Lithium-rich layered titanium sulfides: Cobalt- and Nickel-free high capacity cathode materials for lithium-ion batteries

Abstract

In the context of efforts to develop at the same time high energy density cathode materials for lithium-ion batteries with low content of critical elements such as cobalt and new cell chemistries for all-solid-state batteries, a novel family of lithium-rich layered sulfides (Li[Li t Ti 1-t ]S 2 , 0 < t 0.33) belonging to the LiTiS 2-Li 2 TiS 3 system was investigated as intercalation materials. These sulfides, in which both cations and anions are involved in the redox process, display common features with isotype Li-rich layered oxides (Li[Li x M 1-x ]O 2 , M ¼ Mn, Ni, Co, …). In a particular composition range, they exhibit high electrochemical performance with a reversible capacity and an energy density exceeding respectively 265 mAh⋅g-1 and 600 Wh⋅kg-1 , a very low irreversible capacity in the first cycle, fast activation and a limited voltage decay. Their operation potential within the electrochemical stability window of sulfide-based fast ionic conductors makes them promising cathode materials for all-solid-state lithium and Li-ion batteries.

Delocalized Metal–Oxygen π-Redox Is the Origin of Anomalous Nonhysteretic Capacity in Li-Ion and Na-Ion Cathode Materials

“…11, 46,48 We have shown that O-O distance shortening observed in Li 2 IrO 3 11 is a consequence of π-redox rather than independent O-O interactions. This behavior contrasts with that of sulfides, 49,50 where we find that structure-preserving anion redox through S-S dimerization is favored over π[S]-redox, as described in Supplementary Discussion 1. Finally, the apparent charge redistribution between transition metals and oxygen reported in a number of systems 46,48 is an artefact of the projection of the delocalized π-state onto atomic orbitals.…”

Activation of anionic redox in d0 transition metal chalcogenides by anion doping

“…The synthetic conditions reported for Li 2 TiS 3 were used as a starting point for preparing members of the Li 2 TiS 3 − x Se x series ( x = 0.15, 0.3, 0.45, 0.6, 0.9, 1.5, 2.0, 2.5, and 3) 24 . For compositions x ≤ 2, Li 2 S, TiS 2 , and TiSe 2 were used as reagents, while for compositions x > 2, Li 2 S, Li 2 Se, and TiSe 2 were ground and calcined in evacuated quartz tubes (see Supplementary information for details).…”

“…Pursuing this direction, researchers targeted the electrochemically inactive Li 2 TiS 3 phase, structurally analogous to Li-rich oxides Li 2 MnO 3 , because of its high theoretical capacity (339 mAh/g) 24 . The introduction of non-d 0 cations (Ti 3+ , Fe 2+ , and Co 2+ ) 24 – 26 associated with the concomitant lowering of the cationic d levels (e.g., M 3+/4+ bands just above the S 3 p bands) is a viable strategy to activate Li 2 TiS 3 using either solid-state synthesis in quartz tubes or ball milling 27 .…”

“…Pursuing this direction, researchers targeted the electrochemically inactive Li 2 TiS 3 phase, structurally analogous to Li-rich oxides Li 2 MnO 3 , because of its high theoretical capacity (339 mAh/g) 24 . The introduction of non-d 0 cations (Ti 3+ , Fe 2+ , and Co 2+ ) 24 – 26 associated with the concomitant lowering of the cationic d levels (e.g., M 3+/4+ bands just above the S 3 p bands) is a viable strategy to activate Li 2 TiS 3 using either solid-state synthesis in quartz tubes or ball milling 27 . In this work, we propose an alternative approach to electrochemical activate Li 2 TiS 3 : instead of lowering the cationic levels, we adjust the energy and symmetry of the anionic p levels by doping Se 2− into Li 2 TiS 3 − x Se x (Supplementary Figure 1b ).…”

Cathode–Sulfide Solid Electrolyte Interfacial Instability: Challenges and Solutions

“…Such cathodes exhibited reversible capacities up to and operating voltage ca. 2.5-3.0 V depending on the composition (Flamary-Mespoulie et al, 2020). These materials have also recently been applied to sulfide based ASSBs Marchini and coauthors developed a Li 1.13 Ti 0.57 Fe 0.3 S 2 cathode which showed good cyclability in a cathode + LPS composite/LPS/Li solid-state cell.…”