Negative electrode material and preparation method therefor, and secondary battery

Abstract

A negative electrode material and a preparation method therefor, and a secondary battery, relating to the technical field of battery materials. The negative electrode material comprises: a silicon-based core; and a carbon layer coated on at least part of the surface of the silicon-based core, the silicon-based core comprising nano-silicon, and silicate containing a metal element M; the negative electrode material is sectioned and subjected to energy spectrum analysis, k1 is less than or equal to 10, k2 is less than or equal to 5, and k2 / k1 is greater than 0.1 and less than or equal to 1. The preparation method for the negative electrode material comprises: heating and evaporating a pre-disproportionated silicon monoxide material and an M metal source material, to obtain a silicon monoxide gas and a metal source gas; mixing the two gases, and performing condensation to obtain a core material; and performing carbon coating treatment, to obtain a negative electrode material. Metal silicate in the prepared negative electrode material effectively separates a nano silicon domain and a silicon oxide domain, and is uniformly distributed; thus, the negative electrode material has high first-time efficiency and excellent cycle performance.

Description

Negative electrode material, preparation method thereof, and secondary battery

[0001] This application claims priority to Chinese patent application No. 2023114339212, filed on October 31, 2023. This application incorporates the entirety of the aforementioned Chinese patent application. Technical Field

[0002] The present application relates to the technical field of battery materials, and in particular to a negative electrode material, a preparation method thereof, and a secondary battery. Background Art

[0003] Among the many anode materials, silicon oxide anode materials are currently the most technologically mature, high-capacity anode materials. Compared to graphite-based anode materials, silicon oxide anode materials have a specific capacity as high as 2100mAh / g. Compared to crystalline silicon anode materials, silicon oxide anode materials overcome the problem of large volume expansion and greatly improve the cycle life of the anode materials. However, because the formation of Li2O and lithium silicate during the initial lithium insertion of silicon oxide materials is irreversible, the lithium loss caused by these irreversible reactions leads to a low initial coulombic efficiency. When designing secondary batteries, an excess of positive electrode capacity is required to match the initial capacity. This, on the one hand, offsets the high specific capacity of the anode and reduces the energy density of the secondary battery; on the other hand, it also increases the cost of the positive electrode consumption of the secondary battery.

[0004] To address the issue of low initial charge and discharge coulombic efficiency, the oxygen content in silicon oxide can be reduced in advance to reduce the consumption of lithium ions in the positive electrode material by the irreversible phase Li2O generated during the first charge, thereby improving the energy density of the secondary battery. Common methods include adding exogenous reducing metal elements to react with the oxygen element in silicon oxide to reduce and generate nano-silicon, thereby improving the material's coulombic efficiency. At the same time, the metal oxide or silicate generated by the reduction reaction can act as a buffer matrix, regulating the stress damage caused by volume changes in nano-silicon during lithium alloying and dealloying, thereby maintaining structural integrity and improving the material's long-term cycling performance.

[0005] For example, a method for improving the first-cycle coulombic efficiency of silicon oxide by mixing silicon dioxide powder and metallic magnesium powder and heating them to induce a solid-phase doping reduction reaction. The magnesium silicate in the negative electrode material produced by this method has relatively stable physical and chemical properties, and the aqueous slurry has good stability. However, because the magnesium thermal reduction reaction is a diffusion-controlled reaction, the composition of its products is closely related to the diffusion rate of magnesium vapor. When the powders are mixed at the micron level, the magnesium vapor generated by the heat begins to react from the outside of the silicon dioxide particles and gradually diffuses into the particles. Localized excess magnesium can easily lead to the formation of byproducts such as magnesium silicide and magnesium oxide, and rapid growth of silicon grains. Moreover, because the diffusion rate of magnesium vapor into the solid is generally low, it is difficult to completely and evenly incorporate magnesium into the silicon dioxide material, and the distribution of magnesium in the reduction product is also relatively uneven.

[0006] For the in-situ gaseous magnesium doping technology, a method of mixing a silicon and silicon dioxide mixture with metal M and then vacuum co-evaporating and condensing is also disclosed. The negative electrode material prepared by this method has an initial efficiency of more than 83%, which greatly improves the effective utilization rate of lithium ions in the positive electrode material of the secondary battery, and its aqueous slurry has good stability. However, since the reaction of the silicon and silicon dioxide mixture used to generate silicon oxide vapor under heating conditions is a solid-solid interface reaction, the amount of silicon oxide vapor generated will also fluctuate greatly as the reaction proceeds. Therefore, during the mixed deposition process of magnesium vapor and silicon oxide vapor, the local magnesium incorporation ratio is uncontrollable, which can easily lead to uneven growth of silicon grains, affecting the cycle life and safety of the negative electrode material.

[0007] Clearly, whether using solid-phase doping or in-situ gaseous doping techniques, the resulting anode materials suffer from uneven distribution of doping elements or uneven silicon grain growth. This means it's difficult to achieve uniform distribution of doping elements across single and multiple particles. Consequently, a new anode material is urgently needed to improve its electrochemical performance.

[0008] Summary of the Invention

[0009] The purpose of this application is to provide a negative electrode material, a preparation method thereof, and a secondary battery. Through in-situ doping technology, the doping of nano-scale metal M is achieved to obtain a negative electrode material with uniform distribution of metal M, thereby reducing the oxygen content in the negative electrode material, and further applying it to the battery to improve the first efficiency and cycle performance.

[0010] To achieve the above objectives, the technical solutions of this application are as follows:

[0011] In a first aspect, the present application provides a negative electrode material comprising a silicon-based core and a carbon layer coated on at least a portion of the surface of the silicon-based core, wherein the silicon-based core comprises nano-silicon and a silicate containing a metal M element;

[0012] The negative electrode material is subjected to cross-section and energy spectrum analysis, and the cross-sections of n1 particles are randomly selected for surface scanning analysis to obtain n1 M element content values, and the standard deviation k1 of the n1 M element content values ​​is calculated, where k1≤10; n2 points are randomly selected within the cross-section of any of the above particles for point scanning analysis to obtain n2 M element content values, and the standard deviation k2 of the n2 M element content values ​​is calculated, where k2≤5 and 0.1<k2 / k1≤1, where n1 is a natural number greater than or equal to 5, and n2 is a natural number greater than or equal to 5.

