SECONDARY BATTERY, BATTERY PACK, ELECTRONIC DEVICE, ELECTRIC VEHICLE, ELECTRICITY-STORAGE APPARATUS, AND ELECTRICAL POWER SYSTEM

A secondary battery includes a positive electrode including a positive electrode active material layer having a positive electrode active material, a negative electrode including a negative electrode active material layer having a negative electrode active material, and an electrolyte. The positive electrode active material contains either a lithium iron phosphate compound having an olivine structure or lithium-manganese composite oxide having a spinel structure. The negative electrode active material contains titanium-containing inorganic oxide. In the secondary battery, electrode areas of the positive electrode and the negative electrode, and first charge capacities and irreversible capacities per unit area of the positive electrode and the negative electrode satisfy predetermined formulas.