CN111115623A - Preparation method of natural microcrystalline graphite negative electrode material, negative electrode material and application - Google Patents
Preparation method of natural microcrystalline graphite negative electrode material, negative electrode material and application Download PDFInfo
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- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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Abstract
The invention relates to a preparation method of a natural microcrystalline graphite negative electrode material, the negative electrode material and application, wherein the preparation method comprises the following steps: s1, crushing the microcrystalline graphite ore to obtain microcrystalline graphite secondary particles; s2, performing alkali treatment to obtain alkali-leached graphite; s3, carrying out strong oxidizing acid treatment to obtain acid-dipped graphite; s4, introducing a catalyst for high-temperature graphitization treatment to prepare a microcrystalline graphite negative electrode material; the catalyst is a co-catalyst composed of transition metal oxide and magnesium oxide, wherein: the transition metal oxide is a main catalyst, the magnesium oxide is an auxiliary catalyst, and the weight ratio of the main catalyst to the auxiliary catalyst is 3: 1. the invention also provides the microcrystalline graphite cathode material prepared by the preparation method, and application of the microcrystalline graphite cathode material and the cathode material in a lithium ion battery. The negative electrode material prepared by the method is formed by stacking primary particles with the particle size D50 of 1 mu m, has the graphitization degree of more than 90 percent, the carbon content of more than 99.9 percent, has larger interlayer spacing and high gram capacity, and can be used as a negative electrode material of a lithium ion battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a low-cost natural microcrystalline graphite negative electrode material.
Technical Field
China is a big country of graphite ores, natural graphite comprises crystalline flake graphite and microcrystalline graphite (or earthy graphite), and two existing graphite purification methods mainly comprise a flotation method, a hydrofluoric acid method and an acid-base method:
(1) the flotation method is a common purification method for graphite raw ores, and the common collecting agents are kerosene, heavy oil and the like, the foaming agents are terpineol oil, ether alcohol and the like, the regulators are lime and sodium carbonate, and the inhibitors are water glass and lime. The flotation method is suitable for primary purification, the quality of the flotation method can only reach a certain range, and partial impurities are difficult to remove, so the flotation method is only used as the first step of graphite purification and is difficult to reach the purity requirement of more than 98 percent, and a chemical purification method is generally adopted for further purification.
(2) The hydrofluoric acid method in the chemical purification method has simple process and low cost, and most of graphite purification in China still continues to use the process at present. However, with the expansion of the application range of the microcrystalline graphite, the consumption of hydrofluoric acid is increased sharply, the potential threat to the environment is great, especially in some areas with rare human smoke, the environmental protection standard and monitoring cannot be followed up, the unattended state occurs, the waste water is discharged and dumped in disorder, and the environmental management is critical.
(3) The acid-base method is also a relatively mature process method in chemical purification. The method comprises NaOH-HCl and NaOH-H2SO4、NaoH-HCl-HNO3Among them, the NaOH-HCl method is widely used. The principle of acid-base purification of graphite is that NaOH and graphite are mixed according to a certain proportion and calcined, silicon dioxide and other components in the graphite react with NaOH at high temperature (500-800 ℃) to generate soluble sodium silicate, and then the aim of desiliconization can be achieved by adopting water washing; and the other part of impurities, mainly metal oxides, still remain in the graphite, the metal oxides can be dissolved by treating the graphite after water washing with acid, and the separation from the graphite can be realized by filtering and water washing. The acid-base method has the disadvantages of high-temperature calcination, high energy consumption and serious corrosion to equipment.
In addition, after the microcrystalline graphite is purified, high-temperature graphitization is needed to be carried out to be used as a negative electrode material of the lithium battery, the existing graphitization catalyst is mainly a single oxide catalyst of nickel VIII group metal elements, the graphitization temperature is high (about more than 2800 ℃), the reaction time is long, the energy consumption is high, and the graphitization degree is low.
Based on the background, the preparation method of the natural microcrystalline graphite cathode material, which reduces energy consumption, environmental pollution and cost, needs to be developed.
In the prior art document, CN104495809A discloses a purification method of microcrystalline graphite, which is mainly used for purifying graphite by adding an oxidant and a complexing agent in the purification process, wherein the oxidant consists of sulfuric acid with the concentration of 92-93%, nitric acid with the concentration of 94-95%, hydrochloric acid with the concentration of 20-30% and hydrofluoric acid with the concentration of 42-50%, and the weight ratio of the materials is 31-40% of sulfuric acid, 2-4% of nitric acid, 33-35% of hydrochloric acid and 25-33% of hydrofluoric acid. It provides the idea of using a strong oxidizing acid as an oxidant to achieve purification of microcrystalline graphite, but it is not further graphitized for use as a lithium battery negative electrode material, nor is it disclosed to use a catalyst for graphitization.