[0013] In a second aspect, the present application further provides a method for preparing the negative electrode material of the first aspect, comprising:

[0014] Placing a metal source material and a pre-disproportionated silicon dioxide material at different positions in the same vacuum heating system for heating and evaporation respectively to obtain a metal source gas and silicon dioxide gas;

[0015] mixing and condensing silicon dioxide gas and metal source gas to obtain a core material;

[0016] The core material is subjected to carbon coating treatment to obtain the negative electrode material.

[0017] In a third aspect, the present application further provides a secondary battery, comprising the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0018] Beneficial effects of this application:

[0019] The silicate containing the metal element M in the negative electrode material system of the present application has a distribution of the M element that conforms to certain characteristics through energy spectrum analysis, and the silicate containing the metal element M can effectively separate the nano-silicon domain and the silicon oxide domain, reducing the aggregation of silicon clusters caused by the electrochemical sintering of nano-silicon during the charge and discharge cycle, and reducing the performance degradation problem of the negative electrode material caused by it, so that the negative electrode material has both high initial efficiency and excellent cycle performance, and the silicate can serve as a buffer matrix for nano-silicon and silicon oxide during the process of lithium insertion and extraction to buffer the volume changes caused by lithium insertion and extraction, so that the negative electrode material has low expansion performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0021] FIG1 is an XRD spectrum of the negative electrode material prepared in Example 1;

[0022] FIG2 is a SEM / EDS scan of a cross section of a particle of the negative electrode material prepared in Example 1;

[0023] FIG3 is a high-magnification SEM image of a cross-section of a particle of the negative electrode material prepared in Example 1;

[0024] FIG4 is a cycle capacity performance diagram of the secondary batteries prepared in Example 1 and Comparative Example 1;

[0025] FIG5 is a graph showing the cyclic expansion performance of the secondary batteries prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0026] As used herein:

[0027] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. The conjunction "consisting of" excludes any unspecified element, step, or component.

[0028] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0029] In these examples, parts and percentages are by mass unless otherwise indicated.

[0030] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0031] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0032] To obtain high-performance silicon oxide anode materials, existing research has explored the preparation of silicon-based composite anode materials by uniformly doping silicon powder and silicon micropowder with gaseous lithium generated by the redox reaction of lithium-containing oxides or silicates with a reducing agent. These materials achieve initial efficiency of up to approximately 90%, but the resulting silicon grains are large and exhibit poor cycle performance. Alternatively, silicon powder, SiO2 powder, magnesium powder, and LiCl powder are placed in separate chambers within the same vacuum system, heated and sublimated, and cooled to obtain a magnesium-lithium co-doped modified precursor, which is then coated with a conductive layer. The resulting anode material exhibits not only a high initial efficiency but also combines the high ionic conductivity of lithium silicates with the high bonding strength of magnesium silicates, further improving the material's cycle life. However, these methods present demanding preparation conditions and the anode material expands excessively during charge and discharge. Furthermore, a method for preparing silicon-based anode materials involves mixing a silicon and silicon dioxide mixture with metal M and then using vacuum co-evaporation and condensation. While this method improves initial efficiency, poor mixing uniformity during vapor evaporation results in uneven silicon grain size, poor electrical performance, and certain safety risks.

[0033] The main purpose of this application is to provide a negative electrode material with a metal M element that meets certain distribution characteristics, solve the problem of two-phase and multi-phase steam mixing, and thus make the negative electrode material have high initial efficiency and excellent cycle performance, as well as low expansion performance.

[0034] In a first aspect, the present application provides a negative electrode material comprising a silicon-based core and a carbon layer coating at least a portion of the surface of the silicon-based core. The silicon-based core of the negative electrode material comprises nano-silicon and a silicate containing a metal M element.

[0035] Among them, the negative electrode material was subjected to cross-section and energy spectrum analysis, especially the distribution of the M element in the core was analyzed, and the results were calculated to obtain the k1 value and k2 value.

[0036] Generally, the negative electrode material is a powder material, comprising a plurality of silicon-based cores and particles formed by a carbon layer coating at least a portion of the surface of the silicon-based cores. Specifically, n1 particles of the negative electrode material are randomly selected and sectioned, and the section of the n1 particles is subjected to surface scanning energy spectrum analysis to obtain n1 M element content values. The standard deviation k1 of these n1 metal M element content values ​​is calculated, where k1 ≤ 10. n2 points are randomly selected within the section of any of the above particles and are subjected to point scanning analysis to obtain n2 M element content values. The standard deviation k2 of these n2 M element content values ​​is calculated, where k2 ≤ 5, and the k1 and k2 values ​​also satisfy 0.1 < k2 / k1 ≤ 1, where n1 is a natural number greater than or equal to 5, and n2 is a natural number greater than or equal to 5. The above contents are by mass.

[0037] For negative electrode materials that meet this condition, the metal silicate in its silicon-based core can effectively separate the nano-silicon domain and the silicon oxide domain, reducing the performance degradation problem of the negative electrode material caused by the aggregation of silicon clusters.

[0038] When the negative electrode material satisfies the above-mentioned ranges of k1 and k2 at the same time, the silicate containing the metal element M is evenly distributed in the core, and the nano-silicon or silicon oxide is wrapped and isolated, reducing the processing gas production problem caused by the exposure of active silicon and the sintering problem of nano-silicon clusters during the cycle, thereby bringing a more stable material structure and reducing the consumption of active silicon during the cycle.

[0039] In the present invention, the setting of standard deviations k1 and k2 not only quantifies the distribution uniformity of the metal M element in the negative electrode material, but also achieves the improvement of the performance of the negative electrode material by limiting the regular relationship between the standard deviations of the M element content inside a single particle (k2) and between multiple particles (k1).

[0040] Limiting the standard deviation k2, which reflects uniform distribution within a single particle, to 5 or less indicates that the metal M element is uniformly dispersed throughout the particle at the nanometer scale within a single particle. Limiting the standard deviation k1, which reflects uniform distribution across multiple particles, to 10 or less means that the distribution of the M element content is also quite uniform across different particles. This demonstrates that the metal M element is not only uniformly distributed within a single particle, but also has good consistency across the entire collection of negative electrode material particles, avoiding problems caused by differences in the M element content between different particles.

