High cyclic reversibility in eutectic lithium calcium anodes characterised by electron microscopy

Abstract

Lithium metal is the benchmark anode for lithium-ion battery technology with high theoretical energy density and capacity. However, dendrite formation and solid electrolyte interphase formation limit the practical current density and lifetime, respectively. This study investigates how a lithium–calcium alloy can overcome these challenges by fabricating a simple to manufacture anode made of two phases in a 3D structure. Exploration with different electrolytes and electron microscopy highlights the role the calcium intermetallic plays in lithium cycling. The charge transfer resistance of electrolytes is 255 Ohms for LiTFSI and 315 Ohms for LiPF6. The overpotential value of both electrolytes within a symmetric eutectic anode cell is 0.06 V for LiTFSI compared to 0.26 V for LiPF6, highlighting that the electrolyte can alter the deposition mechanism not just the total cell resistance. We conclude that both the current density and long term cycling performance are improved versus lithium metal anodes, as the 3D Li–Ca matrix can suppress volume changes during cycling and remove the need for lithium metal to be present at the interface with the electrolyte, thereby reducing side reactions.