(Invited) Electrochemical Deposition of Thick and Adherent MnO2 Films for Thin-Film Batteries

Abstract

Electrolytic manganese dioxide (EMD) is fabricated by anodic electrodeposition typically from acid manganese sulfate baths. After electrodeposition it is peeled from the electrode and ground into powder, hence poor adhesion is required. EMD powder is mainly used for primary alkaline-Zn and Li-ion batteries. EMD allows Li-ion intercalation in the open channels in the γ-MnO2 lattice. In our research group we are interested in adapting the EMD process for bulk batteries to be used for fabrication of thin-film Li-ion batteries. EMD thin films deposition was developed on different substrates. Scanning electron microscopy (SEM) and Rutherford Backscattering Spectrometry (RBS) measurements were performed to extract the film porosity. It was found that all the deposited films have similar porosity values around 50 %. Anodic electrodeposition of EMD films from conventional acid manganese sulfate baths is not possible on easy to oxidize substrates like TiN (passivation) or Ni (dissolution). For this reason a neutral and complexing acetate bath was used. Using this deposition bath thick and adhesive EMD film were deposited on Ni and even on TiN substrates. Up to 1 μm thick film on planar substrate and 600 nm on 50 μm high Si pillar array with 2 μm pillar diameter and 2 μm interpillar spacing. A study of the EMD film deposition in a temperatures range from 5 °C to 50 °C using the neutral acetate deposition bath was performed. The relationship between the morphology and the electrochemical performance of the EMD films deposited at different temperatures were investigated.