The present disclosure provides a lithium ion battery, a battery pack, an electric vehicle and an energy storage device. The lithium ion battery includes a casing and an electrode core packaged in the casing. The electrode core includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer on the positive electrode current collector. Among the positive electrode current collector, the positive electrode material layer, the negative electrode sheet, and the separator, the one with the lowest melting point is defined as an effective component. The effective component meets: 1 ≤ d 2 ⁢ ρ ⁢ C p × ( 1.12 nL ( n + 1 ) ⁢ W ) ≤ 500.