CN111613794B

CN111613794B - Modified graphite negative electrode material, preparation method thereof and lithium ion battery

Info

Publication number: CN111613794B
Application number: CN202010467456.4A
Authority: CN
Inventors: 马超; 吴敦勇; 李守斌; 徒雨龙
Original assignee: Beiteri Jiangsu New Energy Materials Co ltd
Current assignee: Beiteri Jiangsu New Energy Materials Co ltd
Priority date: 2020-05-28
Filing date: 2020-05-28
Publication date: 2022-07-01
Anticipated expiration: 2040-05-28
Also published as: CN111613794A

Abstract

The invention provides a modified graphite negative electrode material, a preparation method thereof and a lithium ion battery. The method comprises the following steps: carrying out hydrothermal reaction or solvothermal reaction on the graphite suspension to obtain primary treated graphite; mixing and reacting the primary treated graphite with an intercalation agent to obtain secondary treated graphite; and mixing the secondary treated graphite with a carbon source, and then carrying out pre-oxidation treatment, pre-carbonization treatment and carbonization treatment to obtain the modified graphite cathode material. The modified graphite cathode material obtained by the preparation method provided by the invention has the characteristics of high capacity, good cycle performance, good rate capability and low volume expansion effect.

Description

Modified graphite negative electrode material, preparation method thereof and lithium ion battery

Technical Field

The invention belongs to the technical field of energy storage materials, relates to a negative electrode material, a preparation method thereof and a lithium ion battery, and particularly relates to a modified graphite negative electrode material, a preparation method thereof and a lithium ion battery.

Background

The lithium ion battery is a recyclable energy storage device, and compared with lead-acid, nickel-chromium and nickel-hydrogen batteries, the lithium ion battery has the advantages of high volume (mass) specific capacity, high power density, no memory effect, environmental friendliness and the like, so that the lithium ion battery is widely applied to various notebook computers, mobile phones, digital cameras, portable electronic products, electric automobiles, energy storage devices and the like. However, with the continuous development of society, lithium ion batteries are required to have higher specific capacity, better safety performance and faster charge and discharge rate. In order to achieve these objectives, researchers have started with each module of battery composition, mainly including positive and negative electrode materials, electrolyte, separator, and assembly techniques. Among them, improving the performance of the negative electrode material is one of the important works performed by researchers.

Graphite is mainly used as a negative electrode material of a commercial lithium ion battery in the current market, and the theoretical lithium storage capacity of the graphite can reach 372mAh g^-1Has the advantages of low price, environmental protection and rich resources. However, the natural graphite in the graphite material has poor compatibility with electrolyte, larger first irreversible capacity and poor high-rate charge and discharge performance, influences the long cycle life,modification is generally required to be useful. The artificial graphite in the graphite material has the advantages of stable structure, better compatibility with electrolyte than natural graphite and the like, but still has the problems of rough surface, porosity, large specific surface area, sensitivity to solvent in the electrolyte and the like, and the artificial graphite material with better performance needs to be subjected to surface treatment. At present, the research and the adoption of more technologies are that a coating material and a coke raw material are adopted for coating, a coating layer is formed on the surface of the material after carbonization and granulation, and the graphitization degree is further improved, so that the embedding of an electrolyte solvent is inhibited, and meanwhile, the coating layer can buffer the volume effect of graphite to a certain extent, so that the cycle performance and the rate capability of the whole material are improved; or the raw materials are subjected to surface modification, such as oxidation treatment, and then mixed granulation and graphitization treatment are carried out; or the artificial graphite and the coating material are mixed, granulated and carbonized to improve the cycle performance. The methods can effectively improve the cycle performance of the artificial graphite, but no matter the carbon-coated raw material is carbonized and then graphitized, or the graphitized artificial graphite is subjected to carbon coating, there is still room for improvement, for example, how to realize uniform coating of the coating material, and overcome the influence of capacity reduction brought by the coating on the whole material, so that the high-rate long cycle performance of the artificial graphite cathode material is effectively realized, and the problems still need to be solved in the industry at present.

Disclosure of Invention

In view of the above-mentioned shortcomings in the prior art, the present invention aims to provide a modified graphite negative electrode material, a preparation method thereof and a lithium ion battery. The method provided by the invention can further improve the lithium storage capacity of the negative electrode material on the basis of keeping the stability advantage of the artificial graphite, and simultaneously improve the cycle performance and the rate capability of the artificial graphite negative electrode material.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method for preparing a modified graphite anode material, comprising the steps of:

carrying out hydrothermal reaction or solvothermal reaction on graphite to obtain primary treated graphite;

mixing and reacting the primary treated graphite with an intercalation agent to obtain secondary treated graphite;

and mixing the secondary treated graphite with a carbon source, and then carrying out heating treatment to obtain the modified graphite cathode material, wherein the heating treatment comprises carbonization treatment.

