(Invited) Lithium Ion Transfer Kinetics of Size Regulated TiO_2(B) Nanosheets with Vertical, Random, and Horizontal Alignment for High Rate Lithium Ion Capacitors and Batteries

摘要

TiO_2(B) has a high theoretical capacity of 335 mAh g~(-1) for Li~+ intercalation and thus is a promising candidate as negative electrodes for lithium-ion capacitors and Li-ion batteries. For high rate lithium-ion transfer, it is important to shorten the Li~+ diffusion path by using nanostructured TiO_2(B). In this work, TiO_2(B) nanosheets with different equivalent diameter D_e of 300 nm and 30 nm were prepared. In addition, the orientation of the TiO_2(B) nanosheets was manipulated by altering the deposition method and drying process. For large-sized TiO_2(B)(300 nm) nanosheet electrodes, the orientation effect was not clear and the amount of lithiation (SOC) was almost the same. Even at a rather low loading of 0.35 mg/cm~2, only 1/5 of the theoretical capacity could be intercalated (Li_(0.2)TiO_2, 20% SOC) at 0.2C rate. By downsizing TiO_2(B) to D_e=30 nm, a two time increase in rate performance (Li_(0.4)TiO_2 at 0.2C) was obtained for vertically-aligned electrodes. Although the orientation of small-sized TiO_2(B) had a large influence on Li~+ transfer kinetics, 100% SOC could not be achieved even at 0.2C, suggesting the lack of electronic conductivity as a governing factor.