Negative electrode material and method for manufacturing the same, 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 to Chinese patent application 2023114339212, filed on 31 October 2023. The entire text of the aforementioned Chinese patent application is incorporated herein by reference. [Background technology]

[0002] This application relates to the technology of battery materials, and more particularly to negative electrode materials, methods for manufacturing the same, and secondary batteries. [Overview of the Initiative]

[0003] Among many anode materials, silicon oxide anode materials are currently high-specific-capacity anode materials with relatively mature application technology. Compared to graphite-based anode materials, silicon oxide anode materials have a high specific capacity of 2100 mAh / g, and 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, since the formation process of Li2O and lithium silicate during the initial lithium absorption process of silicon oxide materials is irreversible, lithium loss due to these irreversible reactions lowers the initial Coulomb efficiency, requiring the design of secondary batteries to include an excessive positive electrode capacity. Thus, the high specific capacity of the anode is offset, reducing the energy density of the secondary battery while increasing the consumption cost of the positive electrode of the secondary battery.

[0004] To address the problem of low initial charge-discharge Coulomb efficiency, reducing the oxygen content in the silicon oxide beforehand can reduce the consumption of lithium ions in the cathode material by the irreversible phase Li2O generated during the initial charge, thereby improving the energy density of the secondary battery. A common method involves adding an exogenous reducing metal element, reacting it with the oxygen element in the silicon oxide, and reducing it to nanosilicon. This improves the Coulomb efficiency of the material, and the metal oxide or silicate generated in the reduction reaction acts as a buffer matrix, regulating stress fracture due to volume changes during the lithium alloying and dealloying processes of nanosilicon, thereby maintaining structural integrity and improving the long-term cycle performance of the material.

[0005] For example, in a method to improve the initial Coulomb efficiency of silicon oxide by mixing silicon monoxide powder and metallic magnesium powder and heating them to perform a reduction reaction by solid-phase doping, the physical and chemical properties of magnesium silicate in the negative electrode material produced by this method are relatively stable, and the stability of the aqueous slurry is excellent. However, since the thermal reduction reaction of magnesium is a diffusion-controlled reaction, the composition of the 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 starts the reaction from outside the silicon monoxide particles and gradually diffuses into the inside of the particles, easily leading to the formation of by-products such as magnesium silicide and magnesium oxide due to localized excess magnesium, and rapid growth of silicon crystal grains. Furthermore, because the diffusion rate of magnesium vapor into solids is generally small, magnesium is not easily incorporated completely and uniformly into the silicon monoxide material, and the distribution of magnesium in the reduction products is also relatively non-uniform.

[0006] Regarding in-situ gaseous magnesium doping technology, a method has been disclosed in which a mixture of silicon and silicon dioxide, and a metal M are mixed, followed by vacuum co-evaporation and condensation. The initial efficiency of the negative electrode material produced by this method reaches over 83%, significantly improving the effective utilization rate of lithium ions in the positive electrode material of secondary batteries, and the stability of the aqueous slurry is good. However, the reaction in which the silicon and silicon dioxide mixture used therein generates silicon oxide vapor under heating conditions is a solid-solid interface reaction, and therefore the amount of silicon oxide vapor generated fluctuates greatly as the reaction progresses. Consequently, during the mixing and deposition process of magnesium vapor and silicon oxide vapor, the local magnesium incorporation ratio is uncontrollable, which easily leads to unbalanced growth of silicon crystal grains, affecting the cycle life and safety issues of the negative electrode material.

[0007] Whether using solid-phase doping or in-situ gaseous doping techniques, the distribution of doping elements in the manufactured anode material is often non-uniform, or the growth of silicon crystal grains is non-uniform. In other words, it is difficult to simultaneously achieve a uniform distribution of doping elements between single particles and multiple particles. Based on this, there is a need to actively pursue the manufacture of new anode materials to improve electrochemical performance. [Problems that the invention aims to solve]

[0008] The present invention aims to provide an anode material and a method for manufacturing the same, as well as a secondary battery, which achieve doping of metal M at the nanoscale using in-situ doping technology, obtain an anode material in which metal M is uniformly distributed, reduce the oxygen content in the anode material, and further improve initial efficiency and cycle performance when applied to a battery. [Means for solving the problem]

[0009] To achieve the above objective, the present invention's technical solution 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, which includes the following. Place the metal source material and the pre-dispersed silicon monoxide material at different positions in the same vacuum heating system, and perform heating evaporation respectively to obtain a metal source gas and a 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] In the negative electrode material system of the present application, the metal M element-containing silicate can obtain that the M element satisfies certain distribution characteristics by energy spectrum analysis, and the metal M element-containing silicate can effectively separate the nanosilicon domain and the silicon oxide domain, reducing the aggregation of silicon clusters due to the electrochemical sintering of nanosilicon during the charge-discharge cycle process, thereby reducing the problem of performance degradation of the negative electrode material, enabling the negative electrode material to have both a high initial efficiency and excellent cycle performance, and the silicate can buffer the volume change caused by the lithium insertion and extraction in the lithium insertion and extraction process of nanosilicon and silicon oxide as a buffer matrix, so that the negative electrode material has low expansion performance.