As a preferable technical solution of the present invention, the graphite includes artificial graphite;

preferably, the artificial graphite is a product obtained by crushing, granulating and graphitizing petroleum coke, and a coating material is not added to the product;

preferably, the graphite subjected to the hydrothermal reaction or the solvothermal reaction is a graphite suspension;

preferably, the solvent used for preparing the graphite suspension includes at least one of distilled water, ethanol, ethylene glycol and ethanolamine;

preferably, the graphite suspension is obtained by mixing graphite and a solvent by ultrasonic stirring.

As the preferable technical scheme of the invention, the temperature of the hydrothermal reaction or the solvothermal reaction is 150-180 ℃;

preferably, the hydrothermal reaction or the solvothermal reaction is carried out for 1h to 3 h.

As the preferred technical scheme of the invention, the primary treated graphite also comprises the steps of carrying out centrifugal washing and vacuum drying on the primary treated graphite before being mixed with the intercalation agent;

preferably, the intercalation agent comprises mixed solution or aqua regia consisting of concentrated sulfuric acid and hydrogen peroxide;

preferably, the mass percentage concentration of the concentrated sulfuric acid is 92.5% -98%;

preferably, the mass percentage concentration of the hydrogen peroxide is 25-35%;

preferably, in the mixed solution composed of concentrated sulfuric acid and hydrogen peroxide, the mass ratio of the concentrated sulfuric acid to the hydrogen peroxide is 10: 1-20: 1;

preferably, the mixing reaction in the step of mixing and reacting the primary treated graphite with the intercalation agent is carried out by stirring and mixing reaction under ice bath condition;

preferably, the mixing reaction time in the step of mixing and reacting the primary treated graphite with the intercalation agent is 10min to 30 min.

As the preferable technical scheme of the invention, before the secondary treatment graphite is mixed with the carbon source, the method also comprises the steps of carrying out precipitation, centrifugal washing and vacuum drying on the secondary treatment graphite;

preferably, the carbon source comprises pitch and/or resin;

preferably, the asphalt is modified asphalt with a softening point of 110-120 ℃;

preferably, the resin is a water-soluble resin;

preferably, the mass ratio of the carbon source to the secondary treatment graphite is 10:90-5: 95;

preferably, the mixing method in the step of mixing the secondary treated graphite with a carbon source is wet ball milling;

preferably, the solvent for the wet ball milling comprises kerosene and/or ethylene glycol;

preferably, the mixing time in the step of mixing the secondary treated graphite with a carbon source is 8h-16 h;

preferably, after the step of mixing the secondary treated graphite with the carbon source and before the step of heating treatment, the method further comprises the steps of heating, drying and grinding the mixed product;

preferably, the temperature for heating and drying is 80-160 ℃;

preferably, the grinding time is 10min to 30 min.

As a preferred technical solution of the present invention,

the heating treatment also comprises pre-oxidation treatment and/or pre-carbonization treatment;

preferably, the temperature of the pre-oxidation treatment is 250-300 ℃;

preferably, the time of the pre-oxidation treatment is 1h-3 h;

preferably, the temperature rise rate of the pre-oxidation treatment is 4-6 ℃/min;

preferably, the temperature of the pre-carbonization treatment is 250-300 ℃;

preferably, the temperature of the pre-carbonization treatment is the same as the temperature of the pre-oxidation treatment;

preferably, the time of the pre-carbonization treatment is 1h-2 h;

preferably, the pre-carbonization treatment is performed under a protective atmosphere;

preferably, the temperature of the carbonization treatment is 650-700 ℃;

preferably, the carbonization treatment time is 4-6 h;

preferably, the temperature rise rate of the carbonization treatment is 4-6 ℃/min;

preferably, the carbonization treatment is carried out under a protective atmosphere;

preferably, the protective atmosphere of the pre-carbonization treatment and/or carbonization treatment comprises nitrogen and/or argon.

As a preferable embodiment of the present invention, the step of further performing heat treatment further comprises: and grinding and screening the product obtained after the carbonization treatment.

