A method for synthesizing high-capacity negative electrode material for lithium-ion batteries

Abstract

The present invention provides a method for synthesizing a high-capacity negative electrode material for lithium-ion batteries, comprising the following steps: sand-milling micron-sized silicon oxide to obtain nano-sized silicon oxide; adding nano-sized silicon oxide to an alkali metal solution, mixing and dispersing the mixture evenly, and then drying the mixture to obtain a raw material powder; heating the raw material powder to 750°C to 850°C in an inert gas atmosphere to obtain a composite material in which nano-sized crystalline Si is embedded in SiO and coated with metasilicate; mixing nano-Si / SiO@metasilicate and artificial graphite, and heat-treating the carbon coating with asphalt in an inert gas atmosphere to obtain a high-capacity negative electrode material for lithium-ion batteries. The high-capacity negative electrode material prepared by the present invention has a specific capacity of 1000mAh / g to 1400mAh / g, and has less capacity decay after 50 cycles.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion battery materials, and in particular relates to a method for synthesizing a high-capacity negative electrode material for a lithium ion battery. Background Art

[0002] Lithium-ion battery is a kind of rechargeable battery that relies on the movement of lithium ions between the positive and negative electrodes to achieve the purpose of charging and discharging. It is mainly composed of four parts: positive electrode, negative electrode, electrolyte, and diaphragm. At present, it is mainly used in new energy vehicles, electric motorcycles, solar photovoltaic and wind power generation energy storage systems, smart grid energy storage systems, hospital backup UPS, EPS power supply, security lighting, drones, laptops, mining safety equipment, digital products and other fields.

[0003] Commercial lithium-ion batteries mainly use graphite materials as negative electrode materials. The reversible specific capacity of carbon materials has reached 360mAh / g, but its theoretical specific capacity is only 372mAh / g, indicating that the development of traditional graphite negative electrode materials has reached its limit, but it is still difficult to meet the requirements of battery energy density for future new energy electric vehicles. In order to further improve the energy density of lithium-ion batteries, many high-specific-capacity negative electrode materials have become hot topics in related research. Silicon-based materials (Si, SiO, etc.) have become the focus and hot topic of lithium-ion battery research due to their abundant reserves, high theoretical specific capacity, low lithium insertion and extraction potential, and low price.

[0004] However, the development of Si and SiO faces huge challenges. The most fatal problem is their expansion after lithium insertion. The volume expansion rate of Si after complete lithium insertion is as high as 300%, which causes the material to pulverize and the electrode structure to be destroyed during the charge and discharge process, resulting in a significant decrease in cycle performance. SiO contains less active Si, and because the silicon dioxide (SiO 2 ) and silicon dioxide (SiO x ) will generate irreversible products such as lithium silicate and lithium oxide during the first lithium insertion process to relieve expansion stress, so SiO has a smaller volume change rate than Si. However, its volume change rate is still around 200%, which is much larger than the volume change rate of graphite electrode (~10%). And SiO electrode materials also need to solve the problems of poor conductivity and low first-cycle coulomb efficiency. Therefore, overcoming the shortcomings of silicon-based materials and preparing silicon-based composite materials with excellent performance has become an urgent task for the development of high-capacity power batteries. Summary of the invention

[0005] In view of this, the present invention aims to overcome the defects in the prior art and proposes a method for synthesizing a high-capacity negative electrode material for a lithium-ion battery.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for synthesizing a high-capacity negative electrode material for a lithium-ion battery comprises the following steps:

[0008] S1: adding nano-sized silicon dioxide obtained by sand grinding micron-sized silicon dioxide and alkali metal salt into deionized water to fully dissolve, thereby preparing an alkali metal solution with a mass percentage of 1-5wt%;

[0009] S2: adding nano-sized silicon dioxide into the alkali metal solution, stirring and mixing evenly, and then drying to obtain a raw material powder;

[0010] S3: heating the raw material powder to 750°C-850°C in an inert gas atmosphere for heat treatment to obtain a composite material in which nano-scale crystalline Si of suitable size is embedded in SiO and coated with metasilicate (referred to as nano-Si / SiO@metasilicate, the same below);

[0011] S4: Nano Si / SiO@metasilicate and artificial graphite are mixed, and carbon is coated by heat treatment with asphalt in an inert gas atmosphere to obtain a high-capacity negative electrode material for lithium-ion batteries (referred to as nano Si / SiO@metasilicate-G / C, the same below).

