Composite negative electrode material, preparation method thereof, negative electrode sheet and lithium ion battery

Abstract

The application discloses a composite negative electrode material and a preparation method thereof, a negative electrode sheet and a lithium ion battery, and belongs to the technical field of lithium ion batteries.The composite negative electrode material comprises a core and a coating layer located on the surface of the core; the core comprises a carbon matrix and a filling material, the carbon matrix has a first pore, and the filling material is at least partially distributed in the first pore; and the filling material comprises SiOx, and the filling material has a second pore.The composite silicon negative electrode composite negative electrode material can effectively reduce the volume effect and improve the cycle stability.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and more specifically, to a composite negative electrode material and its preparation method, a negative electrode sheet, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, wide operating voltage range, long lifespan, low self-discharge, no memory effect, and low environmental pollution, making them widely used in 3C consumer electronics, energy storage, and power batteries. The anode material plays a decisive role in the electrochemical performance of lithium-ion batteries. Graphite is a commonly used anode material; however, its theoretical specific capacity of 372 mAh / g is insufficient to meet the demands of higher energy density lithium-ion batteries.

[0003] Silicon possesses a theoretical specific capacity of 4200 mAh / g, exhibiting advantages such as high specific capacity and abundant reserves, making it suitable for use as an anode material. However, silicon as an anode material exhibits a significant volume effect during charge and discharge, resulting in rapid capacity decay. Mixing graphite and silicon can effectively improve its cycle stability. The main methods for silicon-graphite composites include mechanical stirring, adding pitch and heating with stirring, and spray drying. In these methods, silicon is mainly distributed physically on the graphite surface, resulting in weak bonding and making it prone to breaking contact with graphite and losing activity during cycling. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite anode material that can effectively reduce the volume effect and improve cycle stability, as well as its preparation method, anode sheet, and lithium-ion battery.

[0005] To achieve this objective, the following technical solution is adopted in this application:

[0006] In a first aspect, embodiments of this application provide a composite anode material, comprising: a core and a coating layer located on the surface of the core;

[0007] The core comprises a carbon matrix and a filling material, the carbon matrix having a first pore, and the filling material being at least partially distributed within the first pore; the filling material comprises SiOx and has a second pore.

[0008] In some possible implementations, the composite anode material includes at least one of the following features (1) to (9):

[0009] (1) The carbon matrix includes at least one of graphite matrix, mesophase carbon microsphere matrix, soft carbon matrix and hard carbon matrix;

[0010] (2) The first pore includes a plurality of holes, and at least a portion of a portion of the holes is filled with a filling material;

[0011] (3) The first pore includes multiple holes, and the distance between two adjacent holes is 0.5μm to 5μm;

[0012] (4) The depth of the first pore is 0.5μm to 10μm;

[0013] (5) The diameter of the first pore is 0.1 μm to 3 μm;

[0014] (6) The diameter of the second pore is 0.1 nm to 30 nm;

[0015] (7) The value of X in SiOx ranges from 0.5 to 2;

[0016] (8) SiOx contains SiO and silicon grains;

[0017] (9) The coating layer includes a carbon layer.

[0018] In some possible implementations, the coating layer includes a carbon layer, the carbon layer includes a first carbon layer and a second carbon layer, the first carbon layer has a third pore, the first carbon layer coats the core surface, and the second carbon layer coats the surface of the first carbon layer; and / or, the composite negative electrode material includes at least one of the following features (10) to (11);

[0019] (10) The carbon in the first carbon layer includes at least one of hard carbon, graphene carbon material and carbon nanotubes;

[0020] (11) The carbon in the second carbon layer includes soft carbon.

[0021] Secondly, embodiments of this application provide a method for preparing a composite negative electrode material, including:

[0022] Provide a carbon matrix with first pores;

[0023] SiOy is formed in at least the first pore of the carbon matrix to obtain the first precursor, wherein the value of y ranges from 0.2 to 1.5;

[0024] A coating layer is formed on the surface of the first precursor to obtain the second precursor. The SiOy in the second precursor is disproportionated to remove part of the generated silicon dioxide, and then a composite anode material is obtained.

[0025] Alternatively, the SiOy in the first precursor is disproportionated to remove some of the generated silicon dioxide, and a coating layer is formed on the surface of the obtained product to obtain a composite anode material.

[0026] In some possible implementations, the method for preparing a carbon matrix with first pores includes: mixing a carbon matrix precursor with a catalyst and performing heat treatment in an H2 atmosphere to obtain a carbon matrix with first pores;

[0027] And / or, the preparation method includes at least one of the following features (12) to (14):

[0028] (12) The catalyst includes at least one of cobalt catalyst and nickel catalyst;

[0029] (13) The carbon-based precursor is mixed with the catalyst and heat-treated in an H2 atmosphere at a temperature of 200℃~300℃.

[0030] (14) The D50 of the carbon matrix precursor is 1 μm to 80 μm.

[0031] In some possible implementations, the step of forming SiOy at least within the first pores of the carbon matrix includes:

[0032] A silica solution is mixed with a carbon matrix and subjected to heat treatment. The resulting product is then reduced to obtain the first precursor.

[0033] And / or, the preparation method includes at least one of the following features (15) to (18):

[0034] (15) The temperature for heat treatment after mixing the silica solution with the carbon matrix is ​​70℃~95℃;

[0035] (16) The step of reducing the product includes: reducing the product under a reducing atmosphere and a temperature of 1000℃~2000℃;

[0036] (17) The reducing atmosphere includes at least one of H2 and methane;

[0037] (18) The weight ratio of carbon matrix to silica solution is 0.2 to 5:1.

[0038] In some possible implementations, the step of removing part of the silica includes: the coating layer contains an alkaline oxide, which reacts with the silica to form a silicate, which then reacts with an acid solution to form SiOx with a second pore.

[0039] And / or, the preparation method includes at least one of the following features (19) to (22):

[0040] (19) Basic oxides include at least one of calcium oxide, sodium oxide, barium oxide and chromium oxide;

[0041] (20) Acid solutions include any one of hydrochloric acid, sulfuric acid and nitric acid;

[0042] (21) The mass concentration of hydrochloric acid is greater than 37%, and the mass concentrations of sulfuric acid and nitric acid are both greater than 70%;

[0043] (22) The weight ratio of the basic oxide to the first precursor is 6 to 9:1;

[0044] Alternatively, the step of removing part of the silica includes: reacting silica with HF to remove part of the silica, forming SiOx with a second pore, and / or, the mass concentration of HF is greater than 20%.

[0045] In some possible implementations, a carbon layer precursor is formed on the surface of a first precursor, and a second precursor is heat-treated to carbonize the carbon layer precursor to form a carbon layer. The preparation method includes at least one of the following features (23) to (25):

[0046] (23) The heat treatment temperature for the second precursor is 700℃~1200℃;

[0047] (24) While the carbon layer precursor is carbonized, SiOy is partially branched into silicon dioxide; and after the carbon layer precursor is carbonized, part of the silicon dioxide is removed to form SiOx with a second pore.

[0048] (25) The carbon layer precursor contains water-soluble salt. After the carbon layer precursor is carbonized, water is used to remove the water-soluble salt to form a first carbon layer with a third pore, and then a second carbon layer is formed on the surface of the first carbon layer.

[0049] Thirdly, embodiments of this application provide a negative electrode sheet, including a composite negative electrode material as described in the first aspect embodiment or a composite negative electrode material prepared by the preparation method described in the second aspect embodiment.

[0050] Fourthly, embodiments of this application provide a lithium-ion battery, which includes the negative electrode sheet of the third aspect embodiment.

[0051] The technical solution of this application has at least the following beneficial effects:

[0052] (1) The filling material has a second pore, which can provide space for volume expansion during the SiOx lithiation process, thereby reducing the volume effect; and the second pore can provide more lithium storage sites, increasing the specific capacity of the composite anode material; and the second pore can provide a transport path for electrons and lithium ions, shorten the transport distance, improve the electronic conductivity and ionic conductivity of the composite anode material, and improve the charging rate and reversible capacity.

