A Small Molecular Symmetric All-Organic Lithium-Ion Battery.

The structural designability of organic electrode materials makes them attractive for symmetric all-organic batteries (SAOBs) by virtue of different plateaus. However, quite a few works have reported all-organic batteries and it is still challenging to develop a high-performance organic material for SAOBs. Herein, a small molecule, 2,3,7,8-tetraaminophenazine-1,4,6,9-tetraone (TAPT), is reported for SAOBs. The rich C=O and C=N groups ensure the high capacity at both plateaus for C=O/C-O and C=N/C-N redox reactions, which are hence utilized as cathodic and anodic active centers respectively. Moreover, the presence of C=O, C=N and NH2 groups resulted in plentiful strong intermolecular interactions, leading to layered structures, insolubility and high stability. The rich functional groups also facilitated the chelation of N and O with Li cations and hence benefited the storage of Li cations. The electrochemical performances of TAPT-based SAOBs outperformed all of the previously reported SAOBs.

Successive Storage of Cations and Anions by Ligands of π-d-Conjugated Coordination Polymers Enabling Robust Sodium-Ion Batteries.

The oxidation of π-d-conjugated coordination polymers (CCPs) accompanied with anion insertion has the merits of increasing the capacity and elevating the discharge voltages. However, previous reports on this mechanism either required more investigations or showed low capacity and poor cyclablity. Herein, triphenylene-catecholate-based two-dimensional CCPs are constructed by employing inactive transition-metal ions (Zn2+ ) as nodes, forming Zn-HHTP. Substantial characterizations and theoretical calculations indicate the successive storage of cations and anions by redox reactions of only ligands, leading to a high reversible capacity of ≈150 mAh g-1 at 100 mA g-1 and a remarkable capacity retention of 90 % after 1000 cycles. On the contrary, as a control experiment, the analogous CCPs (Cu-HHTP) with Cu2+ nodes, where both ligands and metal ions undergo redox reactions, accompanied by the storage of only Na+ cations, show a much poorer cyclability. These results highlight the importance of redox reactions of only ligands for long-term cycle life and the insight into the storage mechanisms deepens our understanding on CCPs for the further design of CCPs with high performance.