A carbon negative electrode material and a preparation method thereof, a negative electrode sheet, an electrochemical device, and an electronic device

Abstract

The application discloses a kind of carbon negative electrode material and preparation method thereof, negative electrode sheet, electrochemical device and electronic equipment.The preparation method of the carbon negative electrode material includes the following steps: S1.mixture comprising raw coal and pore-forming agent is calcined and crushed to obtain graphite precursor;The mass ratio of the raw coal to the pore-forming agent is (0.5~1.5):1;S2.mixture comprising the graphite precursor and hard carbon source is sequentially pre-solidified and heat-treated to obtain the carbon negative electrode material;The mass percentage of the hard carbon source in the graphite precursor is 10%~35%;The temperature of the pre-solidification is 500~750℃;The temperature of the heat treatment is 1400~2700℃.The carbon negative electrode material provided by the application has high pressure, and when applied in lithium ion battery, the cycle performance is excellent.

Description

Technical Field

[0001] This invention specifically relates to a carbon anode material and its preparation method, an anode sheet, an electrochemical device, and an electronic device. Background Technology

[0002] With the increasing popularity of rechargeable batteries, especially large cylindrical batteries (such as 4680), their application potential in the energy storage field is being explored. However, energy storage systems have extremely high requirements for long-cycle operation, which inevitably places higher demands on anode materials. In existing rechargeable batteries, carbon materials used as anode materials have shortcomings mainly reflected in insufficient specific capacity, purity and side reactions, layered structure stability, rate performance, and charge / discharge plateau.

[0003] CN119240688 A uses lithium metal vaporization to deposit the MOF framework, a process that is cumbersome and extremely costly, making it unsuitable for mass production and promotion; CN120423538A uses residual oil to fill pores, but this will deteriorate the material's kinetic properties.

[0004] How to prepare carbon anode materials with excellent cycle performance in a simple and easy way is one of the problems that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention primarily addresses the shortcomings of existing technologies where carbon materials used as anode materials suffer from complex preparation processes and poor cycle performance when applied to secondary batteries. It provides a carbon anode material, its preparation method, an anode sheet, an electrochemical device, and an electronic device. The carbon anode material provided by this invention exhibits high voltage density and demonstrates excellent cycle performance when applied to electrochemical devices (especially lithium-ion batteries).

[0006] In a first aspect, the present invention provides a method for preparing the carbon anode material, comprising the following steps:

[0007] S1. A mixture containing raw coal and a pore-forming agent is calcined and pulverized to obtain a graphite precursor; the mass ratio of the raw coal to the pore-forming agent is (0.5~1.5):1;

[0008] S2. The mixture containing the graphite precursor and the hard carbon source is subjected to heat treatment to obtain the carbon anode material; the hard carbon source accounts for 10% to 35% of the mass percentage of the graphite precursor; the heat treatment temperature is 1400 to 2700°C.

[0009] Secondly, the present invention provides a carbon anode material, which is prepared by the carbon anode material preparation method described above.

[0010] Thirdly, the present invention provides a negative electrode sheet comprising the carbon negative electrode material as described above.

[0011] Fourthly, the present invention provides an electrochemical device comprising the carbon anode material or the anode sheet as described above.

[0012] Fifthly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0013] 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.

[0014] The reagents and raw materials used in this invention are all commercially available.

[0015] The positive and progressive effects of this invention are as follows:

[0016] The carbon anode material prepared by the method provided by this invention satisfies specific limitations on the pore volume ratio and the equivalent average pore size. When used as an anode material in batteries, especially lithium-ion batteries, it exhibits excellent cycle performance and excellent storage performance. Detailed Implementation

[0017] Preparation method of carbon anode material

[0018] The method for preparing the carbon anode material provided in the first aspect of the present invention includes the following steps:

[0019] S1. A mixture containing raw coal and a pore-forming agent is calcined and pulverized to obtain a graphite precursor; the mass ratio of the raw coal to the pore-forming agent is (0.5~1.5):1;

[0020] S2. The mixture containing the graphite precursor and the hard carbon source is subjected to heat treatment to obtain the carbon anode material; the hard carbon source accounts for 10% to 35% of the mass percentage of the graphite precursor; the heat treatment temperature is 1400 to 2700°C.

[0021] In this invention, in step S1, the raw coal can be coal conventionally used in the art, such as lignite.

[0022] In this invention, in step S1, the carbon content of the raw coal can be 75% or more.

[0023] In this invention, in step S1, the raw coal can be de-impurified before calcination. The de-impurification method is, for example, to co-calcine the raw coal with a strong alkali and then rinse it.

[0024] The mass ratio of the raw coal to the strong alkali can be (1~3):1, for example, 2:1.

[0025] The strong base may be one or more of potassium hydroxide, calcium hydroxide, and sodium hydroxide.

[0026] 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.

[0027] In this invention, in step S1, the preferred mass ratio of the raw coal to the pore-forming agent is (0.8~1.5):1, for example, 1.5:1.

[0028] In this invention, step S1, the calcination can be divided into a first calcination and a second calcination.

[0029] In some embodiments, the temperature of the second calcination can be 1000~1200°C.

[0030] In some implementations, the second calcination time can be 4 to 6 hours, for example, 5 hours.