Brief Description of Drawings

[0015] To more clearly explain the technical solution of the embodiments of the present application, the drawings required for the embodiments are briefly introduced below. Obviously, the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application. [Figure 1] It is the XRD pattern of the negative electrode material manufactured in Example 1. [Figure 2] It is the surface scanning diagram of SEM / EDS of a particle cut surface of the negative electrode material manufactured in Example 1. [Figure 3] It is a high-magnification SEM diagram of a particle cut surface of the negative electrode material manufactured in Example 1. [Figure 4] It is the cycle capacity performance diagram of the secondary batteries manufactured in Example 1 and Comparative Example 1. [Figure 5] It is the cycle expansion performance diagram of the secondary batteries manufactured in Example 1 and Comparative Example 1.

Modes for Carrying Out the Invention

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

[0017] "Made from..." is synonymous with "contains...". The terms "contains," "includes," "have," "contain," or any other variations used herein are intended to cover the non-exclusive "contains." For example, a composition, step, method, product, or apparatus containing the enumerated elements is not necessarily limited to those elements and may include other elements not expressly enumerated, or elements specific to the composition, step, method, product, or apparatus. The connecting term "consisting of..." excludes any elements, steps, or components not enumerated.

[0018] When equivalents, concentrations, or other values ​​or parameters are expressed as a range, a preferred range, or a range limited by a set of preferred upper and lower limits, it should be understood that all ranges formed by any combination of the upper or preferred upper limits of any range and the lower or preferred lower limits of any range are specifically disclosed, regardless of whether such ranges are disclosed alone. For example, if the range "1 to 5" is disclosed, it should be interpreted that such range includes ranges such as "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", and "1 to 3 and 5". Where numerical ranges are described herein, unless otherwise expressly stated, such ranges are intended to include their endpoints and all integers and fractions within that range.

[0019] In the examples, unless otherwise specified, "parts" and "percentage" refer to "parts by mass" and "mass %", respectively.

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

[0021] The terms "and / or" indicate that one or both of the stated conditions 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 superior performance, prior art research has shown that silicon-based composite anode materials can be manufactured by uniformly doping silicon powder and silicon fine powder with gaseous lithium generated by the oxidation-reduction reaction of lithium-containing oxide or silicate with a reducing agent. While the initial efficiency can reach approximately 90%, the silicon crystal grains in the manufactured anode material are large, resulting in poor cycle performance. Alternatively, silicon powder, SiO2 powder, magnesium powder, and LiCl powder can be placed in different chambers within the same vacuum system, heated and sublimated, and then cooled to obtain a modified precursor co-doped with magnesium and lithium. This modified precursor, further coated with a conductive layer, not only has high initial efficiency but also possesses the characteristics of high ionic conductivity of lithium silicate and high bonding strength of magnesium silicate, further improving the cycle life of the material. However, the manufacturing conditions are strict, and the expansion of the anode material during the charge-discharge process is excessive. Alternatively, silicon-based anode materials can be manufactured by mixing a mixture of silicon and silicon dioxide with metal M, followed by vacuum co-evaporation condensation. While this improves the initial efficiency of the material, the poor uniformity of the vapor evaporation mixing results in uneven sizes of the produced silicon crystal grains, leading to poor electrical performance and a certain safety risk.

[0023] The primary objective of this invention is to provide a negative electrode material in which metal element M satisfies certain distribution characteristics, to solve the problem of mixing two-phase and multi-phase vapors, and further to ensure that the negative electrode material has high initial efficiency and excellent cycle performance, as well as low expansion performance.

[0024] In a first embodiment, the present application provides a negative electrode material comprising 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 of this negative electrode material comprises nanosilicon and a metal M-element-containing silicate.

[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, including particles formed by 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 cut in a plane, and plane scanning energy spectrum analysis is performed on the cut surfaces of the n1 particles to obtain the values of the M element content of the n1 particles. When the standard deviation k1 of the values of the M element content of these n1 particles is calculated, k1 ≤ 10. n2 points are randomly selected from the cut surfaces of any of the above particles for point analysis to obtain the values of the M element content of the n2 points. When the standard deviation k2 of the values of the M element content of these n2 points 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 deterioration 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 covers 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 cycling process, thereby resulting in a more stable material structure and reducing the consumption of active silicon during the cycling process.

[0029] In this invention, the setting of standard deviations k1 and k2 quantifies the uniformity of the distribution of metallic M element in the negative electrode material, and improves the performance of the negative electrode material by limiting the regular relationship between the standard deviation of the M element content inside a single particle (k2) and between multiple particles (k1).

