Composite material and preparation method thereof, negative pole piece and lithium ion battery

Abstract

The invention is suitable for the technical field of lithium ion battery materials, and discloses a composite material and a preparation method thereof, a negative electrode plate and a lithium ion battery. Wherein the composite material has a core-shell structure, the core-shell structure comprises an inner core and an outer shell layer coating the outer surface of the inner core, the inner core contains porous carbon doped with boron nitride and nano silicon deposited in pores of the porous carbon, and the outer shell layer contains a solid electrolyte complex. According to the composite material provided by the invention, the electronic conductivity, the structural stability, the first efficiency and the rate capability of the material are improved.

Description

Technical Field

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

[0002] Silicon-carbon materials are composed of porous carbon, nano-silicon deposited in the pores of porous carbon, and amorphous carbon coated on the surface of porous carbon. Due to the poor electronic conductivity and poor compressive resistance of porous carbon itself, the structural stability of silicon-carbon materials deviates, reducing the cycle performance. Although some researchers have improved the initial efficiency and rate performance by doping or coating the surface of silicon-carbon materials with substances that improve the electronic or ionic conductivity of the materials, the effect is not obvious. For example, in the related art, the stability of the material structure is improved by preparing a solid electrolyte coated titanium-doped silicon-carbon composite material, but the electronic conductivity of the material is not greatly improved, that is, the rate performance and cycle performance of the composite material are not effectively improved. Summary of the Invention

[0003] The purpose of the present invention is to provide a composite material and its preparation method, a negative electrode plate and a lithium-ion battery, aiming to solve the technical problems of poor structural stability, low electronic conductivity, poor rate performance and cycle performance of existing silicon-carbon materials.

[0004] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0005] The first aspect of the present invention discloses a composite material having a core-shell structure, wherein the core-shell structure includes an inner core and an outer shell layer coated on the outer surface of the inner core, wherein the inner core contains porous carbon doped with boron nitride and nano-silicon deposited in the pores of the porous carbon, and the outer shell layer contains a solid electrolyte complex.

[0006] It should be noted that the material's electronic conductivity and structural stability can be improved by including a boron nitride-doped porous carbon core. Depositing nanosilicon within the pores of the porous carbon and coating it with a solid electrolyte composite outer shell can enhance the material's rate capability, cycling performance, and initial efficiency.

[0007] In one implementation of the present invention, the composite material satisfies one or more of the following conditions ah:

[0008] a. Based on the mass of the core, the content of the porous carbon is 45-49wt%, for example 45wt%, 46wt%, 47wt%, 48wt% or 49wt%;

[0009] b. Based on the mass of the core, the content of the nano-silicon is 45-49wt%, for example 45wt%, 46wt%, 47wt%, 48wt% or 49wt%;

[0010] c. Based on the mass of the core, the boron nitride content is 2-10wt%, preferably 5-10wt%, for example 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%; more preferably 8-10wt%;

[0011] It should be noted that setting the boron nitride content to 2-10wt% can effectively improve the electronic conductivity and structural stability of the material. If the boron nitride content is too low, the improvement of the electronic conductivity of the material is limited, and if the boron nitride content is too high, the specific capacity of the material will be reduced.

[0012] d. The solid electrolyte composite comprises a solid electrolyte, and the content of the solid electrolyte is 60-90wt%, for example 60wt%, 70wt%, 80wt% or 90wt%, based on the mass of the outer shell;

[0013] e. The solid electrolyte composite comprises a conductive agent, wherein the content of the conductive agent is 1-5wt%, for example, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, based on the mass of the outer shell;

[0014] f. The solid electrolyte composite comprises amorphous carbon, wherein the content of the amorphous carbon is 9-35wt%, preferably 20-30wt%, for example 22wt%, 24wt%, 26wt% or 28wt%, based on the mass of the outer shell;

[0015] g. The particle size of the core-shell structure is 5-10 μm;

[0016] h. Based on the mass ratio of the composite material being 100%, the mass ratio of the core to the shell is (92-98):(2-8).