[0031] In some embodiments, the heating rate of the second calcination can be 6~12℃ / min, preferably 8~12℃ / min, for example 10℃ / min.

[0032] In some implementations, the first calcination is divided into two stages.

[0033] The calcination temperature in the first stage can be 200~300℃, for example, 200℃.

[0034] The heat preservation time in the first stage can be 1 hour to 3 hours, for example, 2 hours.

[0035] The calcination temperature in the second stage can be 400~500℃, for example, 500℃.

[0036] The heat preservation time in the second stage can be 1 hour to 3 hours, for example, 2 hours.

[0037] The heating rate in the second stage can be 1~5℃ / min, for example 2℃ / min.

[0038] In this invention, in step S1, the particle size Dv50 of the graphite precursor can be 9~12μm, for example 10μm.

[0039] In this invention, in step S2, the hard carbon source can be a quinoline insoluble substance; the quinoline insoluble substance can be a quinoline insoluble substance extracted in the temperature range of 380~450℃, which is flowable under heating conditions.

[0040] In this invention, in step S2, the hard carbon source preferably accounts for 15% to 30% of the mass percentage of the graphite precursor.

[0041] In some specific implementations, the hard carbon source may account for 10%, 20%, or 35% of the mass percentage of the graphite precursor.

[0042] In this invention, the heat treatment temperature in step S2 is preferably 1800~2500℃.

[0043] In some specific embodiments, the heat treatment temperature may be 1400°C or 2100°C.

[0044] In this invention, the heat treatment time in step S2 can be 4 to 12 hours.

[0045] In this invention, the pre-curing temperature in step S2 can be 600°C.

[0046] In this invention, the pre-curing time in step S2 can be 0.2~0.4h, for example 0.3h.

[0047] In this invention, in step S2, the product obtained by heat treatment can also be mechanically fused.

[0048] The frequency of the mechanical fusion can be 7000~9500Hz, for example 8000Hz.

[0049] The power of the mechanical fusion can be 150~180kW, for example 160kW.

[0050] The mechanical fusion time can be 1 to 2 hours.

[0051] carbon anode materials

[0052] The carbon anode material provided in the second aspect of the present invention is prepared by the carbon anode material preparation method described above.

[0053] In this invention, the carbon anode material comprises hard carbon and porous graphite, with at least a portion of the hard carbon located within the pores of the porous graphite, and the carbon anode material satisfies the following conditions:

[0054] The mass percentage of the hard carbon in the carbon anode material is 5% to 28%.

[0055] The porosity ratio and pore volume V are limited to 0.01 cm³. 3 / g~0.25cm 3 / g; The defined pore size refers to pores with a diameter of 0.2nm to 3nm;

[0056] The equivalent average pore size d is 0.5 nm to 9 nm.

[0057] In this invention, the carbon anode material is a composite material formed by hard carbon and graphite, that is, a single particle simultaneously includes a hard carbon portion and a graphite portion. The graphite has a porous structure and constitutes the skeleton of the material particle, while the hard carbon is at least distributed inside the pores of the porous graphite.

[0058] In this invention, the defined porosity ratio refers to the total internal volume of the pores (pores with a diameter between 0.2 nm and 3 nm) in a unit mass of carbon anode material.

[0059] In this invention, the specified porosity ratio and pore volume are preferably 0.03 cm³. 3 / g~0.19cm 3 / g.

[0060] In some specific implementations, the defined porosity ratio can be 0.01 cm³. 3 / g, 0.03 cm 3 / g, 0.05cm 3 / g, 0.09 cm 3 / g, 0.11 cm 3 / g, 0.14 cm 3 / g, 0.16 cm 3 / g, 0.17 cm 3 / g, 0.19 cm 3 / g, 0.22cm 3 / g or 0.24 cm 3 / g.

[0061] 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".

[0062] In this invention, the average pore size d of the equivalent pores is preferably 3nm~5nm.

[0063] In some specific embodiments, the equivalent average pore size d can be 3 nm, 3.1 nm, 3.2 nm, 3.5 nm, 3.7 nm, 3.9 nm, 4.3 nm, 4.5 nm, 4.6 nm, 4.7 nm or 8.1 nm.

[0064] In this invention, the pore volume of the defined pores can account for more than 50% of the total pore volume.

[0065] In some implementations, the pore volume percentage of the defined pores may be 50%, 52%, 53%, 55%, 61%, 62%, 67%, 70%, 72%, or 89%.

[0066] In this invention, the hard carbon accounts for 5% to 18% of the mass percentage of the carbon anode material.

[0067] In some embodiments, the mass percentage of the hard carbon to the mass percentage of the carbon anode material may be 8.30%, 10.10%, 10.70%, 11.20%, 14.70%, 15.30%, 16.50%, 19.80%, 21.20%, or 27.60%.

[0068] In this invention, the porous graphite accounts for 72% to 95% of the mass percentage of the carbon anode material, preferably 82% to 95%.

[0069] In this invention, the powder compaction of the carbon anode material can be 1.6 g / cm³. 3 The preferred values ​​are 1.6~2.0 g / cm³. The powder compaction mentioned above refers to powder compaction at 5T.

