Silicon oxide negative electrode material and preparation method thereof, negative electrode for secondary battery

Abstract

The present application relates to the field of lithium batteries, and more specifically, to a silicon-oxygen negative electrode material, a preparation method thereof, and a negative electrode for a secondary battery. The carbon-coated silicon monoxide and the metal material are heat-treated so that at least a portion of the silicon monoxide in the carbon-coated silicon monoxide reacts with the metal material to generate silicate and silicon element, thereby obtaining a silicon-oxygen negative electrode material. Silicate does not have the ability to insert lithium, which not only inhibits the volume expansion of the material, but also improves the initial effect of the silicon-oxygen negative electrode material. In addition, during the reaction between the metal material and the silicon monoxide, due to the presence of the carbon layer, the carbon layer can slow down the reaction process, thereby avoiding the generation of a large amount of heat and causing the silicon grain size to be too large. The smaller silicon grain size can make the silicon-oxygen negative electrode material exhibit better cycle performance.

Description

[0001] This application is a divisional application of the application document with application number 2020107355170 and titled “Silicon oxide negative electrode material and preparation method thereof, negative electrode for secondary battery”. Technical Field

[0002] The present application relates to the field of lithium batteries, and more specifically, to a silicon-oxygen negative electrode material and a preparation method thereof, and a negative electrode for a secondary battery. Background Art

[0003] With the rapid development of the new energy industry, lithium-ion batteries are required to have higher energy density and cycle life. The capacity of silicon oxide negative electrode materials is 1500-1800mAh / g, and it has a lower volume expansion (160%) than silicon negative electrodes, and has great application potential. The lithium silicon oxide compound formed during the lithium insertion process of silicon oxide materials can effectively inhibit volume expansion and improve the cycle life of the material, but excessive use will lead to a decrease in the first efficiency (the first coulomb efficiency of the battery, referred to as "first efficiency"); the current commercial silicon oxide material first efficiency is generally 75%.

[0004] The silicon grain size of existing silicon-oxygen negative electrode materials is relatively large, and the silicon-oxygen negative electrode materials exhibit poor cycle performance. Summary of the Invention

[0005] The purpose of the embodiments of the present application is to provide a silicon oxide negative electrode material and a preparation method thereof, and a negative electrode for a secondary battery, which aims to improve the initial efficiency and cycle performance of the negative electrode material of a lithium battery.

[0006] The first aspect of the present application provides a method for preparing a silicon-oxygen negative electrode material, comprising:

[0007] The carbon-coated silicon monoxide and the metal material are heat-treated to make at least a portion of the silicon monoxide in the carbon-coated silicon monoxide react with the metal material to generate silicate and silicon element, thereby obtaining a silicon-oxygen negative electrode material.

[0008] Metal is used to reduce carbon-coated silicon monoxide, so that at least a portion of the silicon monoxide reacts to form silicate. Since silicate does not have the ability to insert lithium, it can not only inhibit the volume expansion of the material, but also improve the initial efficiency of the silicon-oxygen negative electrode material. In addition, during the reaction between metal and silicon monoxide, due to the presence of the carbon layer, the carbon layer can slow down the reaction process, avoiding the generation of a large amount of heat and causing the silicon grain size to be too large. The smaller silicon grain size makes the silicon-oxygen negative electrode material exhibit better cycle performance.

[0009] In some embodiments of the first aspect of the present application, the metal material includes at least one of Mg, Li, Na, K, Ca, Sr, Ba, Ti, Zr, B, Al, Co and alloys thereof.

[0010] In some embodiments of the first aspect of the present application, the mass ratio of the metal material to the carbon-coated silicon monoxide is 1:5-9;

[0011] Optionally, the mass ratio of the metal material to the carbon-coated silicon monoxide is 1:6.5-7.5.