CN109592677A discloses an interlayer spacing-enlarged microcrystalline graphite material, a preparation method thereof and application thereof in a sodium ion battery, wherein the interlayer spacing-enlarged microcrystalline graphite material is prepared by purifying microcrystalline graphite micro powder with an acid solution to obtain purified microcrystalline graphite; carrying out oxidation intercalation treatment on the purified microcrystalline graphite to obtain oxidized microcrystalline graphite; and reducing the oxidized microcrystalline graphite to obtain the interlayer spacing-enlarged microcrystalline graphite material. The oxidative intercalation process disclosed in this document is: mixing the purified microcrystalline graphite with sodium nitrate, concentrated sulfuric acid and potassium permanganate, placing the mixture in an ice water bath, stirring for 30-40 min, adding a hydrogen peroxide solution, and continuing stirring for 5-15 min to obtain the oxidized microcrystalline graphite. The intercalation is mainly realized by oxidation of graphite and strong oxide, but the use of catalyst is not involved.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of natural microcrystalline graphite and a prepared microcrystalline graphite cathode material.
In order to solve the technical problems, the invention adopts the following technical scheme:
the preparation method of the natural microcrystalline graphite negative electrode material comprises the following steps:
s1, crushing treatment: crushing natural microcrystalline graphite ore to obtain microcrystalline graphite secondary particles;
s2, alkali treatment: and (3) mixing the crushed microcrystalline graphite secondary particles obtained in the step (S1) with an alkaline solution according to a solid-liquid mass ratio (5-10): 1, mixing, refluxing and stirring at 100-200 ℃ for 2-3 h, filtering, washing (generally water washing), and drying to obtain alkaline leaching graphite;
s3, acid treatment: and (5) mixing the alkaline leaching graphite obtained in the step (S2) with an acid solution according to a solid-liquid mass ratio of (5-10): 1 mixing, and carrying out reflux stirring at 100-200 ℃ for 2-3 h, wherein: the acid solution is a strong oxidizing acid; then filtering, washing (generally water washing), and drying to obtain acid-dipped graphite; the fixed carbon content of the acid-dipped graphite is generally more than 99 percent;
s4, introducing a catalyst for high-temperature graphitization treatment to prepare a microcrystalline graphite negative electrode material: and (4) adding a certain proportion of catalyst into the acid-dipped graphite obtained in the step (S3) for blending, stirring for 1-3 hours, heating to 2000-2500 ℃ in a stepped manner, preserving heat for 5-48 hours, and gradually cooling to room temperature to obtain black powder, namely the microcrystalline graphite cathode material. The fixed carbon content of the obtained microcrystalline graphite negative electrode material is more than 99.9 percent.
Wherein: the catalyst is a co-catalyst composed of transition metal oxide of VIII group metal elements and magnesium oxide, wherein: the transition metal oxide is used as a main catalyst, and the magnesium oxide is used as an auxiliary catalyst.
Further, in step S1, the particle size D50 of the natural graphite secondary particles obtained after the treatment is 10-20 μm.
In the step S1, the microcrystalline graphite ore is preferably cryptocrystalline graphite ore in the middle areas of Hunan, Hunan and Jiangnan, wherein the water content is 1-3%, the volatile matter is 1-5%, the ash content is 10-20%, and the carbon content is 70-85%.
Further, the air conditioner is provided with a fan,
the crushing treatment in the step S1 usually adopts jet milling, specifically adopts a jet mill, and can simultaneously realize normal jet milling, classification removal of micro powder and bottom particles, sieving and magnetic separation, wherein the crushing pressure of the jet mill is 0.1-1.0 Mpa. The invention adopts the grading treatment equipment, can effectively remove micro powder and large particles in the product, further reduce impurities in the product and obtain the microcrystalline graphite material with higher carbon content and high quality.
Further, the mixing operation of step S2 was performed in a sealed stirred tank reactor with a liner.
Further, the alkaline solution used in step S2 is a sodium hydroxide solution, a potassium hydroxide solution, or a mixed solution of both.
Preferably, the concentration of the alkaline solution is 0.5-1.0 mol/L.
Further, the mixing operation of step S3 was also performed in a sealed stirred tank reactor with a liner.
Further, the air conditioner is provided with a fan,
the strongly oxidizing acid used in step S3 is nitric acid, or a mixture of nitric acid and hydrochloric acid, or a mixture of nitric acid and hydrofluoric acid, or a mixture of nitric acid and sulfuric acid.
Preferably, the concentration of the nitric acid is 0.5-1.0 mol/L.
Preferably, the mass percentage of each of the nitric acid and the hydrochloric acid or the hydrofluoric acid or the sulfuric acid is 50%.
Further, the sealed stirred tank reactor used in steps S2 and S3 is a stainless steel reactor with an inner liner and an outer jacket, the inner liner is made of corrosion-resistant teflon, the outer jacket is filled with cooling water, and the water inlet temperature is normal temperature.
