Spin-Dependent Processes in Organic Radical Batteries / Спин-зависимые процессы в аккумуляторах на основе органических радикалов



Information on the Envisioned Activity
This proposal aims at fostering the recently initiated interdisciplinary collaboration between the research groups of Prof. Oleg Levin (Institute of Chemistry, SPbU) and Prof. Jan Behrends (Physics Department, FUB). The first contact between both scientist was established during the German-Russian Interdisciplinary Science Center Workshop at the FU Berlin in December 2018 and, since then, has resulted in a fruitful scientific discussion about the influence of electron spins on the operation principles of organic radical batteries. This discussion led to a proposal on an “Electron Paramagnetic Resonance Study of Organic Radical Batteries”, which was recently submitted by Dr. Elena Alekseevain the frame of the St. Petersburg State University and Freie Universität Berlin Joint Postdoctoral Fellowship Program. The research activities described in the present proposal are complementary to the collaborative efforts suggested in Dr. Alekseevain’s postdoc fellowship application and will, if it will be funded, provide excellent leverage.
Within the framework of this project it is envisioned to study spin-dependent processes in organic radical batteries. For this purpose we are planning to develop suitable sample geometries that allow us to perform spin-sensitive measurements on fully-processed organic radical batteries under realistic operating conditions. The results will contribute to a better understanding of charging and discharging processes on a molecular level and will help to identify efficiency limitations and possible loss mechanisms.

State of the Art and Preliminary Work
Batteries based on conjugated polymers containing stable radical substituents as high-capacitance groups, in particular nitroxide-radical groups, represent a promising class of future electrochemical power sources. They combine the advantages of high-power supercapacitors and high-energy batteries . The attractiveness of such organic radical batteries results from their high potential of charging/discharging and theoretical specific capacitance. An important advantage of organic materials over traditional inorganic materials is their availability and the low cost of the starting materials for the synthesis of the target polymers combined with good mechanical properties of the latter such as flexibility, elasticity and ease of treatment. At the same time, low electron conductivity of materials based on nitroxide/nitroxyl radicals, as well as many other classes of organic cathode materials, hampers their broad application as cathode material. In this regard, creation of novel materials based on nitroxyl radicals that possess high conductivity while retaining high power density, represents an actual task in the development of new kinds of batteries.
A possible solution of the conductivity problem is the design of new types of polymers, called redox-conducting polymers. Such compounds are based on polymers possessing a system of conjugated π-bonds and functional groups bearing free nitroxyl radicals. Successful creation of such materials solves simultaneously two tasks of the studied problem, namely it enables the creation of organic materials with high electron conductivity due to the previously proven fact of high electron conductivity of the conjugated polymers, and keeps the high redox capacitance of nitroxyl-radicals based materials by combining these two structural motifs in a single polymer molecule or composite material. As an example of such material, in a recent work a novel series of conjugated polymers bearing stable nitroxide pendant groups was reported to be suitable for possible applications as active cathode material in secondary batteries. However, despite the impressing performance of organic radical batteries, the charging and discharging processes on the molecular level are far from being well understood at the moment.
In order to elucidate these highly-relevant processes, suitable in-situ techniques are required. Electron Paramagnetic Resonance (EPR) spectroscopy is a good candidate for providing new insights as it was recently shown for e.g. inorganic lithium-based batteries . It allows real-time monitoring of the spin density on different molecular fragments, making it possible to detect charge localization and oxidation mechanisms. It is applied to ex-situ and in-situ study of the spin density in conducting polymers and others redox compounds , . Nitroxyl radicals have unpaired electron spins and can be easily detected by EPR techniques in their neutral state, but they become diamagnetic in the oxidized state. In fact, nitroxide radicals are probably the most studied paramagnetic system because they are routinely used for EPR-based distance measurements in proteins . Conducting polymers, on the contrary, are diamagnetic in the neutral state, but they become paramagnetic in their oxidized state due to formation of cation-radicals ("polarons") . This opens the intriguing perspective to simultaneously monitor the oxidation states of the conducting polymer backbone and pendant radical groups in conducting-redox polymer materials.
The Levin group has extensive experience in the synthesis of materials for organic radical batteries and their electrochemical characterisation. In contrast, the Behrends group has not yet worked on batteries, but has developed a strong expertise in studying charge-transfer and charge-transport processes in devices for solar energy conversion (mainly solar cells) using EPR techniques. The envisioned collaborate effort will thus combine the complementary expertise of the Levin group at SPbU and the Behrends group at FUB in a particularly useful manner.

AcronymJSMF 2019
Effective start/end date22/03/1930/09/19