Graphite composite transition metal fluoride positive electrode material and preparation method and application thereof

Abstract

The embodiment of the invention relates to a graphite composite transition metal fluoride positive electrode material and a preparation method and application thereof. The method comprises the following steps: dissolving a transition metal compound in a solvent, and mixing and stirring with a graphite raw material to obtain a mixture containing transition metal ions; the mixture is treated, so that a material with a cementite structure is formed in the mixture in the heat treatment process, transition metal ions are gradually diffused into the material, an onion carbon layer is formed on the outer layer of the material, and a primary carbonized material is obtained after smashing and grading; the primary carbonized material is subjected to heat preservation for 1-2 hours at the temperature of 600-2500 DEG C in a protective atmosphere environment, so that transition metal elements in the primary carbonized material escape through pore parts of the material, and a precursor material is obtained; putting the precursor material into a rotary furnace, introducing fluorine-containing gas, and generating nano metal fluoride in the precursor material through gas-phase reaction; and then introducing a mixed gas containing a carbon source gas for chemical vapor deposition coating to obtain the positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a graphite composite transition metal fluoride cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries are currently the battery category with the most mature technology development and the largest industrialization scale in the battery industry. Currently, the commercially available cathode materials mainly include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, ternary materials, etc. Their actual capacity has approached the theoretical value. In the current lithium-ion battery system, the specific capacity of the entire battery is limited by the capacity of the cathode material. In addition, in the production of batteries, the cost of the cathode material accounts for more than 30% of the total cost. Therefore, preparing a cathode material with low cost and high energy density is an important goal in the research and production of lithium-ion batteries.

[0003] Transition metal fluorides, such as iron fluoride, nickel fluoride, cobalt fluoride, etc., are a new type of lithium-ion cathode battery material. As a kind of electrode material with high specific capacity, low cost, and environmental friendliness, they have the advantages of simple synthesis and wide raw material sources. However, the large energy band width of transition metal fluorides themselves leads to poor electronic conductivity, and structure collapse is likely to occur in the conversion reaction, resulting in disadvantages such as low initial efficiency, poor rate performance, and poor cycle performance of the electrode material, which limits its practical application in battery materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a graphite composite transition metal fluoride cathode material, a preparation method thereof, and an application thereof. Through the preparation method of the present invention, a composite cathode material with high capacity and long cycle life is obtained.

[0005] In a first aspect, an embodiment of the present invention provides a preparation method of a graphite composite transition metal fluoride cathode material, and the preparation method includes:

[0006] Dissolve a transition metal compound in a solvent, add the graphite raw material according to the mass ratio of the transition metal compound to the graphite raw material of 1:10 to 1:100, and perform mixing and stirring to obtain a mixture containing transition metal ions;

[0007] Place the mixture in a heat treatment device, and perform heat treatment at 700°C to 1600°C in a protective atmosphere environment for 10 hours to 48 hours, so that the mixture forms a material with a cementite structure during the heat treatment process, and the transition metal ions diffuse into the interior of the material as the heat treatment progresses, and an onion carbon layer is formed on the outer layer of the material; crush and classify the heat-treated material to obtain a primary carbonized material;

[0008] Put the primary carbonized material into an induction furnace, and heat it to 1600°C - 2500°C at a rate of 1°C / min - 10°C / min under a protective atmosphere environment, and keep it warm for 1 hour - 2 hours, so that the transition metal elements inside the primary carbonized material escape through the pore part of the material to obtain a precursor material;

[0009] Put the precursor material into a rotary furnace, introduce a fluorine-containing gas, and heat it to 400°C - 1000°C, and keep it warm for 3 hours - 10 hours to generate nano metal fluorides inside the precursor material through a gas-phase reaction;

[0010] Then introduce a mixed gas composed of a carbon source gas and a protective gas, and perform coating by chemical vapor deposition. The coating temperature is 600 - 1000°C, and the coating time is 1 - 12h to obtain the graphite composite transition metal fluoride cathode material.

[0011] Preferably, the transition metal compound includes: one or more of an iron-containing compound, a cobalt-containing compound, a nickel-containing compound, a manganese-containing compound, a copper-containing compound, a zinc-containing compound, a niobium-containing compound, and a titanium-containing compound; wherein, the compound refers to one or more of sulfates, nitrates, carbonates, and chlorides;

[0012] The petroleum raw material includes: needle coke or petroleum coke;

[0013] The mass ratio of the transition metal compound to the graphite raw material is 1:50 - 1:70.