[0012] In some embodiments of the first aspect of the present application, the step of heat-treating the carbon-coated silicon monoxide and the metal material comprises:

[0013] The carbon-coated silicon monoxide and the metal material are kept at 300-600° C. for 1-10 hours; and then kept at 850-1100° C. for 0.5-10 hours;

[0014] Optionally, the carbon-coated silicon monoxide and the metal material are kept at 300-600° C. for 1-10 hours, then heated to 850-1100° C. at a heating rate of 5-20° C. / min and kept at this temperature for 0.5-10 hours;

[0015] Optionally, the heat treatment is carried out at a pressure of 1-140 Pa; optionally, the heat treatment is carried out at a pressure of 8-30 Pa.

[0016] In some embodiments of the first aspect of the present application, before the step of heat-treating the carbon-coated silicon monoxide and the metal material, the step further includes:

[0017] The step of coating the surface of silicon monoxide with a carbon layer to obtain the carbon-coated silicon monoxide;

[0018] Optionally, a carbon layer is coated on the surface of silicon monoxide by chemical vapor deposition;

[0019] Optionally, the silicon monoxide is coated with a carbon layer with a thickness of 10-1000 nm.

[0020] In some embodiments of the first aspect of the present application, the particle size distribution of the silicon monoxide is:

[0021] D10: ≥3μm;

[0022] D50: 5-8μm;

[0023] D100:<15μm.

[0024] In some embodiments of the first aspect of the present application, the mass fraction of carbon in the carbon-coated silicon monoxide is 0.2-20%;

[0025] Optionally, the mass fraction of carbon in the carbon-coated silicon monoxide is 1-8%.

[0026] A second aspect of the present application provides a silicon-oxygen negative electrode material, which is prepared by the above-mentioned method for preparing the silicon-oxygen negative electrode material.

[0027] Silicates can inhibit volume expansion, increasing cycle life and improving initial efficiency. The carbon layer on the surface can improve conductivity and inhibit volume expansion to a certain extent, which is conducive to the formation of a stable SEI film.

[0028] In a third aspect, the present application provides a silicon-oxygen negative electrode material, comprising: a core and a carbon layer covering the core, wherein the core comprises Mg2SiO4, MgSiO3, and silicon grains dispersed between the Mg2SiO4 and MgSiO3;

[0029] Mg2SiO4 and MgSiO3 do not have the ability to insert lithium, which can effectively inhibit the expansion of the material, increase the cycle life, and at the same time improve the initial efficiency.

[0030] A fourth aspect of the present application provides a negative electrode for a secondary battery, wherein the negative electrode for a secondary battery comprises the above-mentioned silicon oxide negative electrode material.

[0031] The negative electrode for the secondary battery has the advantages of the above-mentioned silicon-oxygen negative electrode material and has better electrical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 This is a scanning electron microscope image of the silicon-oxygen negative electrode material provided in Example 1.

[0034] Figure 2 This is the XRD pattern of the silicon-oxygen negative electrode material provided in Example 1.

[0035] Figure 3 This is a scanning electron microscope image of the CP cross-section of the silicon-oxygen negative electrode material provided in Example 1.

[0036] Figure 4 This is the distribution curve of each element in the cross section of the silicon-oxygen negative electrode material provided in Example 1 from the inside to the outside of the particle.

[0037] Figure 5 This is a scanning electron microscope image of the CP cross-section of the silicon-oxygen negative electrode material provided in Example 2.

[0038] Figure 6This is the distribution curve of each element in the cross section of the silicon-oxygen negative electrode material provided in Example 2 from the inside to the outside of the particle.

[0039] Figure 7 This is a scanning electron microscope image of the silicon-oxygen negative electrode material provided in Comparative Example 1.

[0040] Figure 8 This is the XRD pattern of the silicon-oxygen negative electrode material provided in Comparative Example 1.

[0041] Figure 9 The charge and discharge curves of the button batteries obtained in Example 1 and Comparative Example 1 of the present application are shown. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0043] The silicon oxide negative electrode material and its preparation method, and the negative electrode for secondary batteries in the embodiments of the present application are described in detail below.

[0044] A method for preparing a silicon-oxygen negative electrode material comprises: heat-treating carbon-coated silicon monoxide and a metal material, so that at least a portion of the silicon monoxide in the carbon-coated silicon monoxide reacts with the metal material to generate silicate and silicon element, thereby obtaining the silicon-oxygen negative electrode material.

