Negative electrode material, manufacturing method thereof, and secondary battery

Abstract

The present invention provides a negative electrode material, a manufacturing method thereof, and a secondary battery, and relates to the technical field of battery materials. The negative electrode material includes a silicon-based core and a carbon layer covering at least a portion of the surface of the silicon-based core, the silicon-based core including nanosilicon and a silicate containing a metal M element; and when the negative electrode material is cut and energy spectrum analysis is performed on the cut surface, k1≦10, k2≦5, and k3≦0.1

Description

[Technical Field]

[0001] This application claims priority from Chinese Patent Application No. 2023114339212, filed on October 31, 2023. The entire text of the above Chinese patent application is incorporated herein by reference. [Background technology]

[0002] The present application relates to the technical field of battery materials, and in particular to a negative electrode material, a method for producing the same, and a secondary battery. Summary of the Invention

[0003] Among the many anode materials, silicon oxide anode materials are currently a high-specific-capacity anode material with relatively mature application technology. Compared to graphite-based anode materials, silicon oxide anode materials have a higher specific capacity (2100 mAh / g). Compared to crystalline silicon anode materials, silicon oxide anode materials overcome the problem of large volume expansion, significantly improving the cycle life of the anode material. However, because the formation of Li2O and lithium silicate during the initial lithium absorption process in silicon oxide materials is irreversible, the lithium loss caused by these irreversible reactions results in low initial coulombic efficiency, making it necessary to design secondary batteries with excess positive electrode capacity. This offsets the high specific capacity of the anode, reducing the energy density of the secondary battery while increasing the consumption cost of the secondary battery's positive electrode.

[0004] To solve the problem of low initial charge / discharge Coulombic efficiency, the oxygen content of silicon oxide can be reduced in advance to reduce the consumption of lithium ions in the positive electrode material due to the irreversible phase Li2O formed during the first charge, thereby improving the energy density of the secondary battery. A common method involves adding an exogenous reducible metal element to react with the oxygen element in the silicon oxide and reduce it to form nanosilicon. This improves the Coulombic efficiency of the material, and the metal oxide or silicate formed in the reduction reaction acts as a buffer matrix to accommodate stress fractures caused by volume changes during the lithium alloying and dealloying processes of the nanosilicon, thereby maintaining structural integrity and improving the long-term cycling performance of the material.

[0005] For example, in a method for improving the initial Coulombic efficiency of silicon oxide by mixing silicon monoxide powder and metallic magnesium powder and heating them to perform a reduction reaction through solid-state doping, the physical and chemical properties of the magnesium silicate in the anode material produced by this method are relatively stable, and the stability of the aqueous slurry is excellent. However, because the thermal reduction reaction of magnesium is a diffusion-controlled reaction, the composition of the resulting product is closely related to the diffusion rate of magnesium vapor. When the powders are mixed at the micron level, the magnesium vapor generated by heating initiates a reaction from the outside of the silicon monoxide particles and gradually diffuses into the particles, easily resulting in localized excess magnesium, which can lead to the production of by-products such as magnesium silicide and magnesium oxide, and rapid growth of silicon crystal grains. Furthermore, because the diffusion rate of magnesium vapor into solids is generally slow, it is difficult for magnesium to be completely and uniformly incorporated into the silicon monoxide material, and the distribution of magnesium in the reduction product is relatively uneven.

[0006] A method for in-situ gaseous magnesium doping has been disclosed in which a mixture of silicon and silicon dioxide and metal M is mixed followed by vacuum co-evaporation and condensation. The initial efficiency of the anode material produced by this method reaches over 83%, significantly improving the effective lithium ion utilization rate in the cathode material of secondary batteries, and the aqueous slurry has good stability. However, because the reaction in which the silicon and silicon dioxide mixture used in this method produces silicon oxide vapor under heated conditions is a solid-solid interfacial reaction, the amount of silicon oxide vapor produced varies greatly as the reaction progresses. Therefore, during the mixing and deposition process of magnesium vapor and silicon oxide vapor, the local magnesium uptake ratio is uncontrollable, which is likely to lead to uneven growth of silicon crystal grains and affect the cycle life and safety of the anode material.

[0007] Whether solid-state doping or in-situ gaseous doping is used, the resulting negative electrode material often has uneven distribution of the doping element and uneven growth of silicon crystal grains, i.e., it is difficult to simultaneously achieve uniform distribution of the doping element among both single particles and multiple particles. Therefore, there is a need to actively seek new negative electrode materials to improve electrochemical performance. [Problem to be solved by the invention]

[0008] The present application aims to provide a negative electrode material, a method for producing the same, and a secondary battery, which achieves nano-level doping of metal M using in-situ doping technology, obtains a negative electrode material in which metal M is uniformly distributed, reduces the oxygen content in the negative electrode material, and further improves initial efficiency and cycle performance when applied to batteries. [Means for solving the problem]

[0009] To achieve the above object, the technical solution of the present application is as follows.

[0010] In a first aspect, the present application provides the following negative electrode material. The negative electrode material includes a silicon-based core and a carbon layer covering at least a part of the surface of the silicon-based core, and the silicon-based core includes nanosilicon and a metal M element-containing silicate; When performing energy spectrum analysis on the cut surface by cutting the negative electrode material, randomly select the cut surfaces of n1 particles for surface analysis to obtain the values of the M element contents of n1 particles, calculate the standard deviation k1 of the values of the M element contents of n1 particles, and k1 ≤ 10; randomly select n2 points from the cut surface of any of the above particles for point analysis to obtain the values of the M element contents of n2 particles, calculate the standard deviation k2 of the values of the M element contents of n2 particles, and k2 ≤ 5 and 0.1 < k2 / k1 ≤ 1, where n1 is a natural number of 5 or more, and n2 is a natural number of 5 or more.

[0011] In a second aspect, the present application further provides a method for manufacturing the negative electrode material of the first aspect, including the following. Place the metal source material and the pre-disproportionated silicon monoxide material at different positions in the same vacuum heating system, perform heating evaporation respectively to obtain metal source gas and silicon monoxide gas; Mix and condense the silicon monoxide gas and the metal source gas to obtain a core material; Perform carbon coating treatment on the core material to obtain a negative electrode material.

[0012] In a third aspect, the present application further provides a secondary battery including the negative electrode material of the first aspect or the negative electrode material manufactured by the manufacturing method of the second aspect.

