Fig. 6: First-principle calculations of the four-electron selenium cathode chemistry.
From: Enabling fast-charging selenium-based aqueous batteries via conversion reaction with copper ions
a Atomic structures of CuSe, Cu3Se2, Cu1.75Se, and Cu2Se and their unit cells are marked with black color, and Se parallelepiped skeleton are marked with red color; to simplify calculation, Cu1.75Se is used as a representative form of Cu2−xSe. b The relative total energy (per atom) of Se, CuSe, Cu3Se2, Cu1.75Se, and Cu2Se with respect to strain; The variation of particle number density over the entire process is about 69% corresponding to 19% deformation in length, therefore strain ranges from −20% to 20% in our calculation; The top and side view of crystalline Se (d) with or (c) without copper-ion embedded; Note that only one copper ion is embedded here, multiple ions appear in (d) are used to describe the trajectory of copper ions diffusion, and the corresponding energy variations along this trajectory under different volumetric deformation (0%, 5% and 10% equal-axis strain) are shown in (e). f The side and g top view of CuSe with one copper-ion embedded; In g, only one slice of f (marked with the red dash line) is shown to facilitate viewing the diffusion path of the interstitial copper ion (marked by CuI in f and g). h The energy curve of copper-ion diffusion in CuSe, and the local atomic structures at different transition states are given in insets.
