Electrodeposition of atmosphere-sensitive ternary sodium transition metal oxide films for sodium-based electrochemical energy storage

Significance Layered sodium transition metal oxides constitute an important class of materials with applications including electrochemical energy storage, high-temperature superconductivity, and electrocatalysis. However, electrodeposition of these compounds, an approach commonly used to grow oxides, has been elusive due to their atmosphere instability and intrinsic incompatibility with aqueous electrolytes. Using a molten sodium hydroxide electrolyte, we demonstrate electrodeposition of O3 (O′3)- and P2-type layered sodium transition metal oxides and apply these electrodeposits as high areal capacity cathodes in sodium-ion batteries. The electrodeposits are micrometers thick, polycrystalline, and structurally similar to materials synthesized classically at high temperature. This work enables fabrication of previously inaccessible alkali and alkaline earth ion intercalated, higher valent transition group oxides in important thick film form factors.