RESUMO
The principle of encapsulation/release of a guest molecule from stimuli responsive hydrogels (SRHs) is mainly realised with pH, temperature or light stimuli. However, only a limited number of redox responsive hydrogels have been investigated so far. We report here the development of a SRH that can release its guest molecule upon a redox stimulus. To obtain this redox hydrogel, we have introduced into the hydrogel the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) stable nitroxide radical, which can be reversibly oxidized into an oxoammonium cation (TEMPO+). Water solubility is provided by the presence of the (oligoethyleneglycol)methacrylate (OEGMA) comonomer. Electrochemical and mechanical characterization showed that those gels exhibit interesting physicochemical properties, making them very promising candidates for practical use in a wide range of applications.
RESUMO
The electrochemistry of poly(2,5-dihydroxyaniline) (PDHA), a novel hybrid molecular configuration with redox active sites and electrical charge conduction along the polymer chain, has been recently reported. The theoretical capacity of this material is estimated at 443 mAh g-1, with high power performances being proposed given the intrinsic electrical conductivity. However, the initial results were below the expectations: only half the theoretical capacity attained, poor cycling stability and modest power behavior calling for further investigations on improving these performances. Herein we detail the optimized chemical synthesis and electrode formulation for poly(2,5-dihydroxyaniline) resulting in improved cycling stability, power performances and defined electrochemical response. We also detail the alternative electrochemical synthesis and activation route for PDHA and compare the results with the chemical approach.
RESUMO
Water-soluble binders can enable greener and cost-effective Li-ion battery manufacturing by eliminating the standard fluorine-based formulations and associated organic solvents. The issue with water-based dispersions, however, remains the difficulty in stabilizing them, requiring additional processing complexity. Herein, we show that mechanochemical conversion of a regular poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) water-based dispersion produces a hydrogel that meets all the requirements as binder for lithium-ion battery electrode manufacture. We particularly highlight the suitable slurry rheology, improved adhesion, intrinsic electrical conductivity, large potential stability window and limited corrosion of metal current collectors and active electrode materials, compared to standard binder or regular PEDOT:PSS solution-based processing. When incorporating the active materials, conductive carbon and additives with PEDOT:PSS, the mechanochemical processing induces simultaneous binder gelation and fine mixing of the components. The formed slurries are stable, show no phase segregation when stored for months, and produce highly uniform thin (25 µm) to very thick (500 µm) films in a single coating step, with no material segregation even upon slow drying. In conjunction with PEDOT:PSS hydrogels, technologically relevant materials including silicon, tin, and graphite negative electrodes as well as LiCoO2, LiMn2O4, LiFePO4, and carbon-sulfur positive electrodes show superior cycling stability and power-rate performances compared to standard binder formulation, while significantly simplifying the aqueous-based electrode assembly.
RESUMO
A solvent-free, melt polymerization process of a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) precursor for rechargeable organic radical batteries is proposed. Inâ situ carbon incorporation in the melted monomer phase yields a nanoscale homogenous polymer composite. Superior battery performances including higher power and cycling stability are attained by using the melt-polymerization method.