Graphite negative electrode material, preparation method thereof, negative electrode and lithium ion battery

Abstract

The application provides a graphite negative electrode material, a preparation method thereof, a negative electrode and a lithium ion battery. The preparation method comprises the following steps: carrying out an activation reaction on the graphite negative electrode material and an inorganic alkali to obtain an activation product; carrying out ultrasonic acidification treatment on the activation product and an inorganic acid to obtain an acidification product; finally, carrying out a coating process on the acidification product and a modifier to obtain a modified graphite negative electrode material, wherein the modifier is selected from one or more of 1H, 1H, 2H-perfluoro-1-decene, 1H, 1H, 2H-perfluoro-1-octene and 1H, 1H, 2H-perfluoro-1-dodecene. The coating process can retain sufficient surface area of the S-M graphite, reduce the Li + ion transmission path, the long carbon chain of the perfluorocarbon provides a channel for electron transmission, the kinetics of the battery electrochemical reaction is strengthened, the lithium extraction and intercalation rate is increased, the rate performance of the material is improved, the perfluorocarbon load layer reduces the electrolyte liquid absorption amount, and the first charge and discharge efficiency and the energy density are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium battery negative electrode materials, in particular to a kind of graphite negative electrode material, its preparation method, negative electrode and lithium ion battery. BACKGROUND

[0002] Lithium ion battery has been widely used in our daily life due to its long service life, high working voltage platform, no memory effect, small self-discharge, fast charge and discharge and wide working temperature range.

[0003] Due to high electronic conductivity, high lithium intercalation capacity and low potential, and small volume change before and after lithium intercalation, graphite has advantages as a negative electrode material for secondary rechargeable lithium ion batteries. However, its large specific surface area not only improves the reactivity but also causes some problems: ① Large specific surface area of graphite negative electrode material will result in large electrolyte absorption, which will reduce the mass energy density of the battery and affect the utilization effect of the battery; ② Large specific surface area will result in the formation of more and thicker SEI films, thereby reducing the efficiency of the battery and affecting the electrochemical performance of the battery.

[0004] In terms of modification of lithium ion battery negative electrode materials, carbon coating as a very cheap and effective modification method has received widespread attention. CN106684360A prepares a mixed solution by mixing a polymer and an ionic liquid, adds artificial graphite and stirs to obtain a suspension, filters and washes with pure water to obtain filter residue of polymer-coated artificial graphite, and carbonizes the filter residue to obtain uniformly carbon-coated artificial graphite negative electrode material. The specific surface area of the obtained negative electrode material decreases, but the discharge capacity also decreases when applied in a battery, and the discharge efficiency is not significantly improved; CN112490443A heat-stirs and graphitizes petroleum coke in turn to obtain graphitized return material, mixes the graphitized return material with liquid phenolic resin uniformly, and carbonizes to obtain liquid-coated graphite negative electrode material. Similarly, after reducing the specific surface area of the negative electrode material, the battery capacity decreases.

[0005] Both of the above carbon-coat the graphite negative electrode material to reduce the specific surface area of the graphite negative electrode material, thereby reducing its electrolyte absorption and improving the first charge and discharge efficiency of the battery. However, the active sites of the electrochemical reaction on the graphite negative electrode material also decrease when its specific surface area is reduced, and the rate performance and capacity performance of the battery also decrease, which also affects its performance. SUMMARY

[0006] The main purpose of the present application is to provide a graphite negative material, a preparation method thereof, a negative electrode and a lithium ion battery, so as to solve the problem of how to reduce the reduction of battery mass energy density, initial efficiency and electrochemical performance caused by the reduction of specific surface area of graphite negative material while ensuring the rate performance and capacity performance of the battery.

[0007] In order to achieve the above-mentioned purpose, one aspect of the present application provides a preparation method of a modified graphite negative material, which comprises:

[0008] Under a first inert atmosphere, the graphite negative material is subjected to an activation reaction with an inorganic base to obtain an activation product; the activation product is subjected to an ultrasonic acidification treatment with an inorganic acid to obtain an acidification product; under a second inert atmosphere, the acidification product is subjected to a coating process with a modifier to obtain the modified graphite negative material, wherein the modifier is selected from one or more of the group consisting of 1H, 1H, 2H-perfluoro-1-decene, 1H, 1H, 2H-perfluoro-1-octene and 1H, 1H, 2H-perfluoro-1-dodecene.

