초록 |
Sodium ion batteries (SIB) attracted attention as candidates for next generation of secondary, rechargeable batteries. For large-scale application such as energy storage system (ESS), especially, SIB are expected to be economically advantageous. Many studies focused on intercalation reaction based materials such as transition metal oxides as cathode materials for SIB in order to achieve high capacity and long cycle life. Most approaches in previous reports of transition metal oxides as cathode materials involved substituting foreign element on transition metal layer. Compared to substitution on transition metal site, reports about substitution on alkali site is relatively less and substitution elements were limited. We report preferential substitution of Li on alkali site of Nax[Fe0.5Mn0.5]O2. Crystal structure and electrochemical performance was analyzed with high-resolution synchrotron X-ray diffraction, neutron diffraction, ex-situ inductively coupled plasma (ICP) and cycle test of Na-half cell.. The interlayer distance decreased with substitution of small, Li ion. Despite smaller interlayer distance, its electrochemical performance showed improved cycle life and rate capability, indicating that lithium on alkali site stabilized structure and enabled fluent sodium diffusion. DFT calculation of Na diffusion path showed Li lowered energy barrier of Na hopping within layered structure. |