Rechargeable Batteries with Earth Abundant Elements – Organic Redox Polymers for Li-Organic Batteries

Abstract

The energy storage needs of the 21st century demand solutions that are both 'efficient' and 'sustainable.' The research explores alternatives to transition metal-based electrode materials traditionally used in LIBs, with a particular focus on redox-active organic materials, such as ample availability of precursors, structural diversity, non-toxicity, and low cost.[1] Conductive polymers, organosulfur compounds, organic radicals, small carbonyl compounds, carbonyl polymers, imine and azo compounds are the few classes of organics explored. This study focuses on the development of rechargeable batteries using earth-abundant elements, with a specific emphasis on organic redox polymers for Li-ion batteries (LIBs).[2] The investigation focuses on poly(3-vinyl-N-methylphenothiazine) (PVMPT), a p-type material, showcasing its excellent rate capability, cyclic stability, and reasonable theoretical capacity (112 mAh g−1). Despite the promising electrochemical performance of PVMPT, the electrode processing methods involve the use of toxic and flammable solvents, such as N-methyl-2-pyrrolidone (NMP), and expensive binders like polyvinylidene fluoride (PVDF).[3] To address these challenges, this study proposes the use of green solvents (Cyrene, Ƴ-valerolactone, and Dimethyl sulfoxide) for electrode processing, eliminating the need for toxic solvents and promoting the sustainability and safety of organic materials.[4] A shift to sustainable aqueous binders, such as carboxymethyl cellulose (CMC), sodium alginate (SA), and styrene-butadiene rubber (SBR),[5] is explored (Figure 1a-c), with the CMC system showing superior capacity retention.Additionally, the study delves into the Phenoxazine class of redoxomers, particularly polyvinylphenoxazine (PVMPO), a fast-charging cathode with a theoretical capacity of 120mAh g−1.[6] Challenges related to the dissolution of the oxidized state in the carbonate electrolyte are addressed by employing highly porous conductive additives and exploring different electrolyte compositions. A shift from toxic PVDF/NMP binder systems to aqueous binders (CMC, SBR, SA) is implemented, with the CMC-based electrodes demonstrating superior adhesion even after 10,000 cycles at 1C rate (Figure 1d-f).To conclude, the study believes that the strategic selection of conductive additives and electrolytes, coupled with the use of green solvents and aqueous binders, will contribute to the development of eco-friendly and sustainable energy storage systems. The comprehensive performance evaluation of the proposed systems is presented in detail, utilizing various characterization tools such as XRD, FT-IR, UV-VIS, and SEM.References Lee et al., Adv Mater., 2018, 42,1704682.Dühnen et al., Small Methods, 2020, 4, 2000039.Kolek et al., Energy Environ. Sci., 2017, 10, 2334.Ravikumar et al., ACS Appl. Energy Mater., 2021, 4, 696−703Bresser et al., Energy Environ. Sci., 2018,11, 3096-3127.Otteny et al., ACS Sustainable Chem. Eng., 2020, 8, 238−247 Figure 1