SECONDARY BATTERY AND PREPARATION METHOD THEREOF, POSITIVE ELECTRODE PLATE, NEGATIVE ELECTRODE PLATE AND ELECTRICALLY-POWERED DEVICE

The present disclosure provides a secondary battery and a preparation method thereof, a positive electrode plate, a negative electrode plate and an electrically-powered device. A positive electrode active material includes a lithium iron phosphate (LFP) positive electrode material, LiNiOand LiFeO. By adjusting a mixing ratio and limiting the mixing ratio, a specific capacity of active materials and an electrolyte filling coefficient to satisfy a specific relationship, the specific capacity and cycle performance of LFP batteries can be significantly improved, thereby making the lithium-ion batteries simultaneously exhibit superior energy density, cycle performance and safety.