Revisiting the Na metal half-cell at low-temperature
Na metal-based coin-type half-cells are widely used to evaluate the electrochemical performance of electrode materials.This work presents the limitations of Na half-cells when evaluating the low-temperature performance of electrode materials in a commercial ester electrolyte.Due to the high interface and charge transfer resistance of Na metal at low temperatures,a large deposition/stripping overpotential was reached.This interferes with the evaluation of the low-temperature performance.When the Na||hard carbon(HC)half battery was charged/discharged at 0.2C(1C=300 mA/g)at-20℃,the change in potential of Na metal is as high as 0.94 V.The specific capacity of the HC electrode material is only 21.1 mAh/g,thus an inaccurate evaluation of the electrochemical performance is likely.Herein,a Na15Sn4@Na composite electrode was used to evaluate the performance of electrode materials at low temperature.The electrode potential of the composite is the same than that of the Na metal.At-20℃,the deposition/stripping overpotential of the Na15Sn4@Na||Na15Sn4@Na cell is only 0.09 V at 0.1 mA/cm2,much smaller than that of the Na metal electrode(0.96 V).In the Na15Sn4@Na||HC half-cell,the HC anode exhibits a high specific capacity of 100.8 mAh/gbefore Na metal deposition at-20℃,much higher than that of the Na||HC half-cell(21.1 mAh/g),indicating that the Na15Sn4@Na-based half-cell would allow for a more accurate evaluation of the low-temperature performance of electrode materials.This work provides an experimental basis for accurate assessment of the low-temperature electrochemical performance.
Na metalNa batterylow temperatureelectrochemistryhalf-cell
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