Interrupted anion-network enhanced Li+-ion conduction in Li3+yPO4Iy

For solid-state batteries to outperform the current lithium-ion battery technology in energy density and cost, high-performance solid electrolytes produced using low-cost precursors and scalable processes are the key. In this study, we demonstrate using inexpensive Li 3 PO 4 of low conductivity 10 −6 mS/cm and turning it into a fast Li + -ion conductor, with an ionic conductivity of ≥ 0.15 mS/cm, by engineering the anion sublattice. I − anions are used to interrupt the ordered PO 4 3− network in Li 3 PO 4 , which destabilizes Li + -PO 4 3− interaction and liberates Li + -ions with enhanced Li + mobility as evidenced by NMR relaxometry measurements. The optimal conductivity and activation energy are achieved when PO 4 3− /I − =1, in which Li + -ions spend equal time with PO 4 3− and I − on their diffusion paths without being trapped. Tracer-exchange NMR shows that Li 4 PO 4 I is more conductive than Li 3+y PO 4 I y when y ≠ 1. Further conductivity enhancement is possible by stabilizing pure-phase glassy Li 4 PO 4 I. Overall, this study shows an effective and general strategy to significantly enhance ion conduction for creating inexpensive solid electrolytes with high performance.