[0012] In some embodiments of the present invention, the molar ratio of nano-sized silicon dioxide to alkali metal salt in step S2 is (25-35):1.

[0013] In some embodiments of the present invention, the molar ratio of nano-sized silicon dioxide to alkali metal salt in step S2 is 30:1.

[0014] In some embodiments of the present invention, the heating temperature in step S3 is 800°C.

[0015] In some embodiments of the present invention, the Dv50 particle size of the nano-scale silicon dioxide in step S1 is 20-900 nm.

[0016] In some embodiments of the present invention, the alkali metal salt is Li 2 CO 3 、Na 2 CO 3 , K 2 CO 3 One or a mixture of two or more.

[0017] In some embodiments of the present invention, the alkali metal salt is Li 2 CO 3 .

[0018] In some embodiments of the present invention, the heat treatment time in step S3 is 3 to 5 hours.

[0019] In some embodiments of the present invention, the heating time in step S3 is 4 hours.

[0020] In some embodiments of the present invention, the mass ratio of nano-Si / SiO@metasilicate, artificial graphite, and asphalt in step S4 is (1-10): (1-5): (1-10).

[0021] In some embodiments of the present invention, the inert gas is nitrogen or argon.

[0022] In some embodiments of the present invention, the rotation speed of the stirring process in step S2 is 300-600 revolutions per minute, and the stirring time is 12-24 hours.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention uses nano-SiO. Compared with commercially available micron-SiO, nano-SiO will bring shorter Li + The diffusion path and smaller expansion stress during lithium insertion are beneficial to improving the electrode cycle performance. Metasilicates generated by the uniform solid-liquid reaction of alkali metal salt solution and SiO can alleviate the volume expansion of nano-SiO materials during lithium insertion and provide Li + At the same time, the alkali metal cations in the alkali metal salt solution modify the SiO amorphous network structure and promote the disproportionation reaction of SiO (SiO → crystalline Si + SiO 2 ), and by controlling the amount of alkali metal salt added and the heat treatment temperature, the crystalline Si in SiO can be regulated to reach a suitable size (5~10nm). A suitable size of crystalline Si is beneficial to inhibit the volume expansion of SiO during the charge and discharge cycle and improve the cycle performance of the electrode. Then, the conductivity and cycle stability of the negative electrode material are improved by introducing graphite and carbon coating. After assembling it into a half-cell, it was innovatively discovered through electrochemical performance testing that it is a new type of high-capacity negative electrode material.

[0025] (2) The high-capacity negative electrode material prepared by the present invention has a specific capacity of 1000 mAh / g to 1400 mAh / g, and has a small capacity attenuation after 50 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The particle size distribution diagram of the commercial micron SiO used in Example 1, Dv50 = 5.73 μm;

[0027] Figure 2The particle size distribution diagram of nano-SiO obtained by grinding commercial micron-SiO sand in Example 1, Dv50=879nm;

[0028] Figure 3 This is a SEM image of the commercial micron SiO used in Example 1;

[0029] Figure 4 This is a SEM image of nano-SiO obtained after sand grinding in Example 1;

[0030] Figure 5 The 50-cycle performance diagram of the negative electrode material made of commercial micron SiO and the negative electrode material made of nano-SiO obtained by sand grinding;

[0031] Figure 6 The molar ratio of Comparative Examples 2 to 4 is SiO:Li 2 CO 3 =16:1 50-cycle performance diagram of negative electrode materials prepared by heating at 600℃, 700℃ and 800℃ for 4h;

[0032] Figure 7 The molar ratio of Comparative Examples 5 to 7 is SiO:Li 2 CO 3 =20:1 50-cycle performance diagram of negative electrode materials prepared by heating at 600℃, 700℃ and 800℃ for 4h;

[0033] Figure 8 The molar ratio of Example 1, Comparative Example 8 and Comparative Example 9 is SiO:Li 2 CO 3 =30:1 50-cycle performance diagram of negative electrode materials prepared by heating at 600℃, 700℃ and 800℃ for 4h;

