Graphite composite material, preparation method thereof and lithium ion battery

Abstract

The embodiment of the invention discloses a graphite composite material, a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: step S1, preparing carbon nanotube doped porous graphite; s2, sintering a mixed raw material containing a titanium source, a niobium source, the soft template and a hard carbon source to prepare a porous titanium niobate hard carbon material; s3, performing physical vapor deposition treatment by taking the porous titanium niobate hard carbon material as a target material and taking the carbon nanotube doped porous graphite as a matrix to prepare a graphite and titanium niobate-hard carbon composite material; s4, the graphite and titanium niobate-hard carbon composite material is subjected to CVD carbon deposition treatment after being subjected to heat preservation in an atmosphere containing lithium hydride, and a porous titanium lithium niobate coated graphite composite material is prepared; and S5, mixing the porous titanium lithium niobate coated graphite composite material with an organic solvent of a lithium phosphate derivative, and carrying out spray drying to obtain the graphite composite material. According to the embodiment of the invention, the low-temperature, fast-charge and cycle performance of the prepared material can be remarkably improved.

Description

Technical Field

[0001] The invention relates to the field of material preparation, and in particular to a graphite composite material and a preparation method thereof, and a lithium ion battery. Background Art

[0002] As the market's requirements for fast charging and low-temperature performance of lithium-ion batteries increase, the negative electrode materials used are required to have excellent fast charging performance and good low-temperature performance. The main factors affecting the fast charging and low-temperature performance of graphite negative electrode materials are: particle size, carbon coating amount, different coating methods and types of coating agents. The fast-charging graphite currently on the market mainly coats 2-3% of soft carbon or hard carbon on the surface of small-sized graphite particles to improve the fast charging and low-temperature performance of the material. However, there are defects such as deviation in the electronic conductivity of the coating layer material and slow ion transmission rate, which have limited improvement in the fast charging and low-temperature performance of the material. Summary of the invention

[0003] Therefore, in order to overcome at least some of the defects and shortcomings in the prior art, the embodiments of the present invention provide a graphite composite material and a preparation method thereof and a lithium-ion battery that can significantly improve low temperature, fast charging and cycle performance.

[0004] The present invention provides a method for preparing a graphite composite material, comprising the following steps:

[0005] Step S1, preparing carbon nanotube-doped porous graphite;

[0006] Step S2, sintering a mixed raw material including a titanium source, a niobium source, a soft template, and a hard carbon source to obtain a porous titanium niobate hard carbon material;

[0007] Step S3, using the porous titanium niobate hard carbon material as a target material and the carbon nanotube-doped porous graphite as a matrix to perform physical vapor deposition treatment to obtain a graphite@titanium niobate-hard carbon composite material;

[0008] Step S4, heat-preserving the graphite@titanium niobate-hard carbon composite material in an atmosphere containing lithium hydride and then subjecting it to CVD carbon deposition treatment to obtain a porous lithium titanium niobate-coated graphite composite material;

[0009] Step S5, mixing the porous lithium titanium niobate-coated graphite composite material with an organic solvent of a lithium phosphate derivative and spray-drying the mixture to obtain the graphite composite material.

[0010] In some embodiments, the sintering temperature in step S2 is 1200-1500°C, and the sintering time is 1-6h; and / or, the mass ratio of the titanium source, the niobium source, the soft template and the hard carbon source in step S2 is 10-30:10-30:5-10:100; in step S2, the titanium source includes one or more of titanium-containing oxides, organic esters, and inorganic salts; and / or, the niobium source includes one or more of niobium-containing oxides, hydroxides and salts; and / or, the soft template includes one or more of anionic surfactants and neutral surfactants; and / or, the hard carbon source is one or more of glucose, sucrose, maltose, polyvinyl alcohol, and polyacrylonitrile.

[0011] In some embodiments, the mass ratio of the graphite@titanium niobate-hard carbon composite material and the lithium hydride in step S4 is 100:5-10; and / or, in step S4, the carbon source of the CVD carbon precipitation treatment is one or more of hydrocarbons, alcohols, aldehydes, ketones, phenols, and esters with a carbon number of less than 8.

[0012] In some embodiments, the mass ratio of the lithium phosphate derivative, the porous lithium titanium niobate-coated graphite composite material and the organic solvent in step S5 is 40-70:1000:5000-10000; and / or, in step S5, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, and ethyl propionate; and / or, the lithium phosphate derivative is one or more of lithium difluorophosphate, lithium hexafluorophosphate, and lithium difluorooxalophosphate.

[0013] In some embodiments, step S1 specifically includes:

[0014] S11, dissolving a conductive polymer in an organic solvent to prepare a solution, adding a catalyst, a coupling agent, porous graphite and an oxidant to the solution, uniformly dispersing the solution, reacting the solution and filtering the solution to obtain a filter residue;

[0015] S12, carbonizing the filtered residue to obtain catalyst-doped porous graphite;

[0016] S13, reacting the catalyst-doped porous graphite with a carbon source gas in a vapor deposition manner to obtain the carbon nanotube-doped porous graphite.