[0070] In some specific embodiments, the powder compaction of the carbon anode material can be 1.6 g / cm³. 3 1.61 g / cm 3 1.64 g / cm 3 1.65 g / cm 3 1.7 g / cm 3 1.73 g / cm 3 1.76 g / cm 3 1.77 g / cm 3 1.79 g / cm 3 1.8g / cm 3 Or 1.83 g / cm 3 .

[0071] negative electrode sheet

[0072] The negative electrode sheet provided in the third aspect of the present invention comprises the carbon negative electrode material as described above.

[0073] 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 negative electrode material as described above.

[0074] 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.

[0075] In this invention, the negative electrode material layer may further include a conductive agent.

[0076] 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.

[0077] In this invention, the negative electrode material layer may further include a binder.

[0078] 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.

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

[0080] 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).

[0081] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: coating a negative electrode slurry containing the carbon negative electrode material onto at least one surface of the negative electrode current collector, drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0082] In some specific embodiments, the negative electrode slurry includes: the carbon negative electrode 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 negative electrode material, single-walled carbon nanotube, CMC, and PAA is 96.5:0.35:0.5:2.65.

[0083] Electrochemical device

[0084] An electrochemical device provided in a fourth aspect of the present invention includes a carbon anode material or an anode sheet as described above.

[0085] In this invention, the electrochemical device is preferably a battery, such as a lithium-ion battery, a sodium-ion battery, or a potassium-ion battery.

[0086] In some embodiments, the electrochemical device may be a lithium-ion battery.

[0087] In some embodiments, the lithium-ion battery may be a liquid lithium-ion battery, an all-solid-state lithium-ion battery, or a semi-solid-state lithium-ion battery. The battery type does not limit the scope of protection of this invention.

[0088] In some specific embodiments, the liquid lithium-ion battery includes a positive electrode, a negative electrode as described above, a separator, and an electrolyte.

[0089] In some specific implementations, the all-solid-state lithium-ion battery includes a positive electrode, a negative electrode as described above, and a solid electrolyte membrane.

[0090] In this invention, the liquid lithium-ion battery includes a positive electrode, a negative electrode as described above, a separator, and an electrolyte.

[0091] Positive electrode film

[0092] 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.

[0093] In this invention, the positive electrode active material can be a positive electrode active material conventionally used in the art. When used in lithium-ion batteries, the positive electrode active material is, for example, one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

[0094] 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.

[0095] 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.

[0096] In some implementations, the positive electrode material layer includes a positive electrode active material, Super P, CNT, and PVDF.

[0097] 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.

[0098] 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.

[0099] In some alternative implementations, the positive current collector is aluminum foil.

[0100] In this invention, the positive electrode sheet can be prepared using methods conventional in the art.

[0101] 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.

[0102] electrolyte

[0103] In this invention, the electrolyte can be a conventional electrolyte used in batteries, generally including non-aqueous solvents and salts.

[0104] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0105] 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.

[0106] In this invention, when used in lithium-ion batteries, the salt is a lithium salt, which can be a conventional lithium salt in the art, preferably one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3 and LiN(CF3SO2)2, for example, LiPF6; the concentration of the lithium salt is preferably 1 mol / L.

[0107] In this invention, the electrolyte may include additives, which may be conventional additives in the art, such as fluoroethylene carbonate (FEC).

[0108] In some embodiments, the electrolyte includes LiPF6, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0109] 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.

[0110] 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.

[0111] diaphragm

[0112] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0113] In some alternative embodiments, the thickness of the diaphragm may be 9 μm to 18 μm, for example, 11 μm.

[0114] In some alternative embodiments, the air permeability of the diaphragm can be 180s / 100mL to 380s / 100mL.

[0115] In some alternative embodiments, the porosity of the diaphragm may be 30% to 50%.

[0116] In this invention, the method for preparing the lithium-ion battery can be a conventional method in the art. It can be that the positive electrode, separator, and negative electrode are wound in sequence to obtain the battery cell, which is then packaged in a packaging shell and injected with the electrolyte. Alternatively, the positive electrode, separator, and negative electrode are stacked in sequence to obtain the battery cell, which is then packaged in a packaging shell and injected with the electrolyte. After that, the lithium-ion battery is obtained through processes such as settling, hot and cold pressing, formation, clamping, and capacity testing.

[0117] electronic devices

[0118] An electronic device provided in a fifth aspect of the present invention includes the electrochemical device as described above.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] Example 1

[0123] 1. Negative electrode sheet

[0124] (1) Preparation of carbon anode materials

[0125] 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.

[0126] S1. The precursor coke obtained in step S0 is mixed with sodium ferric oxalate (pore-forming agent) at a mass ratio W1 of 1:1, and then subjected to a first calcination in two stages: the first stage calcination temperature is 200℃ and the time is 2h, then the temperature is increased to 500℃ at a rate of 2℃ / min and held for 2h for the second stage calcination, and then the temperature is increased to 1200℃ at a rate of 10℃ / min (i.e., k) and held for 5h for the second calcination; then it is pulverized by a pulverizer into a graphite precursor with a Dv50 of 10μm;

[0127] S2. The graphite precursor obtained in step S1 is subjected to depressurization treatment in a stirred tank to a pressure of 0.2 MPa, and then mixed with quinoline insolubles (hard carbon source) extracted in the range of 380℃~450℃. The hard carbon source accounts for 20% (W2) of the graphite precursor by mass. The mixture is pre-cured by calcination at 600℃ for 0.3 h, and then heat-treated at 2100℃ (T) for 12 h. The heat-treated material is then subjected to mechanical fusion treatment at a frequency of 8000 Hz and a power of 160 kW. The fine powder is then removed by shaping, and the particle size distribution width is controlled to be less than 1.05. Finally, the mixture is rinsed to remove impurities, resulting in a carbon anode material comprising porous graphite and hard carbon.

