High-rate long-circulation natural graphite-based composite negative electrode material and preparation method and application thereof

Abstract

The invention provides a high-rate long-cycle natural graphite-based composite negative electrode material and a preparation method and application thereof. The natural graphite-based composite negative electrode material has the characteristics of high rate performance, low volume expansion performance and long cycle performance. The preparation method comprises the following steps: firstly, granulating crystalline flake graphite particles with the particle size of submicron into particles with pore structures in a spray granulation form; then carrying out heat treatment in a protective atmosphere to convert the asphalt into amorphous carbon; then nano titanium is uniformly distributed in pore structures among crystalline flake graphite with the submicron particle size in the spherical graphite particles and on the surfaces of the spherical graphite particles by adopting a chemical vapor deposition technology; and then converting the nano titanium into titanium nitride through nitriding treatment, namely depositing titanium nitride in pore structures among crystalline flake graphite with submicron particle size in the spherical graphite particles and on the surfaces of the spherical graphite particles to prepare the natural graphite-based composite negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon negative electrode materials for lithium - ion batteries, and particularly to a high - rate and long - cycle natural graphite - based composite negative electrode material, its preparation method and application. Background Art

[0002] Lithium - ion batteries have a series of advantages such as high specific capacity, high working voltage, good safety, and no memory effect, and are widely used in fields such as 3C products, power devices, and energy storage equipment. In recent years, with the continuous improvement of the requirements for miniaturization, lightweight, multi - functionality, and long - time driving of electronic products, vehicle - mounted and energy storage equipment, the requirements for high energy density, high - rate performance, and long cycle life of lithium - ion batteries have been continuously increasing.

[0003] As an important part of lithium - ion batteries, the performance of the negative electrode directly affects the performance of the entire battery system. Natural graphite is widely used due to its high charge - discharge capacity, good charge - discharge platform, wide source, and low cost. However, the large first - cycle irreversible capacity loss and fast capacity decay during the cycling process are its fatal drawbacks.

[0004] To solve this problem, the existing technology mainly uses natural graphite that has been crushed and spheroidized into spherical graphite. This treatment improves the isotropy of natural graphite, can alleviate its volume expansion during charge - discharge, and thus improves its cycling performance. However, the size of the spherical graphite particles prepared by this method is large, which results in a long migration path for lithium ions and low rate performance of natural graphite, affecting its fast - charging performance.

[0005] To improve the fast - charging performance of natural graphite, the existing technology usually crushes or ball - mills graphite into sub - micron - sized graphite particles (0.1 - 1 μm), and then obtains a regular spherical graphite structure through spray granulation. Since small primary particles help shorten the migration path of lithium ions, the rate performance of spherical graphite is significantly improved. However, the sub - micron - sized graphite particles inside the spherical graphite particles prepared by this method are still anisotropic flaky in orientation. During charge - discharge, the sub - micron - sized graphite particles expand differently in each direction, resulting in fast capacity decay during cycling, thus significantly reducing the cycling performance of natural graphite.

[0006] Therefore, how to simultaneously improve the cycling performance and rate performance of natural graphite negative electrode materials is still a problem to be solved at present. Summary of the Invention

[0007] To solve the problem in the prior art that the cycling performance and rate performance of natural graphite cannot be taken into account simultaneously, the present invention provides a high-rate and long-cycle natural graphite-based composite anode material, its preparation method and application. The natural graphite-based composite anode material has the characteristics of high rate performance, low volume expansion performance and long cycle performance. The preparation method provided by the present invention has simple process and low production cost, and has great commercial application prospects in the field of power batteries with strong market demand.

[0008] The object of the present invention is achieved through the following technical solutions:

[0009] A preparation method of a natural graphite-based composite anode material, the method comprising the following steps:

[0010] (1) Crushing natural flake graphite to obtain flake graphite with a particle size of sub-micron level;

[0011] (2) Mixing the flake graphite with a particle size of sub-micron level obtained in step (1), pitch and a solvent, and performing spray granulation to obtain powder 1;

[0012] (3) Heat-treating the powder 1 obtained in step (2) in a protective atmosphere to obtain powder 2;

[0013] (4) Performing chemical vapor deposition of titanium on the powder 2 obtained in step (3) to obtain powder 3;

[0014] (5) Performing nitriding treatment on the powder 3 obtained in step (4) to obtain the natural graphite-based composite anode material.

[0015] According to the embodiment of the present invention, in step (1), the median particle size of the natural flake graphite is not particularly defined, and it is only necessary to obtain flake graphite with a particle size of sub-micron level after crushing it.

[0016] According to the embodiment of the present invention, in step (1), the natural flake graphite is preferably the irregular flake graphite tailings (median particle size such as 1-3 μm) generated during the preparation of spherical graphite; by selecting the irregular flake graphite tailings generated during the preparation of spherical graphite as the raw material, the utilization rate of natural flake graphite can be improved, and the production cost of the natural graphite-based composite anode material can be reduced.

[0017] According to the embodiment of the present invention, in step (1), the purity of the natural flake graphite is ≥99%.

[0018] According to the embodiment of the present invention, in step (1), the median particle size of the sub-micron level flake graphite is 0.1 μm - 1 μm, such as 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm or 1 μm.