[0045] In the present application, metal is used to reduce carbon-coated silicon monoxide (SiO), so that at least a portion of the silicon monoxide reacts to form silicate. The lack of lithium insertion capability of silicate not only inhibits the volume expansion of the material, but also improves the initial efficiency of the silicon-oxygen negative electrode material. In addition, during the reaction between metal and silicon monoxide, due to the presence of the carbon layer, the carbon layer can slow down the reaction, avoiding the generation of a large amount of heat that causes the silicon grain size to be too large. The smaller silicon grain size enables the silicon-oxygen negative electrode material to exhibit better cycle performance.

[0046] In the present application, the reaction of at least part of the silicon monoxide to form silicate includes the reaction of part of the silicon monoxide to form silicate and the reaction of all of the silicon monoxide to form silicate. In the embodiment of partial silicon monoxide reaction, although the final silicon-oxygen negative electrode material contains some silicon monoxide, it can also suppress the volume expansion of the material and improve the initial efficiency of the silicon-oxygen negative electrode material.

[0047] In an embodiment of the present application, the metal material is selected from materials that can form silicates with silicon monoxide, for example, the metal material includes at least one of Mg, Li, Na, K, Ca, Sr, Ba, Ti, Zr, B, Al, Co and alloys thereof.

[0048] The alloy may contain at least two of Mg, Li, Na, K, Ca, Sr, Ba, Ti, Zr, B, Al, and Co.

[0049] Furthermore, in some embodiments, the mass ratio of the metal material to the carbon-coated silicon monoxide is 1:5-9, for example, 1:5, 1:6, 1:6.5, 1:6.9, 1:7, 1:7.2, 1:7.5, 1:8, or 1:9, etc. The ratio of the metal material to the carbon-coated silicon monoxide within the above range can enable the silicon monoxide to be more fully reduced, thereby avoiding too low a first efficiency; and at the same time, avoid too high a ratio resulting in excessively large grain size and poor cycle performance.

[0050] It should be noted that, in other embodiments of the present application, if factors such as raw material utilization rate and yield are not considered, the mass ratio of the metal material to the carbon-coated silicon monoxide may not be within the above range.

[0051] In this embodiment, the step of heat treating the carbon-coated silicon monoxide and the metal material includes:

[0052] The carbon-coated silicon monoxide and the metal material are kept at 300-600° C. for 1-10 hours; and then kept at 850-1100° C. for 0.5-10 hours.

[0053] The metal material and carbon-coated silicon monoxide are reacted at a low temperature (300-600°C) for a period of time, so that the metal material is doped into the carbon layer and reacts with the silicon monoxide to form metal oxide, which helps to inhibit the increase in silicon crystal size. Then, the metal oxide and silicon monoxide are reacted at a high temperature (850-1100°C) for a period of time in the high temperature range to form silicate.

[0054] As an example, the temperature of the low temperature section may be 300° C., 350° C., 400° C., 450° C., 500° C., 546° C., or 600° C., etc.

[0055] The temperature of the high temperature section can be 850°C, 895°C, 920°C, 970°C, 1005°C, 1058°C, 1100°C, etc.

[0056] Accordingly, the temperatures of the low temperature section and the high temperature section can be set according to the reaction temperature of the metal material and silicon monoxide.

[0057] Furthermore, in some embodiments of the present application, the reaction temperature is increased from the low temperature range to the high temperature range at a heating rate of 5-20°C / min. For example, the heating rate may be 5°C / min, 10°C / min, 15°C / min, 20°C / min, etc. A slow temperature increase helps prevent the growth of silicon grains.

[0058] Furthermore, in some embodiments of the present application, the heat treatment is performed under a pressure of 1-140 Pa, for example, 1 Pa, 10 Pa, 20 Pa, 30 Pa, 60 Pa, 80 Pa, 110 Pa, 140 Pa, etc. A pressure of 1-140 Pa is conducive to the sublimation of the metal material at a lower pressure, and the reaction of the sublimated gas-phase metal material with the carbon-coated silicon monoxide can make the reaction more uniform.

