Silicon-carbon 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 silicon-carbon composite material and a preparation method thereof, a negative electrode plate and a lithium ion battery. The silicon-carbon composite material is of a core-shell structure and comprises an inner core, an outer shell and a middle layer located between the inner core and the outer shell. The inner core is hard carbon, the middle layer is composed of a porous metal frame and nanometer silicon deposited on the porous metal frame, and the shell comprises amorphous carbon. According to the silicon-carbon composite material provided by the invention, the specific capacity of the material can be improved and the expansion can be reduced through the arrangement of the hard carbon as the core and the synergistic effect between the hard carbon and silicon, and the expansion can be further inhibited and the electronic conductivity can be further improved through the arrangement of the porous metal frame which has high pore volume and high electronic conductivity; by arranging the shell comprising amorphous carbon, the side reaction of the middle layer can be reduced, the specific surface area can be reduced, and the first efficiency can be improved.

Description

Technical Field

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

[0002] Silicon-carbon materials have attracted much attention in the field of negative electrode materials due to their advantages such as high specific capacity (1800-2000mAh / g), low expansion, and good cycle performance. However, as the market gradually increases the amount of silicon-carbon added to negative electrodes to enhance energy density, silicon-carbon materials face higher performance requirements, requiring further reduction of expansion and improvement of initial efficiency. Summary of the Invention

[0003] The purpose of the present invention is to provide a silicon-carbon composite material and a preparation method thereof, a negative electrode plate, and a lithium-ion battery, aiming to solve the technical problem of how to further reduce expansion and improve initial efficiency.

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

[0005] A first aspect of the present invention provides a silicon-carbon composite material, wherein the silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0006] The core is hard carbon, the middle layer is composed of a porous metal framework and nano-silicon deposited on the porous metal framework, and the shell comprises amorphous carbon.

[0007] It should be noted that the synergistic effect of a hard carbon core and silicon can increase the material's specific capacity while reducing expansion. The porous metal framework, with its high pore volume and high electronic conductivity, further suppresses expansion and improves electronic conductivity. The amorphous carbon shell reduces side reactions in the intermediate layer and reduces the specific surface area, thereby improving initial efficiency.

[0008] In one implementation of the present invention, based on the mass ratio of the silicon-carbon composite material being 100%, the mass ratio of the core, the intermediate layer and the shell is (85-90): (5-10): (1-5).

[0009] It should be noted that setting the mass ratio of the core, the middle layer and the outer shell to (85-90): (5-10): (1-5) can improve the specific capacity of the material while maintaining a relatively good level of the material's initial efficiency, fast charging performance and gas production; when the mass ratio of the core is too high, it will cause excessive expansion and high impedance; when the mass ratio of the core is too low, it will lead to low specific capacity; when the mass ratio of the middle layer is too high, it will reduce the specific capacity and reduce the initial efficiency; when the mass ratio of the middle layer is too low, it will have little effect on improving material expansion; when the mass ratio of the outer shell is too high, it will reduce the specific capacity; when the mass ratio of the outer shell is too low, it will cause excessive expansion and high gas production.

[0010] In one implementation of the present invention, the particle size of the core-shell structure is 2 to 8 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm.

[0011] In one implementation of the present invention, the intermediate layer is composed of 50-60 wt% of the porous metal framework and 40-50 wt% of the nano-silicon.

[0012] It should be noted that the middle layer is composed of 50-60wt% of a porous metal frame and 40-50wt% of nano-silicon. The high specific capacity of nano-silicon, the porous structure of the porous metal frame to reduce the expansion of nano-silicon and the high electronic conductivity of the porous metal frame itself are relied upon to improve the rate performance. When the amount of the porous metal frame is too high, the initial efficiency and the specific capacity of the silicon-carbon composite material will be reduced. When the amount of the porous metal frame is too low, the improvement of the material's expansion and the reduction of impedance are limited. When the amount of nano-silicon is too high, it will cause greater expansion. When the amount of nano-silicon is too low, the specific capacity will be reduced and the deposition amount of nano-silicon will be low, resulting in a large interface impedance.

