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Anatase TiO 2 used as the sodium-storage anode is coupled with a graphite cathode to construct dualion batteries. The batteries display wide voltage window (1.0− 4.7 V), long cycling stability (98 mAh g −1 after 1400 cycles at 500 mA g −1 ), and considerable rate performance (102 mAh g −1 at 1500 mA g −1 ). Furthermore, the kinetic behaviors of Na + and PF 6 − ions are investigated through electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and the potentiostatic intermittent titration technique. The corresponding apparent ion diffusion coefficient is calculated, and the results indicate that the transport of PF 6 − anions in the graphite cathode is swift.

A careful examination of the dissolution/diffusion through liquid/precipitation steps of the well-accepted vapor-liquid-solid whisker growth mechanism has been conducted. Various diffusional processes involved in the whisker growth, such as solid surface diffusion, liquid surface diffusion, and bulk liquid diffusion, have been evaluated. It is noted that the diffusion along liquid alloy droplet surfaces, driven by both a concentration gradient and surface energy decrease, should not be ignored. Mass transport rate calculations using a simplified one-dimensional model show that the surface diffusion becomes more important with decreasing whisker diameter, decreasing solubility of growth species in the liquid phase, and increasing ratio of surface diffusion coefficient to bulk liquid diffusion coefficient. The diffusion along the liquid alloy droplet surface may play a major role in the growth of compound whiskers. Inclusion of the liquid droplet surface diffusion in the vapor-liquid-solid mechanism is proposed.