Effects of Na+ doping on crystalline structure and electrochemical performances of LiNi0.5Mn1.5O4 cathode material

Pristine LiNi0.5Mn1.5O4 and Na-doped Li0.95Na0.05Ni0.5Mn1.5O4 cathode materials were synthesized by a simple solid-state method. The effects of Na+ doping on the crystalline structure and electrochemical performance of LiNi0.5Mn1.5O4 cathode material were systematically investigated. The samples were characterized by XRD, SEM, FT-IR, CV, EIS and galvanostatic charge/discharge tests. It is found that both pristine and Na-doped samples exhibit secondary agglomerates composed of well-defined octahedral primary particle, but Na+ doping decreases the primary particle size to certain extent. Na+ doping can effectively inhibit the formation of LixNi1-xO impurity phase, enhance the Ni/Mn disordering degree, decrease the charge-transfer resistance and accelerate the lithium ion diffusion, which are conductive to the rate capability. However, the doped Na+ ions tend to occupy 8a Li sites, which forces equal amounts of Li+ ions to occupy 16d octahedral sites, making the spinel framework less stable, therefore the cycling stability is not improved obviously after Na+ doping.