As a further preferable technical scheme of the preparation method, the method comprises the following steps:

ultrasonically stirring and mixing graphite and a solvent to obtain a graphite suspension, and placing the graphite suspension in a sealed reaction kettle to perform hydrothermal reaction or solvothermal reaction at the temperature of 150-180 ℃ to obtain primary treated graphite;

carrying out centrifugal washing and vacuum drying on the primary treated graphite, and then mixing and reacting the primary treated graphite with an intercalator for 10-30 min under the ice-bath stirring condition to obtain secondary treated graphite;

precipitating, centrifugally washing and vacuum drying the secondary-treated graphite, carrying out wet ball milling for 8-16 h with a carbon source, carrying out heating drying at 80-160 ℃ and grinding for 10-30 min on a product obtained by the wet ball milling, then heating to 250-300 ℃ at a heating rate of 4-6 ℃/min for carrying out pre-oxidation treatment for 1-3 h, keeping the temperature under protective gas for carrying out pre-carbonization treatment for 1-2 h, heating to 650-700 ℃ at a heating rate of 4-6 ℃/min under protective gas for carrying out carbonization treatment for 4-6 h, and grinding and screening the product obtained after carbonization treatment to obtain the modified graphite cathode material.

In a second aspect, the present invention provides a modified graphite anode material obtained by the method for preparing a modified graphite anode material according to the first aspect.

Preferably, the modified graphite anode material comprises graphite and a carbon layer coated on the graphite.

Preferably, the carbon layer is an amorphous carbon layer.

In a third aspect, the present invention provides a lithium ion battery comprising the modified graphite anode material of the second aspect.

Advantages of embodiments of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the invention.

Drawings

Fig. 1 is an SEM image of the modified graphite anode material prepared in example 1.

Fig. 2 is a graph of cycle performance of the modified graphite anode material prepared in example 1.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

In a first aspect, an embodiment of the present invention provides a method for preparing a composite graphite anode material, where the method includes the following steps:

According to the preparation method provided by the invention, the graphite sheet layer can be opened to a certain degree by carrying out hydrothermal or solvent heat treatment on the graphite, so that the graphite sheet layer is expanded to a certain degree integrally to improve the lithium storage performance. Meanwhile, the number of surface functional groups can be increased (in the hydrothermal or solvent heat treatment process, the solvent can act with some carbon atoms on the surface, especially the edge, of the graphene generated by opening the graphite sheet layer, so that some carboxyl or hydroxyl oxygen-containing functional groups can be introduced), and the later-period coating effect is improved. The graphite after hydrothermal or solvent heat treatment (namely the primary treated graphite) is subjected to intercalation treatment, the corrosive oxidizability of an intercalation agent is utilized to increase the surface defects of the graphite, and lithium storage positions and lithium ion transmission channels are provided to obtain the micro-expanded graphite (namely the secondary treated graphite).

In an embodiment of the invention, the graphite comprises artificial graphite. The artificial graphite used in the invention has the advantages of more uniform particle size distribution and improved coating effect.

In the embodiment of the invention, the artificial graphite is a product obtained by crushing, granulating and graphitizing petroleum coke, and a coating material is not added to the product.

Preferably, the graphite subjected to the hydrothermal reaction or the solvothermal reaction is a graphite suspension.

Preferably, the solvent used to prepare the graphite suspension includes at least one of distilled water, ethanol, ethylene glycol, and ethanolamine.

In the embodiment of the invention, the graphite suspension is obtained by ultrasonically stirring and mixing graphite and a solvent.

In the embodiment of the present invention, the temperature of the hydrothermal reaction or the solvothermal reaction is 150 ℃ to 180 ℃, for example, 150 ℃, 160 ℃, 170 ℃ or 180 ℃. In the invention, if the temperature of the hydrothermal reaction or the solvothermal reaction is too high, the vapor pressure is too high, the reaction is accelerated, and the integrity of the material is damaged; if the temperature of the hydrothermal reaction or the solvothermal reaction is too low, it may not function to slightly expand the graphite.

In the embodiment of the present invention, the hydrothermal reaction or solvothermal reaction time is 1h to 3h, for example, 1h, 1.5h, 2h, 2.5h, or 3 h.

In the embodiment of the invention, the primary treated graphite further comprises the steps of carrying out centrifugal washing and vacuum drying on the primary treated graphite before being mixed with the intercalation agent.

In the embodiment of the invention, the intercalation agent comprises mixed liquid or aqua regia consisting of concentrated sulfuric acid and hydrogen peroxide. The use of these two intercalators has the advantage of effectively intercalating into graphite defects, opening channels, while increasing the number of reactive functional groups. When the mixed liquid consisting of concentrated sulfuric acid and hydrogen peroxide is used, concentrated sulfuric acid can be added for treatment, and hydrogen peroxide is added for treatment, so that the hydrogen peroxide is prevented from being decomposed too quickly.

In the embodiment of the invention, the mass percentage concentration of the concentrated sulfuric acid is 92.5% -98%, such as 92.5%, 93%, 94%, 95%, 96%, 97% or 98%.