[0053] The carbon matrix can improve the conductivity of the composite anode material, and the coating layer is coated on the core surface, so the electrolyte does not come into direct contact with SiOx, which helps to avoid capacity decay.

[0054] Furthermore, the carbon matrix of this application has a first pore, and at least part of the filling material is distributed within the first pore. Even if the SiOx volume expands during charging, the filling material within the first pore is not easily detached and loses contact with the carbon matrix, thus becoming inactive. This is beneficial for improving the cycle stability of the composite anode material. Moreover, the porous structure of the carbon matrix can provide more active sites during the charging and discharging process of lithium-ion batteries, accelerating the lithium-ion diffusion rate and increasing the charging rate.

[0055] (2) In the preparation method of composite anode material, by disproportionating SiOx to generate silicon dioxide and then removing part of the silicon dioxide, pores can be effectively formed, which helps to reduce the volume effect of composite anode material. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 This is a structural schematic diagram of a composite negative electrode material according to a specific embodiment of this application;

[0058] Figure 2 This is a schematic diagram of the structure of another composite negative electrode material in a specific embodiment of this application;

[0059] Figure 3 This is a schematic diagram of the structure of the carbon matrix formed in the composite anode material preparation method according to a specific embodiment of this application;

[0060] Figure 4 This is a schematic diagram of the structure of the first precursor formed in the composite negative electrode material preparation method according to a specific embodiment of this application;

[0061] Figure 5 This is a schematic diagram of the structure of the first carbon layer formed on the surface of the core in the composite anode material preparation method according to a specific embodiment of this application.

[0062] Figure 6 This is a process flow diagram of a method for preparing composite negative electrode materials according to a specific embodiment of this application;

[0063] Figure 7 This is another process flow diagram of the composite negative electrode material preparation method in a specific embodiment of this application.

[0064] Icons: 10-Composite anode material; 11-Core; 111-Carbon matrix; 1111-First pore; 1121-Second pore; 112-Filling material; 12-Covering layer; 121-First carbon layer; 1211-Third pore; 122-Second carbon layer. Detailed Implementation

[0065] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0066] In a first aspect, embodiments of this application provide a composite negative electrode material 10, which includes: a core 11 and a coating layer 12 located on the surface of the core 11 (see reference). Figure 1 and Figure 2 ).

[0067] The core 11 includes a carbon matrix 111 and a filling material 112. The carbon matrix 111 has a first pore 1111, and the filling material 112 is at least partially distributed within the first pore 1111. The filling material 112 includes SiOx and has a second pore 1121.

[0068] The carbon matrix 111 improves the conductivity of the composite anode material 10, and the coating layer 12 covers the surface of the core 11, preventing the electrolyte from directly contacting SiOx, which helps avoid capacity decay. The second pore 1121 can reduce the volume expansion of SiOx during charging, providing channels for lithium-ion and electron transport, improving charging speed, enhancing rate performance, and storing lithium ions to increase capacity. Furthermore, compared to existing methods such as mechanical mixing, thermal mixing, and spray drying to distribute silicon on the graphite surface, the carbon matrix 111 of this application has a first pore 1111, with at least a portion of the filling material 112 distributed within the first pore 1111. Even if SiOx expands in volume during charging, the filling material 112 within the first pore 1111 is less likely to detach and lose contact with the carbon matrix 111, thus improving the cycle stability of the composite anode material 10. Moreover, the porous structure of the carbon matrix 111 provides more active sites during the charging and discharging process of the lithium-ion battery, accelerating lithium-ion diffusion and increasing the charging rate.

[0069] It is understood that the filling material 112 being at least partially distributed within the first pore 1111 means that the filling material 112 can be entirely distributed within the first pore 1111, or that a portion of the filling material 112 is distributed within the first pore 1111, while another portion of the filling material 112 is distributed on the surface of the carbon matrix 111.

[0070] In some possible implementations, the first pore 1111 includes a plurality of holes, at least a portion of which is filled with a filler material 112. That is, some of the holes may be partially filled with filler material 112, or all of the holes may be partially filled with filler material 112. Holes partially filled with filler material 112 can provide space for the volume expansion of SiOx, thus reducing the volume expansion effect.

[0071] Optionally, the pores of the first pore 1111 extend from the surface of the carbon matrix 111 to the interior of the carbon matrix 111.

[0072] In some possible implementations, the spacing between two adjacent pores of the carbon matrix 111 is 0.5 μm to 5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. Optionally, the spacing between two adjacent first pores 1111 of the carbon matrix 111 is 1 μm to 3 μm. This range of pore spacing will not result in too few pores, thus reducing the SiOx loading space, nor will it result in too many pores, leading to poor pore structure stability.

[0073] In some possible implementations, the carbon matrix 111 includes at least one of a graphite matrix, a mesophase carbon microsphere matrix, a soft carbon matrix, and a hard carbon matrix. Compared to silicon / amorphous carbon composites, the carbon matrix 111 in the embodiments of this application can improve the tap density of the composite silicon composite.

[0074] For example, the graphite in the graphite matrix includes at least one of natural crystalline graphite, natural microcrystalline graphite, and artificial graphite.

[0075] In some possible implementations, the depth of the first pore 1111 of the carbon matrix 111 is 0.5 μm to 10 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. Optionally, the depth of the first pore 1111 of the carbon matrix 111 is 2 μm to 6 μm. This range of first pore depth ensures that lithium ions can quickly reach the interior of the carbon matrix through the first pore, improving the charging speed and rate performance of the material, providing more space for loading SiOx, and preventing the entire particle structure from becoming unstable due to excessive pore depth.

[0076] In some possible embodiments, the diameter of the first pore 1111 of the carbon matrix 111 is 0.1 μm to 3 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. Optionally, the diameter of the first pore 1111 of the carbon matrix 111 is 0.5 μm to 1 μm. This range of first pore diameter allows the SiOx precursor to smoothly enter and fill the pores without being too large, which would result in an excessively large specific surface area of ​​graphite and poor SiOx adhesion.

[0077] In some possible implementations, the specific surface area of ​​the carbon matrix 111 is 0.5 m². 2 / g~30m 2 / g, for example, 0.5m 2 / g, 1m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g、12m 2 / g, 15m 2 / g、18m 2 / g、20m 2 / g、23m 2 / g、25m 2 / g or 30m 2 / g. Optionally, the specific surface area of ​​the carbon matrix 111 is 1–15 m². 2 / g.

[0078] The filler material 112 in the composite anode material 10 has a second pore 1121, which can provide space for volume expansion during the SiOx lithiation process, thereby reducing the volume effect; and the second pore 1121 can provide more lithium storage sites, increasing the specific capacity of the composite anode material 10; and the second pore 1121 can provide a transport path for electrons and lithium ions, shorten the transport distance, improve the electronic conductivity and ionic conductivity of the composite anode material 10, and improve the charging rate and reversible capacity.

[0079] In some possible implementations, the diameter of the second pore 1121 is 0.1 nm to 30 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 3 nm, 5 nm, 10 nm, 15 nm, 18 nm, 20 nm, 25 nm, or 30 nm. Optionally, the diameter of the second pore 1121 is 1 nm to 15 nm. Within this range, the second pore is not too small, which can accommodate the transport of lithium ions and the battery and alleviate the volume expansion of the material. However, it is not too large either, as excessively large pores require a high degree of disproportionation reaction of the SiOy material and the removal of a large proportion of SiO2 by acid washing, which reduces the overall reversible specific capacity of the material. Excessively large pores can also lead to instability of the SiOx structure and excessively large specific surface area, which aggravates interfacial side reactions and reduces cycle stability.

[0080] In some possible implementations, the specific area of ​​kernel 11 is 0.5m². 2 / g~50m 2 / g, for example, 0.5m 2 / g, 1m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g or 50m 2 / g. Optionally, the specific area of ​​the core 11 is 1–20 m². 2 / g.