[0059] In this embodiment, description is made by taking the case where the metal material includes Mg as an example.

[0060] Carbon-coated silicon monoxide reacts with magnesium metal, which in turn reacts with silicon monoxide to form magnesium silicate and silicon (silicon crystals). Tests by the inventors have revealed that the silicon-oxygen anode material contains Mg2SiO4 and MgSiO3. The resulting silicon-oxygen anode material improves initial efficiency and cycle performance, and the silicon crystals are smaller.

[0061] Accordingly, the inventors reacted silicon monoxide without a carbon layer with metallic magnesium, and then coated it with a carbon layer. After testing, the inventors found that the obtained material contained Mg2SiO4, but no MgSiO3 was detected. The silicon grains of the silicon-oxygen negative electrode material in this material were larger, and the initial efficiency was also lower.

[0062] Furthermore, in the embodiments of the present application, carbon-coated silicon monoxide can be directly purchased from the market or prepared.

[0063] As an example, an embodiment of the present application provides a method for preparing carbon-coated silicon monoxide, which mainly includes coating a carbon layer on the surface of silicon monoxide. It is understood that coating the carbon layer on the surface of silicon monoxide can be achieved by various methods. For example, in this embodiment, the carbon layer is coated on the surface of silicon monoxide by chemical vapor deposition.

[0064] As an example, one or more small molecular organic substances with a gasifiable molecular structure and a certain ring structure are used as carbon sources to vapor-deposit a carbon layer on the surface of silicon monoxide.

[0065] For example, the carbon source can be selected from alkanes, alkenes, alkynes and their derivatives with a certain ring structure, heterocyclic compounds, pyridines, pyrimidines, complexes containing benzene rings and nitrogen, benzene derivatives, amide derivatives, heterocyclic aromatic hydrocarbons, etc.

[0066] In some embodiments, the particle size distribution of silicon monoxide is:

[0067] D10: ≥3μm;

[0068] D50: 5-8μm;

[0069] D100:<15μm.

[0070] The particle size of silicon monoxide within the above range is beneficial to improving the initial efficiency of silicon-oxygen negative electrode materials and is also beneficial to the subsequent production of electrodes.

[0071] Furthermore, in some embodiments of the present application, the mass fraction of carbon in the carbon-coated silicon monoxide is 0.2-20%; for example, it can be 0.2%, 0.5%, 1%, 5%, 6%, 9%, 13%, 17%, 19% or 20%, etc.

[0072] Furthermore, a carbon layer with a thickness of 10-1000nm is coated on the surface of the silicon monoxide. If the carbon layer is too thin, it will not be enough to slow down the reduction rate. If it is too thick, it will affect the contact between the metal and SiO, resulting in too little silicate being generated, and the expansion inhibition effect will be poor.

[0073] The preparation method of the silicon-oxygen negative electrode material provided in the embodiment of the present application has at least the following advantages:

[0074] Carbon-coated silicon monoxide is heat-treated with a metal. This process requires only a simple solid-phase mixing of the carbon-coated SiO and the metal, and the morphology of the material remains unchanged after metal modification. The carbon layer on the surface of the silicon monoxide effectively slows the reduction reaction between the SiO and the metal, helping to control the silicon grain size. The entire reaction process effectively suppresses the growth of silicon grains, resulting in a silicon-oxygen anode material with excellent cycle life and initial efficiency.

[0075] An embodiment of the present application further provides a silicon-oxygen negative electrode material, which is prepared by the above-mentioned method for preparing the silicon-oxygen negative electrode material.

[0076] The silicon-oxygen anode material provided in this application has small silicon crystal grains, and the silicate can suppress volume expansion, thereby improving cycle life and initial efficiency. The carbon layer on the surface can improve conductivity and suppress volume expansion to a certain extent, which is conducive to the formation of a stable SEI (solid electrolyte interphase) film.

