NATURAL GRAPHITE, MODIFIED NATURAL GRAPHITE MATERIAL PREPARED THEREFROM, PREPARATION METHOD, AND APPLICATIONS

Abstract

Provided are a natural graphite, a modified natural graphite material prepared therefrom, a preparation method, and applications. The natural graphite has the following characteristics: a particle size D50 smaller than 10 m, and D90/D10<2.5; a 002 interplanar spacing ranging from 0.336 to 0.360 nm, I.sub.002/I.sub.11035; a saturated tap density greater than or equal to 0.6 g/cc and smaller than 1.3 g/cc; and a specific surface area greater than or equal to 1.0 m.sup.2/g and smaller than 10.0 m.sup.2/g. The provided natural graphite has specific particle size, orientation, tap density and surface area and can serve as a raw material for preparing modified natural graphite material, and the prepared modified natural graphite material has high isotropy and thus has better rate performance and cycle performance.

Claims

1. A natural graphite, having a particle size D50 smaller than 10 m, and D90/D10<2.5; a 002 interplanar spacing in a range of 0.336 to 0.360 nm, and I002/I11035; a saturated tap density greater than or equal to 0.6 g/cc and smaller than1.3 g/cc; and a specific surface area greater than or equal to 1.0 m2/g and smaller than 10.0m2/g.

2. The natural graphite according to claim 1, wherein the natural graphite is prepared by crushing natural flake graphite or by crushing and shaping microcrystalline graphite.

3. A modified natural graphite material, wherein the modified natural graphite material is prepared with the natural graphite according to claim 1 as a raw material.

4. A preparation method of modified natural graphite material, the preparation method comprising: modifying the natural graphite according to claim 1, to obtain the modified natural graphite material.

5. The preparation method according to claim 4, wherein the solidification is performed with a solidifying agent selected from phenolic resin, epoxy resin, petroleum resin, coal pitch, petroleum pitch, mesophase pitch, coal tar, heavy oil, and combinations thereof, and wherein the solidifying agent has a softening point in a range of 20 C. to 300 C.

6. The preparation method according to claim 4, wherein a mass ratio of the natural graphite to the solidifying agent is 1: (0.05-1).

7. The preparation method according to claim 4, wherein the solidification is performed under heating and stirring.

8. The preparation method according to claim 12, wherein the carbonization treatment is performed at a temperature ranging from 1000 C. to 3000 C.

9. The preparation method according to claim 4, wherein the preparation method, after the crushing, further comprises sieving.

10. A lithium ion battery, comprising the modified natural graphite material according to claim 3.

11. The lithium ion battery according to claim 10, wherein an anode plate of the lithium ion battery comprises the modified natural graphite material.

12. The preparation method according to claim 4, wherein said modifying comprises: sequentially performing a solidification, an isotropic treatment, a carbonization treatment, and a crushing on the natural graphite.

13. The preparation method according to claim 7, wherein the heating is performed at a temperature ranging from 50 C. to 800 C.

14. The preparation method according to claim 7, wherein the stirring is performed for 0 min to 300 min.

15. The preparation method according to claim 12, wherein the isotropic treatment is selected from the group consisting of a cold isostatic pressing treatment, a hot isostatic pressing treatment, a molding treatment, and combinations thereof.

16. The preparation method according to claim 12, wherein the carbonization treatment is performed in an atmosphere of an inert gas.

17. The preparation method according to claim 16, wherein the inert gas is selected from the group consisting of helium, neon, argon, nitrogen, krypton, and combinations thereof.

18. The preparation method according to claim 9, wherein the sieved material has a particle size D50 satisfying 7 mD5018 m.

Description

DESCRIPTION OF EMBODIMENTS

[0041] The technical solutions of the present application are further described below with reference to specific embodiments. Those skilled in the art can understand that these embodiments are merely to explain the present application, but are not intended to limit the present application.

EXAMPLE 1

[0042] A modified natural graphite material was prepared with the following method.