Advantages of the Invention

[0013] The beneficial effects of the present application are as follows.

[0014] The metallic M element-containing silicate in the negative electrode material system of the present application can be found to have a certain distribution characteristic of the M element through energy spectrum analysis, and the metallic M element-containing silicate can effectively separate nano-silicon domains and silicon oxide domains, reducing the aggregation of silicon clusters caused by electrochemical sintering of nano-silicon during charge-discharge cycling and the resulting performance degradation of the negative electrode material, allowing the negative electrode material to have both high initial efficiency and excellent cycle performance. Furthermore, the silicate can act as a buffer matrix for nano-silicon and silicon oxide during the lithium absorption-desorption process, buffering the volume change caused by lithium absorption-desorption, thereby ensuring low expansion of the negative electrode material. [Brief explanation of the drawings]

[0015] In order to more clearly explain the technical solutions of the embodiments of the present application, the following briefly introduces drawings necessary for the embodiments. Obviously, the following drawings only illustrate some embodiments of the present application, and therefore should not be considered as limiting the scope of the present application. [Figure 1] 1 shows an XRD pattern of the negative electrode material produced in Example 1. [Figure 2] 1 is a SEM / EDS scanning image of a cross section of a particle of the negative electrode material produced in Example 1. FIG. [Figure 3] 2 is a high-magnification SEM image of a cross section of a particle of the negative electrode material produced in Example 1. FIG. [Figure 4] FIG. 2 is a graph showing the cycle capacity performance of the secondary batteries manufactured in Example 1 and Comparative Example 1. [Figure 5] 1 is a graph showing the cycle expansion performance of the secondary batteries manufactured in Example 1 and Comparative Example 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms used in this specification are explained below.

[0017] "Manufactured from" is synonymous with "comprising." As used herein, the terms "comprise," "include," "have," "contain," or any other variation thereof, are intended to cover a non-exclusive "comprising." For example, a composition, step, method, product, or device that includes recited elements is not necessarily limited to those elements, but may include other elements not expressly recited or inherent in the composition, step, method, product, or device. The conjunction "composed of" excludes any unrecited element, step, or ingredient.

[0018] When an equivalent amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range limited by a series of preferred upper and lower limits, it should be understood to specifically disclose all ranges formed by any combination of any upper or preferred upper limit with any lower or preferred lower limit, regardless of whether the range is disclosed alone. For example, if a range of "1 to 5" is disclosed, it should be interpreted as including ranges such as "1 to 4," "1 to 3," "1 to 2," "1 to 2 and 4 to 5," "1 to 3 and 5," etc. When a range of numerical values ​​is described herein, unless otherwise specified, it is intended that the range include the endpoints thereof, and all integers and fractions within the range.

[0019] In the examples, unless otherwise specified, the terms "parts" and "percentages" used mean "parts by mass" and "% by mass", respectively.

[0020] "Parts by mass" refers to a basic unit of measurement that expresses the mass proportion relationship of multiple components, and 1 part can represent any unit mass, for example, 1 g or 2.689 g. If the parts by mass of component A are a parts and the parts by mass of component B are b parts, this indicates that the ratio of the mass of component A to the mass of component B is a:b. Alternatively, this indicates that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number that indicates a multiplicative factor). Note that, unlike parts by mass, the total value of the parts by mass of all components is not limited to 100 parts.

[0021] "And / or" is used to indicate that either or both of the stated items may occur; for example, "A and / or B" includes "A and B" and "A or B."

[0022] In order to obtain a silicon oxide anode material with excellent performance, prior art research has uniformly doped silicon powder and silicon fine powder with gaseous lithium generated by the oxidation-reduction reaction of a lithium-containing oxide or silicate with a reducing agent to produce a silicon-based composite anode material. While the initial efficiency of the resulting anode material can reach approximately 90%, the silicon crystal grains in the resulting anode material are large, resulting in poor cycle performance. Alternatively, silicon powder, SiO2 powder, magnesium powder, and LiCl powder are placed in different chambers of the same vacuum system, heated and sublimated, and cooled to obtain a modified precursor co-doped with magnesium and lithium, which is then coated with a conductive layer. The resulting anode material not only has a high initial efficiency, but also combines the high ionic conductivity of lithium silicate and the high bonding strength of magnesium silicate, further improving the cycle life of the material. However, the production conditions are strict, and the anode material expands too much during charging and discharging. Alternatively, silicon-based anode materials can be produced by mixing a mixture of silicon and silicon dioxide with metal M and then co-evaporating and condensing in vacuum. This improves the initial efficiency of the material, but the resulting silicon crystal grains are not uniform in size due to the poor uniformity of the vapor-evaporation and mixing process, resulting in poor electrical performance and certain safety risks.

[0023] The primary objective of the present application is to provide an anode material in which the metal M element has a certain distribution characteristic, thereby solving the problem of two-phase and multi-phase vapor mixing, and further ensuring that the anode material has high initial efficiency, excellent cycle performance, and low expansion performance.

[0024] In a first aspect, the present application provides an anode material comprising a silicon-based core and a carbon layer covering at least a portion of the surface of the silicon-based core, wherein the silicon-based core comprises nanosilicon and a silicate containing a metal M element.

[0025] Here, the negative electrode material is cut, and energy spectrum analysis is performed on the cut surface. In particular, the distribution of element M in the core is analyzed, and the results are calculated to obtain the k1 value and the k2 value.

[0026] Generally, the negative electrode material is a powder material and includes particles formed of a plurality of silicon-based cores and a carbon layer covering at least a part of the surface of the silicon-based cores. Specifically, n1 particles of the negative electrode material are randomly selected and surface-cut, and surface scanning energy spectrum analysis is performed on the cut surfaces of the n1 particles to obtain n1 values of the content of element M. When the standard deviation k1 of these n1 values of the content of metal element M is calculated, k1≤10. n2 points are randomly selected from the cut surfaces of any of the above particles for point analysis to obtain n2 values of the content of element M. When the standard deviation k2 of these n2 values of the content of element M is calculated, k2≤5, and the k1 value and the k2 value further satisfy 0.1<k2 / k1≤1. Here, n1 is a natural number of 5 or more, and n2 is a natural number of 5 or more. The above content is the mass content.

