I of the negative electrode material is controlled. D / I G Controlling the ratio within the above range is beneficial for regulating the sp ratio in the anode material. 3 The molar content of hybrid carbon atoms is beneficial for controlling the brightness L, red-green hue a, and yellow-blue hue b of the negative electrode material within a reasonable range.

[0022] In some embodiments, the negative electrode material is subjected to Lab color difference testing, and the brightness L of the negative electrode material is 15 ≤ L ≤ 35. Specifically, L can be 15, 15.21, 18, 20, 25, 28, 29.01, 29.23, 28.77, 30.65, 31.19, 32.59, 30.45, 34.87, or 35, etc., and of course, other values ​​within the above range are not limited here. The brightness L of the negative electrode material mainly depends on the uniformity of the carbon material distribution on the surface of the silicon-based active material; preferably, 23.5 ≤ L ≤ 35.

[0023] In some implementations, Lab color difference tests are performed on the negative electrode material. The red-green hue (a) and yellow-blue hue (b) of the negative electrode material are -2≤a≤5 and -2≤b≤5, respectively. a and b can specifically be -2, -1.97, -1.92, -1.5, -1.2, -1.0, -1.02, -0.5, -0.32, -0.11, -0.1, -0.2, 0.03, 0.05, 0.1, 0.15, 0.18, 0.2, 0.27, 0.42, 0.5, 0.72, 0.87, 0.95, 1, 1.02, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 4.93, 4.95, or 5, etc., and can also be other values ​​within the above ranges, which are not limited here. The red-green hue (a) and yellow-blue hue (b) of the negative electrode material mainly depend on the exposure degree of the silicon-based active material. As the exposed area decreases, the red-green hue (a) and yellow-blue hue (b) will also decrease. Preferably, -0.5 ≤ a ≤ 1.5 and -0.5 ≤ b ≤ 1.5.

[0024] In some embodiments, the silicon oxide comprises silicon and oxygen elements, and the atomic ratio of silicon to oxygen is 0 to 2, excluding 0. The atomic ratio of silicon to oxygen may specifically be 0.05, 0.11, 0.21, 0.26, 0.31, 0.41, 0.51, 0.59, 0.61, 0.69, 0.71, 0.74, 0.76, 0.79, 0.89, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc., which are not limited herein. Preferably, the atomic ratio of silicon to oxygen is 0 to 1, excluding 0.

[0025] In some embodiments, the chemical general formula of the silicon oxide is SiO x , where 0 < x ≤ 2. x may specifically be 0.05, 0.11, 0.21, 0.26, 0.31, 0.41, 0.51, 0.59, 0.61, 0.69, 0.71, 0.74, 0.76, 0.79, 0.89, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc., which are not limited herein. Preferably, 0 < x < 1. The silicon oxide may be a material formed by silicon particles dispersed in SiO2; or a material having a tetrahedral structural unit, with silicon atoms located at the center of the tetrahedral structural unit and oxygen atoms and / or silicon atoms located at the four vertices of the tetrahedral structural unit.

[0026] In some embodiments, the compound of metal M comprises at least one of metal silicide and metal silicate.

[0027] In some embodiments, metal M comprises at least one of Li, Mg, Al, Ti, and Cu.

[0028] In some embodiments, the metal silicate comprises at least one of lithium silicate, magnesium silicate, aluminum silicate, lithium magnesium silicate, lithium aluminum silicate, and lithium aluminum titanium silicate.

[0029] In some embodiments, FWHM (M) / FWHM (Si) may specifically be 0.21, 0.22, 0.221, 0.25, 0.28, 0.3, 0.394, 0.4, 0.411, 0.421, 0.423, 0.459, 0.479, 0.5, 0.6, 0.7, 0.789, 0.79, etc. Of course, it may also be other values within the above range, which are not limited herein. When the ratio of FWHM (M) / FWHM (Si) is too large, the crystallinity of silicon单质 in the negative electrode material is relatively high, the silicon grain size is relatively large, and the cycling performance of the negative electrode material is poor. When FWHM (M) / FWHM (Si) When the ratio is too small, the metal M compound in the negative electrode material decreases, the mass ratio of silicon and silicon oxide increases, the side reactions between the negative electrode material and the electrolyte intensify, gas production during charging and discharging intensifies, and the battery's initial efficiency and cycle stability decrease.

[0030] In some embodiments, the full width at half maximum (FWHM) of the strongest characteristic peak in the metal M compound in the anode material's XRD pattern is 1000 M / s. (M) FWHM (M) >0.2. Specifically, FWHM (M) Specifically, values ​​can be 0.209, 0.21, 0.25, 0.3, 0.4, 0.418, 0.5, 0.518, 0.599, 0.6, 0.617, 0.653, 0.644, 0.7, 0.829, etc., and are not limited here. FWHM (M) If the mass content of the metal M compound is too low, it indicates that the metal M compound in the negative electrode material is low. Since the metal M compound is inert, if the mass of the metal M compound is too low, the side reactions between the negative electrode material and the electrolyte will be aggravated, the interfacial stability between the negative electrode material and the electrolyte will be worse, which is not conducive to improving the first coulombic efficiency and specific capacity of the negative electrode material.

[0031] In some embodiments, the full width at half maximum (FWHM) of the characteristic peaks of the silicon (111) surface in the XRD pattern of the anode material is 1000 m / s. (Si) FWHM (Si) >0.2. Specifically, FWHM (Si) Specifically, values ​​can be 0.26, 0.265, 0.3, 0.5, 0.8, 1.0, 1.2, 1.225, 1.4, 1.421, 1.5, 1.530, 1.519, 1.530, 1.6, 1.602, 1.7, 1.732, 1.892, etc., and are not limited here. FWHM (Si) If the silicon crystals are too small, the silicon grains will be too large, resulting in severe phase segregation and a decrease in the rate capability and cycle efficiency of the anode material.

[0032] In some embodiments, the mass content of the metallic element M in the negative electrode material is m. M wt%, 2.0≤m M The specific mass content of metallic M in the anode material can be 2wt%, 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 13wt%, 14wt%, or 15wt%, or other values ​​within the above range, and is not limited here. When the mass content of metallic M in the anode material is controlled within the above range, it is beneficial to improve the initial coulombic efficiency and cycle stability of the anode material.

[0033] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon. Preferably, the carbon material includes amorphous carbon, which can be soft carbon or hard carbon, and the graphitized carbon can be diamond-like carbon, high-temperature carbides, etc. Combining amorphous carbon with silicon-based active materials can comprehensively improve the conductivity of the negative electrode material and reduce expansion.

[0034] In some embodiments, the mass content of carbon in the negative electrode material is m. C %, 2≤m C ≤15, the specific mass content of carbon element can be 2%, 5%, 6%, 8%, 10%, 12%, 13%, 14% or 15%, etc., and of course it can also be other values ​​within the above range, which are not limited here.

