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, γ -Li 3+ x V 1– x – y Ge x P y O 4 (LVGePO) anode materials with lithium superionic conductor (LISICON)-related crystal structures 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 Li 3 VO 4 –Li 4 GeO 4 –Li 3 PO 4 system. The crystal phase formation and surface stability can be controlled by the Ge 4+ - and/or P 5+ - substitution ratio; 5 at% or more Ge 4+ -substitution resulted in a pure γ -phase structure with high Li + conductivity, while the presence of P 5+ suppressed the SEI formation. Fine-tuning of the chemical composition 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 Li 3.05–3.1 V 0.7–0.8 Ge 0.05–0.1 P 0.1–0.25 O 4 with the γ -phase crystal structure. Such co-substituted LVGePO anodes exhibited superior rate performances compared to any binary solid solutions of Li 3+ x V 1– x Ge x O 4 and Li 3 V 1– y P y O 4 . The improvement in the electrochemical performances are induced by the distinct roles of co-substituted cations, viz. , P 5+ suppresses the reductive decomposition of electrolytes on the LVGePO crystal surfaces, while Ge 4+ stabilizes the high Li + conductive γ -phase structure.