[0017] A second aspect of the present invention discloses a method for preparing a composite material, comprising the following steps:

[0018] S1, mixing a phenolic compound, an aldehyde compound, an alkali solution and a heteroatom dispersant to obtain a solution A;

[0019] S2, mixing boric acid, melamine and ethanol to obtain solution B;

[0020] S3, mixing solution A and solution B, reacting, filtering, solidifying the filter residue, and then introducing carbon dioxide gas to activate and form pores to obtain boron nitride-doped porous carbon;

[0021] S4, adding the boron nitride-doped porous carbon to a fluidized bed, introducing a silane mixed gas into the boron nitride-doped porous carbon for treatment, and then introducing an acetylene gas into the boron nitride-doped porous carbon for treatment, to obtain a boron nitride-doped silicon-carbon material;

[0022] S5. Mixing the solid electrolyte, dispersant, sodium polyacrylate resin, organic solvent and the boron nitride-doped silicon-carbon material, drying, carbonizing and crushing to obtain the composite material.

[0023] It should be noted that phenolic compounds, aldehyde compounds, and heteroatom dispersants are added to an alkaline solution to undergo a phenol-formaldehyde reaction, and heteroatom doping is used to enhance the electronic conductivity of the material. Boric acid is reacted with melamine to generate boron nitride, which is then doped into a heteroatom-doped resin solution. Carbonization and activation are then performed to obtain boron nitride-doped porous carbon, which exhibits advantages such as high electrical conductivity and strong structural stability. By coating the surface of the boron nitride-doped silicon-carbon material with a solid electrolyte, the high ionic conductivity of the solid electrolyte itself can effectively improve the initial efficiency and rate performance.

[0024] In one implementation of the present invention, step S1 satisfies one or more of the following conditions ag:

[0025] a. The step S1 comprises: adding the phenolic compound to the alkali solution and dispersing it uniformly, and then adding the heteroatom dispersant and the aldehyde compound and dispersing them uniformly to obtain the solution A;

[0026] b. In the step S1, the phenolic compound, the aldehyde compound, the alkali solution and the heteroatom dispersant are mixed in a mass ratio of 100: (150-300): (500-1000): (1-10);

[0027] c. In step S1, the phenolic compound is at least one of resorcinol, phenol, xylenol, cresol, cardanol, octylphenol and bisphenol A;

[0028] d. In step S1, the aldehyde compound is at least one of formaldehyde, acetaldehyde, phenylacetaldehyde, benzaldehyde, furfural and valeraldehyde;

[0029] e. In step S1, the alkali solution is at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide;

[0030] f. In the step S1, the concentration of the alkali solution is 0.5-1.5wt%, preferably 1wt%;

[0031] g. In the step S1, the heteroatom dispersant is at least one of sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate;

[0032] Alternatively, step S2 satisfies one or both of the following conditions hi:

[0033] h. Step S2 comprises: mixing the boric acid solution and the melamine and adding the mixture to the ethanol to obtain a solution B having a mass concentration of 5-15 wt %, for example, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt % or 15 wt % of solution B;

[0034] i. In step S2, the boric acid and the melamine are mixed in a mass ratio of 100:(10-50), for example, 100:10, 100:20, 100:30, 100:40 or 100:50.

[0035] In one implementation of the present invention, step S3 satisfies one or more of the following conditions ad:

[0036] a. In step S3, the solution A and the solution B are mixed in a mass ratio of 1000:(50-200), for example, 1000:50, 1000:100 or 1000:200;

[0037] It should be noted that when solution A and solution B are mixed in a mass ratio of 1000:(50-200), a boron nitride precursor is deposited on the surface of the phenolic resin; when the mass of the added solution B is too low, the amount of boron nitride precursor coating is too small to improve the electronic conductivity of the material. When the mass of the added solution B is too high, the phenolic resin content is too low, which reduces its porous carbon content, thereby reducing the content of nano-silicon that the material can accommodate and reducing the specific capacity.

[0038] b. In step S3, the reaction temperature is 50-150°C and the reaction time is 2-24h;

[0039] c. In step S3, the curing temperature is 400-600°C and the curing time is 1-6h;

[0040] d. In step S3, the activation pore-forming temperature is 1100-1400°C, the time is 60-600 min, and the flow rate of the carbon dioxide gas is 100-500 SCCM.

[0041] In one implementation of the present invention, step S4 satisfies one or more of the following conditions ac:

[0042] a. In the step S4, the temperature of the silane mixed gas is 450-650°C for 30-300min, and the flow rate of the silane mixed gas is 100-500SCCM;

[0043] b. In step S4, the silane gas mixture comprises silane gas and nitrogen; preferably, the volume ratio of the silane gas and the nitrogen is (1-5): 10; preferably, the silane gas is at least one of monosilane, disilane, trichlorosilane, tetrachlorosilane or dimethylchlorosilane;

[0044] c. In step S4, the acetylene gas is introduced at a temperature of 700-900°C for 30-300 min, and a flow rate of 10-50 SCCM.

