CN112830484B

CN112830484B - Modified graphite and preparation method thereof, lithium battery negative electrode material, lithium battery negative electrode sheet and lithium battery

Info

Publication number: CN112830484B
Application number: CN202110082159.2A
Authority: CN
Inventors: 郭道峰; 程兴旺; 吴敦勇
Original assignee: Beiteri Jiangsu New Energy Materials Co ltd
Current assignee: Beiteri Jiangsu New Energy Materials Co ltd
Priority date: 2021-01-21
Filing date: 2021-01-21
Publication date: 2022-11-25
Anticipated expiration: 2041-01-21
Also published as: CN112830484A

Abstract

The invention provides modified graphite and a preparation method thereof, a lithium battery negative electrode material, a lithium battery negative electrode sheet and a lithium battery, wherein the preparation method of the modified graphite comprises the following steps: carrying out oxidation pretreatment on graphite to obtain pretreated graphite; carrying out complex reaction on a mixture containing pretreated graphite and hydroxyl-containing polymer and zinc chloride, and then drying to obtain a precursor; and carbonizing the precursor to obtain the modified graphite. The method comprises the steps of carrying out oxidation pretreatment on graphite, carrying out complex reaction on a mixture of the graphite and a hydroxyl-containing polymer and zinc chloride, drying to obtain a gelatinous precursor, and carrying out carbonization treatment on the precursor to obtain sp ² +sp ³ Amorphous carbon coated sp ² Porous modified graphite of a core-shell structure of graphite; the modified graphite is applied to the lithium battery, provides a new mode for electron conduction, lithium ion storage and electrolyte soaking, and greatly improves the electrochemical performance of the lithium battery.

Description

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

Technical Field

The invention relates to the technical field of battery materials, in particular to modified graphite and a preparation method thereof, a lithium battery negative electrode material, a lithium battery negative electrode sheet and a lithium battery.

Background

With the continuous development of society, the demand of people for energy is continuously increasing. The conventional energy utilization causes problems of greenhouse effect, environmental pollution and the like, so that the research and development and utilization of new energy are imminent. As an energy system which has been developed for a long time, the lithium ion battery has the advantages of environmental friendliness, low recovery cost and the like, and has become a hot point of research of scholars.

The negative electrode material for lithium battery includes a carbon negative electrode material and a non-carbon negative electrode material. Non-carbon cathode material such as silicon nano-structured cathode material of alloy type has large volume change (>300 percent), unstable formation of a solid electrolyte interface film, poor circulation stability and the like; the scholars also propose zero strain spinel Li ₄ Ti ₅ O ₁₂ As an anode material, the lithium ion secondary battery has the problems of low first discharge specific capacity (approximately 175 mAh/g) and high working potential. At present, carbon cathode materials are mainly used as cathode materials of lithium batteries, such as graphite cathode materials, which are regarded as commercial cathode materials of lithium batteries because of long cycling stability and high conductivity, and high thermal and mechanical stability. But nowThe theoretical initial discharge specific capacity of some lithium battery graphite cathode materials can reach 370mAh/g, and the actual initial discharge specific capacity does not exceed 350mAh/g. Therefore, the electrochemical performance of the graphite negative electrode material of the lithium battery, such as the first discharge specific capacity, still needs to be improved.

Disclosure of Invention

In view of the above, the present invention aims to provide a porous material having a porous structure, which can not only be Li ⁺ The migration provides more ways, and can also promote the electrolyte to penetrate into the active material and shorten Li ⁺ The migration distance of the graphite is short, the modified graphite has good electrochemical performance, the preparation method of the modified graphite, the lithium battery negative electrode material, the lithium battery negative electrode sheet and the lithium battery are provided.

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

a method of preparing modified graphite comprising:

carrying out oxidation pretreatment on graphite to obtain pretreated graphite;

carrying out complex reaction on a mixture containing pretreated graphite and hydroxyl-containing polymer and zinc chloride, and then drying to obtain a precursor;

and carbonizing the precursor to obtain the modified graphite.

The method comprises the steps of carrying out oxidation pretreatment on graphite, mixing the graphite with hydroxyl-containing polymer, zinc chloride and solvent for reaction, drying to obtain a gelatinous precursor, and carrying out carbonization treatment on the precursor to obtain sp ² +sp ³ Amorphous carbon coated sp ² Porous modified graphite with a core-shell structure of graphite; the modified graphite provides a new mode for electron conduction, lithium ion storage and electrolyte soaking, electrons can be conducted through the neural network-shaped amorphous carbon and can reach the internal graphite by the simplest and shortest path, so that more Li can be reduced in a certain time ⁺ To form LiC ₆ (ii) a Furthermore, the porous structure is Li ⁺ Migration provides more ways, li ⁺ This migration behavior allows more Li to be incorporated into the graphite not only from the edges, but also from the surface into the interior of the graphite ⁺ Is inserted into the graphite at a faster rate, andbesides, the electrolyte can be promoted to penetrate into active substances, and Li can be shortened ⁺ The migration distance of (c).

In some embodiments, the process of oxidatively pretreating graphite comprises: calcining the graphite in air or oxygen atmosphere;

preferably, the flow rate of the oxygen is 0.1mL/s-10mL/s;

preferably, the graphite is calcined in the oxygen atmosphere at the temperature of 500-750 ℃ for 0.5mL/s-2.5h.

