Carbon material, silicon-carbon composite material and application thereof

Abstract

The present application relates to a kind of carbon materials and silicon-carbon composite material, especially suitable for lithium ion battery negative material field.The carbon material particle has dense outer surface and internal hole, its internal hole shows that dense part and hole part can be observed in the internal section of the carbon material particle, the dense part is continuous, and the hole part is separated and surrounded;The hole part is not connected, is isolated, dispersed hole, hole size is 10 nm-4 μm, hole area accounts for 0.0001-20% of cross-sectional area.The present application also provides a kind of silicon-carbon composite material, comprising above-mentioned carbon material and the size of 2-5 nm silicon nanoparticles, its internal hole size is 10 nm-4 μm.The silicon-carbon composite material of the present application can be used as negative active material for lithium ion battery negative, and has excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon material preparation and the field of lithium electronic batteries, and in particular to a carbon material, a silicon-carbon composite material and applications thereof. BACKGROUND

[0002] Silicon has a huge volume expansion (about 300%) during the charging and discharging process, which leads to pulverization of the electrode material, capacity attenuation and shortening of the cycle life. The volume expansion of silicon-based materials particularly limits their application in the consumer electronics field, such as mobile phones, etc. Silicon-carbon composite materials have both the high capacity of silicon and the high conductivity of carbon, and have been favored by the industry in the field of lithium-ion batteries in recent years, with CVD silicon-carbon negative electrodes being the best among them. The CVD silicon-carbon negative electrode uses porous carbon as a skeleton, and silicon is deposited in the pore channels of the porous carbon. The pore size of the porous carbon determines the upper limit of the size of the silicon particles, and the size of the silicon particles can be controlled by adjusting the pore size distribution and porosity of the carbon material. Nanosized silicon particles help to reduce the lithium intercalation expansion of silicon; however, since most carbon skeleton materials have microporous or mesoporous pore channels, and are usually connected channels, the silicon nanoparticles in the composite material can also be continuous, and the volume expansion of the silicon nanoparticles can have a chain effect, leading to intensified expansion of the composite material and ultimately to particle pulverization failure; therefore, how to limit the lithium intercalation volume expansion of the silicon particles within a limited range and avoid overall failure is a problem that needs to be solved, and there is no related prior art.

[0003] In view of the above, the present application is proposed. SUMMARY

[0004] One of the purposes of the present application is to provide a carbon material that solves the problem of difficulty in controlling the volume change of the contents in the connected channels in the prior art.

[0005] The second purpose of the present application is to provide a silicon-carbon composite material, which has non-continuous holes inside that can limit the lithium intercalation volume expansion of the silicon particles within a limited range, effectively alleviate the volume expansion of the silicon-carbon negative electrode during the cycle process, and solve the problem of high expansion rate of the existing silicon-carbon composite material.

[0006] The third purpose of the present application is to provide a negative electrode to improve the structural stability of the silicon-carbon negative electrode material, improve the first coulombic efficiency, and improve the cycle life and rate performance.

[0007] The fourth purpose of the present application is to provide a battery to optimize the overall performance of the battery by using the negative electrode, improve the energy density, cycle stability and service life.

[0008] In order to achieve the above purposes of the present application, the following technical solutions are adopted:

[0009] In a first aspect, the present application provides a carbon material, which comprises carbon material particles, the carbon material particles having a dense outer surface and internal pores, the internal pores being manifested as that a dense portion and a pore portion are observed in an internal cross section of the carbon material particles, the dense portion being continuous and separating and surrounding the pore portion; the pore portion being not connected, being isolated and dispersed pores.

[0010] Further, the internal pores of the carbon material particles have a size of 10 nm to 4 μm; and / or, in the internal cross section of the carbon material particles, the area ratio of the pores to the cross section area is 0.0001 to 20%.

[0011] Further, the carbon material is prepared from a carbon precursor through carbonization and / or activation, the carbon precursor comprising resin, polysaccharide, biomass material, pitch and the like; preferably, the resin comprises one or more of phenolic resin, epoxy resin, polyester resin, polyurethane, polyethylene and polypropylene.

[0012] Further, the carbon precursor is prepared by a suspension polymerization method and / or a spray method; preferably, the slurry of the suspension polymerization method and / or the spray method comprises one or more of resin, polysaccharide, biomass material, pitch and the like; further preferably, the slurry comprises a crosslinking agent and / or a pore-forming agent.

