NEGATIVE ELECTRODE ACTIVE MATERIAL AND PREPARATION METHOD THEREOF, SECONDARY BATTERY, AND ELECTRIC APPARATUS

1 . A negative electrode active material, comprising:

a core material; and

a first coating layer provided on at least part of a surface of the core material, wherein the first coating layer comprises a porous carbon material and nano silicon-based particles, and the nano silicon-based particles are embedded into pore structures of the porous carbon material.

2 . The negative electrode active material according to claim 1 , wherein a median particle size by volume D v 50 of the core material is denoted as D0, a median particle size by volume D v 50 of the core material after a 300 MPa pressure test is denoted as D1, and the core material satisfies D0/(D0−D1)≥3.

3 . The negative electrode active material according to claim 1 , wherein the core material comprises at least one of graphite, hard carbon, meso-carbon microbeads, elemental metal, metal alloy, metal compound, and non-metal compound.

4 . The negative electrode active material according to claim 1 , wherein the core material satisfies at least one of the following conditions (1)-(4):

(1) a number of the core materials coated within one first coating layer is ≤3;

(2) a median particle size by volume D v 50 of the core material is ≤10 μm, and optionally 2.0 μm-7.0 μm;

(3) a span of the core material is 0.7-1.2; and

(4) a porosity of the core material is ≤5%.

5 . The negative electrode active material according to claim 1 , wherein a porosity of the porous carbon material is ≥20%;

an average pore size of the porous carbon material is ≥1 nm;

an average pore size of the porous carbon material is greater than a median particle size by volume D v 50 of the nano silicon-based particles; and/or

a median particle size by volume D v 50 of the nano silicon-based particles is 1 nm-100 nm.

6 . The negative electrode active material according to claim 1 , wherein the porous carbon material further comprises an oxygen-containing group bonded to carbon of the porous carbon material.

7 . The negative electrode active material according to claim 1 , wherein

a mass percentage of silicon in the first coating layer is ≥20%;

a mass percentage of carbon in the first coating layer is ≥30%; and/or

a mass percentage of oxygen in the first coating layer is ≤15%.

8 . The negative electrode active material according to claim 1 , wherein a thickness of the first coating layer is ≥0.5 μm.

9 . The negative electrode active material according to claim 1 , wherein the negative electrode active material further comprises a second coating layer, the second coating layer is provided on at least part of a surface of the first coating layer, and the second coating layer comprises a conductive material.

10 . The negative electrode active material according to claim 1 , wherein a thickness of the second coating layer is ≥20 nm; and/or

the conductive material includes at least one of a conductive carbon material and a conductive polymer.

11 . The negative electrode active material according to claim 1 , wherein a powder resistivity of the negative electrode active material under a pressure of 4 MPa is denoted as R 4 , a powder resistivity of the negative electrode active material under a pressure of 16 MPa is denoted as R 16 , and the negative electrode active material satisfies R 4 /R 16 ≤4; and/or

R 4 ≤2 Ω·cm.

12 . The negative electrode active material according to claim 1 , wherein the negative electrode active material satisfies at least one of the following conditions I-III:

I. a porosity of the negative electrode active material is ≤30%;

II. a median particle size by volume D v 50 of the negative electrode active material is 3 μm-15 μm; and

III. a specific surface area SSA of the negative electrode active material is 0.5 m 2 /g-10 m 2 /g.

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

S 1 . providing a core material;

S 2 . applying a porous carbon material onto at least part of a surface of the core material; and

S 3 . depositing nano silicon-based particles into pore structures of the porous carbon material using a chemical vapor deposition method to form the first coating layer.

14 . The preparation method according to claim 13 , wherein step S 2 comprises:

applying a carbon material precursor onto at least part of the surface of the core material using a spray drying method, followed by carbonization, to form the porous carbon material.

15 . The preparation method according to claim 14 , wherein in S 2 ,

during the spray drying, a liquid flow rate is controlled to be 1 L/h-5 L/h, a gas flow rate is controlled to be 50 L/min-120 L/min, a drying temperature is controlled to be 150° C.-200° C., and an outlet air temperature is controlled to be 80° C.-130° C.; and/or

a condition for the carbonization is: carbonization is performed at 800° C.-2000° C. under nitrogen protection for 2 h-4 h.

16 . The preparation method according to claim 13 , wherein in step S 3 , deposition gas for a chemical vapor deposition is a mixture of silane gas and H 2 , wherein a volume percentage of the silane gas is 2%-20%, an inlet gas flow rate of the mixture is 100 mL/min-400 mL/min, a reaction temperature is 400° C.-1000° C., and a deposition reaction time is 2 h-10 h; wherein

optionally, the silane gas comprises at least one of monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, and trichlorosilane.

17 . The preparation method according to claim 13 , further comprising the following step:

S 4 . applying a second coating layer onto a surface of the first coating layer, wherein the second coating layer comprises a conductive material.

18 . The preparation method according to claim 17 , wherein in step S 4 , a second coating layer is formed using chemical vapor deposition, and deposition gas for the chemical vapor deposition is a mixture of C 2 H 2 and N 2 , wherein a volume percentage of C 2 H 2 is 2%-20%, an inlet gas flow rate is 100 mL/min-300 mL/min, a reaction temperature is 800° C.-1000° C., and a deposition reaction time is 0.5 h-2 h.

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

20 . An electric apparatus, comprising the secondary battery according to claim 19 .