[0041] Furthermore, limiting the ratio of k2 / k1 to between 0.1 and 1 means that the uniformity within a single particle and between multiple particles is coordinated, that is, the uniformity of the distribution of the M element within a particle and between particles is relatively good, without significant inconsistency. The setting of this ratio avoids two extreme cases: one is uniform distribution within a single particle but uneven distribution between particles, and the other is uniform overall but uneven distribution within the particles. In the prior art, whether it is solid-phase doping or gaseous doping, it is often difficult to ensure both of these uniformities at the same time, especially when there are significant differences in particle size, morphology or internal structure, it is difficult to achieve consistent distribution of the M element. The present invention not only achieves nanoscale uniform doping of the M element, but also maintains this uniformity within a single particle and between multiple particles, effectively solving the problems in the prior art.

[0042] The negative electrode material of the present invention not only has a high initial efficiency, but also has excellent cycle performance and a low volume expansion rate. This is mainly based on the uniform distribution of metal silicates and their effective separation and protection of nano-silicon and silicon oxides. In summary, the standard deviations k1 and k2 of the present invention, as well as the setting of k2 / k1, not only quantify the uniformity of the distribution of the metal M element in the negative electrode material, but also solve the technical problem of the difficulty in achieving uniform distribution of the M element within a single particle and between multiple particles in the prior art, significantly improving the electrochemical performance of the negative electrode material and the secondary battery using the same.

[0043] Silicates containing metal M elements can be written as (MO) n SiO2, in a preferred embodiment, in the negative electrode material of the present application, (MO) n Silicates with a low SiO2 content and a high SiO2 content are the main silicate phases. Taking magnesium silicate as an example, when MgSiO3 (MgO·SiO2) is the main silicate phase in the negative electrode material, the pH value of the negative electrode material will be relatively low. However, if the content of Mg2SiO4 (2MgO·SiO2) is high, Mg2SiO4 will hydrolyze and produce more OH. - , which in turn causes a higher pH, and OH - It is easy to react with naked active Si to generate H2, which causes the initial efficiency of battery capacity to decay. The generated gas will also cause serious processing problems during battery slurry coating, which may cause battery bulging failure or explosion, thus causing safety risks. Therefore, when 0<m(Mg2SiO4) / m(MgSiO3)≤1, the ability to cause pH value to rise is weak; thus, the pH value range of the negative electrode material can be stably maintained within an appropriate range, thus reducing the risk of naked Si in the negative electrode material reacting with OH in the aqueous slurry due to excessively high pH value. - The reaction produces H2, which leads to problems such as initial capacity degradation and processing gas production.

[0044] Therefore, when the silicate containing metal M element is mainly composed of MgSiO3, the H2SiO3 generated by the hydrolysis of MgSiO3 causes the slurry alkalinity to be relatively weak. When the MgSiO3 content is low and the Mg2SiO4 content is high, a large amount of Mg2SiO4 will hydrolyze to generate H4SiO4, and at the same time produce more OH - , which will make the slurry more alkaline, OH - It will react with the exposed active silicon in the negative electrode material to generate H2, which will affect the safety performance of the battery.

[0045] In a preferred embodiment of the present application, the silicon-based core of the negative electrode material further comprises silicon oxide. More preferably, nano-silicon is dispersed in the silicon oxide, and the nano-silicon or silicon oxide is surrounded by a silicate containing a metal M element. The multiple protection of silicon oxide and metal silicate further reduces exposure of active silicon and reduces the volume expansion rate during the charge and discharge process.

[0046] Silicon oxide can be represented by the general formula SiO x (0<x≤2, such as 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2 or a range consisting of any two of these values.) The material may be a material in which silicon particles are dispersed in SiO2, or a material having a tetrahedral structural unit, wherein the silicon atom is located at the center of the tetrahedral structural unit and the silicon atoms and / or oxygen atoms are located at the four vertices of the tetrahedral structural unit.

[0047] In a preferred embodiment of the present application, the D50 of the silicon-based core of the negative electrode material of the present application is 5.0 to 5.5 μm.

[0048] In a preferred embodiment of the present application, the size of the silicon crystal grains of the nano-silicon in the negative electrode material of the present application is less than 10 nm.

[0049] Controlling the relevant dimensions of the negative electrode material within the above range can make the silicon grain size more balanced, and the electrical and safety performance better. At the same time, it can improve the particle size uniformity of the prepared negative electrode material, further making the negative electrode material have high initial efficiency and excellent cycle performance, as well as low expansion performance.

[0050] In a preferred embodiment of the present application, the pH value of the negative electrode material of the present application satisfies 7<pH≤10.5, for example, it can be 7.5, 8, 8.5, 9, 9.5, 10 or 10.5. More preferably, the pH value satisfies 7<pH≤10.

[0051] It is understandable that if the pH value of the negative electrode material is too high, when the negative electrode material is prepared into a negative electrode slurry, the exposed Si will react with the OH in the slurry. - If the reaction produces H2, there will be problems such as bubbles in the slurry coating, deterioration of the binder performance due to excessive alkalinity, and further lead to problems such as deterioration of cycle performance, initial attenuation of battery capacity, and battery safety. The pH value of the negative electrode material of this application does not exceed 10.5, which greatly reduces the generation of gas and improves the performance of the battery. It further solves the problem of active silicon and OH in the alkaline solution when preparing the negative electrode material slurry. - There are problems such as gas production caused by the reaction between the electrodes, bubble problems during electrode coating, and cycle performance degradation caused by degradation of the alkaline binder.

[0052] In a preferred embodiment of the present application, the metal M element includes at least one metal element from Groups IA, IIA, and IIIA.

[0053] In a preferred embodiment of the present application, the M element includes at least one of lithium, sodium, potassium, magnesium, calcium, and aluminum, and is more preferably magnesium.

[0054] The silicate formed by the above-mentioned M element in the negative electrode material can more fully separate the nano-silicon domains and silicon oxide domains, thereby further reducing the aggregation of silicon clusters during charging and discharging. At the same time, it can further buffer the expansion problem caused by lithium insertion and extraction, and better improve the initial efficiency and cycle performance of the negative electrode material.

[0055] In a preferred embodiment of the present application, the true density of the negative electrode material is 2.0 g / cm 3 -2.6g / cm 3 , for example, it can be 2.0 g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 or 2.6g / cm 3 More preferably, the true density is 2.3 g / cm 3 -2.6g / cm 3 .

[0056] The true density of the negative electrode material of the present application is tested by a gas adsorption expansion method.

[0057] In a preferred embodiment of the present application, the specific surface area of ​​the negative electrode material is 2m 2 / g-10m 2 / g, for example, it can be 2m 2 / g、4m 2 / g、6m 2 / g、8m 2 / g or 10m 2 / g.

