SECONDARY BATTERY, BATTERY MODULE, BATTERY PACK, AND ELECTRIC DEVICE

Provided are a secondary battery, a battery module, a battery pack, and an electric device. The secondary battery includes a cathode piece and a non-aqueous electrolyte. The cathode active material includes a core and a shell covering the core. The core includes LiMnAPRO. The shell includes: a first cladding layer covering the core, and a second cladding layer covering the first cladding layer. The first cladding layer includes pyrophosphate MPOand phosphate XPO, and the second cladding layer contains carbon. The non-aqueous electrolyte includes a first lithium salt and a first additives, the first lithium salt is one or more selected from the group consisting of LiN(CFSO)(CFSO) and Li(FSO)N, in which, m and n represent positive integers. The first additive includes one or more of a compound represented by: O═C═N—R—N═C═O.