Carbon composite material and preparation method thereof, negative plate containing same, electrochemical device, and electronic equipment

Abstract

The application discloses a carbon composite material and a preparation method thereof, a negative plate containing the carbon composite material, an electrochemical device and an electronic equipment. The carbon composite material comprises hard carbon and porous soft carbon, and the hard carbon is at least partially distributed inside pores of the porous soft carbon. The carbon composite material satisfies the following conditions: a limited pore ratio pore volume V is 0.02 cm 3 / g~0.05 cm 3 / g; the limited pore refers to a pore with a pore size of 1.5 nm~3.2 nm; an equivalent pore average pore diameter d is 1.1~2.0 mu m; and a limit pressure compaction PD is 1.21~1.47. When the carbon composite material is applied to a sodium ion battery, the carbon composite material has excellent cycle performance and storage performance.

Description

Technical Field

[0001] This invention specifically relates to carbon composite materials and their preparation methods, negative electrode sheets containing the same, electrochemical devices, and electronic devices. Background Technology

[0002] Due to the high energy density of sodium-ion batteries (such as large cylindrical sodium-ion batteries), their application potential in the energy storage field is being explored. However, energy storage systems have extremely high requirements for long-cycle performance, which inevitably places higher demands on anode materials. Hard carbon is widely available, making it a suitable anode material due to its high specific capacity, good structural stability, and good low-temperature performance. However, it also suffers from drawbacks such as low initial charge-discharge efficiency, poor cycle stability, and limited storage performance.

[0003] CN117810447A improves porosity distribution and optimizes cycle performance through phosphorus doping. CN120504319A effectively improves morphology and storage by optimizing the precursor, but the degree of improvement is limited.

[0004] Therefore, how to improve the first-efficiency, cycle performance and storage performance of batteries when hard carbon is used as an anode material has attracted widespread attention in this field. Summary of the Invention

[0005] This invention primarily aims to overcome the shortcomings of existing technologies where hard carbon, when used as the negative electrode material, results in insufficient initial efficiency, cycle performance, and storage capacity. It provides a carbon composite material, its preparation method, a negative electrode sheet containing the composite material, an electrochemical device, and an electronic device. When applied to sodium-ion batteries, the carbon composite material provided by this invention exhibits excellent initial efficiency, cycle performance, and storage capacity.

[0006] In a first aspect, the present invention provides a carbon composite material comprising hard carbon and porous soft carbon, wherein the hard carbon is at least partially distributed within the pores of the porous soft carbon.

[0007] The carbon composite material satisfies the following conditions:

[0008] The porosity V is limited to 0.02 cm³. 3 / g~0.05cm 3 / g; The defined pore size refers to pores with a diameter of 1.5nm to 3.2nm;

[0009] The equivalent average pore size d is 1.1~2.0μm;

[0010] The maximum compression PD is 1.21~1.47.

[0011] Secondly, the present invention provides a method for preparing the carbon composite material, comprising the following steps:

[0012] S1. A mixture containing raw coal and a pore-forming agent is calcined and pulverized to obtain a soft carbon precursor; the mass ratio of the raw coal to the pore-forming agent is (2~4):1;

[0013] S2. The mixture containing the soft carbon precursor and the hard carbon source is heat-treated and then cooled to obtain the carbon composite material.

[0014] Thirdly, the present invention provides a negative electrode sheet comprising the carbon composite material as described above.

[0015] Fourthly, the present invention provides an electrochemical device comprising the carbon composite material as described above or the negative electrode as described above.

[0016] Fifthly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0017] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0018] The reagents and raw materials used in this invention are all commercially available.

[0019] The positive and progressive effects of this invention are as follows:

[0020] The carbon composite material provided by this invention has specific defined porosity ratio, pore volume, equivalent average pore size, and ultimate compressibility. When applied to sodium-ion batteries, the batteries exhibit excellent initial efficiency, cycle performance, and storage performance. Detailed Implementation

[0021] Carbon composite materials

[0022] The carbon composite material provided in the first aspect of the present invention includes hard carbon and porous soft carbon, wherein the hard carbon is at least partially distributed inside the pores of the porous soft carbon.

[0023] The carbon composite material satisfies the following conditions:

[0024] The porosity V is limited to 0.02 cm³. 3 / g~0.05cm 3 / g; The defined pore size refers to pores with a diameter of 1.5nm to 3.2nm;

[0025] The equivalent average pore size d is 1.1~2.0μm;

[0026] The maximum compression PD is 1.21~1.47.

[0027] In this invention, the carbon composite material is a composite material formed by hard carbon and soft carbon, that is, a single particle simultaneously includes a hard carbon part and a soft carbon part, the soft carbon has a porous structure and constitutes the skeleton of the material particle, and the hard carbon is at least distributed inside the pores of the porous soft carbon.

[0028] In this invention, the defined porosity ratio refers to the total internal volume of the pores (pores with a diameter between 1.5 nm and 3.2 nm) in a unit mass of carbon material.

[0029] In this invention, the equivalent average pore diameter is calculated using d=O / S, where O is the oil absorption value (in cm). 3 / g), S refers to specific surface area (unit: m²). 2 / g); (cm 3 / g) / (m 2 / g)=cm 3 / m 2 The dimension of this ratio is volume divided by area, which is length, so this ratio actually has the dimension of length (meter). Therefore, this ratio can be interpreted as an average "pore diameter".

[0030] In this invention, the defined porosity ratio can account for more than 50% of the total porosity.

[0031] In this invention, the ultimate compaction refers to the powder compaction density of the carbon composite material at 100 MPa.

[0032] In this invention, the mass percentage of hard carbon in the carbon composite material can be 0-28%, but not 0.

[0033] In this invention, the mass percentage of the porous soft carbon in the carbon composite material can be 72% to 100%, but not 100%.

[0034] In this invention, the specified porosity ratio and pore volume V are preferably 0.023 cm³. 3 / g~0.042cm 3 / g.

