Composite graphite negative electrode material and preparation method and application thereof

Abstract

The invention discloses a preparation method of a composite graphite negative electrode material, which comprises the following steps: S1, mixing nitric acid and concentrated sulfuric acid to obtain a mixed solution; and S2, adding a raw material containing target expanded-layer graphite into the mixed solution in the step S1, and reacting to obtain the graphite oxide material, and S3, mixing the graphite oxide material in the step S2 with an aqueous solution of a carbon source, stirring at a constant temperature until moisture is completely evaporated, and calcining in an inactive atmosphere to obtain the composite graphite negative electrode material. The preparation process is simple, easy to operate, energy-saving and high in production efficiency; raw material preparation and reaction equipment are simple, the reaction process is easy to regulate and control, and the method is particularly suitable for industrial batch production. And the material has relatively good rate capability and cycle stability. The method is applied to fast charging operation of a lithium ion battery system.

Description

Technical Field

[0001] The present application relates to a composite graphite negative electrode material and a preparation method and application thereof, belonging to the technical field of carbon materials and lithium ion batteries. Background Art

[0002] Lithium-ion batteries have shown great application prospects and broad economic benefits from portable electronic devices to electric vehicles, from civilian fields to national defense construction due to their high energy density, long cycle life, no memory effect, environmental protection and durability, and have become the main battery system for providing power. As the excessive use of fossil fuels will bring about serious energy crises and environmental pollution, the use of clean transportation vehicles instead of fuel vehicles is strongly advocated, which has led to the rapid prosperity of the lithium-ion battery-powered electric vehicle industry. Although electric vehicles are comparable to traditional internal combustion engine vehicles in terms of power and range, the long charging time limits its market penetration and public acceptance. Therefore, improving fast charging performance is the focus of lithium-ion battery technology research and development and is also the only way for the high-quality development and popularization of the electric vehicle industry. Graphite is the most widely used negative electrode material in lithium-ion battery systems due to its abundant reserves, low price, excellent lithium insertion and extraction reversibility, and theoretical specific capacity of 372mAh / g. However, when using graphite as the negative electrode of lithium-ion batteries in fast charging applications, there are some technical bottlenecks, including: (1) Graphite has a typical two-dimensional layered structure with an interlayer spacing of 0.335nm. During multiple charge / discharge reactions, lithium ions are repeatedly embedded in / out of the interlayers, making the graphite structure extremely vulnerable to damage. (2) The path of lithium ion embedding into graphite is from the edge of the layer to the inside. The long path causes a large lithium concentration difference inside the graphite during fast charging and uneven stress distribution between particles, resulting in cracking of the entire electrode and even separation of the material from the current collector. (3) The working potential of graphite is about 0.1V vs. Li / Li + , and the working potential of metallic lithium (0V vs.Li / Li + ) are very close, and surface lithium precipitation is prone to occur during fast charging. The growth of lithium dendrites may cause battery performance degradation or even puncture the diaphragm, leading to thermal runaway and fire of the battery. Therefore, due to the urgent needs of applications and the safety of batteries and their devices, there is an urgent need for a fast-charging lithium-ion battery with a graphite negative electrode that can overcome the above bottlenecks. The oxidative modification of graphite is usually accompanied by an increase in the interlayer spacing, which is very beneficial to the rapid embedding and extraction of lithium ions, and is an effective way to improve the performance of graphite negative electrodes. Surface coating improves the performance of graphite by optimizing the interface between the graphite material and the electrolyte to reduce the interfacial impedance. In the prior art, there are few reports on papers or patents that use a dual modification strategy of surface oxidation and coating of graphite materials to improve the fast charging performance of lithium-ion batteries using graphite negative electrodes. Summary of the invention

[0003] According to one aspect of the present application, in response to the shortcomings of existing preparation technologies, a composite graphite negative electrode material is provided, which adopts a technology that improves the fast charging performance of graphite by a dual method of chemical oxidation combined with carbon coating.

[0004] This application adopts the following technical solutions:

[0005] A method for preparing a composite graphite negative electrode material comprises the following steps:

[0006] S1, mixing nitric acid and concentrated sulfuric acid to obtain a mixed solution;

[0007] S2, adding the raw material containing the target expanded layer graphite to the mixed solution in step S1, reacting to obtain the graphite oxide material;

[0008] S3, mixing the graphite oxide material in step S2 with an aqueous solution of a carbon source, stirring at a constant temperature until the water evaporates completely, and calcining in an inactive atmosphere to obtain the composite graphite negative electrode material.

[0009] Optionally, the volume ratio of the nitric acid to concentrated sulfuric acid is 1:0.1-10;

[0010] Optionally, the volume ratio of the nitric acid to the concentrated sulfuric acid is any value selected from 1:0.1, 1:0.5, 1:1, or any range value between the two.

[0011] Optionally, the volume ratio of the nitric acid to concentrated sulfuric acid is 1:0.25-4.