[0013] Further, the carbon material has a specific surface area of 200 to 2000 m 2 / g;

[0014] And / or, the carbon material has a pore volume of 0.2 to 1.5 cm 3 / g;

[0015] And / or, the carbon material has an average pore size of 1.6 to 4.0 nm;

[0016] And / or, the carbon material has a mesopore ratio of 5 to 50%.

[0017] In a second aspect, the present application provides a silicon-carbon composite material, which comprises silicon-carbon composite material particles, the silicon-carbon composite material particles comprising carbon material and silicon nanoparticles, the silicon-carbon composite material particles having a dense outer surface and internal pores, the internal pores being manifested as that a dense portion and a pore portion are observed in an internal cross section of the silicon-carbon composite material particles, the dense portion being continuous and separating and surrounding the pore portion; the pore portion being not connected, being isolated and dispersed pores.

[0018] Further, the size of the internal pores of the silicon-carbon composite particles is 10 nm to 4 μm; and / or, the area ratio of the pores to the cross-sectional area of the silicon-carbon composite particles is 0.0001 to 20%; and / or, the size of the silicon nanoparticles is 2 to 5 nm.

[0019] Further, the silicon-carbon composite comprises silicon-carbon composite particles, the carbon material is the carbon material provided in the first aspect of the present application, and comprises the resin-sphere carbon material and the silicon nanoparticles provided in the first aspect of the present application.

[0020] Further, the silicon-carbon composite is obtained by chemical vapor deposition of a silicon-containing precursor on the porous carbon material at 150 to 1000 ℃; preferably, the silicon-containing precursor is selected from one or more of monosilane, disilane, trisilane, halosilane, polysilane, silole and derivatives thereof, silafluorene and derivatives thereof.

[0021] Further, the silicon-carbon composite comprises a coating layer on the surface of the silicon-carbon composite; preferably, the material of the coating layer is selected from at least one of solid-state electrolyte, conductive polymer, carbonaceous material, metal, alloy, metal oxide, metal hydroxide, halogen-containing compound, nitrogen-containing compound, phosphorus-containing compound, boron-containing compound, sulfur-containing compound; further preferably, the material of the coating layer is carbonaceous material.

[0022] In a third aspect, the present application provides a negative electrode, characterized in that the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises the silicon-carbon composite provided in the second aspect of the present application.

[0023] In a fourth aspect, the present application provides a battery, characterized in that the battery comprises a positive electrode, a negative electrode, a separator, an electrolyte, etc., the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises the silicon-carbon composite provided in the second aspect of the present application.

[0024] Compared with the prior art, the present application has at least the following beneficial effects:

[0025] The present application provides a carbon material, the internal part of the carbon material particles has a certain number of pores, and the internal pores in the internal part of the carbon material particles provide a buffer space for the volume expansion of silicon, effectively reducing the pulverization and capacity attenuation of the electrode material; and by adjusting the number and size of the pores, the cycle stability of the silicon-carbon negative electrode is significantly improved.

[0026] The present application provides a silicon-carbon composite material, wherein the silicon nanoparticles are controlled at 2-5 nm, and the carbon material has a certain number of holes inside. The silicon nanoparticles in the CVD silicon-carbon composite material can achieve uniform loading and avoid agglomeration. By controlling the size of the silicon nanoparticles at 2-5 nm, the expansion of the silicon particles in the silicon-carbon composite material during the lithium intercalation process is greatly reduced, and the cycle stability is improved. On the other hand, by optimizing the hole size and distribution, the volume expansion of silicon is effectively buffered, and better long cycle stability can be obtained in lithium ion battery applications. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings based on these drawings without creative labor.

[0028] Figure 1 The scanning electron microscope image of the carbon material provided for Example 1 of the present application.

[0029] Figure 2 The scanning electron microscope image of the carbon material provided for Example 5 of the present application.

[0030] Figure 3 The scanning electron microscope image of the carbon material provided for Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be described in detail below in combination with the embodiments and examples, but those skilled in the art will understand that the following embodiments and examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application. It should be noted that the examples in the present application and the features in the examples can be combined with each other without conflict.

[0032] In a first typical embodiment of the present application, a carbon material is provided, which comprises carbon material particles having a dense outer surface and internal holes, wherein the internal holes are observed as dense parts and hole parts in the internal cross section of the carbon material particles, the dense parts are continuous and separate and surround the hole parts; the hole parts are not connected and are isolated and dispersed holes.

