Battery negative electrode material and preparation method thereof, lithium ion battery negative electrode and lithium ion battery

Abstract

The invention provides a battery negative electrode material and a preparation method thereof, a lithium ion battery negative electrode and a lithium ion battery, and relates to the technical field of batteries. The invention provides a battery negative electrode material. The battery negative electrode material comprises a silicon-bismuth-carbon material and a coating layer on the surface of the silicon-bismuth-carbon material, the silicon-bismuth-carbon material comprises a porous bismuth-carbon material and silicon; silicon is deposited in pores of the porous bismuth carbon material; the porous bismuth carbon material comprises porous carbon and bismuth particles embedded in the porous carbon, the number of the bismuth particles is N, and N is greater than or equal to 2; the coating layer is a conductive coating layer and / or an ion-conducting coating layer. The battery negative electrode material provided by the invention has a watermelon-like multi-layer structure taking bismuth as a seed, silicon carbon as a pulp and a coating layer as a shell, and the battery negative electrode material realizes high capacity and low impedance, reduces expansion and stabilizes the overall structure through a conductive network and a stress buffer effect of a bismuth / carbon core and in combination with a confinement design of an ultrathin silicon intermediate layer.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery negative electrode material and a preparation method thereof, a lithium ion battery negative electrode and a lithium ion battery. Background Art

[0002] As a high-efficiency energy storage device, lithium-ion batteries occupy a dominant position in electric vehicles, portable electronic devices and energy storage systems. The negative electrode materials of lithium-ion batteries need to meet the requirements of high specific capacity, long cycle life and high conductivity. The current theoretical capacity of mainstream graphite materials is only 372mAh / g, which is difficult to meet the requirements of high energy density. Silicon (Si) has become a research hotspot due to its ultra-high theoretical capacity (4200mAh / g), but the huge volume expansion (>300%) caused by lithiation / delithiation during the charging and discharging process will cause electrode pulverization and rapid capacity decay. It can be seen that the current negative electrode materials of lithium-ion batteries are difficult to meet the requirements of high specific capacity, long cycle life and high conductivity, and bismuth (Bi) metal has a high density (8.9g / cm 3 ), high conductivity (7.8×10S / m) and low lithiation volume expansion rate are gradually used in various negative electrode materials.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The first object of the present invention is to provide a battery negative electrode material to solve the above technical problems.

[0005] The second object of the present invention is to provide a method for preparing the above-mentioned battery negative electrode material.

[0006] A third object of the present invention is to provide a negative electrode for a lithium ion battery.

[0007] A fourth object of the present invention is to provide a lithium ion battery.

[0008] In order to achieve the above objectives, the following technical solutions are adopted:

[0009] In a first aspect, the present invention provides a battery negative electrode material, comprising a silicon-bismuth-carbon material and a coating layer on its surface;

[0010] The silicon-bismuth-carbon material comprises a porous bismuth-carbon material and silicon;

[0011] The silicon is deposited in the pores of the porous bismuth-carbon material;

[0012] The porous bismuth-carbon material includes porous carbon and bismuth particles embedded in the porous carbon, the number of the bismuth particles is N, and N is greater than or equal to 2;

[0013] The coating layer is a conductive coating layer and / or an ion-conducting coating layer.

[0014] As a further technical solution, the coating layer is composed of at least one of C, O, S, P, N, Si, Cl, Ti, Sc, V, Zn, Co, Zr, Sb, Al, Mg, K, Ga, Li, Mo, Ce, and Sn.

[0015] As a further technical solution, the size of the bismuth particles is 10 to 1000 nm, preferably 10 to 200 nm.

[0016] As a further technical solution, in the battery negative electrode material, the mass proportions of silicon, bismuth particles, porous carbon and coating layer are a, b, c and d respectively, and meet the following conditions:

[0017] 10%≤a≤55%, preferably 15%≤a≤50%; 3%≤b≤35%; preferably 5%≤b≤30%, 25%≤c≤65%, preferably 30%≤c≤60%; 0.8%≤d≤3.5%, preferably 1%≤d≤3%; wherein a+b+c+d=100%.