[0081] In one possible implementation, the value of X in SiOx ranges from 0.5 to 2, for example, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, or 2. SiOx can be any two or a combination of three of SiO, SiO2, and Si.

[0082] In some possible implementations, SiOx comprises SiO and Si grains, with the silicon grains having a higher first-pass efficiency than SiO. Compared to SiOx being solely SiO, SiOx comprising both SiO and Si grains is beneficial for improving the first-pass efficiency of the composite silicon material.

[0083] Optionally, the silicon grains in SiOx have a diameter of 0.1 nm to 20 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 13 nm, 15 nm, 18 nm or 20 nm.

[0084] In some possible implementations, the coating layer 12 comprises a carbon layer. In other implementations, the coating layer 12 may also be made of other materials.

[0085] In some possible embodiments, the carbon layer includes a first carbon layer 121 and a second carbon layer 122. The first carbon layer 121 has a third pore 1211. The first carbon layer 121 covers the surface of the core 11, and the second carbon layer 122 covers the surface of the first carbon layer 121 (see reference). Figure 1 It should be noted that the first carbon layer 121 was obtained through a pore-forming process, while the second carbon layer 122 was not.

[0086] The porous structure in the first carbon layer 121 can further alleviate the volume effect caused by the volume expansion of SiOx material, thus improving the stability of the composite anode material 10. Furthermore, the second carbon layer 122 prevents the electrolyte from entering the core 11 and reacting with SiOx to consume lithium ions, thereby reducing capacity decay. Additionally, the second carbon layer 122 helps reduce the specific surface area of ​​the composite anode material 10, improving its initial efficiency.

[0087] In other embodiments, the carbon layer may include a second carbon layer 122 but not the first carbon layer 121, with the second carbon layer 122 covering the surface of the core 11.

[0088] Optionally, the carbon in the first carbon layer includes at least one of hard carbon, graphene carbon materials, and carbon nanotubes.

[0089] Optionally, the carbon in the second carbon layer includes soft carbon.

[0090] In some possible embodiments, the D50 particle size of the composite anode material 10 is 3 μm to 90 μm, for example, any or any combination of 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, and 90 μm. Optionally, the D50 particle size of the composite anode material 10 is 5 μm to 50 μm; alternatively, the D50 particle size of the composite anode material 10 is 10 μm to 25 μm.

[0091] In some possible embodiments, the carbon matrix 111 content in the composite anode material 10 is 10 wt% to 80 wt%, for example, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% or 80 wt%.

[0092] In some possible embodiments, the content of filler material 112 in the composite negative electrode material 10 is 10 wt% to 80 wt%, for example, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% or 80 wt%.

[0093] In some possible embodiments, the content of the coating layer 12 in the composite negative electrode material 10 is 5 wt% to 50 wt%, for example, 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%.

[0094] In some possible implementations, the specific surface area of ​​the composite anode material 10 is 0.5 m². 2 / g~30m 2 / g, for example, 0.5m 2 / g, 1m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g and 30m 2 The range is any one of / g or any two of them. Optionally, the specific surface area of ​​the composite negative electrode material 10 is 1m². 2 / g~6m 2 / g.

[0095] In some possible implementations, the tap density of the composite anode material 10 is 0.2 g / cm³. 3 ~3g / cm 3 For example, 0.2 g / cm³ 3 0.5g / cm 3 0.8g / cm 3 1g / cm 3 1.2g / cm 3 1.5g / cm 3 1.8g / cm 3 2.0g / cm 3 2.3g / cm 3 2.5g / cm 3 2.8g / cm 3 Or 3g / cm 3 Optionally, the tap density of the composite negative electrode material 10 is 0.5 g / cm³. 3 ~2g / cm 3 .

[0096] Reference Figure 6 and Figure 7 Secondly, embodiments of this application provide a method for preparing a composite negative electrode material 10, comprising:

[0097] S100, providing a carbon matrix 111 having first pores 1111 (refer to) Figure 3 ).

[0098] In some possible embodiments, the preparation steps of the carbon matrix 111 having the first pore 1111 include:

[0099] The carbon matrix precursor and the catalyst were mixed and heat-treated in an H2 atmosphere to obtain a carbon matrix 111 with a first pore 1111.

[0100] The carbon-based precursor is reacted with H2 in the presence of a catalyst to generate methane. After the methane escapes, the carbon-based precursor forms the first pore 1111, thus obtaining a carbon matrix 111 with the first pore 1111.

[0101] In some embodiments, the catalyst includes at least one of a cobalt catalyst and a nickel catalyst.

[0102] In some embodiments, the carbon-based precursor and the catalyst are mixed and heat-treated in an H2 atmosphere at a temperature of 200°C to 300°C, for example, 200°C, 220°C, 240°C, 260°C, 280°C or 300°C.

[0103] In some embodiments, the shape of the carbon-based precursor includes at least one of spherical, near-spherical, elongated, and blocky shapes.

[0104] In some embodiments, the D50 particle size of the carbon-based precursor is 1 μm to 80 μm, for example, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm, 60 μm, 70 μm, or 80 μm. Optionally, the D50 particle size of the carbon-based precursor is 2 μm to 50 μm or 8 μm to 28 μm.

[0105] In some embodiments, the tap density of the carbon-based precursor is 0.4 g / cm³. 3 ~5g / cm 3 For example, 0.4 g / cm³ 3 1g / cm 3 2g / cm 3 3g / cm 3 4g / cm 3 or 5g / cm 3 Optionally, the tap density of the carbon-based precursor is 0.7 g / cm³. 3 ~3g / cm 3 .

[0106] It should be noted that the above preparation process can be omitted, and a carbon matrix with a porous structure can be directly selected.

[0107] S200, SiOy is formed at least within the first pore 1111 of the carbon matrix 111 to obtain the first precursor (refer to...). Figure 4 ), where the value of y ranges from 0.2 to 1.5.

[0108] Optionally, the value of y can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0109] It should be noted that forming SiOy within the first pore 1111 of the carbon matrix 111 means that SiOy can be formed within the first pore 1111 of the carbon matrix 111; it also means that in addition to forming SiOy within the first pore 1111 of the carbon matrix 111, SiOy can also be formed on the surface of the carbon matrix 111.

[0110] In some possible embodiments, the step of forming SiOy at least within the first pore 1111 of the carbon matrix 111 includes:

[0111] A silica solution was mixed with a carbon matrix 111 and subjected to heat treatment. The resulting product was then reduced to obtain the first precursor (see reference). Figure 4 ).

[0112] After mixing the silica solution with the carbon matrix 111, the silica solution can easily penetrate into the first pores 1111 of the carbon matrix 111, resulting in silica solution on both the first pores 1111 and the outer surface of the carbon matrix 111. Following heat treatment, the silica decomposes to generate silica and water. After filtration, a composite material of silica and carbon matrix 111 is obtained. This treatment method results in a high degree of composite between silica and the silica matrix, and the silica is relatively uniformly distributed on the surface of the carbon matrix 111. After reduction treatment of the composite material, the silica in the composite material is reduced to SiOy. SiOy has a high degree of bonding with the carbon matrix 111, is not easily separated, and is uniformly coated on the surface of the carbon matrix 111, preventing agglomeration. This helps reduce volume expansion and material pulverization during cycling of the composite anode material 10, thereby improving the cycling stability of the composite anode material 10.

[0113] In some embodiments, the mass ratio of carbon matrix to silica is 0.2 to 5:1, for example, any one or a range between any two of 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1 and 5:1.

[0114] In some embodiments, the temperature at which the silica solution is mixed with the carbon matrix 111 and then subjected to heat treatment is 70°C to 95°C, for example, 70°C, 75°C, 80°C, 85°C, or 90°C. The heat treatment can be performed under water bath conditions and may be accompanied by stirring.

