Bilayer tetragonal AlN nanosheets as potential cathodes for Li-O₂ batteries

Li-O₂ batteries are considered promising electrochemical energy storage devices due to their high specific capacity and low cost. However, this technology currently suffers from two serious problems: low round-trip efficiency and slow reaction dynamics at the cathode. Solving these problems requires designing novel catalysis materials. In this study, a bilayer tetragonal AlN nanosheet as the catalyst is theoretically designed for the Li-O₂ electrochemical system, and the discharge/charge process is simulated by a first-principles approach. It is found that the reaction path leading to Li₄O₂ is energetically more favored than the path to form a Li₄O₄ cluster on an AlN nanosheet. The theoretical open-circuit voltage for Li₄O₂ is 2.70 V, which is only 0.14 V lower than the formation of Li₄O₄. Notably, the discharge overpotential for forming Li₄O₂ on the AlN nanosheet is only 0.57 V, and the corresponding charge overpotential is as low as 0.21 V. A low charge/discharge overpotential can effectively solve the problems of low round-trip efficiency and slow reaction kinetics. The decomposition pathways of the final discharge product Li₄O₂ and the intermediate product Li₂O₂ are also investigated, and the decomposition barriers are 1.41 eV and 1.45 eV, respectively. Our work shows that bilayer tetragonal AlN nanosheets are promising catalysts for Li-O₂ batteries.