Unraveling the Formation Mechanism of Solid–Liquid Electrolyte Interphases on LiPON Thin Films

Most commercial lithium-ion batteries and other types of batteries rely on liquid electrolytes, which are preferred because of their high ionic conductivity, and facilitate fast charge-transfer kinetics at the electrodes. On the other hand, hybrid battery concepts that combine solid and liquid electrolytes might be needed to suppress unwanted shuttle effects in liquid electrolyte-only systems, in particular if mobile redox systems are involved in the cell chemistry. However, at the then newly introduced interface between liquid and solid electrolytes, a solid–liquid electrolyte interphase forms. In this study, we analyze the formation of such an interphase between the solid electrolyte lithium phosphorous oxide nitride (LixPOyNz, “LiPON”) and various liquid electrolytes using in situ neutron reflectometry, quartz crystal microbalance, and atomic force microscopy measurements. Our results show that the interphase consists of two layers: a nonconducting layer directly in contact with “LiPON” and a lithium-r...