[0035] In some specific embodiments, the defined porosity ratio V can be 0.021 cm³. 3 / g, 0.023 cm 3 / g, 0.025 cm 3 / g, 0.034 cm 3 / g, 0.035 cm 3 / g, 0.036 cm 3 / g, 0.037 cm 3 / g, 0.042 cm 3 / g or 0.046cm 3 / g.

[0036] In this invention, the average pore diameter d of the equivalent pores is preferably 1.5~1.9μm.

[0037] In some specific embodiments, the equivalent average pore diameter d can be 1.1μm, 1.3μm, 1.4μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2μm.

[0038] In this invention, the ultimate compaction PD is preferably 1.25~1.35.

[0039] In some specific implementations, the ultimate compression PD can be 1.21, 1.25, 1.27, 1.28, 1.3, 1.31, 1.35, 1.45 or 1.47.

[0040] Preparation methods of carbon composite materials

[0041] The method for preparing the carbon composite material provided in the second aspect of the present invention includes the following steps:

[0042] S1. A mixture containing raw coal and a pore-forming agent is calcined and pulverized to obtain a soft carbon precursor; the mass ratio of the raw coal to the pore-forming agent is (2~4):1;

[0043] S2. The mixture containing the soft carbon precursor and the hard carbon source is heat-treated and then cooled to obtain the carbon composite material.

[0044] In this invention, in step S1, the raw coal can be coal conventionally used in the art, such as lignite.

[0045] In this invention, in step S1, the carbon content of the raw coal can be 75% or more.

[0046] In this invention, in step S1, the raw coal is first purified before calcination. The purification method is to co-calcine the raw coal with a strong alkali and then rinse it.

[0047] The mass ratio of the raw coal to the strong alkali can be (1~3):1, for example, 2:1.

[0048] The strong base may be one or more of potassium hydroxide, calcium hydroxide, and sodium hydroxide.

[0049] The co-firing temperature is preferably 800~1000℃.

[0050] The co-firing time is preferably 4 to 6 hours.

[0051] In this invention, in step S1, the pore-forming agent may be a sodium salt and / or a potassium salt, and the pore-forming agent includes one or more of the elements Fe, Mn, Ni and Co, such as sodium iron oxalate and / or sodium iron phosphate.

[0052] In this invention, in step S1, the mass ratio of the raw coal to the pore-forming agent can be (3~4):1, for example 3:1 or 4:1.

[0053] In this invention, the calcination temperature in step S1 can be 200~1000℃.

[0054] In this invention, the calcination time in step S1 can be 8-10 hours.

[0055] In this invention, in step S1, the heating rate of calcination can be 2~4℃.

[0056] In this invention, step S1, the calcination can be divided into a first calcination, a second calcination, and a third calcination; the temperature of the first calcination is 200~300℃; the time of the first calcination is 1h~3h, for example 2h; the temperature of the second calcination is 400~500℃; the time of the second calcination is 1h~3h, for example 2h; the heating rate of the second calcination can be 1~3℃ / min; the temperature of the third calcination is 700~900℃; the time of the third calcination is 4~6h.

[0057] In this invention, in step S1, the particle size Dv50 of the soft carbon precursor can be 4~6.5μm.

[0058] In this invention, in step S2, the coking value of the hard carbon source can be 15% to 36%, preferably 15% to 25%, for example 15% or 23%.

[0059] In this invention, in step S2, the hard carbon source may be asphalt and / or phenolic resin, wherein the softening point of the asphalt is ≤110℃.

[0060] In this invention, in step S2, the mass ratio of the hard carbon source to the soft carbon precursor can be (1~3):1, for example 1.2:1 or 1.5:1.

[0061] In this invention, in step S2, the cooling rate can be 10℃ / min or higher, preferably 10~20℃ / min.

[0062] In this invention, in step S2, the cooling method can be natural cooling and / or the introduction of nitrogen gas.

[0063] When nitrogen gas is introduced, the flow rate of the nitrogen gas can be 20~45L / min, for example 30L / min or 45L / min.

[0064] In some implementations, in step S2, the cooling method may be to first allow natural cooling to 450°C, and then introduce nitrogen gas for cooling.

[0065] In this invention, in step S2, the temperature of the heat treatment can be 700~1000℃, for example 850℃.

[0066] In this invention, the heat treatment time in step S2 can be 4 to 6 hours, for example, 6 hours.

[0067] In this invention, in step S2, before the heat treatment, pre-curing may be performed, which may include three stages:

[0068] The first stage of pre-curing temperature is 100~130℃; the pre-curing time is 2 hours.

[0069] The pre-curing temperature for the second stage is 130~180℃; the pre-curing time is 2h; and the pre-curing pressure is 0.2~0.8Mpa.

[0070] The pre-curing temperature for the third stage is 250~320℃; the pre-curing time is 2h; and the pre-curing pressure is 1.5Mpa~2.5Mpa.

[0071] In this invention, step S2 further involves mechanically fusing the cooled product.

[0072] The frequency of the mechanical fusion can be 7000~9000Hz, for example 8000Hz.

[0073] The power of the mechanical fusion can be 120~160kW, for example 160kW.

[0074] The mechanical fusion time can be 2 to 4 hours.

[0075] negative electrode sheet

[0076] The negative electrode provided in the third aspect of the present invention comprises the carbon composite material as described above.

[0077] In this invention, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer is disposed on at least one surface of the negative electrode current collector; the negative electrode material layer includes the carbon composite material as described above.

[0078] In this invention, the negative electrode current collector can be a conventional negative electrode current collector in the art. The negative electrode current collector, serving as the substrate supporting the negative electrode material layer, is typically a metal foil with a thickness of 3-500 μm. There are no particular limitations on the material, as long as it has high conductivity and does not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The negative electrode current collector usually has a smooth surface, but fine textures can also be formed on its surface to improve the adhesion between the negative electrode material layer and the current collector. Besides foil, the negative electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. Generally, the negative electrode current collector is copper foil.

[0079] In this invention, the negative electrode material layer may further include a conductive agent.

[0080] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0081] In this invention, the negative electrode material layer may further include a binder.

[0082] The type of adhesive is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as SBR.

