Mixed polyanion glass cathodes in lithium-ion batteries have high capacities (200-500 mAh/g), but currently these materials have fundamental problems with 1st-cycle irreversible loss, poor cycling efficiency, and capacity fade. It is well established that polyanion substitutions into glasses can dramatically affect their physical properties, but the effect of polyanion content on the electrochemical performance has not been previously established. The proper amount of lithium and borate substitution in copper phosphate/vanadate glasses was shown to nearly eliminate 1st-cycle irreversible loss and improve cycling efficiency. Raman and IR spectroscopy were used to identify polyanions that correlated with the changes in electrochemical performance. (C) 2017 The Electrochemical Society. All rights reserved.