Local distortion of highly conducting glass and glass–ceramics: phosphovanadate glass applied to lithium ion battery (LIB)
摘要
Mössbauer spectroscopy is powerful when applied to atomic- or nano-scale structural study of glass and glass–ceramics. Glass transition temperature (Tg) of inorganic glasses can be regulated from ~ 180 to 800 °C by changing the composition and local distortion of network former (NWF)–oxygen polyhedra, as was proved by Tg-Δ rule, i.e. a linear relationship between Tg and quadrupole splitting (Δ) of FeIII. DC-resistivity of semiconducting vanadate (V2O5-based) glass is “tunable” from the order of MΩ‧cm to Ω‧cm by structural relaxation or a decrease in the local distortion of network. In this study, 20Li2O‧10Fe2O3‧5P2O5‧65V2O5 glass and glass–ceramics were investigated as a new cathode active material of lithium-ion battery (LIB), which yielded large initial discharge capacity of 262–268 mAh‧g−1 at 25 °C when discharged from 3.5 to 1.5 V under a current density of 150 mA‧g−1. Enhanced initial capacities of 342 and 326 mAh‧g−1 were yielded after annealing for 90 min at 400 and 450 °C, respectively. Mössbauer spectra of glass–ceramics containing microcrystals of LiVO3 and LiV6O15 bronzes were composed of one doublet due to distorted FeIIIO4 tetrahedra constituting FePO4-rich phase, of which Δ increased from 0.68 to 0.75 and 0.77 (± 0.02) mm‧s−1 toward amorphous FePO4 phase with Δ of 0.89 ± 0.02 mm‧s−1.