In the embodiment of the present invention, the concentration of the hydrogen peroxide is 25% to 35% by mass, for example, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or the like.

In an embodiment of the present invention, in the mixed solution composed of concentrated sulfuric acid and hydrogen peroxide, the mass ratio of concentrated sulfuric acid to hydrogen peroxide is 10:1 to 20:1, for example, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20: 1.

In the embodiment of the invention, the mixing reaction method in the step of mixing and reacting the primary treated graphite and the intercalation agent is to perform stirring mixing reaction under the ice bath condition.

In an embodiment of the present invention, the temperature of the mixing reaction in the step of mixing and reacting the primary treated graphite and the intercalation agent is about 0 ℃. In the invention, if the temperature of the mixing reaction of the graphite and the intercalation agent is too high, the hydrogen peroxide can be decomposed without exerting the effect.

In an embodiment of the present invention, the mixing reaction time in the step of mixing and reacting the primary treated graphite with the intercalating agent is 10min to 30min, for example, 10min, 15min, 20min, 25min or 30 min.

In the embodiment of the invention, before the secondary treated graphite is mixed with the carbon source, the method further comprises the steps of precipitating, centrifugally washing and vacuum drying the secondary treated graphite.

In an embodiment of the invention, the carbon source comprises pitch and/or resin.

In the embodiment of the invention, the asphalt is modified asphalt with the softening point of 110-120 ℃.

In an embodiment of the present invention, the resin is a water-soluble resin.

In an embodiment of the invention, the mass ratio of the carbon source to the secondary treated graphite is 10:90 to 5:95, for example 10:90, 9:91, 8:92, 7:93, 6:94 or 5: 95. In the invention, if the carbon source is too much, the coating layer is too thick, which is not beneficial to the rate capability of the material; if the secondary treatment is too much graphite, non-uniform coating can result.

In the embodiment of the invention, the mixing method in the step of mixing the secondary treated graphite and the carbon source is wet ball milling.

In the invention, the carbon source is coated by adopting a wet ball milling mode, which is beneficial to uniformly coating the material and improving the consistency of the material, thereby improving the overall stability.

In an embodiment of the present invention, the solvent for wet ball milling comprises kerosene and/or ethylene glycol.

In an embodiment of the present invention, the mixing time in the step of mixing the secondarily treated graphite with the carbon source is 8h to 16h, for example, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, or the like.

In the embodiment of the invention, after the step of mixing the secondary treated graphite with the carbon source and before the step of heating treatment, the method further comprises the steps of heating, drying and grinding the mixed product.

In the embodiment of the invention, the temperature for heating and drying is 80-160 ℃, such as 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃ or 160 ℃ and the like.

In an embodiment of the present invention, the grinding time is 10min to 30min, for example, 10min, 20min or 30 min.

In an embodiment of the present invention, the heating treatment further comprises a pre-oxidation treatment and/or a pre-carbonization treatment.

In the invention, the pre-oxidation pre-carbonization treatment is adopted, so that the structure of the coating layer is more stable, and meanwhile, the introduced oxygen atoms overflow in a micromolecule form during the post-heat treatment to form a microporous structure, thereby being beneficial to the infiltration of electrolyte and the de-intercalation of lithium ions. The carbon source is fully carbonized through the pre-carbonization treatment, and the caking problem caused by violent reaction is avoided, so that the rate capability and the cycle performance of the material are improved.

In the embodiment of the present invention, the temperature of the pre-oxidation treatment is 250 ℃ to 300 ℃, for example, 250 ℃, 260 ℃, 270 ℃, 280 ℃, 290 ℃, or 300 ℃.

In the embodiment of the present invention, the time of the pre-oxidation treatment is 1h to 3h, for example, 1h, 1.5h, 2h, 2.5h, or 3 h.

In the embodiment of the present invention, the temperature increase rate of the pre-oxidation treatment is 4 ℃/min to 6 ℃/min, for example, 4 ℃/min, 4.5 ℃/min, 5 ℃/min, 5.5 ℃/min, or 6 ℃/min.

In the embodiment of the invention, the temperature of the pre-carbonization treatment is 250-300 ℃, such as 250 ℃, 260 ℃, 270 ℃, 280 ℃, 290 ℃ or 300 ℃ and the like.

In an embodiment of the present invention, the temperature of the pre-carbonization treatment is the same as the temperature of the pre-oxidation treatment.

In the embodiment of the invention, the time of the pre-carbonization treatment is 1h-2h, such as 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2 h.

In an embodiment of the invention, the pre-carbonization treatment is performed under a protective atmosphere.

In an embodiment of the invention, the protective atmosphere comprises a nitrogen atmosphere and/or an argon atmosphere.

