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

Abstract

We introduce an intermediate-temperature (350 °C) dry molten sodium hydroxide-mediated binder-free electrodeposition process to grow the previously electrochemically inaccessible air- and moisture-sensitive layered sodium transition metal oxides, NaxMO2 (M = Co, Mn, Ni, Fe), in both thin and thick film form, compounds which are conventionally synthesized in powder form by solid-state reactions at temperatures ≥700 °C. As a key motivation for this work, several of these oxides are of interest as cathode materials for emerging sodium-ion–based electrochemical energy storage systems. Despite the low synthesis temperature and short reaction times, our electrodeposited oxides retain the key structural and electrochemical performance observed in high-temperature bulk synthesized materials. We demonstrate that tens of micrometers thick >75% dense NaxCoO2 and NaxMnO2 can be deposited in under 1 h. When used as cathodes for sodium-ion batteries, these materials exhibit near theoretical gravimetric capacities, chemical diffusion coefficients of Na+ ions (∼10−12 cm2⋅s−1), and high reversible areal capacities in the range ∼0.25 to 0.76 mA⋅h⋅cm−2, values significantly higher than those reported for binder-free sodium cathodes deposited by other techniques. The method described here resolves longstanding intrinsic challenges associated with traditional aqueous solution-based electrodeposition of ceramic oxides and opens a general solution chemistry approach for electrochemical processing of hitherto unexplored air- and moisture-sensitive high valent multinary structures with extended frameworks.

In Situ Investigation of Lattice Oxygen Loss from Preferentially Faceted Electrodeposited LiCoO2 via Scanning Electrochemical Microscopy

“…Further details of the electrodeposition process can be found in previous works. 27,29,30 Scanning Electrochemical Microscopy (SECM) Measurements Detailed procedure of the SECM measurement and data analysis methodology are described in a previous work. 24 In brief, substrate electrodes (LiCoO 2 ) were assembled in an open Teflon cell, with a 3 mm o-ring isolating the substrate electrode.…”

Engineering Electrodeposition for Next-generation Batteries

“…A variety of transition metal oxides can be directly electroplated-at elevated temperatures from their corresponding molten salts-onto planar Al current collectors. 37,38 In particular, these electroplated electrodes manifest extraordinary rate capabilities at areal capacities (i.e., 20 mAh/cm 2 ) that are a few times higher than normal commercial Li-ion electrodes. This type of dense electroplated cathode-possible because of the continuous ion and electron conduction network formed during electroplating-can be seamlessly integrated into solid state batteries.…”

Electrodeposition of Li-Ion Cathode Materials: The Fascinating Alternative for Li-Ion Micro-Batteries Fabrication

“…Braun et al 90 also described molten salt ECD of air-sensitive O3-Na x MO 2 (M = Co, Mn, Ni, Fe) in a molten hydroxide bath at 350 °C. This group reported ECD of Na x MnO 2 and Na x CoO 2 polycrystalline forms with a thickness of 10 μm (>75% dense) under 1 h. The electrodeposited phases were employed as binder/ additive-free films as a cathode of sodium-ion batteries and delivered approximately the theoretical gravimetric capacities.…”