Disordered Rock-Salt Type Li2TiS3 as Novel Cathode for LIBs: A Computational Point of View

Abstract

The development of high-energy cathode materials for lithium-ion batteries with low content of critical raw materials, such as cobalt and nickel, plays a key role in the progress of lithium-ion batteries technology. In recent works, a novel and promising family of lithium-rich sulfides has received attention. Among the possible structures and arrangement, cubic disordered Li2TiS3 has shown interesting properties, also for the formulation of new cell for all-solid-state batteries. In this work, a computational approach based on DFT hybrid Hamiltonian, localized basis functions and the use of the periodic CRYSTAL code, has been set up. The main goal of the present study is to determine accurate structural, electronic, and spectroscopic properties for this class of materials. Li2TiS3 precursors as Li2S, TiS2, and TiS3 alongside other formulations and structures such as LiTiS2 and monoclinic Li2TiS3 have been selected as benchmark systems and used to build up a consistent and robust predictive scheme. Raman spectra, XRD patterns, electronic band structures, and density of states have been simulated and compared to available literature data. Disordered rock-salt type Li2TiS3 structures have been derived via a solid solution method as implemented into the CRYSTAL code. Representative structures were extensively characterized through the calculations of their electronic and vibrational properties. Furthermore, the correlation between structure and Raman fingerprint was established.

Stability and Formation of the Li3PS4/Li, Li3PS4/Li2S, and Li2S/Li Interfaces: A Theoretical Study

“…Therefore, a good solid electrolyte must guarantee not only a high ionic conductivity but also good electrochemical stability under a bias to avoid additional reactivity due to the presence of a voltage window and good chemical stability in order to preserve the structural integrity once coupled with highly oxidative cathodes and highly reductive anodes. Sulfide-type materials − have shown good performance as solid electrolytes, and these materials have drawn a lot of attention due to their low grain-boundary resistance, easy processability, and good structural compatibility.…”

Computational Understanding of Delithiation, Overlithiation, and Transport Properties in Disordered Cubic Rock-Salt Type Li2TiS3

“…The structure for Li 2 TiS 3 was proposed and fully investigated in our previous work [7]. Beginning from the crystallographic experimental data, it was possible to generate a structure capable of reasonably simulating the real system.…”

“…The selected structure for our delithiation study was the most stable one obtained in our previous work [7]. The structure is schematically represented in Figure 1, together with the lithium site label that will be used in the following discussion.…”

“…The effects of electron deficiency and the vacancy formation highly influence the band gap. High variability with the lithiation state can be highlighted: in the fully lithiated structure, a band gap of 2.46 eV is [7], while proceeding with the delithiation, a decrease is observed down to 2.15 eV when 14 lithium atoms are removed (see Table S3). In contrast, when an odd number of lithium atoms are removed, the band gap changes from direct to indirect and reduces significantly to 1.7 eV for 15 Li removed, due to the presence of defect states in the gap along the β channel.…”

“…Lithium-titanium-sulfur compounds can be found with different stoichiometry ratios and crystal structures; among them, the Li 2 TiS 3 cubic rock salt-type has generated considerable attention due to its high capacity and better performance shown by the analogue layered monoclinic structure [5,6]. Its structure and electronic and spectroscopic properties were widely investigated in our previous work [7], where a strong relationship between structure and properties was highlighted. A further step is to evaluate the system evolution during the phenomena occurring during cycling, since the cathode undergoes lithium extraction and insertion.…”