[0058] Limiting the true density and specific surface area of ​​the negative electrode material within the above range is beneficial to improving the structural stability of the negative electrode material and reducing side reactions on the surface of the negative electrode material, reducing electrolyte consumption and thus ensuring higher energy density and good long-cycle performance.

[0059] In a preferred embodiment of the present application, the mass proportion of the M element in the negative electrode material is 3%-20%, for example, it can be 3%, 5%, 7%, 10%, 12%, 15%, 18% or 20%.

[0060] The above-mentioned content of M element is more conducive to playing the role of separating nano-silicon domains and silicon oxide domains in the form of silicate, thereby further improving the first efficiency and cycle performance of the negative electrode material.

[0061] In a preferred embodiment of the present application, the mass proportion of the carbon layer on the surface of the negative electrode material is 1%-20%, for example, it can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18% or 20%, more preferably 3%-7%.

[0062] In a preferred embodiment of the present application, the thickness of the surface carbon layer is 50 nm-500 nm, for example, it can be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm.

[0063] When the mass proportion and thickness of the carbon layer are within the above range, it is more conducive to reducing the exposure and gas production of active silicon in the silicon-based core and the sintering of nano-silicon clusters, making the structure of the negative electrode material more stable, and further reducing the consumption of active silicon during the cycle, which is conducive to obtaining a negative electrode material with significantly improved first-time efficiency and cycle performance.

[0064] In a preferred embodiment of the present application, when the silicate containing the metal M element includes MgSiO3, in the XRD spectrum of the negative electrode material, the diffraction peak of MgSiO3 (610) is between 30°-31°, the diffraction peak of Si (220) is between 45°-50°, and the ratio of the two diffraction peak intensities α=I Si(220) / I MgSiO3(610) , 0<α<2. Under the above conditions, the silicate formed in the negative electrode material can more fully separate the nano-silicon domains and silicon oxide domains, thereby further reducing the aggregation of silicon clusters during charge and discharge. At the same time, it can further buffer the expansion problem caused by lithium insertion and extraction, and better improve the initial efficiency and cycle performance of the negative electrode material.

[0065] In a preferred embodiment of the present application, when the silicate containing the metal M element includes MgSiO3, according to the XRD spectrum of the negative electrode material and the Scherrer formula Kλ=0.9λ / Bcosθ, the average size of the MgSiO3 grains on the (610) crystal plane is calculated to be ≤30nm. The above conditions are conducive to the formation of good Li + The conductive path further reduces the high impedance caused by the excessively thick MgSiO3 layer.

[0066] In a second aspect, the present application further provides a method for preparing the negative electrode material in the first aspect, comprising:

[0067] S1. placing a metal source material and a pre-disproportionated silicon dioxide material at different positions in the same vacuum heating system for heating and evaporation, respectively, to obtain a metal source gas and silicon dioxide gas;

[0068] S2, mixing and condensing silicon dioxide gas and metal source gas to obtain a core material;

[0069] S3. Carbon coating the core material to obtain the negative electrode material.

[0070] The preparation method of the negative electrode material of the present application is simple and easy to operate, and can be quickly industrialized. Through in-situ doping technology, nano-scale doping of metal is achieved by mixed deposition of gaseous metal source and gaseous silicon oxide, and a negative electrode material with uniform distribution of metal silicate is obtained. In particular, pre-disproportionated silicon dioxide material is used in the preparation method, which can continuously and stably generate silicon dioxide vapor, and then after mixing with the stably generated metal source gas, a negative electrode material with uniform distribution of various substances and better performance is obtained, which reduces the problem of unstable silicon dioxide evaporation due to the influence of material contact effect on the interface reaction when the traditional silicon and silicon dioxide mixture is used as raw material, and then the problem of uneven doping of various substances in the prepared negative electrode material is reduced.

[0071] In combination with the second aspect, in a preferred embodiment of the present application, the preparation method of the pre-disproportionated silicon monoxide material in S1 includes: pre-disproportionating the amorphous SiO block to obtain silicon monoxide containing disproportionated silicon grains with a grain size of less than 20 nm, preferably, the grain size of the silicon grains is less than 10 nm, and then pulverizing or crushing to obtain pre-disproportionated silicon monoxide powder or particles.

[0072] In the preparation method of the negative electrode material of the present application, a silicon oxide source is used for pre-disproportionation treatment, wherein Si and SiO x It is uniformly dispersed at the nanoscale everywhere, and the silicon grain size is less than 20nm, reducing the impact of changes in reaction rate caused by changes in contact area of ​​interfacial reaction. Silicon dioxide vapor can be continuously and stably generated, and after mixing with the continuously and stably generated magnesium vapor, a high-first-efficiency silicon oxide negative electrode product with uniform distribution and better performance is obtained.

[0073] Further preferably, the pre-disproportionation treatment is carried out in an inert gas atmosphere, and the inert gas includes at least one of nitrogen, argon and helium.

[0074] Further preferably, the pre-disproportionation treatment temperature is 1000° C. to 1200° C., for example, 1000° C., 1050° C., 1100° C., 1150° C., or 1200° C., and the holding time is 3 hours to 10 hours, for example, 3 hours, 5 hours, 6 hours, 8 hours, or 10 hours. More preferably, the pre-disproportionation treatment is held at 1000° C. for 10 hours.

[0075] Under the above conditions, it is beneficial to make the silicon and silicon oxide in the silicon monoxide source more evenly dispersed and in contact, thereby further continuously and stably generating silicon monoxide vapor, providing a good material basis for the subsequent formation process of the negative electrode material, and is beneficial to improving the initial efficiency and cycle performance of the negative electrode material.

[0076] It should be noted that the use of pre-disproportionated silicon oxide as the silicon oxide source in this application is primarily to reduce the instability of SiO evaporation caused by the interfacial reaction affected by the material contact effect when using traditional silicon and silicon dioxide as raw materials. The homogenization and disproportionation treatment of amorphous SiO produces silicon oxide with disproportionated silicon grains <20 nm. This achieves a silicon oxide vapor source with microscopically uniform nanoscale dispersion of Si and SiO2, stabilizes the generation rate of silicon oxide vapor throughout the reaction process, and achieves relatively uniform generation, mixing, and condensation deposition of silicon oxide gas and metal M source gas.