[0019] According to an embodiment of the present invention, in step (1), the pulverization is carried out by using methods and equipment known in the art, and there is no special definition for the pulverization parameters, as long as flake graphite with a particle size of sub-micron level can be obtained.

[0020] According to an embodiment of the present invention, in step (2), the carbon residue value of the asphalt is 20% - 80%, such as 20%, 30%, 40%, 50%, 60%, 70% or 80%.

[0021] According to an embodiment of the present invention, in step (2), the solvent is selected from ethanol and / or water.

[0022] According to an embodiment of the present invention, in step (2), the mass ratio of the asphalt to the flake graphite with a particle size of sub-micron level is (10 - 20):100, such as 10:100, 11:100, 12:100, 13:100, 14:100, 15:100, 16:100, 17:100, 18:100, 19:100 or 20:100.

[0023] According to an embodiment of the present invention, in step (2), the mass ratio of the solvent to the flake graphite with a particle size of sub-micron level is (30 - 100):100, such as 30:100, 35:100, 40:100, 45:100, 50:100, 55:100, 60:100, 65:100, 70:100, 75:100, 80:100, 85:100, 90:100, 95:100 or 100:100.

[0024] According to an embodiment of the present invention, in step (2), there is no special definition for the mixing time, and it is only necessary to mix the flake graphite with a particle size of sub-micron level, the asphalt and the solvent in step (1) evenly.

[0025] According to an embodiment of the present invention, in step (2), the inlet temperature of the spray granulation is 150 - 210 °C, such as 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C or 210 °C; the outlet temperature of the spray granulation is 90 - 110 °C, such as 90 °C, 92 °C, 95 °C, 98 °C, 100 °C, 102 °C, 105 °C, 106 °C, 108 °C or 110 °C; the spray granulation is carried out in an air atmosphere.

[0026] According to an embodiment of the present invention, in step (2), the shape of the powder 1 is spherical.

[0027] According to an embodiment of the present invention, in step (2), the median particle size of the powder 1 is 5 μm - 16 μm, such as 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm or 16 μm.

[0028] According to an embodiment of the present invention, in step (2), the powder 1 is spherical graphite particles having a plurality of pore structures; preferably, the powder 1 is spherical graphite particles having a plurality of pore structures with pore sizes of 10 - 40 nm. Preferably, the powder 1 includes sub-micron-sized flake graphite and pitch; more preferably, the powder 1 is spherical graphite particles formed by sub-micron-sized flake graphite and pitch having a pore structure, and pitch is filled between some of the sub-micron-sized flake graphite particles, and a pore structure is formed between some of the sub-micron-sized flake graphite particles, and the pore size of the pore structure is 10 - 40 nm.

[0029] According to an embodiment of the present invention, in step (2), during the spray granulation process, the sub-micron-sized flake graphite particles will stack, so that pitch is filled between some of the sub-micron-sized flake graphite particles, and a pore structure is formed between some of the sub-micron-sized flake graphite particles, obtaining spherical graphite particles having a plurality of pore structures with pore sizes of 10 - 40 nm, that is, the powder 1.

[0030] According to an embodiment of the present invention, in step (3), the temperature of the heat treatment is 800 - 1200 °C, such as 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C or 1200 °C; the time of the heat treatment is 2 - 10 hours, such as 3 - 8 hours, and exemplarily 3 hours, 4 hours, 5 hours or 6 hours.

[0031] According to an embodiment of the present invention, in step (3), the protective atmosphere is nitrogen or argon.

[0032] According to an embodiment of the present invention, in step (3), the powder 2 is spherical graphite particles having a plurality of pore structures; preferably, the powder 2 is spherical graphite particles having a plurality of pore structures with pore sizes of 10 - 40 nm. Preferably, the powder 2 includes sub-micron-sized flake graphite and amorphous carbon; more preferably, the powder 2 is spherical graphite particles formed by sub-micron-sized flake graphite and amorphous carbon having a pore structure, and amorphous carbon is in-situ formed between some of the sub-micron-sized flake graphite particles, and a pore structure is formed between some of the sub-micron-sized flake graphite particles, and the pore size of the pore structure is 10 - 40 nm.

[0033] According to an embodiment of the present invention, in step (4), the chemical vapor deposition of titanium includes the following steps:

[0034] First, place the powder 2 in a chemical vapor deposition furnace, introduce argon into the chemical vapor deposition furnace, and then raise the temperature of the chemical vapor deposition furnace to 150 - 280 °C; then introduce titanium diiodide gas into the chemical vapor deposition furnace and pre-deposit for 30 - 60 min. After the pre-deposition ends, raise the temperature of the chemical vapor deposition furnace to 1100 - 1200 °C and deposit for 1 - 5 hours to obtain powder 3.

[0035] According to an embodiment of the present invention, the flow rate of the titanium diiodide gas is 500 - 1000 sccm, for example, 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, or 1000 sccm.

[0036] According to an embodiment of the present invention, the mass - volume ratio of the titanium diiodide gas to the powder 2 is 0.6 - 5 L / g, that is, 0.6 - 5 L of titanium diiodide gas is introduced into 1 g of powder 2, such as 0.6 L / g, 0.8 L / g, 1 L / g, 1.2 L / g, 1.5 L / g, 1.8 L / g, 2 L / g, 2.2 L / g, 2.5 L / g, 2.8 L / g, 3 L / g, 3.2 L / g, 3.5 L / g, 3.6 L / g, 3.8 L / g, 4 L / g, 4.2 L / g, 4.5 L / g, 4.8 L / g, or 5 L / g.

