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

Abstract

The application 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. Firstly, submicron flake graphite particles are granulated into particles with a pore structure in a form of spray granulation; then, heat treatment is performed under a protective atmosphere to convert pitch into amorphous carbon; then, chemical vapor deposition technology is adopted to uniformly distribute nano titanium in the pore structure between the submicron flake graphite inside the spherical graphite particles and on the surface of the spherical graphite particles; subsequently, the nano titanium is converted into titanium nitride through nitriding treatment, that is, titanium nitride is deposited in the pore structure between the submicron flake graphite inside the spherical graphite particles and on the surface of the spherical graphite particles, to prepare the natural graphite-based composite negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon negative electrode materials of lithium ion batteries, in particular to a high-rate long-cycle natural graphite-based composite negative electrode material and a preparation method and application thereof. BACKGROUND

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

[0003] As an important component 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 and discharge capacity, good charge and discharge platform, wide source and low cost. However, the large first irreversible capacity loss and the rapid capacity decay during the cycle process are its fatal shortcomings.

[0004] In order to solve this problem, the existing technology mainly uses natural graphite after crushing and spheroidization to form spherical graphite, which improves the isotropy of natural graphite and alleviates the volume expansion during the charge and discharge process, thereby improving the cycle performance. However, the size of the spherical graphite particles prepared by this method is large, which causes a long migration path of lithium ions and low rate performance of natural graphite, affecting its fast charging performance.

[0005] In order to improve the fast charging performance of natural graphite, the existing technology usually crushes or ball-mills the graphite into sub-micron graphite particles (0.1-1 μm), and then obtains regular spherical graphite structure through spray granulation. Since the small primary particles help to shorten the migration path of lithium ions, the rate performance of spherical graphite is obviously improved. However, the sub-micron graphite particles inside the spherical graphite particles prepared by this method are still oriented as anisotropic scales, and the expansion degree of the sub-micron graphite particles in each direction is different during the charge and discharge process, resulting in rapid capacity decay during the cycle process, thereby significantly reducing the cycle performance of natural graphite.

[0006] Therefore, how to simultaneously improve the cycle performance and rate performance of natural graphite negative electrode material is a problem that still needs to be solved. SUMMARY

[0007] In order to solve the problem that the cycle performance and the rate performance of natural graphite cannot be considered in the prior art, the application 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 provided by the application has simple process and low production cost, and has great commercial application prospect in the field of power batteries with strong market demand.

[0008] The application aims to realize the following technical solutions:

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

[0010] (1) crushing natural flake graphite to obtain flake graphite with a submicron particle size;

[0011] (2) mixing the flake graphite with a submicron particle size of step (1), pitch and a solvent, and performing spray granulation to obtain powder 1;

[0012] (3) performing heat treatment on the powder 1 of step (2) under a protective atmosphere to obtain powder 2;

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

[0014] (5) performing nitriding treatment on the powder 3 of step (4) to obtain the natural graphite-based composite negative electrode material.

[0015] According to the embodiment of the application, in step (1), the natural flake graphite has no particular definition of the median particle size, and the flake graphite with a submicron particle size can be obtained after crushing.

[0016] According to the embodiment of the application, in step (1), the natural flake graphite is preferably irregular flake graphite tailings (with a median particle size of, for example, 1-3 μm) produced in the preparation of spherical graphite; by selecting the irregular flake graphite tailings produced in the preparation of spherical graphite as the raw material, the utilization rate of the natural flake graphite can be improved, and the production cost of the natural graphite-based composite negative electrode material can be reduced.

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

[0018] According to the embodiment of the application, in step (1), the median particle size of the flake graphite with a submicron particle size is 0.1 μm-1 μm, for example, 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 application, in step (1), the pulverization is performed using methods and apparatuses known in the art, and the pulverization parameters are not particularly defined, as long as the flake graphite having a sub-micron particle size can be obtained.

[0020] According to an embodiment of the present application, in step (2), the pitch has a carbon residue value of 20%-80%, for example, 20%, 30%, 40%, 50%, 60%, 70% or 80%.

