Differently Modified ZnO Monolayers as Key Gas Sensors for Lithium-Ion Thermal Runaway: A DFT Study

To address the demand for rapid detection of toxic gases (C₂H₂, C₂H₄, CH₄ and H₂) released during lithium-ion batteries (LIBs) thermal runaway, this study uses first-principles calculations to investigate adsorption behavior. First, two modification methods are considered, namely surface doping of pure ZnO (TM-ZnO) and defect doping containing Zn vacancies (TM_D-ZnO). And the stable structures of transition metals (TM = Ir, Os, W, and Pt) under two modifications were explored. The calculation results show that the geometric structure of TM_D-ZnO is relatively stable. Subsequently, the different adsorption structures of C₂H₂, C₂H₄, CH₄, and H₂ on the two doped structures were studied, and the adsorption properties of the stable adsorption structures were calculated. The results indicate that chemical adsorption of C₂H₂ and C₂H₄ was observed in the two doped systems respectively, while the adsorption performance in the TM-ZnO system is the strongest. Furthermore, the W-ZnO/H₂ system has an E_ad of -0.82 eV, and there is an interaction of a certain strength between molecules, which is mainly chemical adsorption. Finally, the sensing properties of gas molecules on TM-ZnO and TM_D-ZnO were evaluated. The results show that the bandgap width of the W-ZnO/C₂H₄, Pt_D-ZnO/C₂H₂, and Pt_D-ZnO/C₂H₄ systems decreases, and good desorption can be achieved within an appropriate time after heating. Meanwhile, the bandgap width of the W-ZnO/H₂, Ir_D-ZnO/CH₄, and Ir_D-ZnO/H₂ systems changes significantly, with recovery times at room temperature of 7.55 × 10¹, 6.14 × 10^-2, and 2.32 × 10^-2 s, respectively. This makes them potential reusable gas-sensing elements for CH₄ and H₂ detection. This work demonstrates that metal-modified ZnO is a potential material for harmful gas monitoring.