A secondary battery and an electrochemical device are provided. The secondary battery includes a positive electrode plate, a separator, an electrolyte solution, and a negative electrode plate. The negative electrode plate includes a negative electrode current collector, and a negative electrode active material layer disposed on the negative electrode current collector. Non-faradaic electric quantity Q C of the negative electrode plate satisfies: 0.05≤Q≤2.5, wherein Q=Cdl×ΔU, Cdl nF is non-faradaic capacitance of the negative electrode plate, and ΔU V is potential interval of the negative electrode active material layer.