The present application provides a secondary battery, a battery module, a battery pack, and an electrical device. The secondary battery includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate, in which the positive electrode plate comprises a positive electrode coating containing a positive electrode active material comprising a lithium iron phosphate material and a conjugated carbonyl compound. In a discharge process of the secondary battery, in addition to a discharge plateau of the lithium iron phosphate material, a discharge curve further includes a relatively low discharge plateau provided by the conjugated carbonyl compound.