[0034] Fig. 9 The molar ratio of Example 1 is SiO:Li 2 CO 3 =30:1 XRD pattern of negative electrode material prepared by heating at 800℃ for 4h;

[0035] Fig.10 The molar ratio of SiO:Li in Comparative Example 1 is 2 CO 3 =1:0 XRD pattern of nano-SiO prepared by heating at 800℃ for 4h;

[0036] Fig.11 The molar ratio of SiO:Li in Comparative Example 1 is 2 CO 3 =1:0Nano-Si / SiO@Li prepared by heating at 800℃ for 4h 2 SiO3 HRTEM images of

[0037] Fig.12 The molar ratio of Comparative Example 8 is SiO:Li 2 CO 3 =30:1 prepared by heating at 600℃ for 4h 2 SiO 3 HRTEM image (the lattice spacing of the white circle in the figure is d=0.313nm, corresponding to crystalline Si);

[0038] Fig.13 The molar ratio of Comparative Example 9 is SiO:Li 2 CO 3 =30:1 prepared by heating at 700℃ for 4h 2 SiO 3 HRTEM image (the lattice spacing of the white circle in the figure is d=0.313nm corresponding to crystalline Si, and the lattice spacing of the yellow circle is d=0.330nm corresponding to Li 2 SiO 3 Grain);

[0039] Fig.14 The molar ratio of Example 1 is SiO:Li 2 CO 3 =30:1 prepared by heating at 800℃ for 4h 2 SiO 3 HRTEM image (the lattice spacing of the white circle in the figure is d=0.313nm corresponding to crystalline Si, and the lattice spacing of the yellow circle is d=0.330nm corresponding to Li 2 SiO 3 Grain);

[0040] Fig.15 The molar ratio of Comparative Example 5 is SiO:Li 2 CO 3 =20:1Nano-Si / SiO@Li prepared by heating at 800℃ for 4h 2 SiO 3 HRTEM image (the lattice spacing of the white circle in the figure is d=0.313nm, corresponding to crystalline Si);

[0041] Fig.16 This is a SEM image of the negative electrode material prepared in Example 1;

[0042] Fig.17 50 cycle performance diagrams of the negative electrode materials prepared in Examples 1 to 5;

[0043] Fig.18This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 1;

[0044] Fig.19 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 2;

[0045] Fig. 20 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 3;

[0046] Fig.21 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 4;

[0047] Fig. 22 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 5;

[0048] Fig.23 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 6;

[0049] Fig.24 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 7;

[0050] Fig.25 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 8;

[0051] Fig.26 This is a 50-cycle performance diagram of the negative electrode material prepared in Comparative Example 9. DETAILED DESCRIPTION

[0052] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0053] Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0054] Where values ​​are described herein as a range, it should be understood that such disclosure includes disclosure of all possible sub-ranges within that range, as well as specific values ​​falling within that range, regardless of whether a specific value or a specific sub-range is explicitly stated.

[0055] In this document, "multiple" and the like, unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0056] In this document, the terms “preferred” and “more preferred” are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute limitations on the scope of protection of the present invention.

[0057] In this document, the words "further" and the like are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0058] In this article, the term "and / or" is a description of the association relationship of objects, indicating that three relationships may exist. For example, A and / or B means: A or B, or A and B.

[0059] As used herein, the term "about" means + / - 10%, preferably + / - 5%, more preferably + / - 1% of the specified value.

[0060] The terms “include,” “including,” “have,” “contain,” etc. used in this article are open-ended terms, meaning including but not limited to.

[0061] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0062] The present invention will be described in detail below with reference to the embodiments.

[0063] Example 1

[0064] A method for synthesizing a high-capacity negative electrode material for a lithium-ion battery comprises the following steps:

[0065] S1: Micron-sized silicon dioxide (purchased from Hunan Jinsi Technology Co., Ltd., product model KSP1, the same below) is sand-milled to obtain nano-sized silicon dioxide. 2 CO 3 After being fully dissolved in deionized water, an alkali metal solution with a mass percentage of 2wt% was prepared. 2 CO 3 The molar ratio is 30:1;

[0066] Figure 1 is the particle size distribution of commercial micron SiO before sand milling. Figure 2 The particle size distribution after sand milling is shown in Figure 2. By comparison, it can be seen that nano-SiO2 was successfully prepared by sand milling. Figure 3 and Figure 4 The SEM images of commercial SiO before and after grinding prove the successful preparation of nano-SiO.

