Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742.
Electrochemistry Branch, Sensors and Electron Devices Directorate, US Army Research Laboratory, Adelphi, MD 20783.
Proc Natl Acad Sci U S A. 2018 Feb 27;115(9):2004-2009. doi: 10.1073/pnas.1717892115. Epub 2018 Feb 9.
Organic compounds are desirable for sustainable Li-ion batteries (LIBs), but the poor cycle stability and low power density limit their large-scale application. Here we report a family of organic compounds containing azo group (N=N) for reversible lithiation/delithiation. Azobenzene-4,4'-dicarboxylic acid lithium salt (ADALS) with an azo group in the center of the conjugated structure is used as a model azo compound to investigate the electrochemical behaviors and reaction mechanism of azo compounds. In LIBs, ADALS can provide a capacity of 190 mAh g at 0.5 C (corresponding to current density of 95 mA g) and still retain 90%, 71%, and 56% of the capacity when the current density is increased to 2 C, 10 C, and 20 C, respectively. Moreover, ADALS retains 89% of initial capacity after 5,000 cycles at 20 C with a slow capacity decay rate of 0.0023% per cycle, representing one of the best performances in all organic compounds. Superior electrochemical behavior of ADALS is also observed in Na-ion batteries, demonstrating that azo compounds are universal electrode materials for alkali-ion batteries. The highly reversible redox chemistry of azo compounds to alkali ions was confirmed by density-functional theory (DFT) calculations. It provides opportunities for developing sustainable batteries.
有机化合物是可持续锂离子电池（LIB）的理想选择，但较差的循环稳定性和低的功率密度限制了其大规模应用。在这里，我们报告了一系列含有偶氮基团（N=N）的有机化合物，用于可逆的锂化/脱锂。具有共轭结构中心偶氮基团的偶氮苯-4,4'-二羧酸锂盐（ADALS）被用作模型偶氮化合物，以研究偶氮化合物的电化学行为和反应机理。在 LIB 中，ADALS 可以在 0.5 C（对应于 95 mA g 的电流密度）下提供 190 mAh g 的容量，并且当电流密度增加到 2 C、10 C 和 20 C 时，容量分别保留 90%、71%和 56%。此外，ADALS 在 20 C 下经过 5000 次循环后仍保留初始容量的 89%，其容量衰减率缓慢，为 0.0023%/循环，这是所有有机化合物中表现最好的之一。ADALS 在钠离子电池中也表现出优异的电化学性能，表明偶氮化合物是碱离子电池的通用电极材料。偶氮化合物对碱离子的高度可逆氧化还原化学通过密度泛函理论（DFT）计算得到了证实。这为开发可持续电池提供了机会。