Preferably, the hydroxyl-containing polymer is a polymeric polyol; the polymeric polyols comprise at least one of polyethylene glycol, polypropylene glycol and polyglycerol;

preferably, the mass ratio of the pretreated graphite to the hydroxyl-containing polymer is 1: (1-4);

preferably, the mass ratio of the pretreated graphite to the zinc chloride is 1: (1-4).

In some embodiments, a solvent is also included in the mixture;

preferably, the solvent is water;

preferably, the volume ratio of the hydroxyl-containing polymer to the solvent is 1: (10-50);

preferably, the preparation method of the mixture comprises: firstly, mixing the hydroxyl-containing polymer with the solvent, then adding the pretreated graphite and mixing to obtain the mixture;

preferably, the time for adding the pretreated graphite and mixing is 10min-60min;

the time of the complex reaction is 3-6 h;

preferably, the drying method further comprises the following steps: firstly, heating and evaporating a product after the complexing reaction;

preferably, the temperature of the heating evaporation is 80-100 ℃;

preferably, the drying process comprises: and (3) drying the product after the complexing reaction for 12-24 h at the temperature of 60-80 ℃ in vacuum.

In some embodiments, the carbonization treatment is calcining the precursor in a protective atmosphere environment or a vacuum environment;

preferably, the calcination temperature of the precursor in the protective atmosphere environment is 900-1200 ℃, and the calcination time is 2-4 h.

In some embodiments, the graphite is recycled graphite;

preferably, the recovered graphite is recovered from the graphite negative electrode sheets of the waste lithium batteries.

In some embodiments, the method of preparing recycled graphite comprises:

disassembling the graphite negative plate of the waste lithium battery to recover a graphite crude product;

calcining the crude graphite product in an air atmosphere or an oxygen atmosphere to obtain a pretreated crude graphite product;

mixing and reacting the pretreated graphite crude product with an acidic substance and an oxidant, and then carrying out first solid-liquid separation;

preferably, the solid obtained by the first solid-liquid separation is mixed with an alkaline reducing agent for reaction, and then the second solid-liquid separation is carried out, wherein the solid obtained by the second solid-liquid separation is the recovered graphite.

In some embodiments, before the disassembling the waste lithium battery graphite negative electrode sheet, the method further comprises: calcining the waste lithium battery graphite negative electrode sheet in a protective atmosphere or a vacuum environment;

preferably, the calcining temperature of the waste lithium battery graphite negative electrode sheet in the protective atmosphere is 300-600 ℃, and the time is 1-3 h;

preferably, the protective atmosphere comprises at least one of nitrogen, argon, helium and neon;

preferably, disassembling the graphite negative electrode sheet of the waste lithium battery by adopting a flotation process to recover a graphite rough product;

preferably, the dismantling of the crude graphite product comprises: crushing the waste lithium battery graphite negative electrode sheets, pouring the crushed waste lithium battery graphite negative electrode sheets into a flotation tank for stirring, collecting and drying an upper layer substance to obtain a crude graphite product;

preferably, the liquid used in the flotation cell is water;

preferably, the upper layer is dried by adopting a vacuum drying mode; optionally, drying the supernatant at a vacuum drying temperature of 80-120 ℃ for 6-24 h;

preferably, the calcining temperature of the graphite crude product in the air atmosphere is 700-900 ℃, and the time is 1-5 h.

In some embodiments, the acidic material comprises at least one of a hydrochloric acid solution and a sulfuric acid solution; optionally, the acidic substance is a hydrochloric acid solution with a concentration of 0.1mol/L-3 mol/L;

preferably, the oxidizing agent includes at least one of a hydrogen peroxide solution and a perchloric acid solution; optionally, the oxidizing agent is a hydrogen peroxide solution with the mass fraction of 0.5% -20%;

preferably, the alkaline reducing agent comprises at least one of hydrazine and sodium bisulfite; optionally, the alkaline reducing agent is a hydrazine solution with the mass fraction of 0.5% -40%;

preferably, the volume ratio of the acidic substance to the oxidizing agent is (0.5-5): 1;

preferably, the mass ratio of the pretreated crude graphite product to the acidic substance is 1: (1-5);

preferably, the temperature of the mixing reaction of the pretreated crude graphite product, the acidic substance and the oxidant is 60-80 ℃, and the time is 4-12 h;

the time for mixing and reacting the solid obtained by the first solid-liquid separation and the alkaline reducing agent is 4-12 h;

the first solid-liquid separation and the second solid-liquid separation each include at least one of centrifugal separation and filtration;

preferably, the filtration is suction filtered using a buchner funnel;

preferably, the filter paper for suction filtration is polytetrafluoroethylene filter paper, and the aperture of the filter paper is 0.2-0.8 μm;

preferably, the preparation method of the recycled graphite further comprises: drying the solid obtained by the second solid-liquid separation; optionally, the solid obtained from the second solid-liquid separation is dried in vacuum at a temperature of 60 ℃ to 120 ℃.

The invention also provides modified graphite prepared by the preparation method of the modified graphite.

The invention also provides a lithium battery negative electrode material which comprises the modified graphite.

The invention also provides a lithium battery negative electrode sheet which comprises the lithium battery negative electrode material.

The invention also provides a lithium battery which comprises the lithium battery negative plate.