[0027] The negative electrode material that satisfies this condition can effectively separate metal silicate in its silicon-based core into nano-silicon domains and silicon oxide domains, reducing the problem of performance degradation of the negative electrode material due to the aggregation of silicon clusters.

[0028] When the negative electrode material simultaneously satisfies the above k1 and k2 ranges, the metal M element-containing silicate is uniformly distributed in the core, and coats and isolates nano-silicon or silicon oxide, reducing the problem of process gas generation due to the exposure of active silicon and the sintering problem of nano-silicon clusters during the cycle process, thereby resulting in a more stable material structure and reducing the consumption of active silicon during the cycle process.

[0029] In the present invention, the setting of the standard deviations k1 and k2 quantifies the distribution uniformity of the metal M element in the negative electrode material and limits the regular relationship between the standard deviation of the M element content inside a single particle (k2) and between multiple particles (k1), thereby improving the performance of the negative electrode material.

[0030] Limiting the standard deviation k2, which indicates uniform distribution within a single particle, to 5 or less indicates that the metal M element is uniformly dispersed throughout the particle at the nano-level within a single particle. Limiting the standard deviation k1, which indicates uniform distribution among multiple particles, to 10 or less means that the content distribution of the M element among different particles is also fairly uniform. This indicates that the metal M element is not only uniformly distributed within a single particle, but also has good consistency in the particle assembly of the entire negative electrode material, avoiding problems caused by differences in the content of the M element among different particles.

[0031] Furthermore, limiting the k2 / k1 ratio to 0.1 to 1 means that the uniformity within a single particle and among multiple particles is balanced, i.e., the distribution uniformity of the M element within a particle and among multiple particles is favorable, with no significant discrepancy. Setting this ratio avoids two extreme situations: one where the M element is distributed uniformly within a single particle but not among particles, and the other where the M element is uniform throughout but not among particles. In prior art, it has been difficult to ensure both of these uniformities simultaneously, whether through solid-phase doping or gaseous doping, especially when there are significant differences in particle size, morphology, or internal structure, making it difficult to achieve a consistent distribution of the M element. The present invention not only achieves uniform doping of the M element at the nano-level, but also maintains such uniformity within a single particle and among multiple particles, effectively resolving the problems of the prior art.

[0032] 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 silicate and the effective separation and protection effects of the metal silicate on nano-silicon and silicon oxide. From the above, the setting of the standard deviations k1 and k2 and k2 / k1 of the present invention quantifies the distribution uniformity of the metal M element in the negative electrode material, and solves the technical problem that it is difficult to simultaneously achieve the uniform distribution of the M element inside a single particle and between multiple particles in the prior art, and significantly improves the electrochemical performance of the negative electrode material and the secondary battery using the same.

[0033] The metal M element-containing silicate can be represented as (MO) n ·SiO2. In a preferred embodiment, in the negative electrode material of the present application, the silicate with a low proportion of (MO) n and a high proportion of SiO2 is the main silicate phase. Taking the silicate of metal magnesium 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 is relatively low, but when the content of Mg2SiO4 (2MgO·SiO2) is relatively high, Mg2SiO4 hydrolyzes to generate more OH - to generate, and further cause a higher pH. OH - and the exposed active Si react to easily generate H2, thereby reducing the initial efficiency of the battery capacity, and the generated gas also causes serious processing problems during the preparation and coating of the battery slurry, and may lead to safety risks such as battery swelling, failure, and rupture. Therefore, when 0 < m(Mg2SiO4) / m(MgSiO3) ≤ 1, the ability to cause an increase in the pH value is weak, and the pH value range of the negative electrode material is stably maintained within an appropriate range. As a result, the exposed Si in the negative electrode material due to too high pH value reacts with OH - in the aqueous slurry to generate H2, reducing the problems such as attenuation of the initial efficiency of the capacity and generation of processing gas.

[0034] Therefore, when the metal M element-containing silicate has MgSiO3 as the main component, H2SiO3 generated by the hydrolysis of MgSiO3 causes the alkalinity of the slurry to be relatively weak. When the content ratio of MgSiO3 is relatively low and the ratio of Mg2SiO4 is relatively high, a large amount of Mg2SiO4 is hydrolyzed to generate H4SiO4, and at the same time, more OH - is generated, which causes the alkalinity of the slurry to increase, and OH - reacts with the active silicon exposed on the negative electrode material to generate H2, which further affects the safety performance of the battery.

[0035] In one preferred embodiment of the present application, the silicon-based core of the negative electrode material further contains silicon oxide. More preferably, nano-silicon is dispersed in the silicon oxide, and the periphery of the nano-silicon or silicon oxide is coated with a metal M element-containing silicate. Through the multiple protection of silicon oxide and metal silicate, the exposure of active silicon can be further reduced, and the volume expansion rate during the charge and discharge process can be reduced.

[0036] The silicon oxide can be represented by the general formula: SiO x (0 < x ≤ 2, for example, 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2 or a numerical range formed by any combination of two of the above numerical values). The silicon oxide may be a material in which silicon particles are dispersed in SiO2, or a material having a tetrahedral structural unit in which silicon atoms are located at the center of the tetrahedral structural unit and silicon atoms and / or oxygen atoms are located at the four vertices of the tetrahedral structural unit.

[0037] In one 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.

[0038] In one 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.

[0039] By controlling these dimensions of the negative electrode material within the above ranges, the size of the silicon crystal grains can be made more uniform, the electrical performance and safety performance can be improved, the particle size uniformity of the manufactured negative electrode material can be improved, and furthermore, the negative electrode material has a high initial efficiency and excellent cycle performance and has a low expansion performance.

[0040] In one preferred embodiment of the present application, the pH value of the negative electrode material of the present application satisfies 7 < pH ≤ 10.5, and for example, it may be 7.5, 8, 8.5, 9, 9.5, 10 or 10.5. More preferably, the pH value satisfies 7 < pH ≤ 10.

[0041] If the pH value in the negative electrode material is too high, when preparing the negative electrode material as a negative electrode slurry, the exposed Si reacts with OH in the slurry to generate H2, thereby causing problems such as the generation of bubbles during slurry coating and the problem that the alkalinity is too high and the performance of the adhesive deteriorates, further causing problems such as the deterioration of cycle performance, the attenuation of the initial efficiency of battery capacity, and the use safety of the battery. Since the pH value of the negative electrode material of the present application is 10.5 or less, the generation of gas is significantly reduced, the performance of the battery is improved, and the problems of gas generation due to the reaction of active silicon with OH in an alkaline solution, the problem of bubbles during electrode coating, and the problem of deterioration of cycle performance due to the deterioration of the performance of the adhesive due to too high alkalinity are better solved. - -

[0042] In one preferred embodiment of the present application, the metal M element contains at least one metal element of Group IA, IIA, or IIIA.

