Synthesis and Characterization of Ti3C2Tx Mxene for Flexible Current Collectors Fabricated through Inkjet Printing
Authors: Viviani Prisca , Gibertini Eugenio , Lissandrello Federico , Magagnin Luca 
Published: February 2024

Two-dimensional (2D) materials, as transition-metal carbides and/or nitrides (MXenes), have recently gained great attention due to their combination of electrochemical, electrical and mechanical properties, which can be tailored for the specific application by controlling the chemical composition. As a consequence, MXenes find applications in many fields as energy storage, sensing, photocatalysis and many more [1].
MXenes are obtained by selective etching of a precursor layered material, known as MAX phase, and characterized by the general formula Mn+1XnTx, where M is a transition metal with n =1-4, X represents carbon and/or nitrogen atoms and Tx represents surface terminations of different nature (-O, -OH, -F and -Cl). The latter aspect is the one responsible for one important property related to the hydrophilicity of MXenes, which allows easy processing in water and/or solutions [2]. This aspect is particularly attractive for inkjet processing, as an easy water-based ink can be formulated. In addition, in aqueous solutions Ti3C2X flakes are negatively charged allowing the development of additive-free conductive inks.
Ultimately, the MXenes extremely high conductivity is particularly attractive for final application as flexible current collector for lithium-ion batteries. The current collector can be considered as a bottleneck, especially when considering substrates selection, i.e. flexible/wearable substrates. Different silver or copper nanoparticles inks are commercially available, but they do require high curing temperatures, which are incompatible with plastic-based substrates, in order to reach the desired electrical conductivity. Another option is carbon-based inks, which despite being more cost-effective, they have limitations in terms of moderate electrical conductivity, which affects the Ohmic losses, and so the overall performance, of the battery device [3].
Inkjet printing fabrication requires specific ink properties, in order to ensure a clogging-free condition, in terms of viscosity and surface tension of the ink. Generally, a clogging-free jetting is also forecast when particle size dimension is between 1/100 < d < 1/50 of the nozzle diameter [4]. This is a particularly meaningful aspect when considering MXene-based inks, as flake size should be finely controlled in order to avoid large or multilayered flakes, which can favor nozzle clogging. However, too small flakes can compromise the final electric conductivity.
In this study, we provide an in-depth characterization of Ti3C2X MXene synthesis. The as-produced material will be characterized in terms of flake dimensions and electrical conductivity. IJP ink compatibility generally requires adjustments in terms of rheological and physical properties. Once chosen the optimal method, the Ti3C2X aqueous-based ink will be printed to obtain current collectors for lithium-ion batteries, which will be characterized from a morphological, electrical and electrochemical point of view. Preliminary study studies on inkjet printed full cell LTO/LFP were already obtained at the coin level. Flexible LTO/LFP full cell exploiting innovative Ti3C2X MXene current collector will be printed. Morphological and electrical analysis combined with an in-depth electrochemical characterization will be performed to demonstrate the battery device performances retention under different degrees of bending of the device.
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