[0128] (2) Preparation of negative electrode

[0129] The prepared carbon anode material, single-walled carbon nanotubes, CMC, and PAA were mixed in a mass ratio of 96.5:0.35:0.5:2.65, and deionized water was added as a solvent. The mixture was stirred thoroughly to obtain anode slurry. The anode slurry was uniformly coated on one surface of copper foil for anode current collector. After drying, cold pressing, and slitting, anode sheet was prepared.

[0130] 2. Positive electrode plate

[0131] 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.

[0132] 3. Diaphragm

[0133] A porous PE membrane with a thickness of 11 μm was used as the separator.

[0134] 4. Electrolyte

[0135] 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 lithium salt concentration of 1 mol / L.

[0136] 5. Lithium-ion batteries

[0137] 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 lithium-ion battery, is finally prepared.

[0138] Example 2

[0139] Based on Example 1, in step S1 of preparing the carbon anode material, the mass ratio W1 of the precursor coke to sodium iron oxalate was adjusted to 3:2, while the other conditions remained unchanged.

[0140] Example 3

[0141] Based on Example 1, in step S1 of preparing the carbon anode material, the mass ratio W1 of the precursor coke to sodium iron oxalate was adjusted to 1:2, while the other conditions remained unchanged.

[0142] Example 4

[0143] Based on Example 1, the heating rate k in step S1 of preparing the carbon anode material was adjusted to 6℃ / min, while the other conditions remained unchanged.

[0144] Example 5

[0145] Based on Example 1, the heating rate k in step S1 of preparing the carbon anode material was adjusted to 12℃ / min, while the other conditions remained unchanged.

[0146] Example 6

[0147] Based on Example 1, in step S2 of preparing the carbon anode material, the mass percentage W2 of the hard carbon source in the graphite precursor was adjusted to 10%, while the other conditions remained unchanged.

[0148] Example 7

[0149] Based on Example 1, in step S2 of preparing the carbon anode material, the mass percentage W2 of the hard carbon source in the graphite precursor was adjusted to 35%, while the other conditions remained unchanged.

[0150] Example 8

[0151] Based on Example 1, the heat treatment temperature T in step S2 of preparing the carbon anode material was adjusted to 1400℃, while the other conditions remained unchanged.

[0152] Example 9

[0153] Based on Example 1, the pore-forming agent in step S1 of preparing the carbon anode material was changed to sodium iron phosphate, while the other conditions remained unchanged.

[0154] Example 10

[0155] Based on Example 1, in step S2 of preparing the carbon anode material, the type of hard carbon source was changed to boron-modified phenolic resin (purchased from Shandong Shengquan Group Co., Ltd., product model TY03), while the other conditions remained unchanged.

[0156] Example 11

[0157] 1. Negative electrode sheet

[0158] (1) Preparation of carbon anode materials

[0159] The preparation steps are the same as those for the carbon anode material in Example 8.

[0160] (2) Preparation of negative electrode

[0161] The steps for preparing the negative electrode are the same as those in Example 8.

[0162] 2. Positive electrode plate

[0163] The polyanionic active materials NaFePO4, SP, CNT and PVDF were mixed in a mass ratio of 94:2:1:3 and stirred in a vacuum mixer 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.

[0164] 3. Diaphragm

[0165] Thickness: 12μm; air permeability: 280s / 100mL; porosity: 40%.

[0166] 4. Electrolyte

[0167] In an argon atmosphere glove box with a water content of <10 ppm, battery-grade ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and PC are mixed in a mass ratio of 1:1:1 to form an organic solvent. Then, dried sodium salt NaPF6 with a sodium salt content of 15 wt% is added to obtain the electrolyte.

[0168] 5. Sodium-ion batteries

[0169] 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 sodium-ion battery, is finally prepared.

[0170] Example 12

[0171] 1. Negative electrode sheet

[0172] (1) Preparation of carbon anode materials

[0173] The preparation steps are the same as those for the carbon anode material in Example 8.

[0174] (2) Preparation of negative electrode

[0175] The steps for preparing the negative electrode are the same as those in Example 8.

[0176] 2. Positive electrode plate

[0177] 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.

[0178] 3. Diaphragm

[0179] Thickness: 12μm; air permeability: 280s / 100mL; porosity: 40%.

[0180] 4. Electrolyte

[0181] 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 mass ratio of 1:1:1 to form an organic solvent. Then, dried potassium salt KPF6 was added at a concentration of 15 wt%, and the mixture was thoroughly mixed to obtain the electrolyte.

[0182] 5. Potassium-ion batteries

[0183] 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.