[0033] For porous materials, the pores commonly referred to are those that can be contacted by gas molecules such as N2, which can be obtained by N2 static adsorption test on the porous materials; the DFT method can be used to fit the N2 adsorption-desorption isotherm to analyze the pore size and pore distribution of the porous materials; and in the first typical embodiment of the present application, the internal pores of the carbon material particles are essentially different from them, which are enclosed inside the dense outer surface of the carbon material particles and can only be seen after the particles are broken or cut. For dense materials, ordinary breaking methods may not effectively break the particles, and only through the Ar ion polishing / cutting method, the atoms above the pores are peeled off layer by layer to expose the internal cross section of the carbon material particles, and the existence of the internal pores can be observed by electron microscopy.

[0034] The carbon material provided by the present application can be spherical or non-spherical, which does not affect the formation and existence of the internal pores. For example, spherical particles can be obtained by suspension polymerization or spraying method, and non-spherical particles can be obtained by solidification and carbonization of non-spherical carbon precursors, which can introduce a breaking process. These methods only change the appearance and do not affect the internal pores. The formation of internal pores is related to the nature of carbon precursors, cross-linked network, and whether to add a pore-forming agent and the volatilization of organic matter. The formation of internal pores can be realized by adding a suitable pore-forming agent and having a relatively loose cross-linked network.

[0035] The cavities or pores in the carbon material particles can provide a buffer space for the volume change of the filler and limit the volume change within a limited space, preventing damage to the overall material particles. In some embodiments, the size of the pores can be, but is not limited to, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 500 nm, 1 μm or 4 μm, or any value between 10 nm and 4 μm. 10~50 nm, 50~100 nm, 50~4 μm; if the pore size is too large, the structural stability of the material decreases.

[0036] In some embodiments, the area of the pores on the cross section of the carbon material particles accounts for 0.0001~20% of the cross-sectional area, and the cross-sectional area ratio can be, but is not limited to, 0.0001%, 0.001%, 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20% or any value between them.

[0037] In some embodiments, the carbon material is prepared from carbonization and / or activation of a carbon precursor, which comprises resin, polysaccharide, biomass material, pitch, etc.; preferably, the resin comprises one or more of phenolic resin, epoxy resin, polyester resin, polyurethane, polyethylene, polypropylene.

[0038] In some embodiments, the carbon precursor is prepared by a suspension polymerization method and / or a spray method; preferably, the slurry of the suspension polymerization method and / or the spray method comprises one or more of resin, polysaccharide, biomass material, pitch, etc., as obtained by precisely controlling the stirring rate, solid content of the slurry, heating rate, etc.; further preferably, the slurry comprises a crosslinking agent and / or a pore-forming agent to ensure that the carbon precursor after solid-liquid separation has a fixed morphology and controllable internal pores.

[0039] In some embodiments, the specific surface area of the carbon material is 200-2000 m 2 / g. The specific surface area of the carbon material can be, but is not limited to, 200 m 2 / g, 500 m 2 / g, 700 m 2 / g, 800 m 2 / g, 1000 m 2 / g, 1200 m 2 / g, 1500 m 2 / g, 1700 m 2 / g, or 2000 m 2 / g, and can also be any value between 200-2000 m 2 / g. In some embodiments, the pore volume of the carbon material is 0.2-1.5 cm 3 / g. The pore volume of the carbon material can be, but is not limited to, 0.2 cm 3 / g, 0.4 cm 3 / g, 0.6 cm 3 / g, 0.8 cm 3 / g, 1.0 cm 3 / g, 1.2 cm 3 / g, 1.4 cm 3 / g, or 1.5 cm 3 / g, and can also be any value between 0.2-1.5 cm 3 / g. In some embodiments, the average pore size of the carbon material is 1.6-4 nm; in some embodiments, the mesopore ratio of the carbon material is 5-50%.

[0040] In a second exemplary embodiment of the present application, a silicon-carbon composite material is also provided, which comprises silicon-carbon composite material particles, the silicon-carbon composite material particles comprising a carbon material and silicon nanoparticles, the silicon-carbon composite material particles having a compact outer surface and internal pores, the internal pores being observed as compact portions and pore portions in the internal cross section of the silicon-carbon composite material particles, the compact portions being continuous and separating and surrounding the pore portions; the pore portions being not connected and being isolated and dispersed pores.

[0041] As mentioned in the first exemplary embodiment of the present application, the internal pores of the silicon-carbon composite material particles in the present application are also enclosed by the compact surface thereof and can only be detected by Ar polishing and the like.

[0042] The silicon-carbon composite material provided by the present application can provide a buffer space for the volume expansion of silicon in the internal pores of the silicon-carbon composite material particles, limit the volume change in a limited space, and prevent the damage to the whole material particles, thereby effectively reducing the volume expansion of the composite material during the lithium intercalation process.

