Micro-expanded graphite as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of micro-expanded graphite, which comprises the following steps: uniformly kneading and mixing graphite, an oxidant solid and an inorganic acid, standing, then adding water to carry out micro-expansion treatment, carrying out solid-liquid separation, drying, and calcining to obtain the micro-expanded graphite. The invention also discloses the micro-expanded graphite which is prepared according to the preparation method of the micro-expanded graphite. The invention also discloses an application of the micro-expanded graphite in a negative electrode material. The method is simple to operate and low in cost; good conductivity can be maintained while micro-expansion of the graphite is realized; the obtained micro-expanded graphite has high magnification and long cycle performance at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of graphite, and in particular to micro-expanded graphite and a preparation method and application thereof. Background Art

[0002] Natural graphite has the characteristics of low cost, low reversible lithium deintercalation potential and large reversible capacity as a negative electrode material, and is suitable for lithium-ion secondary batteries. However, its practical application is limited by its poor cycle stability and other disadvantages. The main reason for the attenuation of cycle performance is that when lithium ions are embedded and removed from the graphite negative electrode, the volume of the graphite unit cell will expand and shrink by about 10%. In addition, the surface active groups of natural graphite are also an important factor affecting the electrochemical properties of graphite. Expanded graphite can solve the volume effect problem of lithium deintercalation in the graphite layer, but its low density (about 0.01g / cm 3 ) will reduce the volume energy density of the negative electrode. Therefore, moderate expansion of graphite, such as micro expansion, can solve the volume effect problem in the process of lithium insertion and extraction, and will not reduce the volume specific energy density of the material.

[0003] The existing method for preparing micro-expanded graphite is generally as follows: adding graphite to a mixture of an oxidant (such as potassium permanganate, hydrogen peroxide, etc.) and an intercalant (such as concentrated sulfuric acid, concentrated nitric acid, etc.), reacting to expand the graphite, washing, drying, and calcining to obtain micro-expanded graphite. Although the existing method can slightly expand the interlayer spacing of graphite, it will greatly damage the outer surface morphology of the graphite, causing the outer surface to be incomplete, thereby greatly reducing the conductivity of the micro-expanded graphite; and the existing method uses a large amount of oxidant and intercalant, which is costly and will increase the cost of wastewater treatment in the later stage. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a micro-expanded graphite and a preparation method and application thereof. The method of the present invention is simple to operate and has low cost; it can achieve micro-expansion of graphite while maintaining good conductivity; the obtained micro-expanded graphite also has high rate and long cycle performance.

[0005] The invention provides a method for preparing micro-expanded graphite, comprising the following steps: kneading and mixing graphite, oxidant solid and inorganic acid, standing, then adding water for micro-expansion treatment, solid-liquid separation, drying and calcining to obtain the micro-expanded graphite.

[0006] The invention first mixes graphite and oxidant solid, and then kneads and mixes with inorganic acid, which can greatly reduce the amount of oxidant and inorganic acid used, reduce costs and wastewater treatment costs; and the method can cause less damage to the outer surface of graphite, improve the integrity of the outer surface of graphite, and further improve conductivity; the inorganic acid enters the graphite interlayer after standing at room temperature, and after a small amount of water is added, the water and the inorganic acid are replaced and enter the graphite interlayer, the graphite layer is stretched open to achieve micro-expansion, the interlayer spacing of the micro-expanded graphite is 0.336-0.339nm, which is slightly higher than the interlayer spacing of untreated graphite (0.335nm), so that the micro-expanded graphite has good cycle stability and rate performance; in addition, adding water can also remove impurities in the graphite; high-temperature calcination in an inert gas atmosphere can effectively remove the oxidant and inorganic acid, and further improve the purity of the micro-expanded graphite.

[0007] Preferably, the oxidizing agent is a chlorate.

[0008] The above-mentioned chlorate can be sodium chlorate, potassium chlorate or the like.

[0009] Preferably, the inorganic acid is at least one of concentrated nitric acid and concentrated sulfuric acid.

[0010] Preferably, the graphite is at least one of natural graphite and artificial graphite.

[0011] Preferably, the D50 of the graphite is 8-12 μm.

[0012] Preferably, the mixture is allowed to stand at room temperature for 2-6 hours.

[0013] Preferably, the specific steps of the micro-expansion treatment are: stirring at room temperature for 1-3 hours.

[0014] Preferably, calcination is carried out in an inert gas atmosphere.

