Method for determining fast charge performance of a negative electrode plate and method for designing a negative electrode plate

1. A method for determining fast charge performance of a negative electrode plate, the negative electrode plate comprising a negative active material, a conductive additive, and a binder, characterized in that the method comprises:

determining fast charge performance of the negative electrode plate according to an empirical formula A=CW*(PD−1)*(OL−D50+D90)/(w*100), wherein:

in case A<16, the negative electrode plate is applicable to a fast charge battery at a constant current rate of 10 C or higher;

in case 16<A<85, the negative electrode plate is applicable to a fast charge battery at a constant current rate of 4 C-10 C;

in case 85<A<110, the negative electrode plate is applicable to a fast charge battery at a constant current rate of 2 C-4 C; and

in case A>110, the negative electrode plate is applicable to a fast charge battery at a constant current rate of lower than 2 C;

and in the empirical formula,

CW represents the coating weight CW of the negative electrode plate, expressed in mg/cm″:

PD represents the press density of coating on the negative electrode plate, expressed in g/cm}:

OI represents the orientation index of the negative electrode plate as measured by using X-ray powder diffractometer according to X-ray diffraction analysis method and lattice parameter determination method of graphite, and calculating according to formula OI=C004/C110, wherein C004 was peak area of 004 characteristic diffraction peak and C110 was peak area of 110 characteristic diffraction peak;

DS50 represents the particle size which corresponds to 50% of the cumulative volume percentage of negative active material in the negative electrode plate, expressed in μm;

D90 represents the particle size which corresponds to 90% of the cumulative volume percentage of the negative active material in the negative electrode plate, expressed in μm;

D50 and D90 are measured using a laser diffraction particle size distribution measuring instrument according to the laser diffraction method for measuring particle size distribution; and

w represents the mass percentage of active carbon atoms in the negative active material of the negative electrode plate, relative to the mass of the negative active material, and w is measured according to the description; and

wherein the negative active material of the negative electrode plate fulfills the conditions that w is from 1% to 10% and D50 is from 5 μm to 15 μm, and wherein the negative active material of the negative electrode plate comprises one or more of artificial graphite and natural graphite; the weight percentage of graphite material in the negative active material is higher than 90%; and the coating weight CW of the negative electrode plate is further controlled in the range of from 5 mg/cm 2 to 13 mg/cm 2 .

2. The method according to claim 1 , wherein w is 1.6% to 4% and D50 is from 6 μm to 13 μm.

3. The method according to claim 1 , wherein the negative active material further comprises one or more of soft carbon, hard carbon, and silicon-based material.

4. A method for designing a negative electrode plate in a last charge battery, the negative electrode plate comprising a negative active material, a conductive additive, and a binder,

characterized in that the method comprises:

1) screening a negative active material for a fast charge battery, comprising:

(1) determining the mass percentage w of active carbon atoms in the negative active material as measured according to the description;

(2) determining the particle size D50 corresponding to 50% of the cumulative volume percentage of the negative active material, expressed in μm;

(3) determining the particle size D90 which corresponds to 90% of the cumulative volume percentage of the negative active material, expressed in μm;

(4) selecting the negative active material in which the mass percentage w is from 1% to 10% and DS50 is from 5 μm to 15 μm;

D50 and D90 are measured using a laser diffraction particle size distribution measuring instrument according to the laser diffraction method for measuring particle size distribution;

I) determining the process parameters of the negative electrode plate, comprising:

(i) dispersing the negative active material obtained from the above screening and an optional auxiliary agent in a solvent to form a uniform negative electrode slurry, followed by coating a negative electrode current collector with the negative electrode slurry, and after drying the coated negative electrode plate, determining the coating weight CW of the negative electrode plate, expressed in mg/cm″; and

(i1) cold pressing the negative electrode plate obtained from step (i), followed by determining the press density PD of coating on the negative electrode plate (in g/cm*) and the orientation index OI value of the negative electrode plate, wherein the orientation index OI value is measured by using X-ray powder diffractometer according to X-ray diffraction analysis method and lattice parameter determination method of graphite, and calculating according to formula OI=C004/C110, wherein C004 was peak area of 004 characteristic diffraction peak and C110 was peak area of 110 characteristic diffraction peak; and

III) determining fast charge performance of the negative electrode plate according to claim 1 ; and

wherein the negative active material of the negative electrode plate comprises one or more of artificial graphite and natural graphite; the weight percentage of graphite material in the negative active material is higher than 90%; and in step ID, the coating weight CW of the negative electrode plate is further controlled in the range of from 5 mg/cm 2 to 13 mg/cm 2 .

5. The method according to claim 4 , wherein w in step (4) is from 1.6% to 4% and D50 is from 6 μm to 13 μm.

6. The method according to claim 4 , wherein the negative active material of the negative electrode plate further comprises one or more of soft carbon, hard carbon, and silicon-based material.

7. The method according to claim 4 , wherein, in step I), the selected negative active material further has a D90 of from 8 μm to 23 μm.

8. The method according to claim 4 , wherein, in step I), the selected negative active material further has a D90 of from 10 μm to 18 μm.

9. The method according to claim 4 , wherein in step II), the coating weight CW of the negative electrode plate is further controlled in the range of from 8 mg/cm 2 to 12 mg/cm 2 .

10. The method according to claim 4 , wherein in step II), the coating weight CW of the negative electrode plate is further controlled in the range of from 8.4 mg/cm 2 to 11.1 mg/cm 2 .

11. The method according to claim 4 , wherein in step II), the press density PD of coating on the negative electrode plate is further controlled in the range of from 1.4 g/cm 3 to 1.65 g/cm 3 .

12. The method according to claim 4 , wherein in step II), the press density PD of coating on the negative electrode plate is further controlled in the range of from 1.4 g/cm 3 to 1.55 g/cm 3 .

13. The method according to claim 4 , wherein in step II), the orientation index OI value of the negative electrode plate is further controlled in the range of from 8 to 30.

14. The method according to claim 4 , wherein in step II), the orientation index OI value of the negative electrode plate is further controlled in the range of from 12 to 24.

15. The method according to claim 4 , wherein the method further comprises:

IV) changing performance parameters of the negative active material and/or the process parameters of the negative electrode plate to adjust A value, so that the ratio performance of the negative electrode plate meets design requirements.