High-capacity graphite and preparation method thereof, and lithium ion battery negative electrode material

Abstract

The application discloses high-capacity graphite and a preparation method and a lithium ion battery negative electrode material thereof, and the preparation method comprises the following steps: activating a graphite raw material by using a strong oxidant; mixing a lithium salt, the activated graphite raw material and a solvent to obtain a suspension slurry; performing spray drying on the suspension slurry to obtain powder particles; and coating the powder particles with a carbon source, performing isostatic pressing treatment, carbonization and crushing to obtain pre-lithiated high-capacity graphite. The graphite negative electrode material obtained by the treatment method has excellent reversible lithium storage capacity, and a certain expansion space is reserved in the graphite, the lithium ion diffusion channel is shortened, and the rate discharge performance and the cycle performance are improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrode materials, in particular to high-capacity graphite and a preparation method thereof and a lithium ion battery negative electrode material. BACKGROUND

[0002] As a new type of rechargeable battery, the lithium battery has the advantages of light weight, large energy storage, high power, no pollution, long service life, small automatic discharge coefficient and the like, and is widely applied to the fields of energy storage, electric vehicles, portable devices and the like.

[0003] With the increasing requirement of the market for the energy density of the lithium ion battery, the requirement for the electrode material of the lithium ion battery is also continuously improved, and the negative electrode material is a key material for forming the lithium ion battery. The natural graphite has the advantages of high graphitization degree, low cost and high capacity, and the original cycle performance thereof can be improved through spheroidization, purification and modification, and at present, the natural graphite is largely applied to conventional lithium ion batteries.

[0004] Due to the slow diffusion speed of lithium ions in the natural graphite, the slow lithium ion diffusion and the very close operation potential window to the lithium ion deposition voltage, the lithium ions released by the positive electrode are gradually lost in the charging and discharging process, causing the consumption of the total amount of lithium in the battery, and further affecting the coulomb efficiency, cycle life and safety performance of the battery. At the same time, due to the growth of metal lithium dendrites, the rate discharge performance, safety performance and cycle performance of the graphite gradually cannot meet the demand of the power lithium ion battery, which may cause disastrous battery failure risk, and limits the application of the graphite material in the field of power lithium ion batteries.

[0005] At present, a mechanical grinding method such as ball milling is commonly used to enlarge the interlayer spacing of the graphite, to provide the diffusion speed of lithium ions in the natural graphite, and to further improve the rate discharge performance. However, the method will cause uneven particle size, too low active material density, or lead to the rupture of the coating layer caused by the expansion of the lithium intercalation of the graphite. Moreover, even if the rate discharge performance and cycle performance are improved, the reversible lithium storage capacity is still insufficient.

[0006] Although there are methods for supplementing lithium of the negative electrode material of the lithium ion battery, due to the instability of metal lithium, potential safety hazards in the production process and large-scale storage and transportation. In addition, the metal lithium will react with the conventional electrolyte and the binder, which makes it necessary to develop new types of solvents, electrolytes, binders and the like in the actual application process of the metal lithium related negative electrode lithium supplementing process, in addition to the environmental control modification of the production line, the raw material cost is high, the process is complex, and the prelithiation effect after the contact reaction of the negative electrode sheet cannot be guaranteed.

[0007] In summary, it is still the focus of the current research to prepare a graphite material with excellent rate performance and cycle performance, and high reversible lithium storage capacity. At the same time, there is a lack of simple, efficient and maturely operable method for supplementing lithium of the negative electrode. SUMMARY

[0008] In order to solve the above problems existing in the art, the present application aims to provide a high-capacity graphite and a preparation method thereof, and a negative electrode material of a lithium ion battery. The graphite is activated by a chemical method to increase active sites, so that it has excellent reversible lithium storage capacity and significantly improves the rate discharge performance and cycle performance.

[0009] According to an aspect of the present application, a preparation method of high-capacity graphite is provided, comprising:

[0010] activating a graphite raw material with a strong oxidizing agent;

[0011] mixing a lithium salt, the activated graphite raw material, and a solvent to obtain a suspension slurry;

[0012] drying the suspension slurry to obtain a powder particle;

[0013] coating the powder particle with a carbon source, and then performing isostatic pressing, carbonization, and crushing to obtain high-capacity graphite;

[0014] The lithium salt is selected from lithium hydroxide or lithium oxide.

[0015] The mass ratio of the graphite raw material to the lithium salt is 1:(0.002-0.02).

[0016] The activation time is 2-6h.

[0017] According to some embodiments of the present application, the strong oxidizing agent is selected from nitric acid and / or hydrogen peroxide.

[0018] Optionally, the strong oxidizing agent is hydrogen peroxide.

[0019] Further, the mass concentration of the hydrogen peroxide is 20-35%, preferably 30%.

[0020] Preferably, the mass ratio of the strong oxidizing agent to the graphite raw material is 1:(4-20), preferably 3:(20-30)%.

[0021] According to some embodiments of the present application, the lithium salt is lithium hydroxide.

[0022] Optionally, the mass ratio of the graphite raw material to the lithium salt is 1:(0.01-0.014).

[0023] According to some embodiments of the present application, the solvent is a hydrophilic solvent.

[0024] The hydrophilic solvent is selected from one or more of water, dimethylacetamide, acetone, ethanol, and ethyl acetate.

[0025] Preferably, the mass ratio of the solvent to the graphite raw material is (1-10):1;

[0026] More preferably, the mass ratio of the solvent to the graphite raw material is (2-5):1.

