Electrodeposition of Thick MnO2 Films on Restrictive Substrates

Lithiated electrolytic manganese dioxide (EMD or ƴ-MnO₂) is considered to be a promising positive electrode material for rechargeable lithium ion batteries due to its relatively high specific capacity and long-term cyclability along with its low cost and low toxicity [1,2]. Conformal deposition of thick EMD material is needed for its application in 3D solid state batteries. However, during the anodic electrodeposition of manganese dioxide, the underlying current collector is oxidized at the same potential range as the EMD deposition, e.g. titanium nitride (TiN) or aluminum (Al) current collectors. In this work we investigate the use of thin coatings prepared by vapor phase of wet chemical deposition to protect the current collector from the undesirable oxidation and allow the deposition of thick MnO₂ films with good adhesion properties. We show conformal deposition of MnO₂ films up to 600 nm thick from aqueous bath on high aspect ratio silicon pillar arrays. Silicon pillars were covered with 20 nm TiN which acts as a diffusion barrier of Li ions into Si. Reversible insertion and extraction of Li⁺ into thick EMD is demonstrated on both planar and 3D substrates with an expected capacity increase associated with the surface area gain for 3D substrates. We also demonstrate the application of a thin coating to enhance the adhesion between the electrodeposited MnO₂ cathode material and aluminum surface, including Al foil, opening doors towards its use in flexible batteries.

[1] M. Thackeray, Prog. Solid St. Chem., 25, 1997

[2] A. Etman, A. Radisic, M. Emara, C. Huyghebaert, P.Vereecken, J. Phys. Chem. C, 118 (19), 2014