[0115] In some embodiments, the preparation step of silicic acid includes reacting a silicate with an acid to obtain a silicic acid solution. The silicate may optionally be sodium silicate or potassium silicate; the acid may optionally be sulfuric acid, nitric acid, or hydrochloric acid.

[0116] In some embodiments, the preparation steps of potassium silicate include: mixing fly ash with potassium hydroxide to react, centrifuging the product obtained from the reaction, and taking the supernatant containing potassium silicate.

[0117] In other embodiments, the silica may be first mixed with water and carbon matrix 111, dried, and then reduced to obtain the first precursor. Optionally, the silica particle size is 0.1 μm to 3 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm.

[0118] In some embodiments, in the two embodiments described above where SiOy is formed at least within the first pores 1111 of the carbon matrix 111, the reduction treatment step includes performing the reduction treatment under a reducing atmosphere and at a temperature of 1000°C to 2000°C. Optionally, the reducing atmosphere includes either H2 or methane. The temperature for performing the reduction treatment is, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C, or 2000°C.

[0119] Step S300 can be performed in two ways, namely S310 and S320:

[0120] S310. A coating layer is formed on the surface of the first precursor to obtain a second precursor. The SiOy in the second precursor is subjected to a disproportionation reaction to remove part of the generated silicon dioxide, and a composite anode material is obtained.

[0121] S320. The SiOy in the first precursor is subjected to a disproportionation reaction to remove part of the generated silicon dioxide, and a coating layer is formed on the surface of the obtained product to obtain a composite anode material.

[0122] In the preparation method of composite anode material 10, SiOy undergoes a disproportionation reaction to generate silicon dioxide. Removing a portion of the silicon dioxide then forms SiOx with a second pore structure. This second pore structure of SiOx helps to mitigate the volume effect of composite anode material 10. The preparation method of composite anode material 10 is simple and easy to implement, and can be mass-produced industrially.

[0123] It should be noted that, when using both S310 and S320 implementation methods, the step of removing part of the silica can include the following steps:

[0124] Part of the silica is removed by reacting HF with silica to form SiOx with secondary pores. Optionally, the mass concentration of HF is greater than 20%.

[0125] HF reacts with silicon dioxide to generate SiF4 gas and water. The SiF4 gas escapes to form SiOx with a second pore 1121.

[0126] For example, the mass concentration of HF is any one of 20%, 25%, 30%, 35%, 40%, and 50%, or a range between any two.

[0127] The preparation method provided in this scheme is described in detail below:

[0128] When using the S310 implementation, the step of removing part of the silicon dioxide includes: the coating layer contains an alkaline oxide, the alkaline oxide reacts with silicon dioxide to generate silicate, reacts with an acid solution, and the product of the reaction between the acid solution and the silicate is dissolved in water to form SiOx with a second pore.

[0129] The reaction of basic oxides with silicon dioxide can produce silicates. The product obtained by the reaction of acid solution with silicates can be dissolved in water, thus forming SiOx with a second pore 1121.

[0130] Optionally, the alkaline oxide includes at least one of calcium oxide, sodium oxide, barium oxide, and chromium oxide.

[0131] Optionally, the acid solution includes at least one of hydrochloric acid, sulfuric acid, and nitric acid. Exemplarily, the mass concentration of the acid solution is greater than 37%. Optionally, the mass concentrations of both sulfuric acid and nitric acid are greater than 70%.

[0132] Optionally, the weight ratio of the basic oxide to the first precursor is 6 to 9:1, for example, 6:1, 7:1, 8:1 or 9:1.

[0133] When using the S310 implementation, in some embodiments, a carbon layer precursor is formed on the surface of the first precursor, and after carbonization, a portion of the generated silicon dioxide is removed to obtain a composite anode material. A carbon layer precursor is formed on the surface of the first precursor, and a second precursor is heat-treated to carbonize the carbon layer precursor to form a carbon layer. Simultaneously with the carbonization of the carbon layer precursor, SiOy is disproportionated to silicon dioxide; and after the carbon layer precursor is carbonized, a portion of the silicon dioxide is removed to form SiOx with second pores.

[0134] In some embodiments, the temperature at which the second precursor is heat-treated is 700°C to 1200°C, for example, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0135] In some embodiments, step S310 can be: mixing a first precursor with a first carbon source to form a carbon layer precursor on the surface of the first precursor, thus obtaining a second precursor; then performing heat treatment to carbonize the first carbon source to form a second carbon layer 122, while SiOy undergoes disproportionation to generate silicon dioxide; then using HF to remove part of the generated silicon dioxide to obtain a composite anode material, wherein the mass concentration of HF is greater than 20%. HF reacts with silicon dioxide to generate SiF4 gas and water, and the SiF4 gas escapes to form SiOx with second pores 1121.

[0136] For example, the heat treatment temperature is 700°C to 1100°C, such as 700°C, 800°C, 900°C, 1000°C or 1100°C.

[0137] Optionally, the first carbon source includes at least one of bitumen, resin, and polydopamine. Bitumen, resin, and polydopamine become relatively dense after heat treatment and carbonization.

[0138] Furthermore, in some embodiments, the carbon layer precursor contains a water-soluble salt. After the carbon layer precursor is carbonized, the water-soluble salt is removed with water to form a first carbon layer with a third pore, and then a second carbon layer is formed on the surface of the first carbon layer.

[0139] For example, before forming the carbon layer precursor, a solution containing a second carbon source and a water-soluble salt is mixed with the first precursor to form a carbon layer precursor on the surface of the first precursor, thus obtaining a second precursor; the second precursor is heat-treated to carbonize the second carbon source and simultaneously form SiOx with second pores 1121; the water-soluble salt is removed using water to form a first carbon layer 121 with third pores 121 (see reference). Figure 5 Then, a second carbon layer 122 is formed on the surface of the first carbon layer 121 (see reference). Figure 1 ).

[0140] A solution containing a second carbon source and a water-soluble salt is mixed with a first precursor. The second carbon source and the water-soluble salt are coated on the surface of the first precursor. After the second precursor is heat-treated, the second carbon source is carbonized, and the SiOy in the second precursor is diverged to generate silicon dioxide. Removing part of the silicon dioxide can form SiOx with second pores 1121. Dissolving the water-soluble salt with water can remove the water-soluble salt in the second precursor to form a first carbon layer 121 with third pores 1211, and the first carbon layer 121 is formed on the surface of the core 11.

[0141] Optionally, the second carbon source includes an organic carbon source. For example, an organic carbon source includes one or more of starch, glucose, and sucrose.

[0142] For example, water-soluble salts include one or more of potassium chloride and sodium chloride.

[0143] For example, the solution containing the second carbon source and the water-soluble salt is an aqueous solution or an aqueous solution of ethanol.

[0144] Furthermore, in this embodiment, HF can be reacted with silicon dioxide first to form the second pore 1121 of SiOx, and then water can be used to dissolve the water-soluble salt to form the first carbon layer 121; alternatively, water can be used first to dissolve the water-soluble salt to form the first carbon layer 121, and then HF can be reacted with silicon dioxide to form the second pore 1121 of SiOx; alternatively, HF and water can be used for alternating washing. For example, the mass concentration of HF is greater than 20%.

[0145] Optionally, in this embodiment, the solution containing the second carbon source and the water-soluble salt may simultaneously contain an alkaline oxide. The solution containing the second carbon source, the alkaline oxide, and the water-soluble salt is mixed with the first precursor to form a carbon layer precursor containing the alkaline oxide on the surface of the first precursor. During the heat treatment process, the second carbon source carbonizes, and SiOy partially diverges to generate silicon dioxide. The alkaline oxide reacts with the silicon dioxide to generate silicate, which is then reacted with an acid solution. The product of the acid solution and silicate reaction is dissolved in water to form SiOx with second pores. Finally, the water-soluble salt is dissolved in water to form the first carbon layer 121.

[0146] Optionally, the alkaline oxide includes at least one of calcium oxide, sodium oxide, barium oxide, and chromium oxide.

