Electrochemical and ab initio investigations to design a new phenothiazine based organic redox polymeric material for metal-ion battery cathodes

Abstract

Different N-substituted phenothiazines have been synthesized and their electrochemical behavior has been investigated in CH3CN in order to design the best polyphenothiazine based cathodic material candidate for lithium batteries. These compounds exhibit two successive reversible one-electron oxidation processes. Ab initio calculations demonstrate that the potential of the first process is a result of both the hybridization effects between the substituent and the phenothiazine unit as well as the change of conformation of the phenothiazine heterocycle during the oxidation process. More specifically, we show that an asymmetric molecular orbital spreading throughout an external cycle of the phenothiazine unit and the alkyl fragment is formed only if the alkyl fragment is long enough (from the methyl moiety onwards) and is at the origin of the bent conformation for N-substituted phenothiazines during oxidation. Electrochemical investigations supported by ab initio calculations allow the selection of a phenothiazinyl unit which is then polymerized by a Suzuki coupling strategy to avoid the common solubilization issue in carbonate-based liquid electrolytes of lithium cells. The first electrochemical measurements performed show that phenothiazine derivatives pave the way for a promising family of redox polymers intended to be used as organic positives for lithium batteries.

The rise of organic electrode materials for energy storage

“…Investigating a number of phenazine polymers, the authors found that having slightly different substituents has a significant impact on performance. 137 Compound 133 has the best performance because it has the smallest calculated geometry change upon charging, and therefore the largest electron transfer rate. Formulating 133 into a cathode gives an 80 mA h g À1 C sp at 0.1C with a sloping discharging plateau between 4.0 V and 3.2 V vs. Li/Li + .…”

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 .…”

Redox Polymers as Electrode-Active Materials for Batteries

“…45 A heteroaromatic with an attractively high redox potential of around 3.6 V versus Li/Li þ is phenothiazine. Several examples of phenothiazine-based redox polymers of type A [46][47][48][49] or type B [50][51][52] as battery cathode materials have been reported. The poly(vinylene) PVMPT (Figure 3) showed an outstanding cycling stability due to π-interactions between neighboring oxidized (and neutral) phenothiazine units.…”