[0037] According to an embodiment of the present invention, the pre - deposition process can enable the titanium diiodide gas to enter the pore structure of the powder 2 more fully, and can ensure the formation of nano - titanium in the pores of the spherical graphite particles.

[0038] According to an embodiment of the present invention, in step (4), after the chemical vapor deposition of titanium, a cooling step is further included. The cooling step includes: first, the chemical vapor deposition furnace stops heating, then stops introducing titanium diiodide gas, and the powder 3 is cooled to room temperature with the furnace in an argon atmosphere.

[0039] According to an embodiment of the present invention, in step (4), the titanium diiodide gas is prepared by the following method: place metallic titanium in a vacuum furnace, then introduce iodine vapor (flow rate 100 - 300 sccm) into the vacuum furnace, raise the temperature of the vacuum furnace to 150 - 280 °C, and at this temperature, metallic titanium reacts with iodine vapor to generate titanium diiodide gas.

[0040] According to an embodiment of the present invention, in step (4), the powder 3 includes nano titanium, flake graphite with a submicron-sized particle diameter, and amorphous carbon; preferably, the powder 3 is spherical graphite particles formed by nano titanium, flake graphite with a submicron-sized particle diameter, and amorphous carbon, and amorphous carbon is in-situ formed between some of the flake graphite with a submicron-sized particle diameter, and nano titanium is deposited in the pore structure between some of the flake graphite with a submicron-sized particle diameter; the surface of the powder 3 is coated with nano titanium.

[0041] According to an embodiment of the present invention, in step (5), the nitriding treatment includes the following steps: putting the powder 3 into a heating furnace, introducing nitrogen into the heating furnace, and heating the temperature of the heating furnace to 1000 - 1400 °C (such as 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C or 1400 °C), keeping warm for 1 - 5 hours, cooling to room temperature, to obtain a natural graphite-based composite negative electrode material.

[0042] According to an embodiment of the present invention, in step (5), after the nitriding treatment, there is also a cooling step, and the cooling step includes: first, the heating furnace stops heating, and nitrogen continues to be introduced into the heating furnace. When the temperature of the heating furnace drops to 200 - 400 °C, the nitrogen introduction stops, and the solid product is cooled to room temperature with the furnace, to obtain a natural graphite-based composite negative electrode material.

[0043] According to an embodiment of the present invention, in step (5), the flow rate of the nitrogen is above 300 sccm, preferably 300 - 1000 sccm, for example 300 sccm, 400 sccm, 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm or 1000 sccm.

[0044] According to an embodiment of the present invention, in step (5), during the nitriding treatment, nitrogen can react with the nano titanium in the powder 3 to produce titanium nitride.

[0045] According to an embodiment of the present invention, in step (5), the natural graphite-based composite negative electrode material includes titanium nitride, flake graphite with a submicron-sized particle diameter, and amorphous carbon; preferably, the natural graphite-based composite negative electrode material is spherical graphite particles formed by titanium nitride, flake graphite with a submicron-sized particle diameter, and amorphous carbon, and amorphous carbon is in-situ formed between some of the flake graphite with a submicron-sized particle diameter, and titanium nitride is deposited in the pore structure between some of the flake graphite with a submicron-sized particle diameter; the surface of the natural graphite-based composite negative electrode material is coated with titanium nitride.

[0046] The present invention also provides a natural graphite-based composite negative electrode material prepared by the above method.

[0047] According to an embodiment of the present invention, the natural graphite-based composite negative electrode material includes flake graphite with a sub-micron size, amorphous carbon, and titanium nitride; preferably, the natural graphite-based composite negative electrode material is a composite composed of flake graphite with a sub-micron size, amorphous carbon, and titanium nitride.

[0048] According to an embodiment of the present invention, the mass of the flake graphite with a sub-micron size accounts for 90-96% of the total mass of the natural graphite-based composite negative electrode material, such as 90%, 91%, 92%, 93%, 94%, 95%, or 96%.

[0049] According to an embodiment of the present invention, the mass of the amorphous carbon accounts for 1-6% of the total mass of the natural graphite-based composite negative electrode material, such as 1%, 2%, 3%, 4%, 5%, or 6%.

[0050] According to an embodiment of the present invention, the mass of the titanium nitride accounts for 1-4% of the total mass of the natural graphite-based composite negative electrode material, such as 1%, 2%, 3%, or 4%.

[0051] According to an embodiment of the present invention, the amorphous carbon is distributed between the flake graphite with a sub-micron size; the amorphous carbon can bond the flake graphite with a sub-micron size together.

[0052] According to an embodiment of the present invention, the titanium nitride is distributed in the pore structure between the flake graphite with a sub-micron size; the titanium nitride is also distributed on the surface of the composite composed of flake graphite with a sub-micron size, amorphous carbon, and titanium nitride.

[0053] According to an embodiment of the present invention, the natural graphite-based composite negative electrode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron size, amorphous carbon, and titanium nitride; the amorphous carbon is distributed between the flake graphite with a sub-micron size; the titanium nitride is distributed in the pore structure between the flake graphite with a sub-micron size; the shell layer includes titanium nitride.

[0054] According to an embodiment of the present invention, the thickness of the shell layer is 1-10 nm, such as 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm.