[0147] Optionally, the acid solution includes any one of hydrochloric acid, sulfuric acid, and nitric acid, and the mass concentration of the acid solution is greater than 37%.

[0148] Optionally, the weight ratio of the basic oxide to the first precursor is 6 to 9:1, for example, 6:1, 7:1, 8:1 or 9:1.

[0149] In other embodiments, the alkaline oxide can be mixed with the first precursor and then mixed with a solution containing a second carbon source and a water-soluble salt to form a carbon layer precursor on the surface of the first precursor, thus obtaining a second precursor. Then, heat treatment is performed to carbonize the second carbon source, and the SiOy in the second precursor diverges to form silicon dioxide. The silicon dioxide reacts with the alkaline oxide to form silicate, and then an acid solution is used to react the silicate. The product of the reaction between the acid solution and the silicate is dissolved in water to form SiOx with second pores 1121. Then, water-soluble salt is dissolved in water to form a first carbon layer 121, and the first carbon layer 121 is formed on the surface of the core 11.

[0150] Furthermore, the product on which the first carbon layer 121 is formed on the surface of the core 11 can be mixed with the first carbon source and then subjected to heat treatment to carbonize the first carbon source to form a second carbon layer 122 on the surface of the first carbon layer 121. For example, the heat treatment temperature is 700°C to 1100°C, such as 700°C, 800°C, 900°C, 1000°C or 1100°C.

[0151] When the implementation of S320 is adopted, the step of disproportionating SiOy in the first precursor includes, by example, heat-treating the first precursor at a temperature of 700°C to 1200°C.

[0152] The first precursor is heat-treated, and the SiOy in the first precursor undergoes a disproportionation reaction to generate silicon dioxide. For example, the temperature for heat-treating the first precursor is 700°C, 800°C, 900°C, 1000°C, 1100°C, or 1200°C.

[0153] When the implementation of S320 is adopted, the step of removing part of the generated silicon dioxide includes: removing part of the silicon dioxide by reacting it with HF to form SiOx with a second pore, wherein the mass concentration of HF is greater than 20%.

[0154] Alternatively, the following steps can be used: mix the first precursor with a solution containing alkaline oxides, and then perform heat treatment to cause SiOy to diverge and generate silicon dioxide. The silicon dioxide reacts with the alkaline oxides to generate silicates. Water is used to dissolve the product of the reaction between the acid solution and the silicates to form SiOx with second pores.

[0155] Optionally, after removing some of the silicon dioxide, a core containing SiOx is obtained; the core is mixed with a carbon source and heat-treated to form a coating layer on the surface of the core, thus obtaining a composite anode material.

[0156] For example, when the carbon layer is a second carbon layer 122, the preparation method includes the following steps:

[0157] The kernel is mixed with a first carbon source to form a carbon layer precursor on the surface of the kernel, and then heat-treated to carbonize the first carbon source to form a coating layer on the surface of the kernel. For example, the heat treatment temperature is 800°C to 1200°C, such as 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0158] For example, when the carbon layer includes a first carbon layer 121 and a second carbon layer 122, the preparation method includes the following steps:

[0159] The core is mixed with a solution containing a second carbon source and a water-soluble salt to form a precursor for forming a carbon layer on the surface of the core. Then, heat treatment is performed to carbonize the second carbon source. The water-soluble salt is removed using water to form a first carbon layer 121 on the surface of the core. The resulting product is mixed with the first carbon source and heat-treated to carbonize the first carbon source to form a second carbon layer 122, thus obtaining a composite anode material.

[0160] For example, the water-soluble salt includes at least one of potassium chloride and sodium chloride.

[0161] For example, the heat treatment temperature is 700°C to 1200°C, such as 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0162] Thirdly, embodiments of this application provide a negative electrode sheet, including the composite negative electrode material 10 as described in the first aspect embodiment or the composite negative electrode material 10 prepared by the preparation method described in the second aspect embodiment.

[0163] Fourthly, embodiments of this application provide a lithium-ion battery, which includes the negative electrode sheet of the third aspect embodiment.

[0164] The composite negative electrode material 10 of this application embodiment can reduce the volume effect and provide more active sites during the charging and discharging process of lithium-ion batteries, thereby improving the charging rate of lithium-ion batteries.

[0165] The following describes in further detail the composite negative electrode material 10, its preparation method, the negative electrode sheet, and the lithium-ion battery of this application with reference to the embodiments.

[0166] Example 1

[0167] This embodiment provides a composite anode material, the preparation steps of which include:

[0168] (1) 200g of natural graphite particles with a particle size of 8.0μm~25.0μm were mixed evenly with cobalt catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 200℃ in a mixed atmosphere of hydrogen and nitrogen. After reacting for 5 hours, a carbon matrix with the first pore was obtained.

[0169] (2) Add 120g of fly ash to 2L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge and separate the supernatant and place it in a constant temperature water bath, add the carbon matrix with the first pore obtained in step (1), then add 5mL of sulfuric acid with a concentration of 12mol / L, react for 2 hours under water bath conditions at 70℃, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise it to 1500℃ at a rate of 8℃ / min under a mixed atmosphere of nitrogen and hydrogen with a volume ratio of 1:1.5, keep it at the temperature for 4 hours, and cool it naturally to room temperature. SiOy is formed in the first pore of the carbon matrix and on the surface of the carbon matrix to obtain the first precursor.

[0170] (3) The first precursor obtained in step (2) is mixed evenly with 20g starch, 5g potassium chloride, and 10g calcium oxide in an ethanol aqueous solution, and then dried so that the carbon layer precursor coats the surface of the first precursor to obtain the second precursor. The second precursor is placed in a high-temperature sand kiln and heat-treated at 1300℃ to carbonize the starch to form a carbon layer, and to cause the SiOy to diverge to form silicon dioxide. The silicon dioxide reacts with calcium oxide to form calcium silicate. The precursor is washed five times each with 40% concentrated hydrochloric acid and deionized water to form SiOx with a second pore and a first carbon layer with a third pore. Then it is placed in a vacuum drying oven for drying.

[0171] (4) The product obtained in step (3) is mixed with asphalt at a mass ratio of 87:13 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1100℃ at a rate of 5℃ / min, and kept at that temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite anode material. The composite anode material includes graphite, SiOx with second pores in the first pores of graphite and on the surface of graphite, a first carbon layer and a second carbon layer coating the graphite and the surface of the SiOx with second pores. The average diameter of the first pore is about 4.5 μm, the average diameter of the second pore is about 7 nm, the X in SiOx is 1.02, the silicon grain size is 5 nm, the graphite content is 57 wt%, the SiOx content is 32%, and the carbon layer content is 11%.

[0172] Example 2

[0173] This embodiment provides a composite anode material, the preparation steps of which include:

[0174] (1): 150g of natural graphite particles with a particle size of 7.0μm~24.0μm were mixed evenly with nickel catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 300℃ in a mixed atmosphere of hydrogen and nitrogen. After reacting for 4 hours, a carbon matrix with the first pore was obtained.

[0175] (2): Add 900g of fly ash to 1.5L of barium hydroxide solution, stir magnetically for 0.5 hours, centrifuge and separate the supernatant, place it in a constant temperature water bath, add the carbon matrix with the first pore obtained in step (1), then add 3mL of sulfuric acid with a concentration of 12mol / L, react for 3 hours in a water bath at 65℃, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise the temperature to 1600℃ at a rate of 10℃ / min in a mixed atmosphere of nitrogen and hydrogen with a volume ratio of 1:1.5, keep it at the temperature for 3 hours, and cool it naturally to room temperature. SiOy is formed in the first pore of the carbon matrix and on the surface of the carbon matrix, and the first precursor is obtained.