Further, the air conditioner is provided with a fan,
in the co-catalyst of step S4, the weight ratio of the main catalyst to the cocatalyst is 3: 1.
further, the air conditioner is provided with a fan,
the amount of co-catalyst added in step S4 is 0.1% to 1.5% by weight of the total solid mixture.
Further, the air conditioner is provided with a fan,
the cocatalyst in the step S4 is specifically one of NiO-MgO, CoO-MgO and FeO-MgO.
The invention also provides the microcrystalline graphite cathode material prepared by the method, the microcrystalline graphite cathode material is formed by stacking primary particles with the particle size D50 of 1 mu m, the graphitization degree is more than 90%, and the carbon content is more than 99.9%.
The invention also provides application of the preparation method in preparation of the lithium ion battery.
The invention also provides a lithium ion battery cathode which comprises the microcrystalline graphite cathode material prepared by the method.
The invention also provides application of the microcrystalline graphite cathode material prepared by the preparation method in a lithium ion battery, wherein the lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, and the negative electrode comprises the microcrystalline graphite cathode material prepared by the method.
The invention has the following beneficial effects:
compared with the conventional natural microcrystalline graphite purification method, the method has the following remarkable advantages:
1. in the method, a co-catalyst consisting of transition metal oxide of VIII group metal elements and magnesium oxide is adopted, the transition metal oxide is used as a main catalyst, the magnesium oxide is used as a cocatalyst, the magnesium oxide cocatalyst can improve the catalytic activity of the main catalyst and can also improve the heat resistance of the catalyst, and meanwhile, the magnesium oxide is adsorbed on a graphite crystal to improve the oxidation resistance of the graphite crystal grain.
2. The method adopts strong oxidizing acid treatment, not only can remove metal oxide impurities on the surface of graphite through chemical reaction dissolution, but also can enable the surface of the graphite to generate functional groups such as hydroxyl, carboxyl and the like, meanwhile, inorganic acid molecules form intercalation compounds between graphite layers, and the rapid heating in the acid treatment process can enlarge the graphite layer spacing, so that the material can show higher gram capacity and good rate performance, is convenient to be subsequently applied to a lithium ion battery as a lithium ion battery cathode material, and is particularly suitable to be used as a raw material of the high-rate lithium ion battery cathode material.
3. In the method, the sealed stirring reaction kettle is adopted to carry out alkali treatment and acid treatment on the graphite, and high-temperature reflux stirring is carried out in the treatment process, so that the method is beneficial to fully infiltrating and contacting acid and alkali molecules with graphite microparticles and can also promote the formation of a graphite intercalation compound and the expansion of interlayer spacing.
Drawings
FIG. 1 is a schematic flow chart of a preparation method of a natural microcrystalline graphite negative electrode material provided by the invention;
FIG. 2 is an SEM image of sample A1 of microcrystalline graphite negative electrode material prepared in example 1 of the present invention;
FIG. 3 is a TEM image of a microcrystalline graphite negative electrode material sample B2 obtained after non-high temperature heating acid treatment of comparative example 2;
fig. 4 is a TEM image of a microcrystalline graphite anode material sample a1 obtained after the high temperature reflow acid treatment of example 1.
Detailed Description
Referring to fig. 1, the invention provides a preparation method of a natural microcrystalline graphite cathode material and the prepared microcrystalline graphite cathode material.
Specifically, the preparation method of the natural microcrystalline graphite negative electrode material provided by the invention comprises the following steps:
s1, crushing treatment: crushing natural microcrystalline graphite ore to obtain microcrystalline graphite secondary particles; generally, natural microcrystalline graphite ore with the fixed carbon content of 70-85% is adopted;
s2, alkali treatment: and (3) mixing the crushed microcrystalline graphite secondary particles obtained in the step (S1) with an alkaline solution according to a solid-liquid mass ratio (5-10): 1, mixing, refluxing and stirring at 100-200 ℃ for 2-3 h, filtering, washing (generally water washing), and drying to obtain alkaline leaching graphite;
s3, acid treatment: and (5) mixing the alkaline leaching graphite obtained in the step (S2) with an acid solution according to a solid-liquid mass ratio of (5-10): 1 mixing, and carrying out reflux stirring at 100-200 ℃ for 2-3 h, wherein: the acid solution is a strong oxidizing acid; then filtering, washing (generally water washing), and drying to obtain acid-dipped graphite, wherein the fixed carbon content of the acid-dipped graphite can be more than 99 percent generally;
s4, introducing a catalyst for high-temperature graphitization treatment to prepare a microcrystalline graphite negative electrode material: adding a certain proportion of catalyst into the acid-dipped graphite obtained in the step S3, blending, stirring for 1-3 hours, heating in a stepped manner to 2000-2500 ℃, keeping the temperature for 5-48 hours, and gradually cooling to room temperature to obtain black powder, namely the microcrystalline graphite cathode material; the fixed carbon content of the microcrystalline graphite cathode material can reach more than 99.9%;
wherein: the catalyst is a co-catalyst composed of transition metal oxide of VIII group metal elements and magnesium oxide, wherein: the transition metal oxide is used as a main catalyst, and the magnesium oxide is used as an auxiliary catalyst.