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

[0022] According to an embodiment of the present application, in step (2), the mass ratio of the pitch to the flake graphite having a sub-micron particle size is (10-20): 100, for example, 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 application, in step (2), the mass ratio of the solvent to the flake graphite having a sub-micron particle size is (30-100): 100, for example, 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 application, in step (2), the mixing time is not particularly defined, and the flake graphite having a sub-micron particle size, the pitch and the solvent of step (1) are mixed uniformly.

[0025] According to an embodiment of the present application, in step (2), the inlet temperature of the spray granulation is 150-210°C, for example, 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, for example, 90°C, 92°C, 95°C, 98°C, 100°C, 102°C, 105°C, 106°C, 108°C or 110°C; and the spray granulation is performed in an air atmosphere.

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

[0027] According to an embodiment of the present application, in step (2), the powder 1 has a median particle size of 5-16 μm, for example 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 application, in step (2), the powder 1 is a spherical graphite particle having a plurality of pore structures; preferably, the powder 1 is a spherical graphite particle having a plurality of pore structures with pore sizes of 10-40 nm. Preferably, the powder 1 comprises flake graphite and pitch with a particle size of submicron level; more preferably, the powder 1 is a spherical graphite particle having a plurality of pore structures formed by flake graphite and pitch with a particle size of submicron level, and pitch is filled between part of the flake graphite with a particle size of submicron level, and a pore structure is formed between part of the flake graphite with a particle size of submicron level, and the pore structure has pore sizes of 10-40 nm.

[0029] According to an embodiment of the present application, in step (2), in the process of spray granulation, the flake graphite with a particle size of submicron level is stacked, pitch is filled between part of the flake graphite with a particle size of submicron level, and a pore structure is formed between part of the flake graphite with a particle size of submicron level, and a spherical graphite particle having a plurality of pore structures with pore sizes of 10-40 nm, i.e. the powder 1, is obtained.

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

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

[0032] According to an embodiment of the present application, in step (3), the powder 2 is a spherical graphite particle having a plurality of pore structures; preferably, the powder 2 is a spherical graphite particle having a plurality of pore structures with pore sizes of 10-40 nm. Preferably, the powder 2 comprises flake graphite and amorphous carbon with a particle size of submicron level; more preferably, the powder 2 is a spherical graphite particle having a plurality of pore structures formed by flake graphite and amorphous carbon with a particle size of submicron level, and amorphous carbon is formed in situ between part of the flake graphite with a particle size of submicron level, and a pore structure is formed between part of the flake graphite with a particle size of submicron level, and the pore structure has pore sizes of 10-40 nm.

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

[0034] Firstly, the powder 2 is placed in a chemical vapor deposition furnace, argon is introduced into the chemical vapor deposition furnace, and then the temperature of the chemical vapor deposition furnace is increased to 150-280℃; then titanium diiodide gas is introduced into the chemical vapor deposition furnace, and pre-deposition is performed for 30-60 min; after the pre-deposition is completed, the temperature of the chemical vapor deposition furnace is increased to 1100-1200℃, and deposition is performed for 1-5 hours to obtain the powder 3.

[0035] According to an embodiment of the present application, 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 application, 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 the powder 2, for example, 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 application, the pre-deposition process can make the titanium diiodide gas more fully enter the pore structure of the powder 2, and can ensure the generation of nano-titanium in the pores of the spherical graphite particles.

[0038] According to an embodiment of the present application, after the chemical vapor deposition of titanium is completed in step (4), a cooling step is further included, which comprises: firstly stopping heating of the chemical vapor deposition furnace, then stopping the introduction of the titanium diiodide gas, and cooling the powder 3 to room temperature with the furnace under an argon atmosphere.

[0039] According to an embodiment of the present application, in step (4), the titanium diiodide gas is prepared by the following method: placing metallic titanium in a vacuum furnace, then introducing iodine vapor (flow rate 100-300 sccm) into the vacuum furnace, and increasing the temperature of the vacuum furnace to 150-280℃, so that the metallic titanium reacts with the iodine vapor to generate the titanium diiodide gas.

[0040] According to an embodiment of the present application, in step (4), the powder 3 comprises nano-titanium, flake graphite with sub-micron particle size and amorphous carbon; preferably, the powder 3 is spherical graphite particles formed by nano-titanium, flake graphite with sub-micron particle size and amorphous carbon, and part of the amorphous carbon is formed in situ between the flake graphite with sub-micron particle size, and part of the nano-titanium is deposited in the pore structure between the flake graphite with sub-micron particle size; the surface of the powder 3 is coated with nano-titanium.