[0014] Preferably, the fluorine-containing gas is any one of fluorine gas, nitrogen trifluoride, and carbon tetrafluoride; the flow rate of the gas introduced is 2 - 10 L / min.

[0015] Preferably, the protective atmosphere environment is an environment where the protective gas is introduced, and the protective gas includes: nitrogen or argon.

[0016] Preferably, the carbon source gas is one or more of methane, acetylene, ethylene, and propylene; the mixed volume ratio of the protective gas and the carbon source gas is 4:1 - 1:2.

[0017] More preferably, the mixed volume ratio of the protective gas and the carbon source gas is 1:1 - 2:1; the coating time is 4 - 8h.

[0018] Preferably, the solvent includes water or a polar organic solvent.

[0019] In a second aspect, an embodiment of the present invention provides a graphite composite transition metal fluoride cathode material prepared by the preparation method described in the first aspect above.

[0020] In a third aspect, an embodiment of the present invention provides a positive electrode for a lithium-ion battery, comprising the graphite composite transition metal fluoride positive electrode material described in the second aspect above.

[0021] In a fourth aspect, an embodiment of the present invention provides a lithium-ion battery, comprising the positive electrode for a lithium-ion battery described in the third aspect above.

[0022] The preparation method of the graphite composite transition metal fluoride positive electrode material provided by the embodiment of the present invention makes the graphite composite transition metal fluoride material have obvious capacity advantages as a positive electrode material for lithium-ion batteries compared with traditional positive electrode materials by modifying the material during the synthesis process. By forming a penetration body first and then an onion carbon layer structure in the preparation process, problems such as expansion and poor conductivity of the transition metal fluoride material are optimized. Through the complementary advantages of graphite and the transition metal fluoride material, a composite lithium-ion positive electrode material with high capacity and long cycle life is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flowchart of the preparation method of the graphite composite transition metal fluoride positive electrode material provided by the embodiment of the present invention;

[0024] Figure 2 is a transmission electron microscope (TEM) image of the graphite composite transition metal fluoride positive electrode material provided by Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments.

[0026] An embodiment of the present invention provides a graphite composite transition metal fluoride positive electrode material. The steps of its preparation method are as Figure 1 shown and include:

[0027] Step 110: Dissolve the transition metal compound in a solvent, add graphite raw material according to the mass ratio of the transition metal compound to the graphite raw material of 1:10 to 1:100, and perform mixing and stirring to obtain a mixture containing transition metal ions.

[0028] Specifically, the transition metal compound includes one or more of an iron-containing compound, a cobalt-containing compound, a nickel-containing compound, a manganese-containing compound, a copper-containing compound, a zinc-containing compound, a niobium-containing compound, and a titanium-containing compound; wherein, the compound refers to one or more of a sulfate, a nitrate, a carbonate, and a chloride.

[0029] The petroleum raw material includes: needle coke or petroleum coke.

[0030] The mass ratio of the transition metal compound to the graphite raw material is preferably 1:50 to 1:70.

[0031] The solvent may include water or a polar organic solvent.

[0032] Step 120: Place the mixture in a heat treatment device, and heat-treat it at 700°C to 1600°C for 10 hours to 48 hours in a protective atmosphere environment, so that the mixture forms a material with a cementite structure during the heat treatment process, and as the heat treatment progresses, transition metal ions diffuse into the interior of the material, forming an onion carbon layer structure with a ring-shaped graphite carbon layer on the outer layer of the material; crush and classify the heat-treated material to obtain a primary carbonized material.

[0033] Specifically, the protective atmosphere environment is an environment into which a protective gas is introduced, and the protective gas includes: nitrogen or argon.

[0034] Step 130: Put the primary carbonized material into an induction furnace, and heat it from room temperature to 1600°C to 2500°C at a rate of 1°C / min to 10°C / min in a protective atmosphere environment, and hold for 1 hour to 2 hours, so that the transition metal elements inside the primary carbonized material escape through the pore part of the material to obtain a precursor material.

[0035] Preferably, the temperature is 1800°C to 2100°C.

[0036] Step 140: Put the precursor material into a rotary furnace, introduce a fluorine-containing gas, and heat it to 400°C to 1000°C, and hold for 3 hours to 10 hours to generate nano-metal fluorides inside the precursor material through a gas-phase reaction.