[0184] Comparative Example 1

[0185] Based on Example 1, in step S1 of preparing the carbon anode material, the mass ratio W1 of the precursor coke to sodium iron oxalate was adjusted to 2:1, while the other conditions remained unchanged.

[0186] Comparative Example 2

[0187] Based on Example 1, the heating rate k in step S1 of preparing the carbon anode material was adjusted to 2℃ / min, while the other conditions remained unchanged.

[0188] Comparative Example 3

[0189] Based on Example 1, in step S2 of preparing the carbon anode material, the mass percentage W2 of the hard carbon source in the graphite precursor was adjusted to 40%, while the other conditions remained unchanged.

[0190] Comparative Example 4

[0191] Based on Example 1, the heat treatment temperature T in step S2 of preparing the carbon anode material was adjusted to 3000℃, while the other conditions remained unchanged.

[0192] Comparative Example 5

[0193] 1. Negative electrode sheet

[0194] Pure hard carbon (purchased from Kuraray, Japan, model TYPE2) 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 96.85:0.15:0.5:2.5, 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 copper foil of the negative electrode current collector. After drying, cold pressing, and slitting, the negative electrode sheet was prepared.

[0195] 2. Positive electrode plate

[0196] The steps for preparing the positive electrode are the same as those in Example 12.

[0197] 3. Diaphragm

[0198] Same as in Example 12.

[0199] 4. Electrolyte

[0200] Same as in Example 12.

[0201] 5. Sodium-ion batteries

[0202] The steps for assembling the battery are the same as those in Example 12.

[0203] Comparative Example 6

[0204] 1. Negative electrode sheet

[0205] Pure hard carbon (purchased from Kuraray, Japan, model TYPE2) 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 96.85:0.15:0.5:2.5, 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 copper foil of the negative electrode current collector. After drying, cold pressing, and slitting, the negative electrode sheet was prepared.

[0206] 2. Positive electrode plate

[0207] The steps for preparing the positive electrode are the same as those in Example 1.

[0208] 3. Diaphragm

[0209] Same as in Example 1.

[0210] 4. Electrolyte

[0211] Same as in Example 1.

[0212] 5. Lithium-ion batteries

[0213] The steps for assembling the battery are the same as in Example 1.

[0214] Comparative Example 7

[0215] Based on Example 1, in step S2, no pre-curing operation is performed, and the other conditions remain unchanged.

[0216] Table 1

[0217] No. Pore forming agent type W1 k (℃ / min) Hard carbon source type W2 T(℃) Example 1 Sodium iron oxalate 1:1 10 Quinoline insolubles 20% 2100 Example 2 Sodium iron oxalate 3:2 10 Quinoline insolubles 20% 2100 Example 3 Sodium iron oxalate 1:2 10 Quinoline insolubles 20% 2100 Example 4 Sodium iron oxalate 1:1 6 Quinoline insolubles 20% 2100 Example 5 Sodium iron oxalate 1:1 12 Quinoline insolubles 20% 2100 Example 6 Sodium iron oxalate 1:1 10 Quinoline insolubles 10% 2100 Example 7 Sodium iron oxalate 1:1 10 Quinoline insolubles 35% 2100 Example 8 Sodium iron oxalate 1:1 10 Quinoline insolubles 20% 1400 Example 9 Sodium iron phosphate 1:1 10 Quinoline insolubles 20% 2100 Example 10 Sodium iron oxalate 1:1 10 Boron-modified phenolic resin 20% 2100 Example 11 Sodium iron oxalate 1:1 10 Quinoline insolubles 20% 1400 Example 12 Sodium iron oxalate 1:1 10 Quinoline insolubles 20% 1400 Comparative Example 1 Sodium iron oxalate 2:1 10 Quinoline insolubles 20% 2100 Comparative Example 2 Sodium iron oxalate 1:1 2 Quinoline insolubles 20% 2100 Comparative Example 3 Sodium iron oxalate 1:1 10 Quinoline insolubles 40% 2100 Comparative Example 4 Sodium iron oxalate 1:1 10 Quinoline insolubles 20% 3000 Comparative Example 7 Sodium iron oxalate 1:1 10 Quinoline insolubles 20% 2100