[0055] According to an embodiment of the present invention, the median particle size D 50 of the natural graphite-based composite negative electrode material is 5 μm - 16 μm, such as 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, or 16 μm.

[0056] The present invention also provides a use of the above-mentioned natural graphite-based composite anode material, which is used to prepare the anode of a lithium-ion battery.

[0057] The present invention also provides an anode of a lithium-ion battery, which comprises the above-mentioned natural graphite-based composite anode material.

[0058] The present invention also provides a lithium-ion battery, which comprises the above-mentioned natural graphite-based composite anode material or the anode of the above-mentioned lithium-ion battery.

[0059] Advantages of the present invention:

[0060] First, in the present invention, flake graphite particles with a sub-micron size are granulated into spherical graphite particles with a pore structure (i.e., powder 1) by spray granulation. During the spray granulation process, due to the stacking effect, more pore structures will be formed inside the spherical graphite particles among the flake graphite particles with a sub-micron size, specifically, pore structures are formed between the flake graphite particles with a sub-micron size. Then, heat treatment is carried out under a protective atmosphere to convert the pitch into amorphous carbon, and the amorphous carbon is used to tightly bond the flake graphite particles with a sub-micron size to obtain powder 2. Next, the nano-titanium is uniformly distributed in the pore structures between the flake graphite particles with a sub-micron size inside the spherical graphite particles and on the surface of the spherical graphite particles by chemical vapor deposition technology to obtain powder 3. Subsequently, the nano-titanium is converted into titanium nitride by nitridation treatment, that is, titanium nitride is deposited in the pore structures between the flake graphite particles with a sub-micron size inside the spherical graphite particles and on the surface of the spherical graphite particles to obtain the natural graphite-based composite anode material.

[0061] On the one hand, taking advantage of the high hardness of titanium nitride, the titanium nitride inside and on the outer surface together stabilize the structure of the natural graphite-based composite anode material, and can buffer the volume expansion of the flake graphite with a sub-micron size during the process of lithium-ion insertion and extraction in the cycling process, thereby improving the cycling performance of the natural graphite-based composite anode material; the mechanical properties of the natural graphite-based composite anode material prepared in this way are good, and the particles will not break during the compaction process and the process of making into a pole piece, further improving the cycling performance of the natural graphite-based composite anode material.

[0062] On the other hand, taking advantage of the high conductivity of titanium nitride, it can not only accelerate the conduction rate of lithium ions inside the graphite, but also enhance the overall conductivity of the natural graphite-based composite anode material; through the combined action of the titanium nitride inside and outside the natural graphite-based composite anode material, the lithium-ion battery can have the characteristics of high rate performance and long cycle life. Specific embodiments

[0063] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only illustrative explanations of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0064] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; unless otherwise specified, the reagents, materials, etc. used in the following embodiments can all be obtained from commercial channels.

[0065] The purity of natural flake graphite in the following embodiments and comparative examples is ≥99%, and it is derived from the irregular flake graphite tailings generated during the preparation of spherical graphite.

[0066] The titanium diiodide gas used in the following embodiments is prepared by the following method: Place metallic titanium in a vacuum furnace, then introduce iodine vapor with a flow rate of 300 sccm into the vacuum furnace, raise the temperature of the vacuum furnace to 180°C, and at this temperature, metallic titanium reacts with iodine vapor to generate titanium diiodide gas.

[0067] Example 1

[0068] (1) Crush 1000 g of natural flake graphite (D 50 is 2 μm) to obtain flake graphite with a particle size of sub-micron level (D 50 is 0.95 μm);

[0069] (2) Mix 100 g of the sub-micron level flake graphite obtained in step (1), 12 g of asphalt (residual carbon value 60%) and 60 g of ethanol to obtain a slurry, and the slurry is spray granulated (inlet temperature is 180°C, outlet temperature is 100°C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0070] (3) Heat-treat the powder 1 obtained in step (2) in a nitrogen atmosphere at 1000°C for 3 hours, and cool it to room temperature to obtain powder 2;

[0071] (4) First, place 100 g of powder 2 in a chemical vapor deposition furnace, introduce argon into the chemical vapor deposition furnace, and then raise the temperature of the chemical vapor deposition furnace to 200°C; then introduce titanium diiodide gas with a flow rate of 600 sccm into the chemical vapor deposition furnace and pre-deposit for 40 min; after the pre-deposition ends, raise the temperature of the chemical vapor deposition furnace to 1100°C and deposit for 1 hour; after the deposition ends, stop heating the chemical vapor deposition furnace, then stop introducing titanium diiodide gas, and the solid product is cooled to room temperature in an argon atmosphere with the furnace to obtain powder 3;

[0072] (5) Put 100 g of powder 3 from step (4) into a heating furnace, introduce nitrogen gas (300 sccm) into the heating furnace, heat the temperature of the heating furnace to 1000 °C and keep it for 3 hours. After the heat preservation, stop heating the heating furnace, continue to introduce nitrogen gas into the heating furnace, and stop introducing nitrogen gas when the temperature of the heating furnace drops to 200 °C. The solid product cools with the furnace to room temperature to obtain the natural graphite-based composite anode material.