[0043] In some embodiments, the internal pores of the silicon-carbon composite material particles have a size of 10 nm to 4 μm.

[0044] In some embodiments, the area ratio of the pores to the cross-sectional area of the silicon-carbon composite material particles is 0.0001 to 20%.

[0045] In some embodiments, the size of the silicon nanoparticles is 2 to 5 nm.

[0046] In some embodiments, the carbon material is the carbon material described in the first exemplary embodiment, comprising the resin sphere carbon material and the silicon nanoparticles described in the first exemplary embodiment.

[0047] In some embodiments, the silicon-carbon composite material is obtained by chemical vapor deposition of a silicon-containing precursor on the porous carbon material at 150 to 1000 °C; preferably, the silicon-containing precursor is selected from one or more of monosilane, disilane, trisilane, halosilane, polysilane, silole and derivatives thereof, silafluorene and derivatives thereof.

[0048] In some embodiments, the silicon-carbon composite material comprises a coating layer on the surface of the silicon-carbon composite material; preferably, the material of the coating layer is selected from at least one of solid-state electrolytes, conductive polymers, carbonaceous materials, metals, alloys, metal oxides, metal hydroxides, halogen-containing compounds, nitrogen-containing compounds, phosphorus-containing compounds, boron-containing compounds, sulfur-containing compounds; further preferably, the material of the coating layer is a carbonaceous material.

[0049] In a third typical embodiment of the present application, a negative electrode is also provided, which comprises a negative electrode active material, the negative electrode active material comprising the silicon-carbon composite material in the second typical embodiment of the present application.

[0050] In a fourth typical embodiment of the present application, a battery is also provided, which comprises a positive electrode, a negative electrode, a separator, an electrolyte, etc., the negative electrode comprising a negative electrode active material, the negative electrode active material comprising the silicon-carbon composite material in the second typical embodiment of the present application.

[0051] The technical solutions of the present application will be described clearly and completely in combination with the embodiments below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0052] Embodiment 1

[0053] A preparation method of a carbon material is specifically operated according to the following steps:

[0054] Step S1, preparation of a carbon precursor: 100 g of deionized water is added into a beaker, heated to 95 ℃, 0.4 g of polyvinyl alcohol (PVA) is added and stirred for 2 h to fully dissolve, then 0.5 g of a curing agent hexamethylenetetramine is added and stirred for 0.5 h to fully dissolve; 5 g of a thermoplastic resin in ethanol solution is continuously added, and the reaction is stirred at 97 °C for 4 h. The above mixture is subjected to solid-liquid separation, and after drying, the carbon precursor is obtained.

[0055] Step S2, carbonization: the carbon precursor obtained in the above step S1 is heated to 700 ℃ at a rate of 2 ℃ / min under N2 atmosphere, and kept for 2 h.

[0056] Step S3, activation: the carbonized material is subjected to water activation, heated to 900 ℃ at a rate of 2 ℃ / min under a mixed atmosphere of N2 and H2O(g), and kept for 2 h; the carbon material is obtained.

[0057] The internal cross section of the obtained carbon material particles comprises pores, the size of the pores is in the range of 10 nm to 100 nm, including 10 nm and 100 nm; the area ratio of the pores to the cross section area is 0.0004%. The scanning electron microscope image of the carbon material in this embodiment 1 is shown in FIG. 1. Figure 1

[0058] Embodiment 2

[0059] ​The present example provides a carbon material, the difference between the preparation method and example 1 is that the reaction temperature is changed from 97 °C to 93 °C.

[0060] Example 3

[0061] Step S1, preparation of carbon precursor: add 100 g of deionized water in a beaker, heat to 95 ℃, add 0.4 g of polyvinyl alcohol (PVA) and 0.1 mL of pore former toluene and stir for 2 h to fully dissolve, then add 0.5 g of curing agent hexamethylenetetramine and stir for 0.5 h to fully dissolve; continue to add 5 g of hot plastic resin ethanol solution and stir for 4 h. The above mixture is subjected to solid-liquid separation, and the carbon precursor is obtained.

[0062] Step S2, carbonization: the carbon precursor obtained in the above step S1 is heated to 700 ℃ at a rate of 2 ℃ / min under N2 atmosphere, and kept for 2 h.

[0063] Step S3, activation: the carbonized material is subjected to water activation, and is heated to 900 ℃ at a rate of 2 ℃ / min under the mixed atmosphere of N2 and H2O(g), and kept for 2 h; the carbon material is obtained.

