Construction And Performance Research Of Lithium Oxygen Batteries System Based On Wettability-Regulated Two-phase Electrolytes Interface

The heart of new energy vehicle is power battery,but the current commercial lithium-ion battery has low energy density(²00 Wh kg^-1)and short range,which is the main obstacle to the development of new energy vehicle.Thus,it is urgent to develop long-endurance power batteries based on new theory and technique.Lithium oxygen batteries with ultra-high theoretical energy density(³500 Wh kg^-1)are potential long-term power batteries.However,there are still numerous problems in the application of lithium oxygen batteries.Among them,low energy density and poor cycle stability of lithium negative electrode are one of the key bottlenecks restricting the application of lithium oxygen batteries.There are many reasons for the above problems,including:?1?film discharge products induced by adsorbed superoxide intermediates on the surface of solid catalysts lead to premature termination of battery discharge,which makes it difficult to increase battery capacity;?2?electrolyte components and high chemical active lithium negative electrodes are fully infiltrated and side reactions occur,such as solvent with high donor?DN?value,H₂O,CO₂ in air.Side reaction factors such as redox mediators,which promote the reaction rate at the interface of air electrodes,will diffuse from air positive to lithium negative,which will lead to chemical corrosion of lithium negative,resulting in low energy conversion efficiency and poor cycle stability of lithium oxygen batteries.To solve these two problems,inspired by the unique nature of coenzymes in nature,we propose a new catalytic pathway for redox reaction using functional anthraquinone molecules as"coenzymes".Anthraquinone promotes the oxygen reduction rate on the surface of solid-state catalysts to increase discharge capacity.Furthermore,two-phase electrolyte interface is used in lithium oxygen batteries to prevent the diffusion of side reaction factors to lithium negative electrode and improve lithium negative electrode and battery cycle stability.Specific research contents are as follows:Firstly,the concept of"biomimetic enzyme-coenzyme synergistic catalytic oxygen reduction mechanism"was structure based on the principle of"electron transfer or proton conversion or accelerated enzymatic reaction by coenzyme factors in nature".Based on the ability of quinones to capture superoxide free radicals in organisms,the binding and trapping abilities of anthraquinones?AQ?,2,5-tert-butyl-1,4-benzoquinones?DBBQ?and naphthoquinones?NQ?in oxygen reduction process and their ability to enhance the rate of oxygen reduction reaction on electrode surface were systematically studied.The results show that anthraquinone molecule not only significantly increases the rate of redox reaction of solid catalytic electrode?10 times?,but also increases the capacity of lithium oxygen battery to more than three times of the pristine.Secondly,the full infiltration of electrolyte components such as high donor value solvents and soluble redox mediators with lithium negative electrodes and their chemical reactions will lead to corrosion of lithium negative electrodes,resulting in low coulomb efficiency and poor stability of lithium negative electrodes,resulting in low energy conversion efficiency and short cycle life of batteries.Based on the difference of polarity of organic solvents,we constructed two-phase electrolytes with interfacial wettability control to prevent the contact and infiltration of polar solvents,hydrogen peroxide,carbon dioxide,soluble redox mediators and other electrolyte components?known as"side reaction factors"of lithium electrodes?with lithium negative electrodes,and to inhibit their side reactions with lithium negative electrodes,so as to enhance the cycle stability of lithium negative electrodes and lithium oxygen batteries.Firstly,based on the difference of polarity between fluorosilane and dimethyl sulfoxide?DMSO,high DN value?,a two-phase electrolyte of DMSO-fluorosilane with lithium ion transport performance was constructed.The strong lithiphilic and chemical stability of fluorosilane to lithium metal was used to inhibit dendrite growth and improve cycle stability of lithium metal electrode.Then,using lithium oxygen battery as a model,the cycle life of the battery can be increased from 40 cycles to 60 cycles by two-phase electrolyte,which proves the feasibility of this idea.However,the lithium ion transport rate in the two-phase electrolyte interface system is low,which limits the further improvement of the performance of lithium oxygen batteries.Third,the main reason why the cycle life of lithium oxygen batteries based on two-phase electrolyte is difficult to further improve is the poor ion transport performance at the interface.Through simple quaternary amination reaction,we designed and synthesized?1S,2S?-?+?-1,2-hexamethylene diamine gel molecules,which can construct ordered ion channels at the two-phase electrolyte interface to achieve efficient interfacial lithium ion transport process.The study shows that the introduction of three dimensional mesh cis to the two-phase electrolyte interface significantly improves the lithium ion transport rate and increases the cell cycle stability.In order to further improve the rate of lithium ion transfer,inorganic nano SiO₂ aerogel particles were used.Based on Lewis acid-base reaction principle,the composite electrolyte was constructed by adding SiO₂ aerogels on the network gel.On the basis of promoting further dissociation of lithium salts,the number of free lithium ions at the interface of the two phases was increased,which significantly enhanced the lithium ion transport performance.Finally,the cycle life of lithium oxygen batteries assembled with composite electrolytes is increased from 40 cycles to140 cycles.Through the research in this paper,we propose the concept of"enzyme-coenzyme synergistic oxygen reduction catalytic reaction",and confirmed this concept by using anthraquinone molecule as"coenzyme"factor.Anthraquinone not only promotes the oxygen reduction process on the surface of solid catalysts,but also greatly improves the specific capacity of batteries.Furthermore,we constructed DMSO-fluorosilane two-phase electrolyte based on interfacial wettability regulation by using polarity differences of organic solvents,which prevented the contact and infiltration of polar solvents,H₂O,CO₂,and redox mediators with lithium negative electrodes,inhibited their side reactions with lithium negative electrodes and lithium oxygen batteries.In addition,by combining organic gel and nano SiO₂ aerogel in two-phase electrolyte solution,the lithium ion transport rate of the electrolyte interface system is increased,thus significantly improving the cycle life of the battery.The construction of lithium oxygen battery system based on two-phase electrolyte interfacial wettability control effectively avoids the chemical corrosion of lithium negative electrode by side reaction factors,which provides a new research idea and technical means for the development of high performance lithium oxygen battery.