Abstract
Systematic first principles calculations were performed for ZnCo2O4 to clarify its structural and electronic properties, and particularly the structural stability as an electrode material for lithium-ion batteries. For samples with low Li concentration, e.g., LinZnCo2O4 with n < 1, Li atoms take the center of oxygen octahedra and may diffuse rapidly. Structure distortions and volume expansions can be observed in LinZnCo2O4 with n > 1 and amorphous structures eventually prevail. The AIMD simulations for Li9ZnCo2O4 suggest the formation of Li2O, Co3O4 and LiZn local compounds or alloys. In particular, the formation of Zn-Co aggregations and the losing of ZnO pairs are identified as the possible reasons that are responsible to the Li capacity fading in ZnCo2O4 anodes.
Highlights
Lithium-ion batteries (LIBs) are ubiquitous in portable electronics due to their high energy density, low weight and small volume
A few dozen studies have explored the possible causes of capacity degradation, and have identified several possible factors such as the large volume changes and subsequent mechanical instabilities in electrodes[26,27,28,29], the formation of a solid electrolyte interphase (SEI)[30], and the reduction of metal oxide to metal with the formation of Li2O23
The structure of LinZnCo2O4 is stable for a small lithium capacity, e.g., n ≤ 1, and the energy barrier for Li atom diffusing from the center of one oxygen octahedron to its adjacent octahedron is about 0.4 eV
Summary
We insert more Li atoms in the supercell to observe the structural stability of LinZnCo2O4 and the lithium capacity of ZCO. We studied the changes of atomic pairs as a dependence of n value in LinZnCo2O4, as shown, to observe the structure evolution upon lithiation process. In summary we performed systematic density functional studies on the structure, magnetic, and electronic properties of ZnCo2O4, as well as the lithium diffusion and structural stability upon lithiation process as an anode material of LIBs. It was shown that ZCO is a nonmagnetic cubic spinel structure with an indirect band gap of 2.22 eV by using GGA+U functional. Our extensive calculations provide instructive information for understandings of experimental results and give useful insights for the design and optimization of high rate electrode materials
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