[0073] The natural graphite-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron size, amorphous carbon, and titanium nitride; the amorphous carbon is distributed between the flake graphite with a sub-micron size; the titanium nitride is distributed in the pore structure between the flake graphite with a sub-micron size; the shell layer includes titanium nitride; the mass of the amorphous carbon accounts for 3.9% of the total mass of the natural graphite-based composite anode material, and the mass of the titanium nitride accounts for 1.9% of the total mass of the natural graphite-based composite anode material.

[0074] Example 2

[0075] (1) Crush 1000 g of natural flake graphite (D 50 is 1.5 μm) to obtain flake graphite with a sub-micron size (D 50 is 0.9 μm);

[0076] (2) Mix 100 g of flake graphite with a sub-micron size from step (1), 15 g of pitch (residual carbon value 60%) and 70 g of ethanol to obtain a slurry. The slurry is spray granulated (inlet temperature is 180 °C, outlet temperature is 100 °C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0077] (3) Heat-treat powder 1 from step (2) in a nitrogen atmosphere at 900 °C for 6 hours and cool to room temperature to obtain powder 2;

[0078] (4) First, place 100 g of powder 2 in a chemical vapor deposition furnace, introduce argon gas into the chemical vapor deposition furnace, and then raise the temperature of the chemical vapor deposition furnace to 200 °C; then introduce titanium diiodide gas with a flow rate of 500 sccm into the chemical vapor deposition furnace and pre-deposit for 60 min; after the pre-deposition, raise the temperature of the chemical vapor deposition furnace to 1100 °C and deposit for 3 hours; after the deposition, stop heating the chemical vapor deposition furnace, then stop introducing titanium diiodide gas, and the solid product cools with the furnace to room temperature in an argon atmosphere to obtain powder 3;

[0079] (5) Put 100 g of powder 3 from step (4) into a heating furnace, introduce nitrogen gas (500 sccm) into the heating furnace, heat the temperature of the heating furnace to 1200 °C and keep it warm for 3 hours. After the heat preservation time is up, stop heating the heating furnace, continue to introduce nitrogen gas into the heating furnace, and stop introducing nitrogen gas when the temperature of the heating furnace drops to 300 °C. The solid product cools with the furnace to room temperature to obtain the natural graphite-based composite anode material.

[0080] The natural graphite-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron size, amorphous carbon, and titanium nitride; the amorphous carbon is distributed between the flake graphite with a sub-micron size; the titanium nitride is distributed in the pore structure between the flake graphite with a sub-micron size; the shell layer includes titanium nitride; the mass of the amorphous carbon accounts for 4.4% of the total mass of the natural graphite-based composite anode material, and the mass of the titanium nitride accounts for 2.5% of the total mass of the natural graphite-based composite anode material.

[0081] Example 3

[0082] (1) Crush 1000 g of natural flake graphite (D 50 is 1.2 μm) to obtain flake graphite with a sub-micron size (D 50 is 0.85 μm);

[0083] (2) Mix 100 g of the flake graphite with a sub-micron size from step (1), 18 g of pitch (residual carbon value 60%) and 60 g of ethanol to obtain a slurry. The slurry is spray granulated (the inlet temperature is 180 °C, the outlet temperature is 100 °C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0084] (3) Heat-treat powder 1 from step (2) in a nitrogen atmosphere at 1000 °C for 3 hours and cool it to room temperature to obtain powder 2;

[0085] (4) First, place 100 g of powder 2 in a chemical vapor deposition furnace, introduce argon gas into the chemical vapor deposition furnace, and then raise the temperature of the chemical vapor deposition furnace to 200 °C; then introduce titanium diiodide gas with a flow rate of 600 sccm into the chemical vapor deposition furnace and pre-deposit for 40 min; after the pre-deposition is completed, raise the temperature of the chemical vapor deposition furnace to 1100 °C and deposit for 3 hours; after the deposition is completed, stop heating the chemical vapor deposition furnace, then stop introducing titanium diiodide gas, and the solid product cools with the furnace to room temperature in an argon atmosphere to obtain powder 3;

[0086] (5) Put 100 g of the powder 3 from step (4) into a heating furnace, introduce nitrogen gas (300 sccm) into the heating furnace, heat the temperature of the heating furnace to 1280 °C and keep it for 5 hours. After the heat preservation time is up, stop heating the heating furnace, continue to introduce nitrogen gas into the heating furnace, and stop introducing nitrogen gas when the temperature of the heating furnace drops to 300 °C. The solid product cools with the furnace to room temperature to obtain the natural graphite-based composite anode material.

[0087] The natural graphite-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron size, amorphous carbon, and titanium nitride; the amorphous carbon is distributed between the flake graphite with a sub-micron size; the titanium nitride is distributed in the pore structure between the flake graphite with a sub-micron size; the shell layer includes titanium nitride; the mass of the amorphous carbon accounts for 5.2% of the total mass of the natural graphite-based composite anode material, and the mass of the titanium nitride accounts for 3.4% of the total mass of the natural graphite-based composite anode material.

