The quest for removal of cobalt from battery materials has intensified in the face of intensifying demand for batteries. Cobalt-free lithium-rich Li 1.2 Ni 0.13 Mn 0.54 Fe 0.13 O 2 (LNMFO) is synthesized under variation of chelating agent ratio and pH using the sol−gel method. Systematic search of the chelation and pH space found that the extractable capacity of the synthesized LNMFO is most clearly correlated to the ratio of chelating agent to transition metal oxide; a ratio of transition metal to citric acid of 2:1 achieves greater capacity at the expense of relative capacity retention. Charge−discharge cycling, dQ/dV analysis, XRD, and Raman at different charging potentials are used to quantify the different degrees of activation of the Li 2 MnO 3 phase in the LNMFO powders synthesized under different chelation ratios. SEM and HRTEM analysis are employed to understand the effect of particle size and crystallography on the activation of Li 2 MnO 3 phase in the composite particles. An unprecedented use of the marching cube algorithm to evaluate atomic scale tortuosity of crystallographic planes in HRTEM revealed that subtle undulations in the planes in addition to stacking faults correlate to the extracted capacity and stability of the various LNMFO synthesized.
Lithium sulfur (Li-S) batteries have received significant attention as an energy storage system with excellent prospects for emerging applications due to their high energy density and low-cost. However, there are fundamental challenges impeding the commercialization of Li-S batteries. Notorious among those challenges is the “polysulfide shuttle” consisting of the dissolution into the electrolyte solvent and subsequent crossover to the anode of long-chain lithium polysulfides. Sparingly-solvating electrolytes have been exploited as an approach to reduce the dissolution of polysulfides and thereby the shuttle effect. Using an optical in operando lithium-sulfur cell and ex situ UV-vis spectroscopy, we elucidate the speciation of polysulfides in fully and sparingly solvating electrolytes for Li-S batteries. Extensive literature meta-analysis reveals that the most unambiguous effect of sparingly-solvating electrolytes is in improving the coulombic efficiency of sulfur-cells. Experimental optical imaging and UV-vis characterization elucidate a shift towards shorter-chain polysulfides in electrolytes with increasing lithium-salt concentration (more sparingly solvating). The shift to shorter-chain polysulfides corresponds to a reduction of polysulfide species participating in shuttling which corroborate the increased coulombic efficiency in sparingly-solvating electrolytes.
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