[0017] In some embodiments, in step S1, the mass ratio of the porous graphite, the catalyst, the conductive polymer, the oxidant and the coupling agent is 100:1-5:10-30:5-20:1-5; and / or, the concentration of the solution in step S11 is 1-10wt%.

[0018] In some embodiments, the catalyst in step S1 is any one or more of chlorides and nitrates of iron, cobalt, and nickel; and / or the conductive polymer is any one or more of thiophene, dopamine, aniline, and pyrrole; and / or the oxidant is one or more of persulfate, perchlorate, or hydrogen peroxide, with a concentration of 10 wt%; and / or the coupling agent is one or more of 2,3-epoxypropylpropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and 3-trifluoroacetyl-D-camphor; and / or the carbon source gas is one or more of methane, ethane, ethylene, acetylene, and propyne.

[0019] An embodiment of the present invention further provides a graphite composite material, which is prepared by the above-mentioned preparation method.

[0020] In some embodiments, the graphite composite material presents a core-shell structure, the core is carbon nanotube-doped porous graphite, the middle layer is porous lithium titanium niobate, and the outer shell is a lithium phosphate derivative; calculated based on the mass ratio of the graphite composite material as 100%, the mass ratio of the middle layer is 1 to 5wt%, and the mass ratio of the outer shell is 1 to 5wt%.

[0021] The present embodiment also provides a lithium-ion battery, comprising the aforementioned graphite composite material.

[0022] It can be seen from the above that the above technical solution has at least one or more of the following beneficial effects: Graphite@titanium niobate-hard carbon composite material is obtained based on vapor deposition. And lithium is filled by vapor deposition in step S4, and combined with carbon precipitation treatment, titanium niobate and lithium can form titanium lithium niobate compounds to obtain high transmission rate and reduce defects, which can significantly improve the low temperature and fast charging performance of graphite composite materials. And by coating lithium phosphate derivatives by spray drying in step S5, the high solvation ability between lithium phosphate and electrolyte can be used to improve the lithium ion insertion and extraction rate and low temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The specific implementation modes of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Figure 1 A schematic flow chart of a method for preparing a graphite composite material provided in an embodiment of the present invention.

[0025] Figure 2 This is the SEM image of the graphite composite material prepared in Example 1. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0029] It should also be noted that the division of multiple embodiments in the present invention is only for the convenience of description and should not constitute a special limitation. The features in various embodiments can be combined and referenced to each other without contradiction.

[0030] Reference Figure 1 The present invention provides a method for preparing a graphite composite material, comprising the following steps:

[0031] Step S1, preparing carbon nanotube-doped porous graphite;

[0032] Step S2, sintering a mixed raw material including a titanium source, a niobium source, a soft template, and a hard carbon source to obtain a porous titanium niobate hard carbon material;

[0033] Step S3, using the porous titanium niobate hard carbon material as a target material and the carbon nanotube-doped porous graphite as a matrix to perform physical vapor deposition treatment to obtain a graphite@titanium niobate-hard carbon composite material;

[0034] Step S4, heat-preserving the graphite@titanium niobate-hard carbon composite material in an atmosphere containing lithium hydride and then subjecting it to CVD carbon deposition treatment to obtain a porous lithium titanium niobate-coated graphite composite material;

[0035] Step S5, mixing the porous lithium titanium niobate-coated graphite composite material with an organic solvent of a lithium phosphate derivative and spray-drying the mixture to obtain the graphite composite material.

[0036] In the above embodiment of the present invention, step S3 is based on vapor deposition to prepare graphite @ titanium niobate-hard carbon composite material. And in step S4, lithium is filled by vapor deposition, and combined with carbon precipitation treatment, titanium niobate and lithium can form lithium titanium niobate compound to improve the conduction rate of lithium ions and reduce defects, which can significantly improve the low temperature and fast charging performance of graphite composite materials. And the vapor deposition method in step S4 has the effects of more complete reaction, higher efficiency, higher material density, etc. compared with the liquid phase reaction method, and the thickness of the generated lithium titanium niobate can be more accurately controlled. And by coating the lithium phosphate derivative by spray drying in step S5, the high solvation ability between lithium phosphate and the electrolyte can be used to improve the lithium ion insertion and extraction rate and low temperature performance.

[0037] In some specific embodiments, step S1 specifically includes:

[0038] S11, dissolving a conductive polymer in an organic solvent to prepare a solution, adding a catalyst, a coupling agent, porous graphite and an oxidant to the solution, uniformly dispersing the solution, reacting the solution and filtering the solution to obtain a filter residue;

[0039] S12, carbonizing the filtered residue to obtain catalyst-doped porous graphite;

[0040] S13, reacting the catalyst-doped porous graphite with a carbon source gas in a vapor deposition manner to obtain the carbon nanotube-doped porous graphite.

