Space–Charge Layer Effect at Interface between Oxide Cathode and Sulfide Electrolyte in All-Solid-State Lithium-Ion Battery

TLDR

The study theoretically investigates the space–charge layer at oxide cathode/sulfide electrolyte interfaces in all‑solid‑state lithium‑ion batteries and the impact of buffer layer insertion using DFT+U calculations. The authors modeled LiCoO₂/β‑Li₃PS₄ and LiCoO₂/LiNbO₃/β‑Li₃PS₄ interfaces with DFT+U and a systematic interface‑matching procedure to determine stable structures and electronic states. The LCO/LPS interface shows attractive Li adsorption sites and a disordered structure, whereas the LNO buffer layer creates smooth interfaces without Li adsorption sites; Li‑vacancy formation energies and migration barriers reveal that subsurface Li in LPS can transfer under under‑voltage at the LCO/LPS interface, leading to space‑charge layer growth and interfacial resistance, while the LNO interposition suppresses this growth and provides smooth Li transport paths, offering insights for improving ASS‑LIB performance.

Abstract

We theoretically elucidated the characteristics of the space–charge layer (SCL) at interfaces between oxide cathode and sulfide electrolyte in all-solid-state lithium-ion batteries (ASS-LIBs) and the effect of the buffer layer interposition, for the first time, via the calculations with density functional theory (DFT) + U framework. As a most representative system, we examined the interfaces between LiCoO2 cathode and β-Li3PS4 solid electrolyte (LCO/LPS), and the LiCoO2/LiNbO3/β-Li3PS4 (LCO/LNO/LPS) interfaces with the LiNbO3 buffer layers. The DFT+U calculations, coupling with a systematic procedure for interface matching, showed the stable structures and the electronic states of the interfaces. The LCO/LPS interface has attractive Li adsorption sites and rather disordered structure, whereas the interposition of the LNO buffer layers forms smooth interfaces without Li adsorption sites for both LCO and LPS sides. The calculated energies of the Li-vacancy formation and the Li migration reveal that subsurface Li in the LPS side can begin to transfer at the under-voltage condition in the LCO/LPS interface, which suggests the SCL growth at the beginning of charging, leading to the interfacial resistance. The LNO interposition suppresses this growth of SCL and provides smooth Li transport paths free from the possible bottlenecks. These aspects on the atomic scale will give a useful perspective for the further improvement of the ASS-LIB performance.