TMDs Functionalized-SWCNTs Based Nanosensors for the Detection and Early Warning of Gas Leakage in Li-Ion Batteries

Lithium-ion battery technology has seen immense success in consumer electronics and is becoming a leading technology for the mobility electrification with increasingly more attention being paid to battery safety problems¹. Detecting gas molecules (including hydrogen, carbon monoxide, carbon dioxide, ethylene, and methane) released from battery thermal runaway using gas sensors is one of the effective strategies to achieve early safety warnings for Lithium-ion batteries. Benefiting from the superiorities of small size/compactness, high sensitivity, and stable performance, resistive gas sensors are considered promising candidates in this field.<br/>Two-dimensional (2D) materials have demonstrated great potential in the field of gas sensing due to their layered structures. Particularly, 2D Transition Metal Dichalcogenides (TMDs) possess high surface areas and exhibit semiconducting properties with tunable band gaps making them excellent candidates for sensing applications². Among the different TMDs materials, MoS₂ has gas sensing ability comparable to graphene and WS₂can sense both toxic and non-toxic gases. In combination with the general benefits of 2D nanomaterials, the incorporation of one-dimensional (1D) nanomaterials with 2D TMDs is a recent approach for improving the gas sensing performance of these materials by the synergistic effects of hybridization. Indeed, hybrid (2D/1D) nanostructured materials provide the opportunity to fabricate and test the synergy between two or more different materials to achieve new functions. The use of single-wall carbon nanotubes (SWCNTs) as a skeleton for the TMDs enables the tuning of the electrical properties as the d orbitals from the transition metal M may partially overlap with the Π orbitals in the SWCNTs.<br/>The purpose of this work is to fabricate a gas nanosensor based on TMDs@SWCNTs resistive channel and to further couple it to a Lithium-ion battery with the aim of detecting toxic byproducts released due to battery thermal runaway.<br/>In this work, high-quality WS₂@SWCNTs and MoS₂@SWCNTs are fabricated using a bottom-up approach. First, the SWCNTs are synthesized via a chemical vapor deposition (CVD) method on a quartz substrate where the characteristics of the SWCNTs, i.e., diameter, density, and length are controlled by controlling the catalyst and CNT growth conditions. Next, mono and bilayer WS₂ and MoS₂ nanoflakes with diameters ranging between 10-20 nm are directly synthesized on the walls of the CNTs using homemade molecular beam evaporation/epitaxy (MBE) system.<br/>To test the sensing abilities of WS₂@SWCNTs and MoS₂@SWCNTs, the electrical measurements are first performed under tunable relative humidity environments. An opposite electrical response towards humidity is obtained for the two types of heterostructures. The WS2@SWCNTs have shown a positive response followed by a negative response which highlights the change in the intrinsic properties of the material depending on the injected percentage of relative humidity. Whereas, the MoS₂@SWCNTs have shown only a positive response with the change in the percentage of relative humidity. This opposite response can be explained by the fact that intrinsically WS₂ behaves as an n-type semiconductor while MoS₂ behaves as a p-type semiconductor.<br/>Further measurements will be performed to evaluate the selectivity, sensibility, and the ability to perform monitoring functioning of TMDs@SWCNTs nanosensors in the presence of different byproduct gas molecules. Finally, the TMDs@SWCNTs nanosensors will be coupled to a homemade Li-ion pouch cell battery and will be tested under harsh environments.<br/><br/>References:<br/>1 Essl, C., Seifert, L., Rabe, M. & Fuchs, A., <i>Batteries</i> <b>7</b>, 25 (2021)<br/>2 Late, D. J. <i>et al.</i> , <i>ACS Nano</i> <b>7</b>, 4879–4891 (2013)