Organic Radical Battery Approaching Practical Use

Abstract

The electrochemical redox reactions of organic polymers bearing robust unpaired electrons were investigated to determine the applicability of these polymers to rechargeable batteries. Such an "organic radical battery" would be environmentally friendly and have high-power characteristics. This highlight review describes the performance of a battery using a nitroxyl radical polymer as the cathode active material. The electrontransfer mechanism and recent developments that should lead to the practical application of the organic radical battery are also described. Ç 1. IntroductionLithium-ion batteries are widely used power sources for portable electric devices such as cellular phones and laptop computers because of their high-energy density and long life. Application of these batteries is expanding to electric vehicles and domestic energy storage. 15 In these batteries, a lithium transition-metal oxide cathode and a graphite anode are used as energy storage electrodes. Since the lithium transition-metal oxide cathode comprises the main part of a lithium ion battery, the lithium transition-metal oxide mainly determines the battery's energy density and capacity. The lithium transition-metal oxide is charged/discharged electrochemically in accordance with deintercalation/intercalation of the lithium ions and oxidation/ reduction of the transition-metal ions. Although toxicity, safety, and resource availability are known problems with lithium transition-metal oxide, alternatives have been hardly reported except for conducting polymers and disulfide compounds. 6,7 Radical polymers are candidates for replacing lithium transition-metal oxide. 811 We call a polymer which has unpaired electrons a radical polymer. The disappearance of the unpaired electrons due to chemical bond formation can be suppressed by a precisely designed chemical structure through a combination of the resonance effect of the electrons and the sterically hindered effect of the substituent groups. Chemical groups such as nitroxyl, phenoxyl, and hydrazyl are robust structures with lessreactive unpaired electrons in the uncharged state. Radical polymers with alicyclic nitroxyl such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 2,2,5,5-tetramethylpyrrolidine-1-oxyl (PROXYL) in particular have been studied in detail.

Radical-radical rotaxanes with tetracationic cyclophane ring, and quaternary azaaromatic rotaxanes with cage macrocycles

“…41 The radical nature of BIPY •+ units is promising for design of functional composite materials, useful for conductive molecular electronic devices 42 or paramagnetic materials. 43,44 However, an inconvenience for these applications is the low resistance of BIPY •+ radical cations to oxidation by atmospheric oxygen. Today the finding of ways to increase the stability of BIPY…”

The Synthesis of Diquinone and Dihydroquinone Derivatives of Calix[4]arene and Electrochemical Characterization on Au(111) surface

“…7 Depending on the nature of the system, redox active organic molecules can be: a) dissolved in the organic solvents -redox shuttles and redox-flow batteries, 8,9 b) grafted to the solid support -solid cathode in Li-ion batteries, [10][11][12][13] or c) free standing cathode material. 14 Redox active organic molecules are chemically divided into: 6 organosulfur molecules, 15 organic free radical compounds, 16 and carbonyl compounds. 17 The latter, having a quinone/hydroquinone as a key representative, are playing a significant role in electroactivity relevant to biochemistry, medicine and electrochemistry.…”

Hydroalkoxylation of alkynes by a nitroxyl containing alcohol, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl: synthesis of spin-labeled enol ethers

“…In recent years a number of works (mainly patents) describing applications of 4-vinyloxy-TEMPO have appeared. For instance, polymers and copolymers based on this vinyl ether have been proposed as efficient cathode materials for greener organic radical batteries, [25][26][27][28][29][30][31][32][33][34][35] and a nano-scale memory device was constructed by nanolithographic patterning of oxidized poly(4-vinyloxy-TEMPO). 36 The first synthesis of 4-vinyloxy-TEMPO, which goes back to 1986, comprised the hydroalkoxylation of acetylene with 4-hydroxy-2,2,6,6-tetramethylpiperidine in KOH/DMSO followed by oxidation (Na 2 WO 4 as catalyst).…”

“…24 The first polymer of 4-vinyloxy-TEMPO was obtained via polymerization of its reduced form (4-vinyloxy-2,2,6,6-tetramethylpiperidine) followed by its oxidation. 24 Twenty years later, during the last decade, publications in this area have mushroomed (total number of works being 37, selected works [25][26][27][28][29][30][31][32][33][34][35][36] ), although the synthesis of the monomer was based mainly on transvinylation of 4-hydroxy-TEMPO with vinyl acetate in presence of expensive metal complex catalyst, [IrCl(cod) 2 ] (~ 8 mass% relative to the alcohol). [25][26][27][28][29][30][31][32][33][34][35][36] Since the first synthesis of 4-vinyloxy-TEMPO, 24 no attempt to develop an expedient hydroalkoxylation of alkynes with 4-hydroxy-TEMPO has been undertaken.…”

“…24 Twenty years later, during the last decade, publications in this area have mushroomed (total number of works being 37, selected works [25][26][27][28][29][30][31][32][33][34][35][36] ), although the synthesis of the monomer was based mainly on transvinylation of 4-hydroxy-TEMPO with vinyl acetate in presence of expensive metal complex catalyst, [IrCl(cod) 2 ] (~ 8 mass% relative to the alcohol). [25][26][27][28][29][30][31][32][33][34][35][36] Since the first synthesis of 4-vinyloxy-TEMPO, 24 no attempt to develop an expedient hydroalkoxylation of alkynes with 4-hydroxy-TEMPO has been undertaken. Meanwhile, having in mind that direct superbasecatalyzed hydroalkoxylation of alkynes with hydroxyl compounds has proved to be highly efficient, [37][38][39][40][41][42] we decided to revisit the vinylation of 4-hydroxy-TEMPO with various alkynes exploiting our expertise gained during the last decade.…”