Cai Peng, Zou Kangyu, Zou Guoqiang, Hou Hongshuai, Ji Xiaobo
College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, China.
Nanoscale. 2020 Feb 14;12(6):3677-3685. doi: 10.1039/c9nr10339b. Epub 2020 Jan 29.
Lithium ion capacitors (LICs) are regarded as one of the most promising energy storage devices since they can bridge the gap between lithium ion batteries and supercapacitors. However, the mismatches in specific capacity, high-rate behavior, and cycling stability between the two electrodes are the most critical issues that need to be addressed, severely limiting the large energy density and long cycling life of LICs while delivering high-power density output. Herein, quinone and ester-type oxygen-modified carbon has been successfully obtained by chemical activation with alkali, which is beneficial to the absorption of PF together with lithium ions, which would largely improve the electrode kinetics. In particular, the cathode capacity is considerably enhanced with the increase in the amount of oxygen functional groups. Moreover, for the full carbon LIC device, an energy density of 144 W h kg is exhibited at the power density of 200 W kg. Surprisingly, even after 10 000 cycles at 20 000 W kg, a capacity retention of 70.8% is successfully achieved. These remarkable results could be ascribed to the enhancement of cathode capacity and the acceleration of anode kinetics. Furthermore, the density functional theory (DFT) calculations prove that the oxygen functional groups can deliver enhanced electrochemical activity for lithium storage through surface-induced redox reactions. This elaborate study may open an avenue for resolving the issues with the electrode materials of LICs and deepen the understanding on the surface engineering strategies for incorporating oxygen-functional groups.
锂离子电容器（LICs）被视为最有前途的储能装置之一，因为它们能够弥合锂离子电池和超级电容器之间的差距。然而，两个电极在比容量、高倍率性能和循环稳定性方面的不匹配是最关键的问题，需要加以解决，这严重限制了LICs在提供高功率密度输出时的高能量密度和长循环寿命。在此，通过碱化学活化成功获得了醌型和酯型氧修饰碳，这有利于PF与锂离子的吸收，从而极大地改善电极动力学。特别是，随着氧官能团数量的增加，阴极容量显著提高。此外，对于全碳LIC器件，在功率密度为200 W kg时表现出144 W h kg的能量密度。令人惊讶的是，即使在20000 W kg下循环10000次后，仍成功实现了70.8%的容量保持率。这些显著结果可归因于阴极容量的提高和阳极动力学的加速。此外，密度泛函理论（DFT）计算证明，氧官能团可通过表面诱导的氧化还原反应提供增强的锂存储电化学活性。这项精心的研究可能为解决LICs电极材料的问题开辟一条途径，并加深对引入氧官能团的表面工程策略的理解。
