Abstract
In this work, we report first-principle calculations of the electrochemical properties of lithitated and delithiated LiMn_{1-x}Co_{x}BO_3 (x = 0, 0.25, 0.5, 0.75, 1) crystals based on the density functional theory (DFT) with the generalized gradient approximation (GGA) and also considering the on-site Coulomb interaction, the so-called Hubbard correction. We found that the top of the valence band and the bottom of the conduction band of these crystals are mainly formed by the hybridization of the 3d orbitals of mixed Mn_{1-x}Co_{x} ions and oxygen 2p orbitals. We observed a band gap narrowing with an increase of cobalt concentration and that the Hubbard correction implies a better theoretical description of their electronic structures. When considering the delithiated materials, our calculations show a metallic behavior for intermediate cobalt concentrations (x = 0.25, 0.5, 0.75), which is a good quality for cathodic materials, as it improves the battery discharge process. We also obtained high (4.14 V vs. Li^+/Li^0 and 4.16 V vs. Li^+/Li^0) open circuit voltage (OCV) values at cobalt concentrations of x = 0.5 and 0.75, where we believe that if these high OCV values are accompanied by a high charge storage capacity, these compounds can become promising and useful cathode materials. Finally, our results are in accordance with previous calculations and also with experimental results.
Highlights
In this work, we report first-principle calculations of the electrochemical properties of lithitated and delithiated LiMn1−xCoxBO3 ( x = 0, 0.25, 0.5, 0.75, 1) crystals based on the density functional theory (DFT) with the generalized gradient approximation (GGA) and considering the on-site Coulomb interaction, the so-called Hubbard correction
We discuss our results for the crystal structures, the electronic properties by means of density of states (DOS) using both GGA and GGA+U approximations as well as the open circuit voltage (OCV) for these borates
The transition metals (TM) ions Mn and Co occupy the center of the trigonal bipyramids composed by five oxygens ((MnO5 ) or (CoO5 )) and in turn, the Li are embedded in a tetrahedron with four oxygen atoms around them (LiO4 ) so that these two different polyhedras (MnO5)/(CoO5 ) and (LiO4 ) are connected to each other via corner and edge sharing which are condensed
Summary
Bearing all these facts in mind, in this work we report first-principle calculations of electrochemical properties of the LiMn1−xCoxBO3 ( x = 0 , 0.25, 0.5, 0.75, 1) in order to improve the understanding of properties of lithium borate-based materials to help in the design of new materials that can be satisfactory with respect to energy density, specific capacity and stability during battery charging and discharging cycles. The average open circuit voltage (OCV) for LiMn1−xCoxBO3 crystals was calculated as OCV = −E(LiMn1−xCoxBO3) + E(Mn1−xCoxBO3) + yE(Li) ye where x is the concentration of cobalt, E(LiMn1−xCoxBO3 ) and E(Mn1−xCoxBO3 ) are the total energies of fully lithiated and delithiated materials, respectively.
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