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

[0031] Furthermore, limiting the k2 / k1 ratio to 0.1-1 means that the uniformity within a single particle and between multiple particles is harmonized, that is, the uniformity of the distribution of M element both within and between particles is desirable, and there is no significant inconsistency. By setting this ratio, two extreme situations are avoided: one where the distribution is uniform within a single particle but non-uniform between particles, and another where the overall distribution is uniform but the distribution within the particle is non-uniform. In conventional techniques, it is difficult to simultaneously guarantee these two types of uniformity, whether solid-phase doping or gaseous doping, and it is particularly difficult to match the distribution of M element when there are significant differences in particle size, morphology, or internal structure. The present invention not only achieves uniform doping of M element at the nanoscale, but also maintains such uniformity within a single particle and between multiple particles, effectively solving the problems of conventional techniques.

[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 proportion of (MO) n is low, and the silicate with 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 causes a higher pH. OH - and the exposed active Si react to easily generate H2, thereby attenuating 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. Thereby, the exposed Si in the negative electrode material due to the 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 the silicon oxide is coated with a metal M element-containing silicate. Through the multiple protection of the silicon oxide and the metal silicate, the exposure of the 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 - 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 further, 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 greatly reduced, the performance of the battery is improved, and when preparing the negative electrode material into a slurry, the problem of gas generation due to the reaction of active silicon with OH in the alkaline solution - and the problem of bubbles during electrode sheet coating and the problem of deterioration of cycle performance due to the deterioration of the performance of the adhesive due to excessive alkalinity are better solved.

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

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

[0044] The silicate formed by the above-mentioned M element in the anode material can more effectively separate nanosilicon domains and silicon oxide domains, thereby further reducing the aggregation of silicon clusters during charging and discharging, and further mitigating the expansion problem caused by lithium intercalation and deintercalation, thereby better improving the initial efficiency and cycle performance of the anode material.

[0045] In one preferred embodiment of the present application, the true density of the negative electrode material is 2.0 g / cm³. 3 ~2.6g / cm 3 For example, 2.0 g / cm³ 3 , 2.1 g / cm³ 3 , 2.2 g / cm³ 3 2.3 g / cm³ 3 2.4 g / cm³ 3 2.5 g / cm³ 3 Or 2.6 g / cm³ 3 It may also be the case that the true density is 2.3 g / cm³. More preferably, the true density is 2.3 g / cm³. 3 ~2.6g / cm 3 That is the case.

[0046] The true density of the negative electrode material in this application is measured by the gas adsorption expansion method.

[0047] In one preferred embodiment of the present application, the specific surface area of ​​the negative electrode material is 2 m². 2 / g~10m 2 / g, for example, 2m 2 / g, 4m 2 / g, 6m 2 / g, 8m 2 / g or 10m 2 / g is also acceptable.

[0048] Limiting the true density and specific surface area of ​​the negative electrode material within the above range is advantageous for improving the structural stability of the negative electrode material and reducing side reactions on the negative electrode material surface, thereby 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 percentage of element M 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 present in the above-mentioned content is advantageous in that it plays a role in separating nanosilicon domains and silicon oxide domains in the form of silicates, further improving the initial efficiency and cycle performance of the anode material.

[0051] In one preferred embodiment of the present application, the mass percentage of the surface carbon layer of the negative electrode material is 1% to 20%, 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 ratio and thickness of the carbon layer are within the above range, it is advantageous to reduce the problems of gas generation due to the exposure of active silicon in the silicon-based core and nanosilicon cluster sintering, thereby stabilizing the structure of the anode material and further reducing the consumption of active silicon during the cycling process, which is advantageous in obtaining an anode material with significantly improved initial efficiency and cycle performance.

[0054] In one preferred embodiment of the present application, when the metal M element-containing silicate contains MgSiO3, the diffraction peak of MgSiO3(610) in the XRD pattern of the negative electrode material is 30° to 31°, the diffraction peak of Si(220) is 45° to 50°, and the ratio of the intensities of the two diffraction peaks is α = I Si(220) / I MgSiO3(610)The conditions 0 < α < 2 are satisfied. Under the above conditions, the silicate formed on the anode material can more effectively separate nanosilicon domains and silicon oxide domains, thereby further reducing the aggregation of silicon clusters during charging and discharging, further buffering the expansion problem due to lithium intercalation and deintercalation, and better improving the initial efficiency and cycle performance of the anode material.

[0055] In one preferred embodiment of the present application, when the metal M element-containing silicate contains MgSiO3, the XRD pattern and Scherrer formula of the negative electrode material are: D =0.9λ / β cosθ determines the (610) plane of the MgSiO3 crystal grain. Direction perpendicular to Average size in D Calculate ≤30nm. The above conditions are for good Li + This is advantageous for the formation of conduction paths and further reduces the high resistance resulting from an excessively thick MgSiO3 layer.

