SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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We demonstrate short-range ordering in Li-ion battery material Li 1.25 Nb 0.25 Mn 0.5 O 2 , and identify its local structure and correlation length—which is sensitive to synthesis conditions and has important consequences for the material's electrochemistry.
Mechanistic understanding of coupled reaction kinetics, diffusive transport and electrostatic shield mediated electrodeposition stability is elucidated.
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Fluoride ion batteries are potential “next-generation” electrochemical storage devices that offer high energy density. At present, such batteries are limited to operation at high temperatures because suitable fluoride ion–conducting electrolytes are known only in the solid state. We report a liquid fluoride ion–conducting electrolyte with high ionic conductivity, wide operating voltage, and robust chemical stability based on dry tetraalkylammonium fluoride salts in ether solvents. Pairing this liquid electrolyte with a copper–lanthanum trifluoride (Cu@LaF 3 ) core-shell cathode, we demonstrate reversible fluorination and defluorination reactions in a fluoride ion electrochemical cell cycled at room temperature. Fluoride ion–mediated electrochemistry offers a pathway toward developing capacities beyond that of lithium ion technology.
Batteries which use dissolved redox-active species, such as redox flow batteries (RFBs), are often considered to be constrained in their operation and energy density by the solubility limit of the redox species. Here, we show that soluble redox active electrolytes can be reversibly cycled deeply into the precipitation regime, permitting higher effective concentrations, energy densities, and lower costs. Using aqueous sodium polysulfide negative electrolytes cycled in the nominal Na 2 S 2 to Na 2 S 4 capacity range as an example, we show that the effective solubility can be increased from 5 M in the fully-dissolved state to as much as 10 M using the precipitation strategy. Stable cycling was observed at 8 M concentration over more than 1600h at room temperature. We also analyze the range of polysulfide electrochemical stability, and characterize the precipitate composition. This enhanced effective concentration approach may be generalized to other redox chemistries that utilize solubilized reactants, and may be especially useful for long-duration storage applications where slow charge-discharge rates allow equilibration of precipitated species with the redox-active solution.
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Nanoparticles with a tendency to phase separate interact with each other during a process of either intraparticle phase separation (occurring inside the particle) or interparticle phase separation (occurring between particles). In this paper, we examine a halfcell consisting of two particles to systematically analyze the particle interactions and their resulting voltage response at different insertion currents. The kinetics of the interactions between nanoparticles is studied for cases in which particles undergo interparticle and intraparticle phase separation. Our results indicate that the interactions between particles in a cell containing only particles that undergo intraparticle phase separation are similar to those in a cell containing only particles that undergo interparticle phase separation. In both cases, sequential transformation occurs at low currents, whereas a simultaneous transformation occurs at high currents. Furthermore, such transformation dynamics changes in cases where the cell contains a mixture of particles that undergo interparticle and intraparticle phase separations, which exhibits more complex dynamics.
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