The dependence of inter-phase lithium exchange on salt content in hybrid polymer-ceramic solid composite electrolytes

Hybrid polymer-ceramic solid composite electrolytes have been proposed as a means of circumventing common pitfalls that are associated with either polymer (lower ionic conductivity and low mechanical strength) or ceramic (large interfacial resistance with electrodes, brittle) electrolytes. Despite this premise, significant uncertainty remains as to whether both phases participate in ion conduction and whether interactions between phases cause electrolyte degradation via surface reactions, interfacial resistance or corrosion. In this work, a solid composite electrolyte comprising poly(ethylene) oxide (PEO) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) was prepared for the purpose of evaluating lithium exchange between the polymer and ceramic phases of the electrolyte material. The PEO phase contained either lithium bis(oxalato)borate (LiBOB), lithium tri(fluoromethanesulfonyl)imide or a mixture of the two salts. 6Li-enriched LAGP and LiBOB were prepared such that 6Li NMR could be used to detect and quantify lithium exchange between the ceramic and the polymer phases following electrochemical polarization of the samples. The 6Li NMR study revealed that lithium-lithium chemical exchange between the polymer and ceramic phases in PEO-LAGP was dependent on which lithium salts were present in the polymer phase. Chemical exchange between the polymer and ceramic phases was linked to decreased ionic conductivity. This article is part of the theme issue 'Electrolytes within the domain of electrochemistry and electrochemical energy storage'.