[0043] Natural graphite (D50=6 m, D90/D10=2.48, I.sub.002/I.sub.11033.2, saturation tap density of 0.62 g/cc, specific surface area of 9.4 m.sup.2/g) and petroleum pitch (softening point of 140 C.) were mixed in a ratio of 1:0.25, then the mixture was placed into a specific reaction kettle, stirred and heated at a temperature of 360 C. for 3 hours. The heated mixture was subjected to a cold isostatic pressing treatment under a pressure of 120 MPa for 2 min. After the isostatic pressing treatment, the product was subjected to a carbonization treatment at 2800 C., and then the material was crushed to have a particle size similar as the original material and sieved to obtain a modified natural graphite material having a D50 of 8.3 m.

EXAMPLES 2 to 5

[0044] Examples 2 to 5 differ from Example 1 merely in that mass ratios of natural graphite to coal pitch were respectively 1:0.05 (Example 2), 1:1 (Example 3), 1:0.01 (Example 4), and 1:2 (Example 5).

EXAMPLE 6

[0045] Example 6 differs from Example 1 merely in that the solidifying agent is phenolic resin having a softening point of 110 C.

EXAMPLE 7

[0046] Natural graphite (D50=8 m, D90/D10=2.41, I.sub.002/I.sub.11034.2, saturation tap density of 0.76 g/cc, and specific surface area of 6.9 m.sup.2/g) and coal pitch (softening point of 90 C.) were mixed in a ratio of 1:0.3, and then the mixture was placed into a specific reaction kettle, stirred and heated at a temperature of 260 C. for 3 hours. The heated material was subjected to a cold isostatic pressing treatment under a pressure of 110 MPa for 1 min. After the isostatic pressing treatment, the product was subjected to a carbonization treatment at 2800 C., and then the material was crushed to have a particle size similar as the original material and sieved to obtain a modified natural graphite material having a D50 of 11.1 m.

EXAMPLE 8

[0047] Natural graphite (D50=9.8 m, D90/D10=2.47, I.sub.002/I.sub.110=34.8, tap density of 0.86 g/cc, specific surface area of 6.1 m.sup.2 /g) and coal pitch (softening point of 180 C.) were mixed in a ratio of 1:0.2, and then the mixture was placed into a specific reaction kettle, stirred and heated at a temperature of 360 C. for 3 hours. The heated material was subjected to a cold isostatic pressing treatment under a pressure of 80 MPa for 1 min. After the isostatic pressing treatment, the product was subjected to carbonization treatment at 1200 C., and then the material was crushed to have a particle size similar as the original material and sieved to obtain a modified natural graphite material having a D50 of 12.8 m.

Comparative Example 1

[0048] Comparative Example 1 differs from Example 1 merely in that D50 of the natural graphite was 15 m.

Comparative Example 2

[0049] Comparative Example 2 differs from Example 1 merely in that D90/D10 of the natural graphite was 2.64.

Comparative Example 3

[0050] Comparative Example 3 differs from Example 1 merely in that I.sub.002/I.sub.110 of natural graphite was 48

Comparative Example 4

[0051] Comparative Example 4 differs from Example 1 merely in that the saturation tap density of natural graphite was 0.42 g/cc.

Comparative Example 5

[0052] Comparative Example 5 differs from Example 1 merely in that the specific surface area of natural graphite was 12 m.sup.2/g.

Performance Test

[0053] The modified natural graphite material powders prepared in Examples 1-8 and Comparative Examples 1-5 were tested with the following methods.

[0054] (1) The particle size was measured by using a particle size tester;

[0055] (2) XRD test is performed with an XRD tester; and

[0056] (3) The specific surface area is measured by using nitrogen adsorption and desorption instrument.

[0057] The modified natural graphite materials prepared in Examples 1-8 and Comparative Examples 1-5 were used to prepare anode plates and batteries, with the following methods.

[0058] Anode plate: the modified natural graphite material, as an anode active material of an anode plate, was mixed uniformly with a conductive agent, CMC and SBR according to a mass ratio of 95:1.5: 1.5:2 (active material: conductive agent: CMC: SBR), then coated on a copper foil current collector, and dried to obtain an anode plate.

[0059] Battery: the modified natural graphite material as provided, a conductive agent, CMC, and SBR were mixed in a mass ratio of 95:1.5:1.5:2, and coated onto a copper foil to obtain an anode plate; a cathode active material LiCoO.sub.2, a conductive agent, and PVDF were mixed evenly according to a mass ratio of 96.5:2:1.5 and then coated on an aluminum foil to obtain a cathode plate; the electrolyte was 1 mol/L of a mixture of LiPF.sub.6+EC+EMC; and the separator was a polyethylene/propylene composite microporous membrane.