[0067] S2: adding nano-SiO2 into the alkali metal solution and stirring to mix evenly, wherein the stirring speed is 450 revolutions per minute, the stirring time is 24 hours, and the mixed solution is dried to obtain a raw material powder;

[0068] S3: Nano-Si / SiO@Li prepared by heat treatment at 800℃ for 4h in an argon environment 2 SiO 3 (Its XRD pattern is as follows Fig. 9 shown);

[0069] S4: Nano-Si / SiO@Li 2 SiO 3 , artificial graphite and asphalt in a mass ratio of 6:4:5 were carbonized and coated in an argon atmosphere to obtain nano-Si / SiO@metasilicate-G / C.

[0070] The SEM of nano-Si / SiO@metasilicate-G / C prepared in Example 1 is as follows: Fig.16 As shown, we can see nano-Si / SiO@Li 2 SiO 3 The graphite is evenly mixed together, and the amorphous carbon formed by the pyrolysis of asphalt is well coated on the surface of the composite material. Fig.17 As shown, the first discharge capacity is 1281.8 mAh g -1 The first coulombic efficiency is 74.82%. After 50 cycles, the discharge capacity is 818.1 mAh g -1 .

[0071] Example 2

[0072] A method for synthesizing a high-capacity negative electrode material for a lithium-ion battery comprises the following steps:

[0073] S1: The nano-scale silicon dioxide is obtained by sand grinding the micron-scale silicon dioxide. 2 CO 3 After being fully dissolved in deionized water, an alkali metal solution with a mass percentage of 3wt% was prepared. 2 CO 3 The molar ratio is 25:1;

[0074] S2: Add nano-SiO2 into the alkali metal solution and stir to mix evenly, wherein the stirring speed is 500 rpm and the stirring time is 18 hours. Dry the mixed solution to obtain raw material powder;

[0075] S3: Nano-Si / SiO@Li prepared by heat treatment at 750℃ for 4h in an argon environment 2 SiO 3 ;

[0076] S4: Nano-Si / SiO@Li 2 SiO 3, artificial graphite and asphalt in a mass ratio of 6:4:5 were carbonized and coated in an argon atmosphere to obtain nano-Si / SiO@metasilicate-G / C.

[0077] After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C prepared in Example 2 is as follows: Fig.17 As shown, the first discharge capacity is 1277.1 mAh g -1 The first coulombic efficiency is 74.32%. After 50 cycles, the discharge capacity is 706.6 mAh g -1 .

[0078] Example 3

[0079] A method for synthesizing a high-capacity negative electrode material for a lithium-ion battery comprises the following steps:

[0080] S1: The nano-scale silicon dioxide is obtained by sand grinding the micron-scale silicon dioxide. 2 CO 3 After being fully dissolved in deionized water, an alkali metal solution with a mass percentage of 4wt% was prepared. 2 CO 3 The molar ratio is 25:1;

[0081] S2: Add nano-SiO2 into the alkali metal solution and stir to mix evenly, wherein the stirring speed is 450 rpm and the stirring time is 12h. Dry the mixed solution to obtain raw material powder;

[0082] S3: Nano-Si / SiO@Li prepared by heat treatment at 850℃ for 4h in an argon environment 2 SiO 3 ;

[0083] S4: Nano-Si / SiO@Li 2 SiO 3 , artificial graphite and asphalt in a mass ratio of 6:4:5 were carbonized and coated in an argon atmosphere to obtain nano-Si / SiO@metasilicate-G / C.

[0084] After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C prepared in Example 3 is as follows: Fig.17 As shown, the first discharge capacity is 1324.1 mAh g -1 The first coulombic efficiency is 72.88%, and after 50 cycles, the discharge capacity is 796 mAh g -1 .

[0085] Example 4

[0086] The difference between this embodiment and embodiment 1 is that the alkali metal salt solution is Na2 CO 3 The solution has a mass percentage concentration of 1 wt%. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C prepared in Example 4 is as follows: Fig.17 As shown, the first discharge capacity is 1193 mAh g -1 The first coulombic efficiency is 76.82%. After 50 cycles, the discharge capacity is 749.6 mAhg -1 .