[0064] Example 4

[0065] The present example provides a carbon material, the difference between the preparation method and example 3 is that 0.1 mL of pore former toluene is replaced by 2 g of cyclohexane, and other conditions remain unchanged.

[0066] Example 5

[0067] A method for preparing a carbon material, which is specifically operated according to the following steps:

[0068] Step S1, preparation of carbon precursor: mix 10 g of starch with 100 mL of deionized water to form a uniform suspension. Adjust the pH of the solution to 9-11 with 1 mol / L NaOH solution. Then mix the starch slurry with liquid paraffin at a volume ratio of 1:3, add 1 g of emulsifier (Span 80), high-speed stirring to form a water / oil emulsion, and heat to 80 ℃ to solidify the starch balls. Then centrifugal separation, and washed with ethanol to remove the oil phase, and dried at 50 ℃ for 6 h.

[0069] Step S2, carbonization: the carbon precursor obtained in the above step S1 is heated to 700 ℃ at a rate of 2 ℃ / min under N2 atmosphere, and kept for 2 h.

[0070] Step S3, activation: the carbonized material is subjected to water activation, and is heated to 900 ℃ at a rate of 2 ℃ / min under the mixed atmosphere of N2 and H2O(g), and kept for 2 h; the carbon material is obtained.

[0071] Comparative Example 1

[0072] Step S1, carbonization: thermoplastic resin was directly carbonized, and heated to 700 ℃ at a rate of 2 ℃ / min under N2 atmosphere, and kept for 2 h.

[0073] Step S2, activation: the carbonized material was activated by water, and heated to 900 ℃ at a rate of 2 ℃ / min under mixed atmosphere of N2 and H2O(g), and kept for 2 h; to obtain carbon material.

[0074] Example 6

[0075] The present example provides a silicon-carbon composite material, and the preparation method is as follows:

[0076] Step S1, providing carbon material, the carbon material is the carbon material obtained in Example 1;

[0077] Step S2, crushing and grading the carbon material of step S1 to obtain d V50 carbon powder with a particle size of 8 μm;

[0078] Step S3, placing the mesoporous carbon powder obtained in step S2 in a tube furnace, and heating to 550 ℃ at a rate of 2 ℃ / min under N2 atmosphere; then changing to 20% SiH4-N2 mixed gas, and keeping at 550 ℃ for 10 h under 20% SiH4-N2 mixed gas atmosphere; changing to 10% C2H2-N2 mixed gas, and keeping at 600 ℃ for 1 h; naturally cooling under N2 atmosphere to obtain a silicon-carbon composite material.

[0079] Example 7

[0080] The present example provides a silicon-carbon composite material, and the preparation method is as follows:

[0081] Step S1, providing carbon material, the carbon material is the carbon material obtained in Example 2;

[0082] Step S2 and step S3 are the same as step S2 and step S3 in Example 6.

[0083] Example 8

[0084] The present example provides a silicon-carbon composite material, and the preparation method is as follows:

[0085] Step S1, providing carbon material, the carbon material is the carbon material obtained in Example 3;

[0086] Step S2 and step S3 are the same as step S2 and step S3 in Example 6.

[0087] Example 9

[0088] The present example provides a silicon-carbon composite material, and the preparation method is as follows:

[0089] Step S1, providing a carbon material, the carbon material is the carbon material obtained in Example 4;

[0090] Step S2 and Step S3 are the same as Step S2 and Step S3 in Example 6.

[0091] Example 10

[0092] The present example provides a silicon-carbon composite material, and the preparation method is as follows:

[0093] Step S1, providing a carbon material, the carbon material is the carbon material obtained in Example 5;

[0094] Step S2 and Step S3 are the same as Step S2 and Step S3 in Example 6.

[0095] Comparative Example 2

[0096] The present example provides a silicon-carbon composite material, and the preparation method is as follows:

[0097] Step S1, providing a carbon material, the carbon material is the carbon material obtained in Comparative Example 1;

[0098] Step S2 and Step S3 are the same as Step S2 and Step S3 in Example 6.

[0099] (1) N2 adsorption test is a material characterization means well known to those skilled in the art, and the specific test conditions are not repeated here. The specific surface area A of the carbon material is calculated by multi-point BET, and the calculation results meet the conditions of intercept C value > 0 and correlation coefficient R2≥0.9999. The pore volume V is obtained according to the maximum adsorption amount at p / p0>0.99 in the N2 adsorption test, and the average pore diameter D=4V / A*1000 (nm). The average pore diameter can be used to estimate the pore distribution of the carbon material, and when the average pore diameter D<2 nm, the micropore content is usually greater than 80%. The DFT method is used to fit the N2 adsorption-desorption isotherm, analyze the pore distribution of different pore diameters in the carbon material, and obtain the content information of each pore diameter.

