Lithium-magnesium alloy electrode performance
Solid-state lithium-based batteries offer higher energy density than their Li-ion counterparts, yet they are limited in terms of negative electrode discharge performance and require high stack pressure during operation. To circumvent these issues, Jack Aspinall and a team of researchers from this department, The Faraday Institution, the Indian Institute of Technology, and the Department of Engineering in Oxford advocate the use of lithium-rich magnesium alloys as suitable negative electrodes in combination with Li6PS5Cl solid-state electrolyte.
In the paper 'The impact of magnesium content on lithium-magnesium alloy electrode performance with argyrodite solid electrolyte' published in Nature Communications, the authors synthesise and characterise lithium-rich magnesium alloys, quantifying the changes in mechanical properties, transport and surface chemistry that impact electrochemical performance. Increases in hardiness, stiffness, adhesion and resistance to creep are quantified by nanoindentation as a function of magnesium content.
A decrease in diffusivity was quantified with 6Li pulsed field gradient nuclear magnetic resonance, and only a small increase in interfacial impedance due to the presence of magnesium was identified by electrochemical impedance spectroscopy which was correlated with x-ray photoelectron spectroscopy. The addition of magnesium aided contact retention on discharge, although the authors caution this must be balanced against a decrease in lithium diffusivity.
Using electrochemical testing of symmetric cells at 2.5 MPa and 30oC, the authors demonstrate that 1% magnesium content in the alloy increased the stripping capacity compared to both pure lithium and higher magnesium content alloys by balancing the effects.
