Freezing Reveals Lithium Battery Surprise

The solid-liquid interface of the anode and the electrolyte plays an important role in the performance of a lithium-metal battery. However, it often is poorly understood owing to the lack of high-resolution characterization methods that are compatible with both solid and liquid components. It is known that dendritic deposition of lithium metal and the formation of solid-electrolyte interphase layers are key determinants of battery safety and performance in high-energy-density lithium-metal batteries. However, what exactly is involved in these processes occurring at the solid-liquid interface, is unclear.

Lena F. Kourkoutis and colleagues, Cornell University, Ithaca, NY, USA, have adapted a technique that is used for cryo-transmission electron microscopy (cryo-TEM) of hydrated specimens in biology to immobilize liquids by rapid freezing. They used the modified technology to freeze the liquid electrolyte and by this preserve it and the structures at the solid-liquid interfaces in lithium-metal batteries in their native state. The team then mapped their structure and chemistry.

The researchers have identified two dendrite types coexisting on the lithium anode, each with distinct structure and composition. One family of dendrites (lithium metal dendrites) has an extended solid-electrolyte interphase layer, approximately 300 to 500 nm thick, much larger than has been previously observed. This finding suggests that more lithium is irreversibly lost to the solid-electrolyte interphase layer than previously thought. The other family of dendrites unexpectedly consists of lithium hydride instead of lithium metal. These dendrites are thin, brittle, have winding structures, and are likely to break away from the electrode during battery charge-discharge cycling. This may contribute disproportionately to loss of battery capacity.

According to the researchers, these insights into the formation of lithium dendrites demonstrate the potential of cryogenic electron microscopy for probing nanoscale processes at intact solid-liquid interfaces in functional devices such as rechargeable batteries.