[0035] In some embodiments, the mass percentage of water in the negative electrode material is m. 水 %, 0.01≤m 水 ≤0.1; m 水 Specifically, it can be 0.01%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1%, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0036] In some embodiments, at least a portion of the carbon material on the surface of the silicon-based active material forms a carbon layer. The carbon material can be located on the surface of the silicon-based active material, or it can be formed by secondary granulation and coating of the silicon-based active material and carbon material particles to form secondary particles; this is not limited. The presence of the carbon layer can reduce side reactions between the negative electrode material and the electrolyte, reduce the consumption of active lithium ions, improve the initial efficiency and low-temperature performance of the negative electrode material, and reduce the expansion rate of the negative electrode material.

[0037] In some embodiments, the thickness of the carbon layer is 50 nm to 1000 nm, specifically 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 400 nm, 500 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc., and is not limited herein. If the carbon layer is too thick, the carbon content is too high, which is not conducive to obtaining a negative electrode material with high specific capacity; if the carbon layer is too thin, it is not conducive to increasing the conductivity of the negative electrode material and has weak performance in suppressing volume expansion, resulting in poor long-cycle performance. Preferably, the thickness of the carbon layer is 50 nm to 800 nm; more preferably, the thickness of the carbon layer is 100 nm to 500 nm.

[0038] In some embodiments, the negative electrode material is tested by X-ray photoelectron spectroscopy, and the surface of the negative electrode material has at least one oxygen-containing group selected from CO, C=O, and COO-. In this application, because the surface of the negative electrode material has oxygen-containing groups, these groups can enhance the binding ability of the negative electrode material with the polar solvent in the electrolyte, which is beneficial to improving the lithium ion transport efficiency. Combined with a non-polar carbon layer, this facilitates the rapid wetting of the negative electrode material with solvated lithium ions in the electrolyte, further improving the lithium ion transport efficiency.

[0039] In some embodiments, the negative electrode material is tested by infrared spectroscopy, revealing that the surface of the negative electrode material has at least one functional group selected from OH and CH. In this application, the presence of these functional groups creates a polarity difference on the surface of the negative electrode material, thereby enabling the adjustment of the deposition state after electrolyte degradation and enhancing the interfacial stability between the negative electrode material and the electrolyte.

[0040] In some embodiments, the median particle size D of the negative electrode material 50 The value is 4μm to 9μm, specifically 4μm, 5μm, 5.5μm, 6μm, 7μm, 8μm, 8.5μm or 9μm, etc., and is not limited here.

[0041] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~3.0m 2 / g; specifically, it can be 0.5m 2 / g, 0.6m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 2.8m 2 / g or 3.0m 2 / g, but not limited to the listed values; other unlisted values ​​within this range also apply. Controlling the specific surface area of ​​the anode material within the above range is beneficial for improving its initial coulombic efficiency. When the specific surface area of ​​the anode material is too large, side reactions between the anode material and the electrolyte increase, consuming more active lithium ions and reducing the initial coulombic efficiency of the anode material.

[0042] In some embodiments, the tap density of the negative electrode material is 0.75 g / cm³. 3 ~2.00g / cm 3 The tap density of the negative electrode material can specifically be 0.75 g / cm³. 3 0.85g / cm 3 0.9g / cm 31.0g / cm 3 1.2g / cm 3 1.4g / cm 3 1.3g / cm 3 1.5g / cm 3 1.6g / cm 3 1.8g / cm 3 Or 2.0g / cm 3 etc. are not specified here.

[0043] In some embodiments, the powder conductivity of the negative electrode material under 20 kN pressure is 0.2 S / cm to 15.0 S / cm, specifically 0.2 S / cm, 0.5 S / cm, 1 S / cm, 2 S / cm, 3 S / cm, 5 S / cm, 6 S / cm, 7 S / cm, 8 S / cm, 10 S / cm, or 15 S / cm, etc., or other values ​​within the above range, which are not limited here. Good powder conductivity of the negative electrode material is beneficial to improving its cycle performance. When the powder conductivity of the negative electrode material is too low, the structure of the negative electrode material is more porous or the conductive network is worse, resulting in decreased cycle stability.

[0044] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps:

[0045] S10, a mixture of silicon-oxygen raw materials and dopant is subjected to a solid-state pre-reaction. The temperature of the solid-state pre-reaction is increased in a stepwise manner, and the dopant by-product gas is released by exhausting the gas to obtain the pre-reaction product. The stepwise heating process includes a first heating stage, a holding stage, and a second heating stage. The heating rate of the first heating stage is 1℃ / min to 3℃ / min, and the heating time is 4 hours to 12 hours. The temperature of the holding stage is 300℃ to 400℃, and the holding time is 3 hours to 6 hours. The temperature of the second heating stage is 700℃ to 1200℃, and the heating time is 1 hour to 2 hours.

[0046] S20, the pre-reaction product is subjected to high temperature and high pressure heat treatment to obtain the precursor; wherein the heat treatment pressure is 100-200MPa, the heat treatment temperature is 800-1200℃, and the heat treatment time is 6-18 hours.

[0047] S30, the precursor is placed in a surface impregnation solution containing an organic carbon source and thoroughly mixed, so that the organic carbon source is adsorbed on the surface of the precursor, and the solid-liquid separation yields the complex.

[0048] S40 involves coating the composite with a liquid-phase coating solution containing a benzene ring carbon source, thereby carbonizing the organic carbon source and the benzene ring carbon source, and then drying to obtain the negative electrode material.

[0049] In this application, a mixture of silicon-oxygen raw material and dopant is first subjected to solid-phase pre-reaction. The temperature of the solid-phase pre-reaction is increased by a stepped heating process. In the early stage of the stepped heating process, the dopant can be adsorbed on the surface of the silicon source material. As the solid-phase pre-reaction temperature increases, the doping depth also gradually increases, which can improve the dispersion uniformity of the dopant. The pre-reaction product is then subjected to high-temperature and high-pressure heat treatment. This high-pressure and high-temperature reaction allows for full contact between the dopants and the silicon-oxygen raw materials, enhancing the depth of the solid-phase reaction. The high-pressure and high-temperature reaction also modifies the precursor surface, eliminating weak nanostructures and reducing surface porosity to create a highly dense surface. The precursor is then mixed in a surface impregnation solution, allowing the organic carbon source in the solution to adsorb onto the precursor surface and modify surface defects. Finally, the composite is coated with a liquid-phase coating solution containing a benzene ring carbon source. Adsorption of the benzene ring carbon source effectively reduces surface defects, ensuring the integrity of the anode material surface. Furthermore, the benzene ring carbon source is well embedded in the graphitized carbon layer formed after carbonization, improving the optical reflectivity and conductivity of the anode material. The anode material prepared by this method exhibits excellent initial coulombic efficiency, cycle performance, and safety. By coating the composite with a liquid-phase coating solution containing a benzene ring carbon source, the resulting carbon layer can adjust the sp content of the carbon material. 3 The molar content of carbon atoms is adjusted to modify the physicochemical properties of the carbon layer, so that the changes in the carbon layer composition and the changes in the core crystal form are coordinated. This ensures the conductivity and structural stability of the anode material while improving the coulombic efficiency and cycle performance of the anode material.

