RESUMO
Understanding the kinetics of interfacial ion speciation could inform battery designs. However, this knowledge gap persists, largely due to the challenge of experimentally interrogating the evolution of ions near electrode interfaces in a sea of bulk signals. We report here the very first kinetically resolved correlation between interfacial ion speciation and lithium-ion storage in a model system, by applying global target analysis to in situ attenuated total reflectance (ATR) Fourier-Transform infrared (FTIR) spectroelectrochemical data. Our results suggest that it may be more kinetically viable for lithium to be extracted from contact ion pairs (CIPs) to contribute to faster electrode charging compared to fully solvated lithium. As the search for fast-charging lithium-ion batteries and supercapacitors wages on, this discovery suggests that manipulating the ion pairing within the electrolyte could be one effective strategy for promoting faster-charging kinetics.
RESUMO
We describe a new electrochemical cycle that enables capture and release of carbon dioxide. The capture agent is benzylthiolate (RS-), generated electrochemically by reduction of benzyldisulfide (RSSR). Reaction of RS- with CO2 produces a terminal, sulfur-bound monothiocarbonate, RSCO2-, which acts as the CO2 carrier species, much the same as a carbamate serves as the CO2 carrier for amine-based capture strategies. Oxidation of the thiocarbonate releases CO2 and regenerates RSSR. The newly reported S-benzylthiocarbonate (IUPAC name benzylsulfanylformate) is characterized by 1H and 13C NMR, FTIR, and electrochemical analysis. The capture-release cycle is studied in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP TFSI) and dimethylformamide. Quantum chemical calculations give a binding energy of CO2 to benzyl thiolate of -66.3 kJ mol-1, consistent with the experimental observation of formation of a stable CO2 adduct. The data described here represent the first report of electrochemical behavior of a sulfur-bound terminal thiocarbonate.
RESUMO
Sequestering carbon dioxide emissions by the trap and release of CO2 via thermally activated chemical reactions has proven problematic because of the energetic requirements of the release reactions. Here we demonstrate trap and release of carbon dioxide using electrochemical activation, where the reactions in both directions are exergonic and proceed rapidly with low activation barriers. One-electron reduction of 4,4'-bipyridine forms the radical anion, which undergoes rapid covalent bond formation with carbon dioxide to form an adduct. One-electron oxidation of this adduct releases the bipyridine and carbon dioxide. Reversible trap and release of carbon dioxide over multiple cycles is demonstrated in solution at room temperature, and without the requirement for thermal activation.
RESUMO
We are currently in the midst of a race to discover and develop new battery materials capable of providing high energy-density at low cost. By combining a high-performance Si electrode architecture with a room temperature ionic liquid electrolyte, here we demonstrate a highly energy-dense lithium-ion cell with an impressively long cycling life, maintaining over 75% capacity after 500 cycles. Such high performance is enabled by a stable half-cell coulombic efficiency of 99.97%, averaged over the first 200 cycles. Equally as significant, our detailed characterization elucidates the previously convoluted mechanisms of the solid-electrolyte interphase on Si electrodes. We provide a theoretical simulation to model the interface and microstructural-compositional analyses that confirm our theoretical predictions and allow us to visualize the precise location and constitution of various interfacial components. This work provides new science related to the interfacial stability of Si-based materials while granting positive exposure to ionic liquid electrochemistry.
