Atomistic insights into the screening and role of oxygen in enhancing the Li+ conductivity of Li7P3S11−xOx solid-state electrolytes

Abstract

Herein, we implement first-principles calculations to design Li₇P₃S_11−xO_x at an atomic scale, aiming to obtain stable Li₇P₃S_11−xO_x-type solid electrolyte materials with good Li⁺ conductivity. After searching for chemical potentials, Li₂O₂ is expected to be the potential raw material, and it can afford the most favorable growth environment for the synthesis of Li₇P₃S_11−xO_x (x = 0.25, 0.50, 0.75 and 1). Among these compounds, it is found that Li₇P₃S_10.25O_0.75 exhibits the most desirable Li⁺ conductivity of 109 mS cm⁻¹ at 300 K, which is far higher than that of Li₇P₃S₁₁ (50 mS cm⁻¹ at 300 K). By structural analysis, it is demonstrated that the Li diffusion pathway in Li₇P₃S_10.25O_0.75 is significantly broadened relative to that in Li₇P₃S₁₁ (71.38 ųvs. 69.48 ų), which breaks the bottleneck during Li diffusion. Moreover, the resistance of Li ion diffusion in Li₇P₃S_10.25O_0.75 decreases due to the balance of interactions between Li and its neighbouring atoms at the transition state, which induces a much lesser energy barrier of Li₇P₃S_10.25O_0.75 than that of Li₇P₃S₁₁ (0.20 eV vs. 0.31 eV). Moreover, introducing Li vacancies is unlikely to alter the essence of the inherent superionic conductivity of Li₇P₃S_10.25O_0.75. Furthermore, Li₇P₃S_10.25O_0.75 can maintain good thermal stability and similar electrochemical stability to Li₇P₃S₁₁. This study successfully clarifies the role of oxygen in enhancing the Li⁺ conductivity of Li₇P₃S_11−xO_x. Moreover, it affords a new strategy to design other solid-state electrolytes with good Li⁺ conductivity.