[0050] Before step S10, the method further includes selecting a silicon-oxygen raw material with a suitable particle size, wherein the median particle size of the silicon-oxygen raw material is 4μm to 9μm.

[0051] In some embodiments, the mass ratio of dopant to silicon oxide raw material is (2-15):100, specifically 2:100, 2.5:100, 5:100, 7.5:100, 10:100, 12.5:100, or 15:100, etc., or other values ​​within the above range, which are not limited here. Insufficient doping with metal leads to too few metal compounds in the negative electrode material, increasing the alkalinity of the negative electrode material, intensifying gas generation during charge and discharge, and reducing the battery's initial efficiency and cycle stability. Excessive doping with metal increases the number of inert metal compounds in the negative electrode material, reducing its capacity. Furthermore, the defects and porosity caused by metal M during the reduction of silicon oxide also increase, significantly increasing the contact reaction sites between the negative electrode material and the electrolyte, intensifying side reactions, and reducing the initial coulombic efficiency of the negative electrode material.

[0052] In some embodiments, the mixing of the dopant and the silicon-oxygen raw material is carried out in a protective atmosphere. Specifically, atmospheric pressure stirring can be used, with the stirring rate controlled at 500 r / min to 1000 r / min and the stirring time at 30 min to 180 min.

[0053] In some embodiments, the stirring rate can be 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min or 1000 r / min, or other values ​​within the above range, which are not limited here.

[0054] In some embodiments, the stirring time is 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 120 min, 150 min, 160 min or 180 min, etc. Of course, other values ​​within the above range are also possible, and no limitation is made here.

[0055] Understandably, thorough stirring provides a basic reaction interface for the various components in the mixture, enabling uniform doping of the dopant between silicon-oxygen raw material particles and improving the uniformity of the mixture.

[0056] S10 involves a solid-state pre-reaction of a mixture of silicon-oxygen raw materials and dopants, with the temperature of the solid-state pre-reaction being increased in a stepped manner to obtain the pre-reaction product.

[0057] In some embodiments, the silicon-oxygen raw materials include Si and SiO. y Mixtures of SiO2 and SiO y At least one of the following: a mixture of Si and SiO2, wherein 0 < y < 2.

[0058] In some embodiments, the silicon-oxygen raw material may also include carbon materials, i.e., a composite of silicon-oxygen raw material and carbon materials.

[0059] In some embodiments, the stepped heating process includes a first heating stage, a holding stage, and a second heating stage, wherein the heating rate of the first heating stage is 1℃ / min to 3℃ / min, which is a slow heating state.

[0060] In some specific implementations, the first heating stage can be, for example, 100℃-150℃-200℃-250℃, with each stage maintaining the temperature for 1 hour to 3 hours.

[0061] In some embodiments, the temperature during the heat preservation stage is 300°C to 400°C, and the heat preservation time is 3 to 6 hours. During the heat preservation stage, the various components of the mixture undergo sufficient solid-phase pre-reaction.

[0062] In some implementations, the temperature during the heat preservation stage can be 300℃, 310℃, 320℃, 350℃, 360℃, 380℃, or 400℃, and the heat preservation time can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 6 hours, etc., without limitation.

[0063] In some implementations, the solid-phase pre-reaction is carried out under an inert gas atmosphere.

[0064] In some embodiments, the solid-phase pre-reaction is carried out under stirring conditions, with a stirring rate of 1000 to 2000 r / min. Specifically, the stirring rate can be 1000 r / min, 1200 r / min, 1500 r / min, 1800 r / min or 2000 r / min, or other values ​​within the above range, which are not limited here.

[0065] In some embodiments, during the second heating stage, the mixture is stopped from stirring and heated to between 700°C and 1200°C. After the temperature stabilizes, it is kept at that temperature for 1 to 2 hours, and the dopant gas is released by venting.

[0066] In some embodiments, the heating temperature of the second heating stage can be 700℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃ or 1200℃, etc., and the holding time can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours, etc., which are not limited here.

[0067] In this application, the mixture undergoes a solid-phase pre-reaction at a relatively low temperature, allowing the two solid phases to further disperse. At this stage, the solid-phase pre-reaction depth is shallow, and sufficient pre-reaction enables the dopant to further disperse between the silicon-oxygen raw material particles. Through chemical adsorption onto the surface of the pre-reactant, it prevents excessive reaction in individual silicon-oxygen material particles, leading to excessively high doped metal content and improving the uniformity of doped metal dispersion. Furthermore, in the second heating stage, some excess dopant can be vaporized and released as dopant gas, preventing the generation of bubbles during subsequent reactions that could create internal pores in the negative electrode material particles, thus improving the density of the negative electrode material.

[0068] S20, the pre-reaction product is subjected to high temperature and high pressure heat treatment to obtain the precursor.

[0069] In some embodiments, the heat treatment pressure is 100MPa to 200MPa, specifically 100MPa, 120MPa, 140MPa, 150MPa, 160MPa, 180MPa, 190MPa or 200MPa, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0070] In some embodiments, the heat treatment temperature is 800℃ to 1200℃, specifically 800℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0071] In some implementations, the heat treatment duration is 6h to 18h, specifically 6h, 8h, 10h, 12h, 15h, 16h or 18h, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0072] Through high-pressure, high-temperature reaction, the solid-phase reaction allows for full contact and reaction between the silicon-oxygen raw materials and dopants, accelerating the reaction of various elements during the solid-phase reaction process, increasing the depth of the solid-phase reaction, and thus enabling the solid-phase raw materials to fully fuse and form a uniformly reacted powder. Furthermore, the high-pressure, high-temperature reaction can modify the surface of the precursor, eliminating some weak nanostructures on the precursor surface, reducing surface porosity, and forming a highly dense surface. This highly dense surface helps to form a stable SEI, which is beneficial for controlling the wetting rate of the electrolyte slurry on the negative electrode material, reducing side reactions, lowering electrolyte consumption during cycling, and improving cycle stability. This uniform silicon-based active material core formed after high-pressure treatment allows the negative electrode material to achieve uniform expansion during charge and discharge, which is beneficial for dispersing expansion stress, significantly reducing negative electrode sheet expansion, and improving the initial coulombic efficiency, cycle performance, and safety of the negative electrode material.

