In Search of Electrolyte Additives for High Voltage LiNi0.5Mn1.5O4/Graphite Batteries

Current lithium ion battery research has focused on increasing energy density. This can be accomplished by using electrode material with a higher gravimetric/volumetric capacity or using cathode material that operates at a higher voltage than that of today’s lithium ion batteries (~4V). One promising material, LiNi_0.5Mn_1.5O₄ (LNMO), has a gravimetric capacity of ~140 mAh g^-1 and an operating voltage of ~4.7 V, yielding an energy density of 658 Wh kg^-1, compared to current state of the art (SOA) cathode materials LiCoO₂ (518 Wh kg^-1), LiMn₂O₄ (480 Wh kg^-1) or LiFePO₄ (578 Wh kg^-1). However, the SOA electrolyte (LiPF₆ in carbonate solvents) is not stable above ~4.5 V and undergoes oxidation reactions at the cathode surface. A possible solution to this problem is using additives that preferentially oxidize on the cathode surface and form a protective layer that prevents further electrolyte oxidation while still allowing lithium ions to transport back and forth. Current additives under investigation as well as results and interpretation will be discussed.