[0043] In one preferred embodiment of the present application, the M element contains at least one of lithium, sodium, potassium, magnesium, calcium, and aluminum, and more preferably is a magnesium element.

[0044] ​​The silicate formed by the M element in the negative electrode material can better separate the nano-silicon domains and the silicon oxide domains, thereby further reducing the aggregation of silicon clusters during charging and discharging and further alleviating the problem of expansion caused by lithium absorption and desorption, thereby better improving the initial efficiency and cycle performance of the negative electrode material.

[0045] In one 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, 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 2.6 g / cm 3 More preferably, the true density is 2.3 g / cm 3 ~2.6g / cm 3 is.

[0046] The true density of the negative electrode material of the present invention is measured by gas adsorption dilatometry.

[0047] In one preferred embodiment of the present application, the specific surface area of ​​the negative electrode material is 2 m 2 / g~10m 2 / g, for example, 2m 2 / g, 4m 2 / g, 6m 2 / g, 8m 2 / g or 10m 2 / g.

[0048] Limiting the true density and specific surface area of ​​the negative electrode material to within the above ranges is advantageous for 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 ensuring high energy density and good long-term cycle performance.

[0049] In one preferred embodiment of the present application, the mass proportion of the M element in the negative electrode material is 3% to 20%, and may be, for example, 3%, 5%, 7%, 10%, 12%, 15%, 18% or 20%.

[0050] The M element in the above content is advantageous in that it plays a role in separating the nano-silicon domains and the silicon oxide domains in the form of silicate, further improving the initial efficiency and cycle performance of the negative electrode material.

[0051] In one preferred embodiment of the present application, the mass proportion of the surface carbon layer of the negative electrode material is 1% to 20%, and may be, for example, 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%, and more preferably 3% to 7%.

[0052] In one preferred embodiment of the present application, the thickness of the surface carbon layer is 50 nm to 500 nm, and may be, for example, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm.

[0053] When the mass fraction and thickness of the carbon layer are within the above ranges, it is advantageous to reduce the problems of gas generation and nanosilicon cluster sintering due to exposure of active silicon in the silicon-based core, make the structure of the negative electrode material more stable, and further reduce the consumption of active silicon during the cycling process, thereby advantageously obtaining a negative electrode material with significantly improved initial efficiency and cycling performance.

[0054] In one preferred embodiment of the present application, when the silicate containing metal M element contains MgSiO3, in the XRD pattern of the negative electrode material, the diffraction peak of MgSiO3 (610) is at 30° to 31°, the diffraction peak of Si (220) is at 45° to 50°, and the ratio of the intensities of the two diffraction peaks is α=I Si(220) / I MgSiO3(610), satisfying 0<α<2. Under these conditions, the silicate formed in the negative electrode material can better separate the nano-silicon domains and the silicon oxide domains, thereby further reducing the aggregation of silicon clusters during charging and discharging and further mitigating the problem of expansion caused by lithium absorption and desorption, thereby better improving the initial efficiency and cycle performance of the negative electrode material.

[0055] In one preferred embodiment of the present application, when the silicate containing metal M element contains MgSiO3, the average size of the MgSiO3 crystal grains on the (610) plane is calculated to be ≦30 nm using the XRD pattern of the negative electrode material and Scherrer's equation: Kλ=0.9λ / Bcosθ. + This is beneficial to the formation of conductive paths and further reduces the high resistance caused by an excessively thick MgSiO3 layer.

[0056] In a second aspect, the present application further provides a method for producing the negative electrode material of the first aspect, comprising: S1: The metal source material and the pre-disproportionated silicon monoxide material are placed at different positions in the same vacuum heating system, and are heated and evaporated to obtain the metal source gas and the silicon monoxide gas, respectively; S2: Mix and condense silicon monoxide gas and metal source gas to obtain core material; S3: The core material is subjected to a carbon coating process to obtain the negative electrode material.

[0057] The present method for manufacturing anode materials is simple and easy to operate, allowing for rapid industrialization. Using in-situ doping technology, nano-level metal doping is achieved through the mixing and deposition of a gaseous metal source and a gaseous silicon oxide, resulting in anode materials with uniform metal silicate distribution. In particular, the use of pre-disproportionated silicon monoxide material in the manufacturing process allows for continuous and stable generation of silicon monoxide vapor. After mixing with the stably generated metal source gas, the resulting anode material has uniform distribution of each substance, resulting in superior performance. This method reduces the problem of using a mixture of silicon and silicon dioxide as raw materials, where the interfacial reaction is affected by the material contact effect, resulting in unstable silicon monoxide evaporation and uneven doping of each substance in the resulting anode material.

[0058] Referring to the second aspect, in one preferred embodiment of the present application, the method for producing a pre-disproportionated silicon monoxide material in S1 includes pre-disproportionating an amorphous SiO mass to obtain silicon monoxide containing disproportionated silicon grains having a grain size of less than 20 nm, preferably less than 10 nm, and then subjecting the silicon grains to a pulverization or crushing treatment to obtain pre-disproportionated silicon monoxide powder or particles.

[0059] In the method for producing the negative electrode material of the present invention, a silicon monoxide source is used and subjected to a preliminary disproportionation treatment, and the silicon monoxide and SiO x appears in a form that is uniformly dispersed at the nano level at all points, with silicon crystal grain sizes of less than 20 nm, reducing the effect of changes in reaction rate due to changes in contact area in the interfacial reaction and enabling the continuous and stable generation of silicon monoxide vapor. After mixing with the continuously and stably generated magnesium vapor, a silicon oxide anode product with uniform distribution, better performance, and higher initial efficiency is obtained.

[0060] More preferably, the preliminary disproportionation treatment is carried out in an atmosphere of an inert gas containing at least one of nitrogen gas, argon gas, and helium gas.

[0061] More preferably, the temperature of the preliminary disproportionation treatment is 1000°C to 1200°C, for example, 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C, and the temperature retention time is 3 hours to 10 hours, for example, 3 hours, 5 hours, 6 hours, 8 hours, or 10 hours. More preferably, the preliminary disproportionation treatment is performed by isothermal retention at 1000°C for 10 hours.