[0073] In some embodiments, the method further includes crushing and classifying the precursor to reduce precursor agglomeration while controlling the precursor within an optimized particle size range.

[0074] S30, the precursor is placed in a surface impregnation solution and thoroughly mixed, and the solid-liquid separation is performed to obtain the complex.

[0075] In some embodiments, the liquid phase asphalt is dissolved in anhydrous ethanol under stirring to prepare a surface impregnation solution, and the surface impregnation solution is filtered to remove impurities.

[0076] In some embodiments, the mass ratio of liquid asphalt to anhydrous ethanol is (1-10):(90-99), specifically 1:99, 2:98, 4:96, 5:95, 6:94, 8:92, 9:91 or 10:90, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0077] In some embodiments, the dispersed precursor is placed in a surface impregnation liquid, and the mass ratio of the precursor to the surface impregnation liquid is 1:(0.8 to 1.5), specifically 1:0.8, 1:1.0, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0078] In some embodiments, the mixing of the precursor and the surface impregnation solution is carried out under stirring conditions, with a stirring rate of 2500 r / min to 3500 r / min and a stirring time of 30 min to 90 min. Specifically, the stirring rate is 2500 r / min, 2600 r / min, 2800 r / min, 3000 r / min, 3200 r / min, or 3500 r / min, etc., and the stirring time is 30 min, 45 min, 60 min, 75 min, 90 min, etc. Of course, other values ​​within the above ranges are also possible and are not limited here.

[0079] In some embodiments, the thoroughly mixed product is sealed and allowed to stand for 6 to 24 hours, specifically 6, 7, 9, 12, 16, or 24 hours, etc., without limitation. After the material has completely settled and separated into layers, filtration is performed to achieve solid-liquid separation and remove the solvent.

[0080] In some implementations, solvent removal may include drying.

[0081] In some embodiments, a vacuum oven can be used to dry the solvent at a drying temperature of 50°C to 90°C and a drying time of 12 hours to 240 hours. Specifically, the drying temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, or 90°C, and the drying time can be 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours, or other values ​​within the above ranges are also possible and are not limited here.

[0082] In this application, by mixing the precursor with the surface impregnation liquid, the organic carbon source in the surface impregnation liquid can be adsorbed onto the surface of the precursor, especially the surface of the precursor with small defects caused during the crushing process. This can further improve and supplement the surface of the precursor, modify the surface defects of the precursor, and thus help reduce the side reactions between the negative electrode material and the electrolyte.

[0083] S40 involves coating the composite with a liquid-phase coating solution containing a benzene ring carbon source, thereby carbonizing the organic carbon source and the benzene ring carbon source, and then drying to obtain the negative electrode material.

[0084] In some embodiments, the composite is surface-coated with carbon and then surface-modified using plasma-enhanced chemical vapor deposition (PVDC). PVDC can improve the carbon source dissociation efficiency, thereby enabling a wider range of preferred deposition temperatures.

[0085] In some embodiments, the benzene ring-containing carbon source includes at least one of benzene, toluene, ethylbenzene, xylene, and phenol.

[0086] In some embodiments, the liquid coating liquid includes a benzene ring-containing carbon source and a volatile solution, wherein the benzene ring-containing carbon source is carried away by evaporation through the volatile solution, which includes at least one of ethanol, acetone and butanol.

[0087] In some embodiments, the mass ratio of the benzene ring carbon source to the volatile solution in the liquid phase coating solution is 1:(1-2), specifically 1:1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2, etc., or other values ​​within the above range, which are not limited here.

[0088] In some embodiments, the pressure during plasma-enhanced chemical vapor deposition is controlled between 1000 Pa and 5000 Pa, specifically 1000 Pa, 1500 Pa, 2000 Pa, 2500 Pa, 3000 Pa, 3500 Pa, 4000 Pa, 4500 Pa, or 5000 Pa, etc., or other values ​​within the above range, which are not limited here.

[0089] In some embodiments, the deposition temperature during plasma-enhanced chemical vapor deposition is 400°C to 600°C, specifically 400°C, 450°C, 480°C, 500°C, 550°C, 580°C, or 600°C, etc., or other values ​​within the above range, which are not limited here.

[0090] In some embodiments, the deposition time during plasma-enhanced chemical vapor deposition is 1.0h to 3.0h, specifically 1.0h, 1.5h, 2.0h, 2.5h, 2.8h or 3.0h, etc., or other values ​​within the above range, which are not limited here.

[0091] In some embodiments, the composite is preheated before plasma-enhanced chemical vapor deposition, with the heating temperature controlled between 65°C and 85°C. Specifically, it can be 65°C, 70°C, 75°C, 80°C, or 85°C, or other values ​​within the above range, which are not limited here.

[0092] In some embodiments, the carbonization temperature of the organic carbon source and the carbon source containing benzene rings is controlled at 600-1100°C, and the carbonization time is controlled at 2-10 hours. The specific carbonization temperature can be 600°C, 650°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, etc., or other values ​​within the above range; the carbonization time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, or any range of two values.

[0093] In the above scheme, after the composite surface defects adsorb the benzene ring-containing carbon source, they are carbonized at high temperature. During the carbonization process, the benzene ring-containing carbon source shrinks and releases oxygen sources such as carbon dioxide. Although the defects are difficult to completely fill, the surface defects can be effectively reduced by supplementing the deposition with a trace amount of gas phase carbon source, ensuring the integrity of the negative electrode material surface. Furthermore, the benzene ring-containing carbon source can be well embedded in the graphitized carbon material formed after carbonization, improving the optical reflectivity of the negative electrode material surface and enhancing the conductivity of the negative electrode material.

[0094] This invention also provides a battery. Figure 1 is a schematic diagram of the discharge state of the battery provided in this embodiment. As shown in Figure 1, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0095] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0096] In some embodiments, the positive current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0097] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0098] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0099] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0100] In some embodiments, the negative electrode current collector 201 may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or 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 polymer substrate.

[0101] In some embodiments, the negative electrode active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the above preparation method.

[0102] The battery provided in this application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid-state electrolyte battery, etc., and is not limited thereto.

[0103] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0104] Test method:

[0105] 1) Particle size of the negative electrode material:

[0106] The particle size testing method refers to GB / T 19077-2016. The cumulative particle size distribution based on volume is determined by laser diffraction. D10 represents the particle size corresponding to 10% of the cumulative particle size distribution, D50 represents the particle size corresponding to 50% of the cumulative particle size distribution, and D90 represents the particle size corresponding to 90% of the cumulative particle size distribution.