[0009] Further, the weight ratio of the graphite negative material to the inorganic base is 1:(2-4), the reaction temperature is 600-900℃, and the reaction time is 3-8h.

[0010] Further, the inorganic base is hydroxide, preferably KOH and / or NaOH.

[0011] Further, the D50 of the graphite negative material is 5-30μm.

[0012] Further, in the ultrasonic acidification treatment process, 1g of the activation product requires 30-50mL of the inorganic acid; the inorganic acid is a mixture of concentrated nitric acid and concentrated sulfuric acid, preferably, the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is 1:(2-4).

[0013] Further, in the ultrasonic acidification process, the frequency of the ultrasonic is 40-60kHz, the temperature is 40-60℃, and the ultrasonic time is 20-60min.

[0014] Further, the coating process is in an oil bath, 1g of the acidification product requires 10-30mL of the modifier, the reaction temperature is 160-190℃, and the reaction time is 8-15h.

[0015] Another aspect of the present application provides a modified graphite negative material, which is prepared by the above-mentioned preparation method.

[0016] Still another aspect of the present application provides a negative electrode, which comprises a current collector and the above-mentioned modified graphite negative material arranged on the current collector.

[0017] Another aspect of the present application provides a lithium ion battery, comprising a positive electrode, the above-mentioned negative electrode, a separator and an electrolyte.

[0018] By using the technical solution of the present application, the graphite negative electrode material is first reacted with an inorganic base to obtain an activated product (M-graphite), which has a large number of micropores on the surface, which is beneficial to increase the interface of electrochemical reaction, improve the transmission rate of Li + ions, and M-graphite is then reacted with an inorganic acid to obtain an acidified product (S-M-graphite) with functional groups such as hydroxyl groups on the surface, and finally, the S-M-graphite is coated with a modifier to obtain a modified graphite negative electrode material with perfluorocarbon on the surface. Since the C-C bond in perfluorocarbon has a strong bond energy, perfluorocarbon is hard enough to resist friction between particles without causing damage to the modified loading layer. Compared with other carbon coating technologies, the coating process in the present application can retain sufficient surface area of S-M-graphite, reduce the Li + ion transmission path, and the long carbon chain of the stacked perfluorocarbon also provides a channel for electron transmission, the kinetics of the battery electrochemical reaction is strengthened, the rate of lithium extraction and intercalation is increased, and the rate performance of the material is improved; at the same time, the perfluorocarbon loading layer that is hydrophobic to the electrolyte reduces the electrolyte absorption of the battery, improves the first charge and discharge efficiency and energy density. BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, the illustrative embodiments of the present application and the explanations thereof serve to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 is a surface modification flowchart;

[0021] Figure 2 is a schematic diagram of electrolyte infiltration comparison;

[0022] Figure 3 is an SEM diagram of the negative electrode material, in which the right side is the perfluorocarbon modification layer structure, and the left side is the graphite layered structure.

[0023] Among them, the above-mentioned drawings include the following reference signs:

[0024] A is an S-M-graphite electrode sheet without surface modification (Example 6), and B is a surface modified S-M-graphite electrode sheet (Example 1). DETAILED DESCRIPTION

[0025] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0026] As described in the background, the graphite battery anode prepared by the prior art is difficult to solve the problem of reducing the mass energy density, the initial efficiency and the electrochemical performance of the battery caused by the too large specific surface area of the graphite anode material while ensuring the rate performance and capacity performance of the battery. In order to solve the above technical problems, the application provides a preparation method of a modified graphite anode material, which comprises:

[0027] Under a first inert atmosphere, the graphite anode material is subjected to an activation reaction with an inorganic base to obtain an activation product; the activation product is subjected to ultrasonic acidification treatment with an inorganic acid to obtain an acidification product; under a second inert atmosphere, the acidification product and a modifier are subjected to a coating process to obtain a modified graphite anode material, wherein the modifier is selected from one or more of the group consisting of 1H, 1H, 2H-perfluoro-1-decene, 1H, 1H, 2H-perfluoro-1-octene and 1H, 1H, 2H-perfluoro-1-dodecene.

