Nitroxide Based Radical Polymers as Active Materials for Organic Radical Batteries

Research on devices for electrical energy storage systems, such as lithium ion batteries, has currently received significant attention and their applications are very popular in portable electronic devices (mobile phones, laptop PCs, and digital cameras), in electric vehicles (electrics cars and drones), and recently it shows promises for stationary storage (solar- and wind-energy converters). However, to satisfy the demand for their use in the future, the Li-ion batteries should possess higher performances including superior storage capacity, fast charging-discharging process, better safety, long life cycle, adaptability to multiple scales, good processability, lighter weight, flexibility, and, most importantly, cost-effectiveness and non-toxicity.
Current rechargeable batteries are made of traditional metal-based (i.e., Fe, Co, Ni, Sn, Mn, V, Ta, Ru, etc.) active materials. Some of them show a high toxicity leading to serious environmental issues related to production and wastes. To solve these drawbacks, scientists investigate innovative and challenging approaches based on organic redox-active materials. As an example, nitroxides are a versatile class of stable free radicals that have long established themselves in a wide range of applications. Their incorporation into macromolecular architectures has added a further dimension to their use beyond their initial limitations and has led to several remarkable breakthroughs in energy storage applications. Organic-based radical batteries have several advantages over conventional batteries, such as increased safety, adapt- ability to wet fabrication processes, easy disposability, and capability of fabrication from less-limited resources, which are described along the fashion of green chemistry.
The focus of the current work was the synthesis of polymers with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) redox moieties and their applicability as energy storage materials. A series of new monomers with pendant TEMPO moieties were successfully obtained by synthetic approach at the hydroxy function at fourth position of the TEMPO-OH. The controlled radical polymerizations were also investigated to afford well-defined polymers with controlled and tunable molar masses, functionalities, and high radical density. These novel organic materials show promising prospect for lithium ion batteries as active cathode materials.