Interface Modification And Electrochemical Performance Of High Specific Capacity Lithium Metal Anode And Silicon Anode

The popularization of electric vehicles can effectively accelerate the process of carbon neutral.Lithium battery is one of the most promising power systems for electric vehicles due to its advantages of high energy density,low self-discharge and environment-friendly.However,in order to meet the growing demand for electric vehicles,lithium-ion batteries need to be further improved in terms of energy density,safety and service life.At present,the mainstream anode material of commercialized lithium batteries is graphite,and its theoretical specific capacity is only 372 mAh g-1,which limits the improvement of the energy density of lithium batteries.Therefore,the development of high energy density anode materials is the key to the development of lithium batteries.Lithium metal anode has a high theoretical specific capacity(3860 mAh g-1),the lowest working potential(-3.04V vs.standard hydrogen electrode),which is an ideal high energy density lithium battery anode material.However,the interface stability of lithium metal anode is poor,which will cause uncontrolled growth of dendrites and accelerate side reactions between the interface,resulting in rapid deterioration of battery performance.In severe cases,it will also cause short circuit of the battery,and even fire and explosion.Silicon anode is also a candidate for the next generation of anode materials for Lithium batteries,which is used in lithium-ion battery systems.It has a theoretical specific capacity of 4200 mAh g-1 and its operating potential is close to that of graphite.However,the large volume change of silicon in the process of charging and discharging will lead to unstable electrode interface and the pulverization and shedding of active substances,resulting in the rapid attenuation of battery capacity and low charge-discharge efficiency.In view of the above problems of lithium metal anode and silicon anode,we take improving the interface performance as the starting point,and further improve the electrochemical performance of lithium metal anode and silicon anode by two different interface modification methods.Specific research contents are as follows:(1)MgI2 was used to modify the lithium metal interface,and a mixed interface layer of ion-conducting LiI and lithiophilic Mg was formed in situ.The interfacial layer can promote the uniform transport of lithium ions,reduce the lithium nucleation overpotential,and effectively inhibit the formation of dendrites.In the PEO-based all-solid-state battery system,the symmetric cells assembled with modified lithium anodes can achieve a more stable cycle,and the full cells also show good capacity retention ability and high coulomb efficiency.This work provides a new pathway for developing high performance lithium metal anode.(2)The MXene film was used as the current collector of the silicon anode.Compared with commercial current collectors,it has the advantages of flexible,light weight and better adhesion,which can effectively buffer the large volume change in the charging and discharging process of the silicon anode,reduce the interface impedance of the battery and prevent the shedding of active substances.The electrochemical performance of half cells and 5 V-based full cells assembled with MXene films as current collectors has been significantly improved.This work provides a new method for developing high stability silicon anode.