Atomistic and electronic insights into Ca2+ and Li+ intercalation in TiS2: a first-principles approach supported by electrochemical validation

Abstract

Abstract Calcium-ion batteries are emerging as a sustainable and high-energy alternative to lithium systems, yet the atomic-scale origin of their ion–host interactions remains unclear. We clarified the coupling between ion mobility and electronic structure in titanium disulfide (TiS 2 ) by combining multiscale density functional theory with experimental analysis. Periodic VASP simulations and localized DV-Xα analyses revealed that Ca 2+ intercalation induces greater lattice expansion than Li + , lowers diffusion barriers, and enriches the density of states near the Fermi level, enhancing both ionic and electronic transport. Despite weaker Ca–S interactions, strong Ti–S covalency stabilizes the framework, yielding a theoretical open-circuit voltage of 1.383 V, which is lower than that of LiTiS 2 (1.948 V). Orbital overlap and charge-transfer analyses show that this lower voltage reflects a balance between multi-electron charge storage (z = 2 for Ca 2+ ) and moderated electronic restructuring, rather than a simple reduction in electrochemical performance. Electrochemical measurements confirm these results: Ca-intercalated TiS 2 delivers a first-cycle capacity of 201 mAh·g − 1 , superior diffusion coefficients, and 96.3% rate retention with stable cycling. This work provides the first atomistic evidence that Ca 2+ insertion facilitates ion transport while imparting structural resilience, offering a design framework for next-generation multivalent-ion batteries.