Preparation Of Ni-Mo Metal Compound/Carbon Composites And Their Applications In Lithium-Sulfur Battery

In recent years,along with the rapid development of power equipment such as small mobile electronic devices and electric vehicles,exploiting the sustainable energy storage system has attracted widespread attention.Owing to high mass/volume energy density,rich resources,low cost and environmental friendliness,the lithium-sulfur battery has become one of the promising candidates for the next generation of the energy system.However,its application in the future energy storage market is seriously hindered by the low sulfur utilization rate,poor cycle stability and low coulombic efficiency.The slow reaction kinetics and severe shuttle effect are the root causes of the current problem.Based on these problems,the high performance lithium-sulfur battery was realized through applying bidirectional catalyst in the sulfur cathode to accelerate the reductive reaction kinetics of polysulfides and elevate oxidation ability of Li₂S and constructing a stable and high active reaction interface to suppress the shuttle effect and promote the transformation of polysulfides.For alleviating the shuttle effect and improving the kinetics of conversion reaction,hierarchical NiMoO₄ nanosheets anchored on N,S doped carbon clothes composite（NiMoO₄@NSCC）were designed and synthesized as self-supporting sulfur host.The open interconnected three-dimensional conductive network provides flexible space and abundant active sites,which can not only accommodate sulfur species,but also promote the transfer of electrons/ions.In addition,NiMoO₄@NSCC as a bidirectional catalyst can simultaneously accelerate polysulfide reduction and insulative Li₂S oxidation.Therefore,the batterie exhibits impressive cycling stability with capacity retention of 95.94%after 500 cycles at 1C.In allusion to the severe shuttle effect,P-doped NiMoO₄ nanoparticles in-situ growth on reduced graphene oxide（P-NiMoO₄@rGO）,which synthesized by hydrothermal synthesis and high-temperature phosphorus doping method,was used to modify separator for lithium-sulfur batteries.P-doped NiMoO₄,causing the increase of local electron density,has the high activity to catalyze the conversion of sulfur species and effectively inhibits the shuttle effect.The battery with separator modified by P-NiMoO₄@rGO delivers a high discharge capacity of 1497.5 m Ah g^-1 at 0.2C and after 150 cycles,having the capacity retention of 80.3%.In order to synergize the adsorption and transformation of polysulfide,Ni and Mo₂C nanoparticles embedded in N-doped carbon nanofibers（Ni/Mo₂C-NCNFs）were synthesized by electrospinning methods associated with the carbonization strategy.The composites were used as the modified separator for lithium-sulfur batteries.Owing to the high conductivity and excellent adsorption capacity for polysulfides of metal Ni,the high catalytic activity of Mo₂C and the high electrochemical activity caused by strong coupling of Ni and Mo₂C,the lithium-sulfur battery can realize high discharge specific capacity and excellent rate performance.The battery delivers a high initial discharge capacity of 1343.9 m Ah g^-1 at 0.2C,even the current density increased to 2C,it still remains a high discharge capacity of 757.6m Ah g^-1.