The invention has the beneficial effects that:

(1) The method comprises the steps of carrying out oxidation pretreatment on graphite, carrying out complex reaction on the graphite and a mixture of the graphite and a hydroxyl-containing polymer and zinc chloride, drying to obtain a gelatinous precursor, and carrying out carbonization treatment on the precursor to obtain sp ² +sp ³ Amorphous carbon coated sp ² Porous modified graphite with a core-shell structure of graphite; the modified graphite is applied to the lithium battery, a new mode is provided for electron conduction, lithium ion storage and electrolyte soaking, electrons can be conducted through the neural network-shaped amorphous carbon, and the simplest and shortest path can be taken to reach the internal graphite, so that more Li can be reduced within a certain time ⁺ To form LiC ₆ (ii) a Furthermore, the porous structure is Li ⁺ The migration provides more ways, li ⁺ This migration behavior allows more Li to be incorporated into the graphite not only from the edges, but also from the surface into the interior of the graphite ⁺ Can be inserted into graphite at a higher speed, and can promote the electrolyte to penetrate into active substances and shorten Li ⁺ The migration distance is long, so that the electrochemical performance of the lithium battery is greatly improved; in addition, the preparation method of the modified graphite has the characteristics of simple process and environmental friendliness, and is easy to realize industrial production.

(2) Furthermore, the graphite raw material adopts the recycled graphite, and the recycled graphite is obtained by disassembling and recycling a large amount of easily-obtained waste lithium battery graphite cathode plate sources and removing impurities preferably in a simple, low-cost and environment-friendly mode so as to replace the existing graphite mainly obtained from mines by using a more expensive technology, so that the cost is greatly reduced, the resource recycling is realized, and the application requirements of the future graphite can be better met.

In order to make the aforementioned and other objects, features and advantages of the invention more comprehensible, preferred embodiments accompanied with figures are described in detail below.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, and it should be understood that the following drawings only illustrate some embodiments of the present invention, and therefore should not be considered as limiting the scope of the present invention.

FIG. 1a is an SEM topography at 1000 times magnification of the recovered graphite of example 1;

FIG. 1b is an SEM topography at 1500 times magnification of the modified graphite obtained in example 1;

FIG. 1c is an SEM topography at 5000 times magnification of the modified graphite obtained in example 1;

FIG. 1d is an SEM topography at 25000 magnification of the modified graphite obtained in example 1;

fig. 2 is a graph showing electrochemical properties of the graphite negative electrode materials obtained in example 1, comparative example 1 and comparative example 2 applied to a battery.

Detailed Description

In order to facilitate an understanding of the invention, reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings, and specific details will be set forth in the description to provide a thorough understanding of the invention.

This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

The terms as used herein:

"by 8230; \ 8230; preparation" is synonymous with "comprising". The terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

The conjunction "consisting of 823070, 8230composition" excludes any unspecified elements, steps or components. If used in a claim, this phrase shall render the claim closed except for the materials described except for those materials normally associated therewith. When the phrase "consisting of 8230' \8230"; composition "appears in a clause of the subject matter of the claims and not immediately after the subject matter, it defines only the elements described in the clause; other elements are not excluded from the claims as a whole.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4," "1 to 3," "1 to 2 and 4 to 5," "1 to 3 and 5," and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

In these examples, the parts and percentages are by mass unless otherwise indicated.

"parts by mass" means a basic unit of measure indicating a mass ratio of a plurality of components, and 1 part may represent an arbitrary unit mass, for example, 1g or 2.689 g. If the parts by mass of the component A are a parts and the parts by mass of the component B are B parts, the mass ratio of the component A to the component B is expressed as a: b. alternatively, the mass of the A component is aK and the mass of the B component is bK (K is an arbitrary number, and represents a multiple factor). It is unmistakable that, unlike the parts by mass, the sum of the parts by mass of all the components is not limited to 100 parts.

"and/or" is used to indicate that one or both of the illustrated conditions may occur, e.g., a and/or B includes (a and B) and (a or B).

The invention provides a preparation method of modified graphite, which comprises the following steps:

carrying out oxidation pretreatment on graphite to obtain pretreated graphite (PSG);

and carbonizing the precursor.

The zinc chloride (ZnCl) is ₂ ) Is a stronger Lewis acid, zn in zinc chloride ²⁺ Forms a strong bond with O.in the hydroxyl (-OH) group of the hydroxyl group-containing polymer, and can form a stable complex as a central ion because O.is an electron donor.

When the above-mentioned mixture of the pretreated graphite and the hydroxyl group-containing polymer is subjected to a complexing reaction with zinc chloride to form a precursor, H.is transferred to and combined with C = O or C-O of the pretreated graphite to form-OH during the carbonization treatment of the precursor, that is, the reduced pretreated graphite and the oxidized hydroxyl group-containing polymer are formed and Zn is established between the reduced pretreated graphite and the oxidized hydroxyl group-containing polymer ²⁺ A bridge as a core to form O-Zn ²⁺ -an O-bond chain; as the calcination process proceeds, zn ²⁺ The concentration is increased, the bonding capability is enhanced, the stress caused by a strong bonding effect can cause the formation of strain, the stress is continuously enhanced and accumulated, and the system structure tends to be stable along with the change of time; as the temperature is continuously increased, the Zn-O coordination bond is broken and replaced by stronger Zn-Cl ionic bond, and the complex becomes unstable; subsequently, when the temperature rises to ZnCl ₂ At boiling point of (2), znCl ₂ Sublimating to obtainCarbonized gel state precursor, the system must tend to reach a system energy minimum state, i.e., sp due to strong bonding effect ² The carbon distortion can not keep the original structure, and then the carbon distortion is rearranged to form a new three-dimensional carbon skeleton, and finally sp is obtained ² +sp ³ Amorphous carbon coated sp ² Porous modified graphite of graphite ac @ g.

