Studies on Counter Electrode Materials in Aqueous Zinc Half-Cell Configurations.

Coulombic Efficiency (CE) is the primary parameter that evaluates the reversibility of aqueous zinc-ion batteries (ZIBs), as it directly reflects the stripping/plating behavior of zinc ions. However, this parameter is compromised by a lack of understanding and the standard of testing protocols. In the most ubiquitous method, half-cell tests, the poor understanding of diverse metal substrates, namely the current collectors, compromises the reliability and comparability of the measured data. To timely fulfil this knowledge gap and establish a precise testing protocol, we selected four commonly used metal substrates, copper (Cu), titanium (Ti), stainless steel (SS), and aluminium (Al), to systematically compare their performance and disclose their underlying electrochemical reactions. The Ti current collector was determined to be the most reliable metal substrate due to its outstanding electrochemical performance with zinc ions and strong immunity to side reactions. Moreover, in this study, we found that most applied Cu current collectors exhibit severe side reactions and are likely to yield false-positive results in environments with excessive zinc.