An electrolyte composition comprising (i) a block copolymer, (ii) an organic electrolyte (e.g. an ionic liquid), and (iii) a lithium salt, wherein the block copolymer comprises a non-ionic block and an ionic block, the non-ionic block comprising polymerised residues of hydrophobic monomers, and the ionic block comprising polymerised monomer residues having covalently coupled thereto (a) a pendant organic ionic liquid cation, the pendant organic ionic liquid cation having a counter anion, (b) a pendant anionic moiety, the pendant anionic moiety having a counter cation, or (c) a combination thereof, and the electrolyte composition has at least two glass transition temperature (Tg) values.