The lithium-rich anti-perovskite Li₃OCl has emerged as an ideal candidate for next-generation lithium-ion batteries (LIBs) due to its excellent ionic conductivity and wide electrochemical stability window. However, achieving ionic conductivity that meets practical application requirements remains challenging. Strain engineering and opto-ionic effects offer new pathways for performance optimization, but there is currently a lack of research on the quantitative regulatory mechanisms by which strain influences the electronic structure and optical properties of Li₃OCl (both of which are critical for ionic transport and optoelectronic integration). In this study, first-principles calculations were performed using the HSE06 hybrid functional to systematically investigate the effects of biaxial and uniaxial strains (-2% to +2%) on electronic structure and optical properties of Li₃OCl.
The study found that strain-free Li₃OCl exhibits an indirect bandgap of 6.263 eV. Biaxial tensile strain caused a significant downward shift in the energy of the conduction band minimum (Γ point), reducing the bandgap to 6.023 eV (+2% strain) and reinforcing the indirect bandgap characteristics. Biaxial compressive strain (-2%) expanded the bandgap to 6.380 eV and triggered an upward shift in the Γ-point energy level, leading to a transition from an indirect to a direct bandgap. Uniaxial strain exhibited similar trends but with a smaller regulatory magnitude compared to biaxial strain. Density of states analysis shows that tensile strain reduced the Li-p state density near the conduction band minimum while enhancing the hybridization of Li-p with O-p/Cl-p orbitals, optimizing carrier transition channels. Compressive strain increased the electron state density near the Fermi level, enhancing the probability of optical transitions. In terms of optical response, tensile strain induced an overall redshift in the dielectric function (ε₁(ω) and ε₁(ω)), absorption coefficient, and extinction coefficient. Compressive strain caused a systematic blueshift in optical parameters. Despite the expanded bandgap, the optical absorption intensity was significantly enhanced in the ultraviolet region due to the direct bandgap characteristics and increased state density at the band edges.
This study provides new ideas for the application research of Li₃OCl in optoelectronic devices and solid-state batteries. By precisely regulating its bandgap and light absorption properties through strain engineering, Li₃OCl can be adapted to the light excitation requirements of different wavelengths. For example, in light-controlled solid-state batteries, Li₃OCl optimized by tensile strain has a wider light response range (red-shifted to lower energy), which can effectively utilize lower-energy photons (such as near-ultraviolet or the edge of visible light) to excite carriers. On the other hand, Li₃OCl optimized by compressive strain has higher light absorption efficiency in specific ultraviolet bands, potentially increasing the concentration of carriers excited by photons in these bands. The strain-optimized Li₃OCl can synergistically utilize the light field and stress field to enhance ionic conductivity. In addition, its red-shifted light absorption edge makes it promising as an ultraviolet-visible light conversion layer, expanding the range of light energy utilization. However, in practical applications, further research is needed on the synergistic mechanisms of non-uniform strain, temperature effects, and light-force coupling. Moreover, experimental verification of its interfacial stability and cycle performance is required to promote the practical application of high-performance all-solid-state batteries.