Secondary battery, battery module, battery pack, and electrical device

A secondary battery, wherein the secondary battery comprises a positive electrode plate, a negative electrode plate, and a separator between the positive electrode plate and the negative electrode plate:

• wherein the positive electrode plate comprises a positive current collector, a first positive active material layer distributed on one side of the positive current collector and a second positive active material layer distributed on another side of the positive current collector;
• wherein the negative electrode plate comprises a negative current collector, a first negative active material layer distributed on one side of the negative current collector and opposite to the second positive active material layer and a second negative active material layer distributed on another side of the negative current collector;
• a coating weight of a positive active material per unit area of the first positive active material layer is CW1 and a coating weight of the positive active material per unit area of the second positive active material layer is CW2;
• wherein 6.5 mg/cm2≤CW1≤32.5 mg/cm2, 6.5 mg/cm2≤CW2≤32.5 mg/cm2 and 0.5≤CW1/CW2<1;
• wherein the first negative active material layer and the second negative active material layer are different in composition and
• wherein, a resistance of the first positive active material layer is R1, a resistance of the second positive active material layer is R2, a resistance of the first negative active material layer is R3, a resistance of the second negative active material layer is R4, and the resistances R1, R2, R3, and R4 are Ohmic resistances and satisfy the following relationships:
• R2>R1;
• (1)
• R3≥R4;
• (2)
• 0<(R1+R4)/(R2+R3)≤1;
• and (3)
• R1/R2=A×R4/R3, wherein A is 0.8 to 1.2, (4)
• wherein R1 is 0.1Ω to 20Ω, R2 is 0.15Ω to 22Ω, R3 is 0.7 mΩ to 40 mΩ, and
• R4 is 0.5 mΩ to 35 mΩ.