[0028] The first inert atmosphere and the second inert atmosphere are independently selected from nitrogen or an inert gas.

[0029] In the above preparation method, the graphite anode material is first reacted with an inorganic base to obtain an activation product (M-graphite), which has a large number of micropores on the surface, which is beneficial to increase the interface of electrochemical reaction and improve the transmission rate of Li + ions. The activation product M-graphite is then reacted with an inorganic acid to obtain an acidification product (S-M-graphite) with functional groups such as hydroxyl groups on the surface, and finally it is coated with a modifier to obtain a modified graphite anode material with perfluorocarbon on the surface. Since the C—F bond energy in perfluorocarbon is very strong, perfluorocarbon is hard enough to resist inter-particle friction without causing damage to the modified loading layer. At the same time, the van der Waals radius of fluorine atom is slightly larger than that of hydrogen atom, but smaller than that of all other elements, and the mutual repulsion of adjacent fluorine atoms makes the fluorine atoms in the perfluorocarbon on the surface of S-M-graphite not in the same plane, which can just wrap the carbon-carbon chain, so that the carbon chain of perfluorocarbon is well protected in space by the surrounding stable fluorine atoms. Moreover, the polarizability of fluorine atom is low, causing the polarity of C—F bond to be strong, and the shared electron pair of fluorocarbon atom greatly deviates to fluorine atom, making fluorine atom have excess negative charge and forming a layer of negative charge protection, so that the nucleophilic reagent with negative charge cannot approach and react chemically.

[0030] It is known that the SEI film in the prior art is mainly generated because the conventional electrolyte is unstable on the surface of the negative electrode at a low potential, is reduced and decomposed, and then generates a layer of organic and inorganic mixed decomposition products on the surface, which is the SEI film. In the present application, the C-F bond on the surface of the modified negative electrode material has a short bond length and a large bond energy, the carbon chain of the perfluorocarbon layer is strong in rigidity and poor in flexibility, and thus has a small interaction force with active chemicals. When the interaction site density between the perfluorocarbon and the liquid is low, the interaction between them is weaker. Therefore, the perfluorocarbon has hydrophobicity not only to water but also to polar liquids with high binding energy. The surface binding energy of the electrolyte molecules and the perfluorocarbon layer is low, so they are more difficult to be infiltrated. Therefore, the liquid absorption performance of the S-M graphite electrolyte after modification is small, the electrolyte liquid absorption is less, the generation and growth of the SEI film is less, the Li source consumed for forming the SEI film is less, and the first charge-discharge efficiency of the battery is improved.

[0031] Compared with other carbon coating technologies, the coating process in the present application can retain sufficient surface area of the S-M graphite, reduce the Li + ion transmission path, and the long carbon chain of the stacked perfluorocarbon also provides a channel for electron transmission, so that the kinetics of the battery electrochemical reaction is stronger, the lithium extraction and intercalation rate is increased, and the rate performance of the material is improved. At the same time, the perfluorocarbon loading layer that is hydrophobic to the electrolyte reduces the electrolyte liquid absorption amount of the battery, and improves the first charge-discharge efficiency and energy density.

[0032] In a preferred embodiment, the weight ratio of the graphite negative electrode material to the inorganic base is 1:(2-4), the reaction temperature is 600-900℃, and the reaction time is 3-8h. Controlling the addition amount of the graphite negative electrode material and the inorganic base powder within the above range can ensure that the graphite negative electrode material generates more electrochemical reaction active sites.

[0033] In a preferred embodiment, the inorganic base is a hydroxide, preferably KOH and / or NaOH. Such hydroxides mainly activate primary carbonized materials (based on biomass, petroleum coke, coal or polymer precursors), and the main mechanism of pore formation is that the metal ions generated in the heat treatment process intercalate the layered structure in the carbon structure, thereby generating internal pores. The material obtained after activation has a large specific surface area and relatively excellent performance in all aspects.

