Research progress of carbonyl compounds as organic electrode materials for lithium-ion battery

With the application of lithium-ion battery from portable electronic devices to large-scale energy storage systems, it is important to develop lithium-ion battery with high energy density, high power density and long cycle life. As we all know, the performance of lithium-ion battery greatly depends on the electrode materials. However, there are some defects in widely used inorganic electrode materials. First, the conventional inorganic cathodes (e.g., LiCoO2 and LiFePO4) and graphite anode, are restricted by their theoretical specific capacity, making it difficult to further improve their energy density. Second, the large-scale production and use of transition metal (e.g., Mn, Fe, Co and Ni) based inorganic materials, cause more and more concern for resources and environmental issues. Third, although many kinds of high-capacity anode materials (e.g., Si, Sn, and transition-metal oxides) have been widely investigated in the latest two decades, the progress seems to be very sluggish, and these materials still exhibit poor rate capability and cycling behavior. To overcome the limitations arising from the electrode materials, one of the major challenges is finding new electrodes with high energy density and power density. Compared with traditional inorganic materials, organic electrode materials have received extensive attention in recent years because of the following advantages. First, organic compounds are potentially sustainable and renewable materials because many of them can be obtained from natural products and biomass. Second, the electrochemical properties of organic compounds can be tuned through the modification of the structures as well as the introduction of functional groups. Besides, the organic compounds are composed of naturally abundant chemical elements such as C, H, O, N and S, the absence of metals enables easy disposal of the material by low temperature combustion. Among all the electroactive organic compounds, conjugated carbonyl compounds have been extensively studied because of their diverse structures, high theoretical capacity and fast reaction kinetics. Compared to inorganic electrode materials, the research on organic electrodes with high electrochemical performances is still in its early stage, and might not be familiar to many researchers. Although several views on organic materials have been published, no view can be found in the literature that introduces these organic materials from the aspects of anode, cathode and full battery. In this review, the researches of the carbonyl compounds as electrode materials for lithium-ion batteries in recent years were reviewed from the aspects of cathode, anode and full battery. Moreover, recently reported high performance organic electrodes have been included and explained in detail. Especially, we also highlight the recently reported hexahexanone cathode and pyromellitic anhydride anode, which are believed to be potential high performance electrodes due to their unique conjugated structures and high specific capacity. In addition, the design strategy and electrochemical performances of the electrodes are described, and their advantages and disadvantages are analyzed. Last, the problems need to be solved for organic compounds as electrode materials of lithium-ion battery are pointed out. Hopefully, with the increasing interest in exploring organic compounds, organic electrode-based lithium-ion battery would be commercialized and used in our daily life in the near future.