[0027] According to some embodiments of the present application, the drying method comprises spray drying.

[0028] Preferably, the feed temperature of the spray drying is 100-400°C, preferably 120-250°C.

[0029] The discharge temperature of the spray drying is 20-300°C, preferably 80-300°C.

[0030] Preferably, the pressure of the spray drying is 5-150MPa, preferably 10-100MPa.

[0031] More preferably, the frequency of the spray drying is 10-400Hz, preferably 200-350Hz.

[0032] The feed frequency of the spray drying is 2-200Hz, preferably 10-100Hz.

[0033] According to some embodiments of the present application, the carbon source is selected from one or more of low temperature pitch, medium temperature pitch and high temperature pitch; preferably high temperature pitch.

[0034] Preferably, the addition amount of the carbon source is 4.0-6.0% of the mass of the powdered particles, preferably 5.5%.

[0035] According to some embodiments of the present application, the isostatic pressure is 70-90MPa, preferably 85MPa.

[0036] The isostatic time is 50-80s, preferably 60s.

[0037] According to some embodiments of the present application, the carbonization is performed in the presence of a protective gas.

[0038] Preferably, the protective gas is selected from one or more of nitrogen, helium and argon.

[0039] Preferably, the carbonization temperature is 1000-1200°C, preferably 1100-1150°C.

[0040] Preferably, the carbonization time is 3-8h, preferably 6h.

[0041] According to some embodiments of the present application, the graphite raw material is selected from natural spheroidal graphite or artificial spheroidal graphite.

[0042] Preferably, the spherical graphite has a carbon content of ≥95%;

[0043] More preferably, the spherical graphite is natural graphite with a carbon content of ≥95%.

[0044] According to some embodiments of the present application, the method further comprises a purification treatment before the activation treatment step.

[0045] Preferably, the purification treatment comprises at least two treatments of the graphite raw material with a mixed acid.

[0046] Preferably, the mixed acid is selected from a combination of two or more of hydrofluoric acid, hydrochloric acid and nitric acid.

[0047] Preferably, the at least two treatments use different types of mixed acid.

[0048] More preferably, the concentrations of the hydrofluoric acid, the hydrochloric acid and the nitric acid in the mixed acid are 6%-10%, 10%-15% and 6%-14% respectively.

[0049] According to another aspect of the present application, there is provided a high-capacity graphite having a lithium content of 0.2%-1.4% and an interlayer spacing of 0.001 nm-0.004 nm, and having active sites and oxygen-containing functional groups in the interlayer.

[0050] According to yet another aspect of the present application, there is also provided a lithium-ion battery anode material comprising the high-capacity graphite prepared by the method described above, or the high-capacity graphite described above.

[0051] Compared with the prior art, the present application has at least the following beneficial effects:

[0052] The present application provides a method for preparing a high-capacity graphite, which uses graphite as a raw material, increases the active sites of the graphite raw material by treatment with a strong oxidizing agent, generates oxygen-containing functional groups, enhances the ability to bind free ions, stably binds with lithium ions and is not easily detached, achieves the purpose of embedding lithium, and at the same time, the use of a strong oxidizing agent to treat graphite can increase the interlayer spacing of the graphite raw material, widen the lithium ion diffusion channel, and improve the rate discharge performance and cycle performance.

[0053] In the preparation method of the present application, the activation time is 2-6 h, which can avoid the collapse of the layers due to excessive interlayer spacing, and damage the particle size and layer structure of the graphite itself.

[0054] Unlike the current lithium supplement technology which is complex to operate and has poor stability, the preparation method of the high-capacity graphite of the present application, in addition to the strong oxidative activation treatment, also uses lithium hydroxide as a lithium source and converts it into lithium oxide through a carbonization process. This method is simple to operate, and at the same time, the active sites treated by the strong oxidizing agent are more stable in combination with lithium ions and are not easily detached.

[0055] The lithium ions and the graphite in the application are combined through active sites, and the lithium hydroxide can be stably present on the surface of the natural graphite by using a spray drying method for drying and supplementing lithium afterwards. In the first charge and discharge process, a stable SEI film can be formed, the use of the lithium source of the positive electrode is reduced, and the initial efficiency and capacity are obviously improved.

[0056] The use of a certain amount of pitch for coating in the application can effectively reduce the defects on the surface of the natural graphite, and also can reduce the overall specific surface area of the material and improve the initial coulombic efficiency. After supplementing lithium, the isostatic pressing treatment can increase the bulk density of the negative electrode material, thereby improving the bulk energy density of the battery material. At the same time, the isostatic pressing treatment can press the lithium on the surface of the material into the pores, thereby increasing the uniformity of the lithium.

[0057] The application uniformly coats a carbon coating layer on the surface of the natural graphite through pitch mixing, isostatic compaction treatment and high-temperature carbonization, thereby reducing the specific surface area, improving the compatibility with the electrolyte and improving the electrochemical performance of the material.

[0058] The high-capacity graphite material prepared by the method of the application has a lithium content of 0.2%-1.4%, a reversible discharge specific capacity of 375-395 mAh / g, an initial coulombic efficiency of >94%, a specific surface area of 2.0-2.5 m 2 / g, a compacted density of >1.8 g / cm 3 , and a tap density of 0.90-1.16 g / cm 3 . BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 The scanning electron microscope image of the graphite negative electrode material prepared in Example 1 of the application is shown.

[0060] Figure 2 The cross-sectional scanning electron microscope image of the graphite negative electrode material prepared in Example 1 of the application is shown.