[0037] Among them, the fluorine-containing gas is any one of fluorine gas, nitrogen trifluoride, and carbon tetrafluoride; the flow rate of the gas introduced is 2 to 10 L / min.

[0038] Step 150: Introduce a mixed gas composed of a carbon source gas and a protective gas, and perform coating by chemical vapor deposition. The coating temperature is 600 to 1000°C, and the coating time is 1 to 12 h to obtain a graphite composite transition metal fluoride cathode material.

[0039] Among them, the carbon source gas is one or more of methane, acetylene, ethylene, and propylene; in the mixed gas, the volume ratio of the protective gas to the carbon source gas is 4:1 to 1:2, and more preferably 1:1 to 2:1.

[0040] The preparation method of the graphite composite transition metal fluoride cathode material provided by the embodiment of the present invention, compared with most of the existing technologies at present, the improvement of the transition metal fluoride composite material is only simply ball-milled and mixed or coated, which is likely to cause insufficient composite degree and lead to the shedding of transition metal fluoride particles from the graphite matrix during the charge and discharge process. In the present invention, transition metal sources such as iron, cobalt, and nickel are added to the graphite raw material, and cementite is formed during the carbonization process. Under the action of high temperature, the transition metal diffuses towards the center of the material, and finally nanoparticles containing transition metal are formed inside the graphite, and a ring-shaped graphite layer structure is formed around it. Under the further action of induction high temperature, through the gasification and removal of part of the transition metal, pore channels are formed in the outer graphite layer, and finally transition metal fluoride is generated through the fluorination reaction. The composite strength of the constructed graphite and transition metal fluoride is high, and the cycle process is stable. Compared with the amorphous carbon structure formed by the general carbon coating technology for cathode materials, the graphite outer layer formed by this process has more excellent electrical conductivity and compaction density. At the same time, the uniformly dispersed nano-transition metal fluoride prepared by using cementite and fluorination can reduce the expansion stress effect of the particles. In addition, the pore channels formed during the induction high temperature process further provide a buffer space, providing sufficient buffer space for the volume change of the subsequently formed transition metal fluoride and the charge and discharge process. The graphite structure in the fluoride graphite composite material of the present invention can significantly improve the conductivity of the transition metal fluoride cathode material, enhance the charge transfer path, thereby realizing rapid electron transfer and ion migration, reducing the internal stress of the electrode, and alleviating volume expansion; reducing the contact with the electrolyte, inhibiting the corrosion of the electrolyte to the active substance, enhancing the surface stability of the material, and improving the electrochemical stability.

[0041] In order to more clearly illustrate the purpose and advantages of the present invention, the present invention will be further described below in conjunction with embodiments. In addition, the embodiments described in the present invention are only partial embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention. In addition, it should be understood that these embodiments are only used for more detailed description and should not be construed as limiting the present invention in any form, that is, it is not intended to limit the protection scope of the present invention.

[0042] Example 1

[0043] This example provides a preparation method of a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0044] Dissolve 200 g of iron nitrate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0045] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and keep it for 48 hours, then discharge and crush and classify it to obtain 560 g of primary carbonized material;

[0046] Put 560 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, and discharge 530 g after keeping it for 2 hours;

[0047] Load 530 g of the material into a rotary furnace and introduce F 2 gas, heat it to 600 °C, control the gas flow rate at 2 L / min, and the reaction time at 5 h. Then heat it to 1000 °C and introduce a mixed gas composed of nitrogen and acetylene with a volume ratio of 2:1 for carbon coating for 4 hours. After discharging, the graphite composite transition metal fluoride cathode material is obtained. Figure 2 This is the transmission electron microscope (TEM) image of the graphite composite transition metal fluoride cathode material prepared in Example 1 of the present invention.

[0048] Example 2

[0049] This example provides a preparation method of a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0050] Dissolve 200 g of nickel sulfate in 1000 g of deionized water, mix it with 2000 g of needle coke evenly, and then dry it;

[0051] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and keep it for 48 hours, then discharge and crush and classify it to obtain 550 g of primary carbonized material;

[0052] Put 550 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, and discharge 525 g after keeping it for 2 hours;

[0053] Load 525 g of the material into a rotary furnace and introduce F 2 gas, heat it to 600 °C, control the gas flow rate at 2 L / min, and the reaction time at 5 h. Then heat it to 1000 °C and introduce a mixed gas composed of nitrogen and acetylene with a volume ratio of 2:1 for carbon coating for 4 hours. After discharging, the graphite composite transition metal fluoride cathode material is obtained.

