Phenothiazine-Based Polymer Cathode Materials with Ultrahigh Power Densities for Lithium Ion Batteries

Abstract

Lithium ion batteries (LIBs) currently deliver the highest energy density of any known secondary electrochemical energy storage system. However, new cathode materials, which can deliver both high energy and power densities, are needed to improve LIBs. Herein, we report on the synthesis of a new organic-based redox-active material centered about phenothiazine and phenylenediamine units. Improved Coulombic efficiencies and greater capacity retention during cycling are observed through the copolymerization of a phenothiazine-based monomer that yields cross-linked materials. With this as the positive electrode in Li-coin cells, high specific capacities (150 mAh/g) are delivered at very positive operating voltages (2.8−4.3 V vs Li + /Li), yielding high energy densities. The material has low charge transfer resistance as verified by electrochemical impedance spectroscopy, which contributes in delivering previously unseen power densities in coin cells for organic-based cathodes. Excellent retention of capacity (82%) is observed at ultrafast discharge rates (120 C).

Cross‐linking Effects on Performance Metrics of Phenazine‐Based Polymer Cathodes

“…In our previous study on cross‐linked poly(phenothiazine–dimethylphenylenediamine), we observed that, above a certain threshold of cross‐linking density, rate performance declined as a result of lowered ionic transport through the material . Therefore, two molar ratios of 4 and 5 were examined to determine a cross‐linking density that would mitigate dissolution while retaining high ion diffusion (Table , entries 3 and 4).…”

“…Cross‐linking can disrupt ordering and restrict polymer mobility to ensure an open, amorphous structure even in the swelled state. Recently, we reported on a cathode material with 3,7‐diamino‐substituted phenothiazines as charge‐storage elements . In that study, cross‐linking of a linear energy storage polymer led to improved stability on cycling, higher discharge capacity, and improved rate performance.…”

Phenothiazine‐Functionalized Poly(norbornene)s as High‐Rate Cathode Materials for Organic Batteries

“…Another redox‐active group with a similar oxidation potential is phenothiazine (PT). We, among other groups, have investigated PT‐based polymers as cathode materials. In particular poly(3‐vinyl‐ N ‐methylphenothiazine) (PVMPT) showed excellent results regarding cycling stability and rate capability .…”

Symmetric All‐Organic Battery Containing a Dual Redox‐Active Polymer as Cathode and Anode Material

“…Peterson et al. followed this strategy and combined phenothiazine with phenylenediamine units, allowing capacity values of 150 mAh g −1 and high voltages (2.8–4.3 V vs. Li/Li + ) . On the other hand, polyimides containing naphthalene or pyromellitic moieties have been widely investigated as anode materials not only for Li‐ or Na‐ion batteries but also for other alkali‐ion batteries, such as Ca and Mg .…”