| 초록 |
Sodium ion batteries (SIB) received much attention as alternative candidate for lithium ion batteries (LIB), especially in large scale energy storage system. Due to abundance and wide distribution of constituent materials, sodium ion batteries are expected to be economically advantageous at large scale. Many studies focused on intercalation reaction based cathode materials, such as transition metal oxide with layered structure, for SIB in order to achieve stable cycle life and high capacity. Previous reports of transition metal oxides often involved varying composition of transition metal elements or substituting on transition metal site. Compared to substitution on transition metal site, reports about substitution on alkali site is relatively less and substitution elements were limited. Here, we report preferential substitution of Li on alkali site and Li-assisted Na hopping. Lithium was preferentially substituted on alkali site of layered structure, instead of transition metal site, be varying composition of transition metal elements. 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. DFT calculation of Na diffusion path showed Li lowered energy barrier of Na hopping within layered structure. Li substituted material showed higher capacity retention and rate capability despite smaller interlayer distance, supporting that Li-assisted Na hopping enhances electrochemical performance. |
