Provided are a secondary battery, a battery module, a battery pack and an electrical apparatus. The secondary battery includes a positive electrode plate and a non-aqueous electrolyte solution. A positive electrode active material includes an inner core and a shell cladding the inner core. The inner core includes Li1+xMn1−yAyP1−zRzO4. The shell includes a first cladding layer cladding the inner core and a second cladding layer cladding the first cladding layer. The first cladding layer includes pyrophosphate MP2O7 and phosphate XPO4. The second cladding layer includes carbon. The non-aqueous electrolyte solution includes a first additive. The first additive includes one or more compounds in a group consisting of a compound shown in Formula 1, a compound shown in Formula 2 and a compound shown in Formula 3. The rate performance, cycling performance and high temperature stability of a lithium manganese phosphate secondary battery are increased.