An Additive with Carbonate-Sulfate Hybrid Structure Enables High-Voltage and Long-Life Lithium-Ion Batteries.

Driving LiNixCoyMnzO2 (NCM) cathode to operate at high voltage represents an effective strategy to increase battery energy density, however, it also applies extreme electrochemical constraints on both electrode and electrolyte materials, which induce the generation of oxygen gas and formation of vacancies, transition metal ion dissolution, degradation of lattice structure and cracking of particles, as well as electrolyte oxidation. In this study, a new electrolyte molecule that combines the structures of carbonate and sulfates is designed. When used at additive level, the reactivity of this polycyclic structure ensures its early reduction at anode before any other components in the electrolyte, whose products form robust electrolyte-electrode interphases and prevent sustained electrolyte decomposition while preserving electrodes' integrity. Consequently, this carbonate-sulfate hybrid enables 4.4 V graphite||LiNi0.6Co0.1Mn0.3O2 to achieve outstanding thermal stability over 1000 cycles with only minor capacity decay (90% capacity retention) even at elevated temperatures, and with 90% capacity retention and only 3% volume increment after long-term aging at 60 °C. Moreover, the interphasial stability brought by the new molecule renders the battery significantly safer by postponing thermal runaway under abusive conditions. The universal applicability of this hybrid is also demonstrated in diverse battery chemistries including LiCoO2 and LiMn0.6Fe0.4PO4 cathodes with outstanding performances.