In the embodiment of the present invention, the temperature of the carbonization treatment is 650 ℃ to 700 ℃, for example, 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃ or the like.

In the embodiment of the invention, the time of the carbonization treatment is 4h-6h, such as 4h, 4.5h, 5h, 5.5h or 6 h.

In the embodiment of the present invention, the temperature increase rate of the carbonization treatment is 4 ℃/min to 6 ℃/min, for example, 4 ℃/min, 4.5 ℃/min, 5 ℃/min, 5.5 ℃/min, or 6 ℃/min.

Preferably, the carbonization treatment is performed under a protective atmosphere.

In an embodiment of the present invention, the protective atmosphere of the pre-carbonization treatment and/or carbonization treatment includes a nitrogen atmosphere and/or an argon atmosphere.

In an embodiment of the present invention, the further heating step further includes: and grinding and screening the product obtained after the carbonization treatment.

In an embodiment of the present invention, the preparation method comprises the steps of:

The preferred preparation method adopts artificial graphite as a raw material, the graphite sheet layer is expanded to a certain degree integrally through preliminary solvent heat treatment, and then aqua regia intercalation treatment is carried out on the expanded graphite, so that the surface defects are increased. Mixing the obtained micro-expanded artificial graphite with asphalt according to a certain proportion, carrying out wet ball milling to enable the surface of the micro-expanded artificial graphite to be uniformly covered with a carbon layer, and carrying out pre-oxidation pre-carbonization and carbonization treatment on the material to obtain the modified artificial graphite. The modified artificial graphite obtained by the invention has the characteristics of good cycle performance, good rate capability and low volume expansion effect.

Preferably, the carbon layer is an amorphous carbon layer.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the preparation method provided by the invention, hydrothermal or solvent heat treatment is carried out on graphite, so that graphite sheets are opened to a certain degree integrally, and the lithium storage performance is improved. Meanwhile, surface functional groups are added, and the later-period coating effect is improved. The graphite after hydrothermal or solvent heat treatment is intercalated, and the corrosive oxidizability of the intercalant is utilized to increase the surface defects of the graphite and provide lithium storage positions and lithium ion transmission channels. The structure of the coating layer is more stable by adopting pre-oxidation and pre-carbonization treatment, and meanwhile, introduced oxygen atoms overflow in a micromolecule form during post-heat treatment to form a micropore structure, so that the impregnation of electrolyte and the deintercalation of lithium ions are facilitated. The pre-carbonization treatment fully carbonizes the carbon source, and avoids the caking problem caused by violent reaction, thereby improving the multiplying power performance and the cycle performance of the material. And the carbon source is coated by adopting a wet ball milling mode, so that the material can be uniformly coated, the consistency of the material can be improved, and the overall stability can be improved.

(2) The composite graphite cathode material prepared by the preparation method provided by the invention has the advantages of high capacity, low volume expansion effect, and good rate capability and cycle performance.

The following are typical but non-limiting examples of the invention:

example 1

In this example, a modified graphite negative electrode material was prepared as follows:

(1) adding 5g of artificial graphite into a beaker filled with 70mL of ethanol, carrying out ultrasonic treatment for 10min, then carrying out magnetic stirring for 30min, transferring the dispersed suspension into a 100mL reaction kettle, reacting for 3h at 180 ℃, cooling to room temperature after the reaction is finished, carrying out centrifugal washing on the product, and then carrying out vacuum drying at 100 ℃.

(2) Adding the dried graphite into 50mL of prepared aqua regia, stirring in an ice bath (about 0 ℃) for 30min, standing, removing supernatant, pouring distilled water, removing supernatant, performing centrifugal washing, and performing vacuum drying at 100 ℃.

(3) Adding the dried graphite into an asphalt solution, wherein the solvent is kerosene, the mass ratio of asphalt to graphite is 5:95, the ball-to-material ratio is 8:2, and the ball milling time is 8 hours. And after the ball milling is finished, stirring and heating the mixed system at 160 ℃ to remove the kerosene.

(4) After the kerosene is completely volatilized, the ground powder is transferred to a tubular furnace after 30min, pre-oxidation treatment is carried out for 1h in the air atmosphere at the temperature of 250 ℃ at the temperature rising rate of 4 ℃/min, then nitrogen is sealed and introduced, pre-carbonization treatment is carried out for 2h at the temperature of 250 ℃, and the temperature is continuously raised to 700 ℃ at the temperature rising rate of 4 ℃/min for carbonization treatment for 6 h.

(5) And after carbonization, grinding the obtained product, and sieving the ground product with a 200-mesh sieve to obtain the modified graphite cathode material.

