SECONDARY BATTERY, BATTERY PACK, VEHICLE, AND STATIONARY POWER SUPPLY

According to one approach, provided is a secondary battery (100) including a positive electrode (5) containing a positive electrode active material, a negative electrode (3) containing a negative electrode active material, a separator (4) between the positive electrode (5) and the negative electrode (3), and an electrolyte. At least one of the positive electrode (5), the negative electrode (3), and the separator (4) contains an alkali metal oxide. 50% or more of alkali metal ions included in the alkali metal oxide is exchangeable with protons. Among the positive electrode active material and the negative electrode active material, a number of active material particles in contact with the alkali metal oxide is 10% or less of the whole.