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Conductivity Optimization of Tysonite-type La<sub>1–<i>x</i></sub>Ba<sub><i>x</i></sub>F<sub>3–<i>x</i></sub> Solid Electrolytes for Advanced Fluoride Ion Battery
Use of lithium ion batteries is currently
the method of choice
when it comes to local stationary storage of electrical energy. In
the search for an alternative system, fluoride ion batteries (FIBs)
emerge as a candidate due to their high theoretical capacity, and
no lithium is needed for its operation. To improve the cycling performance
and lower the working temperature of a solid-state battery, one of
the critical components is the electrolyte, which needs advanced performance.
This paper aims at developing an electrolyte with enhanced ionic conductivity
for fluoride ions, to be used in a FIB. Tysonite La<sub>1–<i>x</i></sub>Ba<sub><i>x</i></sub>F<sub>3–<i>x</i></sub> (0 ≤ <i>x</i> ≤ 0.15) solid
solutions were synthesized by a facile wet chemical method, and its
ionic conductivity was analyzed using electrochemical impedance spectroscopy.
A composition study shows that the conductivity reaches a maximum
of 1.26 × 10<sup>–4</sup> S·cm<sup>–1</sup> at 60 °C for the La<sub>0.95</sub>Ba<sub>0.05</sub>F<sub>2.95</sub> pellet sintered at 800 °C for 20 h, which is 1 order of magnitude
higher than that for the as-prepared pellet and 2 times higher than
the conductivity of sintered ball-milled batches. The reason for this
dramatic increment is the more efficient decrement of grain boundary
resistance upon sintering. Morphological, chemical, and structural
characterizations of solid electrolytes were studied by X-ray diffraction,
scanning electron microscopy , energy dispersive X-ray spectroscopy,
physisorption by the Brunauer–Emmett–Teller method,
and transmission electron microscopy. Electrochemical testing was
carried out for the FIB cell using La<sub>0.95</sub>Ba<sub>0.05</sub>F<sub>2.95</sub> as electrolyte due to its highest conductivity among
the compositions, Ce as anode, and BiF<sub>3</sub> as a cathode. The
cycling performance was found to be considerably improved when compared
to our earlier work, which used the ball-milled electrolyte