Hybrid cathodes of fluoride-ion batteries with carbon nanotubes

Abstract

Solid-state fluoride-ion galvanic cells (metallic Ce anode, La1-xBaxF3-x (x ≈ 0.05) electrolyte) with carbon components in the cathode material – carbon nanotubes and nanocomposites based on them – have been created and studied. The investigations were carried out by means of cyclic voltammetry, impedance spectroscopy and electron microscopy. Tin fluoride SnF2 was used as a basic cathode material. The basic cathode was modified with additives of carbon nanotubes, which channels were filled with SnF2, PbSnF4 and their eutectic composition. Introduction of these additives lead to the charge-discharge currents improvement. The maximum value of open-circuit voltage (OCV ∼ 1.9 V) is observed with adding into the cathode material the nanocomposite of carbon nanotubes filled with the eutectic composition. Carbon nanotubes filled with tin fluoride SnF2@SWCNT proved to be the best additive in the cathode material. The sample has the biggest current density compared with the other samples (∼1.3 A/m2 at 180 °C, which is ∼4 times higher than that when using the basic cathode). The OCV of the galvanic cell with SnF2@SWCNT additive in the cathode material is stable within the investigated temperature range from 25 to 180 °C. For other galvanic cells temperature dependencies of OCV are decreasing. Results of the direct and alternating current investigations of the solid electrolyte in Ce/electrolyte/Ce symmetric cell show good converging. Direct current internal resistance of the solid electrolyte is defined by grain boundaries resistance. The impedance of a galvanic cell is determined by the composition and structure of SnF2 cathode material as the component of the cell with the highest resistance.