Z.T. Wu

High performance Na-doped lithium zinc titanate as anode material for Li-ion batteries

A series of Li2−xNaxZnTi3O8 (x = 0, 0.05, 0.10, 0.15, 0.20) are prepared for the first time by a simple solid state method. Upon Na-doping, Rietveld refinement reveals that Na+ takes the 8c tetrahedral sites shared with Li+ and Zn2+ in the structure. Due to the larger ionic radius of Na+ than that of Li+, an increased disorder degree of ion locations in the structure is induced by Na doping. Furthermore, the lithium ion diffusion tunnel is also expanded after Na doping. Thus, higher lithium ion diffusion coefficient can be observed for all the Na-doped Li2ZnTi3O8 samples. However, phase analysis shows that high Na-doping content can result in the formation of impurity in the as-obtained titanates. Besides, the existence of too many Na ions in the spinel also decreases the structural stability. Therefore, Na-doping with low dose is beneficial to improve the electrochemical performance of Li2ZnTi3O8. Electrochemical evaluations show that Li1.95Na0.05ZnTi3O8 has the best lithium storage property among all the Li2−xNaxZnTi3O8. It can be found that Li1.95Na0.05ZnTi3O8 can deliver a reversible capacity of 267.3 mA h g−1 after 50 cycles. This finding can provide an experimental support to synthesize high performance Ti-based materials by Na doping.

CrN thin films prepared by reactive DC magnetron sputtering for symmetric supercapacitors

Supercapacitors have been becoming indispensable energy storage devices in micro-electromechanical systems and have been widely studied over the past few decades. Transition metal nitrides with excellent electrical conductivity and superior cycling stability are promising candidates as supercapacitor electrode materials. In this work, we report the fabrication of CrN thin films using reactive DC magnetron sputtering and further their applications for symmetric supercapacitors for the first time. The CrN thin film electrodes fabricated under the deposition pressure of 3.5 Pa show an areal specific capacitance of 12.8 mF cm−2 at 1.0 mA cm−2 and high cycling stability with 92.1% capacitance retention after 20 000 cycles in a 0.5 M H2SO4 electrolyte. Furthermore, our developed CrN//CrN symmetric supercapacitor can deliver a high energy density of 8.2 mW h cm−3 at the power density of 0.7 W cm−3 along with outstanding cycling stability. Thus, the CrN thin films have great potential for application in supercapacitors and other energy storage systems.