[0061] Figure 3 The charge and discharge curve of the graphite negative electrode material prepared in Example 1 of the application is shown. DETAILED DESCRIPTION

[0062] The technical solutions of the application will be described clearly and completely in combination with the embodiments of the application. Obviously, the described embodiments are some of the embodiments of the application, but not all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of the application.

[0063] It is particularly noted that similar substitutions and alterations to those described herein will occur to those skilled in the art and are contemplated as falling within the scope of the present application. It is also noted that the methods and applications described herein integrate and apply the teachings of the present application, and that alterations to methods and applications not described specifically herein are possible and are contemplated as falling within the scope of the present application. Obviously, the embodiments described herein are only some, not all, embodiments of the present application.

[0064] Unless otherwise specified, the present application is carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials or excipients used, and the reagents or instruments used, are not specified by the manufacturer, but are conventional products that can be obtained commercially.

[0065] The present application is described in detail below.

[0066] The working principle of lithium ion battery is that: in the first charge and discharge process, the electrode material and electrolyte react on the solid-liquid phase interface to form a passivation layer covering the surface of the electrode material. This passivation layer is an interface layer with the characteristics of solid electrolyte. The passivation layer is an electronic insulator, but also a good conductor of lithium ions, and lithium ions can freely enter and exit through the passivation layer, so this layer of passivation film is called "solid electrolyte interface film", abbreviated as SEI film. When the lithium battery starts to charge and discharge, lithium ions are released from the positive active material into the electrolyte, penetrate the separator into the electrolyte, and finally embed into the layered interstitial space of the negative carbon material. At this time, the lithium ion completes a complete de-intercalation behavior.

[0067] Natural graphite has the advantages of high graphitization degree, low cost and high capacity, and is often used as a negative material for lithium batteries. However, due to the slow diffusion speed of lithium ions in natural graphite, slow lithium ion diffusion and very close to the operating potential window of lithium ion deposition voltage, the lithium ions released by the positive electrode are gradually lost during the charge and discharge process, affecting the coulombic efficiency, cycle life and safety performance of the battery. In addition, the growth of metal lithium dendrites makes the rate discharge performance, safety performance and cycle performance of graphite unable to meet the demand of power lithium ion batteries, limiting the application of graphite materials in the field of power lithium ion batteries.

[0068] The method for improving the rate discharge performance mainly expands the interlayer spacing of the graphite material, improves the diffusion speed of lithium ions in the interlayer, and improves the rate discharge performance. However, this method is easy to cause the rupture of the coating layer due to the expansion of the graphite lithium intercalation. The second method is to increase the active sites in the graphite and introduce oxygen-containing functional groups, and then embed lithium ions, so as to reduce the loss of lithium ions in the positive electrode in the charging and discharging process. As can be seen from the above, in the case of expanding the interlayer spacing, increasing the oxygen-containing functional groups on the surface of the graphite is the best way to obtain a graphite negative electrode material with good rate discharge performance, high active material filling density and high battery capacity. At present, the commonly used method for expanding the interlayer spacing is mechanical grinding such as ball milling, but it will cause uneven particle size and low active material density.

[0069] There are many solutions to the above problems, but there are still many shortcomings. For example:

[0070] Shaobin Yang et al. proposed using graphite intercalation compound (GIC) preparation technology to treat natural graphite, coat a layer of soft carbon precursor on the surface of the graphite intercalation compound, and heat treat in an inert atmosphere. The obtained sample not only keeps the expanded state of the interlayer spacing, but also reserves expansion space in the natural graphite. A graphite modification method for expanding the interlayer spacing of the graphite while keeping the particle size of the natural graphite and the diameter of the carbon six-edge plane unchanged is successfully found.

[0071] However, through the analysis of the surface of the modified graphite, it is found that a large number of oxygen-containing functional groups on the surface of the graphite intercalation compound hinder the recovery of the interlayer spacing and the reserved space in the process of coating the soft carbon precursor on the graphite intercalation compound. Although the rate discharge performance and cycle performance of the lithium ion battery negative electrode material prepared from this material are improved, the reversible lithium storage capacity changes little.

[0072] Therefore, the problem of how to prepare a graphite material with excellent rate performance and cycle performance and high reversible lithium storage capacity still exists.

[0073] There are documents that propose a lithium supplement method for lithium ion battery negative electrode materials. The common way is to directly supplement lithium to the negative electrode, such as lithium foil supplement, lithium powder supplement, etc., which are the currently developed pre-lithiation process.

[0074] The main technical routes of negative electrode prelithiation include: lithium supplement by mixing (lithium powder, lithium silicide powder, etc.), lithium supplement by contact (lithium foil, etc.), electrochemical lithium supplement and chemical lithium supplement. However, the main problem affecting the progress of lithium supplement by contact and mixing is the instability of metallic lithium, potential safety hazards in the production process and large-scale storage and transportation. In addition, the reaction between metallic lithium and conventional electrolyte and binder will occur, so that in the practical application process of the lithium supplement process related to metallic lithium, in addition to the environmental control modification of the production line, new solvents, electrolytes, binders and other materials need to be developed, resulting in a too complex process.