[0054] Example 3

[0055] This example provides a preparation method of a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0056] Dissolve 200 g of cobalt sulfate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0057] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and keep it for 48 hours, then discharge and crush and classify it to obtain 550 g of primary carbonized material;

[0058] Put 550 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, keep it for 2 hours and then discharge 530 g;

[0059] Put 525 g of the material into a rotary furnace and introduce F 2 gas, heat it to 600 °C, control the gas flow rate to be 2 L / min, the reaction time to be 5 h, then heat it to 1000 °C, introduce a mixed gas composed of nitrogen and acetylene with a volume ratio of 2:1 for carbon coating for 4 hours, and the graphite composite transition metal fluoride cathode material is obtained after discharging.

[0060] Example 4

[0061] This example provides a preparation method of a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0062] Dissolve 200 g of iron nitrate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0063] Put the dried sample into an atmosphere furnace, heat it to 1600 °C under a nitrogen protection atmosphere and keep it for 10 hours, then discharge and crush and classify it to obtain 580 g of primary carbonized material;

[0064] Put 580 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, keep it for 2 hours and then discharge 552 g;

[0065] Put 552 g of the material into a rotary furnace and introduce F 2 gas, heat it to 600 °C, control the gas flow rate to be 2 L / min, the reaction time to be 5 h, then heat it to 1000 °C, introduce a mixed gas composed of nitrogen and acetylene with a volume ratio of 2:1 for carbon coating for 4 hours, and the graphite composite transition metal fluoride cathode material is obtained after discharging.

[0066] Example 5

[0067] This example provides a preparation method of a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0068] Dissolve 200 g of iron nitrate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0069] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and hold for 48 hours, then discharge and crush and classify it to obtain 560 g of primary carbonized material;

[0070] Put 560 g of the primary carbonized material into an induction furnace, heat it to 2500 °C at a rate of 10 °C / min under an argon atmosphere, hold for 2 hours and then discharge 515 g;

[0071] Load 515 g of the material into a rotary furnace and introduce F 2 gas, heat it to 600 °C, control the gas flow rate to be 2 L / min, the reaction time to be 5 h, then heat it to 1000 °C, introduce a mixed gas composed of nitrogen and acetylene with a volume ratio of 2:1 for carbon coating for 4 hours, and the graphite composite transition metal fluoride cathode material is obtained after discharging.

[0072] Example 6

[0073] This example provides a method for preparing a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0074] Dissolve 200 g of iron nitrate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0075] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and hold for 48 hours, then discharge and crush and classify it to obtain 560 g of primary carbonized material;

[0076] Put 560 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, hold for 2 hours and then discharge 530 g;

[0077] Load 530 g of the material into a rotary furnace and introduce F 2 gas, heat it to 600 °C, control the gas flow rate to be 2 L / min, the reaction time to be 5 h, then heat it to 1000 °C, introduce a mixed gas composed of nitrogen and methane with a volume ratio of 2:1 for carbon coating for 4 hours, and the graphite composite transition metal fluoride cathode material is obtained after discharging.

[0078] Example 7

[0079] This example provides a method for preparing a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0080] Dissolve 200 g of iron nitrate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0081] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and hold for 48 hours, then discharge and crush and classify it to obtain 560 g of primary carbonized material;

[0082] Put 560 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, hold for 2 hours and then discharge 530 g;

[0083] Load 530 g of the material into a rotary furnace, introduce nitrogen trifluoride gas, heat it to 800 °C, control the gas flow rate at 5 L / min, react for 3 h, then heat it to 1000 °C, introduce a mixed gas composed of nitrogen and acetylene with a volume ratio of 2:1 for carbon coating for 4 hours, and obtain the graphite composite transition metal fluoride cathode material after discharging.

[0084] Example 8

[0085] This example provides a preparation method of a graphite composite transition metal fluoride cathode material, and the specific preparation steps are as follows.

