Synergistic Effects of Na₂CO₃ as Sacrificial Salt and Water-Soluble Binder for Na-Ion Battery with Na-Deficient P2–Na_2/3Ni_1/3Mn_2/3O₂

High Resolution Image Download MS PowerPoint Slide P2-type transition metal layered oxides have attracted attention as high-capacity positive electrode materials for sodium-ion batteries (NIBs). However, due to their Na-deficient compositions, an additional Na + supplement is necessary for their practical use in NIBs. As we reported recently, the addition of Na 2 CO 3 powder into the P2-type Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 electrode has proven to be effective in addressing this challenge, as its electrochemical oxidative decomposition compensates for the Na + deficient capacity. In this study, a combination of water-soluble Na 2 CO 3 sacrificial salt and an aqueous slurry process using carboxymethyl cellulose (CMC) binder is successfully applied to sodium-deficient P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 (P2-NiMn) positive electrodes. We demonstrate the synergistic effect that promotes interactions among CMC, H 2 O molecules, Na +, and CO 3 2– in the aqueous slurry solution and the slow precipitation of low-crystalline Na 2 CO 3 during the electrode drying process. This mechanism eventually enhances the homogeneous dispersion with nanoparticulation of Na 2 CO 3, thus synergistically improving the decomposition efficiency of the sacrificial salts, enabling the achievement of superior reversible capacity in the P2-type electrode from the first cycle of the Na-ion full cell. Based on these findings, the combination of water-soluble sacrificial salt and aquosity slurry process totally offers a promising approach for developing NIBs with Na-deficient positive electrodes.