[0075] There is also a document disclosing a chemical prelithiation method of a graphite electrode of a lithium ion battery, in which a lithiation reagent containing an anion radical is dissolved in a monovalent ether to obtain a lithiation reagent solution with a concentration of 0.001-10 mol / L, and then the prepared graphite negative electrode sheet of the lithium ion battery is contacted with the lithiation reagent solution for 1 s-48 h, and after washing and drying, a prelithiated graphite electrode is obtained. However, this method uses naphthalene lithium, methyl naphthalene lithium, etc. as the lithiation reagent, methyl propyl ether, methyl butyl ether, etc. as the washing solvent, which has high raw material cost and complex process, and the prelithiation effect of the negative electrode sheet after contact reaction cannot be guaranteed.

[0076] In summary, there is a lack of simple, efficient, mature and operable method for negative electrode lithium supplement.

[0077] The present application provides a high-capacity graphite and a preparation method thereof. The graphite negative electrode material obtained by the treatment method has excellent reversible lithium storage capacity. Compared with lithium ion batteries prepared from ordinary graphite, the loss of part of the positive electrode lithium ions is reduced during the charging and discharging process, the reversible lithium storage capacity of the graphite is significantly improved, a certain expansion space is reserved inside the graphite, the lithium ion diffusion channel is shortened, the rate discharge performance and the cycle performance are greatly improved, and the graphite can be more widely applied in the field of lithium ion batteries.

[0078] The technical scheme of the present application is as follows:

[0079] A preparation method of a high-capacity graphite material, comprising the following steps:

[0080] (1) purifying ordinary graphite or spherical graphite to obtain high-purity spherical graphite with a carbon content of ≥99.95%;

[0081] Optionally, if ordinary graphite is used as the raw material, the ordinary graphite is treated into spherical graphite before or after the activation treatment; the long stone type, mica type and other impurities are removed by reacting with hydrofluoric acid, hydrochloric acid and nitric acid, and then the remaining metal impurities are removed by using hydrochloric acid and nitric acid to obtain high-purity spherical graphite.

[0082] (2) using a strong oxidizing agent to perform a layer treatment on the high-purity spherical graphite obtained in step (1), to obtain activated high-purity spherical graphite;

[0083] The present application increases active sites on the surface of graphite by treating the layer structure with a strong oxidizing agent, enhances the ability of the graphite to bind free ions, generates oxygen-containing functional groups, and also increases the interlayer spacing, widens the lithium ion diffusion channel, and improves the rate discharge performance and cycle performance.

[0084] (3) adding a certain proportion of lithium salt and solvent to the activated high-purity spherical graphite, and stirring to obtain a suspension slurry;

[0085] During the treatment with the lithium source, lithium ions reach the active sites to achieve the purpose of lithium intercalation.

[0086] (4) performing spray drying on the suspension slurry, dispersing the suspension into mist droplets through an atomizer, and removing the solvent by contacting the mist droplets with hot air to obtain powder particles, or performing drying by other methods and then granulating;

[0087] (5) mixing the powder particles with a carbon source, performing isostatic pressing treatment using an isostatic pressing mold, carbonizing, and crushing to obtain a high-capacity spherical graphite material.

[0088] After the lithium intercalation is completed, the lithium ions are tightly combined with the graphite through chemical bonds and are not easily detached during subsequent drying, isostatic pressing treatment, carbonization, crushing, and other steps.

[0089] In step (1), the spherical graphite has a carbon content of ≥95%; alternatively, the spherical graphite is natural spherical graphite with a carbon content of ≥95%.

[0090] The purification treatment is at least two treatments using a mixed acid selected from a combination of two or more of hydrofluoric acid, hydrochloric acid, and nitric acid.

[0091] Further, when any combination of the above-mentioned mixed acid is used, the concentration of the hydrofluoric acid is 6%-10%, the concentration of the hydrochloric acid is 10%-15%, and the concentration of the nitric acid is 6%-14%.

[0092] In step (2), the strong oxidizing agent is selected from one or more of nitric acid or hydrogen peroxide; the strong oxidizing agent is used to increase the interlayer spacing of the graphite and increase active sites, i.e., oxygen-containing functional groups, on the graphite layers;

[0093] Further, the strong oxidizing agent is hydrogen peroxide; the interlayer spacing of the graphite treated with hydrogen peroxide is superior to that of the graphite treated with nitric acid.

[0094] The concentration of the hydrogen peroxide is 20-35%, and preferably the concentration of the hydrogen peroxide is 30%.

[0095] The mass ratio of the strong oxidant to the graphite is 5%-25%, preferably 10-15%.

[0096] Optionally, the oxidation treatment time is 2-6h, preferably 4-5h.

[0097] Optionally, the lithium salt in step (3) is selected from one or more of lithium oxide or hydroxide;

[0098] Optionally, the lithium salt is lithium hydroxide or lithium oxide;

[0099] Further, the lithium salt is lithium hydroxide.

[0100] Optionally, the mass ratio of the spherical graphite to the lithium salt is 1:(0.002-0.02), further preferably 1:(0.01-0.014).

[0101] Optionally, the solvent is a hydrophilic solvent selected from one or more of water, dimethylacetamide, acetone, ethanol, ethyl acetate.

[0102] Optionally, the solvent is used in an amount of (1-10):1, further (2-5):1, of the mass ratio of the solvent to the spherical graphite.

[0103] Optionally, the spray drying in step (4) is performed using a spray dryer, and the inlet temperature of the spray dryer is 100-400℃, further preferably 120-250℃.

[0104] The outlet temperature of the spray dryer is 20-300℃, further preferably 80-300℃.

[0105] The pressure of the spray dryer is 5-150MPa, further preferably 10-100MPa.

[0106] The operating frequency of the spray dryer is 10-400Hz, further preferably 200-350Hz.