[0056] In a second embodiment, the present application further provides a method for manufacturing a negative electrode material according to the first embodiment, which includes the following: S1: The metal source material and the pre-disproportionated silicon monoxide material are placed at different positions in the same vacuum heating system, and each is heated and evaporated to obtain the metal source gas and silicon monoxide gas; S2: The silicon monoxide gas and the metal source gas are mixed and condensed to obtain the core material; S3: The core material is subjected to a carbon coating treatment to obtain the anode material.

[0057] The present invention provides a method for manufacturing anode materials that is simple and easy to operate, enabling rapid industrialization. Using in-situ doping technology, nano-level metal doping is achieved by mixing and depositing a gaseous metal source with gaseous silicon oxide, resulting in anode materials with uniformly distributed metal silicates. In particular, by using a pre-disproportionated silicon monoxide material in the manufacturing method, silicon monoxide vapor can be continuously and stably generated. After mixing with the stably generated metal source gas, anode materials with uniform distribution of each substance and superior performance are obtained. This method reduces the problems associated with conventional methods using a mixture of silicon and silicon dioxide as raw materials, where interfacial reactions are affected by material contact effects, leading to unstable silicon monoxide evaporation and non-uniform doping of each substance in the manufactured anode material.

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

[0059] In the method for manufacturing the negative electrode material of the present invention, a silicon monoxide source is used to perform a preliminary disproportionation treatment, and among the silicon and SiO2 x In all locations, it appears in a uniformly dispersed form at the nanoscale, with silicon crystal grain size being less than 20 nm, reducing the effect of changes in reaction rate due to changes in the contact area of ​​the interfacial reaction, enabling the continuous and stable generation of silicon monoxide vapor, and after mixing with the continuously and stably generated magnesium vapor, a silicon oxide anode product with a uniform distribution and superior performance and high initial efficiency is obtained.

[0060] More preferably, the preliminary disproportionation treatment is carried out in an inert gas atmosphere 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 holding time is 3h to 10h, for example, 3h, 5h, 6h, 8h, or 10h. More preferably, the preliminary disproportionation treatment is maintained at a constant temperature of 1000°C for 10 hours.

[0062] Under the above conditions, it is advantageous to more uniformly disperse and contact silicon and silicon oxides in the silicon monoxide source, thereby enabling more stable generation of silicon monoxide vapor, providing a good material base for the subsequent anode material formation process, and improving the initial efficiency and cycle performance of the anode material.

[0063] In this application, the reason for selecting a pre-disproportionated silicon monoxide material as the silicon monoxide source is primarily to reduce the instability of SiO evaporation caused by the influence of material contact effects in the interfacial reaction when conventional silicon and silicon dioxide are selected and used as raw materials. Specifically, amorphous SiO is subjected to homogenization and disproportionation treatment to obtain silicon monoxide with disproportionated silicon crystal grains of less than 20 nm, thereby realizing a silicon monoxide vapor source in which Si and SiO2 are uniformly dispersed at the nanoscale. This stabilizes the generation rate of silicon monoxide vapor throughout the reaction process and realizes relatively uniform generation, mixing, and condensation 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, and may be, for example, 10 μm, 100 μm, 1 mm, 1 cm, 5 cm, or 10 cm. This is advantageous for further reducing the effect of changes in reaction rate due to changes in the contact area of ​​the interfacial reaction and for stably generating silicon monoxide vapor and continuing to participate 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 magnesium-containing oxide and a reducing substance, or a mixture of magnesium-containing salts and a reducing 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 more effectively separate the nanosilicon domains and silicon oxide domains, thereby better improving the initial efficiency and cycle performance of the anode material.

[0069] In one preferred embodiment of the present application, when a metal source material and a pre-disproportionated silicon monoxide material are heated and evaporated at different locations 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, or 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 the first vacuum heating chamber, and the temperature is heated to 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 heating and evaporation temperatures of the metal source material and the pre-disproportionated silicon monoxide material may be the same or different.

[0073] Under the above conditions, it is advantageous to evaporate the pre-disproportionated silicon monoxide material and metal source material sufficiently at a more appropriate rate to obtain the corresponding gaseous raw materials, and it is also possible to further reduce the occurrence of locally non-uniform evaporation and deposition reactions, thereby improving the structural stability and electrochemical performance of the anode material.

[0074] In one preferred embodiment of the present invention, the mixing of the two gases in S2 is carried out under vacuum conditions where the vacuum level is 0 to 100 Pa.

[0075] In one preferred embodiment of the present application, the condensation temperature 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 and deposition chamber is evacuated, and when the vacuum level reaches 100 Pa or less and the temperature of the condensation chamber reaches 500°C to 900°C, gases from two vacuum heating chambers are introduced into the condensation and deposition chamber and mixed. Subsequently, a precursor mixture of silicon oxide and a metal source is collected on the condenser.