[0060] Performances of the prepared anode plates and batteries were tested with the following methods.

[0061] (4) Specific capacity and first coulombic efficiency: the prepared anode plate was subjected to a button battery test, the battery was assembled in an argon glove box, a metal lithium plate was used as the anode, the electrolyte was 1 mol/L of a mixture of LiPF.sub.6+EC+EMC, and the separator was a polyethylene/propylene composite microporous membrane. The electrochemical performance was tested on a battery test cabinet (5V, 1 A, Neware) at a charge and discharge voltage of 0.01V to 1.5V with a charge and discharge rate of 0.1 C, in order to measure the specific capacity and first coulombic efficiency.

[0062] (5) Full battery test: the prepared negative and cathode plates were assembled to a 18650 cylindrical battery, which is prepared for subsequent tests after capacity sorting.

[0063] Capacity retention rate of 5 C/1 C discharge was measured with a method including: a. after the capacity sorting, continuously charging a battery at 1 C and discharging the battery at 1 C for three times, and calculating an average of the three discharges as 1C discharge capacity; then continuously charging the same battery at 1C and discharging it at 5 C for 5 times, and calculating an average of the last three discharges as 5 C discharge capacity; and dividing the 5 C discharge capacity by the 1 C discharge capacity to obtain the 5 C/1 C discharge capacity retention rate.

[0064] The 1 C/1 C capacity retention rate was measured with a method including: charging continuously a battery at 1 C and discharging the battery at 1 C for 300 cycles, with an interval of 1 minute between two successive charge-discharge cycles.

[0065] The test results are shown in Table 1.

TABLE-US-00001 TABLE 1 5C/1C 1C/1C Particle First discharge discharge size Specific coulombic capacity capacity D50 I.sub.002/ capacity efficiency/ retention retention Sample (m) I.sub.110 (mAh/g) % rate rate Example 1 8.3 33.1 363.1 95.9 96.1 93.3 Example 2 6.4 33.9 364.9 93.6 96.3 91.5 Example 3 11.2 30.8 356.6 96.2 95.8 92.3 Example 4 6.2 33.4 368.2 90.2 96.4 91.1 Example 5 12.6 30.1 348.1 95.9 92.6 91.0 Example 6 9.1 33.4 360.5 94.2 95.9 91.2 Example 7 11.1 36.2 362.1 96.1 94.4 93.1 Example 8 12.8 34.2 353.4 94.7 94.6 92.3 Comparative 17.2 41.5 361.9 96.2 89.5 91.3 Example 1 Comparative 9.4 42.6 362.4 95.1 92.3 90.6 Example 2 Comparative 9.3 49.6 361.4 95.3 91.3 90.3 Example 3 Comparative Processing performance was too poor to be measured. Example 4 Comparative 9.6 34.2 360.2 93.2 94.6 89.2 Example 5

[0066] In view of the examples and test results, it is obvious that the modified natural graphite material provided in the present application has a specific capacity greater than or equal to 348 mAh/g, a first coulombic efficiency greater than or equal to 90.2%, a 5 C/1 C discharge capacity retention rate greater than or equal to 94%, and a 1 C/1 C discharge capacity retention rate greater than or equal to 91%. Through the comparison of Examples 1-3 with Examples 4-5, it can be seen that, when the mass ratio of the natural graphite of the present application and the solidifying agent is 1: (0.05-1), the obtained material has better performances. It can be known through the comparison between Example 1 and Comparative Examples 1-5 that, when the selected raw material for preparation goes beyond the scope defined by the present application, although the specific capacity and the first coulombic efficiency are not significantly different, the modified natural graphite material obtained in the present application has better rate performance. Therefore, only the modified natural graphite material prepared with using the natural graphite defined in the present application and by the preparation method provided in the present application has better performance.

[0067] The above-mentioned embodiments are described to explain the detailed method of the present application, but are not intended to limit the present application. That is, the present application can be implemented not merely depending upon the above-mentioned detailed method. Those skilled in the art understand that any improvements to the present application, equivalent replacements of raw materials of the product of the present application, additions of auxiliary components, selections of specific methods, etc., shall fall within the protection scope and the disclosure of the present application.