Hypercrosslinked Phenothiazine Polymer as a Low-Cost and Durable Organic Cathode for Rechargeable Lithium Batteries

Organic macromolecules bearing redox-active units are projected to be promising candidates as safe and sustainable alternatives to current inorganic intercalation electrodes in Li-ion batteries (LIBs). Although a range of redox polymers with various sizes, architectures, and topologies have been successfully evaluated in LIBs, cost-effective polymerization routes toward their synthesis are rarely considered. Here, a cost-effective synthetic route was employed to synthesize a hypercrosslinked polymeric network bearing a representative p-type organic redox functionality known as phenothiazine. This hypercrosslinked phenothiazine polymer (named IEP-29) was subsequently evaluated as an organic cathode in a lithium battery. The hereby used “knitting” polymerization technique operating through the Friedel–Crafts mechanism allowed us to produce the final atom-economic polymeric network. The material features a remarkably high density of phenothiazine redox units connected by only allylic carbons (−CH₂−), unlike bulky crosslinkers used for the production of common hyperbranched/porous polymers. The IEP-29 cathode delivered high capacity (106 mAh g^–1 at 0.5C), close to the theoretical value, high potential output (3.6 V vs Li/Li⁺), excellent rate capability (60 mAh g^–1 at 15C), and good cycle stability (79% capacity retention after 1000 cycles at 2C). Since the hereby used “knitting” method is a quite facile method to polymerize low-cost materials in high yields, the findings pave the way for valorization of the organic electrode materials for scalable applications without compromising the performance.