The test results of the modified graphite anode material prepared in this example are shown in table 1.

Fig. 1 is a scanning electron microscope SEM image of the modified graphite negative electrode material prepared in this example, and it can be seen from the image that there are gaps on the graphite surface, which is advantageous for providing a lithium intercalation channel.

Fig. 2 is a graph of cycle performance of the modified graphite anode material prepared in this example, where efficiency (%) indicates charge-to-discharge efficiency, and it can be seen from the graph that the material has good cycle stability and rate capability.

Example 2

The present embodiment is different from embodiment 1 in that: the solvent thermal solvent adopted in the step (1) is ethanolamine, and the asphalt selected in the step (3) is modified asphalt with a softening point of 120 ℃. The other raw materials and operations were the same as in example 1.

Example 3

The present embodiment is different from embodiment 1 in that: the solvent adopted in the step (1) is water (namely, hydrothermal reaction is carried out), and the mass ratio of the asphalt to the graphite in the step (3) is 10: 90. The other raw materials and operations were the same as in example 1.

Example 4

The present embodiment is different from embodiment 1 in that: the temperature of pre-oxidation and pre-carbonization is 300 ℃. The other raw materials and operations were the same as in example 1.

Example 5

The present embodiment is different from embodiment 1 in that: step (2) does not use aqua regia, but adopts a mixed solution of 98% concentrated sulfuric acid and 25% hydrogen peroxide in a mass ratio of 20:1 as an intercalating agent (after 40mL of concentrated sulfuric acid is treated, 9.1mL of hydrogen peroxide is added); in the step (3), the carbon source is acrylic resin (melting point 165 ℃) instead of pitch, and distilled water is used as a ball milling solvent, and ball milling is performed. The other raw materials and operations were the same as in example 1.

Example 6

(1) adding 6g of artificial graphite into a beaker filled with 70mL of ethanol, performing ultrasonic treatment for 15min, performing magnetic stirring for 25min, transferring the dispersed suspension into a 100mL reaction kettle, reacting for 1h at 165 ℃, cooling to room temperature after the reaction is finished, performing centrifugal water washing on the product, and performing vacuum drying at 100 ℃.

(2) Adding the dried graphite into 50mL of ready-prepared aqua regia, stirring in an ice bath for 20min, standing, removing supernatant, pouring distilled water, removing supernatant, performing centrifugal water washing, and performing vacuum drying at 100 ℃.

(3) Adding the dried graphite into an asphalt solution, wherein the solvent is kerosene, the mass ratio of the asphalt to the graphite is 8:92, the ball-to-material ratio is 8:2, and the ball milling time is 12 hours. And after the ball milling is finished, stirring and heating the mixed system at 100 ℃ to remove the kerosene.

(4) After the kerosene was completely volatilized, the ground powder was transferred to a tubular furnace after 20min, pre-oxidized at a rate of 5 ℃/min in an air atmosphere at 275 ℃ for 1.5h, then sealed and charged with nitrogen, pre-carbonized at 275 ℃ for 1.5h, and continuously heated to 680 ℃ at a rate of 5 ℃/min for 5 h.

Example 7

(1) Adding 4g of artificial graphite into a beaker filled with 70mL of ethanol, performing ultrasonic treatment for 15min, performing magnetic stirring for 25min, transferring the dispersed suspension into a 100mL reaction kettle, reacting for 2h at 150 ℃, cooling to room temperature after the reaction is finished, performing centrifugal water washing on the product, and performing vacuum drying at 100 ℃.

(2) Adding the dried graphite into 50mL of an intercalation agent (the intercalation agent is a mixed solution of 98% concentrated sulfuric acid and 25% hydrogen peroxide, namely 10: 1), adding concentrated sulfuric acid for treatment, adding hydrogen peroxide, stirring in an ice bath for 10min, standing, removing supernatant, pouring distilled water, removing supernatant, performing centrifugal washing, and performing vacuum drying at 100 ℃.

(3) Adding the dried graphite into an asphalt solution with a softening point of 110 ℃, wherein the solvent is kerosene, the mass ratio of the asphalt to the graphite is 10:90, the ball-to-material ratio is 8:2, and the ball milling time is 16 h. And after the ball milling is finished, stirring and heating the mixed system at 80 ℃ to remove the kerosene.

(4) After the kerosene is completely volatilized, the ground powder is transferred to a tubular furnace after 10min, pre-oxidation treatment is carried out for 3h in the air atmosphere at the temperature of 300 ℃ at the temperature rising rate of 6 ℃/min, then nitrogen is sealed and introduced, pre-carbonization treatment is carried out for 1h at the temperature of 300 ℃, and carbonization treatment is carried out for 4h by continuously rising the temperature to 650 ℃ at the temperature rising rate of 6 ℃/min.