[0013] A second aspect of the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0014] S1. Obtain a metal frame, mix the metal frame with a first organic solvent to obtain a first mixed solution, then add hard carbon to the first mixed solution and disperse it evenly to obtain a second mixed solution, dry the second mixed solution, and then introduce carbon dioxide gas into the second mixed solution to obtain a porous metal frame-coated hard carbon material;

[0015] S2. Transferring the porous metal framework-coated hard carbon material to a fluidized bed, introducing an inert gas to exhaust air from the pipe, and then introducing a chlorosilane mixed gas for treatment to obtain a first intermediate material, and then depositing heteroatoms on the surface of the first intermediate material by a plasma method to obtain a silicon-carbon composite material precursor material;

[0016] S3. Evenly mix the silicon-carbon composite material precursor material, liquid asphalt and conductive agent, transfer them to a vertical tube furnace, fuse them, and carbonize them to obtain a second intermediate material; evenly mix the functional additive with a second organic solvent to obtain a functional additive solution, mix the second intermediate material and the functional additive solution, and dry them to obtain a silicon-carbon composite material.

[0017] It should be noted that using hard carbon as the core reduces expansion; depositing nanosilicon within a metal framework, which has high pore volume and electronic conductivity, further reduces expansion and improves electronic conductivity. By coating the material surface with functional additives, liquid asphalt, and a conductive agent, and carbonizing it to form a conductive agent and lithium salt complex, the electronic and ionic conductivity of the outer shell is enhanced, improving both initial efficiency and rate performance.

[0018] In one implementation of the present invention, step S1 satisfies one or more of the following conditions a to e:

[0019] a. The mass ratio of the metal frame to the hard carbon in the second mixed liquid is (5-10): 100;

[0020] It should be noted that the mass ratio of the metal frame to the hard carbon is set to (5-10):100. Relying on the advantages of the high strength of the hard carbon itself and its high compatibility with the electrolyte, as well as the high electronic conductivity of the metal frame, the rate performance can be improved; when the amount of the metal frame is too high, the initial efficiency will be reduced, and when the amount of the metal frame is too low, the impedance reduction will be limited; when the amount of the hard carbon is too high, the impedance will be too high, and when the amount of the hard carbon is too low, the initial efficiency will be too low and the expansion will be too large.

[0021] b. The concentration of the first mixed solution is 1 to 10 wt%;

[0022] It should be noted that setting the concentration of the first mixed liquid to 1-10 wt % can ensure uniform dispersion and compatibility between the materials; when the concentration is too high, the dispersion uniformity is poor, and when the concentration is too low, the preparation efficiency will be reduced.

[0023] c. The first organic solvent is N,N-dimethylformamide;

[0024] d. The temperature of the carbon dioxide gas introduced for treatment is 1200 to 1500°C for 30 to 300 min, and the flow rate of the carbon dioxide gas introduced is 100 to 500 ml / min;

[0025] e. The metal frame is obtained by dissolving 1 to 5 g of zinc nitrate crystals in 40 to 60 ml of deionized water, adding 0.5 to 2 g of terephthalic acid, and then dropwise adding 0.3 to 0.8 g of hydrofluoric acid solution to obtain a third mixed solution, transferring the third mixed solution to a high-pressure reactor for reaction, filtering, and drying the obtained filter residue to obtain the metal frame; preferably, the reaction temperature in the high-pressure reactor is 180 to 220° C., the pressure is 2 to 6 MPa, and the time is 1 to 6 h; preferably, the obtained filter residue is freeze-dried to obtain the metal frame, and the freeze-drying temperature is -35 to -45° C.

[0026] In one implementation of the present invention, step S2 satisfies one or more of the following conditions a to c:

[0027] a. The chlorosilane gas mixture is introduced at a temperature of 500 to 650°C for 30 to 300 min, and the flow rate of the chlorosilane gas mixture is 10 to 50 ml / min;

[0028] b. The chlorosilane mixed gas is a mixed gas of chlorosilane gas and nitrogen, wherein the chlorosilane gas is at least one of chlorodihydrogen silicon, trichlorosilane, and silicon tetrachloride; preferably, the volume ratio of the chlorosilane gas to the nitrogen is (1 to 5): 10;

[0029] c. The parameters of the plasma method are: microwave power of 900~1100W, pressure of 0.1~0.5Pa, treatment time of 60~240 seconds, the gas introduced is a mixed gas of CH3F and O2, and the flow rate of the mixed gas is 1~5ml / min; preferably, the volume ratio of the CH3F and the O2 in the mixed gas is (1~2):1.

