Differential Voltage Analysis of Lead-Containing Sodium-Ion Full Cells

Sodium- (Na) alloying compounds such as lead (Pb) are of increasing interest for use in Na-ion full cells to increase their volumetric energy density. Full cells with NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM111) as the positive electrode and pure Pb or Pb blended with hard carbon have competitive volumetric energy densities with LiFePO 4 /graphite cells but suffer from limited capacity retention. The cause of the capacity fade is investigated using differential voltage analysis, with the shift loss and active masses of both electrodes compared to a full cell with a pure hard carbon negative electrode as the cells progress through up to 210 cycles. Shift loss from Na inventory loss at the negative electrode is the main culprit for capacity loss, with NFM111 active mass loss a secondary factor. Perhaps surprisingly, the negative electrodes’ active mass loss is minor and mostly occurs during the initial cycles where there is morphological restructuring of the Pb-containing electrodes. Importantly, the capacity fade rate after 106 cycles for the Pb and Pb blended with hard carbon full cells is comparable to the hard carbon full cells and indicates that through tailoring electrolyte recipes, Pb-containing full cells could eventually achieve the excellent lifetimes of hard carbon-based full cells.