Enhancing ionic conductivity and interfacial stability of argyrodite electrolyte by La/Nd doping toward long-cycle...

Sulfide solid-state electrolytes are promising for all-solid-state lithium batteries but suffer from limited interfacial stability against lithium metal. In this work, trace La³⁺ and Nd³⁺ were introduced into Li₆PS₅Cl (LPSC) to improve both ionic transport and interfacial compatibility. At the optimized doping level of x = 0.02, LPSC-0.02La and LPSC-0.02Nd delivered room- temperature ionic conductivities of 3.37 × 10^-3 and 3.53 × 10^-3 S cm^-1, respectively. XPS results after cycling showed much weaker LiCl, P₂S_n, and PO₄^3- related decomposition signals for the doped electrolytes, indicating reduced interfacial degradation. The improved interfacial behavior is discussed in terms of the hard-acid character of La³⁺/Nd³⁺, which may favor interactions with oxygen-containing species. In Li symmetric cells, the critical current densities increased from 0.244 mA cm^-2 for pristine LPSC to 1.499 and 0.919 mA cm^-2 for the La- and Nd- doped samples, respectively. The NCA|LPSC-0.02La|Li cell delivered 147.3 mAh g^-1 at 1 C and retained 94.84 mAh g^-1 after 100 cycles. These results highlight rare-earth doping as an effective route to improve the transport and interfacial properties of LPSC.