In an attempt to raise the transference number of Li+ to nearly unity in a solid polymer electrolyte, block copolymer materials have been prepared in which the counterions are tethered to the polymer backbone. This immobilizes the “anion” and, in effect, renders the material a single-ion conductor. For such so-called self-doped block copolymer electrolytes (SDBCEs) Li+ transference numbers of ∼0.9 have been measured. In parallel, these materials possess significant ionic conductivity (∼10−5 Scm−1 at 35°C). Cyclic voltammetry has shown the SDBCE to be immune to electrochemical breakdown at voltages exceeding 5V.