[0218] Table 2

[0219] No. Limited pore volume V Limited pore volume V ratio Equivalent pore average pore size d Oil absorption value O Specific surface area S Hard carbon mass ratio Graphite mass ratio Powder compaction (g / cm³) Example 1 0.14 67% 3 0.73 2.4 14.70% 85.30% 1.76 Example 2 0.09 52% 3.5 0.69 2 11.20% 88.80% 1.79 Example 3 0.17 89% 3.7 0.92 2.5 16.50% 83.50% 1.7 Example 4 0.03 70% 4.3 0.77 1.8 8.30% 91.70% 1.83 Example 5 0.19 61% 4.6 1.23 2.7 19.80% 80.20% 1.65 Example 6 0.05 72% 3.2 0.64 2 10.10% 89.90% 1.8 Example 7 0.22 55% 8.1 2.92 3.6 27.60% 72.40% 1.61 Example 8 0.24 50% 4.7 1.54 3.3 21.20% 78.80% 1.6 Example 9 0.16 62% 3.1 0.71 2.3 14.70% 85.30% 1.73 Example 10 0.11 53% 3.9 1.34 3.43 10.70% 89.30% 1.77 Example 11 0.24 50% 4.7 1.54 3.3 21.20% 78.80% 1.6 Example 12 0.24 50% 4.7 1.54 3.3 21.20% 78.80% 1.6 Comparative Example 1 0.02 45% 3.7 0.85 2.3 4.20% 95.80% 1.85 Comparative Example 2 0.01 70% 2.6 0.45 1.7 3.00% 97.00% 1.89 Comparative Example 3 0.29 37% 10.5 3.78 3.6 30.70% 69.30% 1.56 Comparative Example 4 0 0 1.8 0.23 1.3 0.90% 99.10% 1.92 Comparative Example 5 / / / / / 100.00% 0 1.28 Comparative Example 6 / / / / / 100.00% 0 1.28 Comparative Example 7 0.01 18% 4.5 2.16 4.7 15.30% 84.70% 1.64

[0220] Example 1

[0221] 1. Content of hard carbon and porous graphite

[0222] Referring to GB / T 24533-2019, the lattice spacing of the material is d. Taking the lattice spacing of hard carbon as the standard value of 0.336 nm and the lattice spacing of hard carbon as the standard value of 0.39 nm, and letting the content of porous graphite phase be x and the content of hard carbon phase be y, the following equation can be obtained:

[0223]

[0224]

[0225] Where d is the value obtained from the test, and the value of y can be obtained by solving the quadratic equation in one variable. The results are recorded in Table 2.

[0226] 2. Define the porosity ratio and pore volume ratio.

[0227] Referring to the method of GB / T 19587-2017, BET tests were performed on the graphite composite materials prepared in the examples and comparative examples. The specific pore volume and pore volume ratio of pores with a pore size range of 0.2nm to 3nm were directly read, and the results are recorded in Table 2.

[0228] 3. Equivalent average pore diameter d

[0229] The equivalent average pore size for each embodiment and comparative example was calculated using the following formula, and the results are recorded in Table 2:

[0230] d=O / S

[0231] O is the oil absorption value, which is measured according to the method in GB / T 3780.2-2017.

[0232] S is the specific surface area, which is obtained by testing according to the method in GB / T 19587~2017.

[0233] 4. Powder compaction / 5T

[0234] The compaction of carbon anode materials prepared in the examples and comparative examples was tested according to the test method of powder compaction in GB / T 24533-2019. The test condition was 5T, and the results are recorded in Table 2.

[0235] 5. Particle size Dv50

[0236] The test was conducted in accordance with GB / T 19587-2017. Particle size Dv50 typically refers to the pore size at which the cumulative pore volume reaches 50% of the total pore volume in the pore size distribution curve. Specifically, a full-range adsorption test was performed on a surface area analyzer, and the BJH (Barrett-Joyner-Halenda) model was selected to calculate the pore size distribution, obtaining the cumulative pore volume curve. From this curve, the x-axis (pore size) corresponding to the cumulative pore volume reaching 50% of the total pore volume was directly found; this value is the particle size Dv50.

[0237] Example 2: Electrical Performance Testing

[0238] 1. Cyclic performance test

[0239] The 1Ah (design capacity) pouch cells prepared in each embodiment and comparative example were activated and capacity-tested according to the following steps:

[0240] For lithium-ion batteries:

[0241] The 1Ah pouch cells prepared in Examples 1-10, Comparative Examples 1-4, 6 and 7 were charged to 4.25V with a constant current of 0.5Ah, and then charged at a constant voltage of 4.25V until the current decayed to 0.01Ah. After that, they were discharged to 2.5V 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.

[0242] For sodium-ion batteries and potassium-ion batteries:

[0243] The 1Ah soft-pack batteries prepared in Examples 11, 12 and Comparative Example 5 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. The batteries were charged and discharged three times in a row, and the average discharge capacity of the three cycles was recorded as C.

[0244] 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:

[0245] (1) Normal temperature cycling performance

[0246] Under 25°C conditions, the soft-pack batteries prepared in the above-mentioned activated and capacity-graded examples and comparative examples were cycled at a 0.5C rate, with lithium-ion batteries at 2.5~4.25V and sodium-ion and potassium-ion batteries at 1.5~3.5V. The number of cycles until the capacity decayed to 80% SOH was recorded as the fast-charge cycle number, and the results are recorded in Table 3.

[0247] (2) High-temperature cycling performance

[0248] Under 45°C conditions, the soft-pack batteries that have undergone the above activation and capacity testing were cycled at a 1C rate, with lithium-ion batteries at 2.5~4.25V and sodium-ion and potassium-ion batteries at 1.5~3.5V. 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.

[0249] 2. Storage performance test

[0250] The 1Ah (design capacity) pouch cells prepared in each embodiment and comparative example were activated and capacity-tested according to the following steps:

[0251] For lithium-ion batteries:

[0252] The 1Ah pouch cells prepared in Examples 1-10, Comparative Examples 1-4, 6 and 7 were charged to 4.25V with a constant current of 0.5Ah, and then charged at a constant voltage of 4.25V until the current decayed to 0.01Ah. After that, they were discharged to 2.5V 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.