In the whole process, znCl ₂ The catalyst has the function of the catalyst, and carbon is not lost, but the planar structure of the catalyst is changed, so that a three-dimensional curled carbon skeleton is formed; that is, the carbon atoms can self-reconstitute with the aid of zinc chloride and hydroxyl-containing polymers.

Further, the graphite is recycled graphite, preferably recycled graphite obtained by recycling waste lithium battery graphite cathode sheets, and certainly can also be recycled graphite obtained by recycling waste materials containing graphite, such as waste graphite components produced in the silicon crystal production process; the recycled graphite can be used as a new graphite source for lithium batteries, is used for replacing the existing battery-grade graphite source mainly obtained from mines by using a more expensive technology, greatly reduces the cost, realizes the resource recycling, and can better meet the application requirements of graphite in the future.

It should be noted that, since the directly recovered graphite has undergone many electrochemical cycles, some active sites and structures on the surface of the graphite may be destroyed, and the electrochemical performance of the graphite may be deteriorated, but sp may be obtained by performing the above modification treatment on the recovered graphite ² +sp ³ Amorphous carbon coated sp ² Porous modified graphite of a core-shell structure of graphite; the modified graphite provides a new mode for electron conduction, lithium ion storage and electrolyte soaking, electrons can be conducted through the neural network-shaped amorphous carbon and can reach the internal graphite by the simplest and shortest path, so that more Li can be reduced in a certain time ⁺ To form LiC ₆ (ii) a Furthermore, the porous structure is Li ⁺ The migration provides more ways, li ⁺ This migration behavior allows more Li to be incorporated into the graphite not only from the edges, but also from the surface into the interior of the graphite ⁺ Insert into graphite at a higher speed to promote the electrolyte to penetrate into the active material and shorten Li ⁺ The migration distance of the graphite is increased, and the electrochemical performance of the recovered graphite is effectively improved.

Further, the preparation method of the recycled graphite comprises the following steps:

disassembling the graphite negative electrode sheet of the waste lithium battery to recover a graphite crude product;

mixing and reacting the pretreated crude graphite product with an acidic substance and an oxidant, and then carrying out first solid-liquid separation;

further, mixing the solid obtained by the first solid-liquid separation with an alkaline reducing agent for reaction, and then carrying out second solid-liquid separation, wherein the solid obtained by the second solid-liquid separation is the recovered graphite.

The purpose of disassembling the waste lithium battery graphite negative electrode sheet is mainly to separate a graphite negative electrode material (containing a binder, metal impurities and the like) and a current collector (such as copper foil).

Furthermore, before disassembly, the waste lithium battery graphite negative electrode sheet is calcined in a protective atmosphere or a vacuum environment, preferably in the protective atmosphere, the calcining temperature is 300-600 ℃, and the calcining time is 1-3 h, so that the electrolyte in the graphite negative electrode material can be volatilized and removed, organic groups in the binder are decomposed, and the graphite negative electrode material and a current collector (such as copper foil) can be separated to obtain a crude graphite product. If the calcination temperature exceeds 600 ℃, the graphite is oxidized, the specific surface area is increased, and other disadvantages are caused; if the temperature is lower than 300 ℃, the electrolyte and the binder in the recovered graphite can be incompletely removed.

The step of disassembling and recycling can be directly and manually stripped from the current collector, but the method wastes time and labor cost and is not beneficial to industrial production; the invention preferably adopts a flotation process to disassemble the graphite cathode sheet of the waste lithium battery and recover a graphite rough product.

Further, the flotation process specifically comprises the following steps: crushing the waste lithium battery graphite negative electrode sheets, pouring the crushed waste lithium battery graphite negative electrode sheets into a flotation tank, stirring, collecting and drying an upper layer substance to obtain a crude graphite product, wherein the liquid used in the flotation tank is water.

Preferably, the upper layer is dried by adopting a vacuum drying mode, the temperature of the vacuum drying is 80-120 ℃, and the time is 6-24 h, so that the upper layer can be effectively dried, and impurities such as dust are prevented from being mixed.

Preferably, the crude graphite product is calcined in a muffle furnace in the air atmosphere at the temperature of 700-900 ℃ for 1-5 h, so that metal impurities such as Cu, ni, co, mn, al and Li in the crude graphite product are changed into corresponding metal oxides, and organic components in a solid electrolyte interface film (SEI) on the surface of the crude graphite product can be removed. If the calcination temperature exceeds 900 ℃, the graphite is oxidized, the specific surface area is increased, and other disadvantages are caused; if the temperature is lower than 700 ℃, the removal of the conductive agent, the SEI film and the metal impurities in the recovered graphite is incomplete.

The pretreated crude graphite product is mixed with an oxidant and an acidic substance to react, so that metal oxides in the crude graphite product and Li-containing compounds in an SEI film are dissolved and recovered, the metal oxides are all converted into soluble metal salts, then the soluble metal salt solution is removed through solid-liquid separation, an alkaline reducing agent is further added into the separated solid to carry out alkaline washing so as to neutralize the residual acidic substance and react with the residual oxidant, and solid-liquid separation is carried out again so as to obtain a recovered graphite product with the metal ion content reduced to the level below ppm.

