Enhanced cycling performance of bilayered vanadium oxide cathode in Li-ion batteries via dual metal-ion preintercalation

Abstract

Chemical preintercalation of Li⁺ or Mg²⁺ ions can improve the specific capacity or cycling stability, respectively, of bilayered vanadium oxide (BVO) electrodes in Li-ion cells. However, advancing both properties simultaneously in a single material via chemical preintercalation of both Li⁺ and Mg²⁺ ions has never been reported. Herein, we experimentally demonstrated that by simultaneously pre-intercalating electrochemically active Li⁺ ions and structure-stabilizing Mg²⁺ ions, the specific capacity and cycling stability of the BVO electrodes in Li-ion cells can be synergistically improved. Additionally, we revealed the role of the interlayer structural water in the charge storage and degradation mechanisms of dual metal-ion preintercalated BVO electrodes. With the simultaneous preintercalation of 0.19 Li⁺ ions and 0.10 Mg²⁺ ions into the interlayer structure of BVO, the LMVO electrode demonstrated a specific capacity of ∼245 mA h g⁻¹ in a potential window of 2.0–4.0 V (vs. Li/Li⁺) with a capacity retention of 58% after 50 cycles. Low-temperature vacuum-annealing at 200 °C reduced the hydration degree (n in δ-Li_0.19Mg_0.10V₂O₅·nH₂O) of LMVO (denoted as LMVO-200) from 0.85 to 0.67 H₂O per V₂O₅ without phase transformation and increased the contribution of diffusion-limited process while reducing the surface-controlled fraction of the charge storage mechanism, demonstrating further enhanced capacity retention of ∼66% after 100 cycles. Additionally, GITT experiments demonstrated that the dual metal-ion preintercalation and vacuum-drying treatment facilitated the diffusion of Li⁺ ions. The ex situ XRD and ATR FTIR analyses of the LMVO-200 electrode revealed its reversible bulk and local structure evolution during the electrochemical operation, enabling excellent cycling stability in Li-ion cells. This work demonstrates a general strategy to synergistically enhance the specific capacity and cycling stability of layered oxide electrode materials for intercalation batteries.