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

[0042] According to an embodiment of the present application, in step (5), after the nitriding treatment, the process further comprises a cooling step, which comprises the following steps: first, stopping heating of the heating furnace, continuing to introduce nitrogen into the heating furnace, stopping the introduction of nitrogen when the temperature of the heating furnace is reduced to 200-400℃, and cooling the solid product with the furnace to room temperature to obtain the natural graphite-based composite negative electrode material.

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

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

[0045] According to an embodiment of the present application, in step (5), the natural graphite-based composite negative electrode material comprises titanium nitride, flake graphite with sub-micron particle size and amorphous carbon; preferably, the natural graphite-based composite negative electrode material is spherical graphite particles formed by titanium nitride, flake graphite with sub-micron particle size and amorphous carbon, and part of the amorphous carbon is formed in situ between the flake graphite with sub-micron particle size, and part of the titanium nitride is deposited in the pore structure between the flake graphite with sub-micron particle size; the surface of the natural graphite-based composite negative electrode material is coated with titanium nitride.

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

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

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

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

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

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

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

[0053] According to an embodiment of the present application, the natural graphite-based composite negative electrode material has a core-shell structure, comprising a core and a shell; the core comprises 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 comprises titanium nitride.

[0054] According to an embodiment of the present application, the thickness of the shell is 1-10 nm, for example 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 application, the median particle size D50 of the natural graphite-based composite negative electrode material is 5-16 μm, for example 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm or 16 μm. 50

[0056] ​The application further provides a use of the natural graphite-based composite negative electrode material in preparation of a negative electrode of a lithium ion battery.

[0057] The application further provides a negative electrode of a lithium ion battery, which comprises the natural graphite-based composite negative electrode material.

[0058] The application further provides a lithium ion battery, which comprises the natural graphite-based composite negative electrode material or the negative electrode of the lithium ion battery.

[0059] Advantages of the application:

[0060] The application first granulates the sub-micron flake graphite particles into spherical graphite particles (i.e. powder 1) in a spray granulation form, and the sub-micron flake graphite particles form more pore structures in the spherical graphite particles during the spray granulation process, specifically, pore structures are formed between the sub-micron flake graphite particles; then the thermal treatment is performed in a protective atmosphere to convert the pitch into amorphous carbon, and the amorphous carbon is used to tightly bond the sub-micron flake graphite particles, thereby obtaining powder 2; then the chemical vapor deposition technology is used to uniformly distribute the nano-titanium in the pore structures between the sub-micron flake graphite particles in the spherical graphite particles and on the surface of the spherical graphite particles, thereby obtaining powder 3; subsequently, the nano-titanium is converted into titanium nitride through the nitriding treatment, i.e. the titanium nitride is deposited in the pore structures between the sub-micron flake graphite particles in the spherical graphite particles and on the surface of the spherical graphite particles, thereby obtaining the natural graphite-based composite negative electrode material.

[0061] On one hand, the high hardness of the titanium nitride is used to stabilize the structure of the natural graphite-based composite negative electrode material, and the internal titanium nitride and the external titanium nitride together buffer the volume expansion of the sub-micron flake graphite during the lithium ion extraction process, thereby improving the cycle performance of the natural graphite-based composite negative electrode material; the natural graphite-based composite negative electrode material prepared in this way has good mechanical properties, and the particles will not be broken during the compaction process and the process of making electrode sheets, thereby further improving the cycle performance of the natural graphite-based composite negative electrode material.

[0062] On the other hand, the high conductivity of the titanium nitride is used to not only accelerate the conduction rate of the lithium ions in the graphite, but also enhance the overall conductivity of the natural graphite-based composite negative electrode material; the internal and external titanium nitride of the natural graphite-based composite negative electrode material together enable the lithium ion battery to have the characteristics of high rate performance and long cycle life. DETAILED DESCRIPTION

[0063] The preparation method of the present application will be further described in detail below in connection with specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application and should not be construed as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is encompassed within the scope of the present application.

[0064] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples are commercially available unless otherwise specified.