[0077] In a preferred embodiment of the present application, the size of the pre-disproportionated silicon dioxide material in S1 is ≤ 10 cm, for example, 10 μm, 100 μm, 1 mm, 1 cm, 5 cm, or 10 cm. This helps further reduce the effect of changes in reaction rate caused by changes in the interfacial reaction contact area, thereby continuously and stably generating silicon dioxide vapor to participate in the reaction.

[0078] In a preferred embodiment of the present application, the metal source material in S1 includes at least one of a magnesium source material, a lithium source material, a sodium source material, a potassium source material, a calcium source material, and an aluminum source material, and is more preferably a magnesium source material.

[0079] Further preferably, the magnesium source material includes at least one of metallic magnesium powder, metallic magnesium ingot, metallic magnesium granules, a mixture of magnesium oxide and a reducing substance, and a mixture of magnesium salts and a reducing substance.

[0080] In a preferred embodiment of the present application, the metal source gas in S1 includes at least one of magnesium vapor, lithium vapor, sodium vapor, potassium vapor, calcium vapor, and aluminum vapor, more preferably magnesium vapor.

[0081] Under the above conditions, the formed metal silicate can more fully separate the nano-silicon domain and the silicon oxide domain, thereby better improving the first efficiency and cycle performance of the negative electrode material.

[0082] In a preferred embodiment of the present application, when the metal source material and the pre-disproportionated silicon dioxide material are heated and evaporated at different positions of the same vacuum heating system, the pre-disproportionated silicon dioxide material can be placed in a first vacuum heating chamber for heating and evaporation to obtain silicon dioxide gas; and the metal source material can be placed in a second vacuum heating chamber for heating and evaporation to obtain metal source gas.

[0083] Specifically, an inert gas is introduced into the first vacuum heating chamber, and the temperature is heated to 1000°C-1500°C to obtain silicon dioxide gas, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C.

[0084] Inert gas is introduced into the second vacuum heating chamber and the temperature is heated to 600°C-1350°C (preferably 700°C-1300°C) to obtain metal source gas, for example, it can be 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0085] It is understandable that, in the same vacuum heating system, the heating and evaporation temperatures of the metal source material and the pre-disproportionated silicon 2 oxide material may be the same or different.

[0086] The above conditions are conducive to fully evaporating the pre-disproportionated silicon dioxide material and the metal source material at a more matched rate to obtain the corresponding gaseous raw materials. At the same time, the occurrence of local excessive uneven evaporation and deposition reactions can be further reduced to improve the structural stability and electrochemical performance of the negative electrode material.

[0087] In a preferred embodiment of the present application, the mixing of the two gases in S2 is carried out under a vacuum condition with a vacuum degree of 0-100 Pa.

[0088] In a preferred embodiment of the present application, the condensation temperature in S2 is 500°C-900°C, for example, it can be 500°C, 600°C, 700°C, 800°C or 900°C.

[0089] Further preferably, the condensation method includes at least one of water cooling and air cooling.

[0090] Specifically, the condensation deposition chamber is evacuated, and when the vacuum degree reaches below 100 Pa and the temperature of the condensation chamber reaches 500℃-900℃, the gases in the two vacuum heating chambers are passed into the condensation deposition chamber for mixing, and then the precursor of the mixture of silicon oxide and metal source is collected on the condenser.

[0091] The above conditions are conducive to the pre-reaction after the two-phase gas mixture is condensed, the deposition state is more stable, and the probability of oxidation of the product after exposure to air is further reduced. The utilization rate of the M metal source to improve the first effect is also higher.

[0092] In a preferred embodiment of the present application, after condensation in S2, the process further includes: collecting the condensed precursor material, and then crushing and grading the precursor material to obtain the core material. Preferably, the volume distribution D50 of the core material is 5.0 to 5.5 μm.

[0093] More preferably, the pulverization method includes any one of mechanical pulverization, ball milling pulverization and air flow pulverization.

[0094] Under the above conditions, the particle size uniformity of the prepared negative electrode material can be further improved, thereby facilitating the smooth progress of the subsequent slurry mixing process and improving the preparation and performance of the battery.

[0095] In a preferred embodiment of the present application, the carbon coating treatment in S3 includes gas phase coating, liquid phase coating or solid phase coating.

[0096] When gas phase coating is used to prepare the surface carbon layer, the gases required for gas phase coating include carbon source gas and carrier gas; the temperature of gas phase coating is 700℃-1000℃, for example, it can be 700℃, 800℃, 900℃ or 1000℃.

[0097] Optionally, the carbon source gas includes at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene.

[0098] Optionally, the carrier gas includes at least one of nitrogen, argon and helium. Preferably, the atmosphere ratio of the carbon source gas, hydrogen and carrier gas is (2-15):1:3.5, more preferably (2-3):1:3.5.

[0099] The above conditions facilitate more complete and uniform coating of the carbon material on the surface of the silicon-based core, thereby encapsulating and isolating the nano-silicon or silicon oxide, reducing processing gas generation caused by exposure of active silicon and sintering of nano-silicon clusters during the cycle, thereby achieving a more stable material structure and reducing the consumption of active silicon during the cycle. Furthermore, preferably, during the vapor phase coating process, in addition to the carbon source gas and carrier gas, a certain proportion of hydrogen can be introduced, primarily to adjust the structure of the carbon layer.

[0100] In a third aspect, the present application further provides a secondary battery comprising the negative electrode material of the first aspect or the negative electrode material prepared by the method for preparing the negative electrode material of the second aspect. The secondary battery of the present application uses the above-mentioned negative electrode material and has higher initial efficiency and excellent charge-discharge cycle performance.

[0101] More preferably, the secondary battery is a non-aqueous electrolyte rechargeable battery.

[0102] Through in-situ doping technology, the technical solution of this application uses gaseous magnesium as a magnesium source and is mixed with gaseous silicon oxide for deposition to achieve nano-scale magnesium doping, thereby obtaining a negative electrode material that meets the distribution characteristics of metal M and further meets a specific pH range. The negative electrode material is then heat-treated and reduced to reduce the oxygen content in the active substance, and then powderized and carbon-coated to obtain a high-efficiency silicon dioxide negative electrode material.

[0103] Typically, but not limited to, k1 is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range of any two thereof; k2 is 1, 2, 3, 4, 5 or a range of any two thereof; k2 / k1 is 0.11, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range of any two thereof; n1 is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 400, 450, 500, 600, 700, 800, 900, 1000 or a range consisting of any two of them; n2 is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000 or a range consisting of any two of them;

[0104] Typically, but not limited to, the volume distribution D50 of the core material is 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm or a range consisting of any two of these values.