[0077] An embodiment of the present application further provides a silicon-oxygen negative electrode material, which includes: a core and a carbon layer coated outside the core, wherein the core includes Mg2SiO4 and MgSiO3 and silicon grains dispersed therein.

[0078] It is understood that in some embodiments of the present application, the core may further include silicon monoxide.

[0079] Mg2SiO4 and MgSiO3 do not have the ability to insert lithium, which can effectively inhibit expansion and increase cycle life, while also improving the initial efficiency.

[0080] Furthermore, in the embodiments of the present application, all silicon monoxide reacts with magnesium to generate silicon grains and Mg2SiO4 and MgSiO3; part of the silicon monoxide reacts with magnesium to generate silicon grains and Mg2SiO4 and MgSiO3, and the remaining silicon monoxide continues to remain in the core.

[0081] An embodiment of the present application further provides a negative electrode for a secondary battery, wherein the negative electrode for a secondary battery comprises any one of the above-mentioned silicon-oxygen negative electrode materials.

[0082] Accordingly, the negative electrode for a secondary battery has the advantages of the above-mentioned silicon oxide negative electrode material.

[0083] The negative electrode active material and optional conductive agent (such as carbon materials such as carbon black and metal particles, etc.), binder (such as SBR), additives (such as PTC thermistor material), etc. are dispersed in a solvent (such as deionized water), stirred evenly and evenly coated on the negative electrode current collector, and dried to obtain a negative electrode sheet containing a negative electrode membrane.

[0084] The negative electrode provided in the embodiments of the present application is beneficial for improving the first coulombic efficiency and cycle performance of the battery.

[0085] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0086] Example 1

[0087] This embodiment provides a silicon-oxygen negative electrode material, which is mainly prepared by the following steps:

[0088] 5 kg of SiO powder was placed in a CVD furnace and heated to 900°C. Acetylene was then introduced as a carbon source and maintained at this temperature for 1 hour. After cooling, the powder was passed through a 325 mesh sieve. The amount of acetylene was controlled to ensure a 10 nm thick carbon layer on the carbon-coated SiO.

[0089] Carbon-coated SiO2 was solid-phase mixed with magnesium powder at a mass ratio of 6:1 using a VC mixer. The mixture was placed in a stainless steel vacuum rotary kiln, evacuated to a pressure of 10 Pa, and then sealed. The temperature was raised to 400°C at a rate of 5°C / min and held for 8 hours, followed by further heating to 950°C and holding for 4 hours.

[0090] Figure 1 The scanning electron microscope image of the silicon oxide negative electrode material provided in Example 1 is shown in FIG. Figure 1 It can be observed that the particles are dispersed relatively evenly without obvious agglomeration. The particle size D50 of the sample measured by Malvern 3000 laser particle size analyzer is 6.1 μm.

[0091] Figure 2The XRD spectrum of the silicon-oxygen negative electrode material provided in Example 1 can be found by calibrating the corresponding peaks through the PDF card. It can be found that the sample prepared in this example contains Si, SiO, Mg2SiO4, and MgSiO3. The grain size of the Si(111) crystal plane is calculated to be 10 nm by the Scherrer equation.

[0092] Figure 3 This is a scanning electron microscope image of the CP cross-section of the silicon-oxygen negative electrode material provided in Example 1. Figure 4 This is the distribution curve of each element in the cross section of the silicon-oxygen negative electrode material provided in Example 1 from the inside to the outside of the particle.

[0093] from Figure 3 and Figure 4 It can be seen that magnesium can penetrate into the interior of the particles and react, and the silicon grains are evenly dispersed in the silicate skeleton. The silicate inhibits the volume expansion of the silicon grains, which is beneficial to improving the cycle life of the material.

[0094] Example 2

[0095] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0096] The carbon-coated SiO2 was solid-phase mixed with magnesium powder and then kept at 400 °C for 4 h.

[0097] Figure 5 This is a scanning electron microscope image of the CP cross-section of the silicon-oxygen negative electrode material provided in Example 2. Figure 6 This is the distribution curve of each element in the cross section of the silicon-oxygen negative electrode material provided in Example 2 from the inside to the outside of the particle.