[0062] The above conditions are advantageous for more uniform dispersion and contact of silicon and silicon oxide in the silicon monoxide source, thereby enabling more stable generation of silicon monoxide vapor, providing a good material base for the subsequent process of forming the negative electrode material, and improving the initial efficiency and cycle performance of the negative electrode material.

[0063] The reason for selecting a pre-disproportionated silicon monoxide material as the silicon monoxide source in this application is to reduce the instability of SiO vaporization caused by the contact effect of materials during the interfacial reaction when conventional silicon and silicon dioxide are selected as raw materials. A homogenized disproportionation process was performed on amorphous SiO to obtain silicon monoxide with disproportionated silicon crystal grains of less than 20 nm, resulting in a silicon monoxide vapor source in which Si and SiO2 are uniformly dispersed at the nanoscopic level. This stabilizes the rate of silicon monoxide vapor generation throughout the entire reaction process, and achieves relatively uniform generation, mixing, condensation, and deposition of silicon monoxide gas and metal M source gas.

[0064] In one preferred embodiment of the present application, the size of the pre-disproportionated silicon monoxide material in S1 is 10 cm or less, for example, 10 μm, 100 μm, 1 mm, 1 cm, 5 cm, or 10 cm, which is advantageous for further reducing the influence of changes in reaction rate due to changes in the contact area of ​​the interfacial reaction and for steadily generating silicon monoxide vapor to continue participating in the reaction.

[0065] In one 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.

[0066] More preferably, the magnesium source material includes at least one of metallic magnesium powder, metallic magnesium ingot, metallic magnesium particles, a mixture of a magnesium-containing oxide and a reducible substance, and a mixture of a magnesium-containing salt and a reducible substance.

[0067] In one 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, and more preferably magnesium vapor.

[0068] Under the above conditions, the formed metal silicate can better separate the nano-silicon domains and the silicon oxide domains, which can better improve the initial efficiency and cycle performance of the negative electrode material.

[0069] In one preferred embodiment of the present application, when the metal source material and the pre-disproportionated silicon monoxide material are heated and evaporated at different positions in the same vacuum heating system, the pre-disproportionated silicon monoxide material may be placed in a first vacuum heating chamber and heated and evaporated to obtain silicon monoxide gas, and the metal source material may be placed in a second vacuum heating chamber and heated and evaporated to obtain metal source gas.

[0070] Specifically, an inert gas is introduced into a first vacuum heating chamber and heated to a temperature of 1000°C to 1500°C to obtain silicon monoxide gas, and the temperature may be, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, or 1500°C.

[0071] An inert gas is introduced into the second vacuum heating chamber and heated to a temperature of 600°C to 1350°C (preferably 700°C to 1300°C) to obtain a metal source gas, and the temperature may be, for example, 700°C, 800°C, 900°C, 1000°C, 1100°C, or 1200°C.

[0072] It is understood that within the same vacuum heating system, the metal source material and the pre-disproportionated silicon monoxide material may have the same or different heating vaporization temperatures.

[0073] The above conditions are advantageous for sufficiently evaporating the pre-disproportionated silicon monoxide material and the metal source material at a more suitable rate to obtain the corresponding gaseous raw materials, and can further reduce the occurrence of locally non-uniform evaporation and deposition reactions, thereby improving the structural stability and electrochemical performance of the negative electrode material.

[0074] In one preferred embodiment of the present application, the mixing of the two types of gases in S2 is carried out under vacuum conditions with a vacuum degree of 0 to 100 Pa.

[0075] In one preferred embodiment of the present application, the temperature of condensation in S2 is 500°C to 900°C, and may be, for example, 500°C, 600°C, 700°C, 800°C, or 900°C.

[0076] More preferably, the condensation method includes at least one of water cooling and air cooling.

[0077] Specifically, the condensation deposition chamber is evacuated, and when the degree of vacuum reaches 100 Pa or less and the temperature of the condensation chamber reaches 500°C to 900°C, the gases in the two vacuum heating chambers are introduced into the condensation deposition chamber and mixed, and then a precursor mixture of silicon oxide and metal source is collected on a condenser.

[0078] Under the above conditions, the pre-reaction is favorable after the two-phase gas is mixed and condensed, the deposition state is more stable, the probability of the product being oxidized after exposure to air is further reduced, and the utilization rate of the M metal source is also higher for initial efficiency improvement.

[0079] In one preferred embodiment of the present application, after condensation in S2, the condensed precursor material is collected, and the precursor material is further pulverized and classified to obtain a core material, and preferably, the volume distribution D50 of the core material is 5.0 to 5.5 μm.

[0080] More preferably, the pulverization method includes any one of mechanical pulverization, ball mill pulverization, and airflow pulverization.

[0081] Under these conditions, the particle size uniformity of the produced negative electrode material can be further improved, which is advantageous for the smooth progress of the subsequent slurrying process and for the improvement of the battery manufacturing and performance.

[0082] In one preferred embodiment of the present application, the carbon coating process in S3 includes vapor phase coating, liquid phase coating, or solid phase coating.

[0083] When producing a surface carbon layer by vapor phase coating, the gas required for vapor phase coating includes a carbon source gas and a carrier gas, and the temperature of vapor phase coating is 700°C to 1000°C, for example, 700°C, 800°C, 900°C, or 1000°C.

[0084] Preferably, the carbon source gas comprises at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene.

[0085] Optionally, the carrier gas contains at least one of nitrogen gas, argon gas, and helium gas, and the ratio of the carbon source gas, hydrogen gas, and carrier gas atmosphere is preferably (2-15):1:3.5, more preferably (2-3):1:3.5.

[0086] The above conditions are favorable for a more complete and uniform coating of the carbon material on the surface of the silicon-based core, and the nano-silicon or silicon oxide is coated and isolated, reducing the problem of process gas generation due to exposure of active silicon and the problem of nano-silicon cluster sintering during the cycle process, thereby resulting in a more stable material structure and reducing the consumption of active silicon during the cycle process.More preferably, in the vapor-phase coating process, in addition to the carbon source gas and carrier gas, a certain proportion of hydrogen gas can be introduced, mainly to adjust the structure of the carbon layer.