Comparative example 1

This comparative example was conducted without conducting the solvothermal treatment of step (1) and the aqua regia intercalation treatment of step (2) of example 1, but by directly conducting the artificial graphite as a raw material in step (1) of example 1 in place of the dried graphite described in step (3) according to steps (3), (4) and (5) of example 1, a modified graphite negative electrode material was obtained.

The test results of the modified graphite anode material prepared in this comparative example are shown in table 1.

Comparative example 2

This comparative example was conducted without conducting the solvothermal treatment in step (1) of example 1, but by directly conducting the artificial graphite as the raw material in step (1) of example 1 in place of the dried graphite in step (2) according to steps (2), (3), (4) and (5) of example 1, a modified graphite negative electrode material was obtained.

Comparative example 3

This comparative example was carried out under the same conditions and with the same raw materials as in example 1, except that the step (2) of example 1 was not carried out (i.e., the royal water intercalation was not carried out), but the ball milling operation of step (3) was carried out directly on the dried graphite obtained after the step (1) of example 1 was vacuum-dried at 100 ℃.

Test method

1) Electrode preparation

The electrode material, the conductive carbon black Super P and the adhesive PVDF are synthesized according to the mass ratio of 8: 1:1, adding a 1-methyl-2-pyrrolidone (NMP) solvent, stirring for 54 hours, uniformly coating the obtained slurry on a copper foil (a copper foil for a negative electrode and an aluminum foil for a positive electrode), and drying in vacuum at 130 ℃ for 12 hours. And cutting the obtained pole piece into different shapes according to different battery specifications (the lithium/sodium ion battery pole piece is a circular piece with the diameter of 1.1 cm).

2) Battery assembly

Electrochemical tests were performed using CR2016 coin cells, completed in an argon glove box with oxygen and water content below 0.1 ppm. A high-purity lithium sheet is selected as a counter electrode, a diaphragm is a Celgard 2500 microporous polypropylene membrane, and an electrolyte is 1M LiPF6 (a solvent is a mixed solution of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 1).

3) Battery testing

After the assembled battery is kept stand for 6 hours, a charge and discharge test is carried out, and after 5 cycles at 0.1C, ten cycles at charge and discharge multiplying power of 0.5C, 1C, 2C and 8C, respectively, long cycles are carried out after returning to 0.1C multiplying power.

The test results are shown in Table 1

TABLE 1

It can be known from the above examples and comparative examples that the preparation method of each example performs hydrothermal or solvent heat treatment on graphite, so that graphite sheets are opened to a certain extent integrally, and lithium storage performance is improved. Meanwhile, surface functional groups are added, and the later-period coating effect is improved. The graphite after hydrothermal or solvent heat treatment is intercalated, and the corrosive oxidizability of the intercalant is utilized to increase the surface defects of the graphite and provide lithium storage positions and lithium ion transmission channels. The pre-oxidation pre-carbonization treatment is adopted, so that the structure of the coating layer is more stable, and meanwhile, the introduced oxygen atoms overflow in a micromolecule form during the post-heat treatment to form a microporous structure, thereby being beneficial to the infiltration of electrolyte and the de-intercalation of lithium ions. The pre-carbonization treatment fully carbonizes the carbon source, and avoids the caking problem caused by violent reaction, thereby improving the multiplying power performance and the cycle performance of the material. And the carbon source is coated by adopting a wet ball milling mode, so that the material can be uniformly coated, the consistency of the material can be improved, and the overall stability can be improved.

Comparative example 1 neither solvent heat treatment nor intercalation treatment resulted in poor rate performance and low capacity of the material.

Comparative example 2 was not solvent heat treated, resulting in a decrease in capacity relative to example 1.

Comparative example 3 was not subjected to intercalation treatment, resulting in a decrease in capacity.

The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A preparation method of a modified graphite anode material is characterized by comprising the following steps:

2. The method of claim 1, wherein the graphite comprises artificial graphite.

3. The preparation method according to claim 2, wherein the artificial graphite is a product obtained by pulverizing, granulating and graphitizing petroleum coke, and no coating material is added to the product.

4. The production method according to claim 1, wherein the graphite subjected to the hydrothermal reaction or the solvothermal reaction is a graphite suspension.

5. The method of claim 4, wherein the graphite suspension is obtained by mixing graphite and a solvent.

6. The method according to claim 5, wherein the solvent used for preparing the graphite suspension includes at least one of distilled water, ethanol, ethylene glycol, and ethanolamine.

7. The method according to claim 1, wherein the temperature of the hydrothermal reaction or the solvothermal reaction is 150 ℃ to 180 ℃.

