Understanding the role of mass transport and lithium interphase design in enabling conversion batteries

Abstract

Lithium-iodine batteries are among a class of next generation conversion-based chemistries that deliver high energy density using abundant, low-cost materials. There are two main obstacles facing these chemistries: the instability of the lithium anode that leads to capacity fade and the low utilization of the active material under practical cell conditions that leads to low specific capacity. In this work we address anode instability through chemical treatment of the surface layer to form a borate rich interphase that protects the lithium from parasitic reactions. We demonstrate that the properties of the treated lithium surface are highly dependent on the treatment environment and require precise tuning to achieve optimal performance. The stabilized lithium surface shows improved capacity retention in lithium-iodine cells at practical mass loadings (above 10 mg/$cm^2$). Further, we explore the relationship between iodine utilization and mass-transport limitations. The results indicate that diffusion limited transport of the dissolved active material is the major source for the reduction of specific capacity with increasing iodine loading. These studies provide design rules for materials discovery to enable stable and high energy density conversion batteries.