Dimensionality-dependent redox chemistry and Li-ion transport kinetics in TiS2 and TiS3 electrodes

Grasping how structural dimensionality affects ion transport and redox processes is crucial for designing low-dimensional electrode materials. This research systematically compares two structurally distinct titanium sulfides, TiS 2 and TiS 3 , despite their identical elemental makeup Density functional theory (DFT) calculations reveal that TiS 3 features significant anionic redox contribution from S 2 2− dimers, as substantiated by crystal orbital Hamilton population (COHP) and Bader charge analyses, whereas TiS 2 primarily involves cationic Ti 4+ /Ti 3+ redox processes. Climbing-image nudged elastic band (CI-NEB) calculations reveal highly anisotropic Li + migration barriers. TiS 2 allows easy in-plane diffusion with a 0.28 eV energy barrier, but interlayer movement faces a high barrier of 1.80 eV. Conversely, TiS 3 enables intra-chain transport with a 0.22 eV barrier, yet struggles with inter-chain migration due to a 2.50 eV barrier. The GITT measurements reveal diffusion coefficients (D Li+ ) ranging from 1.57 × 10 −12 to 6.18 × 10 −12 cm 2 s −1 for TiS 2 and from 1.71 × 10 −12 to 1.92 × 10 −12 cm 2 s −1 for TiS 3 . Additionally, a continuum model, parameterized through DFT and implemented in COMSOL Multiphysics, establishes a connection between atomic-scale transport phenomena and macroscopic electrode behavior. This study creates a framework linking dimensionality, transport, and electrochemical properties to guide the design of advanced metal sulfide electrodes for future applications.