[0086] Dissolve 200 g of iron nitrate in 1000 g of deionized water, mix it evenly with 2000 g of needle coke, and then dry it;

[0087] Put the dried sample into an atmosphere furnace, heat it to 700 °C under a nitrogen protection atmosphere and hold for 48 hours, then discharge and crush and classify it to obtain 560 g of primary carbonized material;

[0088] Put 560 g of the primary carbonized material into an induction furnace, heat it to 1600 °C at a rate of 10 °C / min under an argon atmosphere, hold for 2 hours and then discharge 530 g;

[0089] Load 530 g of the material into a rotary furnace, introduce F 2 gas, heat it to 600 °C, control the gas flow rate at 2 L / min, react for 5 h, then heat it to 1000 °C, introduce a mixed gas composed of nitrogen and methane with a volume ratio of 2:1 for carbon coating for 12 hours, and obtain the graphite composite transition metal fluoride cathode material after discharging.

[0090] Comparative Example 1

[0091] This Comparative Example 1 is used to prepare comparative nano iron fluoride particles.

[0092] Dissolve 200 g of Fe 2 O 3The powder was immersed in HF solution and magnetically stirred for 24 hours. Then, the solution was slowly removed by heating at 80 °C to obtain a light yellow powder. The obtained powder was heated to 300 °C in an Ar atmosphere and held for 5 hours to remove the crystal water, obtaining highly crystalline FeF 3 , and then mixed with acetylene and ground in an N 2 atmosphere using a planetary ball mill. The main disk speed of the planetary ball mill was 60 r / min, the speed of the ball mill pot was 800 r / min, and the ball milling time was 2 hours. Nano iron fluoride particles for comparison were obtained.

[0093] Comparative Example 2

[0094] This Comparative Example 2 was used to prepare a graphitized composite carbon material containing nano iron fluoride for comparison.

[0095] 200 g of iron oxide particles were ball milled. The main disk speed of the planetary ball mill was 60 r / min, the speed of the ball mill pot was 800 r / min, and the ball milling time was 6 hours. Then, 500 g of asphalt was added and ball milled at a main disk speed of 60 r / min and a ball mill pot speed of 400 r / min for 2 hours.

[0096] The ball milled product was put into an atmosphere furnace, and F 2 gas was introduced and heated to 600 °C. The flow rate of F 2 gas was controlled at 0.5 L / min, the flow rate of nitrogen gas was 2 L / min, and the reaction time was 5 h. After the reaction ended, the F 2 gas was turned off, and the temperature was continued to be raised to 1200 °C and held for 6 h to obtain a graphite-like composite carbon material containing nano iron fluoride.

[0097] To verify the electrochemical performance of the graphite composite transition metal fluoride cathode material obtained in the examples of the present invention as a cathode material for lithium ion batteries, the materials prepared in each example and comparative example were used as the cathode active material, and after slurry preparation, electrode sheet preparation and battery assembly, relevant electrical performance tests were carried out as follows:

[0098] The above-prepared cathode active material, acetylene black, and polyvinylidene fluoride (PVDF) were weighed according to a mass ratio of 90∶5∶5, mixed evenly, N-methylpyrrolidone (NMP) solution was added, and stirred until the viscosity reached the requirements for coating. Then, the slurry was evenly coated on the aluminum foil using a coater. The electrode sheet was dried in a blast oven at 80 °C for 2 h and vacuum dried at 100 °C for 12 h. The electrode sheet was cut into circular pieces with a diameter of 12 mm, and the loading amount of the active material on each circular piece was about 2 - 3 mg / cm 2 , and the assembly of the simulated battery was carried out in a glove box containing a high-purity Ar atmosphere. The prepared electrode sheet was used as the cathode, the lithium sheet was used as the anode, Celgard 2500 was used as the separator, and the concentration of LiPF 6Using ethylene carbonate (EC) / dimethyl carbonate (DMC) organic mixture (v:v = 1:1) as the electrolyte, the assembly of CR2032 coin cells was completed entirely inside an argon-filled glove box. The cells were allowed to stand for 10 h and then, at room temperature, electrochemical tests were carried out on a BlueTEC battery test system (CT2001A). The cells were cycled once at 0.1C in the voltage range of 3.0 - 4.4V to test the initial discharge specific capacity and the initial efficiency. Then, they were cycled at 0.5C, and the cycle capacity retention rates at 50 weeks, 100 weeks, and 200 weeks were tested at room temperature of 25°C and high temperature of 45°C respectively. The test data are recorded in Table 1.

