Department of Materials Science and Engineering, and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, USA.
Nature. 2014 Dec 4;516(7529):78-81. doi: 10.1038/nature13970. Epub 2014 Nov 26.
Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors--in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the 'MXene' family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a 'MAX' phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide 'clay' have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.
安全且高效的储能设备正变得日益重要。电化学电容器——尤其是赝电容器——在原则上可以提供数秒至数分钟的充电时间，并具有超过电池的功率密度。最近的研究主要集中在提高此类系统电极的重量性能上，但对于便携式电子设备和车辆而言，体积更为重要。基于碳的电极的最佳体积电容约为每立方厘米 300 法拉；水合氧化钌的体积电容可达每立方厘米 1000 至 1500 法拉，且循环性能极佳，但仅在薄膜中才有此表现。最近，通过在浓氢氟酸中从钛铝合金（Ti3AlC2，一种“MAX”相）蚀刻铝，制备出二维碳化钛（Ti3C2，属于“MXene”家族）的电极，其体积电容超过每立方厘米 300 法拉。在此，我们报告了一种使用氟化锂和盐酸溶液制备该材料的方法。所得亲水性材料在水合时会发生膨胀，可以像粘土一样成型，并干燥成高导电性固体，或卷成数十微米厚的薄膜。这种无添加剂的碳化钛“粘土”薄膜的体积电容高达每立方厘米 900 法拉，具有出色的循环性能和倍率性能。该电容几乎是我们之前报告的两倍，我们的合成方法还提供了更快的薄膜生产途径，同时避免了处理危险的浓氢氟酸。