[0030] In one implementation of the present invention, step S3 satisfies one or more of the following conditions a to h:

[0031] a. The mass ratio of the silicon-carbon composite material precursor material, the functional additive, the liquid asphalt and the conductive agent is 100: (1 to 5): (5 to 10): (0.5 to 2);

[0032] b. The fusion temperature is 200 to 300°C for 1 to 3h;

[0033] c. The carbonization temperature is 1100-1300°C for 1-6 hours;

[0034] d. The concentration of the functional additive solution is 1 to 5wt%;

[0035] e. The functional additive is at least one of lithium difluorophosphate, lithium difluoroborate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide;

[0036] f. The second organic solvent is at least one of dimethyl carbonate, diethyl carbonate and chloroform;

[0037] g. The conductive agent is at least one of graphene, carbon nanotubes, carbon fibers, carbon black, and hollow carbon spheres;

[0038] h. mixing the second intermediate material and the functional additive solution, spray drying, and obtaining the silicon-carbon composite material; preferably, the spray drying conditions are: inlet temperature of 140-160°C, outlet temperature of 70-90°C, flow rate of 0.08-0.13 kg / h, and time of 1.5-2.5 h.

[0039] A third aspect of the present invention provides a silicon-carbon composite material, which is prepared using the preparation method of the silicon-carbon composite material according to the second aspect.

[0040] It should be noted that the silicon-carbon composite material prepared by adopting the preparation method of the silicon-carbon composite material according to the second aspect reduces expansion and improves initial efficiency.

[0041] In one implementation of the present invention, the silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0042] The core is hard carbon, the middle layer is composed of a porous metal framework and nano-silicon deposited on the porous metal framework, and the shell comprises amorphous carbon.

[0043] In one implementation of the present invention, based on the mass ratio of the silicon-carbon composite material being 100%, the mass ratio of the core, the intermediate layer, and the outer shell is (85-90): (5-10): (1-5);

[0044] And / or, the particle size of the core-shell structure is 2 to 8 μm.

[0045] In one implementation of the present invention, the intermediate layer is composed of 50-60 wt% of the porous metal framework and 40-50 wt% of the nano-silicon.

[0046] A fourth aspect of the present invention provides a negative electrode plate comprising the silicon-carbon composite material of the first and third aspects.

[0047] It should be noted that by adopting the above-mentioned silicon-carbon composite material, the expansion of the negative electrode plate is reduced, it has better ionic and electronic conductivity, and the initial efficiency and rate performance are improved.

[0048] A fifth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet of the fourth aspect.

[0049] It should be noted that by adopting the above-mentioned negative electrode plate, the lithium-ion battery has the characteristics of low expansion, good initial efficiency and good rate performance.

[0050] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0051] 1) Using hard carbon as the core and coating it with silicon-carbon material can inhibit expansion. Simultaneously, nano-silicon is deposited within the metal framework. Leveraging the metal framework's high pore volume and high electronic conductivity, this further reduces material expansion and improves electronic conductivity.

[0052] 2) Functional additives, liquid asphalt and conductive agent are coated on the surface of silicon-carbon material, and after carbonization treatment, a conductive agent and its lithium salt complex are formed, which can enhance the electronic and ionic conductivity of the shell, and improve the initial efficiency and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] 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.

[0054] in:

[0055] Figure 1 This is an SEM image of the silicon-carbon composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0056] 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.

[0057] 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.

[0058] A first aspect of the present invention provides a silicon-carbon composite material, wherein the silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell;

[0059] The core is hard carbon, the middle layer is composed of a porous metal framework and nano-silicon deposited on the porous metal framework, and the shell comprises amorphous carbon.

[0060] By using a hard carbon core, the synergistic effect between the hard carbon and silicon increases the material's specific capacity while reducing expansion. A porous metal framework, with its high pore volume and high electronic conductivity, further suppresses expansion and improves electronic conductivity. An amorphous carbon shell reduces side reactions in the intermediate layer and reduces the specific surface area, thereby improving initial efficiency.