[0098] from Figure 5 and Figure 6 It can be seen that in some reaction processes, only the surface layer is doped with metal to form metal silicate, and the inner layer is SiO.

[0099] Example 3

[0100] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0101] The mass ratio of carbon-coated SiO to magnesium powder is 8:1.

[0102] Example 4

[0103] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0104] The mass ratio of carbon-coated SiO to magnesium powder is 5:1.

[0105] Example 5

[0106] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0107] The mass ratio of carbon-coated SiO to magnesium powder is 9:1.

[0108] Example 6

[0109] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0110] The amount of acetylene was controlled so that the thickness of the carbon layer of the carbon-coated SiO was 50 nm.

[0111] Example 7

[0112] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0113] The amount of acetylene was controlled so that the thickness of the carbon layer of the carbon-coated SiO was 100 nm.

[0114] Example 8

[0115] This embodiment provides a silicon-oxygen negative electrode material. The difference between the preparation of the silicon-oxygen negative electrode material of this embodiment and that of Example 1 is as follows:

[0116] The amount of acetylene was controlled so that the thickness of the carbon layer of the carbon-coated SiO was 200 nm.

[0117] Comparative Example 1

[0118] This comparative example provides a silicon-oxygen negative electrode material, which is mainly prepared by the following steps:

[0119] 5 kg of SiO powder was solid-phase mixed with magnesium powder at a powder-to-magnesium ratio of 6:1 (mass ratio) using a VC mixer. After mixing, the mixture was placed in a stainless steel vacuum rotary kiln, evacuated to a pressure of 10 Pa, and then sealed. The temperature was raised to 400°C at a rate of 5°C / min and held for 4 hours. The temperature was then further raised to 900°C and held for 4 hours. After cooling, the mixture was passed through a 325-mesh sieve.

[0120] The metal-modified SiO powder was placed in a CVD furnace, heated to 900°C, and then introduced into an acetylene carbon source. The mixture was kept at this temperature for 1 hour, cooled, and passed through a 325-mesh sieve.

[0121] Figure 7 The scanning electron microscope image of the silicon oxide negative electrode material provided in Comparative Example 1 is as follows: Figure 7 Obvious particle agglomeration can be observed in the sample, and the particle size D50 of the sample measured by Malvern 3000 laser particle size analyzer is 16.0 μm.

[0122] Figure 8 The XRD pattern of the silicon-oxygen negative electrode material provided in Comparative Example 1 is as follows: Figure 8 It can be seen that there are only Si, SiO, and Mg2SiO4 in the XRD pattern, and the Si peak intensity is very high. The grain size of the Si(111) crystal plane is calculated to be 35.5nm by the Scherrer equation.

[0123] Test example

[0124] The silicon oxide negative electrode materials prepared in Examples 1 to 8 and Comparative Example 1 were assembled into 2032 button cells, and their performance was tested. The results are summarized in Figure 9 And Table 1:

[0125] The negative electrode material prepared in the present invention is assembled using 2032 button cells. The specific assembly method is as follows:

[0126] 1. Prepare slurry by mixing active material, conductive agent and binder in a ratio of 94:2.5:3.5. Use water-based binder as binder and stir evenly by wet method.

[0127] 2. Apply the slurry evenly on the copper foil and then dry it.

[0128] 3. Assemble the battery: In the glove box, stack the lithium sheet, diaphragm, and electrode in sequence and add a certain amount of electrolyte to complete the button battery assembly.

[0129] The discharge specific capacity described in Table 1 is the lithium insertion specific capacity of the positive electrode in the button half-cell, and the charge specific capacity is the lithium removal specific capacity of the positive electrode in the button half-cell.

[0130] Grain size testing method: The crystal structure of the composite material is determined by using CuKα radiation source XRD. In the X-ray diffraction pattern, the Si(111) characteristic peak corresponds to the range of 2θ=27.5~29.5°. The half-peak width of the peak is measured and substituted into the Scherrer equation to obtain the Si(111) crystal plane grain size, which is the silicon crystal grain size in this application.