[0100] (2) Swelling rate test of silicon-carbon composite material: use LAND battery test system to perform charge and discharge test on the battery.

[0101] After the CR2032 type button cell is placed for 6 h, it is discharged to 0.005 V at 0.05 C, and then discharged to 0.005 V at 0.01 C; after standing for 5 min, it is charged to 15 V at 0.05 C; the ratio of the first delithiation capacity to the first lithium intercalation capacity is the first coulombic efficiency of the battery.

[0102] After standing for 5 min, repeat the above charge and discharge steps twice;

[0103] Then discharged at 0.25 C to 0.005 V; after resting for 5 min, charged at 0.25 C to 1.5 V, and cycled for 50 times. The capacity retention was calculated by the ratio of the charge capacity of the 50th cycle to the charge capacity of the 1st cycle x 100%.

[0104] The following method was used to test the expansion rate of the electrode plate: after the CR2032 button cell was rested for 6 h, it was discharged at 0.05 C to 0.005 V, and then discharged at 0.01 C to 0.005 V; then the button cell was disassembled in a glove box, the electrode plate was cleaned with DEC, and the thickness of the electrode plate was measured. The expansion rate was calculated as follows: (thickness of the first full-charge electrode plate - thickness of the fresh electrode plate) / thickness of the fresh electrode plate x 100%.

[0105] (3) Si content test in silicon-carbon composite material: 3.0 g of the silicon-carbon composite material was dried to constant weight in a 150 °C oven, and the mass m1 was recorded; the dried composite material was placed in a muffle furnace, heated to 1100 °C and kept for 2 h, cooled and weighed, and the mass m2 was recorded. The Si content calculation formula is: .

[0106] (4) The following is a brief description of the battery test.

[0107] Half-cell test method: the silicon-carbon composite materials obtained in Examples 6-10 and Comparative Example 2 were subjected to electrochemical performance tests, and the results are shown in Table 2. The silicon-carbon composite materials obtained in Examples 6-10 and Comparative Example 2 were used as negative active materials to prepare negative electrode plates, CR2032 button cells were prepared using the negative electrode plates by a conventional method, and the electrical performance of the button cells was tested. The button cells were subjected to charge-discharge tests using a LAND battery test system.

[0108] (1) Half-cell assembly: CR2032 button cells were assembled in a glove box, lithium metal sheets were used as counter electrodes, polypropylene microporous membranes were used as separators, and the electrolyte was LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), wherein the concentration of LiPF6 was 1 mol / L.

[0109] (2) Cycle gram capacity and first efficiency test: after the CR2032 button cell was rested for 6 h, it was discharged at 0.05 C to 0.005 V, and then discharged at 0.01 C to 0.005 V; after resting for 5 min, it was charged at 0.05 C to 1.5 V; the 0.8 V first delithiation gram capacity was the 0.8 V gram capacity (or mass specific capacity) of the electrode material, and the ratio of the 0.8 V first delithiation capacity to the 1.5 V first lithiation capacity was the 0.8 V first coulombic efficiency of the battery.

[0110] High-pressure dense half-cell test method: after the negative electrode sheet is prepared by the conventional method, it is further rolled to prepare a high-pressure dense negative electrode sheet. The pressure density of the conventional electrode sheet is 0.8 g / cm 3 , and the pressure density of the high-pressure dense electrode sheet is about 1.0 g / cm 3 .

[0111] Full-cell test method: the silicon-carbon composite material obtained in Examples 6-10 and Comparative Example 2 is used as the negative electrode active material, and the electrode sheet containing the negative electrode active material is used to prepare a soft package battery by the conventional method and to test the electrical performance.

[0112] (1) Preparation of the positive electrode sheet: the positive electrode active material LiCoO2, the conductive agent Super P, the binder PVDF and the solvent NMP are mixed uniformly in a mass ratio of 92:3:5:150, and then uniformly coated on the positive electrode current collector, and then dried at 80°C to obtain the positive electrode sheet.

[0113] (2) Preparation of the negative electrode sheet: the negative electrode active material, the conductive agent Super P, the binder polyacrylic acid and the solvent deionized water are mixed uniformly in a mass ratio of 95:1:4:120, and then uniformly coated on the negative electrode current collector, and then dried at 100°C to obtain the negative electrode sheet.

