Pseudocapacitive layered iron vanadate nanosheets cathode for ultrahigh-rate lithium ion storage

Pseudocapacitive charge storage has been regarded as a promising mechanism to achieve both high specific energy and power energy storage devices. Some pseudocapacitive anode materials show great high-rate performance, however, it remains a significant challenge to develop the cathode ones. Herein, for the first time, we report a layered iron vanadate (Fe5V15O39(OH)(9)center dot 9H(2)O, named as kazakhstanite) nanosheets (FeVO NSs) with featuring ultrathin layer thickness (< 10 nm). The FeVO NSs are synthesized by a facile wet-chemical approach with a high yield. Compared to the FeVO nanoparticles, the crystalline layered FeVO NSs have additional interlayered Li+ storage sites, leading to the enhanced capacity. Ex-situ X-ray diffraction results demonstrate a non-phase change process and there is only similar to 1.1% layer expansion/shrinkage during lithiation and delithiation process. Based on detail kinetics analysis and ex-situ X-ray photoelectron spectroscopy results, it is found that over 70% of total capacity is pseudocapacitive contribution, which contributes to the ultrahigh-rate capability (a high capacity of 350, 273 and 90 mAh g(-1) is achieved at 0.1, 1 and 20 A g(-1), respectively) and excellent cycling stability over thousands of cycles. This work presents the high performance vanadate material that delivers highly pseudocapacitive behavior, and provides a promising direction to realize both high energy and high power lithium storage.