[0176] (3): The first precursor obtained in step (2) is mixed evenly with 18g of glucose, 4g of potassium chloride, and 8g of calcium oxide in an ethanol aqueous solution so that the carbon layer precursor coats the surface of the first precursor and obtains the second precursor. The second precursor is placed in a high-temperature sand kiln and heat-treated at 1300℃ to carbonize the glucose to form a carbon layer, and to cause the SiOy to diverge to form silicon dioxide. The silicon dioxide reacts with calcium oxide to form calcium silicate. The precursor is washed five times each with 40% concentrated hydrochloric acid and deionized water to form SiOx with a second pore and a first carbon layer with a third pore. Then it is placed in a vacuum drying oven for drying.

[0177] (4): The product obtained in step (3) is mixed with asphalt at a mass ratio of 85:15 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1050°C at a rate of 5°C / min, and kept at that temperature for 3 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite anode material. The composite anode material includes graphite, SiOx with second pores in the first pores of graphite and on the surface of graphite, a first carbon layer and a second carbon layer coated on the graphite and the surface of the SiOx with second pores. The average diameter of the first pore is about 6 μm, the average diameter of the second pore is about 11 nm, the X in SiOx is 0.98, the silicon grain size is 8 nm, the graphite content is 49 wt%, the SiOx content is 38%, and the carbon layer content is 13%.

[0178] Example 3

[0179] This embodiment provides a composite anode material, the preparation steps of which include:

[0180] (1): 300g of natural graphite particles with a particle size of 8.0μm~25.0μm were mixed evenly with nickel catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 240℃ in a mixed atmosphere of hydrogen and nitrogen. After reacting for 4 hours, a carbon matrix with the first pore was obtained.

[0181] (2): Add 180g of fly ash to 3L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge and separate the supernatant and place it in a constant temperature water bath, add the carbon matrix with the first pore obtained in step (1), then add 6mL of sulfuric acid with a concentration of 13mol / L, react for 3 hours under water bath conditions at 70℃, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise it to 1650℃ at a rate of 10℃ / min under a mixed atmosphere of nitrogen and hydrogen with a volume ratio of 1:1.5, keep it at the temperature for 3 hours, and cool it naturally to room temperature. SiOy is formed in the first pore of the carbon matrix and on the surface of the carbon matrix to obtain the first precursor.

[0182] (3): The first precursor obtained in step (2) is mixed evenly with 30g sucrose, 5g sodium chloride, and 4g calcium oxide in an ethanol aqueous solution so that the carbon layer precursor coats the surface of the first precursor to obtain the second precursor. The second precursor is placed in a high-temperature sand kiln and heat-treated at 1300℃ to carbonize the sucrose to form a carbon layer, and to cause the SiOy part to diverge to generate silicon dioxide. The silicon dioxide reacts with calcium oxide to generate calcium silicate. The precursor is washed five times each with 40% concentrated hydrochloric acid and deionized water to remove potassium chloride and silicate, so as to form SiOx with second pores and a first carbon layer with third pores. Then it is placed in a vacuum drying oven for drying.

[0183] (4): The product obtained in step (3) is mixed with asphalt at a mass ratio of 83:17 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1150°C at a rate of 10°C / min, and kept at that temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite anode material. The composite anode material includes graphite, SiOx with second pores in the first pores of graphite and on the surface of graphite, a first carbon layer and a second carbon layer coating the graphite and the surface of the SiOx with second pores. The average diameter of the first pore is about 5 μm, the average diameter of the second pore is about 9 nm, the X in SiOx is 1.00, the silicon grain size is 4 nm, the graphite content is 54 wt%, the SiOx content is 35%, and the carbon layer content is 11%.

[0184] Example 4

[0185] This embodiment provides a composite anode material, the preparation steps of which include:

[0186] (1) 200g of natural graphite particles with a particle size of 8.0μm~25.0μm were mixed evenly with cobalt catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 200℃ in a mixed atmosphere of hydrogen and nitrogen. After reacting for 5 hours, a carbon matrix with the first pore was obtained.

[0187] (2) Add 120g of fly ash to 2L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge and separate the supernatant and place it in a constant temperature water bath, add the carbon matrix with the first pore obtained in step (1), then add 5mL of sulfuric acid with a concentration of 12mol / L, react in a water bath at 70℃ for 2 hours, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise it to 1500℃ at a rate of 8℃ / min in a mixed atmosphere of nitrogen and hydrogen, keep it at the temperature for 4 hours, and cool it naturally to room temperature. SiOy is formed in the first pore of the carbon matrix and on the surface of the carbon matrix to obtain the first precursor.

[0188] (3) The first precursor obtained in step (2) is mixed with asphalt at a mass ratio of 87:13 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1100℃ at a rate of 5℃ / min, and kept at this temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, and to allow the SiOy to diverge and generate silica. 25% HF is used to dissolve the silica to form SiOx with second pores, thereby obtaining a composite anode material. The composite anode material includes graphite, SiOx with second pores in the first pores of graphite and on the surface of graphite, and a second carbon layer covering the graphite and the surface of the SiOx with second pores. Scanning electron microscopy, cross-section, and transmission electron microscopy show that the average diameter of the first pore is about 7 μm, the average diameter of the second pore is about 12 nm, the X in SiOx is 0.96, the silicon grain size is 7 nm, the graphite content is 56 wt%, the SiOx content is 35%, and the carbon layer content is 9%.

[0189] Example 5

[0190] This embodiment provides a composite anode material, the preparation steps of which include:

[0191] (1) 200g of natural graphite particles with a particle size of 8.0μm~25.0μm were mixed evenly with nickel catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 200℃ in a mixed atmosphere of hydrogen and nitrogen. The reaction was carried out for 5 hours to obtain a carbon matrix with the first pore.

[0192] (2) Add 120g of fly ash to 2L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge and separate the supernatant and place it in a constant temperature water bath, add the carbon matrix with the first pore obtained in step (1), then add 5mL of sulfuric acid with a concentration of 12mol / L, react for 2 hours under a water bath at 70℃, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise the temperature to 1500℃ at a rate of 8℃ / min under a mixed atmosphere of nitrogen and hydrogen with a concentration of 12mol / L, keep it at the temperature for 4 hours, and cool it naturally to room temperature. SiOy is formed in the first pore of the carbon matrix and on the surface of the carbon matrix to obtain the first precursor.

[0193] (3) The first precursor obtained in step (2) is mixed evenly with 20g of starch and 5g of potassium chloride in an ethanol aqueous solution, and then dried so that the carbon layer precursor coats the surface of the first precursor to obtain the second precursor. The second precursor is placed in a high-temperature sand kiln and heat-treated at 1300℃ to carbonize the starch to form a carbon layer and cause the SiOy to diverge to form silicon dioxide. It is then washed five times each with HF of 27% mass concentration and deionized water to remove potassium chloride and silicon dioxide, so as to form SiOx with second pores and the first carbon layer with third pores. Then it is placed in a vacuum drying oven for drying.

[0194] (4) The product obtained in step (3) is mixed with asphalt in a mixer at a mass ratio of 87:13 to obtain a mixture. The mixture is placed in a box furnace and heated to 1100°C at a rate of 5°C / min and kept at that temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite negative electrode material. The composite negative electrode material includes graphite, SiOx with second pores in the first pores of graphite and on the surface of graphite, a first carbon layer and a second carbon layer coated on the graphite and the surface of SiOx with second pores. The average diameter of the first pore is about 4 μm and the average diameter of the second pore is about 9 nm, the X in SiOx is 1.01, the silicon grains are 4 nm, the graphite accounts for 55 wt%, the SiOx accounts for 34%, and the carbon layer accounts for 11%.

[0195] Example 6

[0196] This embodiment provides a composite anode material, the preparation steps of which include:

[0197] (1) 200g of natural graphite particles with a particle size of 8.0μm~25.0μm were mixed evenly with cobalt catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 200℃ in a mixed atmosphere of hydrogen and nitrogen. After reacting for 5 hours, a carbon matrix with the first pore was obtained.