[0107] The feeding frequency of the spray dryer is 2-200Hz, further preferably 10-100Hz.

[0108] Preferably, the carbon source in step (5) is selected from one or more of low-temperature pitch, medium-temperature pitch, and high-temperature pitch; further preferably high-temperature pitch.

[0109] Preferably, the carbon source is added in a proportion of 4.0-6.0%, preferably 5.5%.

[0110] Preferably, the isostatic pressing pressure is 70-90MPa, preferably 85MPa.

[0111] The isostatic pressing time is 50-80s, more preferably 60s.

[0112] Preferably, the carbonization is further carried out in the presence of a protective gas selected from one or more of nitrogen, helium or argon.

[0113] The carbonization temperature is 1000-1200°C, preferably 1100-1150°C.

[0114] The carbonization time is 3-8h, more preferably 6h.

[0115] Example 1

[0116] Preparation of high-capacity spherical graphite material of the present application

[0117] 1. Purification treatment: take natural spherical graphite with a carbon content of 95%, add a mixed acid of 6% hydrofluoric acid, 11% hydrochloric acid and 6% nitric acid to react; then carry out at least two reactions with a mixed acid of 10% hydrochloric acid and 14% nitric acid to obtain high-purity natural spherical graphite with a carbon content of ≥99.95%;

[0118] 2. Activation treatment: use 38% hydrogen peroxide to treat the high-purity natural spherical graphite obtained by purification treatment for 4h;

[0119] 3. Add lithium source: take 1kg of graphite sample obtained by activation treatment, add lithium hydroxide at a proportion of 1.2%, i.e. 12g of lithium hydroxide, and then add 2kg of water to prepare a slurry;

[0120] 4. Spray drying: deliver the slurry into a spray drying granulator to carry out pre-lithiation drying, so that the lithium hydroxide is embedded on the surface and inside of the graphite, to obtain pre-lithiated natural spherical graphite; wherein the inlet temperature is 250°C, the outlet temperature is 110°C, the frequency of the atomizer is 350Hz, the pressure is 80MPa, and the feeding frequency is 100Hz;

[0121] 5. Isostatic pressing treatment: mix and coat the pre-lithiated natural spherical graphite with high-temperature pitch at a mass ratio of 5.5%, and use an isostatic pressing mold to carry out isostatic pressing treatment to make it densified; wherein the isostatic pressing pressure is 85MPa, and the pressure holding time is 60s. After isostatic pressing treatment, the blocky material is carbonized at 1150°C for 6h under the protection of a nitrogen atmosphere with a flow rate of 1.5L / min, and after crushing treatment, pre-lithiated high-capacity natural spherical graphite negative electrode material is obtained. Figure 1 、 2 , 3 are scanning electron microscope images, cross-sectional scanning electron microscope images and charge-discharge curves of the graphite negative electrode material, respectively.

[0122] Example 2

[0123] The preparation process is basically the same as that in Example 1, except that:

[0124] 1. A mixed acid of hydrofluoric acid with a concentration of 8%, hydrochloric acid with a concentration of 15%, and nitric acid with a concentration of 6% is added, and then a mixed acid of hydrochloric acid with a concentration of 11% and nitric acid with a concentration of 8% is reacted at least twice;

[0125] 2. 20% hydrogen peroxide treatment for 5h;

[0126] 3. Lithium hydroxide is added at a proportion of 0.2%, i.e. 2g of lithium hydroxide and 5kg of water are added;

[0127] 4. Inlet temperature: 120°C, outlet temperature: 200°C, frequency of the atomizer: 200Hz, pressure: 140MPa, and feeding frequency: 30Hz;

[0128] 5. High-temperature pitch with a concentration of 4% is used, isostatic pressing pressure: 70MPa, holding time: 80s, and carbonization temperature: 1000°C for 7h.

[0129] Example 3

[0130] The preparation process is basically the same as that in Example 1, except that:

[0131] 1. A mixed acid of hydrofluoric acid with a concentration of 10%, hydrochloric acid with a concentration of 10%, and nitric acid with a concentration of 14% is added, and then a mixed acid of hydrochloric acid with a concentration of 15% and nitric acid with a concentration of 6% is reacted at least twice;

[0132] 2. 35% hydrogen peroxide treatment for 3h;

[0133] 3. Lithium hydroxide is added at a proportion of 0.4%, i.e. 4g of lithium hydroxide and 4kg of ethyl acetate are added;

[0134] 4. Inlet temperature: 200°C, outlet temperature: 100°C, frequency of the atomizer: 100Hz, pressure: 30MPa, and feeding frequency: 150Hz;

[0135] 5. High-temperature pitch with a concentration of 4% is used, isostatic pressing pressure: 70MPa, holding time: 80s, and carbonization temperature: 1000°C for 7h.

[0136] Example 4

[0137] The preparation process is basically the same as that in Example 1, except that:

[0138] 1. A mixed acid of hydrofluoric acid with a concentration of 6%, hydrochloric acid with a concentration of 10%, and nitric acid with a concentration of 6% is added, and then a mixed acid of hydrochloric acid with a concentration of 10% and nitric acid with a concentration of 6% is reacted at least twice;

[0139] 2. 20% hydrogen peroxide treatment for 2h;

[0140] 3. Lithium hydroxide was added in a proportion of 0.6%, i.e. 6 g of lithium hydroxide, and 1 kg of ethyl acetate was added;

[0141] 4. Inlet temperature 100°C, outlet temperature 20°C, frequency of operation of the atomizer 10 Hz, pressure 5 MPa, frequency of feeding 2 Hz;

[0142] 5. High temperature pitch 5%; isostatic pressure 90 MPa, pressure holding time 50 s; carbonization at 1000°C for 8 h.