8. The method according to claim 1, wherein the hydrothermal reaction or solvothermal reaction is carried out for 1 to 3 hours.

9. The preparation method of claim 1, wherein the primary treated graphite is subjected to centrifugal washing and vacuum drying before being mixed with the intercalation agent.

10. The method of claim 1, wherein the intercalant comprises a mixed solution of concentrated sulfuric acid and hydrogen peroxide or aqua regia.

11. The method according to claim 10, wherein the concentrated sulfuric acid has a concentration of 92.5-98% by mass.

12. The preparation method of claim 10, wherein the concentration of the hydrogen peroxide is 25-35% by mass.

13. The preparation method according to claim 10, wherein in the mixed solution of concentrated sulfuric acid and hydrogen peroxide, the mass ratio of the concentrated sulfuric acid to the hydrogen peroxide is 10: 1-20: 1.

14. The method for preparing according to claim 1, wherein the mixing reaction in the step of mixing the primary treated graphite with the intercalant is carried out by stirring the mixing reaction under ice bath conditions.

15. The production method according to claim 14, wherein the mixing reaction time in the step of mixing-reacting the primary treated graphite with the intercalating agent is 10min to 30 min.

16. The method of claim 1, wherein the step of precipitating, washing centrifugally and drying under vacuum is further included before mixing the secondary treated graphite with the carbon source.

17. The method of claim 1, wherein the carbon source comprises pitch and/or resin.

18. The production method according to claim 17, wherein the asphalt is an upgraded asphalt having a softening point of 110 ℃ to 120 ℃.

19. The production method according to claim 17, wherein the resin is a water-soluble resin.

20. The method according to claim 1, wherein the mass ratio of the carbon source to the secondary-treated graphite is 10:90 to 5: 95.

21. The method for preparing a graphite material as claimed in claim 1, wherein the mixing step of mixing the secondary processed graphite with a carbon source is wet ball milling.

22. The method of claim 21, wherein the solvent for the wet ball milling comprises kerosene and/or ethylene glycol.

23. The method as set forth in claim 1, wherein the mixing time in the step of mixing the secondary treated graphite with the carbon source is 8 to 16 hours.

24. The preparation method according to claim 1, wherein after the step of mixing the secondary treated graphite with the carbon source and before the step of heating treatment, the method further comprises the step of heating, drying and grinding the product obtained by mixing.

25. The method of claim 24, wherein the temperature of the heat drying is 80 ℃ to 160 ℃.

26. The method of claim 24, wherein the milling time is 10min to 30 min.

27. The production method according to any one of claims 1 to 5, wherein the heating treatment further comprises a pre-oxidation treatment and/or a pre-carbonization treatment.

28. The method of claim 27, wherein the pre-oxidation treatment is performed at a temperature of 250 ℃ to 300 ℃.

29. The method as claimed in claim 27, wherein the time of the pre-oxidation treatment is 1 to 3 hours.

30. The production method according to claim 27, wherein the temperature increase rate of the pre-oxidation treatment is 4 ℃/min to 6 ℃/min.

31. The method of claim 27, wherein the pre-carbonization temperature is 250-300 ℃.

32. The method of claim 27, wherein the temperature of the pre-carbonization treatment is the same as the temperature of the pre-oxidation treatment.

33. The preparation method of claim 27, wherein the pre-carbonization treatment time is 1-2 h.

34. The method of claim 27, wherein the pre-charring is performed under a protective atmosphere.

35. The method according to claim 1, wherein the carbonization treatment is performed at a temperature of 650 ℃ to 700 ℃.

36. The preparation method of claim 1, wherein the carbonization treatment time is 4-6 h.

37. The production method according to claim 1, wherein the temperature increase rate of the carbonization treatment is 4 ℃/min to 6 ℃/min.

38. The method of claim 1, wherein the carbonization treatment is performed under a protective atmosphere.

39. The method according to claim 27, wherein the gas of the protective atmosphere of the pre-carbonization and/or carbonization treatment comprises nitrogen and/or argon.

40. The method of claim 1, wherein the step of further heating further comprises: and grinding and screening the product obtained after the carbonization treatment.

41. The method for preparing according to claim 1, characterized in that it comprises the following steps:

carrying out centrifugal washing and vacuum drying on the primary treated graphite, and mixing and reacting the primary treated graphite with an intercalator under the ice-bath stirring condition for 10-30 min to obtain secondary treated graphite;

42. A modified graphite anode material obtained by the method for producing a modified graphite anode material according to any one of claims 1 to 41.

43. A lithium ion battery comprising the modified graphite anode material of claim 42.