Li(Ni,Co,Al)O₂ Cathode Delithiation: A Combination of Topological Analysis, Density Functional Theory, Neutron Diffraction, and Machine Learning Techniques

Abstract

Here we have combined topological analysis, density functional theory (DFT) modeling, operando neutron diffraction, and machine learning algorithms within the comparative analysis of the known widely LiNiO 2 (LNO) and LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathode materials. Full configurational spaces of the mentioned materials during delithiation were set using the topological approach starting from the 2 × 2 × 1 supercell (12 formula units in total) of the LNO structure (space group R3̅ m). Several types of the DFT models were applied for the structural relaxation of entries of the LNO configurational space (87 configurations) demonstrating a strong dependence of the results of optimization on the initial structure guess (at the latter delithiation stages) and on the Hubbard correction application (for the whole range of delithiation). Within the computationally easiest model considered for LNO, subsequent modeling of the NCA configurational space (20760 configurations) results in structural changes of the model cell that are well-consistent (relative errors <1.5% with respect to the lattice parameter values) with data of operando neutron diffraction experiments during charge−discharge cycling. In the scope of the machine learning approach, topology of Li layers and relative disposition of Li and Al in NCA structure are found to be the most important descriptors during the energy balance estimations.

Topology-based description of the NCA cathode configurational space and an approach of its effective reduction

“…The configurational space used in this study and the results of the DFT modeling are taken from the previous study [8]. In total 20760 independent doped configurations were generated from the 2x2x1 supercell of the parent LNO compound ( In order to build a regression model, we applied a set of structural descriptors [8] for entries of the NCA configurational space that serve as independent variables of the model.…”

“…In total 20760 independent doped configurations were generated from the 2x2x1 supercell of the parent LNO compound ( In order to build a regression model, we applied a set of structural descriptors [8] for entries of the NCA configurational space that serve as independent variables of the model. The pertinent types of descriptors calculated by means of the ToposPro [9] package are: (1) Li distribution within the structure.…”

“…However, direct application of the modeling for a comprehensive study of the cathode materials features is still a complicated task because of high complexity of a disordered system' configurational space. This obstacle is manifested in the necessity to carry out the quantum-mechanical calculation of many thousands (up to millions) configurations belonging to the configurational space of a modeled crystal structure [7,8]. The purpose of the current study is to propose and to verify the scheme that will give an opportunity to perform quantum-mechanical calculation for reduced subsets of the complete configurational spaces of a modeled crystal structure.…”

“…The purpose of the current study is to propose and to verify the scheme that will give an opportunity to perform quantum-mechanical calculation for reduced subsets of the complete configurational spaces of a modeled crystal structure. Application of the proposed scheme is exemplified through the study of the NCA cathode material configurational space that was explored using DFT modeling in our previous study [8].…”

Delithiated states of layered cathode materials: doping and dispersion interaction effects on the structure

“…Previously, the full LiNiO 2 (LNO) and NCA configurational spaces were set using topological approach and studied by means of the DFT calculations and machine learning algorithms [13]. In the scope of the current research, the topological approach is applied for sampling of the configurational space of the LiNi 0.833 Co 0.083 Al 0.083 O 2 (N 10 C 1 A 1 ) cathode.…”