[0045] In one implementation of the present invention, step S5 satisfies one or more of the following conditions af:

[0046] a. The step S5 comprises: dissolving the sodium polyacrylate resin in the organic solvent, adding the dispersant and the solid electrolyte to disperse uniformly, then adding the boron nitride-doped silicon-carbon material to disperse uniformly, spray drying, carbonizing, and pulverizing to obtain the composite material;

[0047] b. In the step S5, the solid electrolyte, the dispersant, the sodium polyacrylate resin, the organic solvent and the boron nitride-doped silicon-carbon material are mixed in a mass ratio of (5-15): (1-3): (5-15): (100-500): 200;

[0048] c. In step S5, the carbonization temperature is 800-1200°C and the time is 2-12h;

[0049] d. In step S5, the solid electrolyte is Li 1+a Al a Ti 2-a (PO4)3、Li x Ti y (PO4)3, LiZr2(PO4)3, Li7La3Zr2O 12 (LLZO), Li 0.33 La 0.56 Any one of TiO3 (LLTO), Li2S-P2S5, Li2S-SiS2 or a combination of at least two thereof, wherein 0<a≤1, 0<x<2, 0<y<3;

[0050] e. In step S5, the organic solvent is at least one of methanol, ethanol, ethylene glycol or 1,4-butanediol;

[0051] f. In step S5, the dispersant is at least one of polyvinyl pyrrolidone (PVP), polyacrylamide (PAM), and polyethylene glycol (PEG).

[0052] The third aspect of the present invention discloses a composite material, which is prepared by the method for preparing the composite material described in the second aspect of the present invention.

[0053] The fourth aspect of the present invention discloses a negative electrode plate, comprising the composite material described in the first aspect or the third aspect of the present invention.

[0054] The fifth aspect of the present invention discloses a lithium-ion battery, comprising the negative electrode sheet described in the fourth aspect of the present invention.

[0055] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0056] 1) adding a phenolic compound, an aldehyde compound, and a heteroatom dispersant to an alkaline solution to carry out a phenol-aldehyde reaction, thereby improving the electronic conductivity of the material by doping with heteroatoms;

[0057] 2) boric acid is reacted with melamine to generate boron nitride, and the boron nitride is doped in a heteroatom-doped resin solution, carbonized, and activated to obtain boron nitride-doped porous carbon. The boron nitride-doped porous carbon has the advantages of high conductivity and strong structural stability;

[0058] 3) By coating the surface of the boron nitride-doped silicon-carbon material with a solid electrolyte through a liquid phase method, the first efficiency and its rate performance are improved by relying on the high ionic conductivity of the solid electrolyte itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only 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.

[0060] in:

[0061] Figure 1 This is an SEM image of the composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. In the following embodiments, many detailed descriptions are intended to enable the present application to be better understood. However, those skilled in the art can readily appreciate that some of the features may be omitted in different circumstances, or may be replaced by other materials or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid overwhelm the core of the present application with excessive descriptions, and for those skilled in the art, it is not necessary to describe these related operations in detail. The related operations can be fully understood based on the description in the specification and the general technical knowledge in the art.

[0063] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various embodiments. Furthermore, the steps or actions in the method description may be reordered or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various sequences in the specification and drawings are provided solely for the purpose of clearly describing a particular embodiment and are not intended to be mandatory, unless otherwise specified.

[0064] A first aspect of the present invention provides a composite material having a core-shell structure, comprising an inner core and an outer shell coating the outer surface of the inner core, wherein the inner core comprises porous carbon doped with boron nitride and nanosilicon deposited within the pores of the porous carbon, and the outer shell comprises a solid electrolyte composite. By providing the inner core with the boron nitride-doped porous carbon, the electronic conductivity and structural stability of the material can be improved. By depositing nanosilicon within the pores of the porous carbon and coating the outer shell with the solid electrolyte composite, the rate capability, cycle performance, and initial efficiency of the material can be improved.