[0012] Optionally, the weight ratio of the raw material to the mixed liquid is 0.03 to 0.8:1.

[0013] Optionally, the weight ratio of the raw material to the mixed liquid is any value among 0.03:1, 0.04:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, or a range value between any two of them.

[0014] Optionally, the weight ratio of the raw material to the mixed liquid is 0.03 to 0.5:1.

[0015] Optionally, the target expanded layer graphite is selected from at least one of natural flake graphite, natural microcrystalline graphite, natural block graphite, and artificial graphite.

[0016] Optionally, the raw material further contains a coating agent;

[0017] The coating agent is selected from at least one of glucose, citric acid and sucrose;

[0018] Optionally, the weight ratio of the target expanded layer graphite to the coating agent is 1:0.1-1.

[0019] Optionally, the weight ratio of the target expanded layer graphite to the coating agent is selected from any value of 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or any range value between two of them.

[0020] Optionally, in step S2, the reaction conditions are: constant temperature reaction, the temperature is 0 to 50° C., and the reaction time is 0.15 to 12 h.

[0021] Optionally, in step S2, the reaction conditions are: constant temperature reaction, the temperature is selected from any value of 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or any range between two values.

[0022] Optionally, in step S2, the reaction conditions are: constant temperature reaction, the temperature is 0 to 50° C., and the reaction time is 1 to 6 hours.

[0023] Optionally, in step S2, the reaction conditions are: the reaction time is selected from any value of 1h, 2h, 3h, 4h, 5h, 6h, or any range between two values.

[0024] Optionally, after the reaction is completed, the product is washed with distilled water until the pH is 7, and then dried at a temperature of 50 to 80° C. for 0.5 to 6 hours.

[0025] Optionally, the drying temperature is selected from any value of 50° C., 60° C., 70° C., 80° C., or any range between the two.

[0026] Optionally, the drying time is any value among 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, or a range value between any two of them.

[0027] Optionally, in step S3, the calcination conditions are: temperature of 550-950° C., and calcination time of 0.5-6 h.

[0028] The inert atmosphere is argon.

[0029] Optionally, in step S3, the calcination conditions are: a heating rate of 1 to 15°C / min, a temperature of 550 to 950°C, and a calcination time of 0.5 to 12h.

[0030] Optionally, in step S3, the calcination conditions are: a heating rate of 1 to 15°C / min, a temperature of 550 to 950°C, and a calcination time of 0.5 to 6h.

[0031] Optionally, in step S3, the calcination conditions include:

[0032] The heating rate is selected from any value of 1°C / min, 3°C / min, 6°C / min, 9°C / min, 12°C / min, 15°C / min, or any range between the two values;

[0033] The temperature is selected from any value among 550°C, 650°C, 750°C, 850°C, 950°C, or any range between the two;

[0034] The calcination time is selected from any value of 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, or any range between the two.

[0035] Optionally, in step S3, the temperature of the constant temperature stirring is 15-35°C.

[0036] According to another aspect of the present application, a composite graphite negative electrode material prepared according to the above preparation method is also provided, wherein the composite graphite negative electrode material comprises a core of graphite oxide material and a carbon coating layer.

[0037] The interlayer spacing of the composite graphite negative electrode material is 0.335-0.5 nm.

[0038] Optionally, the interlayer spacing of the composite graphite negative electrode material is selected from any value among 0.335nm, 0.35nm, 0.375nm, 0.4nm, 0.45nm, 0.5nm, or any range between two values.

[0039] The thickness of the carbon coating layer is 1 to 10 nm.

[0040] According to another aspect of the present application, there is also provided a composite graphite material prepared by the above preparation method and at least one of the above composite graphite negative electrode materials for use as a negative electrode material in the manufacture of a fast-charging lithium-ion battery.

[0041] The technical solution of the present application adopts a simple and feasible dual strategy of chemical oxidation and surface coating to realize fast-charging lithium-ion battery technology with graphite as the negative electrode.

[0042] The beneficial effects of this application include:

[0043] The preparation method of the composite graphite negative electrode material provided in the present application has a simple preparation process, is easy to operate, saves energy and has high production efficiency; the raw material preparation and reaction equipment are relatively simple, and the reaction process is easy to control. The method of the present application is particularly suitable for industrial mass production. The composite graphite negative electrode material prepared in the present application has excellent electrochemical properties. The prepared composite graphite negative electrode material can be used in high-performance lithium-ion battery systems and for preparing fast-charging lithium-ion batteries. DETAILED DESCRIPTION

[0044] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0045] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0046] According to one implementation of the present application:

[0047] The preparation of graphite oxide material includes the following:

[0048] (1) preparing an oxidizing solvent: mixing nitric acid and concentrated sulfuric acid in a volume ratio of 1:0.1 to 1 to prepare a mixed solvent;

[0049] (2) Mixing ingredients: mixing the target expanded graphite raw material and the oxidizing solvent in any ratio between 1:0 and 5 by weight;

[0050] (3) dispersing the material: dispersing the solid powder of step (2) in the mixed solvent prepared in step (1) in order to form a solid-liquid suspension;

[0051] (4) Reaction: The solid-liquid suspension of step (3) was stirred for 30 min and then allowed to stand and react at a constant temperature;

[0052] (5) Washing: Separate the solid and liquid of the reactants by centrifugation or vacuum filtration, and wash the resulting solid precipitate with ultrapure water for at least 3 times, or until the pH of the washed liquid reaches 7;

[0053] (6) Drying: The solid precipitate washed in step (5) is dried using a drying device to obtain a product, namely, graphite oxide material.