[0088] Example 4

[0089] (1) Crush 1000 g of natural flake graphite (D 50 is 1 μm) to obtain flake graphite with a sub-micron size (D 50 is 0.8 μm);

[0090] (2) Mix 100 g of the flake graphite with a sub-micron size from step (1), 20 g of pitch (residual carbon value 60%) and 80 g of ethanol to obtain a slurry. The slurry is spray granulated (inlet temperature is 180 °C, outlet temperature is 100 °C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0091] (3) Heat-treat powder 1 from step (2) in a nitrogen atmosphere at 1000 °C for 3 hours and cool to room temperature to obtain powder 2;

[0092] (4) First, place 100 g of powder 2 in a chemical vapor deposition furnace, introduce argon gas into the chemical vapor deposition furnace, and then raise the temperature of the chemical vapor deposition furnace to 200 °C; then introduce titanium diiodide gas with a flow rate of 600 sccm into the chemical vapor deposition furnace and pre-deposit for 40 min; after the pre-deposition is completed, raise the temperature of the chemical vapor deposition furnace to 1100 °C and deposit for 5 hours; after the deposition is completed, stop heating the chemical vapor deposition furnace, then stop introducing titanium diiodide gas, and the solid product cools with the furnace to room temperature in an argon atmosphere to obtain powder 3;

[0093] (5) Put 100 g of powder 3 from step (4) into a heating furnace, introduce nitrogen gas (300 sccm) into the heating furnace, heat the temperature of the heating furnace to 1000 °C and hold for 3 hours. After the holding time, stop heating the heating furnace, continue to introduce nitrogen gas into the heating furnace, and stop introducing nitrogen gas when the temperature of the heating furnace drops to 200 °C. The solid product cools with the furnace to room temperature to obtain the natural graphite-based composite anode material.

[0094] The natural graphite-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron particle size, amorphous carbon, and titanium nitride; the amorphous carbon is distributed between the flake graphite with a sub-micron particle size; the titanium nitride is distributed in the pore structure between the flake graphite with a sub-micron particle size; the shell layer includes titanium nitride; the mass of the amorphous carbon accounts for 6% of the total mass of the natural graphite-based composite anode material, and the mass of the titanium nitride accounts for 4% of the total mass of the natural graphite-based composite anode material.

[0095] Comparative Example 1

[0096] (1) Crush 1000 g of natural flake graphite (D 50 is 2 μm) to obtain flake graphite with a sub-micron particle size (D 50 is 0.95 μm);

[0097] (2) Mix 100 g of flake graphite with a sub-micron particle size from step (1), 12 g of pitch (residual carbon value 60%), and 60 g of ethanol to obtain a slurry. The slurry is spray granulated (inlet temperature is 180 °C, outlet temperature is 100 °C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0098] (3) Heat-treat powder 1 from step (2) in a nitrogen atmosphere at 1000 °C for 3 hours, and cool to room temperature to obtain a natural graphite anode material.

[0099] Comparative Example 2

[0100] (1) Crush 1000 g of natural flake graphite (D 50 is 2 μm) to obtain flake graphite with a sub-micron particle size (D 50 is 0.95 μm);

[0101] (2) Mix 100 g of flake graphite with a sub-micron particle size from step (1), 12 g of pitch (residual carbon value 60%), 60 g of ethanol, and 1.7 g of nano titanium nitride to obtain a slurry. The slurry is spray granulated (inlet temperature is 180 °C, outlet temperature is 100 °C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0102] (3) Heat the powder 1 from step (2) at 1000 °C for 3 hours under a nitrogen atmosphere, and then cool it to room temperature to obtain powder 2;

[0103] (4) Put 100 g of the powder 2 from step (3) into a chemical vapor deposition furnace, heat it to 1015 °C at a rate of 5 °C / min, and simultaneously introduce nitrogen with a flow rate of 120 sccm and argon gas containing titanium tetrachloride with a flow rate of 100 sccm obtained by bubbling into the chemical vapor deposition furnace, and keep the temperature for 5 hours; after the heat preservation is completed, introduce argon carrier gas with a flow rate of 200 sccm, stop introducing the titanium source, cool down to 800 °C, stop introducing the nitrogen source, continue to cool down, when the temperature drops to 300 °C, stop introducing argon, and then cool it to room temperature to obtain the natural graphite-based composite anode material.

[0104] The natural graphite-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron particle size, amorphous carbon, and titanium nitride; part of the amorphous carbon is distributed between the flake graphite with a sub-micron particle size; part of the amorphous carbon is distributed between the flake graphite with a sub-micron particle size and titanium nitride; pore structures are formed between some of the flake graphite with a sub-micron particle size and between some of the flake graphite with a sub-micron particle size and titanium nitride in the core, and the pore size of the pore structure is 10 - 40 nm; the shell layer includes titanium nitride; the mass of the amorphous carbon accounts for 3.9% of the total mass of the natural graphite-based composite anode material, and the mass of the titanium nitride accounts for 1.9% of the total mass of the natural graphite-based composite anode material.

[0105] Comparative Example 3

[0106] (1) Crush 1000 g of natural flake graphite (D 50 is 2 μm) to obtain flake graphite with a sub-micron particle size (D 50 is 0.95 μm);

[0107] (2) Mix 100 g of the flake graphite with a sub-micron particle size from step (1), 12 g of pitch (residual carbon value 60%) and 60 g of ethanol to obtain a slurry, and the slurry is spray granulated (inlet temperature is 180 °C, outlet temperature is 100 °C; air atmosphere) to obtain powder 1 (D 50 is 8 μm);

[0108] (3) Heat the powder 1 from step (2) at 1000 °C for 3 hours under a nitrogen atmosphere, and then cool it to room temperature to obtain powder 2;

[0109] (4) Put 100 g of Powder 2 from step (3) into a chemical vapor deposition furnace, heat it to 1015 °C at a rate of 5 °C / min, and simultaneously introduce nitrogen with a flow rate of 120 sccm and argon gas containing titanium tetrachloride with a flow rate of 100 sccm obtained by bubbling into the chemical vapor deposition furnace, and keep it at a constant temperature for 5 hours; after the constant temperature is reached, introduce argon carrier gas with a flow rate of 200 sccm, stop introducing the titanium source, cool down to 800 °C, stop introducing the nitrogen source, continue to cool down, when the temperature drops to 300 °C, stop introducing argon, and then cool to room temperature to obtain the natural graphite-based composite negative electrode material.