[0131] Table 1 Electrochemical properties of negative electrode materials obtained in Examples 1 to 8 and Comparative Example 1

[0132]

[0133] Figure 9The charge and discharge curves of the button cells obtained in Example 1 and Comparative Example 1 of the present application are shown. The experimental results show that the negative electrode materials provided in Examples 1 to 8 of the present application, when assembled into 2032 button cells, have excellent electrochemical performance, with an initial charge capacity of 1200 to 1500 mAh / g, an initial charge and discharge coulombic efficiency of 83% to 90%, and a capacity retention rate greater than 87% after 200 cycles.

[0134] Furthermore, the electrochemical performance of Example 1 is better than that of Example 2, the electrochemical performance of Examples 1 and 3 is better than that of Examples 4 and 5, and the electrochemical performance of Examples 1, 6, and 7 is better than that of Example 8.

[0135] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a silicon-oxygen negative electrode material, characterized in that: include: heat-treating the carbon-coated silicon monoxide and the metal material so that at least a portion of the silicon monoxide in the carbon-coated silicon monoxide reacts with the metal material to generate silicate and silicon element, thereby obtaining a silicon-oxygen negative electrode material; The metal material includes Mg; The step of heat treating the carbon-coated silicon monoxide and the metal material comprises: The carbon-coated silicon monoxide and the metal material are kept at 300-600° C. for 1-10 hours; and then kept at 850-1100° C. for 0.5-10 hours; The heat treatment is carried out under a pressure of 1-140 Pa; The step of heat treating the carbon-coated silicon monoxide and the metal material further includes: The step of coating the surface of silicon monoxide with a carbon layer having a thickness of 10-1000 nm to obtain the carbon-coated silicon monoxide; the mass fraction of carbon in the carbon-coated silicon monoxide is 0.2-20%.

2. The method for preparing the silicon-oxygen negative electrode material according to claim 1, wherein: The mass ratio of the metal material to the carbon-coated silicon monoxide is 1:5-9.

3. The method for preparing the silicon-oxygen negative electrode material according to claim 2, wherein: The mass ratio of the metal material to the carbon-coated silicon monoxide is 1:6-8.

4. The method for preparing the silicon-oxygen negative electrode material according to claim 1, wherein: The carbon-coated silicon monoxide and the metal material are kept at 300-600° C. for 1-10 hours, and then heated to 850-1100° C. at a heating rate of 5-20° C. / min and kept for 0.5-10 hours.

5. The method for preparing the silicon-oxygen negative electrode material according to claim 4, wherein: The heat treatment is carried out under a pressure of 8-30 Pa.

6. The method for preparing the silicon-oxygen negative electrode material according to claim 1, wherein: A carbon layer is coated on the surface of silicon monoxide using chemical vapor deposition.

7. The method for preparing the silicon-oxygen negative electrode material according to claim 1, wherein: The particle size distribution of the silicon monoxide is: D10: ≥3μm; D50: 5-8μm; D100:<15μm.

8. The method for preparing the silicon-oxygen negative electrode material according to claim 1, wherein: The mass fraction of carbon in the carbon-coated silicon monoxide is 1-8%.

9. A silicon-oxygen negative electrode material, characterized in that: The silicon-oxygen negative electrode material is prepared by the method for preparing the silicon-oxygen negative electrode material according to any one of claims 1 to 8.

10. The silicon-oxygen negative electrode material according to claim 9, characterized in that: The silicon-oxygen negative electrode material includes: a core and a carbon layer covering the core, wherein the core includes Mg2SiO4, MgSiO3 and silicon grains dispersed between the Mg2SiO4 and MgSiO3.

11. The silicon-oxygen negative electrode material according to claim 10, characterized in that: The thickness of the carbon layer is 10-100 nm.

12. A negative electrode for a secondary battery, characterized in that: The negative electrode for a secondary battery comprises the silicon-oxygen negative electrode material according to any one of claims 9 to 11.

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