Synthesis and Electrochemical Investigation of O3-Type High-nickel NCM Cathodes for Sodium-ion Batteries

Sodium ion batteries(SIBs) are promising energy storage devices for smart grid applications due to their low cost and the high abundance of sodium, but few cathode materials of SIBs with high energy density are available for practical applications. Herein, a series of NaNCM ternary materials(NCM=nickel-cobalt-manganese) is obtained by solid- phase reaction with well-regulated temperature and other reaction conditions. XRD results show that impure NiO phase is more likely to occur under high nickel content. The cross-section SEM indicates that the primary particles in the electrode materials are radially distributed along the radial direction, and the internal porous structure is conducive to the infiltration of electrolyte. The initial specific capacities of Na[Ni0.68Co0.10Mn0.22]O2 (NaNCM712), Na[Ni0.6Co0.2Mn0.2]O2 (NaNCM622) and Na[Ni0.4Co0.3Mn0.3]O2(NaNCM433) at 0.2 C are 165.5, 153.1 and 146.8 mA·h/g, and the corresponding capacity retention rates are 63.2%, 78.5% and 71.7% after 100 cycles. NaNCM712 possesses the highest initial specific capacity, and NaNCM433 delivers the best rate capability. The rate capabilities of high-nickel and low-cobalt NaNCM cathodes need to be further improved. Moreover, ex-situ XRD pattern reveals the structure evolution (from O3 type to P2 type) during a long cycling charge and discharge process.