Current Collector Corrosion in Ca-Ion Batteries

With significant improvements in electrical energy storage, researchers could change the way energy is generated and used. One emerging approach is to change the cation that shuttles charge from lithium to calcium. Calcium cations, roughly the same size as Na+, have many attributes that make them a desirable charge carrier for energy storage applications, including deposition voltage and a porous passivation layer. However, system level issues, such as corrosion, have yet to be investigated. Corrosion of the current collectors must be considered whenever you change the electrolyte and we show that this is particularly true for calcium based systems. Reversible charge/discharge behavior that is due to corrosion can be seen with stainless steel in electrolytes containing calcium salts. This reversible behavior is similar to what might be expected from materials that are intercalating Ca, making the interpretation of electrochemical data challenging. We have found that this corrosion reaction requires either carbon black and/or a transition metal oxide to catalyze the reaction, making it more difficult to detect. Unlike stainless steel, Graphite foil electrodes do not show high voltage reactions and can be used as a tool for testing Ca-ion cathode materials, although some reactions at low potentials have been observed. (C) 2015 The Electrochemical Society. All rights reserved.