Electroactive decomposition products cause erroneous intercalation signals in sodium-ion batteries

Three-electrode configurations allow targeted studies of reaction mechanisms, including charge storage in and interphase formation on electrode materials for emerging sodium-ion batteries. However, using sodium metal as a reference electrode results in spontaneous formation of electroactive soluble decomposition products in an ester-based electrolyte. These electrolyte decomposition products undergo oxidation at carbon electrodes at potentials that can be mistaken for reversible sodium (de)intercalation, thus obscuring true measurements of material properties. [Display omitted] •Electrolyte decomposes at Na counter and reference electrodes at open circuit.•Soluble decomposition products oxidized