Natural graphite-based modified composite material, preparation method therefor, and lithium ion battery comprising modified composite material

Abstract

A natural graphite-based modified composite material, a preparation method therefor, and a lithium ion battery comprising the modified composite material. The natural graphite-based modified composite material comprises natural graphite and non-graphitized carbon coated on the inner and outer surfaces of the natural graphite. The preparation method comprises: (1) subjecting spherical natural graphite to isotropic treatment; (2) performing granularity control and shaping treatment; (3) subjecting the inner surface and the outer surface of the material obtained in step (2) to simultaneous modification; and (4) performing carbonization, so as to obtain a natural graphite-based modified composite material.

Claims

1. A natural graphite-based modified composite material, wherein the modified composite material comprises natural graphite and non-graphitized carbon coated on the inner and outer surfaces of the natural graphite, wherein the modified composite material has a I.sub.002/I.sub.110 value of less than 39 as measured by XRD test analysis.

2. The modified composite material according to claim 1, wherein the non-graphitized carbon is converted from a modifier through carbonization treatment.

3. The modified composite material according to claim 2, wherein the modifier is a modifier having a softening point of 20° C.−300° C.

4. The modified composite material according to claim 3, wherein the modifier comprises any one selected from the group consisting of coal pitch, petroleum pitch, mesophase pitch, phenolic resin, epoxy resin, petroleum resin, coal tar and heavy oil, or a mixture of at least two selected therefrom.

5. The modified composite material according to claim 2, wherein the temperature for the carbonization treatment is 800° C. −3000° C.

6. The modified composite material according to claim 1, wherein the modified composite material has a particle size of 5 μm-30 μm.

7. A method for preparing the modified composite material according to claim 1, comprising the following steps: (1) isotropic treatment: subjecting natural spherical graphite to isotropic treatment; (2) granularity control and shaping treatment: subjecting the material after isotropic treatment to pulverization and classification treatment; (3) simultaneous modification of the inner surface and the outer surface of the material: adding the pulverized and classified material and a modifier to the reaction container, and heating to 30° C.−800° C. and keeping the temperature constant and stirring under an inert atmosphere; (4) conducting carbonization treatment under an inert atmosphere, so as to obtain the natural graphite-based modified composite material.

8. The method according to claim 7, wherein the isotropic treatment in step (1) is cold isostatic pressing.

9. The method according to claim 7, wherein the natural spherical graphite in step (1) has an average particle size of 3 μm-30 μm.

10. The method according to claim 7, wherein the processing pressure ranges from 10 MPa-500 MPa, during the isotropic treatment in step (1).

11. The method according to claim 7, wherein the material obtained after pulverization and classification treatment in step (2) has an average particle size of 3 μm-30 μm.

12. The method according to claim 7, wherein the modifier in step (3) is a modifier having a softening point of 20° C.−300° C.

13. The method according to claim 7, wherein the preparation mass ratio of the material after pulverization and classification treatment to the modifier is 1:(0.05-1) in step (3).

14. The method according to claim 7, wherein the method further includes a step of stirring before the heating in step (3), wherein the stirring time is 10 min.

15. The method according to claim 7, wherein the temperature for the carbonization treatment in step (4) is 800° C. to 3000° C.

16. The method according to claim 7, wherein the time for the carbonization treatment in step (4) is 1 h-10 h.

17. The method according to claim 7, wherein the method comprises the following steps: (1) isotropic treatment: subjecting natural spherical graphite having an average particle size of 3 μm-30 μm to cold isostatic pressing under a pressure of 10 MPa-500 MPa for 1 min-60 min to achieve isotropic treatment; (2) granularity control and shaping treatment: subjecting the material after isotropic treatment to pulverization and classification treatment so as to obtain the material having an average particle size of 3 μm-30 μm; (3) simultaneous modification of the inner surface and the outer surface of the material: adding the pulverized and classified material and the modifier to the reaction container, stirring under an inert atmosphere for 10 min first, and then heating to 30° C.−800° C. and keeping the temperature constant, stirring for 0-300 min excluding 0; (4) conducting carbonization treatment under an inert atmosphere at 800° C.−3000° C. for 1 h-10 h, so as to obtain the natural graphite-based modified composite material.