[0083] In this invention, the negative electrode material layer may further include a thickener.

[0084] The addition of the thickener can increase the viscosity of the system of each component in the negative electrode slurry. It can be a thickener commonly used in the art to prepare negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0085] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: coating a negative electrode slurry containing the carbon composite material onto at least one surface of the negative electrode current collector, drying, cold pressing, and slitting to obtain the final product.

[0086] In some specific embodiments, the negative electrode slurry includes: the carbon composite material, a conductive agent, a thickener, and a binder, wherein the conductive agent is a single-walled carbon nanotube; the thickener is CMC; and the binder is PAA; preferably, the mass ratio of the carbon composite material, single-walled carbon nanotube, CMC, and PAA is 96.5:0.35:0.5:2.65.

[0087] Electrochemical device

[0088] An electrochemical device provided in a fourth aspect of the present invention includes a carbon composite material as described above or a negative electrode as described above.

[0089] In this invention, the electrochemical device is preferably a battery.

[0090] In some embodiments, the electrochemical device may be a sodium-ion battery, a lithium-ion battery, or a potassium-ion battery.

[0091] In some embodiments, the sodium-ion battery may be a liquid sodium-ion battery, an all-solid-state sodium-ion battery, or a semi-solid-state sodium-ion battery. The battery type does not limit the scope of protection of this invention.

[0092] In some specific embodiments, the liquid sodium-ion battery includes a positive electrode, a negative electrode as described above, a separator, and an electrolyte.

[0093] In some specific implementations, the all-solid-state sodium-ion battery includes a positive electrode, a negative electrode as described above, and a solid electrolyte membrane.

[0094] In this invention, the liquid sodium-ion battery includes a positive electrode, a negative electrode as described above, a separator, and an electrolyte.

[0095] Positive electrode film

[0096] In this invention, the positive electrode sheet may include a positive current collector and a positive electrode material layer, wherein the positive electrode material layer is disposed on at least one surface of the positive current collector; the positive electrode material layer includes a positive electrode active material.

[0097] In this invention, the positive electrode active material can be a positive electrode active material conventionally used in the art.

[0098] When used in sodium-ion batteries, the positive electrode active material can be a conventional positive electrode active material for sodium-ion batteries, such as nickel iron phosphate polyanionic material.

[0099] In some embodiments, the positive electrode material layer further includes a conductive agent. The conductive agent is a reagent used to ensure that the electrode has good charge-discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as Super P, conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers such as carbon nanotubes (CNTs), carbon fibers, and metal fibers; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; and conductive metal oxides or polyphenylene derivatives such as titanium dioxide, for example, Super P and CNTs.

[0100] In some embodiments, the positive electrode material layer further includes a binder. The binder may be a component that facilitates bonding between the positive electrode material and the conductive agent, and also facilitates bonding between the positive electrode material and the positive electrode current collector. It can typically be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0101] In some implementations, the positive electrode material layer includes a positive electrode active material, Super P, CNT, and PVDF.

[0102] In some specific implementations, the mass ratio of the positive electrode active material, Super P, CNT and PVDF is 97:1.0:0.5:1.5.

[0103] In this invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without limitation. For example, commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0104] In some alternative implementations, the positive current collector is aluminum foil.

[0105] In this invention, the positive electrode sheet can be prepared using methods conventional in the art.

[0106] In some optional embodiments, the method for preparing the positive electrode sheet includes the following steps: mixing the positive electrode material, binder and conductive agent in a certain mass ratio, adding a solvent and mixing evenly to obtain a positive electrode slurry; then uniformly coating the positive electrode slurry onto at least one surface of the positive electrode current collector; and then preparing the positive electrode sheet by drying, rolling, slitting and other processes.

[0107] electrolyte

[0108] In this invention, the electrolyte can be a conventional electrolyte used in batteries, generally including non-aqueous solvents and salts.

[0109] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0110] In some embodiments, the non-aqueous solvent preferably comprises ester solvents and / or dimethyl sulfoxide (DMSO), more preferably carbonate solvents. The carbonate solvent may optionally be one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate, propylene carbonate, and butyl carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0111] In this invention, when used in sodium-ion batteries, the salt is a sodium salt, which can be a conventional sodium salt in the art, preferably one or more of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium difluorooxalate borate (NaDFOB), for example, NaPF6; the concentration of the sodium salt is preferably 1 mol / L.

[0112] In this invention, the electrolyte may include additives, which may be conventional additives in the art, such as fluoroethylene carbonate (FEC).

[0113] In some embodiments, the electrolyte includes NaPF6, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0114] In some preferred embodiments, the electrolyte comprises EC, EMC, and DEC. The volume ratio of EC, EMC, and DEC is, for example, 1:1:1.

[0115] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: mixing the various non-aqueous solvents in proportion in an argon atmosphere glove box with a water content of <10 ppm, and then adding a fully dried lithium salt and mixing evenly to obtain the electrolyte.

[0116] diaphragm

[0117] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0118] In some alternative embodiments, the thickness of the diaphragm may be 9 μm to 18 μm, for example, 11 μm.

[0119] In some alternative embodiments, the air permeability of the diaphragm can be 180s / 100mL to 380s / 100mL.

[0120] In some alternative embodiments, the porosity of the diaphragm may be 30% to 50%.

[0121] In this invention, the sodium-ion battery can be prepared using conventional methods in the art. It can involve sequentially winding a positive electrode, a separator, and a negative electrode to obtain a battery cell, then packaging it in a casing and injecting the electrolyte. Alternatively, it can involve sequentially stacking a positive electrode, a separator, and a negative electrode to obtain a battery cell, then packaging it in a casing and injecting the electrolyte. Afterward, the sodium-ion battery is obtained through processes such as settling, hot and cold pressing, formation, clamping, and capacity testing.

[0122] electronic devices

[0123] An electronic device provided in a fifth aspect of the present invention includes the electrochemical device as described above.

