High-efficacy multi-sodium carboxylate self-sacrificed additives for high energy density sodium-ion batteries

Sodium-ion batteries (SIBs) have gained significant interest in large-scale energy storage due to the abundance of sodium resources. However, interfacial side reactions lead to high irreversible Na+ loss and low Coulombic efficiency, which constrains the energy density of SIBs. Herein, two multi-sodium carboxylate cathode additives (sodium succinate and sodium malate) have been proposed for the first time to replenish the Na+ loss through in-situ decomposition. Breaking the double bond in the structure of disodium maleate lowered its decomposition voltage by 0.31V; then, introducing a hydroxyl group further lowered its decomposition voltage by 0.2V. With the addition of 10 wt% sodium succinate or sodium malate, the energy densities of the hard carbon/ /Na0.78Ni0.2Mn0.7Li0.05Ti0.05O2 full cells increases from 240 Wh kg−1 to 282 Wh kg−1 and 284 Wh kg−1, respectively. Moreover, the capacity retentions are improved from 62% to 80% and 79% after 50 cycles with sodium succinate or sodium malate, respectively. This improvement occurs without sacrificing the rate and cycling performances, which is promising for large-scale application of SIBs.