Bifunctional mechanism and electrochemical performance of self-healing nitrile ether electrolyte additives in 4.5 V LiCoO2/artificial graphite lithium-ion batteries

To increase the lifespan, energy density, and temperature performance of LiCoO2/artificial graphite lithium-ion batteries (LCO/AG LIBs) to meet the requirements of 5G devices, three nitrile ether molecules are developed as bifunctional electrolyte additives to match 4.5 V LCO/AG LIBs. The commonalities and differences of these three nitrile ether molecules as additives are revealed. The batteries with nitrile ether additives can be cycled more than 1000 cycles at 4.5 V, 25 °C, and 1C, while the capacity retention of battery without additives after 200 cycles is close to 0%. At 45 °C, additive with four CN bonds can also lead to stable cycling over 600 cycles, whereas the batteries without additives fail after 100 cycles. It is demonstrated that nitrile ether additives participate in the repair and stabilization of interface films, which decreases the electrolyte decomposition. And the greater the number of CN bonds contained in the molecules, the stronger ability inhibits Co3+ dissolution from LCO, which is the main reason for the difference in the properties of the nitrile ether molecule. These results not only reveal the promising prospects of nitrile ether additives in practical applications but also provide a strategy to develop functional electrolytes for high voltage LCO/AG LIBs.