The acidic substance comprises at least one of hydrochloric acid solution and sulfuric acid solution, and preferably hydrochloric acid solution with concentration of 0.1-3 mol/L is used.

The oxidant comprises at least one of hydrogen peroxide solution and perchloric acid solution, and preferably the hydrogen peroxide solution with the mass fraction of 0.5-20% is adopted.

The alkaline reducing agent comprises at least one of hydrazine and sodium bisulfite, and preferably adopts 0.5-40% hydrazine solution by mass fraction.

Preferably, the volume ratio of the acidic substance to the oxidizing agent is (0.5-5): 1; the mass ratio of the pretreated crude graphite product to the acidic substance is 1: (1-5).

Preferably, the temperature of the mixing reaction of the pretreated crude graphite product, the acidic substance and the oxidant is 60-80 ℃, and the time is 4-12 h. The time for mixing and reacting the solid obtained by the first solid-liquid separation and the alkaline reducing agent is 4-12 h, so that the reaction is more complete.

When the concentration of the hydrochloric acid solution, the mass fraction of the hydrogen peroxide solution, the mass fraction of the hydrazine solution, the reaction temperature and the reaction time exceed the upper limit of the respective preferable ranges, the distance between graphite layers is increased, and when the graphite is applied to a lithium battery, the negative electrode graphite layer is easy to peel off in the battery cycle process; on the other hand, when the content is less than the lower limit of the above-mentioned preferable range, the SEI film and the metal ions in the recovered graphite are not completely removed.

The first solid-liquid separation and the second solid-liquid separation each include at least one of centrifugal separation and filtration.

Preferably, the filtration is performed by suction filtration by using a Buchner funnel; the filter paper for suction filtration is made of polytetrafluoroethylene filter paper, and the aperture of the filter paper is 0.2-0.8 μm.

The preparation method of the recycled graphite further comprises the following steps: and drying the solid obtained by the second solid-liquid separation, preferably adopting a vacuum drying mode, wherein the vacuum drying temperature is 60-120 ℃.

Further, the step of oxidizing the graphite comprises: the graphite is calcined in an air or oxygen atmosphere, preferably in an oxygen atmosphere, such that O combines with C in oxygen to form C = O or C-O.

Preferably, in the oxidation pretreatment process, the flow of oxygen is controlled to be 0.1mL/s-10mL/s, the calcination temperature is 500-750 ℃, and the calcination time is 0.5h-2.5h, so that the graphite is more fully oxidized, and the subsequent zinc chloride is favorably fully participated in the reaction. If the flow rate of oxygen and the calcination temperature and time exceed the upper limits of the respective preferable ranges, the graphite is excessively oxidized and excessively formedSp of (A) ² +sp ³ Amorphous carbon coating; and lower than the lower limit of the respective preferable range, the pretreatment of graphite oxidation is not obvious, and the subsequent zinc chloride does not sufficiently participate in the reaction.

The hydroxyl group-containing polymer may be a polymeric polyol; the number of carbon atoms in the main chain of the polymeric polyol is not more than 4.

In a specific example, the polymeric polyol may be at least one of polyethylene glycol, polypropylene glycol, and polyglycerol.

Further, the mixture also comprises a solvent; the solvent is water, and can be deionized water or distilled water.

The preparation method of the mixture comprises the following steps: firstly, mixing the hydroxyl-containing polymer with a solvent, then adding the pretreated graphite for mixing, and then adding the zinc chloride for secondary stirring and mixing reaction.

Preferably, the time for adding the pretreated graphite and mixing is 10min-60min; the time of the complex reaction is 3h-6h.

Preferably, the volume ratio of the hydroxyl-containing polymer to the solvent in the preparation process of the precursor is controlled to be 1: (10-50); the mass ratio of the pretreated graphite to the hydroxyl-containing polymer is controlled to be 1: (1-4); the mass ratio of the pretreated graphite to the zinc chloride is controlled to be 1: (1-4) so that an appropriate amount of sp is obtained after calcination ² +sp ³ Amorphous carbon coated graphite. If the amounts of the pretreated graphite, the hydroxyl group-containing polymer and zinc chloride added exceed the upper limit of the above-mentioned preferable range, sp is generated ² +sp ³ Too much amorphous carbon coating; if it is lower than the lower limit of the above preferred range, sp ² +sp ³ Amorphous carbon coating was not apparent.

Preferably, the method further comprises, before drying the product after the complexing reaction: firstly, heating and evaporating the product after the complexing reaction; the temperature of heating evaporation is preferably 80-100 ℃; the drying process adopts a vacuum drying mode, preferably vacuum drying at the temperature of 60-80 ℃, and the drying time is 12-24 h.

The carbonization treatment is to calcine the precursor in a protective atmosphere environment or a vacuum environment; preferably, the calcination temperature of the precursor in the protective atmosphere environment is 900-1200 ℃, and the calcination time is 2-4 h.

The protective atmosphere comprises at least one of nitrogen, argon, helium and neon;

Embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1

(1) Disassembling the waste ternary NCM battery, taking out the graphite negative plate, and calcining the graphite negative plate for 2 hours at 400 ℃ in a high-purity nitrogen protective atmosphere environment; crushing the calcined graphite cathode plate by a rolling crusher, pouring the crushed material into a flotation tank (liquid in the flotation tank is water), stirring for a period of time, collecting an upper layer, drying for 10 hours in a 100 ℃ vacuum drying oven, and calcining the obtained crude graphite product in a muffle furnace at 800 ℃ for 1.5 hours to obtain the crude pretreated graphite product.