[0198] (2) Add 120g of fly ash to 2L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge, and place the supernatant in a constant temperature water bath. Add the carbon matrix with the first pores obtained in step (1), and then add 5mL of 12mol / L sulfuric acid. React in a water bath at 70℃ for 2 hours. Centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, and raise the temperature to 1500℃ at a rate of 8℃ / min under a nitrogen and hydrogen mixed atmosphere with a volume ratio of 1:1.5. Hold the temperature for 4 hours and allow it to cool naturally to room temperature. SiOy is formed in the first pores of the carbon matrix and on the surface of the carbon matrix, thus obtaining the first precursor. Heat treat the first precursor to cause the SiOy to diverge and generate silicon dioxide. Wash away the silicon dioxide with HF with a mass concentration of 25% to form SiOx with the second pores, thereby obtaining the core.

[0199] (3) The core obtained in step (2) is mixed with asphalt at a mass ratio of 87:13 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1100℃ at a rate of 5℃ / min, and kept at that temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite anode material. The composite anode material includes graphite, SiOx with second pores in the first pores of graphite and on the surface of graphite, and a second carbon layer coating the graphite and the surface of the SiOx with second pores. The average diameter of the first pore is about 6μm, the average diameter of the second pore is about 3nm, the X in SiOx is 0.99, the silicon grain size is 5nm, the graphite content is 53wt%, the SiOx content is 31%, and the carbon layer content is 16%.

[0200] Comparative Example 1

[0201] This comparative example provides a composite anode material, the preparation steps of which include:

[0202] (1) 200g of natural graphite particles with a particle size of 8.0μm~25.0μm were mixed evenly with cobalt catalyst in a mixer to obtain a mixture. The mixture was placed in a rotary kiln and heated to 200℃ in a mixed atmosphere of hydrogen and nitrogen. After reacting for 5 hours, a carbon matrix with the first pore was obtained.

[0203] (2) Add 120g of fly ash to 2L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge and separate the supernatant and place it in a constant temperature water bath, add the carbon matrix with the first pore obtained in step (1), then add 5mL of sulfuric acid with a concentration of 12mol / L, react for 2 hours under water bath conditions at 70℃, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise it to 1500℃ at a rate of 8℃ / min under a mixed atmosphere of nitrogen and hydrogen with a volume ratio of 1:1.5, keep it at the temperature for 4 hours, and cool it naturally to room temperature. SiOy is formed in the first pore of the carbon matrix and on the surface of the carbon matrix to obtain the first precursor.

[0204] (3) The first precursor obtained in step (2) is mixed evenly with 20g of starch and 5g of potassium chloride in an ethanol aqueous solution, and then dried so that the carbon layer precursor coats the surface of the first precursor and obtains the second product. The second product is placed in a high-temperature sand kiln and heat-treated at 1300℃ to carbonize the starch and form a carbon layer. The potassium chloride is then washed away with deionized water to make the carbon layer become a first carbon layer with a third pore. The product is then placed in a vacuum drying oven for drying.

[0205] (4) The product obtained in step (3) is mixed with asphalt at a mass ratio of 87:13 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1100℃ at a rate of 5℃ / min, and kept at that temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite anode material. The composite anode material structure includes graphite, SiOx in the first pores of graphite and on the graphite surface, a first carbon layer and a second carbon layer coated on the graphite and SiOx surfaces. The average diameter of the first pores is about 5μm, observed by scanning electron microscopy, cross-section, and transmission electron microscopy. The X content in SiOx is 1.02, the silicon grain size is 3nm, the graphite content is 54wt%, the SiOx content is 35%, and the carbon layer content is 11%.

[0206] Comparative Example 2

[0207] This comparative example provides a composite negative electrode material and its preparation method. The difference between this preparation method and Example 6 is that step (3) in Example 6 is omitted in this comparative example. The material structure consists of graphite from the inside out and SiOx with second pores in the first pores of graphite and on the surface of graphite. The average size of the first pore is about 5 μm and the average size of the second pore is about 12 nm, observed by scanning electron microscope, cross section and transmission electron microscope. The X in SiOx is 1.02, the silicon grain size is 3 nm, the graphite content is 64 wt%, and the SiOx content is 36%.

[0208] Comparative Example 3

[0209] This comparative example provides a composite anode material, the preparation steps of which include:

[0210] (1) Add 120g of fly ash to 2L of potassium hydroxide solution, stir magnetically for 1 hour, centrifuge and separate the supernatant and place it in a constant temperature water bath, add 200g of natural graphite particles with a particle size of 8.0μm~25.0μm, then add 5mL of sulfuric acid with a concentration of 12mol / L, react in a water bath at 70℃ for 2 hours, centrifuge and dry the reaction product, place it in a high temperature atmosphere furnace, raise the temperature to 1500℃ at a rate of 8℃ / min under a mixed atmosphere of nitrogen and hydrogen, keep it at the temperature for 4 hours, and cool it naturally to room temperature to obtain the first product containing SiOy.

[0211] (2) The first product obtained in step (1) is mixed evenly with 20g starch, 5g potassium chloride and 10g calcium oxide in an ethanol aqueous solution, and then dried to obtain the second product. The second product is placed in a high sand kiln and heat-treated at 1300℃ to carbonize the starch to form a carbon layer, causing SiOy to diverge to form silicon dioxide, and silicon dioxide to react with calcium oxide to form calcium silicate. The product is then washed 5 times each with 40% concentrated hydrochloric acid and deionized water to form SiOx with second pores, and the carbon layer is transformed into a first carbon layer with third pores. The product is then placed in a vacuum drying oven for drying.

[0212] (3) The product obtained in step (2) is mixed with asphalt at a mass ratio of 87:13 in a mixer to obtain a uniform mixture. The mixture is placed in a box furnace and heated to 1100℃ at a rate of 5℃ / min, and kept at that temperature for 2 hours to allow the asphalt to carbonize and form a second carbon layer, thus obtaining a composite anode material. The structure of the composite anode material, from the inside out, consists of graphite without the first pore, SiOx with the second pore on the graphite surface, the first carbon layer, and the second carbon layer. The average diameter of the second pore is about 8nm, as observed by scanning electron microscopy, cross-section, and transmission electron microscopy. The X content in SiOx is 0.97, the silicon grain size is 5nm, the graphite content is 56wt%, the SiOx content is 34%, and the carbon layer content is 10%.

[0213] It should be noted that the graphite particles used in Examples 1 to 6 and Comparative Examples 1 to 3 of this application are from the same manufacturer, from the same batch, and of the same specification.

[0214] Test case

[0215] (1) The composite negative electrode materials of Examples 1 to 6 and Comparative Examples 1 to 3 were mixed with conductive agent and binder in a solvent at a mass percentage of 93:2:5, and the solid content was controlled to be 60wt%. The mixture was coated on aluminum foil and kept at 120°C for 12 hours in a vacuum drying oven to obtain a negative electrode sheet. Lithium cobalt oxide was used as the positive electrode material, and 1 mol / L LiPF6, ethyl carbonate (EC): dimethyl carbonate (DMC): methyl ethyl carbonate (EMC) = 1:1:1 was used as the electrolyte. Celgard 2400 was used as the separator to assemble a coin cell. The full charge expansion rate of the coin cell was tested, and the results are recorded in Table 1.

[0216] (2) The composite negative electrode materials of Examples 1 to 6 and Comparative Examples 1 to 3 were mixed with conductive agent and binder in a solvent at a mass percentage of 93:2:5, and the solid content was controlled to be 60wt%. The mixture was coated on aluminum foil and kept at 120°C for 12 hours in a vacuum drying oven to obtain a negative electrode sheet. Using NCM523 as the positive electrode material, 1mol / L LiPF6, ethyl carbonate (EC): dimethyl carbonate (DMC): methyl ethyl carbonate (EMC) = 1:1:1 as the electrolyte, and Celgard 2400 as the separator, 18650 cylindrical batteries were assembled. The initial charge specific capacity, initial discharge specific capacity, initial efficiency, 300-cycle capacity retention, 1C rate discharge, and 2C rate discharge of the 18650 cylindrical batteries were tested, and the results are recorded in Table 1.

