Enhancement in the electrochemical stability at high voltage of high nickel cathode through constructing ultrathin LiCoPO4 coating

Abstract

The challenge of commercial layered-structure nickel-rich cathodes in lithium-ion batteries (LIBs) are the rapid capacity/voltage degradation at high rate capability and thermal runaway. The wide operational voltage range and excellent electrochemical stability of the coating material are key points to improve electrochemical performance and thermal stability at high voltage and high rate conditions. The uniformly olivine-type LiCoPO4 (LCP) coatings were successfully prepared on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode combining sol–gel method and heat treatment. The capacity retention and operating voltage stability of the cathode at high cutoff voltage of 4.6 V were dramatically improved due to the ultrathin and stable interface is designed. The modified NCM811 exhibited a high cycling capacity of 157.7 mAh·g−1 at 5 C with a capacity loss of only 12.1 %. In high nickel cathode coating modification, LCP as the thinnest phosphate coating effectively improves the capacity decay of the cathode at high rate. The interface reconstruction provided a stable channel of Li+ transport, which suppressed the cathode/electrolyte interface reaction to enhance the stability. The formation of strong covalent PO bonds at the interface significantly reduced the oxidizing activity on the NCM811 surface, further inhibiting the oxygen release and irreversible phase transition.