[0015] Preferably, the inert gas is at least one of argon and nitrogen.

[0016] Preferably, the calcination temperature is 1450-1550°C.

[0017] Preferably, the calcination time is 2-4 hours.

[0018] Preferably, the weight ratio of graphite to oxidant is 1:0.1-0.5.

[0019] Preferably, the usage ratio of graphite to inorganic acid is 1 g:0.4-1 mL.

[0020] Preferably, the usage ratio of graphite to water is 1 g: 2-4 mL.

[0021] Preferably, the specific steps of kneading and mixing the graphite, the oxidant solid and the inorganic acid are: mixing the graphite and the oxidant solid, then dropping the inorganic acid and kneading and mixing.

[0022] Preferably, the interlayer distance of the micro-expanded graphite is 0.336-0.339 nm.

[0023] The kneading and mixing may be performed by kneading.

[0024] The water mentioned above is deionized water.

[0025] The invention also provides a micro-expanded graphite, which is prepared according to the preparation method of the micro-expanded graphite.

[0026] The present invention also proposes the application of the micro-expanded graphite in negative electrode materials.

[0027] The method of the present invention is simple to operate, uses less reagents, has low cost, and has low wastewater treatment cost; and can achieve micro-expansion of graphite while maintaining good conductivity; the obtained micro-expanded graphite also has high rate and long cycle performance, and can be used as a negative electrode material for a battery to improve the cycle stability and rate performance of the entire battery. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described in detail below through specific embodiments.

[0029] Example 1

[0030] A method for preparing micro-expanded graphite comprises the following steps:

[0031] Natural graphite is crushed, ground and shaped to obtain sample 1 with a D50 of 8-12 μm;

[0032] 10g of sample 1 and 2g of sodium chlorate powder were dried and mixed, and then 5mL of concentrated nitric acid was slowly added, and the mixture was kneaded and kneaded for 10min using a plastic pressing plate in the same manner as kneading dough, and then allowed to stand at room temperature for 2h, and 20mL of deionized water was added and stirred for 1h; after filtering, the mixture was dried in an oven at 80°C for 12h to obtain sample 2;

[0033] Sample 2 was taken and calcined at 1500°C for 2 h in an argon atmosphere to obtain slightly expanded graphite.

[0034] Example 2

[0035] A method for preparing micro-expanded graphite comprises the following steps:

[0036] Natural graphite is crushed, ground and shaped to obtain sample 1 with a D50 of 8-12 μm;

[0037] 10g of sample 1 and 4g of sodium chlorate powder were dried and mixed, and then 5mL of concentrated nitric acid was slowly added, and the mixture was kneaded for 10min using a plastic pressing plate in the same manner as kneading dough, and then allowed to stand at room temperature for 2h, and 20mL of deionized water was added and stirred for 1h; after filtering, the mixture was dried in an oven at 80°C for 12h to obtain sample 2;

[0038] Sample 2 was taken and calcined at 1500°C for 2 h in an argon atmosphere to obtain slightly expanded graphite.

[0039] Example 3

[0040] A method for preparing micro-expanded graphite comprises the following steps:

[0041] Natural graphite is crushed, ground and shaped to obtain sample 1 with a D50 of 8-12 μm;

[0042] 10g of sample 1 and 5g of sodium chlorate powder were dried and mixed, and then 10mL of concentrated nitric acid was slowly added, and the mixture was kneaded and mixed for 10min using a plastic pressing plate in the same manner as kneading dough, and then allowed to stand at room temperature for 2h, and 20mL of deionized water was added and stirred for 2h; after filtering, the mixture was dried in an oven at 80°C for 12h to obtain sample 2;

[0043] Sample 2 was taken and calcined at 1500°C for 2 h in an argon atmosphere to obtain slightly expanded graphite.

[0044] Comparative Example 1

[0045] This is sample 1 in Example 1.

[0046] Comparative Example 2

[0047] A method for preparing micro-expanded graphite comprises the following steps:

[0048] 5 g of hydrogen peroxide and 50 g of concentrated nitric acid were mixed, 10 g of sample 1 of Example 1 was added, and oxidation intercalation was carried out at 25° C. for 60 min. A glass rod was used for stirring during the oxidation intercalation reaction; then the temperature was naturally restored to room temperature, solid matter was separated by filtration, the solid matter was washed with deionized water until the pH value of the filtrate was 6-7, and then the solid matter was washed twice with anhydrous ethanol; the solid matter was sent to a vacuum drying oven for drying at 60° C. for 6 h; then the solid matter was sent to a horizontal tube furnace, and the temperature was raised to 650° C. at a rate of 10° C. / min under the protection of high-purity Ar, and the temperature was kept for 1 min to obtain micro-expanded graphite.