[0107] 2) Test method for specific surface area of ​​negative electrode material:

[0108] The specific surface area of ​​the negative electrode material was determined using the gas adsorption BET method. A TriStar 3020 specific surface area and pore size analyzer (USA) was used to test the specific surface area of ​​the powder sample. The static volumetric method was performed according to GB / T 19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method". First, a specific surface area tube, dried at high temperature, was weighed (M1). A certain amount of sample (1 / 2 to 2 / 3 of the tube volume) was added and degassed at 300℃ for 1 hour. After cooling, the tube weight (M2) was measured; the sample mass is M2-M1. The sample mass was entered into the computer, and the instrument was used for testing. The instrument automatically completed the test, read the data, and recorded the results. It is important to note that after heating the sample to 300℃ and purging with nitrogen for 1 hour, it was cooled to room temperature, and N2 purging was still required during the cooling process.

[0109] 3) Test method for the mass content of carbon in negative electrode materials:

[0110] Equipment Information: Infrared carbon-sulfur analyzer, Model: Bruker G4 ICARUS HF (Germany). Test Procedure: Accurately weigh 0.05-0.1g of sample using a 0.001g balance and spread it evenly in a ceramic crucible. Then add 1.5g of a multi-component flux (1.0g tungsten + 0.3g tin dioxide + 0.2g pure iron). Place the crucible under oxygen-enriched conditions for high-frequency heating. The carbon in the sample is completely oxidized to carbon dioxide gas. After purification, the carbon dioxide is introduced into the carbon detection cell. CO2 exhibits the strongest absorption signal for infrared radiation at 4.26μm, which is converted into an electrical signal by the detector. The results are then processed by a computer and output.

[0111] 4) Test method for the mass content of oxygen in negative electrode materials:

[0112] 10mg to 13mg of negative electrode material was weighed and wrapped in nickel foil, and then sent into the graphite crucible of the ONH elemental analyzer (ONH-2000) for testing to obtain the total mass content of oxygen and nitrogen elements in the negative electrode material.

[0113] 5) Test method for the mass content of metallic M element in negative electrode materials:

[0114] Using ICP (Inductively Coupled Plasma Optical Emission Spectrometry), referring to GB / T 24533-2019, 0.10 g of the negative electrode material was placed in a clean platinum crucible and then calcined at 750 °C for 2 h in an air atmosphere muffle furnace to remove carbon. The cooled residue was then reacted thoroughly with a mixture of 4 mL nitric acid (65% HNO3 by mass) and 6 mL hydrofluoric acid (45% HF by mass). The platinum crucible containing this solution was then placed on a 350 °C hot plate until the solvent was completely evaporated. After the crucible cooled, 6 mL of concentrated hydrochloric acid (36% HCl by mass) was added, and the mixture was heated until the residue was completely dissolved. The solution was then diluted to a 100 mL plastic volumetric flask. Finally, the mass content of doped elements Li, Mg, Al, P, S, and B in the negative electrode material was determined by ICP (Inductively Coupled Plasma Optical Emission Spectrometry, Agilent 5800V DVICP-OES).

[0115] 6) Test method for the mass content of silicon in anode materials:

[0116] Based on the measured mass content m of carbon in the negative electrode material C Mass content of oxygen element m O and the mass content m of element M M The mass content of silicon element, m, was calculated. Si =1-m C -m O -m M -m 水 .

[0117] 7) Lab color difference test method for negative electrode materials:

[0118] The color difference test was performed using a Konica Minolta CM-5 colorimeter in reflective mode, including specular reflection. This measurement method includes the reflection of light from all surfaces of the object, regardless of the surface structure or roughness, and the results reflect the true color of the object.

[0119] 8) Powder conductivity test of negative electrode material

[0120] The powder conductivity of the material was tested according to the equipment and methods specified in BTRTC / ZY / 02-093 "Operating Instructions for Powder Conductivity Testing". The volume resistivity of the sample was determined using the four-probe method. The testing equipment was from Mitsubishi Chemical, Japan, model MCP-PD51, and was a powder conductivity meter.

[0121] Test parameters: Initial resistance in the order of -3, voltage limit 10V, sample thickness 3-5mm under 20kN pressure, pressures set at 4, 8, 12, 16, and 20kN. Electrode radius 0.7mm, sample radius 10mm; maintain pressure at each point for 3s, measure the conductivity of the powder at the five pressure points of 4, 8, 12, 16, and 20kN, and then the computer automatically calculates the resistivity of the powder. The specific testing method is as follows: The sample to be tested is placed in a circular mold cavity. Four equally spaced probes, numbered 1, 2, 3, and 4, are fixed on a ceramic disc at the bottom center of the mold cavity. In the mold cavity filled with the sample, pressure is applied to the sample using a cylindrical top post with the same diameter as the mold cavity and equipped with ceramic probes. This causes the four probe electrodes on the ceramic disc at the bottom of the sample in the mold cavity to come into close contact and be gradually pressed together. A current I passes between probes numbered 1 and 4, and a potential difference V is generated between probes numbered 2 and 3. By using the dynamic four-probe method to test the resistance of the circular block material under different pressures, the resistivity and conductivity of the powder sample under different pressures can be accurately calculated. At the same time, the relationship curve between pressure and conductivity can be obtained.

[0122] 9) XRD testing of negative electrode materials:

[0123] The negative electrode material was fabricated into a sheet and tested using an X-ray diffraction analyzer (manufacturer: Panaco, model X'pert PRO). Angle range: 10–90°, scanning mode: step scan, slit width: 1.0, voltage: 40kW, current: 40mA. The measured data were analyzed using Jade 6.5 software to obtain the full width at half maximum (FWHM) of each characteristic peak.

[0124] 10) Raman data testing

[0125] Raman spectroscopy of the anode material was performed using an XPLORA laser confocal Raman spectrometer. Samples were prepared according to the equipment's standard procedures. Ten points at different locations were tested on each sample to obtain the average intensity of the characteristic D and G peaks of the anode material, thus obtaining the Ig. D / I G ratio.

[0126] 11) Test method for tap density of negative electrode material:

[0127] Referring to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders", the tap density was measured using a Canta DAT-4-220 tap density analyzer manufactured by Anton Paar (Shanghai) Trading Co., Ltd. The tap density T is the value after 3000 vibrations, and the unit is g / cm³. 3 .

[0128] 12) Test method for carbon layer thickness:

[0129] The material was cross-sectioned using FIB-SEM (Focused Ion Beam Scanning Electron Microscopy). Ten particles were randomly selected, and the carbon layer thickness of each particle was measured three times to calculate the carbon layer thickness.

[0130] 13) Test method for water content in negative electrode materials

[0131] The moisture content was determined according to GB / T 6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method (General Method)" using a Mettler Toledo coulometric moisture analyzer (C30S-Inmotion KF). A certain amount of sample was placed in a dedicated dry glass bottle. The sample was heated in the sample inlet of the coulometric moisture analyzer to evaporate the moisture into water vapor, which was then transferred to the titration cup of the moisture analyzer by a drying carrier gas. The water vapor reacted with Karl Fischer reagent until the titration endpoint, and the moisture content was determined by the amount of Karl Fischer reagent consumed.