[0124] For example, the electronic devices described in this invention may be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0125] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0126] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0127] Example 1

[0128] 1.1 Negative electrode sheet

[0129] (1) Preparation of carbon composite materials

[0130] S0. The raw coal (high-quality lignite purchased from Xilingol League, Inner Mongolia, with a carbon content of over 75%) is dehydrated using conventional methods, then co-fired with potassium hydroxide at a mass ratio of 2:1 to remove impurities, and then rinsed with deionized water to obtain precursor coke.

[0131] S1. The precursor coke obtained in step S0 is mixed with sodium ferric oxalate (pore-forming agent) at a mass ratio W of 3:1, and then calcined in three stages: the first calcination temperature is 200℃ for 2 hours, the second calcination is carried out by raising the temperature to 500℃ at a rate of 2℃ / min and holding for 2 hours, and the third calcination is carried out by raising the temperature to 800℃ at a rate of 2℃ / min and holding for 5 hours; then it is pulverized into a soft carbon precursor with a Dv50 of 5μm by a pulverizer.

[0132] S2. The soft carbon precursor obtained in step S1 is subjected to reduced pressure treatment in a stirred tank, and then mixed with asphalt (softening point 105℃, coking value S 23%, mass ratio of asphalt to soft carbon precursor 1.2:1) for pre-curing: heating and stirring at 120℃ for 2 hours, then pressurizing the tank to 0.5MPa by introducing nitrogen, heating and stirring at 150℃ for 2 hours, then pressurizing the tank to 2MPa, heating and stirring at 280℃ for 4 hours; then transferring it to a carbonization furnace. The material is heat-treated at 850℃ for 6 hours, then naturally cooled to 450℃ in a nitrogen atmosphere. A high flow rate of nitrogen (Q) is then introduced for rapid cooling (cooling rate 15℃ / min). The heat-treated material is then mechanically fused for 2 hours at a frequency of 8000Hz and a power of 160kW. Afterward, fine powder is removed by shaping, controlling the particle size distribution width to be less than 1.0, and then the material is rinsed to remove impurities, yielding a carbon composite material.

[0133] (2) Preparation of negative electrode

[0134] The prepared carbon composite material was used as the negative electrode material, single-walled carbon nanotubes as the conductive agent, CMC as the thickener, and PAA as the binder. They were mixed in a mass ratio of 96.85:0.35:0.5:2.5, and then deionized water was added as a solvent. The mixture was stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of the negative electrode current collector copper foil. After drying, cold pressing, and slitting, a negative electrode sheet was prepared.

[0135] 1.2 Positive electrode plate

[0136] Nickel-iron phosphate polyanionic material NaFePO4 (NFPP), Super P, CNT, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97:1.0:0.5:1.5, and N-methylpyrrolidone (NMP) solvent was added. The mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was coated on one surface of the positive electrode current collector aluminum foil, and the positive electrode sheet was prepared by drying, cold pressing, and slitting.

[0137] 1.3 Diaphragm

[0138] A porous PE membrane with a thickness of 11 μm was used as the separator.

[0139] 1.4 Electrolyte

[0140] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried sodium salt NaPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a sodium salt concentration of 1 mol / L.

[0141] 1.5 Sodium-ion battery

[0142] The positive electrode, separator, and negative electrode prepared in the aforementioned steps are stacked sequentially, with the separator positioned between the positive and negative electrode to act as a separator. Then, an aluminum-plastic film is wrapped around the separator, dried, and the electrolyte prepared above is injected. After encapsulation, settling, and formation processes, a soft-pack battery with a designed capacity of 1 Ah, i.e., a sodium-ion battery, is finally prepared.

[0143] Example 2

[0144] Based on Example 1, in step S1 of preparing the carbon composite material, the mass ratio W of the precursor coke to sodium iron oxalate was adjusted to 4:1, while the other conditions remained unchanged.

[0145] Example 3

[0146] Based on Example 1, in step S1 of preparing the carbon composite material, the mass ratio W of the precursor coke to sodium iron oxalate was adjusted to 2:1, while the other conditions remained unchanged.

[0147] Example 4

[0148] Based on Example 1, in step S2 of preparing the carbon composite material, the coking value S of the asphalt was adjusted to 15%, while the other conditions remained unchanged.

[0149] Example 5

[0150] Based on Example 1, in step S2 of preparing the carbon composite material, the coking value S of the asphalt was adjusted to 36%, while the other conditions remained unchanged.

[0151] Example 6

[0152] Based on Example 1, in step S2 of preparing the carbon composite material, the flow rate Q of nitrogen gas during the cooling process was adjusted to 45 L / min (cooling rate of 20 °C / min), while the other conditions remained unchanged.

[0153] Example 7

[0154] Based on Example 1, in step S1 of preparing the carbon composite material, the pore-forming agent was changed to sodium iron phosphate, while the other conditions remained unchanged.

[0155] Example 8

[0156] Based on Example 1, in step S2 of preparing the carbon composite material, the type of hard carbon source was changed to phenolic resin (purchased from Shandong Shengquan Group Co., Ltd., model TY01), while the other conditions remained unchanged.

[0157] Example 9

[0158] Based on Example 1, in step S2 of preparing the carbon composite material, the mass ratio of hard carbon source to soft carbon precursor was adjusted to 1.5:1, while the other conditions remained unchanged.

[0159] Example 10

[0160] 10.1 Negative electrode sheet

[0161] (1) Preparation of carbon composite materials

[0162] The preparation steps are the same as those for the carbon composite material in Example 1.

[0163] (2) Preparation of negative electrode

[0164] The steps for preparing the negative electrode are the same as those in Example 1.

[0165] 10.2 Positive Electrode

[0166] The ternary cathode material NCM (LiNi) 0.90 Co 0.05 Mn 0.05 O2), Super P, CNT, and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.0:0.5:1.5, and N-methylpyrrolidone (NMP) is added as a solvent. The mixture is stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry is coated on one surface of the positive electrode current collector aluminum foil, and the positive electrode sheet is prepared by drying, cold pressing, and slitting.

[0167] 10.3 Diaphragm

[0168] A porous PE membrane with a thickness of 11 μm was used as the separator.

