The development of sodium ion batteries is largely motivated by the growing cost and limited resources of lithium. Titanium dioxide (TiO 2 ), in the form of selforganized and well-oriented nanotube arrays, are considered as a highly attractive anode material for sodium ion batteries, due to their inherent safety, low cost, and structural stability. This work reports on the sodiation and desodiation characteristics of anodically grown, self-organized TiO 2 nanotubes annealed in an Ar/C 2 H 2 atmosphere (TiO 2−x − C). It is found that anatase TiO 2−x −C nanotubes demonstrate substantial self-improving charge storage capacities as cycling proceeds, leading to a specific capacity of 202.2 ± 50.6 mAh g −1 at a current rate of 30 mA g −1 (C/20). Subsequent kinetic analysis reveals a pseudocapacitive contribution which dominates the Na storage process in TiO 2−x −C nanotubes at fast sodiation rates. This pseudocapacitance in TiO 2−x −C nanotubes is found to enable exceptional high-rate capabilities with a specific capacity of 58.4 ± 14.6 mAh g −1 at a current rate of 12 A g −1 (20C).
In this work 3,4,9,10-perylenetetracarboxylic diimide (PTCDI)i si nvestigated as electrode material for organic Na-ion batteries. Since PTCDI is aw idely used industrial pigment, it may turn out to be ac ost-effective, abundant, and environmentally benign cathode materialf or secondary Na-ion batteries. Among other carbonyl pigments, PTCDI is especially interesting due to its high Na-storage capacity in combination with remarkable high rate capabilities.T he detailed analysiso fc yclic voltammetry measurements reveals a diffusion-less mechanism,s uggesting that Na-ion storagei n the PTCDI film allows for exceptionally fast charging/dischargingr ates. This finding is furtherc orroborated by galvanostatics odiation measurements at high rates of 17 C (2.3 Ag À1), showing that 57 %o ft he theoretically possible capacityo fP TCDI,o r7 8mAh g À1 ,a re attained in only 3.5 min charging time.
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