Enhancing the Phase Stability of γ-Phase Li₃VO₄ for High-Performance Hybrid Supercapacitors: Investigating Influential Factors and Mechanistic Insights

This study explores the potential of titanium ion (Ti4+) substitution in γ-Li3VO4 (γ-LVO) as an anode material for high-energy supercapacitors. A series of Li3+xV1–xTixO4 (x = 0, 0.05, 0.10, 0.15, and 0.20) are systematically synthesized to vary the Ti-substitution ratio within LVO, and their crystal phases were analyzed using X-ray diffraction (XRD). Additionally, the reactivity of Ti during charge–discharge cycles is assessed by monitoring in situ X-ray absorption fine structure (XAFS) spectral changes. Quenching methods and XRD measurements quantitatively reveal that substituting 20 atom % of V5+ with Ti4+ achieves a single-phase γ-LVO, distinct from the nonsubstituted LVO (β-phase LVO). The Ti-substituted γ-phase LVO electrode displays a supercapacitor-like voltage curve and exceptional high-power performance during charge–discharge tests, benefiting from its high ionic conductivity stemming from the LISICON (Lithium Super Ionic CONductor) crystal structure. Furthermore, the Ti-substituted γ-phase LVO electrode exhibits an impressive rate capability, retaining 50% of its capacity at a very high current density of 2 A g–1 (10C-rate), while the nonsubstituted LVO retained only 13% under the same conditions. GITT analysis confirms a 100-fold higher Li+ diffusion coefficient for the Ti-substituted γ-phase LVO electrode. A novel approach is employed to examine the kinetic effects of Ti substitution on γ-phase stabilization: halting or quenching the γ → β phase transition during cooling using liquid nitrogen, coupled with XRD measurements, facilitates a quantitative evaluation of the phase transition rate. The primary goal of this study is to conduct a comprehensive assessment of the crystal structure and its stability by taking advantage of the excellent traceability of the Ti element through X-ray measurements to achieve this aim.