[0065] A second aspect of the present invention provides a method for preparing a composite material, comprising the following steps:

[0066] S1, mixing a phenolic compound, an aldehyde compound, an alkali solution and a heteroatom dispersant to obtain a solution A;

[0067] S2, mixing boric acid, melamine and ethanol to obtain solution B;

[0068] S3, mixing solution A and solution B, reacting, filtering, solidifying the filter residue, and then introducing carbon dioxide gas to activate and form pores to obtain boron nitride-doped porous carbon;

[0069] S4, adding the boron nitride-doped porous carbon to a fluidized bed, introducing a silane mixed gas into the boron nitride-doped porous carbon for treatment, and then introducing an acetylene gas into the boron nitride-doped porous carbon for treatment, to obtain a boron nitride-doped silicon-carbon material;

[0070] S5. Mixing the solid electrolyte, dispersant, sodium polyacrylate resin, organic solvent and the boron nitride-doped silicon-carbon material, drying, carbonizing and crushing to obtain the composite material.

[0071] Phenolic compounds, aldehyde compounds, and heteroatom dispersants are added to an alkaline solution to initiate a phenol-formaldehyde reaction. Heteroatom doping enhances the electronic conductivity of the material. Boric acid reacts with melamine to generate boron nitride, which is then doped into a heteroatom-doped resin solution. Carbonization and activation yield boron nitride-doped porous carbon, which exhibits high electrical conductivity and structural stability. By coating the surface of the boron nitride-doped silicon-carbon material with a solid electrolyte, the high ionic conductivity of the solid electrolyte itself can effectively improve initial efficiency and rate performance.

[0072] A third aspect of the present invention provides a composite material prepared using the method for preparing the composite material described in the second aspect of the present invention. The composite material prepared using this method comprises a core comprising boron nitride-doped porous carbon and nano-silicon deposited within the pores of the porous carbon, and an outer shell comprising a solid electrolyte complex. This composite material exhibits improved electronic conductivity, structural stability, initial efficiency, and rate capability.

[0073] A fourth aspect of the present invention provides a negative electrode plate comprising the composite material of the first or third aspect of the present invention. By using the composite material, the negative electrode plate has good fast charging performance and initial efficiency.

[0074] A fifth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the fourth aspect of the present invention. By adopting the negative electrode sheet, the lithium-ion battery has excellent fast charging performance and high initial efficiency.

[0075] The present application is further described in detail below through specific examples. The following examples are only provided to further illustrate the present application and should not be construed as limiting the present application. It should be noted that if specific conditions are not specified in the examples, the process is carried out according to conventional conditions or the conditions recommended by the product manufacturer; the equipment and reagents used in the examples, for which the manufacturer is not specified, are all conventional products that can be purchased through commercial channels.

[0076] Example 1

[0077] A method for preparing a solid electrolyte-coated boron nitride-doped silicon-carbon composite material comprises the following steps:

[0078] Step S1:

[0079] 100g of resorcinol was added to 800g of 1wt% sodium hydroxide solution and dispersed evenly, and then 5g of sodium tripolyphosphate and 200g of formaldehyde were added and dispersed evenly to prepare solution A;

[0080] Step S2:

[0081] 100 g of boric acid solution and 30 g of melamine were mixed and added to 1300 g of ethanol mixed solution to prepare solution B with a mass concentration of 5-15 wt %;

[0082] Step S3:

[0083] 1000 g of solution A and 100 g of solution B were mixed and reacted at 100 ° C for 12 h, filtered, and the resulting filter residue was cured at 500 ° C for 3 h. Then, the temperature was raised to 1200 ° C, and carbon dioxide gas was introduced at a flow rate of 300 SCCM for activation and pore formation for 300 min to obtain boron nitride-doped porous carbon;

[0084] Step S4:

[0085] 1000 g of boron nitride-doped porous carbon was added to a fluidized bed, and then the temperature was raised to 550° C. and a disilane mixed gas (volume ratio of disilane to nitrogen = 3:10) was introduced at a flow rate of 300 SCCM for 150 minutes. The temperature was then raised to 800° C. and acetylene gas was introduced at a flow rate of 30 SCCM for 150 minutes to obtain a boron nitride-doped silicon-carbon material.

[0086] Step S5:

[0087] 10g sodium polyacrylate resin was dissolved in 300g methanol organic solvent, and then 2g polyvinyl pyrrolidone dispersant, 10g Li 1+a Al a Ti 2-a (PO4)3 (where 0<a≤1) is evenly dispersed to obtain a mixed liquid, and then 200g of boron nitride-doped silicon-carbon material is added and evenly dispersed, spray-dried, and then the obtained material is heated to 950℃ and carbonized for 6h, crushed and classified to obtain a solid electrolyte-coated boron nitride-doped silicon-carbon composite material.