[0078] Under the above conditions, it is advantageous for the preliminary reaction to occur after mixing and condensing the two phase gases, resulting in a more stable deposition state, further reducing the probability of oxidation of the product after exposure to air, and also leading to a higher utilization rate for improved initial efficiency of the M metal source.

[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 subjected to grinding and classification to obtain a core material, preferably having a volume distribution D50 of 5.0 to 5.5 μm.

[0080] More preferably, the grinding method includes mechanical grinding, ball mill grinding, or air-jet grinding.

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

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

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

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

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

[0086] The above conditions are advantageous for a more sufficient and uniform coating of carbon material on the surface of the silicon-based core, coating and isolating nanosilicon or silicon oxide, reducing the problem of processing gas generation due to exposure of active silicon and the problem of sintering of nanosilicon clusters during the cycling process, thereby resulting in a more stable material structure and reducing the consumption of active silicon during the cycling process. More preferably, in the gas phase coating process, in addition to the carbon source gas and carrier gas, a certain proportion of hydrogen gas may be introduced mainly to adjust the structure of the carbon layer.

[0087] In a third embodiment, the present invention further provides a secondary battery comprising a negative electrode material manufactured by a method for manufacturing the negative electrode material of the first embodiment or the negative electrode material of the second embodiment. The secondary battery of the present invention uses the above-mentioned 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 proposed technology, using in-situ doping technology, nano-level magnesium doping is achieved by mixing gaseous magnesium with gaseous silicon oxide using gaseous magnesium as a magnesium source and depositing the mixture, thereby obtaining an anode material that matches the distribution characteristics of metal M and is also suitable for a specific pH range. Subsequently, the oxygen content in the active material is reduced by heat treatment reduction, and a silicon monoxide anode material with high initial efficiency is produced through pulverization and carbon coating, etc.

[0090] Typical but non-restrictive, k1 is a numerical range formed by 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any combination of these numbers; k2 is a numerical range formed by 1, 2, 3, 4, 5 or any combination of these numbers; k2 / k1 is a numerical range formed by 0.11, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any combination 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 a numerical range formed by 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000 or any combination of any two numbers; n2 is a numerical range formed by 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 any combination of any two numbers.

[0091] Typically, but not limited to, the volume distribution D50 of the core material is a numerical range formed by 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, or any combination of any two of these values.

[0092] Typically, but not limited to, the atmospheric ratios of carbon source gas, hydrogen gas, and carrier gas are numerical ranges formed by 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 any combination of any two of these values. [Examples]

[0093] The embodiments of this application will be described in detail below with reference to specific examples, but those skilled in the art should understand that the following examples are merely illustrative of this application and do not limit its scope. Specific conditions not explicitly stated in the examples have been replaced with general conditions or conditions provided by the manufacturer. Unless otherwise specified, the reagents or equipment used are conventional products available commercially.

[0094] Example 1 This application provides a negative electrode material, the method for which the negative electrode material is manufactured includes the following steps. 1) Amorphous SiO blocks were pre-disproportionated at 1200°C in an argon gas atmosphere for 10 hours, and after cooling, they were powdered to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 6.0 nm. The volume distribution D50 of this powder was 100 μm. Subsequently, this powder was placed in the first vacuum heating chamber of a vacuum heating system, argon gas was introduced, and it was heated to 1400°C to obtain silicon monoxide gas; 2) The magnesium metallic powder was placed in the second vacuum heating chamber of the vacuum heating system, argon gas was introduced, and it was heated to 700°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated until the vacuum level reached 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 and deposition chamber with a vacuum of 10 Pa, and the precursor material was collected on a water-cooled substrate at a temperature of 700°C in the condensation and deposition chamber; 5) The precursor from step 4) was pulverized to a volume distribution D50 of 5.5 μm by means of mechanical grinding, 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 (carrier gas) were introduced to adjust the atmospheric ratio to 2:1:3.5, followed by 8 hours of gas phase coating; 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 method for manufacturing the secondary battery includes the following steps. A negative electrode slurry was prepared by mixing the negative electrode material, conductive carbon black, and PAA rubber manufactured in the above embodiment in a mass ratio of 75:15:10. This slurry was then applied to copper foil and dried to produce a negative electrode piece. A metallic lithium sheet was used as the counter electrode, and the button cell was assembled in a glove box filled with argon gas to complete the process. The button-type battery was subjected to charge-discharge testing at a current density of 0.1C within a charge-discharge range of 0.01 to 1.5V. The initial reversible ratio capacity and initial efficiency of the obtained battery were measured.