In step S1, the particle size D50 of the natural graphite secondary particles obtained after treatment is 10-20 μm.
In a preferred embodiment, in step S1, the microcrystalline graphite ore is preferably cryptocrystalline graphite ore in central areas of Hunan, North and Jiangnan, wherein the water content is 1-3%, the volatile matter is 1-5%, the ash content is 10-20%, and the carbon content is 70-85%.
In a preferred embodiment, the step S1 is performed by using a jet mill, which can perform normal jet milling, classification to remove micro powder and bottom particles, sieving, and magnetic separation at the same time, wherein the milling pressure of the jet mill is 0.1-1.0 Mpa. The invention adopts the grading treatment equipment, can effectively remove micro powder and large particles in the product, further reduce impurities in the product and obtain the microcrystalline graphite material with higher carbon content and high quality.
As a preferred embodiment, the mixing operation of step S2 is performed in a sealed stirred tank reactor with a liner.
In a preferred embodiment, the alkaline solution used in step S2 is a sodium hydroxide solution, a potassium hydroxide solution, or a mixture thereof. The concentration of the alkaline solution is 0.5-1.0 mol/L.
As a preferred embodiment, the mixing operation of step S3 is also performed in a sealed stirred tank reactor with a liner.
In a preferred embodiment, the strongly oxidizing acid used in step S3 is nitric acid, or a mixture of nitric acid and hydrochloric acid, or a mixture of nitric acid and hydrofluoric acid, or a mixture of nitric acid and sulfuric acid. The concentration of the nitric acid is 0.5-1.0 mol/L. The mass percentage of each of the nitric acid and the hydrochloric acid or the hydrofluoric acid or the sulfuric acid is 50%.
In a preferred embodiment, the sealed stirred tank reactor used in steps S2 and S3 is a stainless steel reactor with an inner liner and an outer jacket, the inner liner is made of corrosion-resistant teflon, cooling water is introduced into the outer jacket, and the water inlet temperature is normal temperature.
In a preferred embodiment, in the co-catalyst of step S4, the weight ratio of the main catalyst to the cocatalyst is 3: 1; the amount of co-catalyst added is 0.1% to 1.5% by weight of the total solid mixture.
In a preferred embodiment, the cocatalyst in step S4 is one of NiO-MgO, CoO-MgO and FeO-MgO.
The microcrystalline graphite cathode material prepared by the preparation method is formed by stacking primary particles with the particle size D50 of 1 mu m, the graphitization degree is more than 90%, and the carbon content is more than 99.9%.
To better illustrate the contents of the present invention, the present invention is further verified by specific examples 1 to 6 and comparative examples 1 to 5. It should be noted that the examples are given for the purpose of describing the invention more directly and are only a part of the present invention, which should not be construed as limiting the invention in any way.
Example 1
Referring to fig. 1, the present embodiment provides a method for preparing a low-cost natural microcrystalline graphite negative electrode material, including the following steps:
s1, crushing treatment: adding the microcrystalline graphite ore into a jet mill for jet milling, wherein the milling pressure is 0.1-1.0 Mpa, and simultaneously milling, grading, removing micro powder and bottom particles, sieving and magnetically separating are completed to obtain microcrystalline graphite secondary particles with the fixed carbon content of 70-85%, wherein the microcrystalline graphite secondary particles are formed by stacking primary particles with the particle size of about 1 mu m;
s2, alkali treatment: mixing the microcrystalline graphite secondary particles treated by the S1 with a sodium hydroxide solution according to a solid-liquid mass ratio of 5: 1, mixing, wherein the concentration of a sodium hydroxide solution is 1.0mol/L, the mixing operation is carried out in a sealed stirring reaction kettle with a lining, the stirring temperature is 100-200 ℃, and the reflux stirring is carried out for 2-3 hours; then filtering, washing and drying to obtain alkaline leaching graphite;
s3, acid treatment: and (3) mixing the alkaline leaching graphite obtained in the step (S2) with nitric acid according to a solid-liquid mass ratio of 5: 1, mixing, wherein the concentration of nitric acid is 1.0mol/L, the mixing operation is carried out in a sealed stirring reaction kettle with a lining, the stirring temperature is 100-200 ℃, and the reflux stirring is carried out for 2-3 h; then filtering, washing and drying to obtain acid-dipped graphite;
s4, introducing a catalyst and carrying out high-temperature graphitization treatment to obtain the microcrystalline graphite negative electrode material: adding acid-leached graphite obtained in S3 into NiO-MgO superfine catalyst powder with the content of 1%, and blending, wherein the NiO-MgO superfine catalyst powder comprises the following components in percentage by weight: NiO is used as a main catalyst, MgO is used as an auxiliary catalyst, and the ratio of NiO: stirring for 1 hour by adopting a VC high-speed stirrer with the mass ratio of MgO being 3: 1;
then adding the acid-dipped graphite which is uniformly stirred and mixed into a graphite crucible, heating to 2000-2500 ℃ by adopting a step-type heating program, preserving heat for 5-48 h, and gradually cooling to room temperature; this gave a black powder product designated sample A1.
