Abstract
The replacement of cobalt in the lattice of lithium-rich layered oxides (LRLO) is mandatory to improve their environmental benignity and reduce costs. In this study, we analyze the impact of the cobalt removal from the trigonal LRLO lattice on the structural, thermodynamic, and electronic properties of this material through density functional theory calculations. To mimic disorder in the transition metal layers, we exploited the special quasi-random structure approach on selected supercells. The cobalt removal was modeled by the simultaneous substitution with Mn/Ni, thus leading to a p-doping in the lattice. Our results show that cobalt removal induces (a) larger cell volumes, originating from expanded distances among stacked planes; (b) a parallel increase of the layer buckling; (c) an increase of the electronic disorder and of the concentration of Jahn–Teller defects; and (d) an increase of the thermodynamic stability of the phase. Overall p-doping appears as a balanced strategy to remove cobalt from LRLO without massively deteriorating the structural integrity and the electronic properties of LRLO.
Highlights
Lithium-ion batteries are a power source widely used for numerous applications, including electric vehicles (EVs), computer and consumer electronic products, and energy storage devices for renewable and smart grids [1,2,3,4]
Starting from each optimized supercell, we evaluated the hexagonal symmetry without any distortion and the layered structure, in line with the the hexagonal hR12-apparent lattice parameters for all cobalt concentrations, using the experimental evidence [54,55,56,57]
We have investigated using firsts principles methods based on density functional theory (DFT), four
Summary
Lithium-ion batteries are a power source widely used for numerous applications, including electric vehicles (EVs), computer and consumer electronic products, and energy storage devices for renewable and smart grids [1,2,3,4]. Over-stoichiometric Li-rich nickel-manganese-cobalt layered oxides (LRLO, lithiumrich layered oxides) are a family of promising positive electrode materials with a general formula Li[Lix M1−x ]O2 (with M= transition metal blend) characterized by an overstoichiometric lithium content, implying the simultaneous presence in the same crystallographic site of a mixture of transition metals and lithium atoms (TM atomic sites) [7,10,11,12] These materials have a sluggish and ambiguous crystal structure [5,13,14,15], where two similar layered lattices are integrated [16]. Both lattices stack a repeated motif constituted by four parallel layers containing Li, O, TM, and O atomic species (where TM stands for a blend of transition metal ions and lithium ions), respectively, and differ by the local mutual arrangements of the TMO6 and LiO6 octahedra, as well as in the layers’
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