[0096] This embodiment further provides a secondary battery, the specific manufacturing method of which includes the following steps. A negative electrode slurry was prepared using the negative electrode material (Super-P:KS-6:CMC:SBR=92:2:2:2:2) manufactured in the above example. This slurry was applied to copper foil and dried to produce a negative electrode piece. A metallic lithium sheet was used as the counter electrode, and the button cell was assembled in a glove box filled with argon gas to complete the process. The button-type battery was subjected to charge-discharge tests at a current density of 1C within a charge-discharge range of 0.01V to 1.5V. The volume expansion rate and capacity retention rate after 50 cycles were measured, and the expansion performance during the cycle process was further studied using the in-situ expansion rate test method for basic pouch batteries.

[0097] Example 2 This embodiment provides a negative electrode material, and the method for manufacturing the negative electrode material includes the following steps. 1) Amorphous SiO blocks were pre-disproportionated at 1200°C in an argon gas atmosphere for 10 hours, and after cooling, they were powdered to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 6.0 nm. The volume distribution D50 of this powder was 100 μm. Subsequently, this powder was placed in the first vacuum heating chamber of a vacuum heating system, argon gas was introduced, and it was heated to 1300°C to obtain silicon monoxide gas; 2) The metallic magnesium powder was placed in the second vacuum heating chamber of the vacuum heating system, argon gas was introduced, and it was heated to 900°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated until the vacuum level reached 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 and deposition chamber with a vacuum of 5 Pa, and the precursor material was collected on a water-cooled substrate at a temperature of 800°C in the condensation and deposition chamber; 5) The precursor from step 4) was pulverized to a volume distribution D50 of 5.0 μm by means of mechanical grinding, 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 (the carrier gas) were introduced to adjust the atmospheric ratio to 3:1:3.5, followed by a gas phase coating for 10 hours. 7) The coated material was collected, dispersed, sieved, and demagnetized to obtain a composite negative electrode material containing silicon oxide. The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0098] Example 3 This embodiment provides a negative electrode material, and its manufacturing method is the same as in Example 1, with the differences being as follows. In step 2), the metallic calcium powder is placed in the second vacuum heating chamber of the vacuum heating system, argon gas is introduced, and it is heated to 1300°C. The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0099] Example 4 This embodiment provides a negative electrode material, and its manufacturing method is the same as in Example 1, with the differences being as follows. In step 1), the temperature of the preliminary disproportionation treatment is set to 1000°C and the time to 10h to obtain a preliminary disproportionated silicon monoxide powder with silicon-containing crystal grains of 5.5 nm. The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0100] Example 5 This embodiment provides a negative electrode material, and its manufacturing method is the same as in Example 1, with the differences being as follows. In step 3), the vacuum level is 50 Pa, and in step 4), the precursor material is collected on an 800°C water-cooled substrate. The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0101] Example 6 This embodiment provides a negative electrode material, and its manufacturing method is the same as in Example 1, with the differences being as follows. In step 1), the size of the preliminary disproportionated silicon monoxide material is a 5 cm block. The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0102] Example 7 This embodiment provides a negative electrode material, and its manufacturing method is the same as in Example 1, with the differences being as follows. 1) Amorphous SiO blocks were pre-disproportionated at 1000°C in an argon gas atmosphere for 10 hours, and after cooling, they were powdered to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 5.4 nm, with a volume distribution D50 of 500 μm. Subsequently, the powder was placed in the first vacuum heating chamber of a vacuum heating system, argon gas was introduced, and it was heated to 1000°C to obtain silicon monoxide gas; 2) The magnesium metallic powder was placed in the second vacuum heating chamber of the vacuum heating system, argon gas was introduced, and it was 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 and deposition chamber with a vacuum of 0 Pa, and the precursor material was collected on a water-cooled substrate at a temperature of 500°C in the condensation and deposition chamber; 5) The precursor from step 4) was pulverized to a volume distribution D50 of 5.5 μm by means of mechanical grinding, 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 atmospheric ratio to 2:1:3.5, and gas phase coating was performed for 8 hours; The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0103] Example 8 This embodiment provides a negative electrode material, and its manufacturing method is the same as in Example 1, with the differences being as follows. 1) Amorphous SiO blocks were pre-disproportionated at 1200°C in an argon gas atmosphere for 3 hours, and after cooling, they were powdered to obtain pre-disproportionated silicon monoxide powder containing silicon crystal grains with an average size of 6.0 nm, with a volume distribution D50 of 100 μm. Subsequently, the powder was placed in the first vacuum heating chamber of a vacuum heating system, argon gas was introduced, and it was heated to 1500°C to obtain silicon monoxide gas; 2) The metallic magnesium powder was placed in the second vacuum heating chamber of the vacuum heating system, argon gas was introduced, and it was heated to 1350°C to obtain magnesium vapor; 3) The vacuum heating system was evacuated until the vacuum level reached 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 and deposition chamber with a vacuum of 100 Pa, and the precursor material was collected on a water-cooled substrate at a temperature of 800°C in the condensation and deposition chamber; 5) The precursor from step 4) was pulverized to a volume distribution D50 of 5.5 μm by means of mechanical grinding, 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 atmospheric ratio to 2:1:3.5, followed by 8 hours of gas phase coating; The manufacturing and evaluation of the secondary battery according to this embodiment are the same as in Example 1.