[0132] 14) Button cell battery test

[0133] The prepared negative electrode material, conductive carbon black, and polyacrylic acid binder were dissolved in a solvent at a mass ratio of 75:15:10 and mixed. The mixture was then coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the cells were assembled into a coin cell in an argon-filled glove box. Charge-discharge tests were conducted at a current density of 0.1C, within a charge-discharge range of 0.01-1.5V.

[0134] Anode material capacity test: Using a coin cell battery charge and discharge device, charge at 0.1C constant current to 10mV, then switch to 0.02C constant current charge to 5mV, and discharge at 0.1C constant current to 1.5V cutoff.

[0135] 50-week cycle test: Using a coin cell battery charge / discharge device, week 1: discharge at 0.1C to 0.01V, then gradually decrease at 0.01C to 0.01V, then discharge at 0.01C to 0.005V, then charge at 0.1C to 1.5V; week 2: discharge at 0.2C to 0.01V, then gradually decrease at 0.02C to 0.01V, then discharge at 0.02C to 0.005V, then charge at 0.2C to 1.5V; week 3: discharge at 0.5C to 0.01V. V, discharge at 0.05C decreasing rate to 0.01V, discharge at 0.05C to 0.005V, charge at 0.5C to 1.5V; from week 4 to week 50, discharge at 1C to 0.01V, discharge at 0.1C decreasing rate to 0.01V, discharge at 0.1C to 0.005V, charge at 1C to 1.5V; in week 51, discharge at 0.1C to 0.01V, discharge at 0.01C decreasing rate to 0.01V, discharge at 0.01C to 0.005V.

[0136] 15) Electrochemical performance testing

[0137] The prepared negative electrode material was mixed with graphite in a specific ratio to achieve a standard capacity of 450 mAh / g. Then, it was mixed with sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder, Super-P conductive agent, and KS-6 conductive agent in a mass ratio of 92:2:2:2 to form a slurry. This slurry was coated onto copper foil and then vacuum-dried and rolled to prepare the negative electrode sheet. Next, a ternary positive electrode sheet prepared using conventional mature processes, a 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing were assembled into a CR2016 analog battery using conventional manufacturing processes. Cycle performance testing was performed using a constant current charge-discharge experiment at 30 mA, with the charge-discharge voltage limited to 0–1.5 V.

[0138] The LAND battery testing system from Wuhan Jinno Electronics Co., Ltd. was used for testing. Capacity retention was tested at a high temperature (60 degrees Celsius) and charge / discharge was performed at a current density of 0.2C within a charge / discharge range of 2.75-4.2V.

[0139] Initial Coulomb efficiency = First discharge capacity / First charge capacity.

[0140] Repeat the cycle 50 times. Use a micrometer to measure the thickness of the electrode at this time, which is H1. After 50 cycles, the expansion rate is (H1-H0) / H0×100%, and the initial thickness of the electrode is H0.

[0141] Repeat the cycle 100 times and record the discharge capacity as the remaining capacity of the lithium-ion battery; capacity retention rate = remaining capacity / initial capacity * 100%.

[0142] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the main claims.

[0143] Example 1

[0144] A method for preparing a negative electrode material includes the following steps:

[0145] (1) Select carbon-coated SiO y (y=1) Material (carbon content 3%±0.1%), 1000g of powder with D50=6.0±0.3um was screened as silicon-oxygen raw material and mixed with 100g of lithium carbonate as dopant. After argon gas protection was introduced into a sealed container, the mixture was stirred at 750r / min for 180min.

[0146] (2) The mixture was sealed and placed in a high-temperature reactor. After sealing, argon protective gas was introduced. The first heating stage was carried out at a heating rate of 1℃ / min. When the heating gradient was 100℃-150℃-200℃-250℃, the temperature was maintained for 3 hours in each stage. The heating rate was continued to 300℃ and held for 3 hours. Stirring was carried out throughout the process at a stirring rate of 1500r / min. The powder solid phase pre-reaction was carried out in the second heating stage. Stirring was stopped in the second heating stage, and heating was continued at a heating rate of 1℃ / min. The temperature was continued to 980℃. After the temperature stabilized, heat treatment was carried out for 120min. The dopant gas was released by exhausting the gas to obtain the pre-reaction product.

[0147] (3) The pre-reaction product was placed in a high-pressure enclosure and subjected to high-pressure and high-temperature heat treatment. The pressure was set to 200 MPa, the heat treatment temperature was 1200 °C, and the heat treatment time was 12 hours to obtain the precursor.

[0148] (4) The precursor was crushed and dispersed. A surface impregnation solution was prepared by dissolving liquid asphalt in anhydrous ethanol at a mass ratio of 5%. The solution was stirred thoroughly for 120 min, and impurities were filtered out to obtain the surface impregnation solution. The dispersed precursor powder was added to the impregnation solution, and the mass ratio of the material to the liquid was controlled at 1:1. The solution was stirred at 3000 rpm for 90 min. After standing for 24 hours, the solution was filtered. The filtered material was dried in a vacuum oven at 90°C for 24 hours to obtain the composite.

[0149] (5) The composite was subjected to vacuum PECVD (plasma-enhanced chemical vapor deposition) for organic carbon source carbonization. Specifically, xylene was dissolved in ethanol at a mass ratio of 1:1 to prepare a coating solution. The coating solution was preheated to 85°C to obtain a benzene-containing liquid coating solution. After evacuation, argon gas was introduced into the chamber at a flow rate of 200 sccm. The chamber pressure was controlled at 5000 Pa by a vacuum valve. After the liquid coating solution was coated onto the surface of the composite by PECVD, the temperature was raised to 600°C. After the temperature and pressure stabilized, the deposition time was 2.0 h. The product was then dispersed and sieved, vacuum dried after evacuation, and encapsulated under inert gas protection to obtain the negative electrode material.

[0150] Example 2

[0151] The difference from Example 1 is:

[0152] (1) Select carbon-coated SiO y(y=1) Material (carbon content 3%±0.1%), 1000g of powder with D50=6.0±0.3um was screened as silicon-oxygen raw material, mixed with 50g of magnesium powder, and stirred for 180min at 750r / min after purging argon gas in a sealed container.

[0153] Example 3

[0154] The difference from Example 1 is:

[0155] (1) Select carbon-coated SiO y (y=1) Material (carbon content 3%±0.1%), 1000g of powder with D50=6.0±0.3um was screened as silicon oxide raw material, mixed with 54g of aluminum powder and 14g of lithium powder, and stirred for 180min at 750r / min after purging argon gas in a sealed container.

