Three-dimensional (3D) architectures for high-performance energy storage devices has been the subject of ongoing investigations targeting their integration in autonomous microelectronic systems. In this paper we present a route toward the realization of high capacity LiMn₂O₄ (LMO) cathode films for 3D thin-film lithium-ion batteries. One of the critical steps in the process is the electrodeposition of MnO₂ coatings also known as electrolytic manganese dioxide (EMD) films. The main challenges of depositing thick enough EMD films directly on the current collector often lay in achieving a good film adhesion and preventing oxidation of non-noble current collectors such as TiN and Ni. Indeed, whereas EMD is typically used as powder for primary MnO₂ based batteries and thus delamination from the current collector is desired, well adherent films are required for 3D thin-film batteries. To improve the adhesion of the EMD films we modify the surface of the current collector by means of nanometer thin seed layer coatings, which also prevent the oxidation of the underlying current collector substrate during the anodic deposition process. As a result, submicron to micron thick EMD films with good adhesion were deposited on various current collectors. The acidity of the electrolyte solutions was adjusted depending on the type of the surface coating or current collector used. The mechanism of the EMD film growth and morphology on different substrates will be discussed. Compatibility of the proposed current collector interface modification for the electrodeposition of conformal thick EMD films on high-aspect ratio microstructures was demonstrated. Finally, conversion of the EMD to LMO films is shown at low enough temperatures to be compatible with the underlying substrates. The functionality and high rate performance of the 3D LMO electrodes in Li-ion cell is demonstrated.

Figure: Electrolytic manganese dioxide (EMD) films coated conformally on high aspect ratio pillar arrays for 3D thin-film batteries.