Enhancement of ionic conductivity and air stability by co-doping Li10SnP2S12 with Nb and O

Li₁₀SnP₂S₁₂ represents a quintessential sulfide solid-state electrolyte that has garnered considerable interest within the domain of solid-state batteries. However, it still has much room for enhancing its ionic conductivity and air stability. In this paper, Li₁₀SnP₂S₁₂ was modified by solid-phase sintering method using different doping amounts of Nb₂O₅. XRD refinement confirmed that Nb and O elements were successfully doped into the P and S sites, in which the ionic conductivity of Li₁₀SnP_1.96Nb_0.04S_11.9O_0.1 was up to 2.93 mS cm⁻¹ at room temperature. After Nb₂O₅ doping, the lattice volume expands due to the larger ionic radius of Nb⁵⁺ compared to P⁵⁺. This expansion broadens the channels through which lithium ions travel, thereby enhancing Li⁺ conductivity. O doping improves the stability of the sulfide against moisture and forms a strong PO bond with P, which resists further oxidation. The air stability test demonstrated enhanced air stability of the doped electrolyte. The AC impedance test conducted at various temperatures confirmed that the doped electrolyte exhibits lower activation energy, which facilitates an enhancement in Li⁺ conductivity. Finally, the assembled Li-In/Li₁₀SnP_1.96Nb_0.04S_11.9O_0.1/LNO@LCO battery exhibits higher first turn discharge specific capacity and good cycle stability.