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 O-3 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. (C) 2015 Elsevier B.V. All rights reserved.