[0104] Comparative Example 1 This comparative example provides a negative electrode material, and its manufacturing method is the same as in Example 2, with the differences being as follows. In step 1), silicon dioxide powder with a volume distribution D50 = 30 μm and silicon powder with a volume distribution D50 = 10 μm were directly and uniformly mixed in a molar ratio of 1:2, placed in the first vacuum heating chamber of the vacuum heating system, argon gas was introduced, and heated to 1400°C; in step 4), the temperature of the water-cooled substrate in the condensation deposit chamber was 850°C; in step 6), only methane and nitrogen gas as the carrier gas were introduced, and the atmospheric ratio was adjusted to 3:3.5. The manufacturing and evaluation of the secondary battery in this comparative example are the same as in Example 1.

[0105] Energy spectral analysis of the element Mg was performed on the negative electrode materials produced in the above examples and comparative examples, and energy spectral analysis of the element Ca was performed on the negative electrode material produced in Example 3, and the k1 and k2 values ​​were obtained, respectively.

[0106] The specific measurement method for energy spectrum analysis involves cutting negative electrode material particles manufactured using a Hitachi E-3500 ion polishing machine, observing the morphological structure of the cut surface with a Hitachi S-4800 cold cathode field emission scanning electron microscope, and then observing 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] Furthermore, the pH values ​​of the negative electrode materials produced in the examples and comparative examples were measured. 5.00 ± 0.01 g of powder sample was weighed, added to 45 mL of pure water, stirred to disperse, sonicated for 5 minutes, and then allowed to stand. The supernatant after standing was measured using a Mettler FE20 pH meter, and the pH value was read.

[0108] True density test: The true density of the anode material was measured using the gas adsorption expansion method with a Mike true density meter (AccuPyc II) from the United States.

[0109] Measurement of specific surface area: Using a specific surface area and pore analysis instrument (TriStar II) from Mike, USA, the specific surface area of ​​the material was calculated by adsorption with nitrogen gas and the BET method.

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

[0111] Carbon content (%): Infrared absorption method is used, referring to standard GB / T20123-2006.

[0112] Carbon layer thickness: Using the cross-sectional SEM method, the material is first cut using a Hitachi E3500 ion polishing machine, and then analyzed using a Hitachi S-4800 scanning electron microscope.

[0113] Mg mass content and Ca mass content: Tested using an ICP spectrometer (instrument model: Agilent 5800VDV-ICP-OES).

[0114] pH value: Measured using a pH meter (device model: 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 each example and comparative example in secondary batteries.

[0116] [Table 1]

[0117] [Table 2]

[0118] Analysis of the data from Examples 1-8 and Comparative Example 1 shows that setting the standard deviations k1 and k2, and k2 / k1 of the anode material quantifies the uniformity of the distribution of metallic M element in the anode material and solves the technical problem of difficulty in simultaneously achieving a uniform distribution of M element inside a single particle and between multiple particles in conventional technology, thereby significantly improving the electrochemical performance of the anode material and the secondary battery using it. The anode materials of Examples 1-8 not only have high initial efficiency but also excellent cycle performance and a low volume expansion coefficient.

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

[0120] Figures 2 and 3 show the SEM / EDS plane scan map of the Mg element in a particle cross-section of the anode material produced in Example 1, and a high-magnification SEM image of the particle cross-section, respectively. As can be seen from the figures, the metal silicate domains, nanosilicon domains, and silicon oxide domains are uniformly dispersed amongst themselves, and the XRD pattern of the anode material and Scherrer's formula: D =0.9λ / β cosθ determines the (610) plane of the MgSiO3 crystal grain. Direction perpendicular to Average size in D The value is calculated to be 11.1 nm.

[0121] Figures 4 and 5 show the cycle-capacity diagram and cycle-expansion diagram of the secondary batteries manufactured in Example 1 and Comparative Example 1, respectively. Comparison shows that the negative electrode material manufactured in this application has superior cycle performance and lower cycle expansion performance.

[0122] Furthermore, the above embodiments are for illustrative purposes only and are not intended to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art may still modify the inventions described in the above embodiments or make equivalent substitutions for some or all of their technical features. However, it should be understood that such modifications or substitutions will not cause the essence of the corresponding inventions to deviate from the scope of the inventions described in the embodiments of the present application.