[0156] Example 4

[0157] The difference from Example 1 is:

[0158] (3) The pretreated material is placed in a high-pressure enclosure for high-pressure and high-temperature treatment. The pressure is set to 150 MPa, the heat treatment temperature is 1200℃, and the heat treatment time is 12 hours to obtain the precursor.

[0159] Example 5

[0160] The difference from Example 1 is:

[0161] (3) The pretreated material is placed in a high-pressure enclosure for high-pressure and high-temperature treatment. The pressure is set to 100 MPa, the heat treatment temperature is 1200℃, and the heat treatment time is 12 hours to obtain the precursor.

[0162] Example 6

[0163] The difference from Example 1 is:

[0164] (3) The pretreated material is placed in a high-pressure enclosure for high-pressure and high-temperature treatment. The pressure is set to 200 MPa, the heat treatment temperature is 800℃, and the heat treatment time is 18 hours to obtain the precursor.

[0165] Example 7

[0166] The difference from Example 1 is:

[0167] (5) The composite was subjected to vacuum PECVD for organic carbon source carbonization. Specifically, benzene was dissolved in ethanol at a mass ratio of 1:1 to prepare a coating solution. The coating solution was preheated to 85°C to obtain a benzene-containing liquid-phase coating solution. After evacuation, argon gas was introduced into the chamber at a flow rate of 200 sccm. The chamber pressure was controlled at 5000 Pa by a vacuum valve. The benzene-containing liquid-phase coating solution was coated onto the surface of the composite using PECVD. The temperature was then raised to 550°C. After the temperature and pressure stabilized, the deposition time was 1.5 h. The product was then dispersed and sieved, vacuum dried after evacuation, and encapsulated under inert gas protection to obtain the negative electrode material.

[0168] Example 8

[0169] The difference from Example 1 is:

[0170] (5) The composite was subjected to vacuum PECVD for organic carbon source carbonization. Specifically, phenol was dissolved in ethanol at a mass ratio of 1:1 to prepare a coating solution. The coating solution was preheated to 85°C to obtain a phenol-containing liquid-phase coating solution. After evacuation, argon gas was introduced into the chamber at a flow rate of 200 sccm. The chamber pressure was controlled at 5000 Pa by a vacuum valve. After the liquid-phase coating solution was coated onto the surface of the composite by PECVD, the temperature was raised to 400°C. After the temperature and pressure stabilized, the deposition time was 2.0 h. The product was then dispersed and sieved, vacuum dried after evacuation, and encapsulated under inert gas protection to obtain the negative electrode material.

[0171] Example 9

[0172] The difference from Example 1 is that in step (1), carbon-coated SiO material (carbon content 3% ± 0.1%) was selected, and 1000g of powder with D50 = 6.0 ± 0.3um was screened as silicon-oxygen raw material. It was mixed with 25g of lithium powder, and after being protected by argon gas in a sealed container, it was stirred at a speed of 750r / min for 180min.

[0173] In step (3), a high-pressure high-temperature heat treatment is performed at a temperature of 800°C for 6 hours to obtain the precursor.

[0174] Comparative Example 1

[0175] A method for preparing a negative electrode material includes the following steps:

[0176] (1) Select carbon-coated SiO y (y=1) Material (carbon content 3%±0.1%), 1000g of powder with D50=6.0±0.3um was screened as silicon-based raw material, mixed with 100g of lithium carbonate, and stirred for 180min at 750r / min after purging argon gas in a sealed container.

[0177] (2) The mixed materials were sealed and placed in a high-temperature reactor. After sealing, argon protective gas was introduced, and the temperature was increased to 300°C at a rate of 1°C / min and held for 3 hours to carry out the solid-phase pre-reaction of the powder. The reaction was carried out by stirring at a rate of 1500 r / min. After the heat treatment was completed, stirring was stopped, and heating was continued at a rate of 1°C / min until the temperature reached 1200°C. After the temperature stabilized, the heat treatment was carried out for 120 min.

[0178] (3) The pretreated material was heated to 900°C and carbon coated for 5 hours using methane as a gaseous carbon source. The methane flow rate was set to 500 sccm. The carbon-coated product was then dispersed and sieved, vacuum dried, and sealed with inert gas to obtain the negative electrode material.

[0179] Comparative Example 2

[0180] The difference from Example 1 is:

[0181] (3) The pre-reaction product of step (2) is heat-treated at normal pressure at a temperature of 600°C for 12 hours; the heat-treated product is then broken up and sieved, vacuum dried, and sealed with inert gas to obtain the negative electrode material.

[0182] Comparative Example 3

[0183] The difference from Example 1 is:

[0184] No dopant is added in step (1), that is, step (2) is carried out directly using silicon-oxygen raw materials.

[0185] The performance of the anode materials prepared in the examples (abbreviated as S1 to S9) and the comparative examples (abbreviated as D1 to D3) was tested, and the results of the above performance tests are shown in Tables 1 to 2:

[0186] Table 1. Summary of Performance Test Results of Anode Materials

[0187] Table 2. Summary of Performance Test Results of Anode Materials

[0188] According to the data in Tables 1 and 2, by controlling the color difference parameter of the negative electrode material and synergistically controlling the FWHM, (M) / FWHM (Si)The value of is in the range of 0.2 to 0.8. It can adjust the mass content of metal M compound, silicon grain size and phase segregation, reduce the side reactions between silicon-based active materials (especially silicon and silicon oxide) and electrolyte, reduce the consumption of active lithium ions, enhance the interfacial stability between the negative electrode material and electrolyte, improve the first coulombic efficiency and specific capacity of the negative electrode material, and reduce the expansion efficiency of the negative electrode material.

[0189] According to Examples 1-3 and Comparative Example 3, the chromaticity of the anode materials prepared with different doped metals differs. The Lab values ​​of the anode materials containing metal M compound are generally higher than those of the anode materials in Comparative Example 3. As the FWHM(M) / FWHM(Si) ratio increases, the crystallinity of silicon in the anode material is higher and the silicon grain size is larger. The cycle performance of the anode material in Example 3 is slightly lower than that in Example 1, and the capacity of the anode material in Example 3 is slightly lower than that in Example 1.

[0190] According to the test data from Examples 1 and 4-5, by adjusting the temperature, pressure, and duration of the high-temperature and high-pressure heat treatment of the pre-reaction product, the high-pressure treatment alters the crystal growth. In particular, the high-pressure environment inhibits grain growth and atomic diffusion rearrangement to a certain extent, thereby controlling core phase separation. The M element is in a dispersed state, and the lithium-ion diffusion resistance decreases during charge and discharge, which is beneficial to improving the capacity of the anode material. Furthermore, the silicon-based active material in the anode material includes small silicon grains, resulting in low interfacial resistance and high reversible capacity. As the pressure decreases, the crystal phase in the core silicon-based active material is mainly silicon crystals and silicate grains, the FWHM(M) / FWHM(Si) ratio decreases, the content of metal M compounds in the anode material decreases, and the mass proportion of silicon and silicon oxides increases. During charge and discharge, the initial coulombic efficiency of the anode material decreases, and the cycle stability is poor.

