Provided is a secondary battery, comprising a positive electrode, the positive electrode comprises a positive electrode material layer, and the positive electrode material layer comprises a positive electrode active material and a compound represented by structural formula I: the positive electrode active material includes one or more of the compounds represented by Li1+xNiaCobM′1−a−bO2−yAy and Li1+zMncL2−cO4−dBd; the positive electrode material layer meets the following requirements: 0.05≤p·u/v≤15 wherein, u is the percentage mass content of element phosphorus in the positive electrode material layer, and the unit is wt %; v is the percentage mass content of element M in the positive electrode material layer, element M is selected from one or two of Mn and Al, and the unit is wt %; p is the surface density of one single surface of the positive electrode material layer, and the unit is mg/cm2.