One of the problems in early commercialization of lithium-ion batteries was graphite anode corrosion: propylene carbonate-based electrolytes interacted well with metallic lithium, but proved to be extremely corrosive to graphite. This prevented the use of graphite electrodes until ethylene carbonate was offered as an alternative solvent in the electrolyte composition. Despite similarity of the ethylene and propylene carbonate molecules, their behavior towards graphite anodes is different. However, until recently, there was no consensus in science concerning the nature of these differences.
The Skoltech scientists made a supposition that it is all about the formation of a thin layer of viscous liquid, which occurs when there is ethylene carbonate on the surface of graphite. The layer protects the graphite from corrosive delamination. Subsequent experiments confirmed that this layer forms indeed in ethylene carbonate-based electrolytes and is unavailable when propylene carbonate is used.
The mentioned viscous liquid layer appears before the formation of an important element of the lithium-ion battery – the so-called solid electrolyte layer – and therefore, it should make an impact on its formation. The solid electrolyte layer is a thin film of solid electrolyte formed on the anode surface during an initial charge and discharge of the battery. The film prevents both graphite anode degradation and electrolyte regeneration (the process that degrades device performance).
The Skoltech scientists’ discovery is applicable not only to lithium-ion batteries, but also to sodium-ion batteries which also have a problem of solid electrolyte layer formation. Therefore, the results of the study are important for the creation of more stable and efficient batteries.