[0018] As a further technical solution, the Dv50 particle size of the battery negative electrode material is between 1-20 μm, preferably between 2-10 μm; the specific surface area is 0.1-90 m 2 / g, preferably 0.1-10m 2 / g; total pore volume is 0.002-1.35cm 3 / g, preferably 0.005-1.28cm 3 / g between;

[0019] The Dv50 particle size of the porous bismuth-carbon material is between 1-20 μm, preferably between 3-11 μm; the pore volume is between 0.3-1.7 cm 3 / g, preferably 0.5-1.5cm 3 / g; the pore size distribution is between 1-10nm, preferably between 2-9nm.

[0020] In a second aspect, the present invention provides a method for preparing the above-mentioned battery negative electrode material, comprising the following steps:

[0021] Step S1, mixing an organic bismuth compound and a carbon precursor, then sintering them under an inert atmosphere, and then crushing them to obtain a porous bismuth-carbon material;

[0022] Step S2, placing the porous bismuth-carbon material in a reaction furnace, then introducing a mixture of silicon source gas and carrier gas, and preparing the silicon-bismuth-carbon material through chemical vapor deposition;

[0023] Step S3: coating the surface of the silicon-bismuth-carbon material to prepare a battery negative electrode material.

[0024] As a further technical solution, the sintering temperature in step S1 is 400-1200°C, preferably 600-1000°C;

[0025] The reaction temperature of the chemical vapor deposition in step S2 is 200-800° C., preferably 400-700° C.;

[0026] The coating method in step S3 includes: solid phase coating, liquid phase coating, gas phase coating or a combination thereof.

[0027] As a further technical solution, the organic bismuth compound includes one or more of bismuth citrate, bismuth tartrate, bismuth acetylacetonate, ammonium bismuth nitrate or bismuth acetate;

[0028] The carbon precursor includes one or more of phenolic resin, citric acid, benzenetricarboxylic acid, polyacrylic acid, phenolic resin, epoxy resin, urea-formaldehyde resin, glucose, sucrose, fructose, cellulose, starch, asphalt, polyvinyl alcohol, urea, methyl methacrylate, polyvinyl chloride or polystyrene.

[0029] As a further technical solution, the silicon source gas includes at least one of silane or silicon tetrachloride;

[0030] The carrier gas is an inert gas;

[0031] The volume ratio of the silicon source gas to the carrier gas is 2:1-5:1.

[0032] In a third aspect, the present invention provides a lithium-ion battery negative electrode, wherein the active material of the negative electrode comprises the battery negative electrode material.

[0033] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery is the negative electrode of the lithium-ion battery described above.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The battery negative electrode material provided by the present invention has a watermelon-like multilayer structure with bismuth as the "seed", Si / C as the "pulp", and carbon as the "shell", and has the following advantages:

[0036] 1. Through the conductive network and stress buffering effect of the bismuth / carbon core, combined with the confined design of the silicon-carbon intermediate layer, high capacity is achieved while reducing the volume expansion rate;

[0037] 2. Utilize the high conductivity of metallic bismuth and the strong interface bonding of Si-C bonds to improve the efficiency of electron / ion transmission and reduce the stripping of active materials;

[0038] 3. The preparation method provided by the present invention is simple, low-cost, suitable for industrial production, and can avoid high-cost problems such as nano-silicon synthesis and the use of complex templates. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 This is a structural diagram of the battery negative electrode material of the present invention. DETAILED DESCRIPTION

[0041] Below in conjunction with embodiment and example, embodiment of the present invention is described in detail, but those skilled in the art will appreciate that the following embodiment and example are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Unspecified conditions are carried out according to the conditions of normal conditions or manufacturer's recommendations. Reagents used or instruments not specified by the manufacturer are conventional products that can be purchased commercially.

[0042] The present invention provides a battery negative electrode material, comprising a silicon-bismuth-carbon material and a coating layer on its surface;

[0043] The silicon-bismuth-carbon material comprises a porous bismuth-carbon material and silicon;

[0044] The silicon is deposited in the pores of the porous bismuth-carbon material;

[0045] The porous bismuth-carbon material includes porous carbon and bismuth particles embedded in the porous carbon, the number of the bismuth particles is N, and N is greater than or equal to 2;

[0046] The coating layer is a conductive coating layer and / or an ion-conducting coating layer.

[0047] The battery negative electrode material provided by the present invention has a watermelon-like multilayer structure ( Figure 1 ):

[0048] Bismuth as a "seed": Highly conductive bismuth particles act as electron transport nodes, dispersed in the Si / C matrix, reducing overall resistance;

[0049] Si / C is the "core": the porous carbon matrix and amorphous silicon work together to provide high capacity (silicon contribution ≥1500mAh / g) and buffer local stress;

[0050] Carbon as the "shell": Continuously doped carbon layers inhibit silicon volume expansion, enhance structural stability, and block electrolyte side reactions.