[0169] 10.4 Electrolyte

[0170] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0171] 10.5 Lithium-ion Battery

[0172] The positive electrode, separator, and negative electrode prepared in the aforementioned steps are stacked sequentially, with the separator positioned between the positive and negative electrode to act as a separator. Then, an aluminum-plastic film is wrapped around the separator, dried, and the electrolyte prepared above is injected. After encapsulation, settling, and formation processes, a soft-pack battery with a capacity of 1 Ah, i.e., a lithium-ion battery, is finally prepared.

[0173] Example 11

[0174] 11.1 Negative electrode sheet

[0175] (1) Preparation of carbon composite materials

[0176] The preparation steps are the same as those for the carbon composite material in Example 1.

[0177] (2) Preparation of negative electrode

[0178] The steps for preparing the negative electrode are the same as those in Example 1.

[0179] 11.2 Positive Electrode

[0180] The polyanionic active materials KFePO4, SP, CNT and PVDF were mixed in a mass ratio of 94:2:1:3 and stirred under vacuum until the system was homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto aluminum foil. After the aluminum foil was dried at room temperature, it was transferred to an oven for drying and then cold-pressed and slit to obtain a positive electrode sheet.

[0181] 11.3 Diaphragm

[0182] A PE membrane with a thickness of 12 μm; an air permeability of 280 s / 100 mL; and a porosity of 40%.

[0183] 11.4 Electrolyte

[0184] In an argon-atmospheric glove box with a water content of <10 ppm, battery-grade ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and PC were mixed in a volume ratio of 2:4:2:1 to form an organic solvent. Sodium salt KPF6 was added at a concentration of 15 wt% and mixed thoroughly to obtain the electrolyte.

[0185] 11.5 Assembling Potassium-ion Batteries

[0186] The positive electrode, separator, and negative electrode prepared in the aforementioned steps are stacked sequentially, with the separator positioned between the positive and negative electrode to act as a separator. Then, an aluminum-plastic film is wrapped around the separator, dried, and the electrolyte prepared above is injected. After encapsulation, settling, and formation processes, a soft-pack battery with a capacity of 1 Ah, i.e., a potassium-ion battery, is finally prepared.

[0187] Comparative Example 1

[0188] Based on Example 1, the pore-forming agent sodium ferrate was not added in step S1 of preparing the carbon composite material, while the other conditions remained unchanged.

[0189] Comparative Example 2

[0190] Based on Example 1, in step S1 of preparing the carbon composite material, the mass ratio W of the precursor coke to sodium iron oxalate was adjusted to 1:1, while the other conditions remained unchanged.

[0191] Comparative Example 3

[0192] Based on Example 1, in step S2 of preparing the carbon composite material, the coking value S of the asphalt was adjusted to 50%, Q was adjusted to 10 L / min, and the other conditions remained unchanged.

[0193] Table 1

[0194] serial number Types of pore-forming agents The mass ratio of precursor coke to pore-forming agent W Types of hard carbon sources Hard carbon source coking value S The ratio of hard carbon source to product I Nitrogen flow rate Q Example 1 Sodium ferric oxalate 3:1 asphalt 23% 120% 30 Example 2 Sodium ferric oxalate 4:1 asphalt 23% 120% 30 Example 3 Sodium ferric oxalate 2:1 asphalt 23% 120% 30 Example 4 Sodium ferric oxalate 3:1 asphalt 15% 120% 30 Example 5 Sodium ferric oxalate 3:1 asphalt 36% 120% 30 Example 6 Sodium ferric oxalate 3:1 asphalt 23% 120% 45 Example 7 Sodium iron phosphate 3:1 asphalt 23% 120% 30 Example 8 Sodium ferric oxalate 3:1 Phenolic resin 23% 120% 30 Example 9 Sodium ferric oxalate 3:1 asphalt 23% 150% 30 Example 10 Sodium ferric oxalate 3:1 asphalt 23% 120% 30 Example 11 Sodium ferric oxalate 3:1 asphalt 23% 120% 30 Comparative Example 1 / / asphalt 23% 120% 30 Comparative Example 2 Sodium ferric oxalate 1:1 asphalt 23% 120% 30 Comparative Example 3 Sodium ferric oxalate 3:1 asphalt 50% 120% 10

[0195] Table 2

[0196] Limited porosity V Equivalent average pore diameter d Ultimate compression Hard carbon mass percentage Soft carbon mass percentage Example 1 0.034 1.6 1.31 18.00% 82.00% Example 2 0.023 1.4 1.35 13.00% 87.00% Example 3 0.042 1.7 1.28 24.00% 86.00% Example 4 0.036 1.8 1.25 26.00% 74.00% Example 5 0.025 1.3 1.45 10.00% 90.00% Example 6 0.037 2 1.27 27.00% 73.00% Example 7 0.021 1.1 1.47 8.00% 92.00% Example 8 0.035 1.7 1.3 19.00% 81.00% Example 9 0.046 1.9 1.21 28.00% 72.00% Example 10 0.034 1.6 1.31 18.00% 82.00% Example 11 0.034 1.6 1.31 18.00% 82.00% Comparative Example 1 0.011 0.8 1.09 16.00% 84.00% Comparative Example 2 0.058 1.9 1.22 21.00% 79.00% Comparative Example 3 0.015 0.6 1.49 8.30% 91.70%

[0197] Example 1

[0198] (1) Limiting the porosity ratio and pore volume V

[0199] The carbon composite materials of the examples and comparative examples were subjected to BET tests according to the methods described in GB / T 19587~2017. The pore volume of the pores with a pore size range of 1.5 nm to 3.2 nm was directly read, and the results are recorded in Table 2.

[0200] (2) Equivalent average pore diameter d

[0201] The results are calculated using the following formula and are recorded in Table 2.

[0202] d=O / S

[0203] Where: O represents the oil absorption value (cm²) 3 / g), measured according to the method described in GB / T 35266~2017;

[0204] S is the specific surface area (m²) 2 (g), measured according to the method described in GB / T 19587~2017.

