The present application provides a separator, a method for preparing the same, a secondary battery and an electrical device related thereto. The separator includes a porous substrate and a coating layer disposed on one or more surfaces of the porous substrate, wherein the coating layer includes nanocellulose, and the porous substrate has a surface tension of 1 mN/m, the coating layer has a surface tension of 2 mN/m, and the separator satisfies 1/20.68. The separator provided in the present application has the characteristics of excellent heat resistance and high bonding strength, thus the secondary battery using the separator can have the combined characteristics of high energy density, high thermal safety performance, and long service life.