Mechanism of Reaction in NaAlCl4 Molten Salt Batteries with Nickel Felt Cathodes and Aluminum Anodes: II . Experimental Results and Comparison with Model Calculations

Abstract

The battery systems: normalAl/normalNaCl‐AlCl3‐Al2X3/normalNi‐normalfelt false(X=S,normalSe,normalTefalse) and the corresponding system without chalcogen have been studied experimentally at 175°C. Charge/discharge experiments, performed on cells with normalNaCl saturated melts, show that advantages with regard to rate capability and cyclability can be obtained with systems containing dissolved chalcogen compared with the chalcogen‐free system. Exchange of chalcogen between cathode and electrolyte during cycling was confirmed by performing gravimetric analysis and Raman spectroscopy of the electrolytes. Cathode reactions were studied by coulometric titrations (performed on cells with slightly acidic normalNaCl‐AlCl3 melts and small amounts of chalcogen) and compared with model calculations. Cells containing chalcogen revealed at least three voltage plateaus during cycling. The lowest plateau is associated with formation/decomposition of essentially NiySz and NiySez in the sulfide and selenide system, respectively. Cells containing selenide revealed extra capacity below the NiySez‐normalplateau , most probably associated with a AlvNiySez compound. On the second plateau of sulfide systems NiCl2 or a NiySzCl2y−2z compound with y>false(4.4±0.2false)·z is formed during charging. Reduction of the formed compound to Ni takes place via consumption of sodium chloride. For acidic melts, sulfide at the cathode was found to be present asnormalClSnormalCl/\Al\//\Al\/normalClnormalClnormalCl−species.

Novel sodium aluminium borohydride containing the complex anion [Al(BH4,Cl)4]−

“…The Raman spectra show one of the four fundamental modes of [AlCl 4 ] À at n 1 (A 1 ) ¼ 349 cm À1 as found in NaAlCl 4 . 30,31 The sharp bands around 400 cm À1 are related to Al-Cl modes in Al(BH 4 ) x Cl 3Àx and [Al(BH 4 ) x Cl 4Àx ] À . The broad peak at about 490 cm À1 can be associated with the mode of Al-B as also found in Al-Li-borohydride with respect to the pure Al(BH 4 ) 3 .…”

A High‐Performance Na–Al Battery Based on Reversible NaAlCl4 Catholyte

“…However, the actual current density applied on Al wool, taking C/3 as an example, should be 20 mA/29.5 cm 2 ≈ 0.68 mA cm −2 , which is way below the critical current density of 4.3 mA cm −2 reported in ref. [ 16 ] for dendrite‐free Al deposition from NaAlCl 4 .…”

“…[ 15 ] However, a reversible Al deposition from NaAlCl 4 is not entirely impossible especially at elevated temperatures above its melting point (157 °C) where it is in molten state. [ 16 ] For instance, Li et al reported that a smooth Al deposition from molten NaAlCl 4 can be achieved on the glassy carbon under a certain current limit (≈4.3 mA cm −2 ) at a temperature of 175 °C. [ 17 ]…”

Electrochemical Properties of Al/Vanadium Chloride Batteries with AlCl3-1-Ethyl-3-methylimidazolium Chloride Electrolyte

“…• C. 9, 10 Gilbert and Osteryoung have investigated the electrochemical properties of nickel in inorganic molten salts consisting of AlCl 3 and KCl at 175-210…”