[0065] The natural flake graphite used in the following examples and comparative examples has a purity of ≥ 99% and is derived from irregular flake graphite tailings produced during the preparation of spherical graphite.

[0066] The titanium diiodide gas used in the following examples is prepared by placing metallic titanium in a vacuum furnace and then introducing iodine vapor at a flow rate of 300 seem into the vacuum furnace, increasing the temperature of the vacuum furnace to 180°C, and allowing the metallic titanium to react with the iodine vapor at this temperature to produce titanium diiodide gas.

[0067] Example 1

[0068] (1) 1000 g of natural flake graphite (D 50 of 2 μm) was pulverized to obtain flake graphite (D 50 of 0.95 μm) having a submicron particle size;

[0069] (2) 100 g of the flake graphite having a submicron particle size from step (1), 12 g of pitch (carbon residue value of 60%) and 60 g of ethanol were mixed to obtain a slurry, and the slurry was spray granulated (inlet temperature of 180°C and outlet temperature of 100°C; air atmosphere) to obtain powder 1 (D 50 of 8 μm);

[0070] (3) Powder 1 from step (2) was heat treated at 1000°C for 3 hours under a nitrogen atmosphere and cooled to room temperature to obtain powder 2;

[0071] (4) 100 g of powder 2 was first placed in a chemical vapor deposition furnace, argon gas was introduced into the chemical vapor deposition furnace, and then the temperature of the chemical vapor deposition furnace was increased to 200°C; titanium diiodide gas at a flow rate of 600 seem was then introduced into the chemical vapor deposition furnace and pre-deposited for 40 minutes; after the pre-deposition was completed, the temperature of the chemical vapor deposition furnace was increased to 1100°C and deposition was carried out for 1 hour; after the deposition was completed, the chemical vapor deposition furnace was stopped heating and the introduction of the titanium diiodide gas was stopped, and the solid product was cooled to room temperature under an argon atmosphere to obtain powder 3;

[0072] (5) Put 100 g of the powder 3 of step (4) into a heating furnace, introduce nitrogen gas (300 seem) into the heating furnace, and heat the temperature of the heating furnace to 1000℃ for 3 hours. When the temperature of the heating furnace is cooled to 200℃, stop the introduction of nitrogen gas, and cool the solid product to room temperature in the furnace to obtain the natural graphite-based composite negative electrode material.

[0073] The natural graphite-based composite negative electrode material has a core-shell structure, comprising a core and a shell layer; the core comprises submicron flake graphite, amorphous carbon and titanium nitride; the amorphous carbon is distributed between the submicron flake graphite; the titanium nitride is distributed in the pore structure between the submicron flake graphite; the shell layer comprises 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.

[0074] Example 2

[0075] (1) Crush 1000 g of natural flake graphite (D 50 to obtain submicron flake graphite (D 50 0.9 μm);

[0076] (2) Mix 100 g of the submicron flake graphite of step (1), 15 g of pitch (carbon residue value 60%) and 70 g of ethanol to obtain a slurry, and spray granulate the slurry (inlet temperature 180℃, outlet temperature 100℃; air atmosphere) to obtain powder 1 (D 50 8 μm);

[0077] (3) Heat treat the powder 1 of step (2) at 900℃ for 6 hours under a nitrogen atmosphere, and cool to room temperature to obtain powder 2;

[0078] (4) First, place 100 g of the powder 2 in a chemical vapor deposition furnace, introduce argon gas into the chemical vapor deposition furnace, and then increase the temperature of the chemical vapor deposition furnace to 200℃. Then introduce titanium diiodide gas with a flow rate of 500 seem into the chemical vapor deposition furnace, and pre-deposit for 60 min. After the pre-deposition, increase the temperature of the chemical vapor deposition furnace to 1100℃, and deposit for 3 hours. After the deposition, stop heating the chemical vapor deposition furnace, and then stop introducing the titanium diiodide gas. Cool the solid product to room temperature in the argon atmosphere to obtain powder 3;

[0079] (5) Put 100 g of the powder 3 of step (4) into a heating furnace, introduce nitrogen gas (500 seem) into the heating furnace, and heat the temperature of the heating furnace to 1200℃ for 3 hours. When the temperature of the heating furnace is cooled to 300℃, stop the introduction of nitrogen gas. The solid product is cooled to room temperature in the furnace to obtain the natural graphite-based composite negative electrode material.