[0061] A second aspect of the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0062] S1. Obtain a metal frame, mix the metal frame with a first organic solvent to obtain a first mixed solution, then add hard carbon to the first mixed solution and disperse it evenly to obtain a second mixed solution, dry the second mixed solution, and then introduce carbon dioxide gas into the second mixed solution to obtain a porous metal frame-coated hard carbon material;

[0063] S2. Transferring the porous metal framework-coated hard carbon material to a fluidized bed, introducing an inert gas to exhaust air from the pipe, and then introducing a chlorosilane mixed gas for treatment to obtain a first intermediate material, and then depositing heteroatoms on the surface of the first intermediate material by a plasma method to obtain a silicon-carbon composite material precursor material;

[0064] S3. Evenly mix the silicon-carbon composite material precursor material, liquid asphalt and conductive agent, transfer them to a vertical tube furnace, fuse them, and carbonize them to obtain a second intermediate material; evenly mix the functional additive with a second organic solvent to obtain a functional additive solution, mix the second intermediate material and the functional additive solution, and dry them to obtain a silicon-carbon composite material.

[0065] By using a hard carbon core, the hard carbon reduces expansion. Nano-silicon is deposited within a metal framework, which has high pore volume and electronic conductivity, further reducing expansion and improving electronic conductivity. By coating the material surface with functional additives, liquid asphalt, and a conductive agent, and carbonizing it to form a conductive agent and lithium salt complex, the electronic and ionic conductivity of the outer shell is enhanced, improving both initial efficiency and rate performance.

[0066] A third aspect of the present invention provides a silicon-carbon composite material, which is prepared using the preparation method of the silicon-carbon composite material according to the second aspect.

[0067] The silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material according to the second aspect reduces expansion and improves initial efficiency.

[0068] A fourth aspect of the present invention provides a negative electrode plate comprising the silicon-carbon composite material of the first and third aspects.

[0069] By adopting the above-mentioned silicon-carbon composite material, the expansion of the negative electrode plate is reduced, it has better ionic and electronic conductivity, and the initial efficiency and rate performance are improved.

[0070] A fifth aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet of the fourth aspect.

[0071] By adopting the above-mentioned negative electrode plate, the lithium-ion battery has the characteristics of low expansion, good initial efficiency and good rate performance.

[0072] 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.

[0073] Example 1

[0074] The preparation method of the metal frame is as follows:

[0075] Weigh 3 g of zinc nitrate crystals and dissolve them in 50 ml of deionized water. After sufficient dissolution, add 1 g of terephthalic acid, and then add 0.5 g of hydrofluoric acid solution dropwise to obtain a third mixed solution. Then, transfer the third mixed solution to a high-pressure reactor, react for 3 hours at a temperature of 200°C and a pressure of 4 MPa, filter, and freeze-dry the resulting residue at -40°C for 48 hours to obtain an organic metal framework.

[0076] A method for preparing a silicon-carbon composite material comprises the following steps:

[0077] Step S1:

[0078] 8g of organic metal framework was dissolved in 100g of N,N-dimethylformamide organic solvent and dispersed evenly to form an 8wt% first mixed liquid. Then, 100g of hard carbon was added to the first mixed liquid and dispersed evenly to obtain a second mixed liquid. The second mixed liquid was spray-dried, and then the obtained material was heated to 1350°C and carbon dioxide gas was introduced at a flow rate of 300ml / min for 150 minutes to obtain a porous metal framework-coated hard carbon material.

[0079] Step S2:

[0080] The porous metal frame-coated hard carbon material is transferred to a fluidized bed, and then argon inert gas is introduced to exhaust the air in the tube. The temperature is then raised to 600°C, and a chlorosilane mixed gas (volume ratio, chlorosilane: nitrogen = 3:10) is introduced at a flow rate of 30 ml / min for 150 minutes to obtain a first intermediate material; the first intermediate material is then transferred to a microwave device, and heteroatoms are deposited on the surface of the first intermediate material by a plasma method to obtain a silicon-carbon composite material precursor material. The parameters of the plasma method are: microwave power of 1000 W, pressure of 0.3 Pa, processing time of 120 seconds, the gas introduced is a CH3F / O2 mixed gas (volume ratio of 1.5:1), and the flow rate of the mixed gas is 3 ml / min.

[0081] Step S3:

[0082] 100g of silicon-carbon composite material precursor material, 8g of liquid asphalt and 1g of graphene conductive agent were mixed evenly, then transferred to a vertical tube furnace, fused at a temperature of 250°C for 2h, and then heated to 1200°C for carbonization for 3h to obtain a second intermediate material; 1g of lithium difluorophosphate was added to 50g of dimethyl carbonate to prepare a functional additive solution with a mass concentration of 2wt%, and the second intermediate material was added and mixed evenly, and spray dried (inlet temperature of 150°C, outlet temperature of 80°C, flow rate of 0.1kg / h, time for 2h) to obtain a silicon-carbon composite material. Among them, the steps of preparing the second intermediate material and the steps of preparing the functional additive solution are not in particular order.

