In a new report, researchers from Skoltech and their colleagues describe an organic material for the next generation of energy storage devices, with a structure based on an elegant molecular design principle. It was recently published in the journal ACS Applied Energy Materials and made it to the cover of the issue.
As the modern world increasingly relies on energy storage devices, the implementation of sustainable battery technologies becomes more important. These technologies are more environmentally friendly, easier to recycle, use only a limited number of elements, and are cheaper. Organic batteries are desirable candidates for such purposes. However, organic cathode materials that can store a lot of energy per unit mass, charge quickly, have high durability, and can be easily produced at large scales, are still underdeveloped.
To address this issue, researchers from Skoltech proposed a simple oxidatively active polyimide. It was synthesized by heating a mixture of aromatic dianhydride and meta-phenylenediamine — both easily available reagents. The material showed promising potential in various types of energy storage devices, such as lithium, sodium, and potassium batteries. It has high specific capacities (up to ~140 mAh/g), relatively high oxidation-reduction potentials, good stability under cyclic loads (up to 1000 cycles), and fast charge capability (<1 min).
The energy and output power of the new material were better compared to its previously known isomer derived from para-phenylenediamine. With the help of colleagues from the Institute of Chemical Physics of the Russian Academy of Sciences, it was shown that there are two main reasons for the superior performance of the new polyimide. First, it had smaller particles and significantly larger specific surface area, which allowed charge carriers to diffuse more easily. Second, the spatial arrangement of adjacent imide units in the polymer provided more energetically favorable binding of metal ions, increasing the oxidation-reduction potentials.
“This work is interesting not only because a new organic cathode material was studied,” says Roman Kapayev, a PhD student at Skoltech who developed the research, “but we are proposing a new molecular design principle for polyimides in batteries, which involves using aromatic molecules with amino groups in meta-positions as building blocks. For a long time, scientists paid little attention to this structural motif, replacing it with para-phenylenediamine or similar structures. Our results provide useful insight into how polyimides for batteries should be designed at the molecular level, which may lead to the development of cathode materials with even better characteristics.”