[0034] In a preferred embodiment, the D50 of the graphite negative electrode material is 5-30μm. Selecting graphite with this particle size distribution is beneficial to controlling the specific surface area of the negative electrode material to some extent, maximizing the modification effect, and then ensuring the energy density of the modified negative electrode material when applied to a battery.

[0035] In a preferred embodiment, during the ultrasonic acidification process, the inorganic acid required for 1 g of the activated product is 30-50 mL. If the M graphite is too much, the M graphite is not completely acidified, resulting in too few surface hydroxyl functional groups of S-M graphite, and 1H, 1H, 2H-perfluoro-1-decene cannot achieve complete surface modification of the material; if too much inorganic acid, the surface of the graphite is acidified too much, 1H, 1H, 2H-perfluoro-1-decene "attacks" too much, the surface modification layer is too thick, and the electrolyte enters the modified negative electrode material less, and the electrochemical performance is poor. Therefore, the addition of M graphite and mixed acid is controlled within the above range, and the electrochemical performance of the negative electrode material prepared subsequently and applied to the battery is better. The inorganic acid is a mixture of concentrated nitric acid and concentrated sulfuric acid, and preferably the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:(2-4). Selecting a mixture of concentrated nitric acid and concentrated sulfuric acid as the inorganic acid, and controlling the volume ratio of the two within the above range, is beneficial to controlling the acidity of the inorganic acid, so as to obtain enough surface active groups during the acidification process, and not to destroy the structure of the activated product M graphite.

[0036] In a preferred embodiment, during the ultrasonic acidification process, the frequency of the ultrasonic is 40-60 kHz, the temperature is 40-60°C, and the ultrasonic time is 20-60 min. Ultrasonic treatment of the acidification system and control of the ultrasonic conditions within the above range are beneficial to enhancing the mixing effect of the inorganic acid and the activated product M graphite, thereby improving the acidification effect, so as to obtain a sufficient number of surface hydroxyl functional groups.

[0037] Before the ultrasonic acidification treatment, the preparation method of the modified graphite negative electrode material comprises: first washing the activated product with a 0.1-0.5 mol / L dilute hydrochloric acid solution, then washing with water until the pH of the washing solution is neutral, and performing a first vacuum drying treatment. This step is to remove the unreacted inorganic base remaining in the activation process to avoid affecting the subsequent acidification effect. Preferably, the temperature of the first vacuum drying treatment is 50-80°C, and the drying time is 2-12 h.

[0038] In a preferred embodiment, after the ultrasonic acidification treatment, the preparation method of the modified graphite negative electrode material further comprises repeatedly filtering, washing with water and filtering again the product after ultrasonic acidification until the pH of the washing solution is neutral, and then performing a second vacuum drying treatment. Preferably, the filtering process uses a Buchner funnel to perform suction filtration. This step is to remove the unreacted inorganic acid in the acidification process to avoid damaging the structure of the subsequent modified negative electrode material. Preferably, the temperature of the second vacuum drying is 50-80°C, and the drying time is 2-12 h.

[0039] In a preferred embodiment, the coating process is in an oil bath, the required modifier for 1g acidified product is 10-30mL, the reaction temperature is 160-190℃, and the reaction time is 8-15h. During the modification process, the addition of acidified product S-M graphite and modifier needs to be controlled within a certain range, for example, if S-M graphite is too much, the material cannot be completely surface modified; and if the modifier is too much, the surface modification layer will be too thick, the electrolyte will be less in contact with the modified negative electrode material, and the electrochemical performance will be poor. Therefore, the addition amount of acidified product and modifier is controlled within the above range, so that better modification effect can be obtained; and the reaction temperature and time are controlled within the above range, so that the modification can be completely performed.

[0040] In a preferred embodiment, after the coating process is completed, the preparation method of the modified graphite negative electrode material further comprises sequentially performing centrifugation and cleaning on the coating product system, and performing third vacuum drying. More preferably, the rotation speed of the centrifugation process is 5000-10000 rad / min, and the centrifugation time is 3-5 min; the centrifugation product is cleaned multiple times, for example, 3 times, by using perfluorohexane; and the temperature of the third vacuum drying process is 50-80℃, and the drying time is 1-4h.

[0041] Another aspect of the present application provides a modified graphite negative electrode material prepared by the above preparation method.

