| Large-scale use of renewable energy sources instead of fossil fuels is the key to tackling climate change,achieving sustainable development and carbon neutrality.Electrochemical energy storage devices represented by lithium-ion batteries,have great potential for efficient energy storage and conversion using renewable energy sources.The widespread use of lithium-ion batteries in the past few decades has driven technological change in society.However,the energy density of lithium-ion battery is gradually reaching theoretical levels that are difficult to meet the needs of rapidly developing portable electronic devices and electric vehicles.Therefore,there is a need to develop an economical and environmentally friendly energy storage technology with higher energy density.Lithium-sulfur(Li-S)batteries,as next generation energy storage technology,have attracted much attention for their high specific energy(2600 W h kg-1),high theoretical capacity(1675 m A h g-1)and reversible redox reaction kinetics.In addition,elemental sulfur is an abundant,inexpensive and environmentally friendly cathode material.However,the complex multi-step electrochemical reaction process and the conversion between multi-phases severely limit the commercial application of Li-S batteries.The main problems of Li-S batteries are as follows:(I)The electrical insulating of S and Li2S reduce the utilization of active materials;(II)The huge volume change during charging and discharging leads to the easy pulverization and shedding of electrodes;(III)The shuttle of polysulfide(Li PSs)leads to the rapid decay of capacity;(IV)The overgrowth of lithium dendrite leads to puncture of the separator.Rational design and construction of heterostructure is one of the effective strategies to solve all the above challenges with only one material.In this paper,we take metal oxides as the main object of study,by combining with different types of functionalized materials(Carbon or Metal sulfides)to form composite materials or heterostructures.Based on the synergistic effect,we study the role of different components on Li PSs adsorption-fixation-conversion process.The main work is as follows.1?In this section,we embed the polar La2O3 onto highly conductive graphene as a separator coating for Li-S batteries.In this composite material,carbon substrates not only improve the conductivity of the modified layer,but also limits the dissolution of Li PSs.While polar La2O3 nanoparticles provide a strong adsorption ability to anchor Li PSs and promote their conversion.The results of experiments and density functional theoretical(DFT)calculations revealed that the La2O3 nanoparticles is a desirable separator modification material that can effectively tuning the absorption and conversion interactions with polysulfides through S-La and Li-O chemical interactions.Benefiting from the synergistic effect,the corresponding Li-S batteries display good cycling stability(capacity fading rate 0.051%per cycle after 500 cycles),high initial specific capacity(1423.7 m A h g-1 at 0.2 A g-1),and excellent cycling performance at high sulfur loading(5.03 mg cm-2).In this chapter,it is difficult to integrate the advantages between the materials by simple physical mixing.2?The WO3-WS2 heterostructure was prepared by directly in situ sulfurization of WO3 nanoparticles,which combine the advantages between different components.In this experiment,the ratio of WO3 and WS2 in the heterostructure can be precisely regulated by precisely controlling the reaction conditions,so as to effectively balance the relationship between adsorption,trapping and conductivity,catalytic properties.Nitrogen doping can optimize the adsorption performance of heterostructure on Li PSs.It is proved that the heterostructure can accelerate the process of lithiation and delithiation,and improve the charge transfer and Li+diffusion efficiency.When WO3-WS2 heterostructure is used as both positive electrode and separator coating material for Li-S battery,the initial capacity of the battery is 1292.6 m A h g-1 at 0.2 A g-1.Even under high current(5.0 A g-1),high sulfur loading(2.6 mg cm-2)and 1600cycles,the cell still showed only 0.03%capacity fading rate per cycle.Moreover,the WO3-WS2 heterostructure can be used as“vice-electrode”during the reaction,which can inhibit the shuttle effect,thus improving the thermal stability and safety of the battery.This work also provides ideas for the development of high energy density and safe Li-S batteries. |
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