[0205] (3) Ultimate compaction

[0206] Referring to the powder compaction test in GB / T 24533~2019, the powder compaction at 100 MPa was taken as the ultimate compaction, and the results are recorded in Table 2.

[0207] (4) Mass ratio of hard carbon and soft carbon

[0208] Referring to GB / T 24533~2019, the lattice spacing of the carbon composite materials prepared in the examples and comparative examples was measured as d. Taking the lattice spacing of soft carbon as the standard value of 0.345 nm and the lattice spacing of hard carbon as the standard value of 0.39 nm, and letting the content of soft carbon phase be x and the content of hard carbon phase be y, the following equation can be obtained:

[0209] x+y=1

[0210] 0.345x + 0.39y = d

[0211] Where d is the value obtained by testing, the x and y values ​​can be obtained by solving the quadratic equation in one variable, and the results are recorded in Table 2.

[0212] Example 2: Electrical Performance Test

[0213] The 1Ah (design capacity) pouch cells prepared in each embodiment and comparative example were activated and capacity-tested according to the following steps:

[0214] For sodium-ion batteries and potassium-ion batteries:

[0215] The 1Ah soft-pack batteries prepared in Examples 1-9, Example 11, and Comparative Examples 1-3 were charged to 3.5V with a constant current of 0.5Ah, and then charged at a constant voltage of 3.5V until the current decayed to 0.01Ah. After that, they were discharged to 1.5V with a constant current of 0.5Ah. The above process is recorded as one charge-discharge cycle. After three consecutive charge-discharge cycles, the average discharge capacity of the three cycles is recorded as C.

[0216] For lithium-ion batteries:

[0217] The 1Ah soft-pack battery prepared in Example 10 was charged at a constant current of 0.5Ah to 4.25V, and then charged at a constant voltage of 4.25V until the current decayed to 0.01Ah. After that, it was discharged at a constant current of 0.5Ah to 2.5V. The above process is recorded as one charge-discharge cycle. After three consecutive charge-discharge cycles, the average discharge capacity of the three cycles is recorded as C.

[0218] The pouch cells that have undergone the above activation and capacity testing were subjected to the following fast-charging cycle performance and high-temperature cycle performance tests:

[0219] 1. Cyclic performance test

[0220] (1) Normal temperature cycling performance

[0221] Under 25°C conditions, the soft-pack batteries that have undergone the above activation and capacity testing were cycled at a 0.5C rate, with 1.5~3.5V for sodium-ion and potassium-ion batteries and 2.5~4.25V for lithium-ion batteries. The number of cycles until the capacity decayed to 80% SOH was recorded as the fast-charge cycle number. The results are recorded in Table 3.

[0222] (2) High-temperature cycling performance

[0223] Under 45°C conditions, the soft-pack batteries that have undergone the above activation and capacity testing were cycled at a 0.5C rate, with sodium-ion and potassium-ion batteries at 1.5~3.5V and lithium-ion batteries at 2.5~4.25V. The number of cycles until the capacity decayed to 80% SOH was recorded as the high-temperature cycle number. The results are recorded in Table 3.

[0224] 2. Storage performance test

[0225] The 1Ah (design capacity) pouch cells prepared in each embodiment and comparative example were activated and capacity-tested according to the following steps:

[0226] For sodium-ion batteries and potassium-ion batteries:

[0227] The 1Ah soft-pack batteries prepared in Examples 1-9, Example 11, and Comparative Examples 1-3 were charged to 3.5V with a constant current of 0.5Ah, and then charged at a constant voltage of 3.5V until the current decayed to 0.01Ah. After that, they were discharged to 1.5V with a constant current of 0.5Ah. The above process is recorded as one charge-discharge cycle. After three consecutive charge-discharge cycles, the average discharge capacity of the three cycles is recorded as C.

[0228] For lithium-ion batteries:

[0229] The 1Ah soft-pack battery prepared in Example 10 was charged at a constant current of 0.5Ah to 4.25V, and then charged at a constant voltage of 4.25V until the current decayed to 0.01Ah. After that, it was discharged at a constant current of 0.5Ah to 2.5V. The above process is recorded as one charge-discharge cycle. After three consecutive charge-discharge cycles, the average discharge capacity of the three cycles is recorded as C.

[0230] The above-mentioned activated and capacity-graded pouch cells were subjected to the following storage performance tests:

[0231] At 25°C, the soft-pack battery that has undergone the above activation and capacity testing is calibrated with a 0.33C rate current and recorded as C0. Then, the battery is stored at a high temperature of 60°C. After that, the battery is taken out every 7 days and its capacity is tested at room temperature and recorded as C1, C2, ..., Cn. The number of days until Cn first falls below 80% of C0 is used as the standard for measuring storage capacity. The results are recorded in Table 3.

[0232] 3. Full charge expansion

[0233] (1) The thickness of the negative electrode sheet prepared in the example and the comparative example was measured with a micrometer and recorded as the initial thickness;

[0234] (2) For sodium-ion batteries and potassium-ion batteries

[0235] The 1Ah soft-pack batteries prepared in Examples 1-9, Example 11, and Comparative Examples 1-3 were charged with a constant current of 0.5Ah to 3.5V, and then charged with a constant voltage of 3.5V until the current decayed to 0.01Ah. After that, they were discharged with a constant current of 0.5Ah to 1.5V. The above process is recorded as one charge-discharge cycle. After two consecutive charge-discharge cycles, the batteries were charged with a constant current of 0.5Ah to 3.5V and then charged with a constant voltage of 3.5V until the current decayed to 0.01Ah. The batteries were then immediately moved back to the glove box and carefully disassembled.

[0236] For lithium-ion batteries:

[0237] The 1Ah soft-pack battery prepared in Example 10 was charged at a constant current of 0.5Ah to 4.25V, and then charged at a constant voltage of 4.25V until the current decayed to 0.01Ah. After that, it was discharged at a constant current of 0.5Ah to 2.5V. The above process is recorded as one charge-discharge cycle. After two consecutive charge-discharge cycles, the battery was charged at a constant current of 0.5Ah to 4.25V again, and then charged at a constant voltage of 4.25V until the current decayed to 0.01Ah. The battery was then immediately moved back to the glove box and carefully disassembled.

