| The rapid growth of the global economy and population have consumed a large number of fossil fuels,causing an energy crisis and a series of environmental problems.Therefore,solving the energy crisis and developing renewable energy are the key to achieve sustainable development of human society.The core of large-scale application of renewable energy depends on the development of energy storage technologies.Among many energy storage systems,lithium-oxygen batteries have attracted widespread attention of scientific researchers due to their ultra-high theoretical energy density.Currently,lithium-oxygen batteries have made great progress in the reaction mechanism,discharge capacity,energy efficiency,and cycle stability.However,there are still many key scientific and technological problems need to be solved.The main problems are the slow ORR/OER reaction kinetics and the instability of lithium anodes,electrolytes,and redox mediator?RM?.In view of the above problems,the research contents of this paper mainly include the following aspects:?1?Due to the problems of unstable anode interface,flammable and volatile organic electrolytes in lithium-oxygen batteries,in this work,we propose a non-volatile and non-flammable ammonium ionic liquids[?C1OC2?C2C2C1N][NTf2]instead of organic electrolysis as an electrolyte to improve the safety of batteries.Using ionic liquid?IL?as the electrolyte and Ru O2 as the cathode,the average coulomb efficiency of the lithium-oxygen battery is 99.2%after 100 cycles,but the capacity retention is only 45%of the first cycle.After research,it is found that the main reason for the rapid capacity decay is the serious deterioration of the anode interface,which makes the internal impedance of the battery increase sharply.Furthermore,by incorporating a solid-state Li1.5Al0.5Ge1.5?PO4?3?LAGP?film onto the Li metal anode,an in situ hybrid IL-SSE interfacial layer is formed.The hybrid IL-SSE interfacial layer contains organic and inorganic components,which exhibits ionic activation behaviour through a dispersing redistribution and bridging process,achieving fast Li+transfer between lithium metal and solid electrolyte.The coulombic efficiency of IL-SSE-based Li-O2 battery is 99.5%and capacity retention is significantly improved for 100 cycles.?2?Organic iodide as a bi-functional redox mediator is used to improve the energy efficiency and cycle stability of lithium-oxygen batteries.Lithium iodide?Li I?is widely used in lithium-oxygen batteries,which can greatly reduce the charging voltage of lithium-oxygen batteries.However,the I3-ions produced by the oxidation of Li I could diffuse through the electrolyte and be reduced at the Li anode.The so-called“shuttle effect”leads to the consumption of the redox mediator and the increase of the charging voltage.In this study,an organic iodide,triethylsulfonium iodide as a bi-functional redox mediator,is used to suppress the"shuttle effect"of Li I.TESI releases both I-and TES+in the electrolyte.Among them,I-acts as a redox mediator to reduce the charging voltage of the battery.Meanwhile,organic cation TES+,as a solid electrolyte interphase-forming agent,in situ generates an interfacial layer on lithium anode via reductive ethyl detaching and the subsequent oxidation.This layer prevents the lithium anode from reacting with the redox mediator and allows efficient lithium-ion transfer leading to dendrite-free lithium anode.Significantly improved cycling performance has been achieved by the bi-functional organic iodide redox mediator.?3?The synergy between strong electrolyte solvation and cathode adsorption is used to suppress the"shuttle effect"of Li I and improve the energy efficiency of lithium-oxygen batteries.So far,there has been no solution to the shuttle effect from the cathode side even though the effect is originated from the cathode where the RMoxis formed.In this work,we carried out a novel strategy,utilizing the synergy between strong electrolyte solvation and cathode adsorption to anchor the RMox,I2,to suppress the shuttle effect of RM.An exceptionally strong solvation effect of dimethyl sulfoxide?DMSO?on I2 is identified by so far the largest observed shift of I2 Raman peak with respect to I2 vapor and by elongated I–I bond length in first-principles molecular-dynamics simulation.This effect together with the strong binding of Ru O2surface to I2 is found to invert the direction of the well-known reaction I-+I2?I3-to the left-hand side.So that Ru O2 nanoparticles can successfully adsorb I2 from the I3-solution,avoiding the diffusion of I3-to the Li anode.Inspired by this finding,we fabricated a Li–O2 battery with the Li/DMSO+Li I/Ru O2 structure.The synergic action of DMSO and Ru O2 on I2 is found to suppress the shuttle effect of redox mediator by anchoring I2 molecules,the oxidation product of the RM.Significantly enhanced stability is demonstrated over 100 cycles at charging voltage below 3.65 V.?4?Bromonitromethane is used to suppress the"shuttle effect"of Li Br and improve the cycle stability of lithium-oxygen batteries.In researches?2?and?3?,researches are focused on iodine species as the redox mediator.However,in the presence of H2O,higher concentrations of I–ions?>100 m M?will promote the formation of Li OH,causing the surface of the cathode to be passivated,which reduces the cycling performance of the Li–O2 battery.The Li–O2 battery with Li Br additive has few side reactions.Even when the concentration of Li Br is as high as 1 M,the main discharge product of the battery is still Li2O2.But,the"shuttle effect"accompanied by Li Br results in gradually increased charging overpotential after a certain number of cycles.In order to avoid the formation of Li OH and suppress the"shuttle effect"of Li Br,we propose bromonitromethane?Br CH2NO2?as a new bi-functional RM.Br CH2NO2 is reduced at the lithium anode to generate bromine ion?Br–?and a protective layer on lithium anode surface.The Br–ions act as RM to reduce charging voltage.Meanwhile,the protective layer generated in situ prevents the lithium anode from reacting with the oxidized bromine species and allows efficient Li+transfer leading to dendrite-free lithium anode.The lithium-oxygen battery with Br CH2NO2 additive achieves excellent cycle stability,and the cycle life of the battery is increased by 3 times. |
PDF Full Text Request