POSITIVE ELECTRODE ACTIVE MATERIAL WITH CORE-SHELL STRUCTURE AND PREPARATION METHOD THEREOF, POSITIVE ELECTRODE PLATE, SECONDARY BATTERY, BATTERY MODULE, BATTERY PACK, AND ELECTRIC APPARATUS

1 . A positive electrode active material with a core-shell structure, comprising a core and a shell enveloping the core, wherein

the core comprises Li m A x Mn 1-y B y P 1-z C z O 4-n D n , wherein m is any value selected in a range from 0.5 to 1.2;

x is any value selected in a range from 0.001 to 0.5;

y is any value selected in a range from 0.001 to 0.5;

z is any value selected in a range from 0.001 to 0.2;

n is any value selected in a range from 0.001 to 0.5;

A is one or more elements selected from of Zn, Al, Na, K, Mg, Nb, Mo, and W;

B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;

C is one or more elements selected from B, S, Si, and N;

D is one or more elements selected from S, F, Cl, and Br; and

the shell comprises a first coating layer covering the core and a second coating layer covering the first coating layer; and, wherein

the first coating layer comprises a crystalline pyrophosphate M a P 2 O 7 and an oxide M′ b O c , wherein a is greater than 0 and less than or equal to 4;

b is greater than 0 and less than or equal to 2;

c is greater than 0 and less than or equal to 5; M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; and

M′ is one or more elements selected from alkali metals, alkaline earth metals, transition metals, group IIIA elements, group IVA elements, lanthanides, and Sb; and

the second coating layer comprises carbon.

2 . The positive electrode active material according to claim 1 , wherein in the core,

a ratio of 1-y to y is 1 to 4; and/or,

a ratio of m to x is 1 to 1200.

3 . The positive electrode active material according to claim 1 , wherein

x is any value in the range from 0.001 to 0.005;

y is any value in the range from 0.01 to 0.5;

z is any value in the range from 0.001 to 0.005; and/or,

n is any value in the range from 0.001 to 0.005.

4 . The positive electrode active material according to claim 1 , wherein

a coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight.

5 . The positive electrode active material according to claim 1 , wherein

a weight ratio of the pyrophosphate to the oxide in the first coating layer is 1:3 to 3:1.

6 . The positive electrode active material according to claim 1 , wherein

the pyrophosphate in the first coating layer has an interplanar spacing of 0.293-0.326 nm and an included angle of 26.41°−32.57° for a (111) crystal orientation.

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

a crystallinity of the pyrophosphate in the first coating layer is 10% to 100%.

8 . The positive electrode active material according to claim 1 , wherein

a coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight.

9 . The positive electrode active material according to claim 1 , wherein

A is any element selected from Zn, Al, Na, K, Mg, Nb, Mo, and W;

B is at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;

C is any element selected from B, S, Si, and N, and optionally, C is S; and/or

D is any element selected from S, F, Cl, and Br, and optionally, D is F.

10 . The positive electrode active material according to claim 1 , wherein

the positive electrode active material has a Li/Mn antisite defect concentration of 4% or less.

11 . The positive electrode active material according to claim 1 , wherein

a lattice change rate of the positive electrode active material before and after complete lithium deintercalation and intercalation is 9.8% or less.

12 . The positive electrode active material according to claim 1 , wherein

a valence state of surface oxygen of the positive electrode active material is −1.55 or less.

13 . The positive electrode active material according to claim 1 , wherein

a compacted density of the positive electrode active material under 3 tons is 1.89 g/cm 3 or more.

14 . A preparation method of positive electrode active material, comprising:

providing a core material: the core comprising Li m A x Mn 1-y B y P 1-z C z O 4-n D n , wherein m is any value selected in a range from 0.5 to 1.2;

x is any value selected in a range from 0.001 to 0.5;

y is any value selected in a range from 0.001 to 0.5;

z is any value selected in a range from 0.001 to 0.2;

n is any value selected in a range from 0.001 to 0.5;

A is one or more elements selected from of Zn, Al, Na, K, Mg, Nb, Mo, and W;

B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;

C is one or more elements selected from B, S, Si, and N;

D is one or more elements selected from S, F, Cl, and Br;

providing powder comprising pyrophosphate M a P 2 O 7 and a suspension comprising a carbon source and an oxide M′ b O c ; and

mixing the core material, the powder comprising pyrophosphate M a P 2 O 7 , and the suspension comprising the carbon source and the oxide M′ b O c , followed by sintering, to obtain a positive electrode active material, wherein

a is greater than 0 and less than or equal to 4;

b is greater than 0 and less than or equal to 2;

c is greater than 0 and less than or equal to 5;

M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; and

M′ is one or more elements selected from alkali metals, alkaline earth metals, transition metals, group IIIA elements, group IVA elements, lanthanides, and Sb; and, wherein the positive electrode active material has a core-shell structure, comprising a core and a shell enveloping the core, the core comprising Li m A x Mn 1-y B y P 1-z C z O 4-n D n , and the shell comprising a first coating layer covering the core and a second coating layer covering the first coating layer, wherein the first coating layer comprises a crystalline pyrophosphate M a P 2 O 7 and an oxide M′ b O c , and the second coating layer comprises carbon.

15 . The preparation method according to claim 14 , wherein providing the core material comprises:

mixing a manganese source, a source of element B, an acid, and an optional solvent to obtain a mixture; and

mixing the mixture with a lithium source, a phosphorus source, a source of element A, a source of element C, and a source of element D, followed by drying and sintering, to obtain a core material comprising Li m A x Mn 1-y B y P 1-z C z O 4-n D n .

16 . The preparation method according to claim 14 , wherein the source of element A is one or more selected from elementary substance, oxides, phosphates, oxalates, carbonates, and sulfates of element A;

the source of element B is one or more selected from elementary substance, oxides, phosphates, oxalates, carbonates, and sulfates of element B;

the source of element C is one or more selected from sulfates, borates, nitrates, and silicates of element C; and/or,

the source of element D is one or more selected from elementary substance and ammonium salts of element D.

17 . The preparation method according to claim 14 , wherein

the powder comprising pyrophosphate M a P 2 O 7 is prepared by the following:

mixing a source of element M, a phosphorus source, and an optional solvent to obtain a mixture, adjusting the pH of the mixture to 4-6, continuing the mixing, and then carrying out drying and sintering.

18 . The preparation method according to claim 14 , wherein

during the coating, the sintering temperature is 500° C.-800° C. and the sintering time is 4-10 h.

19 . A positive electrode plate comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material according to claim 1 , and a percentage of the positive electrode active material in the positive electrode film layer is 10% or more by weight based on a total weight of the positive electrode film layer.

20 . A secondary battery, comprising the positive electrode active material according to claim 1 .