Expandable Li Percolation Network: The Effects of Site Distortion in Cation-Disordered Rock-Salt Cathode Material

Cation-disorderedrock-salt (DRX) materials receive intensive attentionas a new class of cathode candidates for high-capacity lithium-ionbatteries (LIBs). Unlike traditional layered cathode materials, DRXmaterials have a three-dimensional (3D) percolation network for Li+ transportation. The disordered structure poses a grand challengeto a thorough understanding of the percolation network due to itsmultiscale complexity. In this work, we introduce the large supercellmodeling for DRX material Li1.16Ti0.37Ni0.37Nb0.10O2 (LTNNO) via the reverseMonte Carlo (RMC) method combined with neutron total scattering. Througha quantitative statistical analysis of the material's localatomic environment, we experimentally verified the existence of short-rangeordering (SRO) and uncovered an element-dependent behavior of transitionmetal (TM) site distortion. A displacement from the original octahedralsite for Ti4+ cations is pervasive throughout the DRX lattice.Density functional theory (DFT) calculations revealed that site distortionsquantified by the centroid offsets could alter the migration barrierfor Li+ diffusion through the tetrahedral channels, whichcan expand the previously proposed theoretical percolating networkof Li. The estimated accessible Li content is highly consistent withthe observed charging capacity. The newly developed characterizationmethod here uncovers the expandable nature of the Li percolation networkin DRX materials, which may provide valuable guidelines for the designof superior DRX materials.

Automated summary

Cation-disordered rock-salt (DRX) materials have gained significant attention as potential cathode candidates for high-capacity lithium-ion batteries (LIBs). In this study, a large supercell model of DRX material Li1.16Ti0.37Ni0.37Nb0.10O2 (LTNNO) was developed using the reverse Monte Carlo (RMC) method in combination with neutron total scattering. Through experimental analysis and density functional theory (DFT) calculations, the existence of short-range ordering (SRO) and element-dependent behavior of transition metal (TM) site distortion were confirmed. It was found that site distortions affect the diffusion barrier for Li+ ions, expanding the theoretical percolating network of Li in DRX materials. The newly developed characterization method provides valuable insights for the design of improved DRX materials.