Design,Preparation And Applications Of Titanium-based Heterostructures For The Lithium-sulfur Batteries

Traditional lithium-ion batteries can not adapt the rapid development of the portable electronic equipment and electric industry.Therefore,lithium-sulfur?Li-S?batteries develop rapidly for the high energy density and the relatively low cost.But due to the shuttle effect of polysulfides between the cathode and anode,the active materials greatly lost and long-life cycling stability was hard to achieve,which has become an important bottleneck limiting the large-scale application.Therefore,people design and prepare various materials as the physical barrier and chemical adsorption for the polysulfide to improve the utilization of sulfur and enhance electrochemical properties.However,the simple physical barrier and chemical adsorption can not improve the kinetic.In order to solve these problems,it is necessary to design and prepare the materials which can simultaneously confine and accelerate the conversion of polysulfides.Based on the aforementioned issues in this paper,conductive polar TiN-graphene was prepared as the cathode host for lithium-sulfur batteries.And this paper further presents a unique design of twinborn TiO₂-TiN heterostructures for accelerating the conversion of polysulfides.For another,the paper proposes an in-plane heterostructure composed of graphene and titanium carbide?TiC?synthesized by chemical vapor deposition using graphene as the template and carbon sources for the TiC preparation,which helps decrease the Li ion/electron barrier and effectively converts the polysulfides.Firstly,this paper focuses on the TiN-graphene composite,which was prepared by hydrothermal method,and its effect on the electrochemical performance of lithium-sulfur battery was further studied.Then,twinborn TiO₂-TiN heterostructure with an interface was designed and prepared for further improving the conversion efficiency.Two-phase component can be easily tuned by changing the ratio of TiCl₄ and urea.The interfaces between TiO₂ and TiN enable that the redundant trapped polysulfides can diffuse to the surface of conductive polar TiN for nucleation from the saturated adsorption surface on TiO₂,which improves the adsorption and conversion of polysulfides.So the kinetic and electrochemical performance are achieved with the heterostructure.Even with high sulfur loadings of 3.1 and 4.3 mg cm^-2,the capacity retentions at 1 C after about 2000 cycles are73.1%and 67.2%respectively.Finally,from the perspective of structure design,the paper focuses on the design of in-plane TiC-graphene heterostructures,which is one-step synthesized by a direct graphene template reacting with TiCl₄ via a simple chemical vapor deposition.Importantly,the conductive TiC nanosheets enhance the utilization for the anchoring and conversion of polysulfides,meanwhile,the in-plane structure facilitates electron and ion transportation.A capacity retention of 84%at 1 C over 500 cycles is retained,and the high rate performance and enhanced redox kinetics are also achieved with the heterostructure.