Research On The Interface Construction And Application For Lithium Metal Anode

Nowadays,Lithium-ion batteries have had a profound impact in many areas of our society,however,with the rapid development of advanced portable electronic products,electric vehicles,grid energy storage systems and aerospace technologies,the inherent limitations of lithium-ion chemistry hinder their further application in the face of huge energy demand in the future.Due to the high specific capacity(3861 mA h g-1),the lowest electrochemical potential(-3.04 V vs.the standard hydrogen electrode),and the lower density(0.534 g cm-3),metallic lithium has always been considered as the "Holy Grail"anode for the high specific energy rechargeable battery.Unfortunately,the inherent problems of lithium metal anodes have been hindering their practical application for decades,mainly including short circuits caused by the formation of lithium dendrites,open circuits caused by infinite volume changes during cycling,and unstable solid-electrolyte interphase(SEI)layer resulting in performance degradation and low efficiency.More seriously,these problems will interweave and affect each other during the battery operation,which will further deteriorate the safety and stability of the lithium metal batteries.Therefore,in order to solve the above problems,this paper designed a safe and stable lithium metal battery from several aspects such as electrolyte,artificial interface layer,solid electrolyte,etc.The specific research contents are as follows:Tetrachloro-1,4-benzoquinone(TCBQ)with a relatively low lowest unoccupied molecular orbital energy was adopted as an additive for traditional electrolyte for lithiumion batteries.TCBQ was easily reduced to form a novel lithiophilic quinone Li salt(Li2TCBQ),which distributed uniformly in the SEI layer on the lithium metal surface during the cycling.According the molecular dynamics simulation,it confirmed Li2TCBQ has high lithophilicity and can serve as a guide site for uniform lithium deposition,which can avoid the growth of dendrites,and effectively improve the interface stability of lithium anodes.The cells with TCBQ-added electrolyte can deliver the stable lithium plating/stripping under the high-capacity deep cycle of 5 mA h cm-2 and effectively inhibit the continuous decomposition of the electrolyte.The use of TCBQ additives provided a new way to achieve high energy density lithium metal batteries.Lithium-sulfur(Li-S)batteries,as one of the representatives of lithium metal batteries,are severely limited by not only the inherent problems of lithium metal anodes but also the shuttle effect of soluble lithium polysulfides that generate by sulfur cathodes during the discharge process.Aiming at above problems,bio-inspired by hydrophobic structure in nature,a scaly polysulfiphobic artificial interface layer was constructed on the lithium metal surface through the spontaneous reaction between decylphosphonic acid(DPA)and lithium metal.The obtain artificial interface was rich in functional decylphosphonate groups,which could repel the polysulfides and prevent the capacity loss and efficiency reduction caused by the shuttle effect.In addition,it can also stabilize interface of the lithium anode and inhibit dendrites.The Li-S batteries with prepared polysulfiphobic anodes realized stable cycling for 200 cycles with a high specific capacity of 1000 mA h g-1 with an efficiency of up to 99%at a current density of 1675 mA g-1.The hydrophobic graphite fluoride(GF)was adopted to fabricate a hydrophobic protective layer composed of graphite fluoride(GF)and lithium fluoride(LiF)on the surface of lithium metal(GF-LiF-Li)through a surface reaction between GF and molten lithium at high temperature,which can protect the lithium from corrosion by water and oxygen in the air,and prevent fresh lithium metal from directly contacting the electrolyte to form unstable SEI during the cycling.GF-LiF-Li anodes effectively inhibited the growth of lithium dendrites during charge-discharge process,and solved the problems that restrict the development of large-scale lithium metal batteries,including:1)dendrite-free metal lithium anode replaces low-capacity carbon anode materials,and realize safe and rapid charge and discharge;2)the manufacturing cost of lithium metal batteries is cut down greatly;3)The hidden dangers are eliminated which caused by the use of ethylene carbonate electrolyte additives.During the plating/stripping measurements,compared with the bare metal lithium anode,the GF-LiF-Li anode can deliver extremely low overpotential and excellent cycling stability even at a current density of as high as 10 mA cm-2 with no dendritic morphology.The safety and cycle life of lithium metal batteries was significantly improved and extended.A non-flammable and high-voltage-tolerated polymer electrolyte(HVTPE)was synthesized by polymerization of fluoroethylene carbonate containing lithium difluoro(oxalato)borate(LiDFOB).Young modulus of the prepared HVTPE was as high as 2.3 GPa,which can effectively inhibit lithium dendrites,and the good non-combustibility of HVTPE improved the safety of lithium metal batteries.In addition,HVTPE has lower HOMO energy and higher oxidation resistance,which can effectively avoid the decomposition and consumption of the electrolyte near the cathodes,and expand the voltage window of the polymer battery to 5.5 V.The 4.45 V-class LiCoO2 battery based on HVTPE can obtain a high capacity of 173.2 mA h g-1 at 0.05 C(1C=274 mA g-1).The polymer batteries using 4.9 V-class LiNi0.5Mn1.5O4 as cathode show excellent cycle stability.The research of HVTPE has opened up a new way to realize high-safety high-voltage polymer lithium metal batteries.