Physics

Dr. Abhik Banerjee
University of California, USA

Abstract :

Enabling high-voltage oxide cathodes is a persistent challenge for all-solid-state batteries based on sulfides solid electrolytes (SSEs). Although most of them have the ionic conductivity comparable to or higher than that of liquid electrolytes, their electrochemical performance remains unsatisfactory when compared to the liquid electrolyte, mainly due to a high cathodic charge transfer resistance. In this work, we succeeded to engineer a stable interface between the electrolyte Li₆PS₅Cl (LPSCl) and the cathode LiNi_0.85Co_0.1Al_0.05O₂ (NCA) after figuring out their interfacial problems. Both the chemical reactions between NCA and LPSCl, and the electrochemical decomposition of LPSCl increase the cathode charge transfer. These interfacial reactions are differentiated and their products were probed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and cryo-STEM. The reaction driving force is analyzed by the first-principles calculation. Both experimental and computational results demonstrate that the thermodynamic instability between NCA and LPSCl can be significantly reduced by LiNbO3 (LNO) coating. We also reveal that in situ passivation takes place when the LPSCl is electrochemically decomposed during the first charge. This self-limiting interfacial reaction along with LNO coating helps to construct a stable interphase and enables to achieve a long-life high-energy all solid-state battery. Same observation was also noticed for all solid state Na ion battery where coating Li₄Ti₅O₁₂ coating drastically improves the electrochemical performance.