[0051] The battery's negative electrode material achieves high capacity while reducing expansion through the conductive network and stress buffering effect of the bismuth / carbon core, combined with the confined design of the ultra-thin silicon intermediate layer.

[0052] The present invention is further described below by way of specific examples. However, it should be understood that these examples are merely provided for more detailed description and are not to be construed as limiting the present invention in any form.

[0053] Example 1

[0054] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 14%, the silicon content is 40%, the porous carbon content is 45%, and the carbon coating content is 1%. The preparation method is as follows:

[0055] First, bismuth citrate particles and phenolic resin were dispersed in water, stirred, and ultrasonically treated for 1 hour; after spray drying (inlet temperature 200°C, outlet temperature 80°C), precursor microspheres uniformly loaded with organic bismuth were obtained.

[0056] Then, under an inert atmosphere, the temperature was raised to 600°C at 4°C / min and kept at this temperature for 4 hours. After crushing, the porous bismuth-carbon material was obtained with a particle size of Dv50: 9.0 μm and a pore volume of 1.00 cm 3 / g, and the pore size is 5.6nm.

[0057] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor, and SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 1:2) were used to control the reaction temperature to 500°C and deposit for 12 hours. The gas flow was controlled to ensure the silicon content and to make the silicon uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 14:40:45.

[0058] Finally, acetylene / nitrogen mixed gas was introduced into the CVD reactor, the temperature was controlled at 600°C, and the coating was carried out for 2 hours. The gas flow rate was controlled to ensure the carbon layer content, and a carbon coating layer was formed. The lithium-ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 10μm and 30m respectively. 2 / g, 0.01cm 3 / g.

[0059] Example 2

[0060] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 14%, the silicon content is 45%, the porous carbon content is 40%, and the carbon coating content is 1%. The preparation method is as follows:

[0061] First, bismuth tartrate particles and phenolic resin were dispersed in water, stirred, and ultrasonically treated for 1 hour; and spray-dried (inlet temperature 200° C., outlet temperature 80° C.) to obtain precursor microspheres uniformly loaded with organic bismuth.

[0062] Then, under an inert atmosphere, the temperature was raised to 600°C at a rate of 4°C / min and kept at this temperature for 4 hours. After crushing, a porous bismuth-carbon material was obtained with a particle size of Dv50: 8.5 μm and a pore volume of 0.60 m 3 / g, pore size 6nm;

[0063] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor, and SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 1:3) were used to control the reaction temperature to 500°C and the deposition time to 5 hours. The gas flow was controlled to ensure the silicon content and to make the silicon uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 14:45:40.

[0064] Finally, acetylene / nitrogen mixed gas was introduced into the CVD reactor, the temperature was controlled at 600°C, and the coating was carried out for 2 hours. The gas flow rate was controlled to ensure the carbon layer content, and a carbon coating layer was formed. The lithium-ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 9.2μm and 25m respectively. 2 / g, 0.008cm 3 / g.

[0065] Example 3

[0066] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 8.5%, the silicon content is 50%, the porous carbon content is 40%, and the carbon coating content is 1.5%. The preparation method is as follows:

[0067] First, bismuth citrate particles and citric acid solution were dispersed in water, stirred, and ultrasonically treated for 1 hour; spray dried (inlet temperature 200°C, outlet temperature 80°C) to obtain precursor microspheres uniformly loaded with organic bismuth.

[0068] Then, under an inert atmosphere, the temperature was raised to 700°C at a rate of 4°C / min and kept at this temperature for 4 hours. After crushing, a porous bismuth-carbon material was obtained with a particle size of Dv50: 8.5 μm and a pore volume of 0.70 m 3 / g, pore size 6.5nm;

[0069] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor, and SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 1:2) were used to control the reaction temperature to 500°C and the deposition time to 8 hours. The gas flow was controlled to ensure the silicon content and to make the silicon uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 8.5:50:40.

[0070] Finally, acetylene / nitrogen mixed gas was introduced into the CVD reactor, the temperature was controlled at 600°C, and the coating was carried out for 3 hours. The gas flow rate was controlled to ensure the carbon layer content, and a carbon coating layer was formed. The lithium-ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 9.3μm and 28m respectively. 2 / g, 0.012cm 3 / g.

