| The energy situation,environmental pressures and social development,especially the development of electric vehicles,require us to develop clean,sustainable and innovative energy storage systems.Besides the lithium-ion battery,the alternative systems are metal air battery,lithium sulfur battery and fuel cell.Among them,the theoretical energy density of lithium-O2 battery(5217W·h·kg-1)is the highest,even much higher than that of fuel cell(3500W·h·kg-1),therefore,lithium-O2 battery should be our ultimate goal of exploration of new energy.However,the development of lithium-O2 batteries still faces many problems:?1?The electrochemical reaction process of the cathode is complicated and its mechanism is not clear;?2?The anodic metal lithium is very active and the formation of lithium dendrites during charging limits the improvement of the battery life;?3?Both non-aqueous electrolyte and solid electrolyte are unstable;?4?The as-designed battery structure can't resist water and carbon dioxide in the air.Thus,the study on the cathode of lithium-O2 battery is particularly critical.Exploring the high-efficiency cathodic catalyst that can promote the decomposition of Li2O2,properly deal with the deposition of insoluble reaction products and inhibit side reactions are the current research hotspots of lithium air battery.Carbon materials with high specific surface area can not only provide a large number of catalyst-attachment sites,but also its rich pore space benefits the generation and storage of lithium peroxide.In addition,loading modified materials or doping on carbon materials can improve the catalytic activity of the materials,effectively catalyze the decomposition of Li2O2,even inhibit the occurrence of side reactions,and improve the cycle life of the battery.In conclusion,carbon materials are of great significance to construct the ideal lithium air cathode.Focusing on the surface properties of electrode materials,this paper explored the performance and mechanism of the battery,and made the following progresses in improving the cycle life of the lithium-O2 battery and lithium-ion battery:?1?A composite of FeOOH nanocube anchored on carbon ribbons has been synthesized and used as a cathode material for lithium-O2 batteries.Fe2+ion-exchanged resin serves as a precursor for both FeOOH nanocube and carbon ribbons,which are formed simultaneously.The as?prepared FeOOH cubes are proposed to have a core-shell structure,with FeOOH as the shell and Prussian blue as the core,based on information from XPS,TEM,and EDS mapping.As the cathode material for lithium-O2 batteries,FeOOH delivers a specific capacity of 14816 mA·h·g-1cathode with a cycling stability of 67 cycles over 400h.The high performance is related to the low overpotential of the oxygen reduction/evolution reaction on FeOOH.The cube structure,the supporting carbon ribbons,and the?OOH moieties all contribute to the low overpotential.The discharge product Li2O2 can be efficiently decomposed in the FeOOH cathode after a charging process,leading to higher cycling stability.The high activity and stability make FeOOH a good candidate for non?aqueous lithium-O2 batteries.?2?Nitrogen doped carbon with a series of nitrogen contents was synthesized through a method named“salt template”and used as cathode material for lithium-O2 battery.In terms of low nitrogen content,the cyclicity of lithium-O2 battery increased with the rising of nitrogen content,however,it is found that excess nitrogen defects could lead to poor performance resulting from its good catalytic active to side reaction.It is also found that 6%is the optimized nitrogen content for lithium-O2 battery,which delivered a low charge potential and cycling stability of 71 cycles over 420 hours.?3?In order to protect the cathode of lithium-O2 battery and prevent adverse reactions,we modified the solid electrolyte film?SEI film?formed during battery discharge to obtain a stable SEI film with the purpose of protecting the electrode materials.We take molybdenum disulfide in lithium-ion battery as the anode material,and modified a layer of octadecane molecules on the surface of molybdenum disulfide,which can induce the generation of stable SEI film,thus significantly improving the cycle stability of the lithium-ion battery.To sum up,we tried to explore lithium-O2 battery cathode materials from two key points:?1?promote the decomposition of lithium peroxide,and accelerate the kinetic process of the reaction;?2?inhibit the occurrence of side reactions and prevent by-products from slowing down the kinetic process of the overall reaction.In addition,modifying the surface of the electrode material to induce the creation of a stable SEI film can significantly improve the battery cycle life. |
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