Structure Design And Key Issues Research Of Soft Packing Lithium-air Batteries

Lithium-air batteries with high energy density have attracted wide attention in recent years and are expected to be a ultimate solution for power batteries.However,the development of lithium-air battery is still in its infant stage and the practical application of lithium-air batteries is limited by serveral scientific and technical problems,such as,high overpotential,poor cycling performance,CO₂and H₂O poinsing,worse rate capability,lithium dendrite growing and undesirablesafety.A large number of researches are devoted to protect lithium anode,develop high-performance catalysts,find stable electrolytes and oxygen selective membranes,hard to solve the problems of lithium air battery from all aspects.At present,the main research on lithium-air batteries is still limited to a laboratory stage,and the practical research on lithium-air batteries is rarely reported.In this paper,a high-performance noble metal catalyst was developed,and a compound oxygen selective membrane was sucessfully prepared through an electrospinning process,and which were further applied to the optimized lithium-air battery to achieve an enhanced specific energy.In this work,a co-precipitation method was used to load Ru O₂catalyst onto carbon nanotubes(CNTs).It was found that Ru O₂has an obvious catalytic effect on OER process.The full decomposition of Li₂O₂can be achieved in the range of 3.3V-4.1 V,the charging potential decreased from 4.5 V to 4.0 V,more than 10%decrease compared with the pure CNTs cathode.After 500 cycles there was no obvious deterioration.Polyvinylidene fluoride hexafluoropropene(PVDF-HFP)oxygen selective membrane has been prepared through an electrospinning process.Under an ambient air condition,a lithium-air battery with the PVDF-HFP oxygen selecitve membrane can be continously cycled for more than 100 times without obvious decay.In order to further improve the performance of oxygen selective membrane,PVDF-HFP was used as the substrate impregnated withsilicone oil or perfluorinated polyethylene(PFPE)that was served as hydrophobic and oxygen-permeable liquids.It was found that the discharge performance and cycling performance of these two kinds of composite oxygen selective membrane were both improved compared with pure PVDF-HFP membrane.Through cmparasion,PVDF-HFP@PFPE oxygen selective membrane exhibited the best performance.It can circulate steadily for more than200 cycles without decay in ambient air condition.In this work,with the consideration of battery assembly,interface contact,gas transport,current collection and energy release,a symmetrical soft packing lithium-air battery with an area size of 25 cm²was designed and prepared,where CNT@Ru O₂composite was served as cathode while PVDF-HFP+PFPE was served as oxygen selective membrane.The battery exhibited a specific energy of 957 Wh kg^-1in an ambient air,the number of which was caculated based on the whole battery rather than single catalyst.The specific energy is 3-4 times of commerical lithium ion batteries.The battery can be cycled for more than 200 cycles without obvious decay.