ELECTROLYTE ADDITIVE, ELECTROLYTE FOR BATTERIES INCLUDING ELECTROLYTE ADDITIVE, AND SECONDARY BATTERY INCLUDING ELECTROLYTE

The present invention relates to an electrolyte additive including a compound containing a substituent represented by Chemical Formula 1, an electrolyte including the electrolyte additive, and a secondary battery including the electrolyte. Chemical Formula 1: In Chemical Formula 1, P and O are phosphorus and oxygen, respectively; A is a bond or oxygen; Q is oxygen or an unshared electron pair; R, R, R, and Rare each independently hydrogen, a linear or branched alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, an alkoxy group, an alkoxycarbonyl group, an alkoxyalkyl group, a fluoroalkyl, or a cyclic sulfate; optionally, Ror Ris connected to Ror Rto form a double bond or a ring; n is an integer from 0 to 3; and * is a binding position.