[0071] Example 4

[0072] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 3%, the silicon content is 48%, the porous carbon content is 48%, and the carbon coating content is 1%. The preparation method is as follows:

[0073] First, bismuth citrate particles and asphalt solid phase were dispersed in water, stirred, and ultrasonically treated for 1 hour; spray dried (inlet temperature 200°C, outlet temperature 80°C) to obtain phenolic resin-coated organic bismuth precursor microspheres.

[0074] Then, under an inert atmosphere, the temperature was raised to 900°C at 4°C / min and kept at this temperature for 4 hours. After crushing, a porous bismuth-carbon material was obtained with a particle size of Dv50: 8.0 μm and a pore volume of 0.5 m 3 / g, pore size 5.2nm;

[0075] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor. SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 5:1) were used, the reaction temperature was controlled at 500°C, and the deposition was carried out for 10 hours. The gas flow was controlled to ensure the silicon content, so that the silicon was uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 3:48:48.

[0076] Finally, acetylene / nitrogen mixed gas was introduced into the CVD reactor, the temperature was controlled at 500°C, and the coating was carried out for 6 hours. The gas flow rate was controlled to ensure the carbon layer content, and a carbon coating layer was formed. The Si / Bi-C@C lithium ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 8.5μm and 21m respectively. 2 / g, 0.011cm 3 / g.

[0077] Example 5

[0078] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 29%, the silicon content is 10%, the porous carbon content is 60%, and the titanium coating content is 1%. The preparation method is as follows:

[0079] First, bismuth citrate particles and asphalt solid phase were dispersed in water, stirred, and ultrasonically treated for 1 hour; spray dried (inlet temperature 200°C, outlet temperature 80°C) to obtain phenolic resin-coated organic bismuth precursor microspheres.

[0080] Then, under an inert atmosphere, the temperature was raised to 900°C at 4°C / min and kept at this temperature for 4 hours. After crushing, a porous bismuth-carbon material was obtained with a particle size of Dv50: 8.6 μm and a pore volume of 0.5 m 3 / g, pore size is 6nm;

[0081] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor, and SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 5:1) were used. The reaction temperature was controlled at 500°C and the deposition was carried out for 10 hours. The gas flow was controlled to ensure the silicon content and to make the silicon uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 29:10:60.

[0082] Finally, silicon bismuth carbon and TiH2 were mixed and ground according to the mass ratio of bismuth: silicon: carbon: titanium of 29:10:60:1, and then heated to 1500℃ at 10℃ / min under nitrogen protection for 1h to reduce TiH2 to TiC and form a titanium coating layer. The lithium ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 9.2μm and 22m respectively. 2 / g, 0.009cm 3 / g.

[0083] Example 6

[0084] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 19%, the silicon content is 15%, the porous carbon content is 65%, and the carbon coating content is 1%. The preparation method is as follows:

[0085] First, bismuth citrate particles and asphalt solid phase were dispersed in water, stirred, and ultrasonically treated for 1 hour; spray dried (inlet temperature 200°C, outlet temperature 80°C) to obtain phenolic resin-coated organic bismuth precursor microspheres.

[0086] Then, under an inert atmosphere, the temperature was raised to 900°C at 4°C / min and kept at this temperature for 4 hours. After crushing, a porous bismuth-carbon material was obtained with a particle size of Dv50: 8.6 μm and a pore volume of 0.5 m 3 / g, pore size is 7nm;

[0087] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor. SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 5:1) were used, the reaction temperature was controlled at 500°C, and the deposition was carried out for 10 hours. The gas flow was controlled to ensure the silicon content and to make the silicon uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 19:15:65.

[0088] Finally, acetylene / nitrogen mixed gas was introduced into the CVD reactor, the temperature was controlled at 500°C, and the coating was carried out for 6 hours. The gas flow rate was controlled to ensure the carbon layer content, and a carbon coating layer was formed. The Si / Bi-C@C lithium ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 9μm and 17m respectively. 2 / g, 0.013cm 3 / g.

[0089] Example 7

[0090] This embodiment provides a lithium-ion battery negative electrode material, wherein the bismuth particle content is 12%, the silicon content is 40%, the porous carbon content is 45%, and the carbon coating content is 3%. The preparation method is as follows:

[0091] First, bismuth citrate particles and asphalt solid phase were dispersed in water, stirred, and ultrasonically treated for 1 hour; spray dried (inlet temperature 200°C, outlet temperature 80°C) to obtain phenolic resin-coated organic bismuth precursor microspheres.