[0041] In step S11, the catalyst, coupling agent and porous graphite are added to the solution and then dispersed evenly, and the oxidant is added dropwise and dispersed evenly, and the mixture is reacted at 0-15° C. for 1-6 hours and then filtered. In step S12, the filter residue is carbonized at 1000-1400° C. for 2-12 hours. In step S13, the catalyst-doped porous graphite is transferred to a tubular furnace, heated to 800-1000° C. by a vapor deposition method, and a carbon source gas is introduced at a flow rate of 100-500 SCCM for 30-300 minutes.

[0042] Among them, the coupling agent in steps S11 and S12 is conducive to forming a porous structure, and the porous carbon structure is generated by carbonization and decomposition of the organic polymer, which has the characteristics of high isotropy and low expansion. By doping the catalyst and growing carbon nanotubes in a carbon source atmosphere in step S13, the electronic conductivity of the porous core can be improved, and the rate performance of the core can be improved.

[0043] Specifically, in step S1, the mass ratio of the porous graphite, the catalyst, the conductive polymer, the oxidant and the coupling agent is 100: 1 to 5: 10 to 30: 5 to 20: 1 to 5. In step S11, the concentration of the solution is 1 to 10 wt%.

[0044] Specifically, the catalyst in step S1 is any one or more of chlorides and nitrates of iron, cobalt, and nickel. The surface of the catalyst such as iron has abundant active sites, which can adsorb and react reactants, thereby promoting the reaction and serving as a basis for growing carbon nanotubes in the subsequent step S13. The conductive polymer is any one or more of thiophene, dopamine, aniline, and pyrrole. The oxidant is one or more of persulfate, perchlorate, or hydrogen peroxide, with a concentration of 10wt%. The coupling agent is one or more of 2,3-epoxypropylpropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and 3-trifluoroacetyl-D-camphor. The carbon source gas is one or more of methane, ethane, ethylene, acetylene, and propyne.

[0045] Specifically, the porous graphite in step S1 can be prepared by mixing artificial graphite, an organic pore-forming agent and an imidazole crosslinking agent. More specifically, the method for preparing a graphite composite material provided in an embodiment of the present invention also includes step S0, preparing porous graphite. Step S0 is specifically: 100 parts of artificial graphite are mixed evenly with 5 to 10 parts of an organic pore-forming agent and 5 to 10 parts of an imidazole crosslinking agent, heated to 600 to 1000°C for carbonization for 1 to 6 hours, and then heated to 2800 to 3200°C for graphitization for 6 to 24 hours to obtain porous graphite.

[0046] In step S0, the imidazole crosslinking agent is one or more of 2-dimethylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-methyl-4-ethylimidazole, and 1-vinyl-1H-imidazole. The organic pore-forming agent is one or more of polystyrene, polyethylene glycol, polyvinyl chloride, polyoxymethylene, epoxy resin, polyglycolic acid, and lignin.

[0047] Specifically, the sintering temperature in step S2 is 1200-1500°C, and the sintering time is 1-6 hours. At this sintering temperature, the titanium source and the niobium source can react more fully, preventing the problem of high material impedance caused by residual impurities in the hard carbon source and residual hydrogen that is not fully volatilized due to low temperature. It can also avoid problems such as waste of energy and poor material structure stability caused by too high temperature.

[0048] Specifically, the mass ratio of the titanium source, the niobium source, the soft template and the hard carbon source in step S2 is 10-30:10-30:5-10:100. This mass ratio can ensure that the niobium source and the titanium source are sufficient to effectively improve the fast charging performance, and can also avoid the ratio of the niobium source and the titanium source being too high to reduce the specific capacity and compaction density of the material. Maintaining the soft template at an appropriate ratio can ensure that more pores are formed to increase the specific capacity of the material, thereby improving the diffusion coefficient of the material, and can also avoid the soft template ratio being too high to reduce the compaction density of the material and increase the powder resistivity.

[0049] In step S2, the titanium source includes one or more of titanium-containing oxides, organic esters, and inorganic salts. Further, the titanium source is selected from one or more of titanium tetraisopropoxide, titanium tetrafluoride, titanium sulfate, titanium tetrachloride, and butyl titanate.

[0050] The niobium source includes one or more of niobium-containing oxides, hydroxides and salts, and is further selected from one or more of niobium hydroxide, niobium oxalate or niobium pentoxide.

[0051] The soft template includes one or more of anionic surfactants and neutral surfactants, and is further selected from one or more of hexadecyltrimethylammonium bromide and polypropylene glycol and ethylene oxide addition polymers (polyethers).

[0052] The hard carbon source is a precursor material capable of forming hard carbon, such as one or more of glucose, sucrose, maltose, polyvinyl alcohol, and polyacrylonitrile.

[0053] The mixed raw material in step S2 can be obtained by solid phase from the titanium source, the niobium source, the soft template and the hard carbon source, or can be obtained by mixing and then desolvating.