[0114] (3) The positive electrode sheet and the negative electrode sheet are stacked in a square shape and separated by a polypropylene separator film to form a battery core, and then packaged in an aluminum plastic bag, and then the electrolyte with a capacity corresponding to the aluminum plastic bag is injected into the aluminum plastic bag, and then vacuum sealed to obtain a soft package battery. The electrolyte is a mixture of EC and DEC with LiPF6, wherein the concentration of LiPF6 is 1 mol / L, and the volume ratio of EC to DEC is 1:1.

[0115] (4) Formation and capacity distribution: after the battery is injected and sealed, it is formed in a constant temperature box at 25°C for 12 h, and then charged at 0.02C to 3.3 V, and then rested for 30 min, and then charged at 0.025C to 3.8 V, and then rested for 10 min, and then charged at 0.33C to 4.2 V. The formed battery is vacuumed and the air bag is cut, and then distributed, and then charged at 0.33C to 4.45 V, and then rested for 10 min, and then discharged at 1C to 3 V, and then rested for 10 min, and then discharged at 0.33C to 3 V, and then the distribution is completed. The ratio of the discharge capacity to the charge capacity in the formation and capacity distribution of the soft package battery is the first efficiency of the battery.

[0116] (5) 25 ℃ cycle test: the battery was placed in a 25 ℃ constant temperature box, and charged at 1 C constant current to 4.45 V, and then charged at 4.45 V constant voltage until the current was 0.1 C; after standing for 10 min, discharged at 1 C constant current to 3.0 V, and standing for 10 min, repeating the above charging and discharging steps until the discharge capacity was lower than 80% of the first cycle discharge capacity, at which time the cycle number was obtained, i.e. the cycle life of the soft package battery; the 100 cycle capacity retention rate was recorded.

[0117] Table 1 is the physicochemical properties of the carbon materials obtained in Examples 1-5 and Comparative Example 1, and Table 2 is the physicochemical properties and electrochemical performance of the silicon-carbon composite materials obtained in Examples 6-10 and Comparative Example 2.

[0118] Table 1 Physicochemical properties of carbon materials obtained in Examples 1-5 and Comparative Example 1

[0119] Average pore size (nm) Pore volume (cm 3 / g) Mesopore ratio (%) Pore size range (nm) Pore area ratio (%) Example 1 1.75 0.88 7.7 10~100 0.0004 Example 2 1.70 0.79 6.3 50~500 0.01 Example 3 1.67 0.73 5.9 300~2000 0.245 Example 4 1.64 0.63 5.0 200~3000 2.5 Example 5 1.65 0.58 5.9 150~4000 20.0 Comparative Example 1 1.75 0.81 7.4 0 0

[0120] Table 2 Physicochemical properties and electrochemical performance of silicon-carbon composite materials obtained in Examples 6-10 and Comparative Example 2

[0121] Silicon content (wt. %) Specific surface area (m 2 / g)]]> 0.8 V capacity (mAh / g) 0.8 V initial efficiency (%) 25°C 100 cycle capacity retention rate (%) Silicon-carbon expansion rate (%) Example 6 52.6 1.1 1847 86.8 99.3 120 Example 7 50.0 3.3 1763 85.2 99.7 100 Example 8 48.0 1.7 1701 85.7 99.5 78 Example 9 44.3 0.9 1585 84.6 99.1 65 Example 10 42.3 2.7 1520 83.9 99.0 40 Comparative Example 2 50.6 2.1 1783 85.2 97.4 150

[0122] Table 1 data shows that the hole area ratio of Examples 1-5 gradually increases, indicating that different preparation methods (such as resin monomer emulsion polymerization, pore-forming agents toluene and cyclohexane, and starch emulsion method) can control the pore structure. Comparative Example 1 has no holes by directly carbonizing the resin, indicating that the precursor treatment is crucial for the internal pore structure of the material. Example 5 (starch-based) has the highest hole area ratio (20%) but the lowest pore volume (0.58 cm³ / g), as the highest internal hole ratio in the material leads to the lowest pore volume. During the preparation of the carbon precursor, the pore-forming agent (toluene, cyclohexane) and starch emulsion method can significantly increase the hole area ratio (0.245%-20%).

