(Invited) Localized High Concentration Electrolytes for Li Metal and Li Ion Batteries

Abstract

It is well known that a stable and high efficiency Li metal anode (LMA) is critical for rechargeable Li metal batteries (LMBs). Although LMA is kinetically unstable with non-aqueous electrolyte, Localized High Concentration Electrolytes (LHCEs) can largely minimize the side reaction between LMA and electrolyte, therefore enable a dynamically stable LMA for long term cycling of li metal batteries. In this work, we report a series of LHCEs we developed recently that are highly stable with both LMA and high voltage cathode such as Ni rich LiNixCoyMn1-x-yO2 (x ≥ 0.6), LiCoO2 etc. These LHCEs not only exhibit the advantage of high concentration electrolyte, but also exhibit low viscosity, low cost of the low concentration electrolytes. Furthermore, these electrolytes can be tailored to be non-flammable and stable at low temperature. With appropriate additives, these LHCEs can also largely improve the stability of Si based Li ion batteries. The excellent performance of these batteries are mainly due to the formation of inorganic rich (such as LiF and Li2O) solid electrolyte interphase (SEI) on LMA and cathode electrolyte interphase (CEI) in these electrolytes. The monolithic solid electrolyte interphase (SEI) generated in some of these electrolytes is largely different with those of mosaic- or multilayer-type SEIs reported before. These electrolytes not only can improve the stability of LMA, but also greatly suppresses the phase transformation (from layer structure to rock salt) of the cathode and prevent dissolution of transition metal element in bulk cathode. Therefore, excellent cell performances in terms of long-term cycling stability and high rate capability is realized in high voltage LMBs together with reduced safety concerns. The fundamental mechanism behind the stability of these electrolytes to both LMA and high voltage cathode will also be discussed.