Yes, the size of the sodium (Na) counter electrode in a half-cell coin cell test can significantly affect the storage performance and electrochemical behavior of the working electrode.

Sodium Excess: A larger Na counter electrode ensures an excess of Na, maintaining a stable Na+ ion supply during cycling. If the counter electrode is too small, it may deplete faster, causing capacity fade or unstable cycling.

Uniform Na Plating/Stripping: A larger surface area reduces localized current densities, minimizing dendrite formation and ensuring more uniform Na plating/stripping.

Typical Na counter electrodes are often cut from sodium foil (~1 mm thick) and sized to be larger than the working electrode (~12-15 mm in diameter). A sufficiently large counter electrode ensures reproducibility and minimizes experimental artifacts.

Hope this helps.

Thank you Miji Joy for your insightful answer. I'll retry with incorporating your suggestions.