[0123] Table 2 data shows that the capacity retention rate of the silicon-carbon materials obtained in Examples 6-10 is greater than 99%, which is the best, benefiting from the reasonable pore structure (hole ratio 0.0004%-20%) which relieves the expansion of silicon nanoparticles during the cycle process. The capacity retention rate of the silicon-carbon material obtained in Comparative Example 2 is the lowest, only 97.4%, and the expansion rate is as high as 150%, verifying the importance of holes in buffering the expansion of silicon. Example 10 (starch-based carbon, hole ratio 20%) has an expansion rate of only 40%, indicating that large pore structure is more effective in relieving volume change. Comparative Example 1 (no holes) has the worst performance, proving that holes are the key to improving the performance of silicon-carbon composite materials and proving the necessity of hole structure for the long cycle performance of silicon-carbon composite materials.

[0124] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A carbon material, characterized by, The carbon material comprises carbon material particles, the carbon material particles have a dense outer surface and internal pores, the internal pores are observed as dense parts and pore parts in the internal cross section of the carbon material particles, the dense parts are continuous and separate and surround the pore parts; the pore parts are not connected and are isolated and dispersed pores; The internal pore size of the carbon material particles is 150 nm to 4 μm, the ratio of the pore area to the cross-sectional area on the internal cross section of the carbon material particles is 20%; or the internal pore size of the carbon material particles is 200 nm to 3 μm, the ratio of the pore area to the cross-sectional area on the internal cross section of the carbon material particles is 2.5%; or the internal pore size of the carbon material particles is 300 nm to 2 μm, the ratio of the pore area to the cross-sectional area on the internal cross section of the carbon material particles is 0.245%.

2. The carbon material of claim 1, wherein, The carbon material is prepared by carbonization and / or activation of a carbon precursor, the carbon precursor comprises resin, polysaccharide, biomass material, pitch; the resin comprises one or more of phenolic resin, epoxy resin, polyester resin, polyurethane, polyethylene, polypropylene.

3. The carbon material of claim 2, wherein, The carbon precursor is prepared by a suspension polymerization method and / or a spraying method; the slurry of the suspension polymerization method and / or the spraying method comprises one or more of resin, polysaccharide, biomass material, pitch, the slurry comprises a crosslinking agent and / or a pore-forming agent.

4. The carbon material of claim 1, wherein, The specific surface area of the carbon material is 200-2000 m 2 / g; and / or the carbon material has a pore volume of 0.2 to 1.5 cm 3 / g; And / or, the average pore size of the carbon material is 1.6 to 4.0 nm; And / or, the mesopore ratio of the carbon material is 5 to 50%.

5. A silicon-carbon composite material, characterized by, The silicon-carbon composite material comprises silicon-carbon composite material particles, the silicon-carbon composite material particles comprise carbon material and silicon nanoparticles, the silicon-carbon composite material particles have a dense outer surface and internal pores, the internal pores are observed as dense parts and pore parts in the internal cross section of the silicon-carbon composite material particles, the dense parts are continuous and separate and surround the pore parts; the pore parts are not connected and are isolated and dispersed pores; the internal pore size of the silicon-carbon composite material particles is 150 nm to 4 μm, the ratio of the pore area to the cross-sectional area on the internal cross section of the carbon material particles is 20%; or the internal pore size of the carbon material particles is 200 nm to 3 μm, the ratio of the pore area to the cross-sectional area on the internal cross section of the carbon material particles is 2.5%; or the internal pore size of the carbon material particles is 300 nm to 2 μm, the ratio of the pore area to the cross-sectional area on the internal cross section of the carbon material particles is 0.245%.

6. The silicon-carbon composite of claim 5, wherein, The size of the silicon nanoparticles is 2 to 5 nm.

7. The silicon-carbon composite of claim 5, wherein, The silicon-carbon composite material is obtained by chemical vapor deposition of a silicon-containing precursor on the carbon material at 150 to 1000°C; the silicon-containing precursor is selected from one or more of monosilane, disilane, trisilane, halosilane, polysilane, silole and derivatives thereof, silafluorene and derivatives thereof.

8. The silicon-carbon composite of claim 5, wherein, The silicon-carbon composite material comprises a coating layer on the surface of the silicon-carbon composite material; the material of the coating layer is selected from at least one of solid-state electrolyte, conductive polymer, carbonaceous material, metal, alloy, metal oxide, metal hydroxide, halogen-containing compound, nitrogen-containing compound, phosphorus-containing compound, boron-containing compound, and sulfur-containing compound.

9. A negative electrode characterized by The negative electrode comprises a negative electrode active material, and the negative electrode active material comprises the silicon-carbon composite material according to any one of claims 5 to 8.

10. A battery characterized by The battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the negative electrode comprises the silicon-carbon composite material according to any one of claims 5 to 8.

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