[0088] Example 2

[0089] A method for preparing a solid electrolyte-coated boron nitride-doped silicon-carbon composite material comprises the following steps:

[0090] Step S1:

[0091] 100 g of phenol was added to 500 g of 1 wt% potassium hydroxide solution and dispersed evenly, followed by adding 1 g of sodium hexametaphosphate and 150 g of acetaldehyde and dispersing them evenly to prepare solution A;

[0092] Step S2:

[0093] 100 g of boric acid solution and 10 g of melamine were mixed and added to 2200 g of ethanol mixed solution to prepare solution B with a mass concentration of 5-15 wt %;

[0094] Step S3:

[0095] 1000 g of solution A and 50 g of solution B were mixed and reacted at 50 ° C for 24 h, filtered, and the resulting filter residue was cured at 400 ° C for 6 h. Then, the temperature was raised to 1100 ° C, and carbon dioxide gas was introduced at a flow rate of 100 SCCM for activation and pore formation for 600 min to obtain boron nitride-doped porous carbon;

[0096] Step S4:

[0097] 1000 g of boron nitride-doped porous carbon was added to a fluidized bed, and then the temperature was raised to 450° C. and a disilane mixed gas (disilane:nitrogen volume ratio = 1:10) was introduced at a flow rate of 100 SCCM for 300 minutes. The temperature was then raised to 700° C. and acetylene gas was introduced at a flow rate of 50 SCCM for 30 minutes to obtain a boron nitride-doped silicon-carbon material.

[0098] Step S5:

[0099] 5g of sodium polyacrylate resin was dissolved in 100g of ethanol organic solvent, and then 1g of polyacrylamide and 5g of Li x Ti y (PO4)3 (wherein, 0<x<2, 0<y<3) is evenly dispersed to obtain a mixed liquid, and then 200g of boron nitride-doped silicon-carbon material is added and evenly dispersed, spray-dried, and then the obtained material is heated to 800℃ and carbonized for 12h, crushed and classified to obtain a solid electrolyte-coated boron nitride-doped silicon-carbon composite material.

[0100] Example 3

[0101] A method for preparing a solid electrolyte-coated boron nitride-doped silicon-carbon composite material comprises the following steps:

[0102] Step S1:

[0103] 100 g of xylenol was added to 1000 g of 1 wt% potassium hydroxide solution and dispersed evenly, followed by adding 10 g of sodium pyrophosphate and 200 g of furfural and dispersing evenly to prepare solution A;

[0104] Step S2:

[0105] 100 g of boric acid solution and 50 g of melamine were mixed and added to 1000 g of ethanol mixed solution to prepare solution B with a mass concentration of 5-15 wt %;

[0106] Step S3:

[0107] 1000 g of solution A and 200 g of solution B were mixed and reacted at 150 ° C for 2 h, filtered, and the resulting filter residue was cured at 600 ° C for 1 h. Then, the temperature was raised to 1400 ° C, and carbon dioxide gas was introduced at a flow rate of 500 SCCM for 60 min to activate and form pores to obtain boron nitride-doped porous carbon;

[0108] Step S4:

[0109] 1000 g of boron nitride-doped porous carbon was added to a fluidized bed, and then the temperature was raised to 650° C. and a disilane mixed gas (disilane: nitrogen volume ratio = 5:10) was introduced at a flow rate of 500 SCCM for 30 minutes. The temperature was then raised to 900° C. and acetylene gas was introduced at a flow rate of 10 SCCM for 300 minutes to obtain a boron nitride-doped silicon-carbon material.

[0110] Step S5:

[0111] 15g of sodium polyacrylate resin was dissolved in 500g of ethylene glycol organic solvent, and then 3g of polyethylene glycol and 15g of LiZr2(PO4)3 were added and dispersed evenly to obtain a mixed solution. Then 200g of boron nitride-doped silicon-carbon material was added and dispersed evenly, spray-dried, and the obtained material was heated to 1200℃ and carbonized for 2h, crushed and graded to obtain a solid electrolyte-coated boron nitride-doped silicon-carbon composite material.