[0099]

[0100] Table 1

[0101] From the data comparison in Table 1, it can be seen that in Comparative Example 1, the initial discharge specific capacity of the iron fluoride material is relatively low, and with the volume expansion during charge and discharge, the capacity rapidly decays during the cycling process. In Comparative Example 2, the pitch and iron oxide materials were compounded by ball milling followed by fluorination sintering. The iron fluoride particles could not fully ensure uniform embedding in the carbon substrate, and some iron fluoride particles were exposed. At high temperature cycling, the electrolyte reacted with the iron fluoride material, resulting in the attenuation of the cycling performance. However, for the iron fluoride graphite composite material prepared in the examples of the present invention, in the first step, the liquid phase was used to ensure the uniform distribution of metal ions in the matrix, and the nano-transition metal particles formed by cementite were utilized. Then, the size of the nano-metal particles was reduced by an induction furnace to leave buffer pores and form voids, facilitating the infiltration of the later fluorine-containing gas and the formation of transition metal iron fluoride with the nano-metal particles. The transition metal iron fluoride graphite composite material constructed in this way has excellent cycle stability and rate performance.

[0102] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a graphite composite transition metal fluoride cathode material, characterized in that, the preparation method comprises: dissolving a transition metal compound in a solvent, adding the graphite raw material according to the mass ratio of the transition metal compound to the graphite raw material being 1:10 to 1:100, and performing mixing and stirring to obtain a mixture containing transition metal ions; placing the mixture in a heat treatment device, heat-treating at 700°C to 1600°C for 10 hours to 48 hours in a protective atmosphere environment, so that the mixture forms a material with a cementite structure during the heat treatment process, and as the heat treatment progresses, the transition metal ions diffuse into the interior of the material to form an onion carbon layer structure with a ring-shaped graphite carbon layer on the outer layer of the material; pulverizing and classifying the heat-treated material to obtain a primary carbonized material; placing the primary carbonized material in an induction furnace, heating to 1600°C to 2500°C at a rate of 1°C / min to 10°C / min in a protective atmosphere environment, and holding for 1 hour to 2 hours, so that the transition metal elements inside the primary carbonized material escape through the pores of the material to obtain a precursor material; placing the precursor material in a rotary furnace, introducing a fluorine-containing gas, and heating to 400°C to 1000°C, holding for 3 hours to 10 hours, and generating nano metal fluoride inside the precursor material through a gas-phase reaction; then introducing a mixed gas composed of a carbon source gas and a protective gas, and performing coating by chemical vapor deposition, the coating temperature is 600 to 1000°C, and the coating time is 1 to 12h to obtain the graphite composite transition metal fluoride cathode material.

2. The preparation method according to claim 1, characterized in that, the transition metal compound includes: one or more of an iron-containing compound, a cobalt-containing compound, a nickel-containing compound, a manganese-containing compound, a copper-containing compound, a zinc-containing compound, a niobium-containing compound, and a titanium-containing compound; wherein, the compound refers to one or more of a sulfate, a nitrate, a carbonate, and a chloride; the petroleum raw material includes: needle coke or petroleum coke; the mass ratio of the transition metal compound to the graphite raw material is 1:50 to 1:

70.

3. The preparation method according to claim 1, characterized in that, the fluorine-containing gas is any one of fluorine gas, nitrogen trifluoride, and carbon tetrafluoride; the flow rate of the gas introduced is 2 to 10 L / min.

4. The preparation method according to claim 1, characterized in that, the protective atmosphere environment is an environment into which the protective gas is introduced, and the protective gas includes: nitrogen or argon.

5. The preparation method according to claim 1, characterized in that, the carbon source gas is one or more of methane, acetylene, ethylene, and propylene; the mixing volume ratio of the protective gas and the carbon source gas is 4:1 to 1:

2.

6. The preparation method according to claim 5, characterized in that, the mixing volume ratio of the protective gas and the carbon source gas is 1:1 to 2:1; the coating time is 4 to 8h.

7. The preparation method according to claim 1, characterized in that, the solvent includes water or a polar organic solvent.

8. A graphite composite transition metal fluoride cathode material prepared by the preparation method according to any one of claims 1-7 above.

9. A lithium-ion battery cathode, characterized in that, the lithium-ion battery cathode comprises the graphite composite transition metal fluoride cathode material according to claim 8 above.

10. A lithium-ion battery, characterized in that, the lithium-ion battery comprises the lithium-ion battery cathode according to claim 9 above.

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