Application of Na<sub>2</sub>CO<sub>3</sub> as a Sacrificial Electrode Additive in Na‐ion Batteries to Compensate for the Sodium Deficiency in Na<sub>2/3</sub>[Fe<sub>1/2</sub>Mn<sub>1/2</sub>]O<sub>2</sub>
Masayoshi Matsuzaki, Ryoichi Tatara, Kei Kubota, Kazutoshi Kuroki, Tomooki Hosaka, Kazuteru Umetsu, Nobuhiro Okada, Shinichi Komaba
Abstract
Abstract Owing to their high discharge capacities, P2‐type transition metal layered oxides have attracted attention for use as positive electrode materials in Na‐ion batteries. However, owing to the Na‐deficient compositions of these oxides, additional Na + must be supplied using a Na‐metal negative electrode to attain a high capacity in a half‐cell configuration. In this study, solid Na 2 CO 3 powder was introduced into the P2−Na 2/3 Fe 1/2 Mn 1/2 O 2 composite positive electrode as a sacrificial salt to compensate for the Na deficiency. Na + was supplied through the electrochemical oxidative decomposition of Na 2 CO 3 during the initial charging process; the decomposition mechanism responsible for this process was investigated in detail. Online electrochemical mass spectrometry confirmed that Na 2 CO 3 was oxidatively decomposed in combination with the decomposition of the ethylene carbonate electrolyte. This reaction produced CO 2 , wherein the carbon source was derived from both Na 2 CO 3 and the electrolyte. Consequently, Na + supplementation improved the reversible capacity of the Na‐ion full cell. This study offers practical insights and a mechanistic understanding of the pre‐doping technique for Na‐free negative electrodes. This approach also compensates for the irreversible reductive capacity in a process that can be easily applied to practical sodium‐ and lithium‐ion batteries and capacitors.