PNNL

Abstract

Lithium-ion batteries (LIBs) with high nickel (Ni) content LiNixMnyCozO2 (x+y+z=1) (NMC with Ni?0.6) cathodes operated at high charge voltages have been considered as one of the most promising candidates for addressing the challenge of increasing energy density demand. Conventional LiPF6-organocarbonates electrolytes exhibit incompatibility with such cell chemistries under certain testing conditions due to the instability of electrode/electrolyte interphases. In response to this challenge, ether-based electrolytes with finely tuned structure and composition of solvation sheaths were developed and evaluated in graphite||NMC811 cell chemistry in 2.5-4.4 V, despite ethers were conventionally considered to be unfavorable electrolyte solvents for LIBs due to their anodic instability above 4.0 V and co-intercalation into graphite electrodes. The functional ether-based electrolytes in this work enable both excellent cycle life and high rate capability of graphite||NMC811 cells. Mechanistic studies reveal that the unique structure and composition of the solvation sheath of the functional ether electrolytes is the main reason behind their excellent anodic stability and effective protection of graphite electrode, and consequently, the extraordinary cell performances operated at high charge cut-off voltages. This work also provides a feasible approach in developing highly stable functional electrolytes for high energy density LIBs.