[0092] Then, under an inert atmosphere, the temperature was raised to 900°C at 4°C / min and kept at this temperature for 4 hours. After crushing, a porous bismuth-carbon material was obtained with a particle size of Dv50: 8.5 μm and a pore volume of 0.5 m 3 / g, pore size is 6nm;

[0093] Secondly, the porous bismuth-carbon material was placed in a chemical vapor deposition (CVD) reactor, and SiH4 gas and nitrogen (the volume ratio of SiH4 gas to nitrogen was 5:1) were used. The reaction temperature was controlled at 500°C and the deposition was carried out for 10 hours. The gas flow was controlled to ensure the silicon content and to make the silicon uniformly deposited in the pores of the porous bismuth-carbon material. The bismuth:silicon:carbon mass ratio of the obtained silicon-bismuth-carbon material was 12:40:45.

[0094] Finally, acetylene / nitrogen mixed gas was introduced into the CVD reactor, the temperature was controlled at 500°C, and the coating was carried out for 6 hours. The gas flow rate was controlled to ensure the carbon layer content, and a carbon coating layer was formed. The lithium-ion battery negative electrode material was obtained, and its Dv50 particle size, specific surface area and pore volume were 11μm and 10m respectively. 2 / g, 0.004cm 3 / g.

[0095] Comparative Example 1

[0096] A negative electrode material, which differs from Example 1 in that no bismuth source is added.

[0097] Comparative Example 2

[0098] A negative electrode material, which differs from Example 1 in that silicon deposition is not performed.

[0099] Comparative Example 3

[0100] A negative electrode material, which differs from Example 1 in that it is not carbon-coated.

[0101] The negative electrode materials prepared in the above examples and comparative examples were used as negative electrode active materials to prepare negative electrode sheets. The sheet composition was as follows: active material accounted for 80%, binder PAA accounted for 10%, conductive agent SP accounted for 9.9%, and CNT accounted for 0.1%. The negative electrode sheets were prepared using conventional methods to prepare CR2032 button batteries, and the batteries were tested for electrical performance. The specific test method is as follows:

[0102] (1) Half-cell assembly: CR2032 button cells were assembled in a glove box, with lithium metal sheets as counter electrodes, polypropylene microporous membranes as separators, and the electrolyte being a mixture of LiPF6 dissolved in ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), where the LiPF6 concentration was 1 mol / L.

[0103] The battery was tested for charge and discharge using the LAND battery testing system.

[0104] (2) First efficiency test: After the CR2032 battery is left uncharged for 6 hours, it is discharged at 0.1C to 0.005V, and the capacity is recorded as Q1; then it is discharged at a constant voltage of 0.005V until the current reaches 0.01C, and the total capacity is recorded as Q2; after standing for 5 minutes, it is charged at a constant current of 0.1C to 1.5V; the ratio of the first lithium de-ionization capacity to the first lithium insertion capacity is the first coulombic efficiency of the battery.

[0105] (3) Capacity retention test: After 5 minutes of rest, repeat the above charge and discharge steps twice; then discharge to 0.005V at 0.25C; after 5 minutes of rest, charge to 1.5V at 0.25C constant current, and repeat 50 cycles. The capacity retention is calculated as the charge capacity at the 500th cycle / the charge capacity at the first cycle × 100%.

[0106] (4) Electrode expansion rate: After the CR2032 type buckle battery is left to stand for 6 hours, it is discharged at 0.05C to 0.005V, and then discharged at 0.01C to 0.005V; then the buckle battery is disassembled in the glove box, the electrode is cleaned with DEC and the thickness of the electrode is measured; the expansion rate is calculated as: (the thickness of the electrode in the first fully charged state - the thickness of the fresh electrode) / the thickness of the fresh electrode × 100%.

[0107] (5) Electrochemical impedance spectroscopy (ESI) test: The ESI test was performed using an electrochemical workstation. The test frequency was set to 0.01-1000 kHz and the amplitude was set to 5 mV. The impedance value of the electrode was measured after 10 cycles.

