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.

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The performance of a redox compound in redox flow batteries (RFB) highly depends on the electrolytic medium and operating conditions. It is exemplified in this work with the commercially available and relatively low-cost dye 3,4-dihydroxy-9,10-anthraquinone-2-sulfonic acid (ARS), which was used as negolyte in basic medium. At high pH, the ARS behavior revealed interesting features for RFB applications, such as a low halfwave potential of À 0.99 V (vs Ag/AgCl), negatively shifted by phenolate groups, and an improved solubility compared with acidic medium depending on the nature of the cations. For the highly soluble ARS potassium salt (ARSK), a maximum power density of 117 mW cm À 2 and a demonstrated energy density of 20 Wh L À 1 were obtained with K 4 [Fe(CN) 6 ] as posolyte. The capacity slightly decreased during cycling, reaching 90 % after 325 cycles. A long cycling of ARS sodium salt (ARSNa) over 11 operating months was demonstrated in this work. A slow chemical degradation was highlighted giving rise to the formation of 3-hydroxy-9,10-anthraquinone-2-sulfonic acid (HAQS) as the main degradation product due to hydrodeoxygenation reaction. Interestingly, this compound exhibited high performance in RFB and a good stability with a loss of capacity of 0.29 % per day.

International audiencePhotosensitive dye based boron dipyrromethene polymer has been investigated in the scope of photo-assisted rechargeable batteries. Under visible light, a 0.8 V gain has been observed for the BODIPY moiety reduction process. The light energy contributes advantageously to the charge yield of the organicmaterial potentially involved in lithium batteries

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