A non-aqueous electrolyte including a lithium salt, an organic solvent, and an electrolyte additive is provided. The electrolyte additive is a meta-stable state nitrogen-containing polymer formed by reacting Compound (A) and Compound (B). Compound (A) is a monomer having a reactive terminal functional group. Compound (B) is a heterocyclic amino aromatic derivative as an initiator. A molar ratio of Compound (A) to Compound (B) is from 10:1 to 1:10. A lithium secondary battery containing the non-aqueous electrolyte is further provided. The non-aqueous electrolyte of this disclosure has a higher decomposition voltage than a conventional non-aqueous electrolyte, such that the safety of the battery during overcharge or at high temperature caused by short-circuit current is improved.