[0191] In Example 6, the duration of the high-temperature and high-pressure heat treatment was increased. However, due to the lower temperature, irregularly shaped silicates may have formed. XRD analysis showed that the main peak of the silicate characteristic peak became a broad peak, the half-peak width increased, and the FWHM(M) / FWHM(Si) ratio increased compared to Example 1. However, due to the lower temperature, the silicon and silicate did not undergo complete structural rearrangement, and the diffusion of low surface energy silicates was insufficient. Therefore, the electrolyte had a higher probability of contacting the active silicon during charge and discharge, and the initial coulombic efficiency of the negative electrode material was slightly affected.

[0192] According to the test data from Examples 1 and 7-8, different carbon sources containing benzene rings can effectively improve the surface defects of the anode material, resulting in a color of the anode material within a suitable range. This is because molecular-level carbon sources can be fully adsorbed at surface defect vacancies and carbonized in situ, thus keeping the color difference of the anode material within a suitable range. Furthermore, the initial coulombic efficiency and specific capacity of the anode material also exhibit excellent performance.

[0193] The test data from Examples 1 and 9 show that adding lithium powder to pre-lithiate the silicon-oxygen raw material can improve the specific capacity of the anode material. However, due to the low temperature of the high-temperature and high-pressure treatment, the degree of reaction between the solid components decreases, which leads to an aggravation of the side reactions between the anode material and the electrolyte. As a result, the initial coulombic efficiency and cycle performance of the anode material are slightly lower than those in Example 1.

[0194] According to the test data of Example 1 and Comparative Example 1, Comparative Example 1 did not undergo solid-phase pre-reaction, and there was excessive local doping of metal in the precursor. When metal M reduced silicon oxide, the local exothermic reaction was aggravated, the silicon grain size increased, resulting in a decrease in the half-width at half maximum (WHM) of silicon, an excessively large FWHM(M) / FWHM(Si) ratio, a decrease in the capacity of the anode material, and an increase in defects and pores caused by metal M during the reduction of silicon oxide. This significantly increased the contact reaction sites between the anode material and the electrolyte, aggravated side reactions, and reduced the first coulombic efficiency of the anode material.

[0195] According to the test data of Example 1 and Comparative Example 2, Comparative Example 2 did not use high-pressure and high-temperature treatment and carbon coating treatment. The uniformity of metal doping in the precursor decreased, and local complete enrichment was formed, forming a variety of compounds including silicates and silicon oxides. The proportion of compound components of metal M decreased, FWHM(M) decreased, and the FWHM(M) / FWHM(Si) ratio also decreased. The color difference of the negative electrode material was also significantly different from that of Example 1, which led to the aggravation of the side reaction between the negative electrode material and the electrolyte, the aggravation of gas generation during charging and discharging, and the decrease in the battery's initial efficiency, capacity and cycle stability.

[0196] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

A negative electrode material, characterized in that, The negative electrode material includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, wherein the silicon-based active material includes silicon, silicon oxide, and a metal M compound; Lab color difference test was performed on the negative electrode material to obtain the brightness L, red-green hue a, and yellow-blue hue b of the negative electrode material, wherein 15≤L≤35, -2≤a≤5, and -2≤b≤5; In the XRD pattern of the negative electrode material, the full width at half maximum (FWHM) of the strongest characteristic peak in the metal M compound of the negative electrode material is 0.5 WHM. (M) The full width at half maximum (FWHM) of the characteristic peaks on the silicon (111) surface is 1000 ppm. (Si) 0.2 < FWHM (M) / FWHM (Si) <0.

8. The negative electrode material according to claim 1 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1)23.5≤L≤35； (2)-0.5≤a≤1.5； (3)-0.5≤b≤1.5。 The negative electrode material according to claim 1 is characterized in that, The metal element M includes at least one of Li, Mg, Al, Ti, and Cu. The negative electrode material according to claim 1 is characterized in that, FWHM (M) >0.2; and / or, FWHM (Si) >0.

2. The negative electrode material according to claim 1 is characterized in that, 0.2 < FWHM (M) ≤0.9; and / or, 0.2 < FWHM (Si) ≤1.

9. The negative electrode material according to claim 1 is characterized in that, The metal M compound includes at least one of metal silicides and metal silicates; and / or The mass content of metallic M element in the negative electrode material is m. M %, 2.0≤m M ≤15. The negative electrode material according to claim 6 is characterized in that, The metal M compound includes metal silicates, which include at least one of lithium silicate, magnesium silicate, aluminum silicate, lithium magnesium silicate, lithium aluminum silicate, and lithium titanium aluminum silicate. The negative electrode material according to claim 1 is characterized in that, The negative electrode material is tested by X-ray photoelectron spectroscopy, and the surface of the negative electrode material has at least one oxygen-containing group selected from CO, C=O and COO-; and / or, the negative electrode material is tested by infrared spectroscopy, and the surface of the negative electrode material has at least one functional group selected from OH and CH. The negative electrode material according to claim 1 is characterized in that, The negative electrode material I D / I G The value ranges from 0.4 to 3.

0. The negative electrode material according to claim 1 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The silicon oxide includes silicon and oxygen, wherein the atomic ratio of silicon to oxygen is 0 to 2, excluding 0; (2) The general chemical formula of the silicon oxide is SiO2. x where 0 < x ≤ 2; (3) The carbon material includes at least one of amorphous carbon and graphitized carbon. The negative electrode material according to claim 1 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The silicon oxide includes silicon and oxygen elements, and the atomic ratio of silicon to oxygen in the negative electrode material is 0 to 1, excluding 0; (2) The general chemical formula of the silicon oxide is SiO2. x , where 0 < x < 1. The negative electrode material according to any one of claims 1 to 11 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The median particle size D of the negative electrode material 50 The size ranges from 4μm to 9μm; (2) The specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~3.0m 2 / g. The negative electrode material according to any one of claims 1 to 12 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The powder conductivity of the negative electrode material under a pressure of 20KN is 0.2S / cm to 10.0S / cm; (2) The tap density of the negative electrode material is 0.75 g / cm³. 3 ~2.00g / cm 3 . The negative electrode material according to any one of claims 1 to 13 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The mass content of carbon element in the negative electrode material is m C %, 2≤m C ≤15; (2) The mass percentage of water in the negative electrode material is m 水 %, 0.01≤m 水 ≤0.1; (3) A carbon layer is formed on at least part of the surface of the silicon-based active material, and the thickness of the carbon layer is 50 nm to 1000 nm. A battery characterized in that, Includes the negative electrode material as described in any one of claims 1 to 14.

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