[0238] Then clean the electrode. Gently pick up the fully charged graphite electrode with tweezers and use lint-free paper to very gently absorb the residual electrolyte on the surface. Do not wipe it, so as not to damage the surface structure of the electrode or the SEI film.

[0239] Next, measure the thickness: Immediately use a micrometer to measure the thickness of the fully charged electrode at five points, including the four corners and the center of the rectangular electrode, and record the average value as the "full charge thickness".

[0240] (3) Calculate the full-fill expansion rate according to the following formula, and record the results in Table 3.

[0241] Full charge expansion rate = (Full charge thickness - Initial thickness) / Initial thickness × 100%

[0242] 4. Initial discharge capacity and initial coulombic efficiency

[0243] (1) The carbon composite material prepared in the examples and comparative examples was mixed with CMC, super P and SBR in a mass ratio of 95.5:1.5:1.5:1.5. The mixture was prepared into a slurry using NMP solvent. The slurry was then coated onto one surface of a copper foil using a scraper. After drying, a sheet was obtained. The sheet was then stamped into a film with a diameter of 16 mm.

[0244] Electrolytes of Examples 1-9 and Comparative Examples 1-3: EC, DMC and EMC were mixed in a volume ratio of 1:1:1, and then dried NaPF6 was added to prepare an electrolyte with a sodium salt concentration of 1 mol / L.

[0245] Electrolyte of Example 10: EC, DMC and EMC were mixed in a volume ratio of 1:1:1, and then dried lithium hexafluorophosphate was added to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0246] Electrolyte of Example 11: EC, DMC and EMC were mixed in a volume ratio of 1:1:1, and then dried KPF6 was added to prepare an electrolyte with a potassium salt concentration of 1 mol / L.

[0247] (2) Place the nickel mesh in the center of the negative electrode shell, then place the lithium sheet (19 mm in diameter) flat in the center of the nickel mesh, use a pipette to add an appropriate amount of electrolyte to the center of the lithium sheet, then place the separator (PP separator, 26 mm in diameter) on the upper layer of the lithium sheet, add electrolyte again, and then place the membrane and positive electrode shell obtained in step (1) on the upper layer of the separator in sequence to assemble into a CR2430 button cell;

[0248] (3) The button cell obtained in step (2) was tested on the Blue Electric System, and the discharge capacity and initial coulombic efficiency were directly output. The results are shown in Table 3.

[0249] Table 3

[0250] serial number capacity First effect Number of cycles (revolutions) at 0.5C Number of cycles at 0.5°C Storage performance (days) Full charge expansion Example 1 356.7 88.70% 5320 3210 455 10.80% Example 2 343.2 89.20% 5120 3132 441 12.80% Example 3 363.2 88.00% 5047 2987 420 9.50% Example 4 378.2 86.20% 5235 2889 413 9.00% Example 5 338.7 88.90% 4953 3056 441 13.50% Example 6 378.9 86.00% 5210 2789 399 9.20% Example 7 332.5 89.10% 4763 2881 448 15.10% Example 8 356.7 88.70% 5320 3210 455 10.80% Example 9 381.5 85.90% 5212 2567 399 8.60% Example 10 356.7 80.10% 2675 1356 280 6.50% Example 11 356.7 68.60% 2356 1105 231 23.40% Comparative Example 1 390.4 83.90% 3560 1920 350 6.90% Comparative Example 2 320.6 85.70% 3875 2156 371 8.90% Comparative Example 3 305.2 86.70% 4150 2235 350 15.10%

[0251] As can be seen from the data in Table 3, the carbon composite material provided by this invention, when applied to sodium-ion batteries, exhibits excellent cycle performance, with over 4700 cycles at 0.5C room temperature (attenuation to 80% SOH) and over 2500 cycles at 0.5C high temperature. It also has excellent storage performance and capacity, with a storage life of over 390 days and an initial discharge capacity of over 330mAh / g.

[0252] As can be seen from Examples 10 and 11, the carbon composite material of the present invention also exhibits good initial efficiency, cycle performance and storage performance when applied to lithium-ion batteries and potassium-ion batteries.

[0253] The carbon composite materials prepared in Comparative Examples 1 to 3 do not simultaneously meet the requirements of this invention in terms of the defined porosity ratio, pore volume, equivalent average pore diameter, and ultimate compaction.

[0254] The difference between Comparative Example 1 and Example 1 is that no pore-forming agent was added during the preparation process of Comparative Example 1. The resulting hard carbon composite material has very small defined porosity, pore volume, equivalent average pore size, and ultimate compaction, all of which are outside the scope of this invention. When applied to sodium-ion batteries, its 0.5C room temperature cycle count decreased by 33.1%, its 0.5C high temperature cycle count decreased by 40.2%, and its storage days decreased by 23.1%. It can be seen that the hard carbon composite material of Comparative Example 1 significantly deteriorates both the cycle performance and the storage days.

[0255] The difference between Comparative Example 2 and Example 1 is that the mass ratio of raw coal and pore-forming agent in Comparative Example 2 is not within the scope of this invention. The resulting hard carbon composite material has a larger defined porosity and pore volume, and a smaller ultimate compaction. When applied to sodium-ion batteries, its capacity performance, cycle performance, and storage performance are all reduced to a certain extent. Specifically, the initial discharge capacity decreased by 10.1%, the number of cycles at 0.5C room temperature decreased by 27.2%, the number of cycles at 0.5C high temperature decreased by 32.8%, and the number of storage days decreased by 18.5%.

[0256] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 has a different coking value and a different nitrogen flow rate (and cooling rate). The flow rate is smaller, that is, the cooling rate is slower. The resulting hard carbon composite material has a smaller defined porosity and pore volume, and a larger ultimate compaction. When it is applied to sodium-ion batteries, the capacity performance, cycle performance and storage performance are reduced to a certain extent. Specifically, the initial discharge capacity decreased by 10.1%, the number of cycles at 0.5C room temperature decreased by 22.0%, the number of cycles at 0.5C high temperature decreased by 30.4%, and the number of storage days decreased by 23.1%.

