Two-dimensional Be₂P₄ as a promising thermoelectric material and anode for Na/K-ion batteries

Incredibly effective and flexible energy conversion and storage systems hold great promise for portable self-powered electronic devices. Owing to their large surface area, exceptional atomic structures, superior electrical conductivity and good mechanical flexibility, two-dimensional (2D) materials are recognized as an attractive option for energy conversion and storage application. In this work, we examined the stability, electronic, thermoelectric and electrochemical aspects of a novel 2D Be₂P₄ monolayer by adopting density functional theory (DFT). The Be₂P₄ monolayer exhibits a direct semiconductor gap of 0.9 eV (HSE06), large Young's modulus (∼198 GPa), high carrier mobility (∼10⁴ cm² V^-1 s^-1) and a low excitonic binding energy of 0.11 eV. Our calculated findings suggest that Be₂P₄ shows a lattice thermal conductivity of 1.02 W m K^-1 at 700 K, resulting in moderate thermoelectric performance (ZT ∼ 0.7), encouraging its use in thermoelectric materials. In addition, a higher adsorption energy of -2.28 eV (-2.52 eV) and less diffusion barrier of 0.22 eV (0.17 eV) for Na(K)-ion batteries promote fast ion transport in the Be₂P₄ monolayer. This material also shows a high specific capacity and superior energy density of 8460 W h kg^-1 (8883 W h kg^-1) for Na(K)-ion batteries. Thus, our results offer insightful information for investigating potential thermoelectric and flexible anode materials based on the Be₂P₄ monolayer.