[0087] Example 5

[0088] The difference between this embodiment and embodiment 1 is that the alkali metal salt solution is K 2 CO 3 The solution has a mass percentage concentration of 5 wt%. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C prepared in Example 5 is as follows: Fig.17 As shown, the first discharge capacity is 1115.1 mAh g -1 The first coulombic efficiency is 74.43%. After 50 cycles, the discharge capacity is 738.9 mAh g -1 .

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3 =1:0, nano-SiO (its XRD pattern is shown in Fig.10 As shown in the figure), nano-SiO, artificial graphite and asphalt were carbonized in an argon atmosphere at a mass ratio of 6:4:5 to obtain nano-Si / SiO-G / C. The electrochemical performance of the nano-Si / SiO-G / C was tested as follows: Fig.18 As shown in FIG. 1 , it can be seen that the volume expansion of SiO during the lithium insertion and extraction process leads to a continuous decrease in capacity. The electrochemical performance of Comparative Example 1 is shown in FIG. Fig.18 As shown, the first discharge capacity is 1200.1 mAh g -1 The first coulombic efficiency is 75.32%. After 50 cycles, the discharge capacity is 465.3 mAh g -1 .

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3=16:1. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in Comparative Example 2 is as follows Fig.19 As shown, the first discharge capacity is 146.6 mAh g -1 The first coulombic efficiency is 70.46%. After 50 cycles, the discharge capacity is 98.74 mAh g -1 .

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3 =16:1, and the heat treatment temperature in step S3 is 600°C. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in comparative example 3 is as follows: Fig. 20 As shown, the first discharge capacity is 224.5 mAh g -1 The first coulombic efficiency is 76.5%, and after 50 cycles, the discharge capacity is 212.9 mAh g -1 .

[0095] Comparative Example 4

[0096] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3 =16:1, and the heat treatment temperature in step S3 is 700°C. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in comparative example 4 is as follows: Fig.21 As shown, the first discharge capacity is 226.8 mAh g -1 The first coulombic efficiency is 79.53%. After 50 cycles, the discharge capacity is 208.6 mAh g -1 .

[0097] Comparative Example 5

[0098] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3 =20:1. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in Comparative Example 5 is as follows Fig. 22As shown, the first discharge capacity is 1004.3 mAh g -1 The first coulombic efficiency is 78.11%. After 50 cycles, the discharge capacity is 607 mAh g -1 .

[0099] Comparative Example 6

[0100] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3 =20:1, and the heat treatment temperature in step S3 is 600°C. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in comparative example 6 is as follows: Fig.23 As shown, the first discharge capacity is 1315.8 mAh g -1 The first coulombic efficiency is 69.79%. After 50 cycles, the discharge capacity is 422.5 mAh g -1 .

[0101] Comparative Example 7

[0102] The difference between this comparative example and Example 1 is that in step S1, nano-SiO and Li 2 CO 3 The molar ratio of SiO:Li 2 CO 3 =20:1, and the heat treatment temperature in step S3 is 700°C. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in comparative example 7 is as follows: Fig.24 As shown, the first discharge capacity is 1146 mAh g -1 The first coulombic efficiency is 77.93%. After 50 cycles, the discharge capacity is 470.1 mAh g -1 .

[0103] Comparative Example 8

[0104] The difference between this comparative example and Example 1 is that the heat treatment temperature in step S3 is 600°C. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C negative electrode material prepared in Comparative Example 8 is as follows: Fig.25 As shown, the first discharge capacity is 1149.4 mAh g -1 The first coulombic efficiency is 75.14%. After 50 cycles, the discharge capacity is 460.4 mAh g -1 .

[0105] Comparative Example 9

[0106] The difference between this comparative example and Example 1 lies in that the heat treatment temperature in step S3 is 700 °C. After testing, the electrochemical performance of the nano-Si / SiO@metasilicate-G / C anode material prepared in Comparative Example 9 is as follows Fig.26 shown. The initial discharge specific capacity is 1214 mAh g -1 . The initial Coulombic efficiency is 77.11%. After 50 cycles, its discharge specific capacity is 476.6 mAh g -1 .

