Nanometer-Thin Graphitic Carbon Buffer Layers for Electrolytic MnO₂for Thin-Film Energy Storage Devices

Abstract

In this study, nanometer thin graphitic carbon coatings were applied as an adhesion layer for the growth of submicron to micron thick electrolytic manganese dioxide (EMD) films for thin-film energy storage devices. The graphitic carbon coating served not only as current collector and adhesion layer between the EMD and the substrate, but also prevented the oxidation of the non-noble TiN substrate during the anodic deposition process. The EMD films consisted of a network of interconnected nanometer-size particles with around 50% porosity. The ability to grow a few hundred nanometer thick EMD film with good adhesion to the current collector is critical for reliable thin-film batteries on high aspect ratio microstructured surfaces. Thin EMD films grown on our graphitic carbon coated TiN substrates showed improved reversible Li-ion intercalation kinetics and increased cycle life compared to similar films deposited on noble metal platinum substrates, thus demonstrating the improved interface properties using the graphitic carbon buffer layer.

Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes

“…5 EMD films grown from acidic electrolytes on different substrates were shown to be highly porous (∼50% porosity) consisting of a network of interconnected 5-10 nm nanoparticles. 5,9 However, a very poor adhesion of the EMD films electrodeposited on the noble metal (Pt) coated substrate was observed. The maximum thickness of well-adherent EMD films was limited to 150 nm, with thicker deposits delaminating due to the mechanical film stress.…”

“…5 This was shown for example for the 70 nm thick EMD films grown on C/TiN substrate. 9 Unfortunately, only thin (<50 nm) EMD films show good reversible kinetics with sharp Li-ion intercalation and extraction peaks. As opposed to thin films, thicker EMD films display only broad cathodic (at ∼3-3.4 V vs. Li + /Li) and anodic (at ∼2.4-2.6 V vs. Li + /Li) current peaks in their CVs as shown in Figure 11a for EMD films deposited on the different substrates.…”

“…For 3D battery applications, the thickness of the EMD film on microstructures with an area enhancement of 20-40x (see Figure S1) should be close to 500 nm in order to match the capacity requirements of commercial Li-ion batteries for high-power applications (60-120 mAh/cm 3 ). 8,9 At the same time, the increase of the film thickness should not compromise the electrochemical performance of the material. 10 The main challenges of depositing thicker EMD film directly on the current collector often lay in achieving a good film adhesion, which can be challenged by the dissolution or passivation of the current collector in an acidic environment during the anodic EMD deposition.…”

“…• C, 0.45 Torr and RF power of 300 W 9 . Atomic layer deposition (ALD) was employed for the growth of ultrathin MnO 2 seed layers (2.2-4.6 nm) on top of the TiN current collector.…”

Electrolytic Manganese Dioxide Coatings on High Aspect Ratio Micro-Pillar Arrays for 3D Thin Film Lithium Ion Batteries

“…Previous studies reported the deposition of EMD on Si substrates coated with TiN and Pt seed layers as current collectors. It was revealed that TiN gets oxidized during EMD formation and the TiON x passivating layer prevents much more growth of the deposited film [ 10 , 51 , 52 ]. In the case of Pt current collector, EMD films delaminated when reaching a thickness more than 200 nm because of the poor adhesion between Pt and EMD [ 51 ].…”