Effects of Na+ doping on crystalline structure and electrochemical performances of LiNi0.5Mn1.5O4 cathode material
(Key Laboratory of Special Functional Materials for Ecological Environment and Information, Ministry of Education, Institute of Power Source and Ecomaterials Science, Hebei University of Technology, Tianjin 300130, China)
Abstract: 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.
Key words: cathode material; LiNi0.5Mn1.5O4; Na+ doping; electrochemical performance