[0105] Typically, but not limited to, the atmosphere ratio of carbon source gas, hydrogen gas and carrier gas is 2:1:3.5, 3:1:3.5, 4:1:3.5, 5:1:3.5, 6:1:3.5, 7:1:3.5, 8:1:3.5, 9:1:3.5, 10:1:3.5, 11:1:3.5, 12:1:3.5, 13:1:3.5, 14:1:3.5, 15:1:3.5 or a range consisting of any two of them.

[0106] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0107] Example 1

[0108] The present application provides a negative electrode material, the preparation method of which includes:

[0109] 1) pre-disproportionating an amorphous SiO block at 1200° C. in an argon atmosphere for 10 hours, cooling the block and then pulverizing the block to obtain pre-disproportionated silicon oxide powder containing silicon grains with an average size of 6.0 nm, wherein the volume distribution of the powder is D50 = 100 μm. The powder is then placed in a first vacuum heating chamber of a vacuum heating system, introduced with argon, and heated to 1400° C. to obtain silicon oxide gas.

[0110] 2) placing metallic magnesium powder in a second vacuum heating chamber of a vacuum heating system, introducing argon gas, and heating to 700°C to produce magnesium vapor;

[0111] 3) Evacuate the vacuum heating system to a vacuum degree of 10 Pa;

[0112] 4) The gas obtained from the first vacuum heating chamber and the gas from the second vacuum heating chamber are introduced into a condensation deposition chamber with a vacuum degree of 10 Pa, and the precursor material is collected on a water-cooled substrate in the condensation deposition chamber at a temperature of 700° C.;

[0113] 5) crushing the precursor of step 4) to a volume distribution D50 of 5.5 μm by mechanical crushing, classification treatment, etc.;

[0114] 6) placing the powder material obtained in step 5) in a rotary kiln, heating it to 900° C., introducing methane, hydrogen, and carrier gas nitrogen, adjusting the atmosphere ratio to 2:1:3.5, and vapor-coating for 8 hours;

[0115] 7) Collecting the coated material, breaking it up, screening it, and removing the magnetism to obtain a composite negative electrode material containing silicon oxide.

[0116] This embodiment provides a secondary battery, and a specific preparation method includes:

[0117] The negative electrode material prepared in the above example, conductive carbon black, and PAA glue were mixed in a mass ratio of 75:15:10 to form a negative electrode slurry. This slurry was coated onto copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and button cells were assembled in an argon-filled glove box.

[0118] The button cell was subjected to charge and discharge tests at a current density of 0.1 C in the charge and discharge range of 0.01-1.5 V. The test obtained the initial reversible specific capacity and initial efficiency of the battery.

[0119] This embodiment also provides a secondary battery, and a specific preparation method includes:

[0120] A negative electrode slurry was prepared using the negative electrode materials prepared in the previous example: Super-P: KS-6: CMC: SBR (92:2:2:2:2), coated onto copper foil, and dried to form a negative electrode sheet. A button cell was assembled in an argon-filled glove box using a lithium metal sheet as the counter electrode.

[0121] The button battery was charged and discharged at a current density of 1C in the charge and discharge range of 0.01V-1.5V. The volume expansion rate and capacity retention rate of the battery after 50 cycles were obtained. The expansion performance during the cycle was then studied using the in-situ expansion rate test method of the elementary soft-pack battery.

[0122] Example 2

[0123] This embodiment provides a negative electrode material, and the preparation method thereof includes:

[0124] 1) pre-disproportionating an amorphous SiO block at 1200° C. in an argon atmosphere for 10 hours, cooling the block and then pulverizing the block to obtain pre-disproportionated silicon oxide powder containing silicon grains with an average size of 6.0 nm, wherein the volume distribution of the powder is D50 = 100 μm. The powder is then placed in a first vacuum heating chamber of a vacuum heating system, introduced with argon, and heated to 1300° C. to obtain silicon oxide gas.

[0125] 2) placing metallic magnesium powder in a second vacuum heating chamber of a vacuum heating system, introducing argon gas, and heating to 900° C. to generate magnesium vapor;

[0126] 3) Evacuate the vacuum heating system to a vacuum degree of 5 Pa;

[0127] 4) The gas obtained from the first vacuum heating chamber and the gas from the second vacuum heating chamber are introduced into a condensation deposition chamber with a vacuum degree of 5 Pa, and the precursor material is collected on a water-cooled substrate in the condensation deposition chamber at a temperature of 800° C.;

[0128] 5) crushing the precursor in step 4) to a volume distribution D50 of 5.0 μm by mechanical crushing, classification, etc.;

[0129] 6) placing the powder material obtained in step 5) in a rotary kiln, heating it to 980° C., introducing methane, hydrogen, and carrier argon, adjusting the atmosphere ratio to 3:1:3.5, and vapor coating for 10 hours;

[0130] 7) Collecting the coated material, breaking it up, screening it, and removing the magnetism to obtain a composite negative electrode material containing silicon oxide.

[0131] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0132] Example 3

[0133] This embodiment provides a negative electrode material, and its preparation method is the same as that of Example 1, except that:

[0134] In step 2), the metallic calcium powder is placed in a second vacuum heating chamber of a vacuum heating system, argon gas is introduced, and the mixture is heated to 1300° C.;

[0135] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0136] Example 4

[0137] This embodiment provides a negative electrode material, and its preparation method is the same as that of Example 1, except that:

[0138] The temperature for the pre-disproportionation treatment in step 1) is 1000° C. and the time is 10 h, and a pre-disproportionated silicon oxide powder with silicon-containing grains of 5.5 nm is obtained.

[0139] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0140] Example 5

[0141] This embodiment provides a negative electrode material, and its preparation method is the same as that of Example 1, except that:

[0142] The vacuum degree in step 3) is 50 Pa, and the precursor material is collected on a water-cooled substrate at 800° C. in step 4).

[0143] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0144] Example 6

[0145] This embodiment provides a negative electrode material, and its preparation method is the same as that of Example 1, except that:

[0146] The size of the pre-disproportionated silicon monoxide material in step 1) is a block of 5 cm in size.

