Co-substitution Strategy for Boosting Rate-Capability of Lithium-Superionic-Conductor (LISICON)-Type Anode Materials in γ-Li3VO4–Li4GeO4–Li3PO4 Quasi-Ternary-System


 Using simple solid-state calcination, Li3+xV1–x–yGexPyO4 (LVGePO) anode materials with lithium superionic conductor (LISICON)-related crystal structure have been successfully synthesized for next-generation energy storage applications with high-energy and high-power densities. The correlation among their chemical compositions, crystal-phase formations, and rate performances has been elucidated and mapped in the quasi-ternary phase diagram of the Li3VO4–Li4GeO4–Li3PO4 system. The crystal phase formation can be controlled by the Ge4+-substitution ratio ; 5 at% or more Ge4+-substitution resulted in a pure γ-phase structure with high Li+ conductivity. Fine-tuning of the chemical compositions brings about the highest charge (delithiation) capacity retention of ca. 62% of the theoretical capacity at 10 A g–1 (ca. 40C-rate) obtained in the typical chemical composition range of Li3.05–3.1V0.7–0.8Ge0.05–0.1P0.1–0.25O4 with the γ-phase crystal structure. Further, the co-substituted LVGePO anodes exhibit drastically improved rate performances compared to any binary solid solutions of Li3+xV1–xGexO4 and Li3V1–yPyO4. Such improvement in the electrochemical performances are induced by the distinct roles of co-substituted cations, viz., P5+ suppresses the reductive decomposition of electrolytes on the LVGePO crystal surfaces, while the Ge4+ stabilizes the high Li+ conductive γ-phase structure.