Bilayered vanadium oxides by chemical pre-intercalation of alkali and alkali-earth ions as battery electrodes

Abstract

We report the use of the chemical pre-intercalation synthesis technique to insert alkali (Li+, Na+, K+) and, for the first time, alkali-earth (Mg2+ and Ca2+) ions into the structure of vanadium oxide leading to the formation of the bilayered δ-MxV2O5 (M = Li, Na, K, Mg, Ca) phase with expanded interlayer spacing, enabling a large number of insertion sites for and faster diffusion of charge-carrying ions. By altering the nature of the chemically preintercalated ion, interlayer spacing of the synthesized δ-MxV2O5 materials was varied between 9.62 and 13.40Å. We for the first time show that the interlayer spacing increases with the increase of the hydrated ion radius. The ion (Na+, K+, Mg2+, Ca2+) stabilization effect was investigated in Li-ion cells, with Li-preintercalated phase, δ-LixV2O5, serving as a reference material. Our analyses indicate that cyclability and rate performance of the δ-MxV2O5 improves with increasing interlayer spacing. The highest initial capacity (198 mAh g−1), greatest capacity retention (81.8% after 50 cycles at 20mAg−1), and highest capacity retention at higher current rates (74.5% when current rate was changed from C/15 to 1C) were exhibited by Mg-stabilized δ-V2O5 with the largest interlayer spacing (13.40Å). This research demonstrates the efficacy of a facile chemical pre-intercalation strategy to synthesize ion-stabilized layered electrode materials with improved electrochemical stability. Ion-stabilized layered materials with large interlayer spacing are attractive for applications that involve electrochemically driven movement of ions through two-dimensional diffusion channels, ranging from beyond Li-ion energy storage and electrochromics to actuation and water treatment.