[0123] Furthermore, a person skilled in the art will understand that some embodiments of this specification include some features included in other embodiments and do not include others, but that combinations of features from different embodiments constitute different embodiments within the scope of the present application. For example, any combination of any of the embodiments to be protected described above may be used. The information disclosed in this background art portion is intended solely to enhance the overall understanding of the background art of the present application and should not be considered to acknowledge or imply in any way that such information constitutes prior art known to a person skilled in the art.

Claims

1. A silicon-based core containing nanosilicon and a silicate containing metal element M, A negative electrode material comprising 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 spectral analysis on the cut surface, When the cross-sections of n1 particles were randomly selected and surface analysis was performed to obtain the values ​​of the M element content of n1 particles, the standard deviation k1 of the values ​​of the M element content of n1 particles was calculated, and k1 ≤ 10. When n2 points are randomly selected from the cross-section of an arbitrary particle and point analysis is performed to obtain the values ​​of the M element content of the n2 points, the standard deviation k2 of the n2 M element content values ​​is calculated, and k2 ≤ 5, and 0.1 < k2 / k1 ≤ 1, Herein, the negative electrode material is characterized in that 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 it satisfies at least one of the following (1) to (4). (1) The silicon-based core further comprises silicon oxide. (2) The D50 of the silicon-based core is 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 7 < pH ≤ 10.

5.

3. The negative electrode material according to claim 1, characterized in that it satisfies at least one of the following (1) to (2). (1) The M element includes at least one metallic element from groups IA, IIA, and IIIIA. (2) The M element includes at least one of lithium, sodium, potassium, magnesium, calcium, and aluminum.

4. The negative electrode material according to claim 1, characterized in that it satisfies at least one of the following (1) to (2). (1) The true density of the negative electrode material is 2.0 g / cm³. 3 ~2.6 g / cm 3 That is the case. (2) The specific surface area of ​​the negative electrode material is 2 m² 2 / g to 10m 2 It is / g.

5. The negative electrode material according to claim 1, characterized in that 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 claim 1, characterized in that it satisfies at least one of the following (1) to (2). (1) The metal M element-containing silicate is MgSiO 3 If it includes, in the XRD pattern of the negative electrode material, 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) The equation satisfies 0 < α < 2. (2) When the metal M element-containing silicate contains MgSiO 3 , from the XRD pattern of the negative electrode material and Scherrer's formula: D = 0.9λ / βcosθ, MgSiO 3 The average size D in the direction perpendicular to the (610) plane of the crystal grains is calculated to be D ≤ 30 nm.

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

8. The negative electrode material according to claim 1, characterized in that the thickness of the carbon layer is 50 nm to 500 nm.

9. A method for manufacturing a negative electrode material according to any one of claims 1 to 8, By placing a metal source material and a pre-disproportionated silicon monoxide material at different positions in the same vacuum heating system and heating and evaporating them respectively, metal source gas and silicon monoxide gas are obtained. The silicon monoxide gas and the metal source gas are mixed and condensed to obtain a core material, and A method for producing a negative electrode material, characterized by including carbon coating treatment of the core material to obtain the negative electrode material.

10. The manufacturing method according to claim 9, characterized in that at least one of the following A, C, and F is satisfied. A. The method for producing the pre-disproportionated silicon monoxide material includes pre-disproportionating an amorphous SiO mass to obtain silicon monoxide containing disproportionated silicon crystal grains with a crystal grain size of less than 20 nm, and further pulverizing or crushing the material to obtain pre-disproportionated silicon monoxide powder or particles. C. The metal source material includes at least one of the following: magnesium source material, lithium source material, sodium source material, potassium source material, calcium source material, and aluminum source material. F. The heating and evaporation temperature of the pre-disproportionated silicon monoxide material is 1000°C to 1500°C.

11. The manufacturing method according to claim 9, characterized in that at least one of the following G, J, and K is satisfied. G. The heating and evaporation temperature of the metal source material is 600°C to 1350°C. J. The method further comprises collecting the condensed precursor material after condensation, crushing and classifying it to obtain the core material having a volume distribution D50 of 5.0 to 5.5 μm. K. The carbon coating treatment includes gas-phase coating, liquid-phase coating, or solid-phase coating.

12. The manufacturing method according to claim 11, characterized in that 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 aforementioned gas phase coating includes a carbon source gas and a carrier gas.

13. The manufacturing method according to claim 12, characterized in that at least one of the following R, S, and U is satisfied. R. The temperature of the gas phase coating is 700°C to 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 gas phase coating further contains hydrogen gas, and the ratio of the atmospheres of the carbon source gas, hydrogen gas, and carrier gas is (2-15):1:3.

5.

14. The manufacturing method according to claim 9, characterized in that the silicon monoxide gas and the metal source gas are mixed under vacuum conditions of 0 to 100 Pa.

15. A secondary battery characterized by comprising the negative electrode material described in any one of claims 1 to 8.

Images