Secondary battery, battery module, battery pack, and electric apparatus

A secondary battery, comprising a positive electrode plate and a non-aqueous electrolyte, wherein:

• the positive electrode plate comprises a positive electrode active material with a core-shell structure, the positive electrode active material comprising a core and a shell enveloping the core;
• a chemical formula of the core is Li1+xMn1−yAyP1−zRzO4, wherein x is any value in the range of −0.100 to 0.100, y is any value in the range of 0.001-0.500, z is any value in the range of 0.001-0.100, A is one or more elements selected from a group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, R is one or more elements selected from a group consisting of B, Si, N, and S, and values of x, y, and z satisfy the following condition:
• making the entire core electrically neutral;
• the shell comprises a first coating layer enveloping the core, a second coating layer enveloping the first coating layer, and a third coating layer enveloping the second coating layer;
• wherein
• the first coating layer comprises a crystalline pyrophosphate LiaMP2O7 and/or Mb(P2O7)c, wherein 0≤a≤2, 1≤b≤4, 1≤c≤6, values of a, b, and c satisfy the following condition:
• making the crystalline pyrophosphate LiaMP2O7 and/or Mb(P2O7)c electrically neutral, and each M in the crystalline pyrophosphate LiaMP2O7 and/or Mb(P2O7), is independently one or more elements selected from a group consisting of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al,
• the second coating layer comprises a crystalline phosphate XPO4, wherein X is one or more elements selected from a group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and
• the third coating layer is carbon;
• and
• the non-aqueous electrolyte comprises a first additive, the first additive comprising one or more selected from a group consisting of compounds represented by formula 1 and compounds represented by formula 2,
• wherein:
• R1 and R2 each independently represent any one of a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group;
• and
• R3, R4, R5, and R6 each independently represent any one of a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, or a C2-C6 alkynyloxy group, and R3, R4, R5, and R6 do not all represent a hydrogen atom.