P2-type layered oxides are considered as promising cathode materials for rechargeable sodium ion batteries, but preparing P2-type cathodes with high-operating voltage and long-life is still a big challenge. Herein, spherical P2-type cathode Na0.67Ni0.17Co0.17Mn0.66Ti0.05Mg0.05O2 has been designed, and the critical roles of Ti and Mg on electrochemical performance of the cathodes are systematically investigated. The high-temperature XRD clearly exhibits the forming process of the pure phase material and suggests that the most suitable calcination temperature is 850 °C. The Ti/Mg cosubstitution does not break the long-range P2 structure and the spherical morphology of the material. In the electrochemical processes, the Na0.67Ni0.17Co0.17Mn0.56Ti0.05Mg0.05O2 electrode exhibits better electrochemical performance than that of the undoped Na0.67Ni0.17Co0.17Mn0.66O2. It delivers an initial reversible capacity of 151 mAh g–1 (2–4.5 V) with an average voltage of 3.8 V and exhibits a high capacity retention of 87.7% after 300 cycles at 100 mA g–1. The improved electrochemical performance benefits from the Ti/Mg cosubstitution; Ti improves the average voltage while Mg and Ti significantly mitigate the undesired P2 → O2 phase transition of the cathode, and these two elements jointly promote the development of the electrochemical performance. This strategy is also applicable to the optimization design of layered transition oxides and provides a new approach to prepare high-voltage, long-life cathodes for sodium ion batteries.

No abstract

The present work attempted to investigate the effect of Nb addition on the electrical properties of the (Ca,Si,Ce,Nb)-doped TiO2 ceramics. The content of added niobium is in the range 0.1-1.0mol %, while that of the other additives keeps constant. The results showed that an optimal composition doped with 0.8mol% Nb2O5, followed by sintering at 1350°C, was obtained with low V1 mA of 7.22V, high nonlinear coefficient of 5.76, ultrahigh dielectric constant (er = 86000) as well as relatively low loss (tgd = 0.52) in room temperature at 1 kHz. SEM studies show that change of niobium had significant influence on grain growth and micro structural characteristics of the sintered samples.

No abstract

Li2MnSiO4 cathode materials were prepared by hydrothermal reaction at 150°C using LiOH, Si(OC2H5)4 and Mn(Ac)2.4H2O as raw materials followed by a low temperature heat annealing at 650°C. The samples were characterized by X-ray diffraction, scanning electron microscopy, FTIR. The powders electrochemical performance was investigated in terms of cycling behavior. Nanometer-sized flake crystalline particles of Li2MnSiO4 are obtained with some degree of agglomeration and little impure phases are detected after annealing. The charge capacity of the Li2MnSiO4 samples is 306 mAh/g (about 1.84 Li+ per unit formula extracted), and the discharge capacity is 114 mAh/g (about 0.68 Li+ per unit formula inserted) in the first cycle in the voltage range of 1.5–4.8 V under a rate of C⁄20. With increasing cycle number, the cell exhibits a well cycle performance with more than 95% coulombic efficiency and the maintenance of 61% of its discharge capacity after 50 cycles.