[0143] Example 5

[0144] The preparation process is basically the same as in Example 1, except that:

[0145] 1. A mixed acid of hydrofluoric acid with a concentration of 10%, hydrochloric acid 15% and nitric acid 14% was added, and then a mixed acid of hydrochloric acid 10% and nitric acid 6% was reacted at least twice;

[0146] 2. 30% hydrogen peroxide treatment for 6 h;

[0147] 3. Lithium hydroxide was added in a proportion of 0.8%, i.e. 8 g of lithium hydroxide, and 5 kg of ethyl acetate was added;

[0148] 4. Inlet temperature 400°C, outlet temperature 300°C, frequency of operation of the atomizer 400 Hz, pressure 150 MPa, frequency of feeding 200 Hz;

[0149] 5. High temperature pitch 6%; isostatic pressure 75 MPa, pressure holding time 80 s; carbonization at 1200°C for 8 h.

[0150] Example 6

[0151] The preparation process is basically the same as in Example 1, except that in step (2) nitric acid was used as the strong oxidizing agent.

[0152] Example 7

[0153] The preparation process is basically the same as in Example 1, except that in step (3) lithium oxide was used as the lithium salt.

[0154] Example 8

[0155] The preparation process is basically the same as in Example 1, except that in step (5) a medium temperature pitch was used.

[0156] Comparative Example 1 Adjustment of the amount of lithium hydroxide

[0157] The preparation process is basically the same as in Example 1, except that in step (3) lithium hydroxide was added in a proportion of 2%, i.e. 20 g of lithium hydroxide.

[0158] Comparative Example 2 is not activated

[0159] 1. Purification treatment: Take natural spherical graphite with carbon content of 95%, add a mixture of hydrofluoric acid, hydrochloric acid and nitric acid to it for reaction, the concentration of hydrofluoric acid is 7%, the concentration of hydrochloric acid is 10%, and the concentration of nitric acid is 10%. The product obtained in step 1 is reacted with hydrochloric acid and nitric acid for at least twice, the concentration of hydrochloric acid is 10%, and the concentration of nitric acid is 10%, to obtain high-purity natural spherical graphite with carbon content ≥ 99.95%.

[0160] 2. Add lithium source: Take 1 kg of natural spherical graphite sample obtained by activation treatment, add lithium oxide at a ratio of 1.2%, i.e. 12 g of lithium oxide, and then add 1.5 kg of water to mix uniformly.

[0161] 3. Spray drying: The above uniformly mixed slurry is fed into a spray drying granulator for pre-lithiation drying, the inlet temperature is 250°C, and the outlet temperature is 110°C. The slurry is dispersed into mist droplets by an atomizer, the mist droplets contact with hot dry air to remove moisture and become powder particles, i.e. a mixture of activated natural spherical graphite and lithium hydroxide is obtained, wherein the atomizer operates at a frequency of 350 Hz.

[0162] 4. Isostatic pressing treatment: The above treated mixture is further mixed with high-temperature pitch at a mass ratio of 5.5% for coating. Then isostatic pressing mold is used for isostatic pressing treatment to make it densified. The isostatic pressing pressure is 85 MPa, and the pressure holding time is 60 s. The block material after isostatic pressing treatment is carbonized at 1150°C for 6 h under the protection of nitrogen atmosphere with a flow rate of 1.5 L / min, and finally after crushing treatment, high-capacity natural spherical graphite negative electrode material can be obtained.

[0163] Comparative Example 3 uses lithium carbonate as lithium source

[0164] The preparation process is basically the same as in Example 1, except that in step (3), lithium carbonate is added at a ratio of 1.2%, i.e. 12 g of lithium carbonate.

[0165] Comparative Example 4 does not perform isostatic pressing treatment

[0166] 1. Purification treatment: Take natural spherical graphite with carbon content of 95%, add a mixture of hydrofluoric acid, hydrochloric acid and nitric acid to it for reaction, the concentration of hydrofluoric acid is 7%, the concentration of hydrochloric acid is 10%, and the concentration of nitric acid is 10%. The product obtained in step 1 is reacted with hydrochloric acid and nitric acid for at least twice, the concentration of hydrochloric acid is 10%, and the concentration of nitric acid is 10%, to obtain high-purity natural spherical graphite with carbon content ≥ 99.95%.

[0167] 2. Activation treatment: The high-purity natural spherical graphite with carbon content ≥ 99.95% obtained by activation treatment is treated with 38% hydrogen peroxide.

[0168] 3. Adding lithium source: Take 1 kg of the natural spherical graphite sample obtained after activation treatment, add lithium hydroxide at a proportion of 1.2%, i.e. 12 g of lithium hydroxide, and then add 1.5 kg of water to mix uniformly and stand by.

[0169] 4. Spray drying: The above mixed slurry is delivered into a spray drying granulator for pre-lithiation drying, with an inlet temperature of 250°C and an outlet temperature of 110°C. The slurry is dispersed into mist droplets by an atomizer, the mist droplets are contacted with hot drying air to remove moisture, and become powder particles, i.e. a mixture of activated natural spherical graphite and lithium hydroxide is obtained, wherein the atomizer operates at a frequency of 350 Hz.

