• Hollenkamp, Anthony
• Best, Adam

Abstract

The quest to build batteries with ever-increasing energy density continues, and lithium, the lightest, most electropositive metal is part of the latest developments; i.e., lithium-sulfur and lithium-air(oxygen). Successful utilization of the lithium negative electrode is however predicated on controlling its electrochemical behaviour. The reducing power of lithium means that nearly all prospective electrolyte media will react with the electrode. Only in rare cases, where reaction is limited by the formation of a stable interphase, is reversible operation possible. One important example is the short-chain N,N-dialkylpyrrolidinium salts of the fluorosulfonylimides, such as TFSI, with lithium salts of the same anion. The SEI (solid electrolyte interphase) that forms on contact between LiTFSI and metallic lithium is comprised of LiF and (oxy)sulfur species. The resulting electrode coating is somewhat passivating as it allows movement of lithium ions but also adds considerably to the electrode's resistance. Knowing that the characteristics of the TFSI-derived SEI are influenced by the identity of the substrate metal, it was decided to investigate a broader range of metals and alloys, to introduce some control over SEI formation. For the noble and coinage metals, SEI formation dominates the rate of lithium ion movement and only small variations are noted. By contrast, for the main group metals, the greater propensity to form lithium compounds sees the electrode potential vary over a much greater range. This in turn introduces the possibility of restricting or even eliminating the formation of the SEI, albeit at the cost of a lowering of the device voltage.

Topics

• density
• impedance spectroscopy
• compound
• energy density
• Oxygen
• Lithium