Example 2
Referring to fig. 1, the present embodiment provides a method for preparing a low-cost natural microcrystalline graphite negative electrode material, including the following steps:
s1, crushing treatment: adding the microcrystalline graphite ore into a jet mill for jet milling, wherein the milling pressure is 0.1-1.0 Mpa, and simultaneously milling, grading, removing micro powder and bottom particles, sieving and magnetically separating are completed to obtain microcrystalline graphite secondary particles with the fixed carbon content of 70-85%, wherein the microcrystalline graphite secondary particles are formed by stacking primary particles with the particle size of about 1 mu m;
s2, alkali treatment: mixing the microcrystalline graphite secondary particles treated by the S1 with a sodium hydroxide solution according to a solid-liquid mass ratio of 5: 1, mixing, wherein the concentration of a sodium hydroxide solution is 1.0mol/L, the mixing operation is carried out in a sealed stirring reaction kettle with a lining, the stirring temperature is 100-200 ℃, and the reflux stirring is carried out for 2-3 hours; then filtering, washing and drying to obtain alkaline leaching graphite;
s3, acid treatment: and (3) mixing the alkaline leaching graphite obtained in the step (S2) with nitric acid according to a solid-liquid mass ratio of 5: 1, mixing, wherein the concentration of nitric acid is 1.0mol/L, the mixing operation is carried out in a sealed stirring reaction kettle with a lining, the stirring temperature is 100-200 ℃, and the reflux stirring is carried out for 2-3 h; then filtering, washing and drying to obtain acid-dipped graphite;
s4, introducing a catalyst and carrying out high-temperature graphitization treatment to obtain the microcrystalline graphite negative electrode material: adding acid-leached graphite obtained in S3 into FeO-MgO superfine catalyst powder with the content of 1%, and blending, wherein in the FeO-MgO superfine catalyst powder: FeO as a main catalyst, MgO as a cocatalyst, FeO: the mass ratio of MgO is 3: 1; stirring for 1 hour by adopting a VC high-speed stirrer; then adding the acid-dipped graphite which is uniformly stirred and mixed into a graphite crucible, heating to 2000-2500 ℃ by adopting a step-type heating program, preserving heat for 5-48 h, and gradually cooling to room temperature; this gave a black powder product designated sample A2.
Example 3
Referring to fig. 1, the present embodiment provides a method for preparing a low-cost natural microcrystalline graphite negative electrode material, including the following steps:
s1, crushing treatment: adding the microcrystalline graphite ore into a jet mill for jet milling, wherein the milling pressure is 0.1-1.0 Mpa, and simultaneously milling, grading, removing micro powder and bottom particles, sieving and magnetically separating are completed to obtain microcrystalline graphite secondary particles with the fixed carbon content of 70-85%, wherein the microcrystalline graphite secondary particles are formed by stacking primary particles with the particle size of about 1 mu m;
s2, alkali treatment: mixing the microcrystalline graphite secondary particles treated by the S1 with an alkaline sodium hydroxide solution according to a solid-liquid mass ratio of 5: 1, mixing, wherein the concentration of a sodium hydroxide solution is 1.0mol/L, the mixing operation is carried out in a sealed stirring reaction kettle with a lining, the stirring temperature is 100-200 ℃, and the reflux stirring is carried out for 2-3 hours; then filtering, washing and drying to obtain alkaline leaching graphite;
s3, acid treatment: and (3) mixing the alkaline leaching graphite obtained in the step (S2) with nitric acid according to a solid-liquid mass ratio of 5: 1, mixing, wherein the concentration of nitric acid is 1.0mol/L, the mixing operation is carried out in a sealed stirring reaction kettle with a lining, the stirring temperature is 100-200 ℃, and the reflux stirring is carried out for 2-3 h; then filtering, washing and drying to obtain acid-dipped graphite;
s4, introducing a catalyst and carrying out high-temperature graphitization treatment to obtain the microcrystalline graphite negative electrode material: adding acid-leached graphite obtained in S3 into CoO-MgO superfine catalyst powder with the content of 1%, and blending, wherein the acid-leached graphite in the CoO-MgO superfine catalyst powder comprises the following components: CoO as a main catalyst, MgO as a co-catalyst, CoO: the mass ratio of MgO is 3: 1; stirring for 1 hour by adopting a VC high-speed stirrer; then adding the acid-dipped graphite which is uniformly stirred and mixed into a graphite crucible, heating to 2000-2500 ℃ by adopting a step-type heating program, preserving heat for 5-48 h, and gradually cooling to room temperature; this gave a black powder product designated sample A3.