[0112] Comparative Example 1

[0113] The difference from Example 1 is that steps S1-S3 are omitted, and commercially available porous carbon (model: YP-80F, manufacturer: Japan Kuraray Co., Ltd.) is used to replace the boron nitride-doped porous carbon in step S4. The rest is the same as Example 1.

[0114] Comparative Example 2

[0115] The difference from Example 1 is that in step S3, 1000 g of solution A and 5000 g of solution B are mixed. The rest is the same as Example 1.

[0116] Comparative Example 3

[0117] Different from Example 1, the boron nitride-doped silicon-carbon material in step S4 is used as the negative electrode material, and the solid electrolyte is not coated on its surface.

[0118] Test Case

[0119] 1) Appearance

[0120] The solid electrolyte coated boron nitride doped silicon carbon composite material in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. Figure 1It can be seen that the material has a granular structure, and the particle size of the material is evenly distributed, with the particle size ranging from 5 to 10 μm.

[0121] 2) Physical and chemical testing and button battery testing

[0122] Refer to GB / T38823-2020 "Silicon Carbon" to test the specific surface area and tap density of the solid electrolyte coated boron nitride doped silicon-carbon composite material; and use a four-probe tester to test the powder conductivity of the silicon-carbon composite material, and test the gas production of the powder material (1 mg of powder material is added to 45°C deionized water and soaked for 48 hours to test its gas production V1, and the gas production of the powder material is calculated as V1 / M1*100%); and the pore volume and specific surface area of ​​its porous carbon are tested, and the test method is carried out in accordance with the test method of GB / T-2496-2015 "Activated Carbon".

[0123] The solid electrolyte-coated boron nitride-doped silicon-carbon composite material in Examples 1-3 and Comparative Examples 1-3 was used as the negative electrode material for lithium-ion batteries to prepare button batteries. The preparation method is as follows:

[0124] A binder, conductive agent, and solvent were added to the composite material, stirred to form a slurry, and then coated on copper foil. The slurry was then dried and rolled to produce the negative electrode. The binder used was polyvinylidene fluoride (PVDF), the conductive agent was conductive carbon black (SP), and the solvent was N-methylpyrrolidone (NMP). The ratio of composite material, SP, PVDF, and NMP was 80 g:15 g:15 g:300 mL. The electrolyte consisted of lithium hexafluorophosphate (LiPF6) and a 1:1 volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) as the solvent, with an electrolyte concentration of 1 mol / L. A lithium metal sheet served as the counter electrode, and a polypropylene (PP) film was used as the separator. The button cell was assembled in an argon-filled glove box.

[0125] Electrochemical performance tests were conducted on button cells comprising the solid electrolyte-coated boron nitride-doped silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-3. The tests were performed using a Wuhan Blue Power CT2001A battery tester with a charge and discharge voltage range of 0.005 V to 2.0 V and a charge and discharge rate of 0.1 C. The charged DCR (50% SOC) of the materials was also tested.

[0126] The thickness D1 of the negative electrode plate of the button battery comprising the solid electrolyte-coated boron nitride-doped silicon-carbon composite material of Examples 1-3 and Comparative Examples 1-3 after rolling is tested, and then the full-charge thickness D2 of the negative electrode plate of the button battery is dissected when it is fully charged to 100% SOC, and then the expansion rate is calculated: the expansion rate is = (D1-D2) / D1.

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] The data in Table 1 demonstrates that the solid-state electrolyte-coated boron nitride-doped silicon-carbon composite material prepared in this invention significantly outperforms the comparative example in terms of specific capacity, initial efficiency, powder conductivity, full-charge expansion, and DCR. This is due to the fact that doping the porous carbon with boron nitride improves the material's electronic conductivity, reduces polarization, and increases specific capacity and initial efficiency. Furthermore, the outer coating of the solid electrolyte increases the material's ion diffusion coefficient, improves initial efficiency, and reduces DCR.

[0132] 3) Soft pack battery test

[0133] Anode sheets were prepared using the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-3 mixed with 95% artificial graphite as the negative electrode material. A ternary material (LiNi1 / 3Co1 / 3Mn1 / 3O2) served as the positive electrode. The electrolyte consisted of lithium hexafluorophosphate (LiPF6) and a 1:1 volume ratio mixture of ethylene carbonate (EC) and ethyl methyl carbonate (DEC) as the solvent, with an electrolyte concentration of 1.3 mol / L. 5Ah soft-pack batteries were fabricated using Celgard 2400 membrane as the separator. The negative electrode sheets were tested for their liquid absorption and retention capacity, rate capability, and high-temperature storage performance.

