2, Deakin University, Burwood, Victoria, Australia
The ability to directly utilize Lithium (Li) metal anodes in rechargeable batteries presents itself as an ideal, albeit challenging, situation. Li metal used as an anode would provide Li batteries with the maximum possible specific capacity (3860 mAh/g) in comparison to currently used anodes (e.g. graphite – 380 mAh/g). Nonetheless, Li metal anodes remain rare in commercial devices due to inherent safety concerns associated with the formation of Li dendrites during practical rate cycling, as well as Li metals’ susceptibility to exhibit high reactivity towards commercially available organic electrolytes. Due to possibilities of thermal runaway, such concerns have adversely affected the potential use of Li metal. Additionally, Li metal reacts negatively with water which can be found as an impurity in commercially available organic solvents; or passivate in the presence of small quantities of moisture rendering it un-rechargeable. This presents a significant hurdle when water-tolerant Li cycling is warranted (e.g. Li-air). Hence, significant efforts in recent rechargeable battery literature have targeted the development of robust electrolytes, capable of better stability when used with Li metal.
To date, various strategies have been employed to overcome such concerns; the use of solid electrolytes as a mechanical barrier, or the use of specific organic solvent-based electrolytes which control the properties of the solid-electrolyte interface (SEI), being noted observations. Amongst the various classes of Li battery electrolytes developed to date, ionic liquids (ILs) have been utilized as electrolytes which can facilitate enhanced Li cycling efficiencies and favorable Li plating morphologies while being inherently non-volatile/non-flammable alternatives to commercially available organic electrolytes. Through the capability to combine various cations (Imidazolium, Ammonium, etc.) and anions (TFSI, DCA, etc.); the use of such ILs could produce a more adept SEI, resulting in the improved cycling behaviors reported in literature.
Recently, we reported that certain ILs allowed for successful Li metal cycling in the presence of water mixed into the IL. To our knowledge, no reports have shown the capability to sustain morphologically friendly Li deposition upon application of practical cycling rates while allowing for stable cycling in water containing electrolytes. In recognition of this unique capability, we analytically probed the characteristics of the IL SEI’s to understand their protective capability. Based on such understanding, we now introduce a new method to artificially form these SEI’s on Li metal via the screening of various IL combinations. The electrochemical results, along with fundamental analytical analyses of the ILs capable of Artificial SEI Transplantation on Li metal, while sustaining commercially feasible Li morphologies at practical cycling rates in the presence of water containing electrolytes will be presented and discussed.