Application Of Transition Metal Nitrides In Cathode Materials Of Lithium-Sulfur Batteries

With the continuous development of society,the demands of portable electronic devices,transportation and stationary grid energy storage for rechargeable battery systems are increasing dramatically.Lithium-ion batteries,which have been widely used in the past two decades,cannot fully meet these demands any more.Therefore,designing and developing a new secondary battery system with high energy density and low cost has become the common goal of researchers at this stage.As one of the most promising secondary batteries,lithium-sulfur(Li-S)batteries have a high theoretical specific capacity(1,675 mA h g-1)and high energy density(2,500 W h kg11),which have great potential to be the mainstream of the secondary batteries in the future.Not only that,lithium-sulfur batteries have the advantages of low cost,low toxicity and environmental friendliness.In this paper,the application of transition metal nitrides in cathode materials of Li-S batteries was studied.The cathode composites with high conductivity,high sulfur content and structural stability were designed and prepared The main research contents and conclusions are as follows1.By using ZnO hard template method,nano-ZnO particles are used to make pores in layered V2O5,and a porous layered vanadium nitride(PLVN)material is obtained by NH3 reduction.The material has excellent electron and ion conductivity(conductivity at room temperature is 1.17 × 106 S m-1),high specific surface area(27.8 m2 g-1)and high sulfur content(?70%),and strong adsorption capacity with polysulfides.At a current density of 0.2C,the initial discharge capacity of the PLUN-S electrode reached 1,314 mA h g-1,and after 100 cycles,the discharge capacity remained at 903 mA h g-1,the corresponding capacity retention was 68.7%,showing high specific capacity and excellent cycle performance.2.Based on a free-standing ultra-thin porous titanium plate,the surface was coated with a layer of titanium nitride(TiNx)by surface nitridation,and then loaded with nano-sulfur particles uniformly by chemical liquid deposition,and finally SNPT-S composite is obtained.The SNPT-S electrode not only eliminates the use of conductive agents and binders,but also integrates the sulfur host and the current collector tactfully,so that the overall sulfur content of the cathode reaches 38.7 wt.%,20%higher than that of the ordinary Li-S batteries.In addition,the three-dimensional structure of the metal titanium inside the SNPT-S electrode provides a stable electron transport network,while the TiNh layer on the surface provides strong adsorption capacity with polysulfides.At a current density of 0.2 C,the initial discharge capacity of the SNPT-S electrode reached 1,346 mA h g-1,and after 100 cycles,the discharge capacity remained at 1,111 mA h g-1,the corresponding capacity retention was 82.5%,and the Coulomb efficiency exceeded 99.5%,showing excellent electrochemical cycle performance.