[0257] The mass ratio of raw coal to pore-forming agent differs in Examples 1-3. A higher proportion of pore-forming agent is more beneficial for improving the defined porosity, pore volume, and equivalent average pore size. When the mass ratio of raw coal to pore-forming agent increases from 4:1 to 2:1, both cycle performance and storage performance are improved. Examples 1 and 7 use different types of pore-forming agents, indicating that using sodium iron oxalate as a pore-forming agent is more beneficial for improving battery performance.

[0258] The asphalt in Examples 1, 4, and 5 has different coking values. A higher coking value is more beneficial for improving ultimate compaction. When the coking value increases from 15% to 23%, both cycle performance and storage performance improve. Examples 1 and 8 use different types of hard carbon sources, indicating that using asphalt as a hard carbon source has a more significant advantage in high-temperature cycle performance. Examples 1 and 9 use different amounts of hard carbon source, showing that excessive amounts of hard carbon source are detrimental to battery cycle performance and storage performance.

[0259] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon composite material, characterized in that, It includes hard carbon and porous soft carbon, wherein the hard carbon is at least partially distributed inside the pores of the porous soft carbon; The carbon composite material satisfies the following conditions: The porosity V is limited to 0.02 cm³. 3 / g ~0.05 cm 3 / g; The defined pore size refers to pores with a diameter of 1.5nm to 3.2nm; The equivalent average pore size d is 1.1~2.0μm; The ultimate compression PD is 1.21~1.47; The preparation method of the carbon composite material includes the following steps: S1. A mixture containing raw coal and a pore-forming agent is calcined and pulverized to obtain a soft carbon precursor; the mass ratio of the raw coal to the pore-forming agent is (2~4):1; S2. The mixture containing the soft carbon precursor and the hard carbon source is heat-treated and then cooled to obtain the carbon composite material.

2. The carbon composite material as described in claim 1, characterized in that, The carbon composite material satisfies one or more of the following conditions a to e: a. The mass percentage of the hard carbon in the carbon composite material is 0-28%, but not 0; b. The mass percentage of the porous soft carbon in the carbon composite material is 72% to 100%, but not 100%; c. The defined porosity ratio and pore volume V is 0.023 cm³. 3 / g~0.042cm 3 / g; d. The equivalent average pore size d is 1.5~1.9μm; e. The ultimate compression PD is 1.25~1.

35.

3. A method for preparing a carbon composite material as described in claim 1 or 2, characterized in that, It includes the following steps: S1. A mixture containing raw coal and a pore-forming agent is calcined and pulverized to obtain a soft carbon precursor; the mass ratio of the raw coal to the pore-forming agent is (2~4):1; S2. The mixture containing the soft carbon precursor and the hard carbon source is heat-treated and then cooled to obtain the carbon composite material.

4. The method for preparing the carbon composite material as described in claim 3, characterized in that, The preparation method of the carbon composite material satisfies one or more of the following conditions a to d: a. In step S1, the mass ratio of the raw coal to the pore-forming agent is (3~4):1; b. In step S1, the raw coal is lignite; c. In step S1, the pore-forming agent is a sodium salt and / or a potassium salt, and the pore-forming agent includes one or more of the elements Fe, Mn, Ni and Co; d. In step S1, the particle size Dv50 of the soft carbon precursor is 4~6.5μm.

5. The method for preparing the carbon composite material as described in claim 3, characterized in that, The preparation method of the carbon composite material satisfies one or more of the following conditions a to e: a. In step S1, the raw coal is first purified before calcination. The purification method is to co-calcine the raw coal with a strong alkali and then rinse it. The mass ratio of the raw coal to the strong alkali is (1~3):

1. b. In step S1, the calcination temperature is 200~1000℃; c. In step S1, the calcination time is 8-10 hours; d. In step S1, the calcination is divided into a first calcination, a second calcination, and a third calcination; the temperature of the first calcination is 200~300℃; the time of the first calcination is 1h~3h; the temperature of the second calcination is 400~500℃; the time of the second calcination is 1h~3h; the heating rate of the second calcination is 1~3℃ / min; the temperature of the third calcination is 700~900℃; the time of the third calcination is 4~6h. e. In step S1, the heating rate of the calcination is 2~4℃.

6. The method for preparing the carbon composite material as described in claim 3, characterized in that, The preparation method of the carbon composite material satisfies one or more of the following conditions a to g: a. In step S2, the hard carbon source is asphalt and / or phenolic resin, and the softening point of the asphalt is ≤90℃; b. In step S2, the coking value of the hard carbon source is 15%~36%; c. In step S2, the mass ratio of the hard carbon source to the soft carbon precursor is (1~3):1; d. In step S2, the temperature of the heat treatment is 700~1000℃; e. In step S2, the heat treatment time is 4~6 hours; f. In step S2, the cooling method is natural cooling and / or nitrogen gas cooling; g. In step S2, prior to the heat treatment, a pre-curing process is also performed, which includes three stages: The first stage of pre-curing temperature is 100~130℃; the pre-curing time is 2 hours. The pre-curing temperature for the second stage is 130~180℃; the pre-curing time is 2h; and the pre-curing pressure is 0.2~0.8Mpa. The pre-curing temperature for the third stage is 250~320℃; the pre-curing time is 2h; and the pre-curing pressure is 1.5Mpa~2.5Mpa.

7. The method for preparing the carbon composite material as described in claim 3, characterized in that, In step S2, the cooled product is further subjected to mechanical fusion, wherein the mechanical fusion satisfies one or more of the following conditions a to c: a. The frequency of the mechanical fusion is 7000~9000Hz; b. The power of the mechanical fusion is 120~160KW; c. The mechanical fusion time is 2-4 hours.

8. A negative electrode sheet, characterized in that, It includes carbon composite materials as described in claim 1 or 2.

9. An electrochemical device, characterized in that, It includes the carbon composite material as described in claim 1 or 2 or the negative electrode as described in claim 8.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.