Exploring Li substituted O3-structured layered oxides NaLixNi1/3 − xMn1/3 + xCo1/3 − xO2 (x = 0.07, 0.13, and 0.2) as promising cathode materials for rechargeable Na batteries

A series of new O3 cathode materials, NaLixNi1/3 − xMn1/3 + xCo1/3 − xO2 (x = 0.07, 0.13, and 0.2), are explored by substituting Li in the layered structure. Single phase is achieved at low Li content (x = 0.07) while the increase in the amount of Li leads to impurity phase. The optimized composition, NaLi0.07Ni0.26Mn0.4Co0.26O2, demonstrates good capacity retention and excellent rate performance. Ex-situ synchrotron XRD suggests that the O3 phase is maintained upon cycling, thus results in the excellent performance. X-ray absorption spectroscopy data shows that Ni2 +/Ni4 + is the main redox couple while Co3 +/Co4 + partially contributes to balancing the charge.