Interphase Control in Lithium Metal Batteries Through Electrolyte Design

Future rechargeable Li metal batteries (LMBs) require a rational electrolyte design to stabilizethe interfaces between the electrolyte and both the lithium metal anode and the high voltagecathode. This remains the greatest challenge in achieving high cycling performance inLMBs. We report an ether-aided ionic liquid electrolyte which offers superior Li metaldeposition, high voltage (5 V) stability and non-flammability. High performance cycling ofLiNi0.8Mn0.1Co0.1O2 (4.4 V) and LiNi0.6Mn0.2Co0.2O2 (4.3 V) cells is demonstrated with highcoulombic efficiency (>99.5%) at room temperature and elevated temperatures, even at highpractical areal capacity for the latter of 3.8 mAh/cm2 and with a capacity retention of 91% after100 cycles. The ether-ionic liquid chemistry enables desirable plated Li microstructures withhigh packing density, minimal ‘dead’ or inactive lithium formation and dendrite-free long-termcycling. Along with XPS studies of cycled electrode surfaces, we use molecular dynamicssimulations to demonstrate that changes to the electrolyte interfacial chemistry upon additionof DME plays a decisive role in the formation of a compact stable SEI.