Understanding the Role of Additives on The Electrochemistry and Performance of Zn Energy Storage Devices

As the interest in alternative Li-based energy storage technologies increased during the last years, zinc emerged as a promising candidate. Despite several advantages over Li, Zn cycling stability is still a major issue. In this article, the use of near-neutral electrolytes (non-expensive 2 M ZnSO4) with the addition of different additives (dimethylsulfoxide and tetratethylammonium chloride) is proposed as a solution. The Zn deposition/dissolution electrochemistry has been evaluated and the cycling stability was determined in Zn//Zn symmetric coin-cells. Hybrid supercapacitors were also assembled and tested in a range of 0.2 V-1.8 V for 2000 cycles, using activated carbon electrodes as cathode and Zn foil as anode. The results show that dimethylsulfoxide strongly inhibits the Zn deposition process, evidenced by a decrease in the cathodic current density, as well as in the dissolution peak. DMSO affects the deposition mechanism, whereas tetratethylammonium chloride reduces the exchange current density, consistent with the adsorption of tetraethylammonium ions on the Zn surface. A synergy between both additives leading to further inhibition of Zn2+ reduction is observed allowing cycling up to 250 hours for Zn//Zn devices. In addition, the performance of hybrid supercapacitors has also improved showing better capacity and extended cycle life. Electrolyte optimization: Zn-based energy storage devices have become rather popular in the last decades due to the good electrochemical properties and availability of this material. However, its poor cycle life has prevented its widespread commercialization. This article studies the effect of dimethylsulfoxide and tetratethylammonium chloride on Zn electrochemistry and cycling performance, attempting to establish a methodology which relies on simple and fast experiments. image