Tetra-alkyl ammonium hydroxides as inhibitors of Zn dendrite in Zn-based secondary batteries

Several tetra-alkyl ammonium hydroxides have been proposed and testified as novel inhibitors of Zn dendrite to replace the well-known tetra-alkyl ammonium bromides. In order to assess the efficacy of these hydroxides, current–time technique using potentiostatic electrodeposition, conductivity measurement, cycling test and scanning electron microscopy were undertaken. The ability to inhibit Zn dendrite was found dependent on the size of alkyl groups and the added concentration. Except tetramethyl ammonium hydroxide, significant dendrite inhibition occurs with the other four proposed compounds. Cathodic current profile and morphology of the deposits are found governed by the additives. Conductivity of the electrolyte was not deteriorated by the addition of these additives. From the charge/discharge cycling tests of the Ni–Zn testing cells, it was shown that the rechargeability of Zn anode is highly improved by the introduction of the proposed additives. The mechanism of such inhibition was elucidated. Tetra-alkyl ammonium hydroxides are cleaner and safer as compared to the conventionally used bromide compounds of the same alkyl group, thus they are more promising.