Thin Film Manganese Oxide Electrodes for Batteries and Supercapacitors As Grown By Atomic Layer Deposition

Manganese dioxides are commonly used as electrode materials for charge storage in supercapacitors (e.g. α-MnO₂) and cation intercalation batteries (e.g. λ-MnO₂). Manganese-based electrode materials have particular appeal in these applications due to the earth abundance and low cost of manganese. Nanoscale thin films are expected to increase the specific capacity and rate capability of manganese oxide electrodes by providing shorter bulk diffusion lengths for cations. Here we demonstrate that nanoscale thin films of MnO grown by atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)manganese (Mn(CpEt)₂) and water can be electrochemically oxidized in aqueous electrolytes to produce electrochemically active manganese dioxide for batteries and supercapacitors. However, our results show that the electrochemical oxidation of MnO ALD films results in partial dissolution and delamination.  To avoid this undesirable material loss, we have developed an approach to directly grow more oxidized manganese oxide films by ALD using ozone as the oxidant and Mn(CpEt)₂ as the Mn precursor.  We have also used intermediate ozone doses during Mn(CpEt)₂ and water exposures during ALD growth.  The use of ozone results in more oxidized manganese oxide films without the electrochemical oxidation step.