POSITIVE ELECTRODE ACTIVE MATERIAL 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 covering the core, wherein:

the core comprises Li 1+x Mn 1−y A y P 1−z R z O 4 , wherein:

x is any value in a range from −0.100 to 0.100;

y is any value in a range from 0.001 to 0.500;

z is any value in a range from 0.001 to 0.100;

A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and

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

the shell comprises 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 a crystalline 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:

a ratio of y to 1−y in the core is 1:10 to 10:1.

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

a ratio of z to 1−z in the core is 1:9 to 1:999.

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, based on a weight of the core.

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

A is at least two elements selected from Fe, Ti, V, Ni, Co, and Mg.

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

the positive electrode active material has a Li/Mn antisite defect concentration of 5.1% 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 7.5% 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 −1.83 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 2.0 g/cm 3 or more.

14 . 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 .

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

16 . A battery module, comprising the secondary battery according to claim 15 .

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

providing a core material, the core material comprising Li 1+x Mn 1−y A y P 1−z R z O 4 , wherein:

x is any value in a range from −0.100 to 0.100;

y is any value in a range from 0.001 to 0.500;

z is any value in a range from 0.001 to 0.100;

A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and

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

performing coating, comprising:

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

mixing the core material, the powder, and the suspension for 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;

wherein the positive electrode active material has a core-shell structure, comprising a core and a shell covering the core, the core comprising Li 1+x Mn 1−y A y P 1−z R z O 4 , and the shell comprising 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 a crystalline oxide M′ b O c , and the second coating layer comprises carbon.

18 . The preparation method according to claim 17 , wherein providing the core material comprises:

mixing a manganese source, a source of element A, and an acid to obtain a mixture; and

mixing the mixture with a lithium source, a phosphorus source, and a source of element R for sintering under protection of an inert gas to obtain the core material comprising.

19 . The preparation method according to claim 17 , wherein the powder comprising pyrophosphate M a P 2 O 7 is prepared by:

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

20 . The preparation method according to claim 17 , wherein:

sintering during coating step is performed at a sintering temperature of 500-800° C. for a sintering time of 4-10 h.