Strain tunable ionic transport properties and electrochemical window of Li₁₀GeP₂S₁₂ superionic conductor

The sulfide solid electrolytes with high ionic conductivity at room temperature may become a potential candidate of solid electrolyte in all-solid-state lithium batteries. However, they have a lower intrinsic redox stability against inert electrodes, and generally unstable against lithium metal anode. Here, using density functional theory calculations we show that the ionic transport and band gap can be optimized by adjusting the mechanical strain on sulfide solid electrolyte Li₁₀GeP₂S₁₂(LGPS). Our theoretical results demonstrate that the tensile strain strongly influences the electronic structure and ion channel in LGPS materials, which results in wider band gap and higher lithium ionic conductivity. LGPS crystal can be stretched 15% along c direction without breakage due to its good ductibility. For the LGPS with a strain parallel to c direction, its band gap continuously increases to its maximum width of 4.16 eV as the strain increases up to 12%. In addition, the activation energies for lithium ion migration have been decreased by applying uniaxial strain to lattice with the aid of first principles and molecular dynamics calculations. Significantly, the lithium ion diffusion behavior will transform from one-dimensional into three-dimensional with lower activation energy in the as strained LGPS. The present study enriches the understanding of solid electrolytes and provides a framework for the future design or optimization of high-performance solid electrode.