18. A lithium ion battery, wherein the lithium ion battery comprises the natural graphite-based modified composite material according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scanning electron microscope test chart of a natural graphite-based modified composite anode material in Example 1 of the present application.

DETAILED DESCRIPTION

(2) The present invention is described in detail with reference to specific examples. The following examples will help those skilled in the art to further understand the present application, but should not be regarded as a specific limitation to the present application. For those skilled in the art, the present application may include various modifications and changes.

(3) Unless otherwise specified, the methods in the following examples are conventional methods. The experimental materials used, unless otherwise specified, are used directly after being purchased from conventional biochemical reagent factories without any purification.

Example 1

(4) Natural spherical graphite (having an average particle size of 15 μm) was subjected to cold isostatic pressing at a processing pressure of 130 MPa for 5 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 110° C.) in the mass ratio of 85:15 were added to the stirring heater and stirred for 10 min, then heated to 300° C. and stirred at a constant temperature for 30 min, and subjected to carbonization treatment at 1200° C., to obtain a natural graphite-based modified composite anode material.

(5) Electrochemical Performance Test:

(6) The natural graphite-based composite material obtained in Example 1 was used as an anode active material. The mixture was uniformly mixed according to a mass ratio of active material: hydroxymethyl cellulose (CMC): styrene-butadiene rubber (SBR)=96.5:1.5:2, and then coated on the copper foil current collector. The anode sheet was obtained by drying for backup.

(7) Button cell test: First, the button cell test was performed on the obtained anode sheet. The cell was assembled in an argon glove box, wherein a lithium metal sheet was used as the anode; the electrolyte was 1 mol/L LiPF.sub.6+ethylene carbonate+methyl carbonate vinyl ester (LiPF.sub.6+EC+EMC); the separator was a polyethylene/propylene composite microporous membrane. The electrochemical performance test was performed on a battery tester. The charge and discharge voltage was 0.01-1.5 V, and the charge and discharge rate was 0.1 C. The cycle performance and electrode expansion rate are shown in Table 1.

(8) Finished battery test: The natural graphite-based composite material obtained in Example 1, a conductive agent, CMC and SBR were mixed in a mass ratio of 95:1.5:1.5:2 and coated on copper foil to obtain an anode sheet. The cathode active material LiCoO.sub.2, a conductive agent and polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 96.5:2:1.5, and then coated on an aluminum foil to obtain a cathode sheet. The electrolyte was 1 mol/L LiPF.sub.6+EC+EMC, and the separator was a polyethylene/propylene composite microporous membrane. It was charged and discharged at room temperature at a rate of 1 C. The voltage range was 3.0-4.25 V.

(9) FIG. 1 is a scanning electron microscope result of graphite particles in Example 1.

(10) In order to characterize the isotropy of the material, XRD test analysis was performed on the material, and the results are listed in Table 1. The tests in the following examples were the same.

Example 2

(11) Natural spherical graphite (having an average particle size of 10 μm) was subjected to cold isostatic pressing at a processing pressure of 100 MPa for 5 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 110° C.) in the mass ratio of 60:40 were added to the stirring heater and stirred for 10 min, then heated to 300° C. and stirred at a constant temperature for 30 min, and subjected to carbonization treatment at 1200° C., to obtain a natural graphite-based modified composite anode material.

(12) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(13) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 3

(14) Natural spherical graphite (having an average particle size of 8 μm) was subjected to cold isostatic pressing at a processing pressure of 80 MPa for 5 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 110° C.) in the mass ratio of 90:10 were added to the stirring heater and stirred for 10 min, then heated to 300° C. and stirred at a constant temperature for 30 min, and subjected to carbonization treatment at 1100° C., to obtain a natural graphite-based modified composite anode material.

(15) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(16) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 4

(17) Natural spherical graphite (having an average particle size of 15 μm) was subjected to cold isostatic pressing at a processing pressure of 50 MPa for 15 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 250° C.) in the mass ratio of 95:5 were added to the stirring heater and stirred for 10 min, then heated to 400° C. and stirred at a constant temperature for 30 minutes, and subjected to carbonization treatment at 2800° C., to obtain a natural graphite-based modified composite anode material.

