Influence of Doping, Surface Area, and Porosity of Nanostructure Electrodes in Lithium-Ion Batteries
As an example, Figure 1 shows cycling performance of V2O5 electrodes in pure form (a), after Sn doping (b), and in the nano-belt configuration (c) [1,2]. Both the pure and Sn-doped electrodes exhibit an initial drop in specific capacity followed by an activation period that is somewhat longer for the Sn-doped electrode than for the pure electrode. The specific capacity of the pure electrode decays to about 180 mAh g–1 within 50 cycles. Notably, the Sn-doped electrode retains nearly its maximum capacity of 320 mAh g–1 throughout 50 cycles. Given the similar morphologies of these two electrodes, shown in Fig. 2(a) and (b), the change in capacity is most likely due to a chemical or electronic structure effect brought about by Sn-doping.
In contrast, the Na400 nano-belt electrode, prepared by reaction of V2O5 with H2C2O4 and NaNO3 and subsequent calcining to 400 °C, exhibits a steady yet slightly increasing capacity with cycling. The capacities of the pure V2O5 electrode (a) and the nano-belt electrode (c) become similar at about 40 cycles. This similarity may reflect changes in surface area of the pure electrode. Initially, the nano-belt electrode has, due to its well-formed belt structure [Fig. 2(c)], lower surface area than does the pure electrode. With cycling time the pure electrode eventually loses surface area, reaching a point similar to that of the nano-belt.
The extent of other factors, such as surface and bulk defects and volume change, are currently under investigation. This presentation will consider V2O5 electrodes and a new lithium titanate electrode as two model materials to illustrate the influences of doping, surface defects and carbon coating, and nanostructures on the lithium-ion intercalation properties.
1. Y. Li, J. Yao, E. Uchaker, M. Zhang, J. Tian, X. Liu, and G. Cao, J. Phys. Chem. C, 117, 23507 (2013).