[0042] Compared with the prior art, the modified graphite negative electrode material prepared by the method provided by the present application retains sufficient surface area of S-M graphite, reduces Li + ion transmission path, and the long carbon chain of the stacked perfluorocarbon also provides a channel for electron transmission, so that the electrochemical performance is effectively improved.

[0043] Still another aspect of the present application provides a negative electrode, which comprises a current collector and the above modified graphite negative electrode material arranged on the current collector.

[0044] Compared with the prior art, the negative electrode prepared by the method provided by the present application has stronger kinetics of battery electrochemical reaction, increased rate of lithium extraction and intercalation, and improved rate performance of the material when it is applied to a battery system; at the same time, the perfluorocarbon loading layer of the negative electrode which is hydrophobic to the electrolyte reduces the electrolyte absorption amount of the battery, and improves the first charge and discharge efficiency and energy density.

[0045] Still another aspect of the present application provides a lithium ion battery, which comprises a positive electrode, the above negative electrode, a separator, and an electrolyte.

[0046] Compared with the prior art, the specific surface area of the material will be reduced after the general material coating modification is completed, and the active site of the reaction will be reduced. However, the method provided in the present application retains sufficient surface area of the pore-forming and acidified graphite, and reduces Li+ The ion transmission path, and the long carbon chain of the perfluorocarbon also provides a channel for electron transmission, the kinetics of the battery electrochemical reaction is strengthened, the rate of lithium extraction and insertion of the battery is increased, and the rate performance of the material is improved; at the same time, the perfluorocarbon loading layer of the electrolyte-repellent electrolyte reduces the electrolyte absorption amount of the battery, and improves the first charge-discharge efficiency and energy density. The lithium ion battery prepared by the method provided by the application has high rate performance and relatively high energy density and first circle efficiency.

[0047] The application will be further described in detail below in combination with specific examples, which cannot be understood as limiting the scope of the application claimed.

[0048] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing the specific examples and are not intended to limit the protection scope of the application.

[0049] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the application can be purchased from the market or can be prepared by existing methods.

[0050] Example 1

[0051] A preparation method of a modified graphite negative electrode material comprises:

[0052] (1) 2g of graphite negative electrode material G1 is mixed with 6g of ground KOH powder, and high-temperature reaction is carried out at 800℃ for 6h under the protection of nitrogen gas. The product after reaction is first cleaned with 0.1mol / L dilute hydrochloric acid solution, and then cleaned with water until the cleaning liquid is neutral, and vacuum drying is carried out at 80℃ in a vacuum drying box for 6h to obtain M graphite material;

[0053] (2) Concentrated nitric acid and concentrated sulfuric acid are configured into mixed acid according to the volume ratio (1:3). 1g of M graphite material is added to 30ml of mixed acid, and ultrasonic acidification treatment is carried out at 50℃ water temperature for 30min. Filtration is carried out by using a Buchner funnel, and the solid product after filtration is cleaned with deionized water until the cleaning liquid is neutral, and vacuum drying is carried out at 50℃ in a vacuum drying box for 3h to obtain S-M graphite material after acidification;

[0054] (3) 0.2g of particle A is added to a 50ml round-bottom flask, and nitrogen gas is introduced after air is extracted, and the operation is repeated for 3 times;

[0055] (4) 3ml of 1H, 1H, 2H-perfluoro-1-decene (PFD) is added to the round-bottom flask, and nitrogen gas is introduced after air is extracted, and the operation is repeated for 3 times, and the reaction equation is as follows:

[0056]

[0057] (5) Put the round bottom flask into the oil bath pot, and perform oil bath reaction at 170℃ for 10h;

[0058] (6) Centrifuge, and clean the centrifuged product with perfluorohexane for 3 times. Dry in a vacuum drying box at 50℃ for 1h to obtain the final surface modified graphite negative electrode material.