[0108] The data obtained from the above examples and comparative examples are shown in Table 1 below:

[0109] Table 1

[0110]

[0111]

[0112] According to the data in Table 1, Examples 1 to 7 are negative electrode materials with Bi as "seed", Si / C as "pulp", and carbon coating as "shell". Comparative Examples 1 to 3 are not Bi loaded or silicon loaded or carbon coated relative to the examples. Comparative Example 1 is a conventional silicon-carbon negative electrode material; Comparative Example 2 is a material without Si deposition. Comparative Example 3 is a material without carbon coating. The presence of Bi significantly reduces the electrode resistance, increases the resistivity of the material, and reduces the impedance; the carbon coating provides mechanical constraints, reduces expansion, and optimizes Li + Transmission path.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery negative electrode material, characterized in that: Including silicon bismuth carbon material and coating layer on its surface; The silicon-bismuth-carbon material comprises a porous bismuth-carbon material and silicon; The silicon is deposited in the pores of the porous bismuth-carbon material; The porous bismuth-carbon material includes porous carbon and bismuth particles embedded in the porous carbon, the number of the bismuth particles is N, and N is greater than or equal to 2; The coating layer is a conductive coating layer and / or an ion-conducting coating layer.

2. The battery negative electrode material according to claim 1, characterized in that The coating layer is composed of at least one of C, O, S, P, N, Si, Cl, Ti, Sc, V, Zn, Co, Zr, Sb, Al, Mg, K, Ga, Li, Mo, Ce, and Sn.

3. The battery negative electrode material according to claim 1, characterized in that The size of the bismuth particles is 10 to 1000 nm, preferably 10 to 200 nm.

4. The battery negative electrode material according to claim 1, characterized in that In the battery negative electrode material, the mass proportions of silicon, bismuth particles, porous carbon and coating layer are a, b, c and d respectively, and meet the following conditions: 10%≤a≤55%, preferably 15%≤a≤50%; 3%≤b≤35%; preferably 5%≤b≤30%, 25%≤c≤65%, preferably 30%≤c≤60%; 0.8%≤d≤3.5%, preferably 1%≤d≤3%; wherein a+b+c+d=100%.

5. The battery negative electrode material according to claim 1, characterized in that The Dv50 particle size of the battery negative electrode material is between 1-20 μm, preferably between 2-10 μm; the specific surface area is 0.1-90 m 2 / g, preferably 0.1-10m 2 / g; total pore volume is 0.002-1.35cm 3 / g, preferably 0.005-1.28cm 3 / g between; The Dv50 particle size of the porous bismuth-carbon material is between 1-20 μm, preferably between 3-11 μm; the pore volume is between 0.3-1.7 cm 3 / g, preferably 0.5-1.5cm 3 / g; the pore size distribution is between 1-10nm, preferably between 2-9nm.

6. The method for preparing a negative electrode material for a battery according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step S1, mixing an organic bismuth compound and a carbon precursor, then sintering them under an inert atmosphere, and then crushing them to obtain a porous bismuth-carbon material; Step S2, placing the porous bismuth-carbon material in a reaction furnace, then introducing a mixture of silicon source gas and carrier gas, and preparing the silicon-bismuth-carbon material through chemical vapor deposition; Step S3: coating the surface of the silicon-bismuth-carbon material to prepare a battery negative electrode material.

7. The method for preparing a negative electrode material for a battery according to claim 6, wherein: The sintering temperature in step S1 is 400-1200°C, preferably 600-1000°C; The reaction temperature of the chemical vapor deposition in step S2 is 200-800° C., preferably 400-700° C.; The coating method in step S3 includes: solid phase coating, liquid phase coating, gas phase coating or a combination thereof.

8. The method for preparing a negative electrode material for a battery according to claim 6, wherein: The organic bismuth compound includes one or more of bismuth citrate, bismuth tartrate, bismuth acetylacetonate, ammonium bismuth nitrate or bismuth acetate; The carbon precursor includes one or more of phenolic resin, citric acid, benzenetricarboxylic acid, polyacrylic acid, phenolic resin, epoxy resin, urea-formaldehyde resin, glucose, sucrose, fructose, cellulose, starch, asphalt, polyvinyl alcohol, urea, methyl methacrylate, polyvinyl chloride or polystyrene.

9. A lithium ion battery negative electrode, characterized in that The active material of the negative electrode comprises the battery negative electrode material according to any one of claims 1 to 5.

10. A lithium ion battery, characterized in that: The negative electrode of the lithium ion battery is the negative electrode of the lithium ion battery according to claim 9.

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