[0170] 5. Carbonization and crushing: The above mixture is mixed and coated with high-temperature pitch at a mass ratio of 5.5%. Under the protection of a nitrogen atmosphere with a flow rate of 1.5 L / min, carbonization is carried out at 1150°C for 6 h, and finally after crushing treatment, high-capacity natural spherical graphite negative electrode material is obtained.

[0171] Comparative Example 5: Comparative example with excessively long activation time

[0172] The preparation process is basically the same as in Example 1, except that the activation treatment time in step (2) is 10 h.

[0173] Comparative Example 6: Ball milling intercalation treatment

[0174] The preparation process is basically the same as in Example 1, except that the activation treatment in step (2) is replaced by ball mill treatment for 4 h.

[0175] Comparative Example 7: Ultrasonic pre-lithium treatment

[0176] 1. Purification treatment: Take natural spherical graphite with a carbon content of 95%, and add a mixed acid of 6% hydrofluoric acid, 11% hydrochloric acid, and 6% nitric acid for reaction; then perform at least two reactions with a mixed acid of 10% hydrochloric acid and 14% nitric acid to obtain high-purity natural spherical graphite with a carbon content of ≥99.95%;

[0177] 2. Ultrasonic lithium addition: Take 1 kg of high-purity natural spherical graphite obtained by purification treatment, and add lithium hydroxide at a proportion of 1.2%, i.e. 12 g of lithium hydroxide, then add 40 kg of tetrahydrofuran and 40 kg of water to obtain a mixed solution, stir while using ultrasonic treatment for 1 h, and then perform suction filtration and drying to obtain dry pre-lithiated natural spherical graphite;

[0178] 3. Isostatic pressing treatment: the pre-lithiated natural spherical graphite is mixed and coated with high-temperature pitch with a mass ratio of 5.5%, and isostatic pressing treatment is performed using an isostatic pressing mold to densify it; wherein the isostatic pressing pressure is 85 MPa, and the pressure holding time is 60 s. The blocky material after isostatic pressing treatment is carbonized at 1150°C for 6 h under the protection of nitrogen atmosphere with a flow rate of 1.5 L / min, and is broken to obtain the pre-lithiated high-capacity natural spherical graphite negative electrode material.

[0179] Application Example

[0180] The d002 interlayer spacing of the graphite lithium salt mixture obtained in Examples 1-8 and Comparative Examples 1-7 before isostatic pressing treatment is detected, and the final spherical graphite negative electrode material is detected for lithium content, specific surface area, and tap density, and then lithium ion batteries are prepared according to the following methods for discharge testing.

[0181] The preparation method of the button-type lithium ion battery comprises the following steps:

[0182] I: The spherical graphite negative electrode material, polyvinylidene fluoride (PVDF), and conductive agent acetylene black are uniformly mixed and prepared into a slurry in deionized water at a mass ratio of spherical graphite negative electrode material: PVDF: conductive agent acetylene black = 98: 1: 1, and the slurry is uniformly dispersed to obtain a stirred slurry.

[0183] II: The copper foil is pressed into a round sheet with a diameter of 1.6 cm, and then dried at 80°C under vacuum conditions, weighed, and recorded as weight m1, which is used as the copper foil current collector.

[0184] III: The stirred slurry is uniformly coated on the copper foil current collector, and after vacuum drying at 80°C for 12 h, the negative electrode sheet is rolled to obtain a dried negative electrode sheet, which is weighed and recorded as weight m2. The weight m2 minus the weight m1 is the weight of the active material, which is recorded as weight m3.

[0185] IV: The dried negative electrode sheet is transferred to a glove box, lithium pieces are used as the counter electrode and auxiliary electrode, the electrolyte is 1M LiPF6 / EC:DEC (1:1; v / v), i.e. a mixed solvent of ethylene carbonate and diethyl carbonate with dissolved LiPF6, and the separator is Celgard 2400, and the button-type lithium ion battery is assembled in the glove box with an oxygen and water content of less than 1 ppm.

[0186] The assembled button-type lithium ion battery is left stationary for 12 h. The stationary button-type lithium ion battery is tested for electrochemical performance on a Wuhan Lan electric battery test system.

[0187] The current is 500 mA / g x weight 3 x 0.98 (the first circle current is 200 mA / g x weight 3 x 0.98), and the voltage range is 0.01-3.0 V. After 50 cycles, the capacity retention rate is 90% or more.

[0188] The physical properties of the spherical graphite negative electrode material for lithium ion batteries prepared in each of the above embodiments and the comparative product were tested, and the results are shown in Table 1:

[0189]

[0190] As shown in Table 1, the reversible discharge specific capacity and the first coulombic efficiency of the lithium ion batteries of Examples 1-9 of the present application are higher than those of the comparative example. This shows that, using graphite as the raw material, the present application can increase the active sites on the surface of the graphite by treating with a strong oxidizing agent, thereby enhancing the ability to combine with lithium ions and achieving the purpose of embedding lithium; secondly, the use of a strong oxidizing agent can increase the interlayer spacing of the graphite raw material, thereby shortening the lithium ion transmission path; thirdly, the subsequent drying and lithium supplementing by the spray drying method can ensure that lithium hydroxide is always present on the surface of the natural graphite, and a stable SEI film can be formed during the first charging and discharging process, thereby reducing the use of the positive electrode lithium source and significantly improving the first efficiency and capacity.