[0059] Example 2

[0060] A preparation method of a modified graphite negative electrode material comprises:

[0061] (1) Mix 2g of graphite negative electrode material G1 with 8g of ground KOH powder, and perform high temperature reaction at 700℃ for 8h under nitrogen gas protection. Clean the product after reaction with 0.5mol / L dilute hydrochloric acid solution, and then clean with water until the cleaning liquid is neutral. Dry in a vacuum drying box at 50℃ for 12h to obtain M graphite material;

[0062] (2) Configure mixed acid by mixing concentrated nitric acid and concentrated sulfuric acid according to a volume ratio of 1:3. Take 1g of M graphite material and add it into 40ml of mixed acid, and perform ultrasonic acidification treatment at 60℃ water temperature for 60min. Use a Buchner funnel to filter, and then clean the solid product after filtration with deionized water until the cleaning liquid is neutral. Dry in a vacuum drying box at 80℃ for 12h to obtain acidified S-M graphite material;

[0063] (3) Add 0.2g of particle A into a 50ml round bottom flask, and perform air extraction and nitrogen gas passage repeatedly for 3 times;

[0064] (4) Add 6ml of 1H, 1H, 2H-perfluoro-1-octene into the round bottom flask, and perform air extraction and nitrogen gas passage repeatedly for 3 times;

[0065] (5) Put the round bottom flask into the oil bath pot, and perform oil bath reaction at 190℃ for 15h;

[0066] (6) Centrifuge, and clean the centrifuged product with perfluorohexane for 3 times. Dry in a vacuum drying box at 80℃ for 1h to obtain the final surface modified graphite negative electrode material.

[0067] Example 3

[0068] A preparation method of a modified graphite negative electrode material comprises:

[0069] (1) Take 2g of graphite negative electrode material G1 and 4g of ground KOH powder, mix them under nitrogen gas protection, and react at 600°C for 3h. The product after reaction is first washed with 0.3mol / L dilute hydrochloric acid solution, then with water until the washing liquid pH is neutral, and vacuum dried in a vacuum drying oven at 50°C for 2h to obtain M graphite material;

[0070] (2) Concentrated nitric acid and concentrated sulfuric acid are mixed according to the volume ratio (1:2) to form mixed acid. Take 1g of M graphite material and add it to 30ml of mixed acid, and perform ultrasonic acidification treatment at 40°C water temperature for 20min. Use a Buchner funnel to filter, then use deionized water to wash the solid product after filtration until the washing liquid pH is neutral, and vacuum dry in a vacuum drying oven at 50°C for 2h to obtain the acidified S-M graphite material;

[0071] (3) Add 0.2g of particle A to a 50ml round-bottom flask, evacuate, then pass nitrogen gas, repeat 3 times;

[0072] (4) Add 2ml of 1H,1H,2H-perfluoro-1-decene (PFD) to the round-bottom flask, evacuate, then pass nitrogen gas, repeat 3 times;

[0073] (5) Place the round-bottom flask in an oil bath, and perform oil bath reaction at 160°C for 8h;

[0074] (6) Centrifuge, and wash the centrifuged product with perfluorohexane 3 times. Vacuum dry in a vacuum drying oven at 50°C for 1h to obtain the final surface-modified graphite negative electrode material.

[0075] Example 4

[0076] A method for preparing a modified graphite negative electrode material includes:

[0077] (1) Take 2g of graphite negative electrode material G1 and 8g of ground KOH powder, mix them under nitrogen gas protection, and react at 700°C for 7h. The product after reaction is first washed with 0.3mol / L dilute hydrochloric acid solution, then with water until the washing liquid pH is neutral, and vacuum dried in a vacuum drying oven at 80°C for 10h to obtain M graphite material;

[0078] (2) Concentrated nitric acid and concentrated sulfuric acid are mixed according to the volume ratio (1:3) to form mixed acid. Take 1g of M graphite material and add it to 35ml of mixed acid, and perform ultrasonic acidification treatment at 50°C water temperature for 40min. Use a Buchner funnel to filter, then use deionized water to wash the solid product after filtration until the washing liquid pH is neutral, and vacuum dry in a vacuum drying oven at 60°C for 10h to obtain the acidified S-M graphite material;

[0079] (3) 0.2 g of the particles A was added into a 50 ml round bottom flask, and the gas was pumped out and then replaced by nitrogen gas, which was repeated for 3 times;

[0080] (4) 4 ml of 1H, 1H, 2H-perfluoro-1-dodecene was added into the round bottom flask, and the gas was pumped out and then replaced by nitrogen gas, which was repeated for 3 times;

[0081] (5) The round bottom flask was placed in an oil bath at 170°C for oil bath reaction for 12 h;

[0082] (6) Centrifugation was performed, and the centrifuged product was cleaned with perfluorohexane for 3 times. Vacuum drying was performed at 60°C for 3 h in a vacuum drying box to obtain the final surface-modified graphite negative electrode material.

