Block and Graft Copolymer Electrolytes

An ongoing challenge in the development of LPBs is the need for an all-polymer electrolyte that meets mechanical, electrical and processing requirements. We have developed a class of block and graft copolymer electrolytes (BCEs and GCEs) for lithium polymer batteries that exhibit nanoscale-periodic domains formed from mutually immiscible, covalently joined polymer chains. The nanoscale morphology confers mechanical properties similar to those of a crosslinked rubber and creates continuous Li + ion-conducting pathways through the material. Cycle tests performed on all-solid state (i.e. binder- and additive-free) prototype batteries consisting of a sputtered VO x thin film cathode, GCE, and lithium metal anode show rate capability, cathode capacity, and cyclability comparable to cells equipped with liquid electrolyte. By tethering the anion to the polymer backbone, we have also created block and graft copolymer single-ion conductors that exhibit a Li + transport number of unity (i.e., the entire current is carried by lithium cations.) Although such electrolytes eliminate battery polarization due to salt concentration gradients, our studies on cells fitted with single-ion conductors indicate challenges remain in their effective operation with transition metal oxide cathodes.