[0083] Example 2

[0084] The preparation method of the metal frame is as follows:

[0085] Weigh 1 g of zinc nitrate crystals and dissolve them in 50 ml of deionized water. After sufficient dissolution, add 0.5 g of terephthalic acid, and then add 0.5 g of hydrofluoric acid solution dropwise to obtain a third mixed solution. Then, transfer the third mixed solution to a high-pressure reactor, react for 1 hour at a temperature of 180°C and a pressure of 6 MPa, filter, and freeze-dry the resulting residue at -40°C for 24 hours to obtain an organic metal framework.

[0086] A method for preparing a silicon-carbon composite material comprises the following steps:

[0087] Step S1:

[0088] 5g of the organic metal framework was dissolved in 500g of N,N-dimethylformamide organic solvent and dispersed evenly to form a 1wt% first mixed liquid. Then, 100g of hard carbon was added to the first mixed liquid and dispersed evenly to obtain a second mixed liquid. The second mixed liquid was spray-dried, and then the obtained material was heated to 1200°C and carbon dioxide gas was introduced at a flow rate of 100ml / min for 300 minutes to obtain a porous metal framework-coated hard carbon material.

[0089] Step S2:

[0090] The porous metal frame-coated hard carbon material is transferred to a fluidized bed, and then argon inert gas is introduced to exhaust the air in the tube. The temperature is then raised to 500°C, and trichlorosilane mixed gas (volume ratio, trichlorosilane: nitrogen = 1:10) is introduced at a flow rate of 10 ml / min for 300 minutes to obtain a first intermediate material; the first intermediate material is then transferred to a microwave device, and heteroatoms are deposited on the surface of the first intermediate material by a plasma method to obtain a silicon-carbon composite material precursor material. The parameters of the plasma method are: microwave power of 1000 W, pressure of 0.1 Pa, treatment time of 60 seconds, the gas introduced is a CH3F / O2 mixed gas (volume ratio of 1:1), and the flow rate of the mixed gas is 1 ml / min.

[0091] Step S3:

[0092] 100g of silicon-carbon composite precursor material, 5g of liquid asphalt and 0.5g of carbon nanotube conductive agent were mixed evenly, then transferred to a vertical tube furnace, fused at a temperature of 200°C for 3h, and then heated to 1100°C for carbonization for 6h to obtain a second intermediate material; 5g of lithium difluoroborate was added to 500g of diethyl carbonate to prepare a solution with a mass concentration of 1wt%, and the second intermediate material was added and mixed evenly, and spray dried (inlet temperature of 150°C, outlet temperature of 80°C, flow rate of 0.1kg / h, time for 2h) to obtain a silicon-carbon composite material. Among them, the steps of preparing the second intermediate material and the steps of preparing the functional additive solution are not in particular order.

[0093] Example 3

[0094] The preparation method of the organic metal framework is as follows:

[0095] Weigh 5 g of zinc nitrate crystals and dissolve them in 50 ml of deionized water. After sufficient dissolution, add 2 g of terephthalic acid, and then add 0.5 g of hydrofluoric acid solution dropwise to obtain a third mixed solution. Then, transfer the third mixed solution to a high-pressure reactor, react for 6 hours at a temperature of 220°C and a pressure of 2 MPa, filter, and freeze-dry the resulting residue at -40°C for 24 hours to obtain an organic metal framework.

[0096] A method for preparing a silicon-carbon composite material comprises the following steps:

[0097] Step S1:

[0098] 10g of organic metal framework was dissolved in 100g of N,N-dimethylformamide organic solvent and dispersed evenly to form a 10wt% first mixed liquid. Then, 100g of hard carbon was added to the first mixed liquid and dispersed evenly to obtain a second mixed liquid. The second mixed liquid was spray-dried, and then the obtained material was heated to 1500℃ and carbon dioxide gas was introduced at a flow rate of 500ml / min for 30 minutes to obtain a porous metal framework-coated hard carbon material.

