Fabrication and Multi-Functional Performance of TiO2/TiO2-TiN/MoS2 Composite Films on Ti through Smart Anodization and Anodic Electrodeposition
Authors: WANG Peng , Kure-Chu Songzhu Shochiku , Liu Jiacheng , Matuhira Kouya , Itatsu Shun , Lin Erli , Kurita Noriaki 
Published: December 2024

Nanoporous TiO2-based materials as LIB anodes exhibit robust safety and long-term stability without the formation of lithium dendrites during charge/discharge cycling, owing to their relatively high operating potential (approximately 1.7 V vs. Li/Li+) and extremely small volume expansion (<4%). Recently, an anodizing process of Ti materials is proposed to successfully fabricate various nanoporous anodic TiO2-TiN-based films with large surface area and short diffusion paths for intercalation/extraction of Li+ ions and interfacial transport, which attract tremendous attention as promising anode materials for Li-ion batteries, surpassing traditional carbon-based anodes. Moreover, electrodeposition is a well-known process to deposit various substances, such as metals, metal oxides, and metal sulfide on electrical substrates, which can significantly enhance various performances including electrical conductivity, capacity, corrosion resistance, lubricity, etc. Molybdenum disulfide (MoS2) is widely used as solid lubricant with a low friction coefficient and LIB anode materials with a high theoretical capacity around 669 mA h g⁻¹. In this study, we propose a novel approach to deposit MoS2 into anodic nanoporous TiO2-TiN films to create a new nanostructured TiO2/TiO2-TiN/MoS2 composite film on Ti as multifunctional materials toward high-performance LIB anodes, all-solid-state batteries, as well as versatile mechanical parts with good lubricity and high corrosion/wear resistance.

A two-step anodizing method was applied to form a bi-layered nanoporous TiO2-based film, i.e., a top tier with mesoporous larger pores and a matrix tier with nanoporous structure and improved conductivity. Briefly, a thin flat TiO2 top film with large-pore-size was firstly formed through anodization in a SO4
2--based solution. Subsequently, a thick nanoporous TiO2-TiN film was fabricated beneath the TiO2 top film by anodizing in a NO3
--based solution. Next, the porous TiO2/TiO2-TiN composite films were used as matrix films to fill MoS2 through anodic electrodeposition in a MoS4
2-based solution. The morphology, chemical composition, chemical states, and crystalline structures of the resultant anodized and electrodeposited films were analyzed by FE-SEM, EDX, XRD, XPS, and Raman. Moreover, the performances of the specimens as LIB anodes were evaluated through charge/discharge tests and various electrochemical experiments, and the lubricative properties and corrosion/wear resistance were measured by friction tests and various electrochemical methods.

Fig.1a illustrates the schematic formation process of the composite film by successive anodization in sulfuric- and nitric-based solutions and anodic MoS2 deposition. Following the anodic deposition, Mo-based substances were precipitated into the bi-layered nanoporous TiO2/TiO2-TiN composite films on Ti. Fig.1b showed the surface and fractural cross-section FE-SEM images of the TiO2/TiO2-TiN film before MoS2 electrodeposition, depicting a mesoporous structure with large pore size ranging from 50 to 200 nm at the top layer and a thick nanoporous under layer with pore diameters of 30–50 nm consistent to our previous studies. Fig.1c shows the surface FE-SEM image and EDS analysis result of the TiO2/TiO2-TiN/MoS2 composite film after MoS2 electrodeposition. A smooth layered surface with tiny particles was observed throughout the specimen. EDS analysis detected Ti, Mo, S, and O elements, indicating the formation of molybdenum sulfide on the TiO2-based anodic films. Raman spectroscopy detected strong peaks of MoS2 and several weak peaks of Mo oxides. The XRD and XPS measurements further confirmed the presence of MoO2 and MoO3 in the composite films after heating at 523K for 1 h in air, which attributed to the oxidation of MoS2 under high temperature. Consequently, the TiO2/TiO2-TiN/MoS2-MoOx composite films after heating exhibited a high capacity of 848 μA h cm-2 as LIB anode materials, and the as-prepared TiO2/TiO2-TiN/MoS2 delivered a low friction coefficient of around 0.25 in a friction test, thus demonstrating the effectiveness and efficiency of the designed two-step anodization and electrodeposition process in achieving multifunctional performance.

Figure 1