Positive electrode plate, secondary battery, battery module, battery pack, and electrical device

1. A positive electrode plate, comprising:

a positive current collector; and

a positive active material layer disposed on at least one surface of the positive current collector,

wherein the positive active material layer comprises a first active material layer and a second active material layer that are sequentially stacked in a direction away from the surface, the first active material layer comprises a first composite particle, the first composite particle comprises a first lithium iron phosphate particle and a first carbon layer that coats a surface of the first lithium iron phosphate particle, the second active material layer comprises a second composite particle, the second composite particle comprises a second lithium iron phosphate particle and a second carbon layer that coats a surface of the second lithium iron phosphate particle, and

wherein a graphitization degree of the first composite particle is 0.3 to 0.5, and a graphitization degree of the second composite particle is 0.1 to 0.2.

2. The positive electrode plate according to claim 1 , wherein

the first composite particle comprises a primary particle,

the second composite particle comprises a secondary particle formed by aggregating a plurality of primary particles, and an average particle diameter Ds of the first composite particle is less than an average particle diameter D 50 of the second composite particle.

3. The positive electrode plate according to claim 2 , wherein

the average particle diameter D 50 of the first composite particle is 1 μm to 4 μm; and/or

the average particle diameter D 50 of the second composite particle is 6 μm to 12 μm.

4. The positive electrode plate according to claim 2 , wherein the secondary particle is of a spherical or quasi-spherical morphology.

5. The positive electrode plate according to claim 1 , wherein

a specific surface area of the first composite particle is 10 m 2 /g to 15 m 2 /g; and/or

a specific surface area of the second composite particle is 5 m 2 /g to 10 m 2 /g.

6. The positive electrode plate according to claim 1 , wherein

a ratio of a coating weight CW1 of the first active material layer to a coating weight CW2 of the second active material layer is 0.8 to 1.2.

7. The positive electrode plate according to claim 6 , wherein

the coating weight CW1 of the first active material layer satisfies 0.115 mg/cm 2 ≤ CW1≤ 0.195 mg/cm 2 ; and/or

the coating weight CW2 of the second active material layer satisfies 0.115 mg/cm 2 ≤ CW2≤ 0.195 mg/cm 2 .

8. The positive electrode plate according to claim 1 , wherein

the first active material layer comprises a first conductive agent, and, on a basis that a total weight of the first active material layer is 100%, a mass percent of the first conductive agent is A; and

the second active material layer comprises a second conductive agent, and, on a basis that a total weight of the second active material layer is 100%, a mass percent of the second conductive agent is B, wherein

A<B, and 1 wt %≤B−A≤3 wt %.

9. The positive electrode plate according to claim 1 , wherein

a powder compaction density of the first active material layer under a pressure of 600 MPa is 2.4 g/cc to 2.65 g/cc; and/or

a powder compaction density of the second active material layer under a pressure of 600 MPa is 2.2 g/cc to 2.45 g/cc.

10. A secondary battery, comprising a positive electrode plate, a separator, and a negative electrode plate, wherein the positive electrode plate is the positive electrode plate according to claim 1 .

11. A battery module, comprising the secondary battery according to claim 10 .

12. A battery pack, comprising the battery module according to claim 11 .

13. An electrical device, comprising the battery pack according to claim 12 .