(2) 50ml of 1mol/L HCl solution and 50ml of 10% H by mass ₂ O ₂ Mixing the solutions, adding 5g of the above pretreated graphite crude product, heating to 80 deg.C, stirring for reaction for 4 hr, filtering with Buchner funnel (using polytetrafluoroethylene filter paper with pore size of 0.45 μm), and adding 20% N to the obtained solid ₂ H ₄ Stirring in solutionReacting for 4h, filtering by using a Buchner funnel (adopting polytetrafluoroethylene filter paper with the aperture of 0.45 mu m), and drying the obtained solid in a vacuum drying oven at 60 ℃ for 12h to obtain the recovered graphite.

(3) And placing the recovered graphite in a tube furnace at 680 ℃, and calcining for 1h in an oxygen atmosphere with the oxygen flow of 10mL/s to obtain the pretreated graphite.

(4) Preparing a precursor:

(1) adding 2ml of polyethylene glycol (PEG) into 45ml of deionized water to form a uniform solution I;

(2) adding 1g of pretreated graphite into the solution I to form a solution II, and stirring for 30min;

(3) then 2g ZnCl is added ₂ Adding the solution II into the solution II, and stirring the solution II for 4 hours to form a solution III;

(4) heating the solution III to 80 ℃ for evaporation to obtain a gel-like substance;

(5) and drying the gel-like substance at 60 ℃ in vacuum for 24h to obtain a precursor.

(5) And (3) putting the precursor into a 1000 ℃ tubular furnace, and calcining for 2 hours in a nitrogen atmosphere to obtain modified graphite AC @ G.

(6) And (3) crushing the modified graphite AC @ G, and then sieving the crushed graphite AC @ G with a 300-mesh sieve to obtain the graphite negative electrode material for later use.

Example 2

(1) Disassembling the waste ternary NCM battery, taking out the graphite negative plate, and calcining the graphite negative plate for 1h at 600 ℃ in a high-purity nitrogen protective atmosphere environment; crushing the calcined graphite cathode plate by a rolling crusher, pouring the crushed material into a flotation tank (liquid in the flotation tank is water), stirring for a period of time, collecting an upper layer, drying for 6 hours in a vacuum drying oven at 120 ℃, and calcining the obtained crude graphite product in a muffle furnace at 700 ℃ for 4.5 hours to obtain the crude pretreated graphite product.

(2) 150ml of 0.5mol/L HCl solution and 50ml of 1% H by mass ₂ O ₂ Mixing the solutions, adding 5g of the above pretreated graphite crude product, heating to 70 deg.C, stirring, reacting for 8 hr, filtering with Buchner funnel (using polytetrafluoroethylene filter paper with pore diameter of 0.2 μm), adding the obtained solid into mass fractionNumber 10% of N ₂ H ₄ Stirring the solution for reaction for 8h, filtering the solution by using a Buchner funnel (polytetrafluoroethylene filter paper with the aperture of 0.8 mu m) again, and drying the obtained solid in a vacuum drying oven at the temperature of 90 ℃ for 10h to obtain the recovered graphite.

(3) And placing the recovered graphite in a tubular furnace at 500 ℃, and calcining for 2.5 hours in an oxygen atmosphere with the oxygen flow of 5mL/s to obtain the pretreated graphite.

(4) Preparing a precursor:

(1) adding 2ml of polyethylene glycol (PEG) into 20ml of deionized water to form a uniform solution I;

(2) adding 1g of pretreated graphite into the solution I to form a solution II, and stirring for 10min;

(3) then 1g of ZnCl is added ₂ Adding the solution II into the solution II, and stirring for 3 hours to form a solution III;

(4) heating the solution III to 90 ℃ for evaporation to obtain a gel-like substance;

(5) and (3) drying the gel substance at 70 ℃ for 15h in vacuum to obtain a precursor.

(5) And (3) putting the precursor into a 900 ℃ tubular furnace, and calcining for 4 hours in a nitrogen atmosphere to obtain modified graphite AC @ G.

Example 3

(1) Disassembling the waste ternary NCM battery, taking out the graphite negative plate, and calcining the graphite negative plate at 300 ℃ for 3 hours in a high-purity nitrogen protective atmosphere environment; crushing the calcined graphite cathode plate by a rolling crusher, pouring the crushed material into a flotation tank, stirring for a period of time, collecting an upper layer, drying for 24 hours in a vacuum drying oven at 80 ℃, and calcining the obtained crude graphite product in a muffle furnace at 900 ℃ for 1 hour to obtain the crude pretreated graphite product.

(2) 50ml of 1mol/L HCl solution and 50ml of 10% H by mass ₂ O ₂ Mixing the solutions, adding 5g of the above crude graphite product, heating to 60 deg.C, stirring, reacting for 10 hr, and filtering with Buchner funnel (using 0.8 μm PTFE filter paper) to obtainAdding 0.5 mass percent of N into the obtained solid ₂ H ₄ Stirring the solution for reaction for 12h, filtering the solution by using a Buchner funnel (polytetrafluoroethylene filter paper with the aperture of 0.8 mu m) again, and drying the obtained solid in a vacuum drying oven at 120 ℃ for 8h to obtain the recovered graphite.