[0110] The natural graphite-based composite negative electrode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a sub-micron particle size and amorphous carbon; the amorphous carbon is distributed between the flake graphite with a sub-micron particle size; pore structures are formed between the flake graphite with a sub-micron particle size in the core, and the pore size of the pore structure is 10 - 40 nm; the shell layer includes titanium nitride; the mass of the amorphous carbon accounts for 3.9% of the total mass of the natural graphite-based composite negative electrode material, and the mass of the titanium nitride accounts for 1.9% of the total mass of the natural graphite-based composite negative electrode material.

[0111] Electrochemical performance test

[0112] Half-cell test method: The natural graphite-based composite materials prepared in the examples and comparative examples: conductive carbon black (SP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 95:1:1.5:2.5 (mass ratio) are mixed evenly, coated on a copper foil, and the coated electrode is placed in a vacuum drying oven at 120 °C for 12 hours. Simulated battery assembly is carried out in a Braun glove box under argon protection. The electrolyte is 1 M-LiPF6 + EC:DEC:DMC (volume ratio of 1:1:1), and a lithium metal sheet is used as the counter electrode. Simulated battery tests are carried out in a Neware battery test cabinet at 5 V and 10 mA. The charge-discharge voltage is 0.01 - 1.5 V, and the charge-discharge rate is 0.1 C. The first discharge capacity and efficiency obtained from the tests are listed in Table 1.

[0113] Full-cell test method: Using the natural graphite-based composite materials prepared in the examples and comparative examples as the negative electrode, lithium cobaltate as the positive electrode, and 1 M-LiPF6 + EC:DEC:DMC (volume ratio of 1:1:1) solution as the electrolyte to assemble a full cell, with a voltage range of 0.01 - 1.5 V. The rate performance, cycle performance, and electrode expansion rate obtained from the tests are listed in Table 1.

[0114] Table 1. Electrochemical performance test results

[0115]

[0116] Compared with Examples 1-4, the pores formed between the submicron flake graphite inside the natural graphite-based composite negative electrode material of Comparative Example 1 and the lack of nano-titanium nitride deposited on its surface cannot buffer the volume expansion of the submicron flake graphite during the process of lithium ion insertion and extraction during the cycle process, resulting in a significant reduction in the cycle performance of the battery and a significant increase in the expansion rate of the electrode.

[0117] Compared with Example 1, Comparative Example 2 first granulates submicron flake graphite particles and nano-titanium nitride into spherical graphite / nano-titanium nitride composite particles with a porous structure by spray granulation; in the subsequent chemical vapor deposition, nano-titanium nitride cannot be deposited into these pores, that is, the core of the natural graphite-based composite negative electrode material obtained thereby still has a relatively large number of porous structures. Although nano-titanium nitride can also alleviate the expansion of submicron flake graphite during the cycle, this structure is unstable and easily broken during the cycle, resulting in the obtained battery having a lower cycle performance.

[0118] Compared with Example 1, no nano-titanium nitride is deposited in the pores formed between the submicron flake graphite particles inside the natural graphite-based composite negative electrode material of Comparative Example 3. Nano-titanium nitride cannot be deposited in these pores in the subsequent chemical vapor deposition. The volume expansion of the submicron flake graphite particles in the core during the cycle can only be alleviated by the nano-titanium nitride in the outer shell. However, this structure is unstable and easily broken during the cycle, resulting in a significant reduction in the cycle performance of the obtained battery and a significant increase in the expansion rate of the electrode piece.

[0119] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a natural graphite-based composite negative electrode material, the method comprising the following steps: (1) crushing natural flake graphite to obtain flake graphite with a particle size of submicron level; (2) mixing the submicron-sized flake graphite and asphalt obtained in step (1) with a solvent, and spray granulating the mixture to obtain powder 1; (3) heat treating the powder 1 obtained in step (2) under a protective atmosphere to obtain powder 2; (4) subjecting the powder 2 of step (3) to chemical vapor deposition of titanium to obtain powder 3; (5) The powder 3 of step (4) is subjected to nitriding treatment to obtain the natural graphite-based composite negative electrode material.

2. The preparation method according to claim 1, wherein In step (1), the natural flake graphite is irregular flake graphite tailings produced in the preparation of spherical graphite. Preferably, in step (1), the median particle size of the submicron flake graphite is 0.1 μm-1 μm.