Example 4
The difference from example 1 is that:
in the step S2, the alkali liquor is potassium hydroxide solution;
in the step S3, the strong oxidizing acid is a mixed solution of nitric acid and hydrochloric acid, the concentration of nitric acid is 1.0mol/L, the concentration of hydrochloric acid is 1.0mol/L, and the mass percentages of nitric acid and hydrochloric acid in the mixed solution are respectively: 50% and 50%.
The amount of NiO-MgO powdered ultrafine catalyst added in step S4 was 1%.
The sample obtained is designated A4. The microcrystalline graphite material prepared in this example was evaluated by the method of charging, specifically referring to the procedure in example 1.
Example 5
The difference from example 1 is that:
in the step S3, the strong oxidizing acid is a mixed solution of nitric acid and hydrofluoric acid, the concentration of nitric acid is 1.0mol/L, the concentration of hydrofluoric acid is 1.0mol/L, and the mass percentages of nitric acid and hydrofluoric acid in the mixed solution are respectively: 50% and 50%.
The amount of NiO-MgO powdered ultrafine catalyst added in step S4 was 1.5%.
The sample obtained is designated A5. The microcrystalline graphite material prepared in this example was evaluated by the method of charging, specifically referring to the procedure in example 1.
Example 6
The difference from example 1 is that:
in the step S2, the alkali liquor is potassium hydroxide solution;
in the step S3, the strong oxidizing acid is a mixed solution of nitric acid and sulfuric acid, the concentration of nitric acid is 1.0mol/L, the concentration of sulfuric acid is 1.0mol/L, and the mass percentages of nitric acid and sulfuric acid in the mixed solution are respectively: 50% and 50%.
The amount of NiO-MgO powdered ultrafine catalyst added in step S4 was 0.1%.
The sample obtained is designated A6. The microcrystalline graphite material prepared in this example was evaluated by the method of charging, specifically referring to the procedure in example 1.
The sealed stirred tank reactor used for the alkali treatment in step S2 and the acid treatment in step S3 in the above examples is specifically a stainless steel reactor with an inner liner and an outer jacket, the inner liner is made of corrosion-resistant teflon material, the outer jacket is filled with cooling water, and the temperature of the inlet water is normal temperature.
Comparative example 1: acid treatment and alkali treatment are carried out by adopting conventional stirring equipment
This comparative example is different from example 1 in that the alkali treatment of step S2 and the acid treatment of step S3 were carried out in a conventional stirring apparatus. The resulting sample was designated B1.
Comparative example 2: by treatment with acids, but without heating at high temperatures
The present comparative example is different from example 1 in that the alkali treatment of step S2 and the acid treatment of step S3 are different, and the present comparative example does not perform high temperature heating. The resulting sample was designated B2.
Comparative example 3: using NiO catalyst
This comparative example is different from example 1 in that the catalyst in step S4 used NiO ultrafine catalyst powder. The resulting sample was designated B3.
Comparative example 4: without addition of catalyst
The present comparative example is different from example 1 in that the microcrystalline graphite anode material is directly prepared by high temperature treatment without adding a catalyst in step S4. The resulting sample was designated B4.
Comparative example 5: without acid treatment
The present comparative example is different from example 1 in that step S4 is directly performed after the alkali treatment in step S2, and high-temperature graphitization is performed to obtain a microcrystalline graphite negative electrode material. The resulting sample was designated B5.
The following performance tests were performed on the samples A1-A6 prepared in examples 1-6 and the samples B1-B5 prepared in comparative examples 1-5:
1) the carbon content of the material samples is measured by a sulfur carbon instrument, and the carbon content measurement results of the material samples are shown in the following table 1:
TABLE 1 data for carbon content for samples A1-A6 and samples B1-B5
From the data in table 1 above, it can be seen that: the carbon content of the microcrystalline graphite cathode material prepared by the method can reach 99.9 percent, which shows that the graphite material with higher purity can be obtained.
2) XRD tests show the graphitization degree of the material, and the graphitization degree test result of each material sample is shown in the following table 2:
TABLE 2 graphitization degree data for samples A1-A6 and samples B1-B5
| Degree of graphitization G | |
| Example 1 | 93％ |
| Example 2 | 95％ |
| Example 3 | 92％ |
| Example 4 | 91％ |
| Example 5 | 93％ |
| Example 6 | 92％ |
| Comparative example 1 | 89％ |
| Comparative example 2 | 90％ |
| Comparative example 3 | 85％ |
| Comparative example 4 | 83％ |
| Comparative example 5 | 86％ |
From the data in table 2 above, it can be seen that: the graphitization degree of the microcrystalline graphite cathode material prepared by the method can reach more than 90 percent, and compared with a comparative example (the graphitization degree is below 90 percent), the method can reach higher graphitization degree.
