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Small: kinetics of N-doped porous graphitized carbon supported on VN to enhance sulfur cathode reaction

wallpapers News 2020-08-19
Due to the high theoretical specific capacity of sulfur (1675 MAHG – 1) low price environmental friendliness

is regarded as one of the next generation energy storage devices with great potential. Different from traditional lithium-ion batteries the energy storage principle of sulfur cathode is based on the redox reaction between sulfur (S8) lithium sulfide (Li2S). Due to the insulation of S8 Li2S the redox reaction can only occur at the interface between the positive conductive frame the electrolyte. In addition the conversion between S8 Li2S results in a series of soluble polysulfides. Therefore the sulfur cathode has the disadvantages of more complex reaction mechanism slower kinetics than the insert cathode. Among them the shuttle effect of polysulfides (li2sn 4? N? 8) will lead to irreversible loss of active substances poor cycle stability. In order to overcome these problems carbon materials (including porous carbon graphene carbon tubes) transition metal compounds (including metal oxides sulfides nitrides) sulfur-containing polymers are used to modify the cathode or separator of lithium sulfur battery through physical or chemical action. However the above problems still exist. Recently

have been used to accelerate the reaction of lithium sulfur batteries by adding electrocatalysts to the positive electrode separator. In addition this approach can inhibit the shuttle effect by reducing the accumulation of polysulfides. After Pt promoted the conversion of short chain polysulfides to long chain polysulfides for the first time other metals (including Ni Co Ru IR Fe Mo) were also proved to have catalytic effect. Similar to the above mentioned catalysis the N s B atoms doped in the black scale carbon materials also have catalytic properties to promote the conversion of polysulfides. In addition transition metal compounds are also used to promote the electrochemical reaction process of lithium sulfur batteries such as metal oxides (MnO2 TiO2 MoO3 Nb2O5) sulfides (MoS2 WS2 Cos2 ZnS res2) nitrides (tin co4n ni3fen) phosphates (mop mop2) carbides (W2C Mo2C TIC) heterostructures (SnS2 / SnO2 TiO2 / tin) etc. Despite the above research progress there are still some problems to be solved such as the reasonable design of efficient electrocatalysis structure the understing of electrocatalysis mechanism. In addition transition metal nitrides have higher conductivity so their application prospects may be broader than oxides sulfides. However the synthesis of nitrides by ammoniating the corresponding transition metal oxides at high temperature is complicated which hinders the scalable preparation practical application of transition metal nitrides. Therefore it is still a key challenge to use safe non corrosive raw materials to synthesize transition metal nitrides through simple sustainable methods to clarify their electrocatalytic process in the cathode of lithium sulfur battery.

Professor Geng Jianxin of Beijing University of chemical technology Professor abru NIA of Cornell University proposed a one pot method to prepare nitrogen doped porous graphitized carbon composites (denoted as 3D) with glucose as carbon source urea as nitrogen source ammonium metavanadate as vanadium source sodium chloride as hard template VN@N-PGC )The excellent electrocatalytic effect of VN doped nitrogen atoms on the positive electrode reaction of lithium sulfur battery was proved. Compared with the traditional methods the one pot method proposed in this paper has the advantages of simple operation low cost sustainability scalability. Through X-ray absorption near edge structure (XANES) spectrum observation theoretical calculation the 3D model is confirmed VN@N-PGC The electrocatalytic effect in the application of cathode carrier materials for lithium sulfur batteries. 3D VN@N-PGC The electrocatalytic effect accelerates the key conversion process which promotes the charge discharge process improves the specific capacity of lithium sulfur battery. Using 3D VN@N-PGC The lithium sulfur battery assembled with positive sulfur carrier material shows superior performance in specific capacity rate performance cycle stability. In view of the wide application prospects of transition metal nitrides this work provides a new strategy for the synthesis of transition metal nitride doped porous carbon composites which has potential applications in many electrocatalytic processes.

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