3. The preparation method according to claim 1 or 2, wherein In step (2), the mass ratio of the asphalt to the submicron flake graphite is (10-20):100; the mass ratio of the solvent to the submicron flake graphite is (30-100):

100. Preferably, in step (2), the inlet temperature of the spray granulation is 150-210°C; the outlet temperature of the spray granulation is 90-110°C; and the spray granulation is carried out in an air atmosphere. Preferably, in step (2), the powder 1 is spherical graphite particles with a porous structure formed by flake graphite with a particle size of submicron order and asphalt, and asphalt is filled between some flake graphite with a particle size of submicron order, and a porous structure is formed between some flake graphite with a particle size of submicron order, and the pore size of the porous structure is 10-40nm.

4. The preparation method according to any one of claims 1 to 3, wherein: In step (3), the temperature of the heat treatment is 800-1200° C.; the time of the heat treatment is 2-10 hours. Preferably, in step (3), the powder 2 is spherical graphite particles with a porous structure formed by flake graphite with a particle size of submicron order and amorphous carbon, and amorphous carbon is formed in situ between some flake graphite with a particle size of submicron order, and a porous structure is formed between some flake graphite with a particle size of submicron order, and the pore size of the porous structure is 10-40nm.

5. The preparation method according to any one of claims 1 to 4, wherein: In step (4), the chemical vapor deposition of titanium includes the following steps: first, placing powder 2 in a chemical vapor deposition furnace, introducing argon gas into the chemical vapor deposition furnace, and then raising the temperature of the chemical vapor deposition furnace to 150-280°C; then introducing titanium diiodide gas into the chemical vapor deposition furnace, pre-depositing for 30-60 minutes, and after the pre-deposition is completed, raising the temperature of the chemical vapor deposition furnace to 1100-1200°C, and depositing for 1-5 hours to prepare powder 3. Preferably, the flow rate of the titanium diiodide gas is 500-1000 sccm. Preferably, the mass volume ratio of the titanium diiodide gas to the powder 2 is 0.6-5 L / g. Preferably, in step (4), a cooling step is further included after the chemical vapor deposition of titanium is completed, and the cooling step includes: first, the chemical vapor deposition furnace stops heating, and then the introduction of titanium diiodide gas is stopped, and the powder 3 is cooled to room temperature in the furnace under an argon atmosphere. Preferably, in step (4), the powder 3 is spherical graphite particles formed by nano-titanium, flake graphite with a particle size of submicron order and amorphous carbon, and amorphous carbon is in situ formed between some flake graphite with a particle size of submicron order, and nano-titanium is deposited in the pore structure between some flake graphite with a particle size of submicron order; the surface of the powder 3 is coated with nano-titanium.

6. The preparation method according to any one of claims 1 to 5, wherein: In step (5), the nitriding treatment includes the following steps: placing the powder 3 in a heating furnace, introducing nitrogen into the heating furnace, and heating the heating furnace to a temperature of 1000-1400°C, keeping the temperature for 1-5 hours, and cooling to room temperature to obtain a natural graphite-based composite negative electrode material. Preferably, in step (5), after the nitriding treatment is completed, a cooling step is also included, and the cooling step includes: first, the heating furnace stops heating, and nitrogen continues to be introduced into the heating furnace. When the temperature of the heating furnace drops to 200-400°C, the nitrogen is stopped from being introduced, and the solid product is cooled to room temperature with the furnace to obtain a natural graphite-based composite negative electrode material. Preferably, in step (5), the natural graphite-based composite negative electrode material is spherical graphite particles formed by titanium nitride, flake graphite with a particle size of submicron order and amorphous carbon, and amorphous carbon is formed in situ between some flake graphite with a particle size of submicron order, and titanium nitride is deposited in the pore structure between some flake graphite with a particle size of submicron order; the surface of the natural graphite-based composite negative electrode material is coated with titanium nitride.

7. A natural graphite-based composite negative electrode material prepared by the method according to any one of claims 1 to 6.

8. The natural graphite-based composite negative electrode material according to claim 7, wherein: The natural graphite-based composite negative electrode material comprises flake graphite with a particle size of submicron level, amorphous carbon and titanium nitride; preferably, the natural graphite-based composite negative electrode material is a composite composed of flake graphite with a particle size of submicron level, amorphous carbon and titanium nitride. Preferably, the mass of the submicron flake graphite accounts for 90-96% of the total mass of the natural graphite-based composite negative electrode material; the mass of the amorphous carbon accounts for 1-6% of the total mass of the natural graphite-based composite negative electrode material; the mass of the titanium nitride accounts for 1-4% of the total mass of the natural graphite-based composite negative electrode material. Preferably, the amorphous carbon is distributed between flake graphite with submicron particle size; the titanium nitride is distributed in the pore structure between flake graphite with submicron particle size; the titanium nitride is also distributed on the surface of a composite composed of flake graphite with submicron particle size, amorphous carbon and titanium nitride. Preferably, the natural graphite-based composite negative electrode material has a core-shell structure, including a core and a shell layer; the core includes flake graphite with a particle size of submicron order, amorphous carbon and titanium nitride; the amorphous carbon is distributed between the flake graphite with a particle size of submicron order; the titanium nitride is distributed in the pore structure between the flake graphite with a particle size of submicron order; the shell layer includes titanium nitride.

9. A negative electrode of a lithium ion battery, comprising the natural graphite-based composite negative electrode material according to claim 7 or 8.

10. A lithium ion battery comprising the natural graphite-based composite negative electrode material according to claim 7 or 8 or the negative electrode of the lithium ion battery according to claim 9.

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