In the data in the above table, especially, the lowest graphitization degrees of comparative example 3 (using NiO catalyst) and comparative example 4 (not using catalyst) are 85% and 83%, respectively, which indicates that the use of the catalyst can promote the graphitization of the material to a certain degree, and the selection of the catalyst can also have a great influence on the graphitization degree of the prepared microcrystalline graphite material, and the co-catalyst composed of the oxide of the group VIII metal element and magnesium oxide can significantly improve the graphitization degree of the material, and can also reduce the graphitization temperature to a great extent, so that the graphitization degree of more than 90% can be realized at 2000-2500 ℃, and further the gram capacity of the product can be improved.
3) The electron microscope scanning was performed on each material sample, fig. 2 is an SEM image of sample a1 obtained in example 1, and as shown in fig. 1, microcrystalline graphite negative electrode material sample a1 was formed by stacking primary particles having a particle size of about 1 μm.
4) TEM was used to characterize the graphite interlayer spacing after acid treatment and the graphite interlayer spacing for each material sample was measured with the following results in table 3:
TABLE 3 average interlamellar spacings of the graphite layers of samples A1-A6 and samples B1-B5
| Graphite layer spacing/nm after acid treatment | |
| Example 1 | 0.3550 |
| Example 2 | 0.3552 |
| Example 3 | 0.3550 |
| Example 4 | 0.3555 |
| Example 5 | 0.3555 |
| Example 6 | 0.3552 |
| Comparative example 1 | 0.3425 |
| Comparative example 2 | 0.3420 |
| Comparative example 3 | 0.3548 |
| Comparative example 4 | 0.3548 |
| Comparative example 5 | 0.3405 |
Fig. 3 is a TEM image of a microcrystalline graphite anode material sample B2 obtained after non-high temperature heating and acid treatment of comparative example 2, and fig. 4 is a TEM image of a microcrystalline graphite anode material sample a1 obtained after high temperature reflow acid treatment of example 1, from which it can be seen that: the graphite interlayer spacing d of the sample B2 obtained by non-high-temperature heating acid treatment is 0.3420nm, the graphite interlayer spacing d of the sample A1 obtained by high-temperature reflux acid treatment is 0.3550nm, and the microcrystalline graphite anode material with larger interlayer spacing can be obtained by high-temperature heating acid treatment than by non-high-temperature heating acid treatment, which shows that the graphite interlayer spacing can be expanded to a certain extent by rapid heating in the acid treatment process. And in combination with the interlamellar spacing data of comparative example 5 (without acid treatment), the graphite interlamellar spacing of the resulting material is only 0.3405nm, indicating that high temperature acid treatment can effectively enlarge the graphite interlamellar spacing.
From the data comparison in the above table, it can also be known that: the graphite interlamellar spacing of the comparative example 1 is smaller than that of other material samples prepared by adopting a sealed stirring reaction kettle and is only 0.3425nm when the conventional stirring equipment is adopted for acid treatment and alkali treatment, and the sealed stirring reaction kettle is adopted for carrying out alkali and acid treatment on graphite, and high-temperature reflux stirring is adopted in the treatment process, so that the sufficient infiltration contact of acid and alkali molecules and graphite microparticles is facilitated, and the formation of a graphite intercalation compound and the expansion of interlamellar spacing can also be promoted.
5) The prepared samples are prepared into button cells according to the following method, and the gram capacity and the rate performance (the capacity retention rate of 3C/1C) of each sample material are evaluated by the button cells, wherein the button cells are prepared according to the following method:
the microcrystalline graphite negative electrode materials prepared in the above examples 1 to 6 and comparative examples 1 to 5 were added with 5 wt% of Super P as a conductive agent, 4 wt% of CMC as a thickener, and 6 wt% of SBR (SBR dissolved in water to form a solution) as a binder, and then deionized water was added thereto, followed by sufficient stirring to form a black slurry. The slurry is coated on a copper foil substrate, the prepared negative plate is dried, the punched plate is used as a test electrode, a metal lithium plate is used as a reference electrode, and a PP/PE/PP diaphragm with the thickness of 16 mu m is adopted to assemble the half-cell. The electrolyte is 1mol/L LiPF6EC of (1)&EMC&The gram capacity of the DMC (volume ratio of 1:1:1) solution was measured at a current density of 30mA/g and the rate capability was measured at a current density of 300mA/g and 900 mA/g.