[0253] For sodium-ion batteries and potassium-ion batteries:

[0254] The 1Ah soft-pack batteries prepared in Examples 11, 12 and Comparative Example 5 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. The batteries were charged and discharged three times in a row, and the average discharge capacity of the three cycles was recorded as C.

[0255] The above-mentioned activated and capacity-graded pouch cells were subjected to the following storage performance tests:

[0256] 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.

[0257] 3. Initial discharge capacity and initial coulombic efficiency

[0258] (1) The carbon anode 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.

[0259] Electrolytes of Examples 1-10, Comparative Examples 1-4, 6 and 7: 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.

[0260] Electrolytes of Example 11 and Comparative Example 5: 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.

[0261] Electrolyte of Example 12: 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.

[0262] (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;

[0263] (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.

[0264] Table 3

[0265] No. First discharge capacity (mAh / g) First coulombic efficiency 0.5C cycle number (turns) High-temperature cycle number (turns) Storage days (days) Example 1 378.2 90.6 3523 2675 357 Example 2 371.4 90.8 3675 2278 371 Example 3 385.6 89.2 3374 2650 336 Example 4 365.7 91.2 3690 2190 385 Example 5 390.2 88.5 3169 2550 315 Example 6 369.4 90.7 3603 2265 371 Example 7 407.6 87.4 3059 2347 301 Example 8 401.5 88.1 3289 2337 322 Example 9 381.4 90.2 3416 2534 350 Example 10 370.2 89.4 3425 1854 336 Example 11 401.5 92.3 4320 2120 238 Example 12 401.5 78.3 1785 1320 210 Comparative Example 1 358.4 90.5 2876 1893 336 Comparative Example 2 355.1 90.8 2933 1926 350 Comparative Example 3 412.3 86.1 2678 1768 287 Comparative Example 4 348.2 91.2 2886 2032 336 Comparative Example 5 380 81.2 3570 1650 189 Comparative Example 6 380 63.4 976 650 98 Comparative Example 7 395.2 85.3 2893 1678 210

[0266] As can be seen from the data in Table 2, the compaction of the carbon anode material provided by this invention is 1.6 g / cm³. 3 The lithium-ion battery prepared above exhibits good capacity and cycle performance, with a discharge specific capacity of over 365 mAh / g, over 3000 cycles at 0.5C (attenuation to 80% SOH), and over 1800 cycles at high temperature (attenuation to 80% SOH). It also has excellent storage performance and initial coulombic efficiency, with a storage life of over 300 days at 60℃ and an initial coulombic efficiency of over 87%.

[0267] The carbon anode materials prepared in Comparative Examples 1 to 4 could not simultaneously meet the requirements of this invention in terms of the specified porosity ratio, pore volume, equivalent average pore size, and mass percentage of hard carbon.

[0268] Compared with Example 1, Comparative Example 1 has a different mass ratio of raw coal to pore-forming agent, resulting in a lower proportion of hard carbon in the prepared carbon anode material, which is outside the scope of this invention. Compared with Example 1, Comparative Example 2 has a lower heating rate, resulting in a lower proportion of hard carbon in the prepared carbon anode material, which is also outside the scope of this invention.

[0269] The initial discharge capacity of the batteries in Comparative Example 1 and Comparative Example 2 was much lower than that in Example 1, and their cycle performance and storage performance were also degraded to some extent.

[0270] Compared to Example 1, Comparative Example 3 had a different mass ratio of graphite precursor to hard carbon source, resulting in an excessively high proportion of hard carbon in the prepared carbon anode material. This led to an excessively large porosity ratio and equivalent average pore size, which is outside the scope of this invention. The battery's cycle performance and storage performance decreased significantly, with a 24.0% decrease in 0.5C cycle count, a 33.9% decrease in high-temperature cycle count, and a 19.6% decrease in storage days.

[0271] Compared to Example 1, Comparative Example 4 involved a different heat treatment temperature, resulting in a carbon anode material with a very low mass percentage of hard carbon and a limited porosity-to-pore volume ratio of 0, which falls outside the scope of this invention. The initial discharge capacity of the battery was significantly lower than that of Example 1, decreasing by 7.9%. Cycling and storage performance also deteriorated to some extent, with a 18.1% decrease in 0.5C cycle count, a 24.0% decrease in high-temperature cycle count, and a 5.9% decrease in storage days.

[0272] Comparative Example 5 is a sodium-ion battery made of pure hard carbon material. Compared with Example 11, it has an excessively high hard carbon content, extremely low compaction, and its storage performance is reduced to some extent.

[0273] Comparative Example 6 is a lithium-ion battery made of pure hard carbon material. Compared with Example 1, the hard carbon content is too high, the compaction is extremely low, and the cycle performance and storage performance are significantly reduced.

[0274] In Comparative Example 7, no pre-curing was performed before heat treatment. It can be seen that the lack of pre-curing led to a significant decrease in both the cycle performance and storage performance of the battery.

[0275] The defined porosity ratio reflects the abundance and uniformity of pores (0.2 nm to 3 nm) in carbon anode materials, which is far greater than that of conventional artificial graphite. A richer and more uniform pore size limits expansion, thus improving cycle performance; however, an excessively large pore size can degrade storage capacity. A larger equivalent average pore size is more conducive to electrolyte wetting and better kinetic performance, but an excessively large pore size can worsen first-efficiency performance and compaction.

