Anodic titanium oxide nanostructures as a fast-charging anode material for Li-ion battery

초록

Similar to lithium titanium oxide (LTO), titanium oxide has attracted remarkable interest as a fast chargeable and long-time stable anodic material for next-generation LIBs due to its relatively high lithium reaction potential (~1.7 V vs. Li/Li+), which allows the fast and safe operation of battery without the dendrite formation of Li metal. In addition, titanium oxide shows remarkably small volume expansion of around 3 % during the charge/discharge cycle, which enables to work for battery with good cycling stability and rate capability. Anodization of Ti can produce different types of nanostructures depending on the anodization conditions. In general, F- ion based electrolytes at the moderate anodization voltage (20V~80V) lead to the formation of nanotubular shapes; Aqueous electrolytes make a shorter length of nanotubes (less than 3 μm) whereas nanotubes with extremely high aspect ratio can be produced in non-aqueous electrolyte such as ethylene glycol. Recently, we have found that addition of oxalic, phosphoric, or sulfuric acid into aqueous electrolyte containing small amount of fluoride ions can allow the formation of hollow crystalline microcone with many multilayered nanofragments, which have been successfully demonstrated as a fast charging anode for Li-ion battery. In addition, plasma electrolytic oxidation where very high voltage (above 200 V) is imposed on the Ti substrate in the sulfuric acid containing small amount of silicon oxide precursor allows the formation of irregularly-formed micropores consisting of TiO2 and SiO2, which shows remarkably enhanced charging rate as well as the capacity of battery. Herein, we will discuss on anodically-prepared TiO2 nanostructures with a morphology of nanotubes, microcones, and PEO-formed porous structures, respectively, which can be successfully used for a fast-charging anode materials for Li-ions battery.