[0083] Example 5

[0084] A preparation method of a modified graphite negative electrode material comprises:

[0085] (1) 2 g of a graphite negative electrode material G1 was mixed with 6 g of ground KOH powder, and high-temperature reaction was performed at 750°C for 5 h under the protection of nitrogen gas. The product after reaction was first cleaned with 0.4 mol / L dilute hydrochloric acid solution, and then cleaned with water until the pH of the cleaning solution was neutral. Vacuum drying was performed at 60°C for 8 h in a vacuum drying box to obtain M graphite material;

[0086] (2) Concentrated nitric acid and concentrated sulfuric acid were configured into mixed acid according to a volume ratio of 1:3.5. 1 g of M graphite material was added into 40 ml of the mixed acid, and ultrasonic acidification treatment was performed at 50°C for 60 min. Filtration was performed by using a Buchner funnel, and the solid product after filtration was cleaned with deionized water until the pH of the cleaning solution was neutral. Vacuum drying was performed at 50°C for 3 h in a vacuum drying box to obtain the S-M graphite material after acidification;

[0087] (3) 0.2 g of the particles A was added into a 50 ml round bottom flask, and the gas was pumped out and then replaced by nitrogen gas, which was repeated for 3 times;

[0088] (4) 5 ml of 1H, 1H, 2H-perfluoro-1-decene (PFD) was added into the round bottom flask, and the gas was pumped out and then replaced by nitrogen gas, which was repeated for 3 times;

[0089] (5) The round bottom flask was placed in an oil bath at 180°C for oil bath reaction for 12 h;

[0090] (6) Centrifugation was performed, and the centrifuged product was cleaned with perfluorohexane for 3 times. Vacuum drying was performed at 50°C for 1 h in a vacuum drying box to obtain the final surface-modified graphite negative electrode material.

[0091] Comparative Example 1

[0092] The difference from Example 1 is only that the amount of 1H, 1H, 2H-perfluoro-1-decene (PFD) added in step (4) is 1 ml.

[0093] Comparative Example 2

[0094] The difference from Example 1 is only that the amount of 1H, 1H, 2H-perfluoro-1-decene (PFD) added in step (4) is 7 ml.

[0095] Comparative Example 3

[0096] The difference from Example 1 is only that 1 g of M graphite material is added to 10 ml of mixed acid in step (2).

[0097] Comparative Example 4

[0098] The difference from Example 1 is only that 1 g of M graphite material is added to 80 ml of mixed acid in step (2).

[0099] Comparative Example 5

[0100] The difference from Example 1 is only that the test of step (1), step (2) is directly used the acidized S-M graphite material as the negative electrode material.

[0101] Comparative Example 6

[0102] The difference from Example 1 is only that the test of step (1), step (2) is directly added 1 g of graphite negative electrode material G1 into 30 mL of mixed acid, i.e. without inorganic alkali activation before acidification.

[0103] Comparative Example 7

[0104] The difference from Example 1 is only that step (2) is cancelled, i.e. without acidification, and the activation product is directly reacted with the modifier.

[0105] Comparative Example 8

[0106] The difference from Example 1 is only that the test of step (4) is that the modifier is selected as asphalt.

[0107] Comparative Example 9

[0108] The difference from Example 1 is that without modification, the graphite is directly used as the negative electrode material.

[0109] Performance detection:

[0110] (1) The first circle capacity and the first circle efficiency, the test conditions are as follows:

[0111] 1) Binder: 1.5% CMC, 2.5% SBR;

[0112] 2) Conductive agent: 1.5% Super-P;

[0113] 3) Counter electrode: pure lithium sheet;

[0114] 4) Charge-discharge system:

[0115] 0.1C constant current discharge 0.005V, 0.01C constant current discharge 0.001V;

[0116] 0.1C constant current charge 1.5V.

