Operation of Layered LiCoO₂ to Higher Voltages with a Localized Saturated Electrolyte

The commercialization of lithium-ion batteries started with a layered LiCoO₂ (LCO) cathode for portable electronics, but only 50% of its theoretical capacity can be used in practical cells due to detrimental surface and bulk degradations when charged to high voltages. We demonstrate here that the stability of the electrolyte plays a critical role in the performance of LCO at high voltages by employing a localized saturated electrolyte (LSE). With a cutoff voltage of 4.5 V, LCO achieves an initial 1 C discharge capacity of 176 mA h g^-1 and a capacity retention of 80% over 230 cycles. Even with a cutoff voltage of 4.6 V, LCO with 2% aluminum doping displays an initial discharge capacity of 189 mA h g^-1 at 1 C rate with 80% capacity retention over 137 cycles. With extensive analytical characterization, we show that the improved cycling stability stems from a suppression of the O3 to H1-3 phase transition as well as a robust inorganic-rich cathode-electrolyte interphase (CEI) facilitated by the LSE. This work highlights the importance of protecting the surface as well as the bulk with appropriate electrolytes for the high-voltage, higher-energy-density operation of LCO.