[0087] 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 produced by the method for producing the negative electrode material of the second aspect. The secondary battery of the present application uses the negative electrode material and has higher initial efficiency and excellent charge-discharge cycle performance.

[0088] More preferably, the secondary battery is a rechargeable battery with a non-aqueous electrolyte.

[0089] In this technical proposal, gaseous magnesium is used as the magnesium source, and the mixture is then deposited with gaseous silicon oxide to achieve nano-level magnesium doping, resulting in an anode material that matches the distribution characteristics of metal M and also meets a specific pH range. The oxygen content in the active material is then reduced by heat treatment, and the material is then powdered and carbon-coated to produce a silicon monoxide anode material with high initial efficiency.

[0090] Typically, but not exclusively, k1 is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range formed by a combination of any two of these numbers; k2 is 1, 2, 3, 4, 5, or a range formed by a combination of any two of these numbers; 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 formed by a combination of any two of these numbers; n1 is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, n2 is 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, or a range formed by a combination of any two of these numbers; n3 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 formed by a combination of any two of these numbers.

[0091] Typically, but not exclusively, 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 of values ​​formed by a combination of any two values ​​thereof.

[0092] Typically, but not limited to, the ratio of carbon source gas to hydrogen gas to carrier gas atmosphere 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 formed by combining any two of the numbers therein. [Example]

[0093] Hereinafter, the embodiments of the present application will be described in detail with reference to specific examples. However, those skilled in the art should understand that the following examples are merely for the purpose of illustrating the present application and do not limit the scope of the present application. Specific conditions not specified in the examples were general conditions or conditions provided by the manufacturer. Unless specified by manufacturer, the reagents or equipment used were conventional products that can be purchased commercially.

[0094] Example 1 The present application provides a negative electrode material, and a method for manufacturing the negative electrode material includes the following steps. 1) The amorphous SiO mass was pre-disproportionated at 1200°C in an argon gas atmosphere for 10 hours, cooled, and then pulverized to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 6.0 nm and a volume distribution D50 of 100 μm. The powder was then placed in the first vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 1400°C to obtain silicon monoxide gas; 2) The magnesium metal powder was placed in the second vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 700°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated to a vacuum of 10 Pa; 4) The gas obtained in the first vacuum heating chamber and the gas in the second vacuum heating chamber were introduced into a condensation deposition chamber with a vacuum of 10 Pa, and the precursor material was collected on a water-cooled substrate in the condensation deposition chamber at a temperature of 700°C; 5) The precursor of step 4) was pulverized to a volume distribution D50 = 5.5 μm by means of mechanical pulverization, classification, etc.; 6) The powder material obtained in step 5) was placed in a rotary furnace, heated to 900°C, and methane, hydrogen gas, and nitrogen gas as a carrier gas were introduced to adjust the atmosphere ratio to 2:1:3.5, and vapor coating was carried out for 8 hours; 7) The coated material was collected, dispersed, sieved, and demagnetized to obtain a composite negative electrode material containing silicon oxide.

[0095] This embodiment provides a secondary battery, and a specific manufacturing method of the secondary battery includes the following steps. The negative electrode material prepared in the above example, conductive carbon black, and PAA rubber were mixed in a mass ratio of 75:15:10 to prepare a negative electrode slurry, which was then coated on copper foil and dried to prepare a negative electrode. A lithium metal sheet was used as the counter electrode, and a button cell battery was assembled in an argon-filled glove box. The button cell battery was subjected to a charge-discharge test at a current density of 0.1 C in the charge-discharge range of 0.01 to 1.5 V. The initial reversible specific capacity and initial efficiency of the resulting battery were measured.

[0096] This embodiment further provides a secondary battery, and a specific method for manufacturing the secondary battery includes the following steps: Anode slurry was prepared using the same anode materials as in the previous example (Super-P:KS-6:CMC:SBR = 92:2:2:2:2), coated onto copper foil, and dried to prepare anode pieces. A button cell battery was assembled using a metallic lithium sheet as the counter electrode in an argon-filled glove box. The button battery was subjected to a charge-discharge test at a current density of 1C in the charge-discharge range of 0.01V to 1.5V, and the volume expansion rate and capacity retention rate of the battery after 50 cycles were measured. Furthermore, the expansion performance during the cycle process was studied using an in-situ expansion rate test method for the basic pouch battery.

