Research On Self-Supporting Electrode Materials For Lithium-Sulfur Battery

The Internet of Things,electric vehicles and flexible/wearable electronics will be widely used with the coming ear of intelligent energy.This has greatly inspired researchers to explore advanced power equipment with high energy density,electrochemical sustainability and mechanical flexibility.In recent years,countries around the world have invested variety works in developing new energy,from basic research to practical technology.Researchers have been seeking commercial breakthroughs in next-generation chemical power sources,such as lithium-ion batteries,lithium-air batteries,supercapacitors,and lithium-sulfur batteries.Up to now,lithium-sulfur battery which uses elemental sulfur as the positive electrode and metal lithium as the negative electrode is expected to become the most promising next-generation energy storage device because its high theoretical specific capacity(1675 mAh g^-1)and energy density(2600 Wh kg^-1).In addition,it has the advantages of great abundance and environmental friendliness.However,the low conductivity of both sulfur and its end-discharge product,the large volume expansion?80%?during cycling process and the“shuttle effect”of polysulfides?Li₂S_x,4?x?8?limit the further industrial application of lithium sulfur battery.Thus,solving the above three main problems will effectively promote the commercial application of lithium-sulfur battery.MOF?metal-organic framework?materials have the advantages of high porosity,low density,large specific surface area,regular pore channels,adjustable pore size,topological diversity and tailor ability.Based on the above advantages,the first work is to choose self-supporting cobalt-based materials.The carbon fiber cloth with interconnected conductive network is firstly activated to obtain a modified surface with multifunctional groups,which helps the adsorption of polysulfides in the electrochemical reaction process,thereby increasing the utilization of active materials.Then the Co-MOF-ACC precursor with nanorod structure is obtained by wet-impregnation technique.Consequently,three-dimensional self-supporting Co?PO₃?₂-ACC nanosheet is obtained through phosphating treatment.The electrode exhibits an initial discharge capacity of1275 mAh g^-1 at 0.1C(1C=1675 mAh g^-1)and maintains 638 mAh g^-1 after 240 cycles.Further,our second work is based on a self-supporting nickel-based materials,and carbon fiber cloth with multifunctional groups is also selected as the substrate.The Ni?OH?₂-ACC nanosheet is grown in situ on activated carbon fiber cloth by wet-impregnation technique.Finally,after phosphating the coral-like Ni₂P-ACC nanostructure is obtained.We explore the electrochemical performance by analyzing the micro-morphologies of these two electrodes.Consequently,the Ni₂P-ACC exhibits extremely high capacitance(880 mAh g^-1),and super-long cycle life(660 mAh g^-1 after600 cycles)due to the novel nanorod-nanoflake croal-like structure and enhanced conductivity and wettability.Finally,based on the cobalt and nickel-based materials with novel three-dimensional structure and high conductivity and wettability,these may also get excellent results in the field of supercapacitors.Thus,we try to apply the above two electrodes to supercapacitor field.The results also show that the self-supporting electrodes exhibit extremely high electrochemical capacitance.This work broadens the application of self-supporting electrodes in electrochemical energy storage.