[0107] Figure 5 is the 50-cycle performance graph of the anode material directly prepared from the nano-SiO prepared in Example 1 and the anode material directly prepared from commercially available commercial micron-sized SiO. The initial discharge specific capacity of the anode material directly prepared from commercially available commercial micron-sized SiO is 2282.0 mAh g -1 . The initial Coulombic efficiency is 47.8%. After 10 cycles, its discharge specific capacity is 33 mAh g -1 . It can be seen that the cycling performance of nano-SiO is improved compared to micron-SiO.

[0108] Figure 6-Figure 8 is the 50-cycle performance graph of Si / SiO@Li 2 CO 3 prepared with different amounts of incorporated Li 2 SiO 3 and heat treatment temperature. It can be seen that by controlling the amount of incorporated Li 2 CO 3 and heat treatment temperature, the structure of Si / SiO@Li 2 SiO 3 is controlled, thereby improving the cycling performance of the material. The structure of SiO is composed of amorphous Si surrounded by amorphous SiO 2 and some low-valent silicon oxides SiO x (0 < X < 2). At high temperatures, SiO in SiO 2 reacts with Li 2 CO 3 (Li 2 CO 3 + SiO 2 → Li 2 SiO 3 +CO 2 ). At the same time, the presence of Li 2 CO 3 will promote the disproportionation reaction of SiO (SiO → crystalline Si + SiO 2 ). And the disproportionation reaction of SiO can be controlled by controlling the amount of incorporated Li 2 CO 3The amount of and the temperature of the heat treatment control the size of the crystalline Si. Figure 11-Figure 15 Nano-Si / SiO@Li prepared in different examples and comparative examples 2 SiO 3 In the comparison of HRTEM images, it can be seen that the crystalline Si scales in different materials are different. The molar ratio with the best cycle performance is SiO:Li 2 CO 3 =30:1 prepared by heating at 800℃ for 4h 2 SiO 3 The size of crystalline Si should be optimal (5-10nm).

[0109] Depend on Fig.17 and Fig.18 It can be seen that compared with the negative electrode material prepared in comparative example 1, the negative electrode material prepared in example 1 has extremely excellent cycle stability, and after 50 cycles, the capacity has a smaller attenuation.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing a high-capacity negative electrode material for a lithium-ion battery, characterized in that: The steps include: S1: adding nano-sized silicon dioxide obtained by sand grinding micron-sized silicon dioxide and alkali metal salt into deionized water to fully dissolve, thereby preparing an alkali metal solution with a mass percentage of 1-5wt%; S2: adding nano-sized silicon dioxide into the alkali metal solution, stirring and mixing, and then drying to obtain a raw material powder, wherein the molar ratio of nano-sized silicon dioxide to the alkali metal salt is (25-35):1; S3: heating the raw material powder to 750°C-850°C in an inert gas atmosphere for heat treatment to obtain nano-Si / SiO@ metasilicate; S4: Mixing nano-Si / SiO@ metasilicate and artificial graphite, and using asphalt to perform heat treatment in an inert gas atmosphere for carbon coating to obtain a high-capacity negative electrode material for lithium-ion batteries; The Dv50 particle size of the nano-scale silicon dioxide in step S1 is 20-900 nm; the alkali metal salt is one or a mixture of two or more of Li2CO3, Na2CO3, and K2CO3; and the heat treatment time in step S3 is 3-5 h.

2. The method for synthesizing a high-capacity negative electrode material for a lithium-ion battery according to claim 1, characterized in that: In step S2, the molar ratio of nano-sized silicon dioxide to alkali metal salt is 30:

1.

3. The method for synthesizing a high-capacity negative electrode material for a lithium-ion battery according to claim 1, characterized in that: The heat treatment in step S3 is performed at 800°C.

4. The method for synthesizing a high-capacity negative electrode material for a lithium-ion battery according to claim 1, characterized in that: The heat treatment in step S3 is performed for 4 hours.

5. The method for synthesizing a high-capacity negative electrode material for a lithium-ion battery according to claim 1, characterized in that: In step S4, the mass ratio of nano-Si / SiO@ metasilicate, artificial graphite and asphalt is (1-10): (1-5): (1-10).

6. The method for synthesizing a high-capacity negative electrode material for a lithium-ion battery according to claim 1, characterized in that: The rotation speed of the stirring process in step S2 is 300-600 revolutions per minute, and the stirring time is 12-24 hours.

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