Sodium‐Containing Surface Film Formation on Planar Metal–Oxide Electrodes with Potential Application for Sodium‐Ion and Sodium–Oxygen Batteries

Abstract

Excellent, self‐improving sodiation rate capabilities in combination with high capacity retention upon galvanostatic charge/discharge cycling are found for oxygen‐deficient, carburized, and self‐organized titanium dioxide (TiO2−x) nanotubes (NTs). The sodiation mechanism is attributed to the formation of an acicular surface film as the active storage material with sodium (Na) peroxide (Na2O2) being the main component. Whether the proposed surface chemistry is unique for TiO2 NTs or serves as a common scheme for Na‐ion storage at metal oxide surfaces, in general, is not clear by now. Herein, three different materials, titanium(IV) oxide in the anatase and rutile phase and molybdenum(IV) oxide, are investigated in a planar electrode geometry toward their capability for Na‐ion storage. It is shown that all three materials under investigation demonstrate a significant progression of capacity increase upon cycling in combination with the formation of a Na‐oxide containing surface film. These “self‐improving” characteristics are found to significantly enhance the Na‐ion storage performance of the electrodes during long‐term galvanostatic cycling in a Na‐containing electrolyte.

Enhanced Electrochemical Performance of NTP/C with Rutile TiO2 Coating, as Anode Material for Sodium‐Ion Batteries

“…[5,6] Owing to the fast development of SIB technology, many anode and cathode materials have already been investigated. [7][8][9][10] On the cathode side, layered sodium transition-metal oxides, polyanion-based materials and Prussianblue materials are among the most studied compounds. [3,11,12] Anode materials include insertion type materials, like carbons and transition-metal oxides and phosphates, alloying and conversion reaction materials.…”

“…Owing to the fast development of SIB technology, many anode and cathode materials have already been investigated [7–10] . On the cathode side, layered sodium transition‐metal oxides, polyanion‐based materials and Prussian‐blue materials are among the most studied compounds [3,11,12] .…”

What is limiting the potential window in aqueous sodium‐ion batteries? Online study of the hydrogen‐, oxygen‐ and CO2‐evolution reactions at NaTi2(PO4)3 and Na0.44MnO2 electrodes

“…[3] Consequently, alternative batteries based on sodium (Na) over Li have drawn great interest in recent years, mainly motivated by the high natural abundance of Na. [4][5][6][7] Additionally, traditional organic-electrolyte-based rechargeable batteries use highly toxic and flammable organic solvents that can cause safety hazards. Aqueous rechargeable batteries, on the other hand, employ low-cost and nonflammable water-based electrolytes, Short Communication doi.org/10.1002/elsa.202200012 F I G U R E 1 Analysis of the synthesized NaTi2(PO4)3 (NTP) morphology, structure, and surface chemistry.…”