Positive electrode sheet, secondary battery, battery module, battery pack and electrical apparatus
A positive electrode sheet, a secondary battery, a battery module, a battery pack and an electrical apparatus are described. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector and having a single-layer or multi-layer structure. When the positive electrode film layer is of the single-layer structure, at least one positive electrode film layer comprises both a first positive electrode active material and a second positive electrode active material with a chemical formula of Li a A x Mn 1-y R y P 1-z C z O 4-n D n ; and/or, when the positive electrode film layer is of the multi-layer structure, at least one layer of the at least one positive electrode film layer includes both a first and second positive electrode active material. The secondary battery made of the positive electrode sheet has high energy density and high battery cell rate performance.
1 . A positive electrode sheet, comprising a positive electrode current collector, a positive electrode film layer I and a positive electrode film layer II, wherein the positive electrode film layer I is on a surface of the positive electrode current collector and the positive electrode film layer II is on the opposite surface of the positive electrode current collector; wherein:
a) the positive electrode film layer I is a single layer structure and the positive electrode film layer II is a single layer structure; or
b) the positive electrode film layer I is a two layer structure and the positive electrode film layer II is a single layer structure; or
c) the positive electrode film layer I is a single layer structure and the positive electrode film layer II is a two layer structure; or
d) the positive electrode film layer I is a two layer structure and the positive electrode film layer II is a two layer structure;
wherein one layer of the positive electrode film layer I comprises a first positive electrode active material that comprises particles selected from one or more of Li a A x Mn 1-y R y P 1-z C z O 4-n D n ;
wherein,
A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W,
R comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge,
C comprises one or more elements selected from the group consisting of B, S, Si and N,
D comprises one or more elements selected from the group consisting of S, F, Cl and Br,
a is selected from a range of 0.9 to 1.1, x is selected from a range of 0.001 to 0.1, y is selected from a range of 0.001 to 0.5, z is selected from a range of 0.001 to 0.1, and n is selected from a range of 0.001 to 0.1;
wherein
one layer of the positive electrode film layer II comprises a second positive electrode active material that comprises particles selected from one or more of the group consisting of LiNi b Co c Mn (1-b-c) O 2 , LiNi b Co c Al (1-b-c) O 2 and LiCoO 2 ; wherein b is independently selected from 0.3-0.9, and a sum of b and c is independently selected from 0.3-0.9;
wherein when the positive electrode film layer I, the positive electrode film layer II or both comprise two layers, one layer comprises the first positive electrode active material and the other layer comprises the second positive electrode active material.
2 . The positive electrode sheet according to claim 1 , wherein a mass ratio of the first active material in the positive electrode film layer I to the second active material in the positive electrode film layer II is 1:7 to 7:1.
3 . The positive electrode sheet according to claim 1 , wherein in the first positive electrode active material,
R is selected from at least two elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge;
A is Mg or Nb, and/or,
C is S, and/or,
D is F.
4 . The positive electrode sheet according to claim 3 , wherein in the first positive electrode active material,
R is at least two elements selected from the group consisting of Ti, V, Fe, Mg and Co.
5 . The positive electrode sheet according to claim 1 , wherein in the first positive electrode active material, x is selected from a range of 0.001-0.005; and/or, y is selected from a range of 0.01 to 0.5; and/or, z is selected from a range of 0.001 to 0.005; and/or, n is selected from a range of 0.001 to 0.005; and/or, a ratio of (1-y) to y is selected from 1-4; and/or, a ratio of a to x is selected from 9-1100.
6 . The positive electrode sheet according to claim 1 , wherein in the second positive electrode active material,
a ratio of b to (1-b-c) to c in LiNi b Co c Mn (1-b-c) O 2 is 5:2:3 or 3:1:1 or 8:1:1; or,
a ratio of b to c to (1-b-c) in LiNi b Co c Al (1-b-c) O 2 is 5:2:3 or 3:1:1 or 8:1:1.
7 . The positive electrode sheet according to claim 1 , wherein a sum of mass of the first positive electrode active material and the second positive electrode active material accounts for 88%-98.7% of the mass of the positive electrode sheet.
8 . The positive electrode sheet according to claim 1 , wherein a lattice change rate of the first positive electrode active material is about 2.2 to 8%.
9 . The positive electrode sheet according to claim 1 , wherein a Li/Mn antisite defect concentration of the first positive electrode active material is about 0.4 to 2%.
10 . The positive electrode sheet according to claim 1 , wherein surface oxygen valence of the first positive electrode active material is about −1.82- to −1.98.
11 . The positive electrode sheet according to claim 1 , wherein a compacted density of the first positive electrode active material at 3T is 2.0 g/cm 3 or more.
12 . The positive electrode sheet according to claim 1 , wherein a surface of the particles of the first positive electrode active material is further coated with carbon.
13 . A secondary battery, comprising the positive electrode sheet according to claim 1 .
14 . A battery module, comprising the secondary battery according to claim 13 .
15 . A battery pack, comprising the battery module according to claim 14 .
16 . An electrical apparatus, comprising at least one of the secondary battery according to claim 13 .