Performance-limiting factors of graphite in sulfide-based all-solid-state lithium-ion batteries

A suite of bulk and surface analytical techniques was applied to shed light on the factors limiting fast cycling of composite graphite electrodes in all-solid-state cells based on sulfide electrolytes 0.75Li(2)S-0.25P(2)S(5) (LPS) and 0.3LiI-0.7(0.75Li(2)S-0.25P(2)S(5)). Cracks in the composite electrodes and poor percolation of the ionic conducting particles were identified by both scanning electron microscopy and X-ray tomography and the slow kinetics during lithiation (limiting practical specific charge at rates >C/10, at geometrical current densities >120 mu A cm(-2)) was monitored by operando X-ray diffraction and supported by Raman microscopy. Operando X-ray photoelectron spectroscopy and X-ray absorption spectroscopy detected the formation of Li2S and LixP at the interface between LPS and graphite, both compounds increasing the interfacial resistance. Despite the kinetic limitations, excellent long-term cycling performance is demonstrated at C/20 rate (at current density of about 60 mu A cm(-2)), revealing slow self-passivation processes at the sulfide/graphite interface which stabilizes after approximately 200 full cycles. (C) 2021 The Author(s). Published by Elsevier Ltd.

Automated summary

A suite of analytical techniques were applied to investigate the limitations of fast cycling in composite graphite electrodes in all-solid-state cells with sulfide electrolytes, identifying cracks in the electrodes, poor percolation of conducting particles, and the formation of compounds increasing the interfacial resistance. Despite kinetic limitations, excellent long-term cycling performance was demonstrated at specific rates, suggesting slow self-passivation processes at the interface.