[0147] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0148] Example 7

[0149] This embodiment provides a negative electrode material, and its preparation method is the same as that of Example 1, except that:

[0150] 1) pre-disproportionating an amorphous SiO block at 1000° C. in an argon atmosphere for 10 hours, cooling the block and then pulverizing the block to obtain pre-disproportionated silicon oxide powder containing silicon grains with an average size of 5.4 nm, wherein the volume distribution of the powder is D50 = 500 μm. The powder is then placed in a first vacuum heating chamber of a vacuum heating system, introduced with argon, and heated to 1000° C. to obtain silicon oxide gas.

[0151] 2) placing metallic magnesium powder in a second vacuum heating chamber of a vacuum heating system, introducing argon gas, and heating to 600° C. to produce magnesium vapor;

[0152] 3) Evacuate the vacuum heating system to a vacuum degree of 0 Pa;

[0153] 4) passing the gas obtained from the first vacuum heating chamber and the gas from the second vacuum heating chamber into a condensation deposition chamber with a vacuum degree of 0 Pa, and collecting the precursor material on a water-cooled substrate at a temperature of 500° C. in the condensation deposition chamber;

[0154] 5) crushing the precursor of step 4) to a volume distribution D50 of 5.5 μm by mechanical crushing, classification treatment, etc.;

[0155] 6) The powder material obtained in step 5) is placed in a rotary kiln, heated to 700° C., and methane, hydrogen, and carrier nitrogen are introduced with the atmosphere ratio adjusted to 2:1:3.5, and the gas phase coating is carried out for 10 hours.

[0156] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0157] Example 8

[0158] This embodiment provides a negative electrode material, and its preparation method is the same as that of Example 1, except that:

[0159] 1) pre-disproportionating an amorphous SiO block at 1200° C. in an argon atmosphere for 3 hours, cooling the block and then pulverizing the block to obtain pre-disproportionated silicon oxide powder containing silicon grains with an average size of 6.0 nm, wherein the volume distribution of the powder is D50 = 100 μm. The powder is then placed in a first vacuum heating chamber of a vacuum heating system, introduced with argon, and heated to 1500° C. to obtain silicon oxide gas.

[0160] 2) placing metallic magnesium powder in a second vacuum heating chamber of a vacuum heating system, introducing argon gas, and heating to 1350° C. to produce magnesium vapor;

[0161] 3) Evacuate the vacuum heating system to a vacuum degree of 100 Pa;

[0162] 4) The gas obtained from the first vacuum heating chamber and the gas from the second vacuum heating chamber are introduced into a condensation deposition chamber with a vacuum degree of 100 Pa, and the precursor material is collected on a water-cooled substrate at a temperature of 800° C. in the condensation deposition chamber;

[0163] 5) crushing the precursor of step 4) to a volume distribution D50 of 5.5 μm by mechanical crushing, classification treatment, etc.;

[0164] 6) The powder material obtained in step 5) is placed in a rotary kiln, heated to 1000° C., and methane, hydrogen and carrier gas nitrogen are introduced, the atmosphere ratio is adjusted to 2:1:3.5, and the gas phase coating is carried out for 8 hours.

[0165] The production and evaluation of the secondary battery provided in this embodiment are the same as those in Example 1.

[0166] Comparative Example 1

[0167] This comparative example provides a negative electrode material, and its preparation method is the same as that of Example 2, except that:

[0168] In step 1), silica powder with a volume distribution of D50 = 30 μm and silicon powder with a volume distribution of D50 = 10 μm are directly mixed in a molar ratio of 1:2, placed in the first vacuum heating chamber of the vacuum heating system, introduced with argon gas, and heated to 1400°C; in step 4), the temperature of the water-cooled substrate in the condensation deposition chamber is 850°C; in step 6), only methane and carrier gas nitrogen are introduced, and the atmosphere ratio is adjusted to 3:3.5.

[0169] The preparation and evaluation of the secondary battery provided in this comparative example are the same as those in Example 1.

[0170] Energy spectrum analysis of the Mg element was performed on the negative electrode materials prepared in the above examples and comparative examples, and energy spectrum analysis of the Ca element was performed on the negative electrode material prepared in Example 3, and the k1 and k2 values ​​were obtained respectively.

[0171] The specific test method of energy spectrum analysis is as follows: the prepared negative electrode material particles are cut using a Hitachi E-3500 ion mill, and the cross-sectional morphology and structure are observed on a Hitachi S-4800 cold field emission scanning electron microscope. The elemental composition and distribution of the cross-sectional surface of the negative electrode material particles are also observed in combination with an Oxford energy spectrometer from the UK.

[0172] At the same time, the pH value of the negative electrode materials prepared in the examples and comparative examples was tested: 5.00±0.01 g of powder sample was weighed, added to 45 mL of pure water, stirred and dispersed, and ultrasonicated for 5 minutes before standing. The supernatant after standing was tested using a Mettler FE20 pH meter to read the pH value.

[0173] True density test: The true density of the negative electrode material was measured using a Micromeritics true density meter (AccuPyc II) using the gas adsorption expansion method.

[0174] Specific surface area test: The specific surface area of ​​the material was calculated using an American Micrometer and pore analyzer (TriStar II) with nitrogen adsorption and the BET method.

[0175] XRD test: XRD diffractometer was used to characterize the samples with a scanning range of 10°-90° and a scanning step of 0.05°.

[0176] Carbon content %: using infrared absorption method, reference standard GB / T 20123-2006.

[0177] Thickness of the carbon layer: The cross-sectional SEM method was used. The material was first cut using a Hitachi E3500 ion mill and then analyzed using a Hitachi S-4800 scanning electron microscope.

[0178] Mg mass content and Ca mass content: tested using ICP spectrometer (instrument model: Agilent 5800VDV-ICP-OES).

[0179] pH value: pH meter was used for testing (instrument model: Mettler-Toledo FE20).

[0180] The performance test results of the negative electrode materials prepared in the above examples and comparative examples are shown in Table 1, and the electrochemical test results of the negative electrode materials prepared in the examples and comparative examples in secondary batteries are shown in Table 2.

[0181] Table 1 Performance test results of negative electrode materials prepared in various embodiments and comparative examples

[0182] Table 2 Electrochemical performance results of batteries prepared in various embodiments and comparative examples

[0183] Through the data analysis of Examples 1-8 and Comparative Example 1, the negative electrode material standard deviations k1 and k2, as well as the setting of k2 / k1, not only quantify the distribution uniformity of the metal M element in the negative electrode material, but also solve the technical difficulty in achieving uniform distribution of the M element both within a single particle and between multiple particles in the prior art, significantly improving the electrochemical performance of the negative electrode material and the secondary battery using the same. The negative electrode materials of Examples 1-8 not only have high initial efficiency and excellent cycle performance, but also have a low volume expansion rate.

