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

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 (TiS2) by combining multiscale density functional theory with experimental analysis. Periodic VASP simulations and localized DV-Xα analyses revealed that Ca2+ 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 LiTiS2 (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 Ca2+) and moderated electronic restructuring, rather than a simple reduction in electrochemical performance. Electrochemical measurements confirm these results: Ca-intercalated TiS2 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 Ca2+ insertion facilitates ion transport while imparting structural resilience, offering a design framework for next-generation multivalent-ion batteries.