[0276] Compared with Examples 1 to 3, the difference lies in the mass ratio of raw coal to pore-forming agent. As the ratio of the two increases from 1:2 to 1:1, the initial coulombic efficiency, compaction, circulation performance and storage performance are all improved.

[0277] The difference between Examples 1, 4 and 5 lies in the heating rate. As the heating rate increases from 6°C / min to 12°C / min, the initial discharge capacity continuously increases.

[0278] The difference between Examples 1, 6 and 7 lies in the mass ratio of graphite precursor to hard carbon source. As the mass percentage of hard carbon source increases from 10% to 35%, the initial discharge capacity continuously increases.

[0279] The difference between Example 1 and Example 8 lies in the heat treatment temperature. The heat treatment temperature was increased from 1400℃ to 2100℃, resulting in a significant increase in both cycle performance and storage days.

[0280] The difference between Example 1 and Example 9 lies in the type of pore-forming agent. It can be seen that using sodium iron oxalate as a pore-forming agent is more conducive to improving battery performance.

[0281] The difference between Example 1 and Example 10 lies in the type of hard carbon source. It can be seen that using quinoline insolubles as the hard carbon source has a more obvious advantage in high-temperature cycling performance.

[0282] The difference between Example 11 and Example 8 is that the carbon anode material is assembled into a sodium-ion battery; the difference between Example 12 and Example 8 is that the carbon anode material is assembled into a potassium-ion battery; it can be seen that the carbon anode material of the present invention also has good cycle performance and storage performance when applied to sodium-ion batteries and potassium-ion batteries.

[0283] 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 method for preparing a carbon anode material, 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 graphite precursor; the mass ratio of the raw coal to the pore-forming agent is (0.5~1.5):1; 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; in step S1, the calcination is divided into a first calcination and a second calcination; The heating rate of the second calcination is 6~12℃ / min; the temperature of the second calcination is 1000~1200℃; and the calcination time is 4~6h. The first calcination is divided into two stages: the calcination temperature of the first stage is 200~300℃ and the holding time is 1h~3h; the calcination temperature of the second stage is 400~500℃ and the holding time is 1h~3h; the heating rate of the second stage is 1~5℃ / min. S2. The mixture containing the graphite precursor and the hard carbon source is subjected to pre-curing and heat treatment in sequence to obtain the carbon anode material; the hard carbon source accounts for 10%~35% of the mass percentage of the graphite precursor; the pre-curing temperature is 500~750℃; the heat treatment temperature is 1400~2700℃.

2. The method for preparing the carbon anode material as described in claim 1, characterized in that, Step S1 satisfies one or more of the following conditions a to c: a. In step S1, the mass ratio of the raw coal to the pore-forming agent is (0.8~1.5):1; b. In step S1, the raw coal is first removed from impurities before calcination. The method of removing impurities 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. c. The particle size Dv50 of the graphite precursor is 9~12μm.

3. The method for preparing the carbon anode material as described in claim 1, characterized in that, Step S2 satisfies one or more of the following conditions a to e: a. The hard carbon source is a quinoline insoluble substance and / or phenolic resin; b. The hard carbon source accounts for 15% to 30% of the mass percentage of the graphite precursor; c. The heat treatment temperature is 1800~2500℃; d. The heat treatment time is 4~12 hours; e. The pre-curing time is 0.2~0.4h.

4. The method for preparing the carbon anode material as described in claim 1, characterized in that, In step S2, the product obtained from the heat treatment 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 7000~9500Hz; b. The power of the mechanical fusion is 150~180KW; c. The mechanical fusion time is 1~2 hours.

5. A carbon anode material, characterized in that, It is prepared by the method for preparing carbon anode materials as described in any one of claims 1-4.

6. The carbon anode material as described in claim 5, characterized in that, The carbon anode material comprises hard carbon and porous graphite, with at least a portion of the hard carbon located within the pores of the porous graphite, and the carbon anode material satisfies the following conditions: The hard carbon accounts for 5% to 28% of the mass percentage of the carbon anode material; The porosity V is limited to 0.01 cm³. 3 / g ~0.25 cm 3 / g; The defined pore size refers to pores with a diameter of 0.2nm to 3nm; The equivalent average pore size d is 0.5 nm to 9 nm.

7. The carbon anode material as described in claim 6, characterized in that, The carbon anode material satisfies one or more of the following conditions a to e: a. The porosity V is limited to 0.03 cm³. 3 / g~0.19cm 3 / g; b. The equivalent average pore size d is 3nm~5nm; c. The hard carbon accounts for 5% to 18% of the mass percentage of the carbon anode material; d. The porous graphite accounts for 82% to 95% of the mass percentage of the carbon anode material; e. The powder compaction of the carbon anode material is above 1.6 g / cm³.

8. A negative electrode sheet, characterized in that, It includes the carbon anode material as described in any one of claims 5-7.

9. An electrochemical device, characterized in that, It includes the carbon anode material as described in any one of claims 5-7 or the anode sheet as described in claim 8.

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