[0054] In some embodiments, the vacuum degree during the physical vapor deposition process in step S3 is 1×10 -5 ~10×10 -4 pa, the target current is 15-25A, the gas flow rate of the protective gas is 100-200sccm, the loading bias is 50-150V, and the physical vapor deposition time is 10-60min.

[0055] Specifically, in step S4, the graphite@titanium niobate-hard carbon composite material and lithium hydride are placed in a vacuum furnace, and the lithium hydride is volatilized under vacuum at a temperature of 500-800° C., and metallic lithium is filled and deposited in the pore structure of the graphite@titanium niobate-hard carbon composite material.

[0056] In some embodiments, the mass ratio of the graphite@titanium niobate-hard carbon composite material to the lithium hydride in step S4 is 100:5-10; in step S4, the carbon source for the CVD carbon precipitation treatment is one or more of hydrocarbons, alcohols, aldehydes, ketones, phenols, and esters with a carbon number of less than 8. Preferably, it is one or more of alkanes, alkenes, and alkynes with a carbon number of less than 6. More preferably, it is one or more of methane, ethane, ethylene, and acetylene.

[0057] The temperature of the CVD carbon deposition treatment in step S4 is 600-1000° C. The time of the CVD carbon deposition treatment is 1-6.

[0058] In some embodiments, the mass ratio of the lithium phosphate derivative, the porous lithium titanium niobate-coated graphite composite material and the organic solvent in step S5 is 40-70:1000:5000-10000. The above ratio can ensure that the lithium phosphate derivative is fully dissolved, and too low a proportion of the lithium phosphate derivative has no obvious effect on improving the low-temperature performance of the material, and can prevent too high a proportion of the lithium phosphate derivative from reducing the high-temperature performance of the material.

[0059] Specifically, in step S5, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, and ethyl propionate. The lithium phosphate derivative is one or more of lithium difluorophosphate, lithium hexafluorophosphate, and lithium difluorooxalate phosphate.

[0060] Specifically, in step S5, the inlet temperature of the spray drying is 180° C., the outlet temperature is 80° C., and the flow rate is 0.1 kg / h.

[0061] The embodiment of the present invention further provides a graphite composite material, which can be prepared by the preparation method in the above embodiment.

[0062] Specifically, an embodiment of the present invention provides a graphite composite material, wherein the graphite composite material presents a core-shell structure, wherein the core is carbon nanotube-doped porous graphite, the middle layer is porous lithium titanium niobate, and the outer shell is a lithium phosphate derivative; calculated based on the mass ratio of the graphite composite material of 100%, the mass ratio of the middle layer is 1-5wt%, and the mass ratio of the outer shell is 1-5wt%. The above-mentioned shell ratio range can ensure that the lithium phosphate derivative shell significantly improves the fast charging performance and low temperature performance of the material, and the specific capacity of the lithium phosphate derivative shell itself is low, and the above-mentioned ratio can avoid the energy density of the graphite composite material being reduced due to the shell ratio being too large.

[0063] The embodiment of the present invention further provides a lithium-ion battery, comprising the above-mentioned graphite composite material. The lithium-ion battery can be a fast-charge lithium-ion battery.

[0064] The graphite composite material and the preparation method thereof provided in the embodiments of the present invention are exemplified below in combination with Examples 1 to 3 and Comparative Examples 1 to 4 and related experiments.

[0065] Example 1

[0066] The preparation method of porous graphite is:

[0067] 100 g of artificial graphite, 8 g of polystyrene, and 8 g of 2-dimethylimidazole were mixed evenly, then heated to 750° C. for carbonization for 3 h, and then heated to 3000° C. for graphitization for 12 h to obtain porous graphite.

[0068] The preparation method of the graphite composite material comprises the following steps:

[0069] Step S1:

[0070] 20g of thiophene was dissolved in 400g of N-methylpyrrolidone to prepare a 5wt% solution, and then 3g of ferric nitrate, 3g of 2,3-epoxypropylpropyltrimethoxysilane, and 100g of porous graphite were added and dispersed evenly, and then 10g of ammonium persulfate solution (concentration 10wt%) was added dropwise to disperse evenly, and the mixture was reacted at a temperature of 4°C for 3h, filtered, and the obtained filter residue was carbonized at 1200°C for 6h to obtain catalyst-doped porous graphite; the obtained material was then transferred to a tubular furnace, and then ethylene gas was introduced by vapor deposition method at a flow rate of 300SCCM for 120min to obtain carbon nanotube-doped porous graphite;

[0071] Step S2:

[0072] 20 g of hexadecyltrimethylammonium bromide, 20 g of titanium tetraisopropoxide and 8 g of niobium oxalate were added to 500 g (20 wt%) of glucose in ethyl acetate solution, dispersed evenly, spray dried, and the obtained material was sintered at 1300° C. for 3 h in a nitrogen atmosphere to obtain a porous titanium niobate hard carbon material;

[0073] Step S3:

[0074] By physical vapor deposition, porous titanium niobate hard carbon material was used as the target material, carbon nanotubes doped porous graphite was used as the matrix, and the vacuum degree was 5×10 -5 pa, the target current was 20A, and argon protective gas was introduced to maintain the vacuum degree at 5×10 -4 pa, gas flow rate 150sccm, bias voltage 100V, deposition 30min, depositing porous titanium niobate composite on the surface of carbon nanotube-doped porous graphite to obtain porous titanium niobate composite coated graphite material;

[0075] Step S4:

[0076] 100g of porous titanium niobate composite coated graphite material is transferred to a vacuum furnace and spread flat in an intermediate layer mortar. Then, 5g of lithium hydride is spread flat on the bottom by atomization method, and the vacuum is 0.01MPa. The temperature is heated to 500°C to vaporize the lithium hydride and deposit it in the pores of the porous titanium niobate composite coated graphite material to obtain an intermediate material. Then, the intermediate material is transferred to a tubular furnace, heated to 600°C, and ethylene gas is introduced. It is deposited for 6h at a flow rate of 100ml / min (CVD carbon deposition treatment) to obtain a lithium titanium niobate coated graphite composite material.

[0077] Step S5:

[0078] 50 g of lithium difluorophosphate was added to 7500 g of ethylene carbonate and dispersed evenly, and then 1000 g of lithium titanium niobate-coated graphite composite material was added and dispersed evenly, and spray-dried (inlet temperature 180° C., outlet temperature 80° C., flow rate 0.1 kg / h, 1 h) to obtain a graphite composite material.

[0079] Example 2

[0080] Preparation method of porous graphite:

[0081] 100 g of artificial graphite, 5 g of polyethylene glycol, and 5 g of 2-ethylimidazole were mixed evenly, then heated to 600° C. for carbonization for 6 h, and then heated to 2800° C. for graphitization for 24 h to obtain porous graphite.

[0082] The preparation method of the graphite composite material comprises the following steps:

[0083] Step S1:

[0084] 10g of dopamine was dissolved in 1000g of N-methylpyrrolidone to prepare a 1wt% solution, and then 1g of nickel nitrate, 1g of γ-methacryloxypropyltrimethoxysilane and 100g of porous graphite were added and dispersed evenly, and then 5g of sodium perchlorate solution (concentration 10wt%) was added dropwise and dispersed evenly, and reacted at a temperature of 0°C for 6h, filtered, and the obtained filter residue was carbonized at 1000°C for 12h to obtain catalyst-doped porous graphite; then the obtained material was transferred to a tubular furnace, and then acetylene gas was introduced by vapor deposition method at a flow rate of 100SCCM for 300min to obtain carbon nanotube-doped porous graphite;

[0085] Step S2:

[0086] 10 g of polypropylene glycol, 10 g of titanium tetrafluoride and 5 g of niobium hydroxide were added to 1000 g (10 wt%) of sucrose in ethyl acetate solution, dispersed evenly, spray dried, and then the obtained material was sintered at a temperature of 1200° C. for 6 h in a nitrogen atmosphere to obtain a porous titanium niobate hard carbon material;

[0087] Step S3:

[0088] The porous titanium niobate hard carbon material was used as the target material by physical vapor deposition, and the carbon nanotube-doped porous graphite was used as the matrix. The vacuum degree was 1×10 -5 pa, the target current was 15A, and argon protective gas was introduced to maintain the vacuum degree at 1×10 - 4 pa, gas flow rate 100 sccm, bias voltage 50 V, deposition 60 min, depositing porous titanium niobate composite on the surface of carbon nanotube-doped porous graphite to obtain porous titanium niobate composite coated graphite material;

[0089] Step S4:

[0090] 100 g of porous titanium niobate composite coated graphite material was transferred to a vacuum furnace and spread flat in an intermediate layer mortar. Then, 5 g of lithium hydride was spread flat on the bottom by atomization method, and the vacuum was 0.01 MPa. The temperature was heated to 500°C to vaporize the lithium hydride and deposit it in the pores of the porous titanium niobate composite coated graphite material to obtain an intermediate material. Then, the intermediate material was transferred to a tubular furnace, heated to 600°C, and ethylene gas was introduced. The material was deposited for 6 hours at a flow rate of 100 ml / min to obtain a lithium titanium niobate coated graphite composite material.

[0091] Step S5:

[0092] 40 g of lithium hexafluorophosphate was added to 5000 g of propylene carbonate and dispersed evenly, and then 1000 g of lithium titanium niobate-coated graphite composite material was added and dispersed evenly, and spray-dried (inlet temperature 180° C., outlet temperature 80° C., flow rate 0.1 kg / h, 1 h) to obtain a graphite composite material.

[0093] Example 3

[0094] Preparation method of porous graphite:

[0095] 100 g of artificial graphite, 10 g of polyvinyl chloride, and 10 g of 2-ethyl-4-methylimidazole were mixed evenly, then heated to 1000° C. for carbonization for 1 h, and then heated to 3200° C. for graphitization for 6 h to obtain porous graphite.

