Multiradical-stabilized hollow carbon spheres as a pressure-resistant cathode for fast lithium/sodium storage with excellent performance

Improving the energy density of pressure-tolerant batteries is an important approach to improving the working ability of underwater robots. Organic radical cathodes have a faster reaction mechanism than inorganic transition metal oxide cathodes but, currently, still do not provide high capacity, high rate, and stable cycling performance at the same time. Therefore, we fabricated a pressure-resistant organic radical cathode based on hollow carbon spheres (HCSs) with a stable structure and chemically modified the HCSs with nitroxide radical monomers (TEMPO-HCSs). Enriched nitroxide radicals form more active sites on HCSs, resulting in a better conductivity than that of nitroxide radical polymers and an improved electrochemical performance. The grafted nitroxide radicals stabilize the HCS structure, which is beneficial for application of TEMPO-HCSs as the cathode in lithium ion and sodium ion batteries at 5 MPa, showing high specific capacities of 339 and 297 mA h g^-1, respectively, as well as high rate and stable cycling performances. Constructing high-performance and pressure-resistant cathodes is a prerequisite for an increased efficiency of underwater robots.