[0099] Step S2:

[0100] The porous metal frame-coated hard carbon material is transferred to a fluidized bed, and then argon inert gas is introduced to exhaust the air in the tube. The temperature is then raised to 650°C, and a silicon tetrachloride mixed gas (volume ratio, silicon tetrachloride: nitrogen = 5:10) is introduced at a flow rate of 50 ml / min for 30 minutes to obtain a first intermediate material; the first intermediate material is then transferred to a microwave device, and heteroatoms are deposited on the surface of the first intermediate material by a plasma method to obtain a silicon-carbon composite material precursor material. The parameters of the plasma method are: microwave power of 1000 W, pressure of 0.5 Pa, processing time of 240 seconds, the gas introduced is a CH3F / O2 mixed gas (volume ratio of 2:1), and the flow rate of the mixed gas is 5 ml / min.

[0101] Step S3:

[0102] 100g of silicon-carbon composite material precursor material, 10g of liquid asphalt and 2g of carbon black conductive agent were mixed evenly, then transferred to a vertical tube furnace, fused at a temperature of 300°C for 1h, and then heated to 1300°C for carbonization for 1h to obtain a second intermediate material; 5g of lithium trifluoromethanesulfonate was added to 100g of chloroform to prepare a functional additive solution with a mass concentration of 5wt%, and the second intermediate material was added and mixed evenly, and spray dried (inlet temperature of 150°C, outlet temperature of 80°C, flow rate of 0.1kg / h, time of 2h) to obtain a silicon-carbon composite material. Among them, the steps of preparing the second intermediate material and the steps of preparing the functional additive solution are not in particular order.

[0103] Comparative Example 1

[0104] The difference from Example 1 is that step S1 is omitted. In step S2, porous carbon purchased from the market is used to replace the porous metal frame to coat the hard carbon material and transfer it to the fluidized bed. The rest is the same as Example 1.

[0105] Comparative Example 2

[0106] Different from Example 1, in step S1, no organic metal framework is added to the N,N-dimethylformamide organic solvent. 100 g of hard carbon is directly added to 100 g of N,N-dimethylformamide organic solvent, and spray-dried after uniform dispersion. The rest is the same as Example 1.

[0107] Comparative Example 3

[0108] The difference from Example 1 is that in step S1 , no hard carbon is added, and the first mixed liquid with a concentration of 8 wt % is directly spray-dried. The rest is the same as Example 1.

[0109] Comparative Example 4

[0110] Different from Example 1, in step S1, 50g of metal frame material is dissolved in 100g of N,N-dimethylformamide organic solvent and evenly dispersed to form a 50wt% first mixed liquid, and then 1000g of hard carbon is added to the first mixed liquid. The rest is the same as Example 1.

[0111] Comparative Example 5

[0112] The difference from Example 1 is that in step S3, lithium difluorophosphate is not added, and the second intermediate material is directly added to 50 g of dimethyl carbonate and mixed evenly. The rest is the same as Example 1.

[0113] Comparative Example 6

[0114] The difference from Example 1 is that in step S3 , 10 g of lithium difluorophosphate is added to 50 g of dimethyl carbonate to prepare a functional additive solution with a mass concentration of 20 wt %. The rest is the same as Example 1.

[0115] The silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-6 were tested.

[0116] 1) Appearance

[0117] The silicon-carbon composite material in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the material presents a spherical structure, and the particle size of the material is evenly distributed, with the particle size ranging from 2 to 8 μm.

[0118] 2) Button battery test

[0119] The silicon-carbon composite materials in Examples 1-3 and Comparative Examples 1-6 were used as negative electrode materials for lithium-ion batteries to prepare button batteries. The preparation method was as follows:

[0120] 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:10 g:10 g:250 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 metallic lithium 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.

[0121] The electrochemical performance tests of button cells containing the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 were conducted using a Wuhan Blue Electric CT2001A battery tester. The charge and discharge voltage range was 0.005V to 2.0V, and the charge and discharge rate was 0.1C. The charged DCR (50% SOC) of the material was tested, and the diffusion coefficient of the material was tested by GITT. The resistance of the powder material was tested by a four-probe tester, and the specific surface area and tap density of the material were tested by GB / T 38823-2020 "Silicon Carbon". The test results are shown in Table 1.

[0122] Table 1

[0123]

[0124] The data in Table 1 demonstrate that the silicon-carbon composite material prepared in this invention exhibits significantly superior specific capacity, initial efficiency, powder resistance, and DCR compared to the comparative example. This is due to the fact that by doping the material with a porous metal framework, the inherent high electronic conductivity and large pore size of the framework are utilized to reduce powder resistance and minimize expansion. Furthermore, the inclusion of a lithium sulfonate derivative within the material's outer shell increases the material's diffusion coefficient and reduces the DCR. Furthermore, the outer shell reduces irreversible capacity loss and improves initial efficiency.