[0080] The natural graphite-based composite negative electrode material has a core-shell structure, including a core and a shell layer. The core includes submicron flake graphite, amorphous carbon, and titanium nitride. The amorphous carbon is distributed between the submicron flake graphite. The titanium nitride is distributed in the pore structure between the submicron flake graphite. 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 negative electrode material, and the mass of the titanium nitride accounts for 2.5% of the total mass of the natural graphite-based composite negative electrode material.

[0081] Example 3

[0082] (1) Crush 1000 g of natural flake graphite (D 50 to obtain submicron flake graphite (D 50 of 0.85 μm);

[0083] (2) Mix 100 g of the submicron flake graphite of step (1), 18 g of pitch (carbon residue value 60%), and 60 g of ethanol to obtain a slurry. The slurry is spray granulated (inlet temperature 180℃, outlet temperature 100℃; air atmosphere) to obtain powder 1 (D 50 of 8 μm);

[0084] (3) Heat treat the powder 1 of step (2) at 1000℃ for 3 hours under a nitrogen atmosphere, and cool to room temperature to obtain powder 2;

[0085] (4) First, place 100 g of the powder 2 in a chemical vapor deposition furnace, introduce argon gas into the chemical vapor deposition furnace, and then increase the temperature of the chemical vapor deposition furnace to 200℃. Then introduce titanium diiodide gas with a flow rate of 600 seem into the chemical vapor deposition furnace, and pre-deposit for 40 min. After the pre-deposition, increase the temperature of the chemical vapor deposition furnace to 1100℃, and deposit for 3 hours. After the deposition, stop heating the chemical vapor deposition furnace, and then stop introducing the titanium diiodide gas. The solid product is cooled to room temperature in the argon atmosphere to obtain powder 3;

[0086] (5) Put 100 g of the powder 3 of step (4) into a heating furnace, introduce nitrogen gas (300 seem) into the heating furnace, and heat the temperature of the heating furnace to 1280℃ for 5 hours. When the temperature of the heating furnace is cooled to 300℃, stop the introduction of nitrogen gas. The solid product is cooled to room temperature in the furnace to obtain the natural graphite-based composite negative electrode material.

[0087] The natural graphite-based composite negative electrode material has a core-shell structure, including a core and a shell layer. The core includes submicron flake graphite, amorphous carbon, and titanium nitride. The amorphous carbon is distributed between the submicron flake graphite. The titanium nitride is distributed in the pore structure between the submicron flake graphite. 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 negative electrode material, and the mass of the titanium nitride accounts for 3.4% of the total mass of the natural graphite-based composite negative electrode material.

[0088] Example 4

[0089] (1) Crush 1000 g of natural flake graphite (D 50 of 1 μm) to obtain submicron flake graphite (D 50 of 0.8 μm);

[0090] (2) Mix 100 g of the submicron flake graphite of step (1), 20 g of pitch (carbon residue value 60%), and 80 g of ethanol to obtain a slurry. The slurry is spray granulated (inlet temperature 180℃, outlet temperature 100℃; air atmosphere) to obtain powder 1 (D 50 of 8 μm);

[0091] (3) Heat treat the powder 1 of step (2) at 1000℃ for 3 hours under a nitrogen atmosphere, and cool to room temperature to obtain powder 2;

[0092] (4) First, place 100 g of the powder 2 in a chemical vapor deposition furnace, introduce argon gas into the chemical vapor deposition furnace, and then increase the temperature of the chemical vapor deposition furnace to 200℃. Then introduce titanium diiodide gas with a flow rate of 600 seem into the chemical vapor deposition furnace, and pre-deposit for 40 min. After the pre-deposition, increase the temperature of the chemical vapor deposition furnace to 1100℃, and deposit for 5 hours. After the deposition, stop heating the chemical vapor deposition furnace, and then stop introducing the titanium diiodide gas. The solid product is cooled to room temperature in the argon atmosphere to obtain powder 3;

[0093] (5) Put 100 g of the powder 3 of step (4) into a heating furnace, introduce nitrogen gas (300 seem) into the heating furnace, and heat the temperature of the heating furnace to 1000℃ for 3 hours. When the temperature of the heating furnace is cooled to 200℃, stop the introduction of nitrogen gas, and cool the solid product to room temperature in the furnace to obtain the natural graphite-based composite negative electrode material.