[0097] Example 2 This embodiment provides a negative electrode material, and a manufacturing method of the negative electrode material includes the following steps: 1) The amorphous SiO mass was pre-disproportionated at 1200°C in an argon gas atmosphere for 10 hours, cooled, and then pulverized to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 6.0 nm and a volume distribution D50 of 100 μm. The powder was then placed in the first vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 1300°C to obtain silicon monoxide gas; 2) The magnesium metal powder was placed in the second vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 900°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated to a vacuum of 5 Pa; 4) The gas obtained in the first vacuum heating chamber and the gas in the second vacuum heating chamber were introduced into a condensation deposition chamber with a vacuum of 5 Pa, and the precursor material was collected on a water-cooled substrate in the condensation deposition chamber at a temperature of 800°C; 5) The precursor of step 4) was pulverized to a volume distribution D50 = 5.0 μm by means of mechanical pulverization, classification, etc.; 6) The powder material obtained in step 5) was placed in a rotary furnace, heated to 980°C, and methane, hydrogen gas, and argon gas as a carrier gas were introduced to adjust the atmosphere ratio to 3:1:3.5, and vapor-phase coating was carried out for 10 hours; 7) The coated material was collected, dispersed, sieved, and demagnetized to obtain a composite negative electrode material containing silicon oxide. The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0098] Example 3 This example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 1, with the following differences: In step 2), the calcium metal powder is placed in the second vacuum heating chamber of the vacuum heating system, and argon gas is introduced and heated to 1300°C. The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0099] Example 4 This example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 1, with the following differences: In step 1), the temperature of the pre-disproportionation treatment is set to 1000°C for 10 hours to obtain pre-disproportionated silicon monoxide powder having silicon-containing crystal grains of 5.5 nm. The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0100] Example 5 This example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 1, with the following differences: The vacuum level in step 3) is 50 Pa, and the precursor material is collected on a water-cooled substrate at 800°C in step 4). The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0101] Example 6 This example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 1, with the following differences: In step 1), the size of the pre-disproportionated silicon monoxide material is 5 cm chunks. The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0102] Example 7 This example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 1, with the following differences: 1) The amorphous SiO mass was pre-disproportionated at 1000°C in an argon gas atmosphere for 10 hours, cooled, and then pulverized to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 5.4 nm and a volume distribution D50 of 500 μm. The powder was then placed in the first vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 1000°C to obtain silicon monoxide gas; 2) The magnesium metal powder was placed in the second vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 600°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated until the vacuum level reached 0 Pa; 4) The gas obtained in the first vacuum heating chamber and the gas in the second vacuum heating chamber were introduced into a condensation deposition chamber with a vacuum of 0 Pa, and the precursor material was collected on a water-cooled substrate in the condensation deposition chamber at a temperature of 500°C; 5) The precursor of step 4) was pulverized to a volume distribution D50 = 5.5 μm by means of mechanical pulverization, classification, etc.; 6) The powder material obtained in step 5) was placed in a rotary furnace, heated to 700°C, and methane, hydrogen gas, and nitrogen gas (carrier gas) were introduced to adjust the atmosphere ratio to 2:1:3.5, and vapor coating was carried out for 8 hours; The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0103] Example 8 This example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 1, with the following differences: 1) The amorphous SiO mass was pre-disproportionated at 1200°C in an argon gas atmosphere for 3 hours, cooled, and then pulverized to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 6.0 nm and a volume distribution D50 of 100 μm. The powder was then placed in the first vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 1500°C to obtain silicon monoxide gas; 2) The magnesium metal powder was placed in the second vacuum heating chamber of the vacuum heating system, and argon gas was introduced and heated to 1350°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated to a vacuum of 100 Pa; 4) The gas obtained in the first vacuum heating chamber and the gas in the second vacuum heating chamber were introduced into a condensation deposition chamber with a vacuum of 100 Pa, and the precursor material was collected on a water-cooled substrate in the condensation deposition chamber at a temperature of 800°C; 5) The precursor of step 4) was pulverized to a volume distribution D50 = 5.5 μm by means of mechanical pulverization, classification, etc.; 6) The powder material obtained in step 5) was placed in a rotary furnace, heated to 1000°C, and methane, hydrogen gas, and nitrogen gas (carrier gas) were introduced to adjust the atmosphere ratio to 2:1:3.5, and vapor coating was carried out for 8 hours; The secondary battery according to this example was produced and evaluated in the same manner as in Example 1.

[0104] Comparative Example 1 This comparative example provides a negative electrode material, and the manufacturing method thereof is the same as that of Example 2, with the following differences. In step 1), silicon dioxide powder with a volume distribution D50 of 30 μm and silicon powder with a volume distribution D50 of 10 μm were directly and uniformly mixed in a molar ratio of 1:2, and then placed in the first vacuum heating chamber of the vacuum heating system. Argon gas was introduced and the mixture was heated to 1400°C; in step 4), the temperature of the water-cooled substrate in the condensation deposition chamber was 850°C; in step 6), only methane and nitrogen gas, the carrier gas, were introduced, and the atmosphere ratio was adjusted to 3:3.5. The secondary battery according to this comparative example was produced and evaluated in the same manner as in Example 1.

[0105] The negative electrode materials produced in the above Examples and Comparative Examples were subjected to energy spectrum analysis of Mg element, and the negative electrode material produced in Example 3 was subjected to energy spectrum analysis of Ca element to obtain k1 and k2 values, respectively.

[0106] The specific measurement method for energy spectrum analysis is to cut the produced negative electrode material particles using a Hitachi E-3500 ion polishing machine, observe the morphological structure of the cut surface using a Hitachi S-4800 cold cathode field emission scanning electron microscope, and observe the elemental composition and distribution of the cut surface of the negative electrode material particles in combination with an Oxford spectrometer in the UK.

[0107] The pH values ​​of the negative electrode materials produced in the examples and comparative examples were also measured. 5.00±0.01 g of a powder sample was weighed, added to 45 mL of pure water, and dispersed by stirring. After 5 minutes of ultrasonic treatment, the supernatant was measured using a Mettler FE20 pH meter and the pH value was read.

[0108] True density test: The true density of the negative electrode material was measured by the gas adsorption expansion method using a US Micro True Density Meter (AccuPyc II type).

[0109] Measurement of specific surface area: Using a specific surface area and pore analyzer (TriStar II type) manufactured by Mike, USA, nitrogen gas was adsorbed and the specific surface area of ​​the material was calculated by the BET method.

[0110] XRD measurement: XRD characterization was performed on the samples using an XRD diffractometer, with a scanning range of 10° to 90° and a scanning step width of 0.05°.

[0111] Carbon content %: Using infrared absorption method, refer to standard GB / T20123-2006.

[0112] Carbon layer thickness: Cross-sectional SEM analysis involves first sectioning the material using a Hitachi E3500 ion polisher and then analyzing it using a Hitachi S-4800 scanning electron microscope.

[0113] Mg mass content, Ca mass content: The test is performed using an ICP spectrometer (instrument model number: Agilent 5800VDV-ICP-OES).

[0114] pH value: Measurement is performed using a pH meter (instrument model number: Mettler-Toledo FE20).

[0115] Table 1 shows the performance test results of the negative electrode materials manufactured in the above Examples and Comparative Examples, and Table 2 shows the electrochemical test results of the negative electrode materials manufactured in the respective Examples and Comparative Examples in secondary batteries.

[0116] [Table 1]

[0117] [Table 2]

[0118] Analysis of the data from Examples 1 to 8 and Comparative Example 1 above reveals that the standard deviations k1 and k2, as well as the k2 / k1 setting for the negative electrode material, quantify the uniformity of distribution of the metal M element in the negative electrode material and solve the technical problem of the difficulty of simultaneously achieving uniform distribution of the M element within a single particle and among multiple particles in conventional technology, thereby significantly improving the electrochemical performance of the negative electrode material and secondary batteries using it. The negative electrode materials of Examples 1 to 8 not only have high initial efficiency, but also excellent cycle performance and a low volume expansion coefficient.

[0119] FIG. 1 also shows the XRD pattern of the negative electrode material prepared in Example 1, in which the diffraction peak of MgSiO3 (610) appears between 30° and 31°, the diffraction peak of Si (220) appears between 45° and 50°, and the intensity ratio of the two diffraction peaks, α=I Si(220) / I MgSiO3(610) , α is 0.9.