[0125] 3) Soft pack battery test

[0126] The silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-6 were mixed with 95% artificial graphite as negative electrode materials to prepare negative electrode sheets. 1 / 3 Co 1 / 3 Mn 1 / 3 A 5Ah soft-pack battery was fabricated using lithium hexafluorophosphate (LiPF6) as the positive electrode, a 1:1 volume ratio mixture of ethylene carbonate (EC) and ethyl methyl carbonate (DEC) as the solvent, and a 1.3 mol / L electrolyte concentration. Celgard 2400 membrane was used as the separator. The gas generation of the negative electrode, the high-power permeability test (HPPC) of the soft-pack battery, and its high-temperature storage performance were tested.

[0127] a. Electrode gas production test

[0128] The electrode was weighed and the weight of the active material was calculated as M1. The electrode was then placed in deionized water and allowed to soak at 45°C for 48 hours. The generated gas mass M2 was then collected and the gas production of the electrode was calculated (M2 / M1*100%). The test results are shown in Table 2.

[0129] b. High temperature storage performance

[0130] High-temperature storage performance test: The battery's fully charged capacity was measured at 60°C (X1). After 30 days at 60°C, the battery's capacity was measured again at X2. Charge retention was calculated as X2 / X1*100%. The battery was then fully charged to 100% SOC and tested at X3. Recovery capacity was calculated as X3 / X1*100%. The test results are shown in Table 2.

[0131] Table 2

[0132] lithium-ion batteries Charge retention Capacity recovery Gas production (ml / g) Example 1 94.5％ 97.1％ 0.07 Example 2 94.1％ 96.8％ 0.09 Example 3 94.9％ 97.5％ 0.05 Comparative Example 1 91.3％ 92.1％ 0.17 Comparative Example 2 92.9％ 95.2％ 0.15 Comparative Example 3 92.1％ 94.6％ 0.17 Comparative Example 4 91.1％ 91.7％ 0.21 Comparative Example 5 92.4％ 94.1％ 0.28 Comparative Example 6 93.3％ 95.7％ 0.32

[0133] As can be seen in Table 2, the gas production and high-temperature storage performance of the silicon-carbon composites obtained in Examples 1-3 are significantly superior to those of the comparative examples. This may be due to the fact that the lithium sulfonate coating of the silicon-carbon composites in the examples reduces defects, reduces gas production and surface side reactions, and improves storage performance. Furthermore, the organic metal framework coating of the hard carbon material exhibits fewer defects than porous carbon, reduces side reactions, and improves storage performance.

[0134] C.HPPC test

[0135] HPPC test: The DCR test at 3C charging rate with different SOC (10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%) was tested. The test results are shown in Table 3.

[0136] Table 3

[0137]

[0138] As can be seen from Table 3, the soft-pack lithium-ion battery prepared using the silicon-carbon composite material of the present invention is superior to the comparative example in terms of HPPC (DCR). The reason is that the silicon-carbon composite material of the present invention has an excellent diffusion coefficient and low powder resistance, which reduces DCR and improves rate performance.

[0139] 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 silicon-carbon composite material, characterized in that: The silicon-carbon composite material has a core-shell structure, comprising a core, an outer shell, and an intermediate layer located between the core and the outer shell; The core is hard carbon, the middle layer is composed of a porous metal framework and nano-silicon deposited on the porous metal framework, and the shell comprises amorphous carbon.

2. The silicon-carbon composite material according to claim 1, wherein Taking the mass ratio of the silicon-carbon composite material as 100% as a benchmark, the mass ratio of the core, the intermediate layer and the shell is (85-90): (5-10): (1-5); And / or, the particle size of the core-shell structure is 2 to 8 μm.

3. The silicon-carbon composite material according to claim 1, wherein The middle layer consists of 50-60 wt% of the porous metal framework and 40-50 wt% of the nano-silicon.

4. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: S1. Obtain a metal frame, mix the metal frame with a first organic solvent to obtain a first mixed solution, then add hard carbon to the first mixed solution and disperse it evenly to obtain a second mixed solution, dry the second mixed solution, and then introduce carbon dioxide gas into the second mixed solution to obtain a porous metal frame-coated hard carbon material; S2. Transferring the porous metal framework-coated hard carbon material to a fluidized bed, introducing an inert gas to exhaust air from the pipe, and then introducing a chlorosilane mixed gas for treatment to obtain a first intermediate material, and then depositing heteroatoms on the surface of the first intermediate material by a plasma method to obtain a silicon-carbon composite material precursor material; S3. Evenly mix the silicon-carbon composite material precursor material, liquid asphalt and conductive agent, transfer them to a vertical tube furnace, fuse them, and carbonize them to obtain a second intermediate material; evenly mix the functional additive with a second organic solvent to obtain a functional additive solution, mix the second intermediate material and the functional additive solution, and dry them to obtain a silicon-carbon composite material.

5. The method for preparing the silicon-carbon composite material according to claim 4, wherein: Step S1 satisfies one or more of the following conditions a to e: a. The mass ratio of the metal frame to the hard carbon in the second mixed liquid is (5-10): 100; b. The concentration of the first mixed solution is 1 to 10 wt%; c. The first organic solvent is N,N-dimethylformamide; d. The temperature of the carbon dioxide gas introduced for treatment is 1200 to 1500°C for 30 to 300 min, and the flow rate of the carbon dioxide gas introduced is 100 to 500 ml / min; e. The metal frame is obtained by dissolving 1 to 5 g of zinc nitrate crystals in 40 to 60 ml of deionized water, adding 0.5 to 2 g of terephthalic acid, and then dropwise adding 0.3 to 0.8 g of hydrofluoric acid solution to obtain a third mixed solution, transferring the third mixed solution to a high-pressure reactor for reaction, filtering, and drying the obtained filter residue to obtain the metal frame; preferably, the reaction temperature in the high-pressure reactor is 180 to 220° C., the pressure is 2 to 6 MPa, and the time is 1 to 6 h; preferably, the obtained filter residue is freeze-dried to obtain the metal frame, and the freeze-drying temperature is -35 to -45° C.

6. The method for preparing the silicon-carbon composite material according to claim 4, wherein: Step S2 satisfies one or more of the following conditions a to c: a. The chlorosilane gas mixture is introduced at a temperature of 500 to 650°C for 30 to 300 min, and the flow rate of the chlorosilane gas mixture is 10 to 50 ml / min; b. The chlorosilane mixed gas is a mixed gas of chlorosilane gas and nitrogen, wherein the chlorosilane gas is at least one of chlorodihydrogen silicon, trichlorosilane, and silicon tetrachloride; preferably, the volume ratio of the chlorosilane gas to the nitrogen is (1 to 5): 10; c. The parameters of the plasma method are: microwave power of 900~1100W, pressure of 0.1~0.5Pa, treatment time of 60~240 seconds, the gas introduced is a mixed gas of CH3F and O2, and the flow rate of the mixed gas is 1~5ml / min; preferably, the volume ratio of the CH3F and the O2 in the mixed gas is (1~2):

1.

7. The method for preparing the silicon-carbon composite material according to claim 4, wherein: Step S3 satisfies one or more of the following conditions a to h: a. The mass ratio of the silicon-carbon composite material precursor material, the functional additive, the liquid asphalt and the conductive agent is 100: (1 to 5): (5 to 10): (0.5 to 2); b. The fusion temperature is 200 to 300°C for 1 to 3 hours; c. The carbonization temperature is 1100-1300°C for 1-6 hours; d. The concentration of the functional additive solution is 1 to 5wt%; e. The functional additive is at least one of lithium difluorophosphate, lithium difluoroborate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide; f. The second organic solvent is at least one of dimethyl carbonate, diethyl carbonate and chloroform; g. The conductive agent is at least one of graphene, carbon nanotubes, carbon fibers, carbon black, and hollow carbon spheres; h. mixing the second intermediate material and the functional additive solution, spray drying, and obtaining the silicon-carbon composite material; preferably, the spray drying conditions are: inlet temperature of 140-160°C, outlet temperature of 70-90°C, flow rate of 0.08-0.13 kg / h, and time of 1.5-2.5 h.

8. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material is prepared by the preparation method according to any one of claims 4 to 7.

9. A negative electrode plate, characterized in that: The method comprises the silicon-carbon composite material according to any one of claims 1 to 3 or 8.

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

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