[0094] The natural graphite-based composite negative electrode material has a core-shell structure, comprising a core and a shell layer; the core comprises submicron flake graphite, amorphous carbon and titanium nitride; the amorphous carbon is distributed between the submicron flake graphite; the titanium nitride is distributed in the pore structure between the submicron flake graphite; the shell layer comprises titanium nitride; the mass of the amorphous carbon accounts for 6% of the total mass of the natural graphite-based composite negative electrode material, and the mass of the titanium nitride accounts for 4% of the total mass of the natural graphite-based composite negative electrode material.

[0095] Comparative Example 1

[0096] (1) Crush 1000 g of natural flake graphite (D 50 of 2 μm) to obtain submicron flake graphite (D 50 of 0.95 μm);

[0097] (2) Mix 100 g of the submicron flake graphite of 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 180℃, outlet temperature 100℃; air atmosphere) to obtain powder 1 (D 50 of 8 μm);

[0098] (3) Heat treat the powder 1 of step (2) at 1000℃ for 3 hours under a nitrogen atmosphere, and cool to room temperature to obtain a natural graphite negative electrode material.

[0099] Comparative Example 2

[0100] (1) Crush 1000 g of natural flake graphite (D 50 of 2 μm) to obtain submicron flake graphite (D 50 of 0.95 μm);

[0101] (2) Mix 100 g of the submicron flake graphite of 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, and the slurry is spray granulated (inlet temperature 180℃, outlet temperature 100℃; air atmosphere) to obtain powder 1 (D 50 of 8 μm);

[0102] (3) heat treat the powder 1 of step (2) at 1000℃ for 3 hours under nitrogen atmosphere, cool to room temperature to obtain powder 2;

[0103] (4) put 100g of the powder 2 of step (3) into a chemical vapor deposition furnace, heat to 1015℃ at a rate of 5℃ / min, while introducing nitrogen gas with a flow rate of 120sccm and argon gas containing titanium tetrachloride with a flow rate of 100sccm obtained in a bubbling manner into the chemical vapor deposition furnace, keep for 5 hours; after keeping, introduce argon carrier gas with a flow rate of 200sccm, stop introducing the titanium source, cool to 800℃, stop introducing the nitrogen source, continue to cool, when cooling to 300℃, stop introducing the argon, then cool to room temperature to obtain the natural graphite-based composite negative electrode material.

[0104] The natural graphite-based composite negative electrode material has a core-shell structure, comprising a core and a shell; the core comprises submicron flake graphite, amorphous carbon and titanium nitride; part of the amorphous carbon is distributed between the submicron flake graphite; part of the amorphous carbon is distributed between the submicron flake graphite and the titanium nitride; part of the submicron flake graphite and part of the submicron flake graphite and the titanium nitride in the core form a pore structure, and the pore size of the pore structure is 10-40nm; the shell comprises 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.

[0105] Comparative Example 3

[0106] (1) crush 1000g of natural flake graphite (D 50 of 2μm) to obtain submicron flake graphite (D 50 of 0.95μm);

[0107] (2) mix 100g of the submicron flake graphite of step (1), 12g of pitch (carbon residue value 60%) and 60g of ethanol to obtain a slurry, and the slurry is granulated by spraying (inlet temperature 180℃, outlet temperature 100℃; air atmosphere) to obtain powder 1 (D 50 of 8μm);

[0108] (3) heat treat the powder 1 of step (2) at 1000℃ for 3 hours under nitrogen atmosphere, cool to room temperature to obtain powder 2;

