The effect of Sr2+ and thermal treatment conditions on electrochemical characteristics of Li3OCl solid electrolyte in batteries

Abstract

Lithium-rich oxychloride anti-perovskite solid electrolytes have the potential to be promising for the next generation of batteries. Here, the influence of Sr2+ doping and heat treatment regime on the structure evolution, microstructure, and electrochemical properties of Li3–2xSrxOCl prepared by the hydrothermal route was reported. This research shows that both strategies of doping Sr2+ and the thermal treatment conditions lead to increase ionic conductivity. The lithium-ion conductivity increased with doping Sr2+ content and reached a maximum by x = 0.007 substitution of Sr2+ for Li+. A novel sintering approach is employed with ceramic elements for faster heat treatment that provids more homogeneity with a lower penetration barrier for lithium ions to diffuse in comparison with regular sintering in a furnace. Through this technique, the Li3-2×0.007Sr0.007OCl composition shows a high ionic conductivity of 0.38 × 10−3 S cm−1 at 60 °C. According to differential scanning calorimetry (DSC) measurements, the secondary hydroxide phases were found to have been transformed into the Li3-2xSrxOCl phase upon the first heat treatment cycle. Furthermore, the chemical stability of the Li/Li3-2×0.007Sr0.007OCl/Cu electrochemical cell was verified by cyclic voltammetry at 130 °C during lithiation/delithiation in a wide potential window (−1 to 8 V). The total impedance of the interfaces (RB) and the impedance of the bulk electrolyte (RA) in Li/ Li3-2×0.007Sr0.007OCl /NCM half-cell were obtained at 3690 and 723 Ω, respectively. The electrochemical stability of the Li3-2×0.007Sr0.007OCl electrolyte in contact with lithium metal is confirmed by chronopotentiometry test during charge/discharge conducted for 216 h at 60 °C. Moreover, the charge/discharge performance of Li/ Li3-2×0.007Sr0.007OCl/NCM half-cell showed an initial discharge capacity of 163 mAh/g and a discharge efficiency of 80 % after 20 cycles.