Secondary battery and active material

A secondary battery comprising:

• a positive electrode;
• a negative electrode;
• and
• an electrolyte,
• wherein the positive electrode comprises a positive active material of a lithium metal oxide including a reaction-inducing substance in which the lithium metal oxide is in the form of secondary particles of agglomerated primary particles,
• wherein the reaction-inducing substance is located between the agglomerated primary particles constituting secondary particles,
• wherein the reaction-inducing substance forms a reaction product by consuming thermal energy when exposed to a predetermined temperature or higher in a use environment of the secondary battery, thereby improving thermal safety of the secondary battery, and
• wherein the reaction-inducing substance comprises Li and Si.