[0191] The above description of the embodiments is only used to help understand the method of the present application and its core idea. It should be noted that, for those skilled in the art, without departing from the principles of the present application, the present application can be improved and modified in several ways, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing high-capacity graphite, characterized in that: include: Activate the graphite raw material with a strong oxidant; Mixing lithium salt, activated graphite raw material and solvent to obtain suspension slurry; drying the suspension slurry to obtain powdered particles; The powdered particles are mixed and coated with a carbon source, and then isostatically pressed, carbonized, and crushed to obtain high-capacity graphite; Wherein, the lithium salt is selected from lithium hydroxide or lithium oxide; The mass ratio of the activated graphite raw material to the lithium salt is 1:(0.002-0.02); The activation treatment time is 2-6h; The mass ratio of the strong oxidant to the graphite raw material is 1:(4-20).

2. The preparation method according to claim 1, characterized in that The strong oxidant is selected from nitric acid and / or hydrogen peroxide.

3. The preparation method according to claim 2, characterized in that The strong oxidant is hydrogen peroxide.

4. The preparation method according to claim 3, characterized in that The mass concentration of the hydrogen peroxide is 20-35%.

5. The preparation method according to claim 4, characterized in that The mass concentration of the hydrogen peroxide is 30%.

6. The preparation method according to claim 1, characterized in that The mass ratio of the strong oxidant to the graphite raw material is 3:(20-30).

7. The preparation method according to claim 1, characterized in that The lithium salt is lithium hydroxide.

8. The preparation method according to claim 1, characterized in that The mass ratio of the activated graphite raw material to the lithium salt is 1:(0.01-0.014).

9. The preparation method according to claim 1, characterized in that The solvent is a hydrophilic solvent; The hydrophilic solvent is selected from one or more of water, dimethylacetamide, acetone and ethanol.

10. The preparation method according to claim 9, characterized in that The mass ratio of the solvent to the activated graphite raw material is (1-10):

1.

11. The preparation method according to claim 9, characterized in that The mass ratio of the solvent to the activated graphite raw material is (2-5):

1.

12. The preparation method according to claim 1, characterized in that The drying method includes: spray drying.

13. The preparation method according to claim 12, characterized in that The feed temperature of the spray drying is 100-400°C; the discharge temperature of the spray drying is 20-300°C.

14. The preparation method according to claim 12, characterized in that The feed temperature of the spray drying is 120-250°C; the discharge temperature of the spray drying is 80-300°C.

15. The preparation method according to claim 12, wherein The spray drying pressure is 5-150 MPa.

16. The preparation method according to claim 12, wherein The spray drying pressure is 10-100 MPa.

17. The preparation method according to claim 12, wherein The spray drying operation frequency is 10-400 Hz; the spray drying feeding frequency is 2-200 Hz.

18. The preparation method according to claim 12, wherein The spray drying operation frequency is 200-350 Hz; the spray drying feeding frequency is 10-100 Hz.

19. The preparation method according to claim 1, characterized in that The carbon source is selected from one or more of low-temperature asphalt, medium-temperature asphalt and high-temperature asphalt.

20. The preparation method according to claim 19, characterized in that The carbon source is high-temperature asphalt.

21. The preparation method according to claim 19, characterized in that The added amount of the carbon source is 4.0-6.0% of the mass of the powdered particles.

22. The preparation method according to claim 19, characterized in that The added amount of the carbon source is 5.5% of the mass of the powdered particles.

23. The preparation method according to claim 1, characterized in that The isostatic pressing pressure is 70-90 MPa; the isostatic pressing time is 50-80 s.

24. The preparation method according to claim 1, characterized in that The isostatic pressing pressure is 85 MPa; and the isostatic pressing time is 60 s.

25. The preparation method according to claim 1, characterized in that The carbonization is carried out in the presence of a protective gas.

26. The preparation method according to claim 25, characterized in that The protective gas is selected from one or more of nitrogen, helium and argon.

27. The preparation method according to claim 1, characterized in that The carbonization temperature is 1000-1200° C.; and the carbonization time is 3-8 hours.

28. The preparation method according to claim 1, characterized in that The carbonization temperature is 1100-1150° C.; and the carbonization time is 6 hours.

29. The preparation method according to claim 1, characterized in that The graphite raw material is selected from natural spherical graphite or artificial spherical graphite.

30. The preparation method according to claim 1, characterized in that The graphite raw material is spherical graphite with a carbon content of ≥95%.

31. The preparation method according to claim 1, characterized in that Before the activation treatment step, it also includes: purification treatment.

32. The preparation method according to claim 31, characterized in that The purification process includes: treating the graphite raw material at least twice using a mixed acid.

33. The preparation method according to claim 32, characterized in that The mixed acid is selected from a combination of two or more of hydrofluoric acid, hydrochloric acid and nitric acid.

34. The preparation method according to claim 32, characterized in that The mixed acids in the at least two treatments are of different types.

35. The preparation method according to claim 33, characterized in that In the mixed acid, the concentration of the hydrofluoric acid is 6%-10%, the concentration of the hydrochloric acid is 10%-15%, and the concentration of the nitric acid is 6%-14%.

36. A high-capacity graphite prepared by the preparation method according to any one of claims 1 to 35, characterized in that: The high-capacity graphite contains 0.2%-1.4% lithium, the distance between graphite layers is enlarged by 0.001nm-0.004nm, and the graphite layers contain active sites and oxygen-containing functional groups.

37. A negative electrode material for a lithium ion battery, characterized in that: The invention comprises high-capacity graphite prepared by the method according to any one of claims 1 to 34 or the high-capacity graphite according to claim 36.

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