[0134] Cycling performance tests and rate tests were performed on soft-pack batteries comprising the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-3.

[0135] Magnification test:

[0136] The constant current ratio of the test material under 2C conditions was charged to 4.2V at a rate of 2C, and then charged at a constant voltage of 0.1C for 2h. The constant current ratio was calculated as constant current capacity / (constant current capacity + constant voltage capacity).

[0137] Cycle performance:

[0138] Test voltage range: 2.5-4.2V, 1C / 1C, temperature: 25±3℃, 500 cycles.

[0139] High temperature storage:

[0140] The soft-pack battery is fully charged to 100% SOC at room temperature and its capacity is tested as A1. It is then transferred to a high-temperature oven at 55°C and left stationary for 30 days. After that, it is discharged at a rate of 0.3C at room temperature and its capacity is tested as A2. The high-temperature charge retention rate is calculated as A2 / A1×100%.

[0141] The test results are shown in Table 2.

[0142] Table 2

[0143] Cycle performance Constant current ratio Absorption time (S) High temperature storage performance Example 1 94.5％ 89.6％ 78 94.2％ Example 2 93.7％ 88.2％ 65 94.9％ Example 3 95.2％ 90.1％ 84 93.6％ Comparative Example 1 88.7％ 85.1％ 112 91.2％ Comparative Example 2 89.3％ 87.2％ 143 88.2％ Comparative Example 3 87.5％ 86.3％ 99 90.4％

[0144] As can be seen from Table 2, the liquid absorption capacity, cycle performance, and constant current ratio of the soft-pack lithium-ion battery prepared using the silicon-carbon composite material of the present invention are better than those of the comparative example. The reason is that the silicon-carbon composite material of the present invention has a high specific surface area and low powder resistivity; at the same time, the example material has low expansion, thereby improving the cycle performance and constant current ratio.

[0145] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A composite material, characterized in that The composite material has a core-shell structure, which includes a core and an outer shell layer covering the outer surface of the core. The core contains porous carbon doped with boron nitride and nano-silicon deposited in the pores of the porous carbon, and the outer shell contains a solid electrolyte composite.

2. The composite material according to claim 1, wherein The composite material satisfies one or more of the following conditions: a. Based on the mass of the core, the content of the porous carbon is 45-49wt%, for example 45wt%, 46wt%, 47wt%, 48wt% or 49wt%; b. Based on the mass of the core, the content of the nano-silicon is 45-49wt%, for example 45wt%, 46wt%, 47wt%, 48wt% or 49wt%; c. Based on the mass of the core, the boron nitride content is 2-10wt%, preferably 5-10wt%, for example 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%; more preferably 8-10wt%; d. The solid electrolyte composite comprises a solid electrolyte, and the content of the solid electrolyte is 60-90wt%, for example 60wt%, 70wt%, 80wt% or 90wt%, based on the mass of the outer shell; e. The solid electrolyte composite comprises a conductive agent, wherein the content of the conductive agent is 1-5wt%, for example, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, based on the mass of the outer shell; f. The solid electrolyte composite comprises amorphous carbon, based on the mass of the outer shell layer, the amorphous carbon content is 9-35wt%, preferably 20-30wt%; g. The particle size of the core-shell structure is 5-10 μm; h. Based on the mass ratio of the composite material being 100%, the mass ratio of the core to the shell is (92-98):(2-8).

3. A method for preparing a composite material, characterized in that: The following steps are involved: S1, mixing a phenolic compound, an aldehyde compound, an alkali solution and a heteroatom dispersant to obtain a solution A; S2, mixing boric acid, melamine and ethanol to obtain solution B; S3, mixing solution A and solution B, reacting, filtering, solidifying the filter residue, and then introducing carbon dioxide gas to activate and form pores to obtain boron nitride-doped porous carbon; S4, adding the boron nitride-doped porous carbon to a fluidized bed, introducing a silane mixed gas into the boron nitride-doped porous carbon for treatment, and then introducing an acetylene gas into the boron nitride-doped porous carbon for treatment, to obtain a boron nitride-doped silicon-carbon material; S5. Mixing the solid electrolyte, dispersant, sodium polyacrylate resin, organic solvent and the boron nitride-doped silicon-carbon material, drying, carbonizing and crushing to obtain the composite material.

