Unveiling the pressure-driven metal–semiconductor–metal transition in the doped TiS_(2)

Conventional theories expect that materials under pressure exhibit expanded valence and conduction bands,leading to increased electrical conductivity.Here,we report the electrical properties of the doped 1T-TiS_(2) under high pressure by electrical resistance investigations,synchrotron x-ray diffraction,Raman scattering and theoretical calculations.Up to 70 GPa,an unusual metal-semiconductor-metal transition occurs.Our first-principles calculations suggest that the observed anti-Wilson transition from metal to semiconductor at 17 GPa is due to the electron localization induced by the intercalated Ti atoms.This electron localization is attributed to the strengthened coupling between the doped Ti atoms and S atoms,and the Anderson localization arising from the disordered intercalation.At pressures exceeding 30.5 GPa,the doped TiS_(2) undergoes a re-metallization transition initiated by a crystal structure phase transition.We assign the most probable space group as P2_(1)2_(1)2_(1).Our findings suggest that materials probably will eventually undergo the Wilson transition when subjected to sufficient pressure.

TiS_(2)-graphene heterostructures enabling polysulfide anchoring and fast electrocatalyst for lithium-sulfur batteries:A first-principles calculation

Lithium-sulfur batteries have attracted attention because of their high energy density.However,the "shuttle effect" caused by the dissolving of polysulfide in the electrolyte has greatly hindered the widespread commercial use of lithiumsulfur batteries.In this paper,a novel two-dimensional TiS2/graphene heterostructure is theoretically designed as the anchoring material for lithium-sulfur batteries to suppress the shuttle effect.This heterostructure formed by the stacking of graphene and TiS2 monolayer is the van der Waals type,which retains the intrinsic metallic electronic structure of graphene and TiS2 monolayer.Graphene improves the electronic conductivity of the sulfur cathode,and the transferred electrons from graphene enhance the polarity of the TiS2 monolayer.Simulations of the polysulfide adsorption show that the TiS2/graphene hetero structure can maintain good metallic properties and the appropriate adsorption energies of 0.98-3.72 eV,which can effectively anchor polysulfides.Charge transfer analysis suggests that further enhancement of polarity is beneficial to reduce the high proportion of van der Waals(vdW) force in the adsorption energy,thereby further enhancing the anchoring ability.Low Li2 S decomposition barrier and Li-ion migration barrier imply that the heterostructure has the ability to catalyze fast electrochemical kinetic processes.Therefore,TiS2/graphene heterostructure could be an important candidate for ideal anchoring materials of lithium-sulfur batteries.

Unlocking efficient energy storage via regulating ion and electron-active subunits:an(SbS)_(1.15)TiS_(2)superlattice for large and fast Na^(+)storage

Alloying-type metal sulfides with high sodiation activity and theoretical capacity are promising anode materials for high energy density sodium ion batteries.However,the large volume change and the migratory and aggregation behavior of metal atoms will cause severe capacity decay during the charge/discharge process.Herein,a robust and conductive TiS_(2)framework is integrated with a high-capacity SbS layer to construct a single phase(SbS)_(1.15)TiS_(2)superlattice for both high-capacity and fast Na^(+)storage.The metallic TiS_(2)sublayer with high electron activity acts as a robust and conductive skeleton to buffer the volume expansion caused by conversion and alloying reaction between Na+and SbS sublayer.Hence,high capacity and high rate capability can be synergistically realized in a single phase(SbS)_(1.15)TiS_(2)superlattice.The novel(SbS)_(1.15)TiS_(2)anode has a high charge capacity of 618 mAh g^(-1)at 0.2 C and superior rate performance and cycling stability(205 mAh g^(-1)at 35 C after 2,000 cycles).Furthermore,in situ and ex situ characterizations are applied to get an insight into the multi-step reaction mechanism.The integrity of robust Na-Ti-S skeleton during(dis)charge process can be confirmed.This superlattice construction idea to integrate the Na^(+)-active unit and electron-active unit would provide a new avenue for exploring high-performance anode materials for advanced sodium-ion batteries.

Interlayer gap widened TiS_(2) for highly efficient sodium-ion storage

As an alternative for lithium-ion batteries(LIBs),sodium-ion batteries(SIBs)have lately received tremendous interest due to their abundant reserves as well as low cost.Nevertheless,the lack of suitable anode materials severely hinders the application of sodium-ion batteries.TiS_(2)is elected as a representative material owing to its unique layered structure.But it always suffers from capacity fade due to poor electrochemical kinetics and structural stability.In this work,we fabricate a pre-potassiated TiS_(2)as a host material for sodium storage by an electrochemical pre-potassiation strategy.The intercalation/extraction mechanism,structural changes and reaction kinetics are completely investigated to reveal the outstanding electrochemical property of pre-potassiated TiS_(2)electrode.It turns out that the large interlayer space of pre-potassiated TiS_(2)is conducive to the diffusion of sodium ions,inducing the reduction of entropic barrier for the electrochemical reactions.In addition,the pre-potassiated host structure is still firmly maintained upon repeated cycles.Therefore,the pre-potassiated TiS_(2)presents superior rate capability(165.9 mA h g^(−1) at 1 C and 132.1 mA h g^(−1) at 20 C)and long-term cycling stability(85.3%capacity retention at 5 C after 500 cycles)for SIBs.This research provides an avenue to construct long-life sodium energy storage systems based on pre-potassiated TiS_(2).

Organic interlayer engineering of TiS_(2) for enhanced aqueous Zn ions storage

Aqueous rechargeable zinc-ion batteries(ARZIBs)have a bright future for energy storage due to their high energy density and safety.However,for traditional ARZIBs,cathode materials always suffer from the limited space for large-sized zinc ions storage and transport,leading to low Coulombic efficiency and inferior cycling performance.To build a reliable host with large tunnel,1-butyl-1-methylpyrrolidinium ion(PY14^(+))pre-intercalated TiS_(2)(PY14^(+)-TiS_(2))is designed as an alternative intercalation-type electrode.As the insertion organic guest widens the interlayer space of TiS_(2)and buffers the lattice stress generated during the electrochemical cycles,the structural reversibility,cycling stability and kinetics properties of PY14^(+)-TiS_(2) are enhanced greatly.A specific capacity of 130.9 mAh g^(−1) with 84.3%capacity retention over 500 cycles can be achieved at 0.1 A g^(−1).Therefore,this study paves the way for enhancing the aqueous Zn ions storage capability by organic interlayer engineering.