[0096] The preparation method of the graphite composite material comprises the following steps:

[0097] Step S1:

[0098] 10g of pyrrole was dissolved in 100g of N-methylpyrrolidone to prepare a 10wt% solution, and then 5g of cobalt nitrate, 5g of γ-methacryloxypropyltrimethoxysilane and 100g of porous graphite were added and dispersed evenly, and then 20g of hydrogen peroxide oxidant was added and dispersed evenly, and the mixture was reacted at a temperature of 15°C for 1h, filtered, and the obtained filter residue was carbonized at 1400°C for 2h to obtain catalyst-doped porous graphite; the obtained material was then transferred to a tubular furnace, and then methane gas was introduced by vapor deposition method at a temperature of 1000°C and introduced at a flow rate of 500SCCM for 30min to obtain carbon nanotube-doped porous graphite;

[0099] Step S2:

[0100] 30 g of polypropylene glycol and ethylene oxide addition polymer (polyether), 30 g of titanium tetrachloride, and 10 g of niobium pentoxide were added to 333 g (30 wt%) of maltose in ethyl acetate solution, dispersed evenly, spray dried, and then the obtained material was sintered at a temperature of 1500° C. for 1 h in a nitrogen atmosphere to obtain a porous titanium niobate hard carbon material;

[0101] Step S3:

[0102] By physical vapor deposition, porous titanium niobate hard carbon material is used as the target material, graphite is used as the substrate, and the vacuum degree is 10×10 -5 pa, the target current was 25A, and argon protective gas was introduced to maintain the vacuum degree at 10×10 -4 pa, gas flow rate 200sccm, bias voltage 150V, deposition 10min, depositing porous titanium niobate composite on the graphite surface to obtain porous titanium niobate composite coated graphite material;

[0103] Step S4:

[0104] 100 g of porous titanium niobate composite coated graphite material was transferred to a vacuum furnace and spread flat in an intermediate layer mortar. Then, 10 g of lithium hydride was spread flat on the bottom by atomization method, and vacuum was drawn to 0.1 MPa. The temperature was heated to 800°C to vaporize the lithium hydride and deposit it in the pores of the porous titanium niobate composite coated graphite material to obtain an intermediate material. Then, the intermediate material was transferred to a tubular furnace, heated to 1000°C, and ethane gas was introduced. The material was deposited for 6 hours at a flow rate of 100 ml / min to obtain a lithium titanium niobate coated graphite composite material.

[0105] Step S5:

[0106] 70g of lithium difluorooxalate phosphate was added to 10000g of dimethyl carbonate and dispersed evenly, then 1000g of lithium titanium niobate coated graphite composite material was added and dispersed evenly, and spray dried (inlet temperature 180°C, outlet temperature 80°C, flow rate 0.1kg / h, 1h) to obtain a graphite composite material. Comparative Example 1:

[0107] Compared with Example 1, the only difference is that conventional artificial graphite is used to replace the carbon nanotube-doped artificial graphite in step S1, and the rest is the same as Example 1.

[0108] Comparative Example 2:

[0109] Compared with Example 1, the only difference is that in step S2, titanium tetraisopropoxide and niobium oxalate are not added, and the rest is the same as Example 1.

[0110] Comparative Example 3:

[0111] Compared with Example 1, the only difference is that lithium hydride is not added in step S4, and the rest is the same as Example 1.

[0112] Comparative Example 4:

[0113] The difference from Example 1 is that the outer layer is not coated with lithium difluorophosphate, and the rest is the same as Example 1.

[0114] (1) SEM test

[0115] The graphite composite material prepared in Example 1 was subjected to SEM testing, and the results were as follows: Figure 2 As shown. Figure 2 It can be seen that the material presents a secondary particle structure with a particle size between 8-12 μm.

[0116] (2) Physical and chemical properties test

[0117] The powder resistivity and specific surface area of ​​the graphite composite negative electrode materials in Examples 1-3 and Comparative Examples 1-4 were tested according to the test method in the standard GB / T-24533-2019 "Graphite Negative Electrode Materials for Lithium Ion Batteries". The OI value of the powder material was tested by XRD; the diffusion coefficient was tested by GITT, and the interlayer spacing D002 of the coating material was tested by XRD. The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] It can be seen from Table 1 that the diffusion coefficient and powder resistivity of the graphite composite materials prepared in Examples 1-3 are significantly better than those in Comparative Examples 1-4. The reason is that the material core is doped with carbon nanotubes and the outer coating of lithium phosphate improves the electronic conductivity and ion diffusion coefficient of the material.

[0122] Among them, except that the specific surface area of ​​Example 3 is slightly lower than that of Example 1 and Example 2, other parameters are better than those of Example 1 and Example 2, especially the resistivity is significantly better than that of Example 1 and Example 2. The reason is that the content of cobalt nitrate catalyst in step S3 of Example 3 is good, and the amount of carbon nanotubes grown as a matrix is ​​large, which can reduce the powder resistivity. In addition, more lithium phosphate is doped in the graphite composite material to improve the diffusion coefficient of lithium ions. The high sintering temperature causes the specific surface area of ​​the material to be reduced.