[0049] The micro-expanded graphites obtained in Examples 1-3 and Comparative Examples 1-2 were tested for interlayer spacing, particle size, degree of graphitization, and electrical conductivity. The results are shown in Table 1.

[0050] The resistivity of the graphite was tested using a powder resistivity tester.

[0051] Table 1 Test results of interlayer spacing, particle size, graphitization degree and conductivity

[0052] Test items D50(μm) Graphitization degree (%) Interlayer spacing (nm) Resistivity (Ω·m) Example 1 14.96 95.93 0.336 10.43 Example 2 15.32 95.44 0.337 13.45 Example 3 15.53 94.98 0.338 15.23 Comparative Example 1 14.38 96.25 0.335 8.35 Comparative Example 2 15.74 94.37 0.339 24.85

[0053] It can be seen from Table 1 that the micro-expanded graphite prepared by the method of the present invention has a suitable interlayer spacing, and compared with the untreated graphite and Comparative Example 2, its conductivity is less reduced and still maintains good conductivity.

[0054] The micro-expanded graphite obtained in Example 1-3 and Comparative Example 1-2 was used as the negative electrode material, and lithium-ion batteries were prepared in the same manner. The cyclability and rate performance were tested under the same conditions. The results are shown in Table 2.

[0055] The preparation method of the lithium ion battery is as follows: the positive electrode active material is lithium iron phosphate, and the negative electrode active material adopts the graphite material prepared by the present invention to prepare a 2.5Ah soft-pack battery.

[0056] The test conditions are: 25℃, the cycle test is 1C constant current and constant voltage charging, 1C constant current discharging; the rate test is 1C constant current and constant voltage charging, 2C constant current discharging.

[0057] Table 2 Cyclic and rate performance test results

[0058]

[0059]

[0060] It can be seen from Table 2 that compared with untreated graphite, the cycle stability and rate performance of the treated graphite are improved.

[0061] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing micro-expanded graphite, characterized in that: The method comprises the following steps: kneading and mixing graphite, oxidant solid and inorganic acid, standing, then adding water for micro-expansion treatment, solid-liquid separation, drying and calcining to obtain micro-expanded graphite.

2. The method for preparing micro-expanded graphite according to claim 1, characterized in that: The oxidant is chlorate; preferably, the inorganic acid is at least one of concentrated nitric acid and concentrated sulfuric acid; preferably, the graphite is at least one of natural graphite and artificial graphite; preferably, the D50 of the graphite is 8-12 μm.

3. The method for preparing micro-expanded graphite according to claim 1 or 2, characterized in that: Let stand at room temperature for 2-6 hours.

4. The method for preparing micro-expanded graphite according to any one of claims 1 to 3, characterized in that: The specific steps of the micro-expansion treatment are: stirring at room temperature for 1-3 hours.

5. The method for preparing micro-expanded graphite according to any one of claims 1 to 4, characterized in that: The calcination is carried out in an inert gas atmosphere; preferably, the inert gas is at least one of argon and nitrogen.

6. The method for preparing micro-expanded graphite according to any one of claims 1 to 5, characterized in that: The calcination temperature is 1450-1550°C; preferably, the calcination time is 2-4h.

7. The method for preparing micro-expanded graphite according to any one of claims 1 to 6, characterized in that: The weight ratio of graphite to oxidant is 1:0.1-0.5; preferably, the amount ratio of graphite to inorganic acid is 1g:0.4-1mL; preferably, the amount ratio of graphite to water is 1g:2-4mL.

8. The method for preparing micro-expanded graphite according to any one of claims 1 to 7, characterized in that: The specific steps of kneading and mixing the graphite, the oxidant solid and the inorganic acid are: mixing the graphite and the oxidant solid, then dropping the inorganic acid, and kneading and mixing; preferably, the interlayer spacing of the micro-expanded graphite is 0.336-0.339nm.

9. A micro-expanded graphite, characterized in that: The micro-expanded graphite is prepared according to the method for preparing the micro-expanded graphite according to any one of claims 1 to 8.

10. Use of the micro-expanded graphite as claimed in claim 9 in negative electrode materials.

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