(18) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(19) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 5

(20) Natural spherical graphite (having an average particle size of 15 μm) was subjected to cold isostatic pressing at a processing pressure of 30 MPa for 20 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 250° C.) in the mass ratio of 90:10 were added to the stirring heater and stirred for 10 min, then heated to 400° C. and stirred at a constant temperature for 30 min, and subjected to carbonization treatment at 1200° C., to obtain a natural graphite-based modified composite anode material.

(21) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(22) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 6

(23) Natural spherical graphite (having an average particle size of 15 μm) was subjected to pressing (in a pressor) at a processing pressure of 10 MPa for 30 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 160° C.) in the mass ratio of 80:20 were added to the stirring heater and stirred for 10 min, then heated to 300° C. and stirred at a constant temperature for 60 minutes, and subjected to carbonization treatment at 1200° C., to obtain a natural graphite-based modified composite anode material.

(24) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(25) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 7

(26) Natural spherical graphite (having an average particle size of 8 μm) was subjected to pressing (in a pressor) at a processing pressure of 10 MPa for 30 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 160° C.) in the mass ratio of 90:10 were added to the stirring heater and stirred for 10 min, then heated to 300° C. and stirred at a constant temperature for 30 minutes, and subjected to carbonization treatment at 1100° C., to obtain a natural graphite-based modified composite anode material.

(27) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(28) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 8

(29) Natural spherical graphite (having an average particle size of 15 μm) was subjected to pressing (in a pressor) at a processing pressure of 10 MPa for 60 min. The isostatically pressed product was pulverized to the approximate particle size of the raw material and classified. Then the classified sample and coal tar (having a softening point of 110° C.) in the mass ratio of 90:10 were added to the stirring heater and stirred for 10 min, then heated to 300° C. and stirred at a constant temperature for 60 minutes, and subjected to carbonization treatment at 3000° C., to obtain a natural graphite-based modified composite anode material.

(30) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(31) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

Comparative Example 1

(32) This comparative example is the raw natural spherical graphite in Example 1 having an average particle size of about 15 μm.

(33) The anode was prepared by the same method as in Example 1. The button cell and the finished battery were assembled, and the performance tests were performed. The obtained cycle performance and electrode expansion rate are listed in Table 1.

(34) The XRD test was performed in the same manner as in Example 1. The results obtained are shown in Table 1.

(35) TABLE-US-00001 TABLE 1 Particle size Capacity retention expansion rate D50 of the rate after 300 of electrode final sample I.sub.002/ cycles at room sheet after Samples (Micron) I.sub.110 temperature (%) 20 cycles Example 1 15.8 38.4 92.3 24.4% Example 2 10.3 38.7 92.4 25.1% Example 3 8.1 38.9 92.1 25.5% Example 4 15.5 39.0 92.0 24.9% Example 5 15.4 37.9 91.8 25.3% Example 6 15.6 38.6 92.5 24.6% Example 7 8.4 37.4 92.4 25.6% Example 8 15.3 38.2 91.7 25.0% Comp. Exp. 1 15.2 48.6 84.5 31.1%

(36) It can be seen from Table 1 that, based on the I.sub.002/I.sub.110, the capacity retention rate after 300 cycles at room temperature and the expansion rate of electrode sheet after 20 cycles in Examples 1-8, the natural graphite-based modified composite materials prepared in Examples 1-8 have a significantly reduced 1002/1110 value compared to the raw material natural spherical graphite, indicating that the isotropy degree of the composite material after synthesis has been significantly improved. The corresponding capacity retention rate of this type of material after 300 cycles at normal temperature has increased by more than 7%, and the expansion rate of electrode sheet after 20 cycles has been reduced by more than 5%.

(37) The applicant states that the present application discloses the detailed methods by the above examples, but the present application is not limited to the detailed methods described above, that is, it does not mean that the present application must rely on the above detailed methods to implement.