[0123] According to the results of Example 1 compared with those of Comparative Example 1, the powder resistivity and diffusion coefficient are better. The reason is that in Example 1, carbon nanotubes are doped in the porous graphite, and the high specific surface area and high electronic conductivity of the carbon nanotubes themselves are utilized to reduce the powder resistivity and the high specific surface area of ​​the porous graphite, thereby improving the diffusion coefficient during the charge and discharge process.

[0124] According to the results of Example 1 compared with those of Comparative Example 2, the interlayer spacing D002 has a significant difference. The reason is that titanium niobate has a higher interlayer spacing, while the interlayer spacing of graphite is smaller. In Comparative Example 2, no titanium niobate coating layer is formed, and the interlayer spacing is smaller.

[0125] (3) Button battery test

[0126] The graphite composite materials prepared in Examples 1-3 and the graphite composite negative electrode materials in Comparative Examples 1-4 were assembled into button batteries according to the following methods:

[0127] The graphite composite negative electrode materials prepared in each case were used as negative electrodes (formula: negative electrode: CMC: SBR: H 2 O=96:1.5:2.5:250), and assembled into button cells with lithium sheets, electrolyte and diaphragm in a glove box with argon and water content less than 0.1ppm. The diaphragm is celegard 2400; the electrolyte is LiPF 6 solution, electrolyte, LiPF 6 The concentration is 1 mol / L, and the solvent is a mixed solution obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DMC) in a weight ratio of 1:1.

[0128] The button batteries were tested for their performance using a blue battery tester. The test conditions were: 0.1C rate charge and discharge, voltage range 0.005-2V, and stop after 3 cycles. At room temperature, the first discharge capacity under 1C was tested. At the same time, the specific capacity at 0.1C at -20°C was tested, and the low temperature capacity retention rate and cycle performance (25±3°C,

[0129] 0.2C / 0.2C, 100 cycles) and its normal temperature charging DCR (50% SOC). The test results are shown in Table 2.

[0130] Table 2

[0131]

[0132]

[0133] It can be seen from Table 2 that the button cells made of the graphite composite materials of Examples 1-3 have significantly higher discharge specific capacity, initial efficiency, and low temperature retention rate than those of Comparative Examples 1-4. The reason is that the graphite composite materials of Examples 1-3 have excellent diffusion coefficients and large interlayer spacing, which improve cycle performance and reduce DCR, thereby improving initial efficiency.

[0134] (4) Soft-pack battery performance test

[0135] The graphite composite materials of Examples 1-3 and Comparative Examples 1-4 were used as negative electrode active materials to form negative electrodes (negative electrode active materials, CMC and conductive carbon black in a weight ratio of 9:0.5:0.5), and the positive electrode active materials were ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ) to form a positive electrode (positive electrode active material, PVDF and conductive carbon black with a weight ratio of 9:0.5:0.5), an electrolyte and a separator to assemble a 5Ah soft pack battery. The separator is celegard 2400 and the electrolyte is LiPF 6 Solution (solvent is a mixed solution of EC and DEC with a volume ratio of 1:1, LiPF 6 The concentration of the prepared soft-pack batteries was 1.3 mol / L). The prepared soft-pack batteries were marked as A-2, B-2, C-2, D-2, and E-2, and the cycle and rate performance of the batteries were tested. The test results are shown in Table 3.

[0136] 1) Cycle performance: The cycle performance of the battery is tested at a charge and discharge rate of 2C / 2C, a voltage range of 2.8V-4.2V, a cycle number of 500 cycles, and a temperature of 25±3℃;

[0137] 2) Rate performance: Charge the battery to 100% SOC at a rate of 2C using constant current + constant voltage mode, and then calculate the constant current ratio = constant current capacity / (constant current capacity + constant voltage capacity).

[0138] Table 3

[0139]

[0140] Table 3 shows the cycle performance and fast charging performance of the soft-pack batteries prepared from the graphite composite materials. It can be seen from the table that the cycle performance and fast charging performance of the batteries of Examples 1-3 are significantly better than those of Comparative Examples 1-4.

[0141] In summary, in the method for preparing a graphite composite material provided by an embodiment of the present invention, a catalyst, an organic polymer, an oxidant, and a coupling agent are added to the porous graphite, and the coupling agent is used to form a porous structure, and at the same time, the organic polymer is carbonized and decomposed to generate a porous carbon structure, which has the characteristics of high isotropy and low expansion; at the same time, the porous graphite is doped with a catalyst and used as a matrix to grow carbon nanotubes in a carbon source atmosphere, thereby improving the electronic conductivity of the porous core and improving the rate performance of the core.