[0217] Table 1. Performance Test Results

[0218]

[0219]

[0220] Comparing the results in Table 1, it can be found that the full-charge expansion rates of Examples 1 to 6 are all less than those of Comparative Examples 1 to 3, and the 300-cycle capacity retention rates of Examples 1 to 6 are all higher than those of Comparative Examples 1 to 3. This indicates that the composite anode material and its preparation method in the embodiments of this application can effectively reduce the volume effect and improve cycle stability.

[0221] By comparing Example 6 and Comparative Example 2, it was found that the capacity retention rate of Example 6 after 300 cycles was better than that of Comparative Example 2, indicating that the presence of a second carbon layer in Example 6 does not easily cause capacity decay.

[0222] By comparing Examples 4, 6 and 1, it was found that the full charge expansion rate of Example 1 with the first carbon layer was smaller than that of Examples 4 and 6 compared to Examples 4 and 6 without the first carbon layer. This indicates that the composite anode material with the first carbon layer can better reduce the volume effect.

[0223] By comparing Example 1 and Comparative Example 1, it was found that the specific capacity of Example 1 at 0.2C initial charge and the specific capacity of Example 1 at 0.2C initial discharge are both higher than those of Comparative Example 1. The capacity retention rate after 300 cycles of Example 1 is also higher than that of Comparative Example 1, indicating that the second porosity of SiOx can improve the specific capacity and reversible capacity. It should be noted that the reversible capacity can be reflected by the specific capacity at 0.2C initial discharge and the capacity retention rate after 300 cycles.

[0224] Furthermore, comparing Example 1, Comparative Example 1, and Comparative Example 3, it was found that the 1C rate discharge and 2C rate discharge results of Example 1 were both higher than those of Comparative Example 1 and Comparative Example 3, indicating that in the embodiments of this application, the presence of a first pore in the carbon matrix or a second pore in SiOx can improve the charging rate. It should be noted that the results of 1C rate discharge and 2C rate discharge reflect the charging rate; the higher the value, the faster the charging rate.

[0225] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a composite negative electrode material, characterized in that, include: Provide a carbon matrix with first pores; SiOy is formed at least within the first pores of the carbon matrix to obtain a first precursor, wherein the value of y ranges from 0.2 to 1.5; A coating layer is formed on the surface of the first precursor to obtain a second precursor. The SiOy in the second precursor is subjected to a disproportionation reaction to remove part of the generated silicon dioxide, thereby obtaining the composite negative electrode material. The step of removing part of the silicon dioxide includes: the coating layer contains an alkaline oxide, the alkaline oxide reacts with the silicon dioxide to generate silicate, which reacts with an acid solution, and water is used to dissolve the product of the reaction between the acid solution and the silicate to form SiOx with a second pore. Alternatively, the SiOy in the first precursor is subjected to a disproportionation reaction to remove part of the generated silicon dioxide, and a coating layer is formed on the surface of the obtained product to obtain the composite negative electrode material; wherein, the step of removing part of the silicon dioxide includes: reacting the silicon dioxide with HF to remove part of the silicon dioxide, forming SiOx with a second pore.

2. The method for preparing the composite negative electrode material according to claim 1, characterized in that, The method for preparing the carbon matrix with the first pore includes: mixing a carbon matrix precursor with a catalyst and performing heat treatment in an H2 atmosphere to obtain the carbon matrix with the first pore.

3. The method for preparing the composite negative electrode material according to claim 2, characterized in that, The preparation method includes at least one of the following features (1) to (3): (1) The catalyst includes at least one of a cobalt catalyst and a nickel catalyst; (2) The temperature at which the carbon-based precursor and the catalyst are mixed and heat-treated in an H2 atmosphere is 200℃~300℃; (3) The D50 of the carbon matrix precursor is 1 μm to 80 μm.

4. The method for preparing the composite negative electrode material according to claim 1, characterized in that, The step of forming SiOy at least within the first pores of the carbon matrix includes: The silica solution is mixed with the carbon matrix and subjected to heat treatment. The resulting product is then reduced to obtain the first precursor.

5. The method for preparing the composite negative electrode material according to claim 4, characterized in that, The preparation method includes at least one of the following features (4) to (6): (4) The temperature at which the silica solution is mixed with the carbon matrix and then subjected to heat treatment is 70℃~95℃; (5) The step of reducing the product includes: performing the reduction treatment under a reducing atmosphere and a temperature of 1000℃~2000℃, wherein the reducing atmosphere includes at least one of H2 and methane; (6) The weight ratio of the carbon matrix to the silica is 0.2 to 5:

1.

6. The method for preparing the composite negative electrode material according to claim 1, characterized in that, The preparation method includes at least one of the following features (7) to (9): (7) The alkaline oxide includes at least one of calcium oxide, sodium oxide, barium oxide and chromium oxide; (8) The acid solution includes any one of hydrochloric acid, sulfuric acid and nitric acid, wherein the mass concentration of the hydrochloric acid is greater than 37%, and the mass concentrations of the sulfuric acid and the nitric acid are both greater than 70%; (9) The weight ratio of the alkaline oxide to the first precursor is (6~9):1; Alternatively, the mass concentration of the HF is greater than 20%.

7. The method for preparing the composite negative electrode material according to any one of claims 1 to 6, characterized in that, A carbon layer precursor is formed on the surface of the first precursor, and the second precursor is heat-treated to carbonize the carbon layer precursor to form a carbon layer. The preparation method further includes at least one of the following features (10) to (12): (10) The temperature for heat treatment of the second precursor is 700℃~1200℃; (11) While the carbon layer precursor is carbonized, the SiOy portion is branched into silicon dioxide; and after the carbon layer precursor is carbonized, a portion of the silicon dioxide is removed to form SiOx with a second pore. (12) The carbon layer precursor contains a water-soluble salt. After the carbon layer precursor is carbonized, the water-soluble salt is removed by water to form a first carbon layer with a third pore, and then a second carbon layer is formed on the surface of the first carbon layer.

8. A composite negative electrode material, characterized in that, The composite negative electrode material is prepared by the preparation method described in any one of claims 1 to 7; The composite anode material includes a core and a coating layer located on the surface of the core. The core includes a filling material and a carbon matrix having a first pore. The filling material is at least partially distributed within the first pore, and the filling material includes SiOx having a second pore.

9. The composite negative electrode material according to claim 8, characterized in that, The composite anode material includes at least one of the following features (13) to (21): (13) The carbon matrix includes at least one of graphite matrix, mesophase carbon microsphere matrix, soft carbon matrix and hard carbon matrix; (14) The first pore includes a plurality of holes, and at least a portion of a portion of the plurality of holes is filled with the filling material; (15) The first pore includes multiple holes, and the distance between two adjacent holes is 0.5μm~5μm; (16) The depth of the first pore is 0.5 μm to 10 μm; (17) The diameter of the first pore is 0.1 μm to 3 μm; (18) The diameter of the second pore is 0.1 nm to 30 nm; (19) The value of X in SiOx ranges from 0.5 to 2; (20) The SiOx contains SiO and silicon grains; (21) The coating layer includes a carbon layer.

10. The composite negative electrode material according to claim 8 or 9, characterized in that, The coating layer includes a carbon layer, which includes a first carbon layer and a second carbon layer. The first carbon layer has a third pore. The first carbon layer coats the surface of the core, and the second carbon layer coats the surface of the first carbon layer.

11. The composite negative electrode material according to claim 10, characterized in that, The composite negative electrode material includes at least one of the following features (22) to (23); (22) The carbon in the first carbon layer includes at least one of hard carbon, graphene carbon material and carbon nanotubes; (23) The carbon in the second carbon layer includes soft carbon.

12. A negative electrode sheet, characterized in that, Including the composite anode material as described in any one of claims 8 to 11.

13. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 12.

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