[0054] Among them, the equipment for maintaining constant temperature is a water bath, condensed water, ice water bath, etc.;

[0055] The conditions for implementing the centrifugal method in step (5) are: centrifugal speed of 7000-9000 rpm, centrifugal time of 5-20 minutes; the vacuum filtration device uses a filter membrane with a pore size of 0.2-0.5 microns; optionally: centrifugal speed of 8500 rpm, centrifugal time of 10 minutes. The vacuum filtration device can optionally use a filter membrane with a pore size of 0.22-0.45 microns.

[0056] The drying equipment in step (6) is an oven, a drying box or an infrared lamp.

[0057] Example 1

[0058] 5 ml of nitric acid and 10 ml of concentrated sulfuric acid were mixed evenly as a mixed solvent, 3 g of natural microcrystalline graphite was dispersed in the mixed solvent, stirred evenly for 60 minutes and then allowed to stand for reaction at a temperature of 20°C for 1 hour. After the reaction was completed, the mixture was washed with distilled water until the pH value was 7, and the solid precipitate obtained by filtration was dried in an oven at a temperature of 80°C to obtain an oxidized graphite material.

[0059] After testing, it was found that the interlayer spacing of the graphite oxide material increased to 0.337nm compared to the original graphite oxide powder.

[0060] Example 2

[0061] 0.5 g of glucose was dissolved in 20 ml of water, and then 1.0 g of graphite oxide powder in Example 1 was added to the water, stirred evenly and heated to 25° C. until the water evaporated. The dried powder was then subjected to high-temperature derivatization at 650° C. for 2 h in a tubular furnace filled with argon to form a carbon coating layer on the outside of the graphite oxide powder, thereby obtaining a composite graphite negative electrode material.

[0062] After testing, the thickness of the carbon coating layer was 5nm.

[0063] The composite graphite negative electrode material prepared in the present application greatly improves the rate performance and cycle performance of natural microcrystalline graphite, and is a fast-charging lithium-ion battery at high current densities of 3C, 6C, 8C and 10C (1C = 372 mA / g).

[0064] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a composite graphite negative electrode material, characterized in that: The steps include: S1, mixing nitric acid and concentrated sulfuric acid to obtain a mixed solution; S2, adding the raw material containing the target expanded layer graphite to the mixed solution in step S1, reacting to obtain the graphite oxide material; S3, mixing the graphite oxide material in step S2 with an aqueous solution of a carbon source, stirring at a constant temperature until the water evaporates completely, and calcining in an inactive atmosphere to obtain the composite graphite negative electrode material.

2. The preparation method according to claim 1, characterized in that: The volume ratio of the nitric acid to the concentrated sulfuric acid is 1:0.1-10.

3. The preparation method according to claim 1, characterized in that: The weight ratio of the raw material to the mixed liquid is 0.03 to 0.8:

1.

4. The preparation method according to claim 1, characterized in that: The target expanded layer graphite is selected from at least one of natural flake graphite, natural microcrystalline graphite, natural block graphite and artificial graphite.

5. The preparation method according to claim 1, characterized in that: The raw material also contains a coating agent; The coating agent is selected from at least one of glucose, citric acid and sucrose; Preferably, the weight ratio of the target expanded layer graphite to the coating agent is 1:0.1-1.

6. The preparation method according to claim 1, characterized in that: In step S2, the reaction conditions are: constant temperature reaction, the temperature is 0 to 50° C., and the reaction time is 0.15 to 12 hours.

7. The preparation method according to claim 1, characterized in that: In step S3, the calcination conditions are: temperature of 550-950° C., calcination time of 0.5-6 h; Preferably, in step S3, the temperature of the constant temperature stirring is 15-35°C.

8. The composite graphite negative electrode material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The composite graphite negative electrode material comprises a graphite oxide material core and a carbon coating layer.

9. The graphite negative electrode material according to claim 8, characterized in that: The interlayer spacing of the graphite oxide material is 0.335 to 0.5 nm; Preferably, the carbon coating layer has a thickness of 1 to 10 nm.

10. At least one of the composite graphite material prepared by the preparation method according to any one of claims 1 to 8 and the composite graphite negative electrode material according to claim 9 is used as a negative electrode material in the manufacture of a fast-charging lithium-ion battery.