Solid state lithium batteries and lithium-rich magnesium electrodes
Featured in the Nature Communications Editor's Highlights, this paper* explains how solid-state lithium-based batteries offer higher energy density than their Li-ion counterparts, yet are limited in terms of negative electrode discharge performance and require high stack pressure during operation.
To circumvent these issues, the authors propose the use of lithium-rich magnesium alloys as suitable negative electrodes in combination with Li6PS5Cl solid-state electrolyte. They synthesise and characterise lithium-rich magnesium alloys, quantifying the changes in mechanical properties, transport and surface chemistry that impact electrochemical performance.
Increases in hardness, stiffness, adhesion and resistance to creep are quantified by nanoindentation as a function of magnesium content. A decrease in diffusivity is quantified with 6Li pulsed field gradient nuclear magnetic resonance, and only a small increase in interfacial impedance due to the presence of magnesium is identified by electrochemical impedance spectroscopy which is correlated with x-ray photoelectron spectroscopy.
The addition of magnesium aids contact retention on discharge, but this must be balanced against a decrease in lithium diffusivity. This paper demonstrates via electrochemical testing of symmetric cells at 2.5 MPa and 30oC that 1% magnesium content in the alloy increases the stripping capacity compared to both pure lithium and higher magnesium content alloys by balancing these effects.