[0142] By adopting the spray drying method, lithium phosphate derivatives are coated on the surface of carbon nanotube-doped porous graphite, and the high solvation ability between lithium phosphate and electrolyte solvent is utilized to improve the lithium ion insertion and extraction rate and its low-temperature performance.

[0143] It is deposited on graphite by vapor deposition, and further filled with lithium by LiH vapor deposition. This is further combined with the CVD carbon deposition process. During the sintering process, titanium niobate and lithium form a lithium titanium niobate compound, which has an excellent lithium ion transmission rate and reduces defects. The low temperature, initial efficiency, fast charging and cycle performance of the prepared material can be significantly improved.

[0144] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a graphite composite material, characterized in that: The steps include: Step S1, preparing carbon nanotube-doped porous graphite; Step S2, sintering a mixed raw material including a titanium source, a niobium source, a soft template, and a hard carbon source to obtain a porous titanium niobate hard carbon material; Step S3, using the porous titanium niobate hard carbon material as a target material and the carbon nanotube-doped porous graphite as a matrix to perform physical vapor deposition treatment to obtain a graphite@titanium niobate-hard carbon composite material; Step S4, heat-preserving the graphite@titanium niobate-hard carbon composite material in an atmosphere containing lithium hydride and then subjecting it to CVD carbon deposition treatment to obtain a porous lithium titanium niobate-coated graphite composite material; Step S5, mixing the porous lithium titanium niobate-coated graphite composite material with an organic solvent of a lithium phosphate derivative and spray-drying the mixture to obtain the graphite composite material.

2. The method for preparing the graphite composite material according to claim 1, characterized in that: The sintering temperature in step S2 is 1200-1500°C, and the sintering time is 1-6h; and / or, the mass ratio of the titanium source, the niobium source, the soft template and the hard carbon source in step S2 is 10-30:10-30:5-10:100; in step S2, the titanium source includes one or more of titanium-containing oxides, organic esters, and inorganic salts; and / or, the niobium source includes one or more of niobium-containing oxides, hydroxides and salts; and / or, the soft template includes one or more of anionic surfactants and neutral surfactants; and / or, the hard carbon source is one or more of glucose, sucrose, maltose, polyvinyl alcohol, and polyacrylonitrile.

3. The method for preparing the graphite composite material according to claim 1, characterized in that: In the step S4, the mass ratio of the graphite@titanium niobate-hard carbon composite material to the lithium hydride is 100:5-10; and / or, in the step S4, the carbon source for the CVD carbon precipitation treatment is one or more of hydrocarbons, alcohols, aldehydes, ketones, phenols, and esters with a carbon number of less than 8.

4. The method for preparing the graphite composite material according to claim 1, characterized in that: The mass ratio of the lithium phosphate derivative, the porous lithium titanium niobate-coated graphite composite material and the organic solvent in step S5 is 40-70:1000:5000-10000; and / or, in step S5, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, and ethyl propionate; and / or, the lithium phosphate derivative is one or more of lithium difluorophosphate, lithium hexafluorophosphate, and lithium difluorooxalate phosphate.

5. The method for preparing the graphite composite material according to claim 1, characterized in that: The step S1 specifically includes: S11, dissolving a conductive polymer in an organic solvent to prepare a solution, adding a catalyst, a coupling agent, porous graphite and an oxidant to the solution, uniformly dispersing the solution, reacting the solution and filtering the solution to obtain a filter residue; S12, carbonizing the filtered residue to obtain catalyst-doped porous graphite; S13, reacting the catalyst-doped porous graphite with a carbon source gas in a vapor deposition manner to obtain the carbon nanotube-doped porous graphite.

6. The method for preparing the graphite composite material according to claim 5, characterized in that: In the step S1, the mass ratio of the porous graphite, the catalyst, the conductive polymer, the oxidant and the coupling agent is 100:1-5:10-30:5-20:1-5; and / or, the concentration of the solution in the step S11 is 1-10wt%.

7. The method for preparing the graphite composite material according to claim 5, characterized in that: In the step S1, the catalyst is any one or more of chlorides and nitrates of iron, cobalt and nickel; and / or the conductive polymer is any one or more of thiophene, dopamine, aniline and pyrrole; and / or the oxidant is one or more of persulfate, perchlorate or hydrogen peroxide, with a concentration of 10wt%; and / or the coupling agent is one or more of 2,3-epoxypropylpropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane and 3-trifluoroacetyl-D-camphor; and / or the carbon source gas is one or more of methane, ethane, ethylene, acetylene and propyne.

8. A graphite composite material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. The graphite composite material according to claim 8, characterized in that The graphite composite material presents a core-shell structure, wherein the core is carbon nanotube-doped porous graphite, the middle layer is porous lithium titanium niobate, and the outer shell is a lithium phosphate derivative; calculated based on the mass ratio of the graphite composite material being 100%, the mass ratio of the middle layer is 1-5wt%, and the mass ratio of the outer shell is 1-5wt%.

10. A lithium ion battery, characterized in that: The invention comprises the graphite composite material as claimed in any one of claims 8 to 9.

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