[0184] In addition, FIG1 also shows the XRD spectrum of the negative electrode material prepared in Example 1, wherein the MgSiO3 (610) diffraction peak appears between 30°-31°, and the Si (220) diffraction peak appears between 45°-50°, and the ratio of the two diffraction peak intensities α=I Si(220) / I MgSiO3(610) , α is 0.9.

[0185] Figures 2 and 3 show, respectively, an SEM / EDS scan of the Mg element in a cross-section of a particle of the negative electrode material prepared in Example 1, and a high-magnification SEM image of the cross-section of the particle. These images show that the metal silicate domains are uniformly dispersed with the nanosilicon domains and silicon oxide domains. Based on the XRD spectrum of the negative electrode material and the Scherrer equation (Kλ = 0.9λ / Bcosθ), the average size of the MgSiO3 grains on the (610) plane is calculated to be 11.1 nm.

[0186] Figures 4 and 5 show the cycle-capacity diagram and cycle-expansion diagram of the secondary batteries prepared in Example 1 and Comparative Example 1, respectively. By comparison, it can be seen that the negative electrode material prepared in the present application has better cycle performance and lower cycle expansion performance.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0188] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form different embodiments. For example, any of the above-described claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A negative electrode material, characterized in that: It comprises a silicon-based core and a carbon layer coated on at least a part of the surface of the silicon-based core, wherein the silicon-based core comprises nano-silicon and a silicate containing a metal M element; The negative electrode material is subjected to cross-section and energy spectrum analysis, and the cross-sections of n1 particles are randomly selected for surface scanning analysis to obtain n1 M element content values, and the standard deviation k1 of the n1 M element content values ​​is calculated, where k1≤10; n2 points are randomly selected inside the cross-section of any particle for point scanning analysis to obtain n2 M element content values, and the standard deviation k2 of the n2 M element content values ​​is calculated, where k2≤5 and 0.1<k2 / k1≤1, wherein n1 is a natural number greater than or equal to 5, and n2 is a natural number greater than or equal to 5.

2. The negative electrode material according to claim 1, characterized in that At least one of the following conditions is met: (1) The silicon-based core also includes silicon oxide; (2) The D50 of the silicon-based core is 5.0 to 5.5 μm; (3) The size of the silicon grains of the nano-silicon is less than 10 nm; (4) The pH value of the negative electrode material satisfies 7<pH≤10.

5.

3. The negative electrode material according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) The M element includes at least one metal element from Groups IA, IIA, and IIIA; (2) The M element includes at least one of lithium, sodium, potassium, magnesium, calcium and aluminum.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that At least one of the following conditions is met: (1) The true density of the negative electrode material is 2.0 g / cm 3 -2.6g / cm 3 ; (2) The specific surface area of ​​the negative electrode material is 2 m 2 / g-10m 2 / g.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that In the negative electrode material, the mass proportion of the M element is 3%-20%, and the mass proportion of the carbon layer is 1%-20%.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that At least one of the following conditions is met: (1) When the silicate containing the metal M element includes MgSiO3, in the XRD spectrum of the negative electrode material, the diffraction peak of MgSiO3 (610) is between 30° and 31°, the diffraction peak of Si (220) is between 45° and 50°, and the ratio of the two diffraction peak intensities α=I Si(220) / I MgSiO3(610) , 0<α<2; (2) When the silicate containing the metal M element includes MgSiO3, according to the XRD spectrum of the negative electrode material and the Scherrer formula Kλ=0.9λ / Bcosθ, it is calculated that the average size of the MgSiO3 grains on the (610) crystal plane is ≤30nm.

7. The negative electrode material according to claim 2, characterized in that At least one of the following conditions is also met: (1) The nano-silicon is dispersed in the silicon oxide; (2) The nano-silicon or the silicon oxide is surrounded by the silicate containing the metal M element.

8. The negative electrode material according to any one of claims 1 to 7, characterized in that The thickness of the carbon layer is 50nm-500nm.

9. A method for preparing the negative electrode material according to any one of claims 1 to 8, characterized in that: include: Placing a metal source material and a pre-disproportionated silicon dioxide material at different positions in the same vacuum heating system for heating and evaporation respectively to obtain a metal source gas and silicon dioxide gas; Mixing and condensing the silicon dioxide gas and the metal source gas to obtain a core material; The core material is subjected to carbon coating treatment to obtain the negative electrode material.

10. The preparation method according to claim 9, characterized in that: At least one of the following conditions is met: A. The preparation method of the pre-disproportionated silicon oxide material comprises: pre-disproportionating an amorphous SiO block to obtain silicon oxide containing disproportionated silicon grains <20 nm, and then pulverizing or crushing to obtain pre-disproportionated silicon oxide powder or particles; C. The metal source material includes at least one of a magnesium source material, a lithium source material, a sodium source material, a potassium source material, a calcium source material, and an aluminum source material; F. The temperature at which the pre-disproportionated silicon dioxide material is heated and evaporated is 1000°C-1500°C.

11. The preparation method according to claim 9 or 10, characterized in that: At least one of the following conditions is met: G. The temperature at which the metal source material is heated and evaporated is 600° C.-1350° C.; J. After the condensation, the method further comprises: collecting the precursor material after the condensation, crushing and classifying the precursor material to obtain the core material, wherein the volume distribution D50 of the core material is 5.0 to 5.5 μm; K. The carbon coating treatment includes gas phase coating, liquid phase coating or solid phase coating.

12. The preparation method according to claim 11, characterized in that: At least one of the following conditions is met: M. The temperature of the pre-disproportionation treatment is 1000°C-1200°C; N. The holding time of the pre-disproportionation treatment is 3h-10h; Q. The gas phase coating gas includes a carbon source gas and a carrier gas.

13. The preparation method according to claim 12, characterized in that: At least one of the following conditions is met: R. The temperature of the gas phase coating is 700°C-1000°C; S. The carbon source gas includes at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene; U. The gas phase covering gas also includes hydrogen, and the atmosphere ratio of the carbon source gas, the hydrogen gas and the carrier gas is (2-15):1:3.

5.

14. The preparation method according to any one of claims 9 to 13, characterized in that: The silicon dioxide gas and the metal source gas are mixed under a vacuum condition with a vacuum degree of 0-100 Pa.

15. A secondary battery, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 8.

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