A polymer electrolyte comprising: a lithium salt, characterised in that the polymer electrolyte further comprises a copolymer represented by Formula 1; wherein, in Formula 1, each R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10, R 11, R 12, R 13, R 14, R 15, and R 17 are the same or different, and are each independently a hydrogen atom; a halogen atom; a linear or branched C 1 -C 10 alkyl group that is unsubstituted or substituted with halogen; a C 6 -C 10 cycloalkyl group that is substituted or unsubstituted with halogen; a C 2 -C 10 alkenyl group that is substituted or unsubstituted with halogen; a C 2 -C 10 alkynyl group that is substituted or unsubstituted with halogen; a C 6 -C 10 aryl group that is substituted or unsubstituted with halogen; or a C 2 -C 10 heteroaryl group that is substituted or unsubstituted with halogen, provided that R 15 and R 17 are different from each other, each R 16 is the same or different, and is a covalent bond; a C 1 -C 10 linear or branched alkylene group that is substituted or unsubstituted with halogen; -(-R a -O-) k -, wherein k is an integer of 2 to 100, and R a is a C 2 -C 10 alkylene group that is substituted or unsubstituted with halogen; a C 6 -C 10 cycloalkylene group that is substituted or unsubstituted with halogen; a C 6 -C 10 arylene group that is substituted or unsubstituted with halogen; a C 2 -C 10 heteroarylene group that is substituted or unsubstituted with halogen; or a divalent linking group comprising one or more of the foregoing groups, L 1 is a covalent bond or -R b -C(=O)-O-, and L 2 is a covalent bond or -C(=O)-R c -, wherein R b and R c are each independently a linear or branched C 1 -C 20 alkylene group, n1 is an integer of 2 to 100, and x, y, and z are each mole fractions in repeating units, wherein 0<x<1, 0<y<1, 0<z<1, and x+y+z=1. a lithium salt, characterised in that the polymer electrolyte further comprises a copolymer represented by Formula 1; wherein, in Formula 1, each R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10, R 11, R 12, R 13, R 14, R 15, and R 17 are the same or different, and are each independently a hydrogen atom; a halogen atom; a linear or branched C 1 -C 10 alkyl group that is unsubstituted or substituted with halogen; a C 6 -C 10 cycloalkyl group that is substituted or unsubstituted with halogen; a C 2 -C 10 alkenyl group that is substituted or unsubstituted with halogen; a C 2 -C 10 alkynyl group that is substituted or unsubstituted with halogen; a C 6 -C 10 aryl group that is substituted or unsubstituted with halogen; or a C 2 -C 10 heteroaryl group that is substituted or unsubstituted with halogen, provided that R 15 and R 17 are different from each other, each R 16 is the same or different, and is a covalent bond; a C 1 -C 10 linear or branched alkylene group that is substituted or unsubstituted with halogen; -(-R a -O-) k -, wherein k is an integer of 2 to 100, and R a is a C 2 -C 10 alkylene group that is substituted or unsubstituted with halogen; a C 6 -C 10 cycloalkylene group that is substituted or unsubstituted with halogen; a C 6 -C 10 arylene group that is substituted or unsubstituted with halogen; a C 2 -C 10 heteroarylene group that is substituted or unsubstituted with halogen; or a divalent linking group comprising one or more of the foregoing groups, L 1 is a covalent bond or -R b -C(=O)-O-, and L 2 is a covalent bond or -C(=O)-R c -, wherein R b and R c are each independently a linear or branched C 1 -C 20 alkylene group, n1 is an integer of 2 to 100, and x, y, and z are each mole fractions in repeating units, wherein 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.