(3) And placing the recovered graphite in a tube furnace at 750 ℃, and calcining for 0.5h in an oxygen atmosphere with oxygen flow of 0.5mL/s to obtain the pretreated graphite.

(4) Preparing a precursor:

(1) adding 2ml of polyethylene glycol (PEG) into 90ml of deionized water to form a uniform solution I;

(3) 4g of ZnCl are added ₂ Adding the solution II into the solution II, and stirring the solution II for 6 hours to form a solution III;

(4) heating the solution III to 100 ℃ for evaporation to obtain a gel-like substance;

(5) and (3) drying the gel substance at 80 ℃ for 12h in vacuum to obtain a precursor.

(5) And (3) putting the precursor into a 1200 ℃ tube furnace, and calcining for 2h in a nitrogen atmosphere to obtain the modified graphite AC @ G.

Example 4

The present example differs from example 1 in that: the procedure of example 1 was otherwise the same as that of example 1 except that the recovered graphite prepared in steps (1) and (2) was replaced with commercially available battery grade pure graphite powder.

Example 5

This example differs from example 2 in that: the procedure of example 2 was otherwise the same as that of example 2 except that the recovered graphite prepared in steps (1) to (2) was replaced with commercially available battery grade pure graphite powder.

Comparative example 1

The comparative example differs from example 1 in that: the procedure of example 1 was followed except that the step (3) of step (4) was omitted, namely the step of adding zinc chloride was omitted.

Comparative example 2

This comparative example differs from example 1 in that: the same procedure as in example 1 was repeated except for steps (3), (4) and (5).

Comparative example 3

And (3) sieving commercially available battery grade pure graphite powder with a 300-mesh sieve to obtain the graphite cathode material for later use.

1. The morphology of the recovered graphite and the modified graphite AC @ G obtained in example 1 was examined, and the structures are shown in FIGS. 1a, 1b, 1c and 1 d.

As shown in FIG. 1a, the SEM morphology of the recycled graphite in example 1 shows that the recycled graphite has a particle size of 10 μm to 50 μm.

FIG. 1b, FIG. 1c and FIG. 1d are SEM topography under different magnifications of the modified graphite AC @ G obtained in example 1, respectively, and it can be seen from the figures that amorphous carbon is coated on the surface of graphite and the interior of amorphous carbon is a three-dimensional porous network structure.

2. The graphite negative electrode materials obtained in the above examples 1 to 5 and comparative examples 1 to 3 were applied to lithium batteries and electrochemical performance tests were correspondingly performed, specifically as follows:

1) Preparing a negative plate: according to the weight ratio of polyvinylidene fluoride (PVDF): the mass ratio of N-methylpyrrolidone (NMP) is 1:49 mixing and preparing a binder solution; and (2) mixing a negative electrode material, conductive carbon black Super P and a binder according to a mass ratio of 8:1:1, mixing, defoaming and stirring for 30min to obtain uniform and bright slurry, uniformly coating the slurry on a copper foil, and then placing the copper foil at 100 ℃ for vacuum drying for 2h; and cutting the obtained negative pole piece into different shapes according to different battery specifications (the lithium battery pole piece is a circular piece with the diameter of 0.8cm-1.4 cm).

2) Assembling the lithium battery: assembling according to CR2016 button cells, wherein the cell assembly is completed in an argon glove box with oxygen and water contents lower than 0.1 ppm; selecting a high-purity lithium sheet as a counter electrode, a PE membrane as a diaphragm, and 1M LiPF as an electrolyte ₆ (the solvent is a mixed solution of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1.

3) Testing the electrochemical performance of the lithium battery: standing the assembled lithium battery for 5 hours, and then carrying out constant current charge and discharge test on the battery at room temperature; the test was performed on a blue-electricity (wuhan blue electronics, inc.) battery test system; the discharge is carried out for the first time at 0.05C, and then the discharge is cycled for five circles at the charge-discharge multiplying factors of 0.1C, 0.5C, 1C, 2C and 8C respectively, and then the discharge is returned to 0.1C multiplying factor for long cycle.

The electrochemical performance test results are shown in table 1 and fig. 2 below.

TABLE 1

Fig. 2 is a graph showing the electrochemical performance of the graphite negative electrode materials obtained in example 1, comparative example 1 and comparative example 2 applied to a battery.

According to the result, the modified graphite AC @ G obtained in the embodiment of the invention is applied to the lithium battery, so that the lithium battery has good electrochemical performance, and the specific discharge capacity of the lithium battery is higher than that of the comparative example; the coating of the three-dimensional porous amorphous carbon increases the active sites of the graphite, and the porous structure of the graphite can increase the wettability of the electrolyte, so that the electrolyte can be better contacted with a negative electrode material, and the Li is improved ⁺ Transmission performance; comparative example 1 due to no ZnCl addition ₂ Since PEG is simply dispersed on the surface of SG, no gel precursor is formed, and no three-dimensional porous amorphous carbon coating layer is formed after calcination.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims

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

carrying out oxidation pretreatment on graphite to obtain pretreated graphite;

and carbonizing the precursor to obtain the modified graphite.

2. The method for preparing modified graphite according to claim 1, wherein the step of subjecting the graphite to oxidation pretreatment comprises: calcining the graphite in air or oxygen atmosphere.