[0109] (4) 100 g of the powder 2 of step (3) was placed into a chemical vapor deposition furnace, heated to 1015°C at a rate of 5°C / min, while nitrogen gas with a flow rate of 120 seem and titanium tetrachloride-containing argon gas with a flow rate of 100 seem obtained in a bubbling manner were introduced into the chemical vapor deposition furnace, and the temperature was maintained for 5 hours; after the temperature was maintained, argon carrier gas with a flow rate of 200 seem was introduced, the introduction of the titanium source was stopped, the temperature was lowered to 800°C, the introduction of the nitrogen source was stopped, and the temperature was further lowered; when the temperature was lowered to 300°C, the introduction of the argon gas was stopped, and then the temperature was lowered 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, and includes a core and a shell layer; the core includes submicron flake graphite and amorphous carbon; the amorphous carbon is distributed between the submicron flake graphite; a pore structure is formed between the submicron flake graphite 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 material prepared in the examples and comparative examples, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 95:1:1.5:2.5, and uniformly coated on a copper foil. The coated electrode was dried in a vacuum drying oven at 120°C for 12 hours. Simulated battery assembly was performed in an argon-protected Braun glove box, the electrolyte was 1M-LiPF6+EC:DEC:DMC (volume ratio of 1:1:1), and a lithium metal sheet was used as the counter electrode. Simulated battery testing was performed in a 5V, 10mA new battery test cabinet, the charge and discharge voltage was 0.01-1.5V, and the charge and discharge rate was 0.1C. The initial capacity and efficiency obtained by testing are shown in Table 1.

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

[0114] Table 1. Electrochemical performance test results

[0115]

[0116] Compared with Examples 1-4, the pores formed between the sub-micron flake graphite in the natural graphite-based composite anode material of Comparative Example 1 and the surface thereof have no nano-titanium nitride deposited thereon, and the volume expansion of the sub-micron flake graphite during the process of deintercalating lithium ions cannot be buffered, resulting in a significant decrease 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 the sub-micron flake graphite particles and nano-titanium nitride into spherical graphite / nano-titanium nitride composite particles with a pore structure by spray granulation; in the subsequent chemical vapor deposition, the nano-titanium nitride cannot be deposited into the pores, that is, the core of the natural graphite-based composite anode material thus obtained still has a large number of pore structures, and although the nano-titanium nitride can alleviate the expansion of the sub-micron flake graphite during the cycle process, such structure is unstable and is prone to breakage during the cycle process, resulting in a battery with low cycle performance.

[0118] Compared with Example 1, the pores formed between the sub-micron flake graphite in the natural graphite-based composite anode material of Comparative Example 3 have no nano-titanium nitride deposited thereon, and in the subsequent chemical vapor deposition, the nano-titanium nitride cannot be deposited into the pores, and can only rely on the nano-titanium nitride in the shell to alleviate the volume expansion of the sub-micron flake graphite in the core during the cycle process, but such structure is unstable and is prone to breakage during the cycle process, resulting in a battery with a significantly decreased cycle performance and a significantly increased expansion rate of the electrode.

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

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 sub-micron flake graphite; (2) mixing the sub-micron flake graphite of step (1), pitch and a solvent, spray granulating to obtain powder 1; (3) heat treating the powder 1 of step (2) under a protective atmosphere to obtain powder 2; (4) chemically vapor depositing titanium on the powder 2 of step (3) to obtain powder 3; (5) nitrogenizing the powder 3 of step (4) to obtain the natural graphite-based composite negative electrode material.

2. The production method according to claim 1, wherein, In step (1), the natural flake graphite is irregular flake graphite tailings produced during the preparation of spherical graphite; In step (1), the median particle size of the sub-micron flake graphite is 0.1-1 μm.

3. The production method according to claim 1, wherein, In step (2), the mass ratio of the pitch to the sub-micron flake graphite is (10-20):100; the mass ratio of the solvent to the sub-micron flake graphite is (30-100):

100.

4. The production method according to claim 1, wherein 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; the spray granulation is performed under an air atmosphere.

5. The production method according to claim 1, wherein In step (2), the powder 1 is spherical graphite particles with a pore structure formed by the sub-micron flake graphite and the pitch, and part of the sub-micron flake graphite is filled with the pitch, and part of the sub-micron flake graphite forms a pore structure, and the pore size of the pore structure is 10-40 nm.

6. The production method according to claim 1, wherein In step (3), the heat treatment is performed at a temperature of 800-1200°C for 2-10 hours.

7. The production method according to claim 1, wherein In step (3), the powder 2 is spherical graphite particles with a pore structure formed by the sub-micron flake graphite and amorphous carbon, and part of the sub-micron flake graphite forms amorphous carbon in situ, and part of the sub-micron flake graphite forms a pore structure, and the pore size of the pore structure is 10-40 nm.