The test results are given in table 4 below:
TABLE 4 gram volume and rate performance data for samples A1-A6 and samples B1-B5
From table 4 above, it can be seen that: the gram capacity of a product of the button cell corresponding to the microcrystalline graphite cathode material prepared by the embodiment of the invention is 340(mAh/g) or more, which is higher than that of the samples prepared in the comparative examples 1-5, and the gram capacities of 1C and 3C are also higher than that of the samples prepared in the comparative examples 1-5; in the aspect of rate performance, the ratio of capacity exertion at 3C rate to capacity exertion at 1C rate is adopted for comparison, and the capacity retention rate (3C/1C) shows that the capacity retention rate of the button cell corresponding to the microcrystalline graphite anode material prepared by the embodiment of the method can be kept above 90%, while the capacity retention rate of the conventional method of the comparative example is lower than 90%. In conclusion, the microcrystalline graphite cathode material prepared by the method has higher gram capacity and better rate capability, can be well used as a cathode material of a lithium ion battery, and has lower preparation cost and wide application prospect.
The foregoing is a detailed description of the invention and is not intended to limit the invention to the particular forms disclosed, but on the basis of the present invention, it is expressly intended that all such modifications and improvements are within the scope of the invention.
Claims (10)
1. The preparation method of the natural microcrystalline graphite negative electrode material is characterized by comprising the following steps of:
s1, crushing treatment: crushing natural microcrystalline graphite ore to obtain microcrystalline graphite secondary particles;
s2, alkali treatment: and (3) mixing the crushed microcrystalline graphite secondary particles obtained in the step (S1) with an alkaline solution according to a solid-liquid mass ratio (5-10): 1, mixing, refluxing and stirring at 100-200 ℃ for 2-3 h, and then filtering, washing and drying to obtain alkaline leaching graphite;
s3, acid treatment: and (5) mixing the alkaline leaching graphite obtained in the step (S2) with an acid solution according to a solid-liquid mass ratio of (5-10): 1 mixing, and carrying out reflux stirring at 100-200 ℃ for 2-3 h, wherein: the acid solution is a strong oxidizing acid; then filtering, washing and drying to obtain acid-dipped graphite;
s4, introducing a catalyst for high-temperature graphitization treatment to prepare a microcrystalline graphite negative electrode material: adding a certain proportion of catalyst into the acid-dipped graphite obtained in the step S3, blending, stirring for 1-3 hours, heating in a stepped manner to 2000-2500 ℃, keeping the temperature for 5-48 hours, and gradually cooling to room temperature to obtain black powder, namely the microcrystalline graphite cathode material;
wherein: the catalyst is a co-catalyst composed of transition metal oxide of VIII group metal elements and magnesium oxide, wherein: the transition metal oxide is used as a main catalyst, and the magnesium oxide is used as an auxiliary catalyst.
2. The preparation method of the natural microcrystalline graphite anode material as claimed in claim 1,
in the co-catalyst of step S4, the weight ratio of the main catalyst to the cocatalyst is 3: 1; the amount of co-catalyst added is 0.1% to 1.5% by weight of the total solid mixture.
3. The method for preparing the natural microcrystalline graphite anode material of claim 1 or 2, wherein the cocatalyst in step S4 is one of NiO-MgO, CoO-MgO and FeO-MgO.
4. The preparation method of the natural microcrystalline graphite anode material as claimed in claim 1 or 2, wherein in the step S1, jet milling is adopted for the crushing treatment, specifically, a jet mill is adopted, normal jet milling, classification micro powder and bottom particles removal, sieving and magnetic separation can be simultaneously realized, and the crushing pressure of the jet mill is 0.1-1.0 Mpa.
5. The preparation method of the natural microcrystalline graphite anode material as claimed in claim 1 or 2, wherein the mixing operations of the steps S2 and S3 are all performed in a sealed stirred tank reactor with a liner;
the adopted sealed stirring reaction kettle is a stainless steel reaction kettle, the inside of the reaction kettle is provided with a lining, the outside of the reaction kettle is provided with a jacket, the lining is made of corrosion-resistant Teflon materials, cooling water is introduced into the jacket, and the water inlet temperature is normal temperature.
6. The method for preparing the natural microcrystalline graphite anode material as claimed in claim 1 or 2, wherein the alkaline solution adopted in the step S2 is a sodium hydroxide solution, a potassium hydroxide solution or a mixed solution of the sodium hydroxide solution and the potassium hydroxide solution.
7. The method for preparing the natural microcrystalline graphite anode material of claim 1 or 2, wherein the strong oxidizing acid used in step S3 is nitric acid, or a mixture of nitric acid and hydrochloric acid, or a mixture of nitric acid and hydrofluoric acid, or a mixture of nitric acid and sulfuric acid.
8. The microcrystalline graphite cathode material prepared by the method of any one of claims 1 to 7, wherein the microcrystalline graphite cathode material is formed by stacking primary particles with the particle size D50 of 1 μm, the graphitization degree is more than 90%, and the carbon content is more than 99.9%.
9. Use of the preparation method according to any one of claims 1 to 7 in the preparation of lithium ion batteries.
10. The application of the microcrystalline graphite cathode material prepared by the method of any one of claims 1-7 in a lithium ion battery.
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