[0117] (2) 8C rate charge, test conditions are as follows:

[0118] 1) Binder: 1.5% CMC, 2.5% SBR;

[0119] 2) Conductive agent: 1.5% Super-P;

[0120] 3) Counter electrode: pure lithium sheet;

[0121] 4) Charge-discharge system:

[0122] The battery is discharged at 8C current, and then charged at 8C current, and the 8C charge capacity / initial capacity*100% is calculated.

[0123] The first circle capacity, first circle efficiency and 8C rate charge of the negative electrode material prepared in examples 1-5 and comparative examples 1-9 are shown in table 1.

[0124] Table 1

[0125] Examples First cycle capacity (mAh / g) First cycle efficiency 8C rate charge (delithiation %) Example 1 346.68 90.43％ 82.10％ Example 2 345.93 91.89％ 80.93％ Example 3 347.54 89.72％ 81.26％ Example 4 346.34 90.48％ 81.83％ Example 5 345.03 90.95％ 81.11％ Comparative Example 1 348.14 84.75％ 50.39％ Comparative Example 2 326.63 90.55％ 65.93％ Comparative Example 3 343.54 85.43％ 52.38％ Comparative Example 4 334.74 90.78％ 64.47％ Comparative Example 5 351.63 80.24％ 24.48％ Comparative Example 6 345.75 94.36％ 60.94％ Comparative Example 7 349.63 81.67％ 21.09％ Comparative Example 8 338.48 79.87％ 37.67％ Comparative Example 9 351.88 93.45％ 15.64％

[0126] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects: compared with the prior art, the modified graphite negative electrode material prepared by the method provided by the present application is applied to the lithium ion battery negative electrode, and compared with the unmodified graphite material, the first circle capacity of the obtained battery does not show a significant downward trend, and the first circle efficiency is significantly improved.

[0127] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those described herein.

[0128] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A method for preparing a modified graphite anode material, characterized in that, The preparation method of the modified graphite anode material includes: Under a first inert atmosphere, the graphite anode material is activated with an inorganic base to obtain the activated product; The activated product is subjected to ultrasonic acidification with an inorganic acid to obtain an acidified product; wherein the inorganic acid is a mixture of concentrated nitric acid and concentrated sulfuric acid. Under a second inert atmosphere, the acidification product and the modifier are coated to obtain the modified graphite anode material, wherein the modifier is selected from one or more of 1H,1H,2H-perfluoro-1-decene, 1H,1H,2H-perfluoro-1-octene and 1H,1H,2H-perfluoro-1-dodecene. During the ultrasonic acidification process, the inorganic acid required for 1g of the activated product is 30-50mL; during the coating process in an oil bath, the modifier required for 1g of the acidified product is 10-30mL, the reaction temperature is 160-190℃, and the reaction time is 8-15h.

2. The method for preparing the modified graphite anode material according to claim 1, characterized in that, The weight ratio of the graphite anode material to the inorganic alkali is 1:(2-4), the reaction temperature is 600-900℃, and the reaction time is 3-8h.

3. The method for preparing the modified graphite anode material according to claim 2, characterized in that, The inorganic base is a hydroxide.

4. The method for preparing the modified graphite anode material according to claim 3, characterized in that, The inorganic base is KOH and / or NaOH.

5. The method for preparing the modified graphite anode material according to claim 1, characterized in that, The D50 of the graphite anode material is 5–30 μm.

6. The method for preparing the modified graphite anode material according to claim 1, characterized in that, In the mixture of concentrated nitric acid and concentrated sulfuric acid, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1: (2-4).

7. The method for preparing the modified graphite anode material according to claim 1, characterized in that, During the ultrasonic acidification process, the ultrasonic frequency is 40–60 kHz, the temperature is 40–60 °C, and the ultrasonic time is 20–60 min.

8. A modified graphite anode material, characterized in that, The modified graphite anode material is prepared by any one of claims 1 to 7.

9. A negative electrode, comprising a current collector and a negative electrode material disposed on the current collector, characterized in that, The negative electrode material includes the modified graphite negative electrode material as described in claim 8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is the negative electrode as described in claim 9.

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