4. The method for preparing a composite material according to claim 3, wherein: The step S1 satisfies one or more of the following conditions ag: a. The step S1 comprises: adding the phenolic compound to the alkali solution and dispersing it uniformly, and then adding the heteroatom dispersant and the aldehyde compound and dispersing them uniformly to obtain the solution A; b. In the step S1, the phenolic compound, the aldehyde compound, the alkali solution and the heteroatom dispersant are mixed in a mass ratio of 100: (150-300): (500-1000): (1-10); c. In step S1, the phenolic compound is at least one of resorcinol, phenol, xylenol, cresol, cardanol, octylphenol and bisphenol A; d. In step S1, the aldehyde compound is at least one of formaldehyde, acetaldehyde, phenylacetaldehyde, benzaldehyde, furfural and valeraldehyde; e. In step S1, the alkali solution is at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide; f. In the step S1, the concentration of the alkali solution is 0.5-1.5wt%, preferably 1wt%; g. In the step S1, the heteroatom dispersant is at least one of sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate; Alternatively, step S2 satisfies one or both of the following conditions hi: h. Step S2 comprises: mixing the boric acid solution and the melamine and adding the mixture to the ethanol to obtain a solution B having a mass concentration of 5-15 wt %, for example, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt % or 15 wt % of solution B; i. In step S2, the boric acid and the melamine are mixed in a mass ratio of 100:(10-50), for example, 100:10, 100:20, 100:30, 100:40 or 100:

50.

5. The method for preparing a composite material according to claim 3, wherein: Step S3 satisfies one or more of the following conditions ad: a. In step S3, the solution A and the solution B are mixed in a mass ratio of 1000:(50-200), for example, 1000:50, 1000:100 or 1000:200; b. In step S3, the reaction temperature is 50-150°C and the reaction time is 2-24h; c. In step S3, the curing temperature is 400-600°C and the curing time is 1-6h; d. In step S3, the activation pore-forming temperature is 1100-1400°C, the time is 60-600 min, and the flow rate of the carbon dioxide gas is 100-500 SCCM.

6. The method for preparing a composite material according to claim 3, wherein: Step S4 satisfies one or more of the following conditions ac: a. In the step S4, the temperature of the silane mixed gas is 450-650°C for 30-300min, and the flow rate of the silane mixed gas is 100-500SCCM; b. In step S4, the silane gas mixture comprises silane gas and nitrogen; preferably, the volume ratio of the silane gas and the nitrogen is (1-5): 10; preferably, the silane gas is at least one of monosilane, disilane, trichlorosilane, tetrachlorosilane or dimethylchlorosilane; c. In step S4, the acetylene gas is introduced at a temperature of 700-900°C for 30-300 min, and a flow rate of 10-50 SCCM.

7. The method for preparing a composite material according to claim 3, wherein: Step S5 satisfies one or more of the following conditions af: a. The step S5 comprises: dissolving the sodium polyacrylate resin in the organic solvent, adding the dispersant and the solid electrolyte to disperse uniformly, then adding the boron nitride-doped silicon-carbon material to disperse uniformly, spray drying, carbonizing, and pulverizing to obtain the composite material; b. In the step S5, the solid electrolyte, the dispersant, the sodium polyacrylate resin, the organic solvent and the boron nitride-doped silicon-carbon material are mixed in a mass ratio of (5-15): (1-3): (5-15): (100-500): 200; c. In step S5, the carbonization temperature is 800-1200°C and the time is 2-12h; d. In step S5, the solid electrolyte is Li 1+a Al a Ti 2-a (PO4)3、Li x Ti y (PO4)3, LiZr2(PO4)3, Li7La3Zr2O 12 (LLZO), Li 0.33 La 0.56 Any one of TiO3 (LLTO), Li2S-P2S5, Li2S-SiS2 or a combination of at least two thereof, wherein 0<a≤1, 0<x<2, 0<y<3; e. In step S5, the organic solvent is at least one of methanol, ethanol, ethylene glycol or 1,4-butanediol; f. In step S5, the dispersant is at least one of polyvinyl pyrrolidone (PVP), polyacrylamide (PAM), and polyethylene glycol (PEG).

8. A composite material, characterized in that The composite material is prepared by the preparation method of any one of claims 3 to 7.

9. A negative electrode plate, characterized in that: Comprising the composite material as described in claim 1 or 2 or 8.

10. A lithium ion battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 9.

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