Controllable Preparation And Electrochemical Properties Of Dual-Lithiophilic Gradient 3D Carbon Fibers Skeleton/Lithium Metal Hybrid Anode

With the rapid development of renewable energy fields especially for electronic energy vehicles,the demand for next-generation high specific energy batteries with high safety,high energy density and long lifespan has been dramatically improved.Lithium metal anode with the high theoretical specific capacity(3860 mAh/g)and lowest electrochemical working potential(-3.04 V versus standard hydrogen electrode),has been considered as the ultimate anode material for the next-generation high-energy Li-S and Li-O2 batteries.However,the severe interfacial reactions between lithium anode and electrolyte,uncontrollable dendritic growth and huge volume expansion of lithium metal anode during cycling lead to poor cycle performance,low Coulombic efficiency and low safety of lithium metal batteries,which seriously limit their commercial application.A large number of strategies have been proposed to address these problems,including electrolyte additives,artificial SEI layer,solid electrolyte and 3D structured anode.3D skeleton as Li metal host can not only reduce the electrode current density,inhibit the dendritic growth,but also provide space for Li metal deposition and decrease volume expansion.In this work,3D carbon fibers skeleton has been used as the host of Li metal.Lithiophilic gradient modified layers are introduced to regulate the nucleation and deposition of Li+ions and realize the homogeneous deposition of high-capacity Li metal.The research contents mainly include the following points:(1)Lithophilic Si and ZnO were sputtered on different side of carbon fibers skeleton and covered on the Cu foil modified with ZnO by magnetron sputtering method to realize the controllable preparation of dual-lithophilic gradient 3D carbon fibers skeleton(SCZ).Si and ZnO are gradiently distributed on different side of the CNFs skeleton.The formed lithiophilic LiyZn/Li2O layer during plating process with low Li nucleation overpotential can guide Li metal bottom growth.Compared with the LiyZn/Li2O layer,the introduced LixSi layer on the top of skeleton has higher nucleation overpotential,so the deposition direction of Li has not changed.In addition,the introduced LixSi alloy could build a stable Li metal anode interface and provide more uniform distribution of Li+ions.(2)The lithiophilic LixSi layer on the top of the SCZ skeleton could regulate the uniform nucleation and deposition of Li+ions.Even if there are uncontrolled dendritic Li growth inside the skeleton,the further deterioration can be effectively suppressed by"self-repair" function of 3D dual-lithophilic skeleton.Dendritic-free deposition under high capacity(30 mAh/cm2)Li deposition can be achieved in the SCZ current collector.At the current density of 1 mA/cm2 and capacity of 1 mAh/cm2,the SCZ‖Li half-cells retain a high average CE of 97.5%over 200 cycles and SCZ-Li symmetric-cells can maintain stable more than 900 h with a low overpotential of 14 mV.(3)SCZ-Li‖LFP full-cells provide high capacity of 104 mAh/g at 5 C after 2000 cycles with a high average CE of 94.8%and SCZ-Li electrode remains stable crosslinked structure.The constructed CNTs/S hybrid cathode and SCZ-Li10 anode(with 10 mAh/cm2 Li)are assemble into CNTs/S‖SCZ-Li 10 full-cells.The CNTs/S‖SCZ-Li 10 full-cells possess high initial discharge specific capacity of 1048mAh/g and remain high discharge specific capacity of 646mAh/g after 100 cycles at 0.2 C.These experiment results demonstrate that 3D dual-lithophilic gradient skeleton can promote the practical application of lithium metal anode.