Negative electrode active material and method for preparation thereof, secondary battery, and apparatus including secondary battery

1. A negative electrode active material, comprising a core and a coating layer covering a surface of the core, wherein the core comprises artificial graphite, the coating layer comprises amorphous carbon, the negative electrode active material has a surface area average particle size D(3,2) denoted as A, the negative electrode active material has a surface area average particle size D(3,2) denoted as B after powder compaction under a pressure of 20 kN, and the negative electrode active material satisfies: 72%≤B/A×100%≤82%.

2. The negative electrode active material according to claim 1 , wherein the negative electrode active material satisfies: 74%≤B/A×100%≤80%.

3. The negative electrode active material according to claim 1 , wherein 9 μm≤A≤15 μm, and preferably, 11 μm≤A≤13 μm.

4. The negative electrode active material according to claim 1 , wherein the negative electrode active material before powder compaction has a volume average particle size D v 50 satisfying: 10 μm≤D v 50≤16 μm, and preferably, 12 μm≤D v 50≤14 μm.

5. The negative electrode active material according to claim 1 , wherein the negative electrode active material before powder compaction has a particle size distribution (D v 90−D v 10)/D v 50 satisfying: 1.0≤(D v 90−D v 10)/D v 50≤1.35, and preferably, 1.15≤(D v 90−D v 10)/D v 50≤1.25.

6. The negative electrode active material according to claim 1 , wherein the negative electrode active material before powder compaction has a volume particle size distribution D v 90 satisfying: 18 μm≤D v 90≤26 μm, and preferably, 20 μm≤D v 90≤24 μm.

7. The negative electrode active material according to claim 1 , wherein the negative electrode active material before powder compaction has a tap density of from 0.9 g/cm 3 to 1.15 g/cm 3 , and preferably from 0.95 g/cm 3 to 1.05 g/cm 3 .

8. The negative electrode active material according to claim 1 , wherein the negative electrode active material has a graphitization degree of from 90% to 96%, and preferably from 92% to 95%.

9. A secondary battery, comprising a negative electrode plate comprising the negative electrode active material according to claim 1 .

10. An apparatus, comprising the secondary battery according to claim 9 .

11. A method for preparation of the negative electrode active material according to claim 1 , comprising the following steps of:

a) providing a coke raw material, wherein the coke raw material has a volume average particle size D v 50 of from 7 μm to 12 μm, and the coke raw material has a volatile content C 1 satisfying 1%≤C 1 ≤12%, and preferably, 5%≤C 1 ≤9%;

b) shaping and grading the coke raw material to obtain a precursor with a particle size distribution (D v 90−D v 10)/D v 50 of from 1.0 to 1.55;

c) granulating the precursor to obtain a granulated product, wherein a binder added during the granulating has an amount C 2 satisfying 0%≤C 2 ≤16%, and the C 1 and the C 2 satisfy 10%≤C 1 +C 2 ≤16%, and preferably, 12%≤C 1 +C 2 ≤14%;

d) graphitizing the granulated product at a temperature of from 2800° C. to 3200° C. to obtain artificial graphite;

e) coating the artificial graphite with an organic carbon source, performing heat treatment to form an amorphous carbon coating layer on at least a part of the surface of the artificial graphite, to obtain the negative electrode active material, wherein the organic carbon source added during the coating has an amount C 3 , and the C 3 , the C 1 and the C 2 satisfy 13%≤C 1 +C 2 +C 3 ≤18%, and 1.5%≤C 3 ×carbon residue rate≤3.5%;

wherein the negative electrode active material has a surface area average particle size D(3,2) denoted as A, the negative electrode active material has a surface area average particle size D(3,2) denoted as B after powder compaction under a pressure of 20 kN, and the negative electrode active material satisfies: 72%≤B/A×100%≤82%.

12. The method according to claim 11 , wherein the coke raw material further satisfies at least one of the following:

1) the coke raw material comprises one or more of petroleum-based non-needle coke and petroleum-based needle coke; preferably, the coke raw material comprises petroleum-based green coke; and

2) the coke raw material has a particle size distribution (D v 90−D v 10)/D v 50 of from 1.2 to 1.7.