Perfluorinated Organic Cosolvent And Low Volatile Sulfoxide Solvent For The Electrolyte Of Lithium Oxygen Battery

The energy consumed in the daily life mainly comes from fossil fuels such as petroleum and coal.The global economy,humanities and technology are developing rapidly.The massive consumption of fossil fuels has also caused a series of energy shortages and environmental pollution problems.Therefore,human society is committed to the research of new energy storage devices.Although lithium-ion batteries have been developed well,their practical energy density is close to the theoretical value which cannot meet higher requirements.The lithium-oxygen battery with ultra-high theoretical energy density has attracted the attention of researchers all over the world.At present,the related research of lithium-oxygen battery has made great progress,but there are many problems needed to be solved,such as low practical energy density,difficult decomposition of discharge products,low energy efficiency,and unstable lithium anodes.The design of electrolyte composition is the key method to solve these problems.This paper takes the electrolyte of the lithium-oxygen battery as the starting point of the research,and optimizes the composition of the electrolyte to improve the electrochemical performance of the lithium-oxygen battery.The main research results are as follows:（1）Aiming at the problem that the practical discharge capacity of the lithium-oxygen battery is lower than the theoretical value,this paper uses perfluorotributylamine（PFTBA）with high oxygen solubility as the oxygen co-solvent to increase the oxygen content of the electrolyte.The solubility of oxygen in PFTBA-TEGDME is 1.5 times that in the traditional solvent tetraethylene glycol dimethyl ether（TEGDME）.After adding PFTBA to the TEGDME solvent,it promotes the mass transfer process of the lithium-oxygen battery during discharge.PFTBA can regulate the formation path of the discharge product Li₂O₂from surface growth to solution-phase growth,showing a typical toroid morphology of Li₂O₂,which is not easy to block the porous cathode.Therefore,the discharge capacity of the lithium-oxygen battery increases from 1607.4 m Ah·g^-1to 9548.7 m Ah·g^-1.With the lithium-oxygen battery cycling,the TEGDME solvent will decompose at the cathode to produce water molecules,which diffuse in the electrolyte and corrode the lithium metal.The hydrophobic PFTBA can hinder the migration of water molecules and protect the lithium anode.The lithium-oxygen battery containing PFTBA can achieve stable200 cycles,and the PFTBA can remain stable without decomposition during the cycling.（2）The organic electrolyte of lithium-oxygen battery generally has the problem of being volatile.This paper uses low volatile tetramethylene sulfoxide（TMSO）as the electrolyte solvent to improve the electrochemical performance of the lithium-oxygen battery.The TMSO-based lithium-oxygen battery can obtain stable 230 cycles,while the volatile dimethylsulfoxide-based lithium-oxygen battery can only cycle 66 times.In addition,when Li I is used as a redox mediator to reduce the overcharge potential,I₂ and I₃^-will be generated on the cathode,and then will diffuse to and react with the lithium metal,which is the shuttle effect.This paper uses the adsorption of the cathode in TMSO to absorb I₂ on the cathode and suppress the shuttle effect.The results of adsorption experiments show that Ru O₂ particles have a strong adsorption effect on I₂ in TMSO.We designed a lithium-oxygen battery with Ru O₂@CNT as the cathode and Li I+TMSO as the electrolyte.Ru O₂ at the cathode can absorb I₂ so that the reaction I^-+I₂→I₃^-proceeds to the left to avoid the formation of I₃^-.When the charge cut-off voltage is 4.0 V,the lithium-oxygen battery can show stable 250 cycles;when the charge cut-off voltage is 4.5 V,the discharge capacity of the lithium-oxygen battery does not decay within 328 cycles.