Synthesis Of Nanostructured Materials For High-Performance Lithium-sulfur Battery Cathodes

Efficient energy storage devices have huge market demand in portable electronic devices,electric vehicles,large-scale energy storage,aerospace and defense military.Lithium-sulfur battery is one of the most promising system for high-energy secondary in next-generation batteries due to its high theoretical energy density(2600 Wh kg^-1)and low cost of sulfur.Designing high-capacity,long-life and high-safe electrode materials is the key to the development and application of lithium-sulfur battery.However,the cathode of lithium-sulfur battery suffers from the low conductivity of sulfur and the reduction product lithium sulfide?Li₂S/Li₂S₂?,large volume expansion of electrode and shuttle effect of soluble polysulfide during lithiation,which limit the application of lithium-sulfur battery.Herein,we design mesoporous carbon material loaded with molybdenum phosphide clusters?cMoP-CMK-3?and Co-N-C derived from Metal-Organic Framework?MOF?as high performance sulfur host materials.The cathode materials of lithium-sulfur battery with large capacity,long life and high rate are prepared.The electrochemical properties of sulfur cathodes are studied,and the adsorption and catalytic conversion mechanism on polysulfide of the host materials are revealed.The research contents and innovations are as follows:1.A novel cMoP-CMK-3 host material with synergistic effects including physical limit,chemical adsorption and catalytic conversion is designed and synthesized.In the cMoP-CMK-3 composite,MoP clusters smaller than 1 nm are uniformly loaded in the channels of ordered mesoporous carbon CMK-3.After loading 68.5 wt%sulfur,the initial capacity of S@cMoP-CMK-3 electrode material at a current density of 0.5 C(1 C=1675 mA g^-1)is 1076.6 mAh g^-1,and the capacity retention after 100 cycles is 84.6%.The initial capacity at the current density of 2 C is 849.3 mAh g^-1 and decay rate after 500 cycles is only 0.02%per cycle.And the capacity remains 767.8 mAh g^-1 at at a high current density of 5 C.At a high area sulfur loading of 5.2 mg cm^-2,the area capacity is 3.47 mAh cm^-2 at a current density of 1 C after250 cycles.cMoP-CMK-3 has the following advantages as a novel sulfur host material:?1?Mesoporous pores of CMK-3 can effectively support and inhibit the loss of polysulfide;?2?Polar MoP clusters provide large surface area and abundant active sites,effectively adsorbing and catalyzing the conversion of soluble polysulfides,inhibiting the loss of polysulfide and shuttle effect,improving material utilization and rate performance;?3?High conductivity of MoP and CMK-3 provides fast electron transport,further enhancing the rate performance.2.The Co/Zn-ZIF used as the precursor is carbonized at high temperature to obtain the Co-N-C polyhedron which is rich in microporous structure with specific surface area of 910m² g^-1.The Co content in the Co-N-C polyhedron is 0.7 wt%.As a sulfur host material,the initial capacity of S@Co-N-C cathode material loaded with 72.6 wt%sulfur is 965.6 mAh g^-1at 0.5 C current density,and the capacity retention is as high as 91.9%after 100 cycles.The initial capacity at the current density of 2 C is 684.5 mAh g^-1,and decay rate of 1000 cycles is only 0.023%per cycle.The specific capacity at current density of 5 C is 578.6 mAh g^-1.As a host material for lithium-sulfur battery,Co-N-C has the following advantages:?1?The high specific surface area and microporous structure of polyhedron are beneficial to the loading of sulfur and the physical confinement of polysulfide,which alleviate the loss of polysulfide;?2?The doping of N heteroatom can effectively bind polysulfide relying on chemisorption;?3?Co can catalyze the conversion of polysulfide,further inhibit the shuttle effect of polysulfide,improve capacity,electrode reaction kinetics and cycle performance.