[0120] Figures 2 and 3 show an SEM / EDS area scan of Mg element in a cross section of a particle of the negative electrode material produced in Example 1, and a high-magnification SEM image of the cross section of the particle, respectively. As can be seen from the figures, the metal silicate domains, nanosilicon domains, and silicon oxide domains are uniformly dispersed and distributed. Using the XRD pattern of the negative electrode material and Scherrer's equation: Kλ = 0.9λ / Bcosθ, the average size of the MgSiO3 crystal grains on the (610) plane is calculated to be 11.1 nm.

[0121] 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. From the comparison, it can be seen that the negative electrode material prepared in the present application has better cycle performance and lower cycle expansion performance.

[0122] It should be noted that the above embodiments are only for illustrating the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art may still modify the technical solutions described in the above embodiments or make equivalent substitutions for some or all of the technical features therein, but it should be understood that such modifications or substitutions do not deviate from the essence of the corresponding technical solutions and the scope of the technical solutions of the embodiments of the present application.

[0123] Furthermore, those skilled in the art will understand that some embodiments of this specification may include some features included in other embodiments and not include other features, but that a combination of features from different embodiments constitutes a different embodiment within the scope of this application. For example, any of the embodiments to be protected above may be used in any combination. The information disclosed in this Background section is intended merely to enhance understanding of the overall background of this application, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art.

Claims

1. a silicon-based core containing nanosilicon and a metal M element-containing silicate; a carbon layer covering at least a portion of the surface of the silicon-based core, When cutting the negative electrode material and performing energy spectrum analysis on the cut surface, The cut surfaces of n1 particles were randomly selected and subjected to surface analysis to obtain the n1 values ​​of the M element content, and the standard deviation k1 of the n1 values ​​of the M element content was calculated, and k1≦10 was found. n2 points are randomly selected from a cut surface of any of the particles, and point analysis is performed to obtain the n2 values ​​of the M element content. The standard deviation k2 of the n2 values ​​of the M element content is calculated, and k2≦5; and 0.1<k2 / k1≦1, Here, n1 is a natural number of 5 or more, and n2 is a natural number of 5 or more.

2. The negative electrode material according to claim 1, wherein at least one of the following (1) to (4) is satisfied: (1) The silicon-based core further comprises a silicon oxide. (2) The silicon-based core has a D50 of 5.0 to 5.5 μm. (3) The size of the silicon crystal grains of the nanosilicon is less than 10 nm. (4) The pH value of the negative electrode material satisfies the condition 7<pH≦10.

5.

3. The negative electrode material according to claim 1 or 2, wherein at least one of the following (1) to (2) is satisfied: (1) The M element includes at least one metal element selected from the IA, IIA, and IIIA groups. (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 it satisfies at least one of the following (1) and (2): (1) The true density of the negative electrode material is 2.0 g / cm 3 ~2.6g / cm 3 is. (2) The specific surface area of ​​the negative electrode material is 2 m 2 / g to 10m 2 / g.

5. 5. The negative electrode material according to claim 1, wherein the mass ratio of the M element is 3% to 20%, and the mass ratio of the carbon layer is 1% to 20%.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that it satisfies at least one of the following (1) and (2): (1) The metal M element-containing silicate is MgSiO 3 In the case where the negative electrode material contains MgSiO 3 The diffraction peak of (610) is in the range of 30° to 31°, the diffraction peak of Si (220) is in the range of 45° to 50°, and the ratio of the intensities of the two diffraction peaks is α=I Si(220) / I MgSiO3(610) satisfies 0<α<2. (2) The metal M element-containing silicate is MgSiO 3 When the negative electrode material contains MgSiO 3 The average size of the crystal grains on the (610) plane is calculated to be ≦30 nm.

7. The negative electrode material according to claim 2, further satisfying at least one of the following (1) to (2): (1) The nanosilicon is dispersed in the silicon oxide. (2) The nanosilicon or the silicon oxide is coated with the silicate containing the metal M element.

8. 8. The negative electrode material according to claim 1, wherein the carbon layer has a thickness of 50 nm to 500 nm.

9. A method for producing the negative electrode material according to any one of claims 1 to 8, placing the metal source material and the pre-disproportionated silicon monoxide material at different positions in the same vacuum heating system, and subjecting them to thermal evaporation, respectively, to obtain a metal source gas and a silicon monoxide gas; mixing and condensing the silicon monoxide gas and the metal source gas to obtain a core material; and a core material coated with carbon to obtain the negative electrode material;

10. 10. The manufacturing method according to claim 9, wherein at least one of the following conditions A, C, and F is satisfied: A. The method for producing the pre-disproportionated silicon monoxide material includes pre-disproportionating amorphous SiO agglomerates to obtain silicon monoxide containing disproportionated silicon crystal grains of less than 20 nm, and then pulverizing or crushing the agglomerates to obtain pre-disproportionated silicon monoxide 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 for thermal evaporation of the pre-disproportionated silicon monoxide material is 1000°C to 1500°C.

11. 11. The manufacturing method according to claim 9, wherein at least one of the following conditions G, J, and K is satisfied: G. The temperature for thermal evaporation of the metal source material is 600°C to 1350°C. J. After the condensation, the condensed precursor material is collected, crushed, and classified to obtain the core material having a volume distribution D50 of 5.0 to 5.5 μm. K. The carbon coating process includes vapor coating, liquid coating, or solid coating.

12. The manufacturing method according to claim 11, wherein at least one of the following M, N, and Q is satisfied: M. The temperature of the preliminary disproportionation treatment is 1000°C to 1200°C. N. The incubation time for the preliminary disproportionation treatment is 3 to 10 hours. Q. The gas used in the vapor phase coating includes a carbon source gas and a carrier gas.

13. 13. The manufacturing method according to claim 12, wherein at least one of the following conditions is satisfied: R, S, and U. R. The temperature of the vapor coating is between 700°C and 1000°C. S. The carbon source gas includes at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene. U. The gas used for the vapor-phase coating further contains hydrogen gas, and the ratio of the carbon source gas, the hydrogen gas, and the carrier gas in the atmosphere is (2-15):1:3.

5.

14. 14. The method according to claim 9, wherein the silicon monoxide gas and the metal source gas are mixed under a vacuum condition with a vacuum degree of 0 to 100 Pa.

15. A secondary battery comprising the negative electrode material according to any one of claims 1 to 8.

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