In Situ Formation of Conductive Metal Sulfide Domain in Metal Oxide Matrix: An Efficient Way to Improve the Electrochemical Activity of Semiconducting Metal Oxide

Abstract

wileyonlinelibrary.comreliability of the lithium titanate render this material one of the most suitable anode materials for the EV application. However, the rate performance of lithium titanate is seriously limited by its low electronic and ionic conductivities. Such poor charge transport characteristic of Li 4 Ti 5 O 12 basically results from its wide bandgap energy related to the empty 3d states of Ti 4+ ions. [ 3f,k ] Various attempts such as cationic and anionic doping, and the hybridization and surface coating with conductive carbon are made to circumvent this drawback of lithium titanate. [ 3 ] Although these strategies are somewhat successful in improving the electrode activity of metal oxide, they might cause other several side effects such as the lowering of thermal stability. In general, the metal sulfi de possesses smaller bandgap energy and higher electrical conductivity than does the corresponding metal oxide, since (metal− sulfur) bond is more covalent than (metal−oxygen) bond. [ 4 ] The composite formation with conductive metal sulfi de can provide new effi cient way to improve the electrode performance of semiconducting metal oxide through the increase of electrical conductivity. However, the formation of metal sulfi de domain in the pristine metal oxide domain cannot be achieved by the use of conventional sulfurization agent such as thiourea, ammonium sulfi de, sodium sulfi de, and elemental sulfur due to their limited diffusivity into the solid lattice. Instead of the formation of metal sulfi de domain, this process leads to the formation of sulfate (SO 4 2− ) species on the surface of metal oxide. [ 5 ] The effective formation of metal sulfi de grains in the solid lattice might be achieved by the use of gaseous agents such as H 2 S. However, the high toxicity of hydrogen sulfi de might cause serious safety problems. [ 6 ] Instead, less toxic CS 2 liquid with Ar carrier gas can be used as a sulfurization agent to provide a safe and scalable synthetic method for metal oxide−metal sulfi de nanocomposites. To the best of our knowledge, there is no report about the in situ incorporation of conductive metal sulfi de domain to improve the electrochemical activity of semiconducting metal oxides.In the present study, a novel effective way to improve the electrode activity of semiconducting metal oxide is developed on the basis of the in situ formation of conductive metal sulfi de (Li x-Ti y S 2 ) domain in the metal oxide (Li 4 Ti 5 O 12 ) matrix using the CS 2 liquid. The experimental setup for this experiment is illustrated A new effective way to improve the electrochemical activity of semiconducting metal oxide is developed by the in situ formation of conductive metal sulfi de domain in the metal oxide matrix. The Li 0.96 Ti 1.08 S 2 −Li 4 Ti 5 O 12 nanocomposites with tunable compositions and electrical properties are synthesized by the reaction of Li 4 Ti 5 O 12 with CS 2 at elevated temperature. The resulting incorporation of conductive Li 0.96 Ti 1.08 S 2 domain in the Li 4 Ti 5 O 12 matrix is...

Boosted Charge Transfer in SnS/SnO2 Heterostructures: Toward High Rate Capability for Sodium‐Ion Batteries

“…The significantly improved Na + storage performance might be related to the synergetic enhancement of electron and sodium‐ion transport kinetics, benefiting from the internal electric field within the nanoparticles . Furthermore, the in situ generation of SnS nanoparticles in the SnO 2 matrix can effectively immobilize the SnO 2 , thus reducing the self‐agglomeration of SnO 2 nanocrystals and maintaining good structural stability . We also compare the rate performance of the C@SnS/SnO 2 @Gr electrode in this work with the state‐of‐the‐art results in previously published papers on SnO 2 ‐, SnS‐, SnS 2 ‐ and Sn‐based systems (Table S1).…”

Boosted Charge Transfer in SnS/SnO2 Heterostructures: Toward High Rate Capability for Sodium‐Ion Batteries

“…[22,25] Furthermore,t he in situ generation of SnS nanoparticles in the SnO 2 matrix can effectively immobilize the SnO 2 ,t hus reducing the selfagglomeration of SnO 2 nanocrystals and maintaining good structural stability. [33] We also compare the rate performance of the C@SnS/SnO 2 @Gr electrode in this work with the stateof-the-art results in previously published papers on SnO 2 -, SnS-, SnS 2 -a nd Sn-based systems (Table S1). Thec apacity and high-rate performance of the C@SnS/SnO 2 @Gr composite is greatly superior to those of most reported anodes for Na-ion batteries.S uch excellent performance shows that the as-prepared C@SnS/ SnO 2 @Gr composite has great potential as the anode in applications for Na-ion batteries.…”

Improvement of Na Ion Electrode Activity of Metal Oxide via Composite Formation with Metal Sulfide

“…These advantages of titanium oxide render them one of the most promising electrode materials for NIB. , However, the wide bandgap nature of titanium oxide with larger bandgap energy of >3.2 eV leads to the low electrical conductivity, which has a detrimental effect on the electrode performance of this material, especially under high current density . To overcome the inferior electrode performance of TiO 2 , many attempts have been made such as carbon coating, cation doping, and anion doping including sulfur doping. − Taking into account the lower electronegativity of sulfur than oxygen, the (metal–sulfur) bond has less ionic nature than the (metal–oxygen) bond, leading to the smaller bandgap energy and higher electrical conductivity of metal sulfide than metal oxide. , Thus, the composite formation of metal oxide–metal sulfide would be effective in improving the electrical conductivity and electrochemical activity of metal oxide . Actually, several metal sulfides like TiS 2 show much higher electrical conductivity than corresponding metal oxide like TiO 2 , which can act as conducting path.…”