RESUMEN
Lithium-CO2 batteries are attractive energy-storage systems for fulfilling the demand of future large-scale applications such as electric vehicles due to their high specific energy density. However, a major challenge with Li-CO2 batteries is to attain reversible formation and decomposition of the Li2 CO3 and carbon discharge products. A fully reversible Li-CO2 battery is developed with overall carbon neutrality using MoS2 nanoflakes as a cathode catalyst combined with an ionic liquid/dimethyl sulfoxide electrolyte. This combination of materials produces a multicomponent composite (Li2 CO3 /C) product. The battery shows a superior long cycle life of 500 for a fixed 500 mAh g-1 capacity per cycle, far exceeding the best cycling stability reported in Li-CO2 batteries. The long cycle life demonstrates that chemical transformations, making and breaking covalent CO bonds can be used in energy-storage systems. Theoretical calculations are used to deduce a mechanism for the reversible discharge/charge processes and explain how the carbon interface with Li2 CO3 provides the electronic conduction needed for the oxidation of Li2 CO3 and carbon to generate the CO2 on charge. This achievement paves the way for the use of CO2 in advanced energy-storage systems.
RESUMEN
Gel polymer electrolytes (GPE) and composite GPE (cGPE) using one-dimensional glass microfillers have been developed for their use in lithium-oxygen batteries. Using glass microfillers, tetraglyme solvent, UV-curable polymer, and lithium salt at various concentrations, the preparation of cGPE yielded free-standing films. These cGPEs, with 1 wt % of microfillers, demonstrated increased ionic conductivity and lithium transference number over GPEs at various concentrations of lithium salt. Improvements as high as 50% and 28% in lithium transference number were observed for 0.1 and 1.0 mol kg-1 salt concentrations, respectively. Lithium-oxygen batteries containing cGPE similarly showed superior charge/discharge cycling for 500 mAh g-1 cycle capacity with as high as 86% and 400% increase in cycles for cGPE with 1.0 and 0.1 mol kg-1 over GPE. Results using electrochemical impedance spectroscopy, Raman spectroscopy, and scanning electron microscopy revealed that the source of the improvement was the reduction of the rate of lithium carbonates formation on the surface of the cathode. This reduction in formation rate afforded by cGPE-containing batteries was possible due to the reduction of the rate of electrolyte decomposition. The increase in solvated to paired Li+ ratio at the cathode, afforded by increased lithium transference number, helped reduce the probability of superoxide radicals reacting with the tetraglyme solvent. This stabilization during cycling helped prolong the cycling life of the batteries.