8. The production method according to claim 1, wherein In step (4), the chemical vapor deposition of titanium comprises the following steps: firstly, placing the powder 2 in a chemical vapor deposition furnace, introducing argon into the chemical vapor deposition furnace, and then increasing the temperature of the chemical vapor deposition furnace to 150-280℃; secondly, introducing titanium diiodide gas into the chemical vapor deposition furnace, pre-depositing for 30 60min, increasing the temperature of the chemical vapor deposition furnace to 1100-1200℃ after the pre-deposition, and depositing for 1-5 hours to obtain the powder 3.

9. The production method according to claim 8, wherein The flow rate of the titanium diiodide gas is 500 1000 sccm; The mass-volume ratio of the titanium diiodide gas to the powder 2 is 0.6-5 L / g.

10. The production method according to claim 8, wherein In step (4), after the chemical vapor deposition of titanium is completed, a cooling step is further included, which comprises: first stopping heating in the chemical vapor deposition furnace, then stopping the introduction of the titanium diiodide gas, and cooling the powder 3 to room temperature in the furnace under an argon atmosphere.

11. The method of producing according to claim 1, wherein, In step (4), the powder 3 is nanometer titanium, spherical graphite particles formed by the sub-micron flake graphite and amorphous carbon, and part of the sub-micron flake graphite forms amorphous carbon in situ, and part of the sub-micron flake graphite has nanometer titanium deposited in the pore structure; the surface of the powder 3 is coated with nanometer titanium.

12. The method of making according to any one of claims 1-11, wherein, In step (5), the nitrogenizing treatment comprises the following steps: placing the powder 3 in a heating furnace, introducing nitrogen into the heating furnace, heating the temperature of the heating furnace to 1000-1400°C, maintaining the temperature for 1-5 hours, and cooling to room temperature to obtain the natural graphite-based composite negative electrode material.

13. The method of making according to claim 12, wherein, In step (5), the nitrogenization treatment further comprises a cooling step after the nitrogenization treatment is completed, the cooling step comprising: firstly, stopping the heating of the heating furnace, continuing to introduce nitrogen into the heating furnace, and stopping the introduction of nitrogen when the temperature of the heating furnace is reduced to 200 400℃, and cooling the solid product with the furnace to room temperature to obtain the natural graphite-based composite negative electrode material.

14. The method of producing according to claim 1, wherein, In step (5), the natural graphite-based composite negative electrode material is a spherical graphite particle formed by titanium nitride, flake graphite with a sub-micron particle size and amorphous carbon, and amorphous carbon is formed in situ between part of the flake graphite with a sub-micron particle size, and titanium nitride is deposited in the pore structure between part of the flake graphite with a sub-micron particle size; the surface of the natural graphite-based composite negative electrode material is coated with titanium nitride.

15. A natural graphite-based composite negative electrode material prepared by the method of any one of claims 1-14.

16. The natural graphite-based composite anode material of claim 15, wherein, The natural graphite-based composite negative electrode material comprises flake graphite with a sub-micron particle size, amorphous carbon and titanium nitride.

17. The natural graphite-based composite anode material of claim 15, wherein, The natural graphite-based composite negative electrode material is a composite of flake graphite with a sub-micron particle size, amorphous carbon and titanium nitride.

18. The natural graphite-based composite anode material according to claim 16 or 17, wherein, The mass of the flake graphite with a sub-micron particle size 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; and the mass of the titanium nitride accounts for 1-4% of the total mass of the natural graphite-based composite negative electrode material.

19. The natural graphite-based composite anode material of claim 16 or 17, wherein, 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; and the titanium nitride is also distributed on the surface of the composite of flake graphite with a sub-micron particle size, amorphous carbon and titanium nitride.

20. The natural graphite-based composite anode material of claim 16 or 17, wherein, The natural graphite-based composite negative electrode material has a core-shell structure, comprising a core and a shell; the core comprises 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; and the shell comprises titanium nitride.

21. A negative electrode of a lithium ion battery, comprising the natural graphite-based composite negative electrode material of any one of claims 15-20.

22. A lithium ion battery, comprising the natural graphite-based composite negative electrode material of any one of claims 15-20 or the negative electrode of the lithium ion battery of claim 21.

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