Lithium Metal Anode Protection Strategy In Li-O₂ Batteries

With the wide use of fossil energy,the shortage of fossil energy and serious environmental problems have forced humans to turn to new clean energy sources.At present,after vigorous development,lithium-ion batteries have been widely used in small devices such as notebook computers and mobile phones.However,the low energy density of lithium-ion batteries is difficult to support the long-term use of large-scale equipment such as electric vehicles.Therefore,it is urgent and important to find a new type of battery with higher energy density.The lithium oxygen battery has attracted the attention of researchers with its energy density as high as 3500 Wh kg-1.The lithium metal anode with the lowest potential and extremely high capacity is the key to achieve high energy density of lithium oxygen battery.However,its wide application faces many challenges such as safety accidents resulted from uncontrollable lithium dendrite growth and battery failure caused by severe corrosion.In order to solve the above problems,we have carried out a series of studies on the different protection strategies of the lithium metal anode in lithium oxygen battery.The main contents are as follows:1.In order to solve the serious lithium metal corrosion problem in lithium oxygen batteries,we prepared a tetraethyl orthosilicate(TEOS)film-forming additive,which can react with the inevitable corrosive(LiOH)on lithium to form silica-rich protection film.This protective film can effectively prevent the corrosion of oxygen,water,and strong oxidizing substances.In addition,TEOS electrolyte additive also provides a dynamic repair effect to cure the protective film when it was damaged in long cycles under severe corrosion conditions.This strategy can effectively protect the lithium metal anode to reduce corrosion,and significantly increase the life of the lithium oxygen battery to 144 cycles.2.A fluorine-doped carbon/lithium fluoride gradient protective layer was prepared by the one-step in-situ reaction between molten lithium metal and polytetrafluoroethylene micropowder.The rich fluorine-doped carbon on the surface with high adsorption energy can effectively uniform the lithium ion flux at the electrode/electrolyte interface.The rich lithium fluoride in the bottom layer with a lower lithium ion diffusion barrier can help uniform deposition of lithium.At the same time,the fluorine-doped carbon can regulate the electrons constructure of the lithium fluoride to help lithium ions to diffuse nearly spontaneously,effectively preventing the uncontrollable growth of lithium dendrite,serious corrosion,as well as improving the cycle life of lithium oxygen batteries.3.A new type of hydrophobic nano-silica colloidal electrolyte was prepared to protect the lithium metal anode in Li-O2 batteries.Through the electrostatic interaction between colloidal particles and ions,silica and trifluoromethanesulfonate ions were coupled together,which effectively increased the lithium ion transference number of the electrolyte.This strategy reduces the space charge effect near the lithium metal anode and significantly suppresses the uncontrollable dendrite growth.In addition,the electrolyte has a relatively large viscosity,which significantly reduces the diffusion coefficient of contaminant in the electrolyte and reduces the corrosion.This strategy can significantly improve the electrochemical performances of lithium oxygen battery.4.A renaissance of N,N-dimethylacetamide-based electrolyte has been achieved to effectively stabilize lithium metal anode in Li-O2 battery.By adjusting the lithium ion solvation structure,the optimized electrolyte has fewer free solvent molecules and promotes the formation of anion-derived solid electrolyte interface(SEI)film under lower concentration,which not only provides the advantages of high-concentration electrolytes,but also overcomes the weaknesses of high-concentration electrolytes.As a result,the lithium oxygen battery with this electrolyte shows a lower overpotential,better cycle performance,faster mass transfer,faster electrode reaction kinetics,and stable lithium metal anode.