3. The method of preparing modified graphite according to claim 2, wherein the flow rate of oxygen is 0.1mL/s to 10mL/s;

the calcining temperature of the graphite in the oxygen atmosphere is 500-750 ℃, and the time is 0.5-2.5 h.

4. The method for producing modified graphite according to claim 1, wherein the hydroxyl group-containing polymer is a polymeric polyol; the polymeric polyols comprise at least one of polyethylene glycol, polypropylene glycol and polyglycerol;

the mass ratio of the pretreated graphite to the hydroxyl-containing polymer is 1: (1-4);

the mass ratio of the pretreated graphite to the zinc chloride is 1: (1-4).

5. The method of preparing modified graphite according to claim 1, wherein the mixture further comprises a solvent;

the solvent is water;

the volume ratio of the hydroxyl-containing polymer to the solvent is 1: (10-50).

6. The method of preparing the modified graphite of claim 5, wherein the mixture is prepared by: firstly, mixing the hydroxyl-containing polymer with a solvent, then adding the pretreated graphite and mixing to obtain a mixture; adding the pretreated graphite and mixing for 10-60 min; the time of the complex reaction is 3h-6h.

7. The method of preparing modified graphite according to claim 1, further comprising, before said drying: firstly, heating and evaporating a product after the complexing reaction; the temperature of the heating evaporation is 80-100 ℃;

the drying process comprises the following steps: and (3) drying the product after the complexing reaction for 12-24 h at the temperature of 60-80 ℃ in vacuum.

8. The method for preparing modified graphite according to claim 1, wherein the carbonization treatment is calcination of the precursor in a protective atmosphere environment or a vacuum environment;

the calcination temperature of the precursor in the protective atmosphere environment is 900-1200 ℃, and the calcination time is 2-4 h.

9. The process for preparing modified graphite according to any one of claims 1 to 8, wherein the graphite is recycled graphite; and the recovered graphite is recovered from the graphite negative plate of the waste lithium battery.

10. The method of preparing modified graphite according to claim 9, wherein the method of preparing recycled graphite comprises:

mixing the solid obtained by the first solid-liquid separation with an alkaline reducing agent for reaction, and then carrying out second solid-liquid separation, wherein the solid obtained by the second solid-liquid separation is the recovered graphite.

11. The method for preparing modified graphite according to claim 10, wherein before disassembling the negative graphite electrode sheets of the waste lithium batteries, the method further comprises: calcining the waste lithium battery graphite negative electrode sheet in a protective atmosphere or a vacuum environment; the calcining temperature is 300-600 ℃, and the time is 1-3 h; the protective atmosphere comprises at least one of nitrogen, argon, helium and neon.

12. The method for preparing modified graphite according to claim 10, wherein the crude graphite product is recovered by disassembling the graphite negative electrode sheets of the waste lithium batteries by a flotation process;

the process of disassembling and recovering the crude graphite product comprises the following steps: and crushing the waste lithium battery graphite negative electrode sheets, pouring the crushed waste lithium battery graphite negative electrode sheets into a flotation tank, stirring, collecting and drying an upper layer substance, and thus obtaining a crude graphite product.

13. The process for preparing modified graphite according to claim 12, wherein the liquid used in the flotation cell is water;

drying the upper layer substance by adopting a vacuum drying mode;

and drying the upper layer at the temperature of 80-120 ℃ for 6-24 h in vacuum.

14. The method for preparing modified graphite according to claim 10, wherein the calcination of the graphite crude product in an air atmosphere is carried out at a temperature of 700 ℃ to 900 ℃ for 1 hour to 5 hours.

15. The method for preparing modified graphite according to claim 10, wherein the acidic substance includes at least one of a hydrochloric acid solution and a sulfuric acid solution;

the oxidizing agent comprises at least one of a hydrogen peroxide solution and a perchloric acid solution;

the alkaline reducing agent includes at least one of hydrazine and sodium bisulfite.

16. The method for preparing modified graphite according to claim 15, wherein the acidic substance is a hydrochloric acid solution having a concentration of 0.1mol/L to 3 mol/L;

the oxidant is a hydrogen peroxide solution with the mass fraction of 0.5-20%;

the alkaline reducing agent is hydrazine solution with the mass fraction of 0.5-40%.

17. The method for preparing modified graphite according to claim 10, wherein the volume ratio of the acidic substance to the oxidizing agent is (0.5 to 5): 1;

the mass ratio of the pretreated crude graphite product to the acidic substance is 1: (1-5);

the temperature of the mixing reaction of the pretreated crude graphite product, the acidic substance and the oxidant is 60-80 ℃, and the time is 4-12 h.

18. The method for preparing modified graphite according to claim 10, wherein the time for mixing and reacting the solid obtained by the first solid-liquid separation with the alkaline reducing agent is 4 to 12 hours;

the first solid-liquid separation and the second solid-liquid separation each comprise at least one of centrifugal separation and filtration;

the preparation method of the recycled graphite further comprises the following steps: drying the solid obtained by the second solid-liquid separation;

and (3) drying the solid obtained by the second solid-liquid separation in vacuum at the temperature of between 60 and 120 ℃.

19. A modified graphite produced by the method for producing a modified graphite according to any one of claims 1 to 18.

20. A negative electrode material for a lithium battery, comprising the modified graphite as claimed in claim 19.

21. A negative electrode sheet for a lithium battery comprising the negative electrode material for a lithium battery as claimed in claim 20.

22. A lithium battery comprising the negative electrode sheet for a lithium battery as claimed in claim 21.