Ag@TiO₂ Nanotube Arrays As Three-dimensional Current Collector For Stable Lithium Metal Anode

Lithium metal is one of the most promising anode materials for next-generation Lithium metal batteries due to its high theoretical specific capacity(3860 mAh g^-1)and low electrode potential（-3.04 V vs SHE）.However,several obstacles,especially lithium dendrite growth and electrode volume expansion,greatly hinder the commercial application of lithium metal anode.Therefore,rational design of stable lithium anode which can effectively suppres lithium dendrite growth and buffer electrode volume expansion is crucial to achieve high performance lithium metal batteries.The research shows that depositing lithium metal into three-dimensional（3D）current collectors to built composite lithium anode materials is an effective strategy to solve above problems.Herein,highly-ordered TiO₂ nanotube arrays（TNTAs/Ti）were fabricated by electrochemical anodization.Lithiophilic Ag nanoparticles were deposited onto the TiO₂ nanotube arrays surface to obtain Ag@TNTAs/Ti arrays.TNTAs/Ti and Ag@TNTAs/Ti 3D current collectors can achieve uniform Li deposition,thereby suppressing lithium dendrite growth and mitigate electrode volumn change.The main research results are as follows:（1）Highly-ordered TiO₂ nanoarrays（TNTAs/Ti）were prepared by electrochemical anodic oxidation method.Then,Ag@TNTAs/Ti composite nanoarrays（Ag@TNTAs/Ti）were obtained by depositing lithophilic Ag nanoparticles onto surface of TiO₂ nanotubes by impregnation method.TiO₂nanotubes present hollow and tublar structure with an inner diameter of around150 nm and tube length of around 7μm.Ag nanoparticles with the diameter of about 15-20 nm are uniformly dispersed on the surface of TiO₂ nanotubes.（2）TNTAs/Ti was used as the 3D current collector for hosting lithium metal.The electrochemical deposition behaviors of lithium metal in Ti foil and TNTAs/Ti were compared.The results indicate that TNTA/Ti can guide the uniform Li deposition and suppress lithium dendrite growth.On the one hand,high specific surface of TNTAs can effectively reduce the local current density,regulate the electric field distribution,and guide the uniform Li deposition.On the other hand,Li_0.5TiO₂ nanocrystals in-situ formed by insertion of Li ions into TiO₂ lattice during first discharge process are served as active sites to effectively reduce the nucleation overpotential.Therefore,the CE of the TNTAs/Ti half cells is 97%after 280 cycles at 1 mA cm^-2.The symmetrical TNTAs/Ti-Li|Li cells maintain a relatively stable and low voltage hysteresis of～28 m V for 600 h at 1mA cm^-2.TNTAs/Ti-Li|LFP full cell delives an initial discharge specific capacity of 150.2 mAh g^-1 with 82.6%capacity retention after 90 cycles at 0.5 C.（3）Ag@TNTAs/Ti was used as the 3D current collector.The electrochemical deposition behaviors of lithium metal in TNTAs/Ti and Ag@TNTAs/Ti current collector were compared.The results indicate that Ag nanoparticles not only serve as heterogeneous nucleation sites to reduce nucleation overpotential,but also promote fast electron transport.The synergistic effect of Ag and TNTAs/Ti achieves the uniform deposition of lithium metal and suppresses the Li dendrites growth.The CE of Ag@TNTAs/Ti half cells is 98.2%over 990 cycles at 1 mA cm^-2.Symmetrical Ag@TNTAs/Ti-Li|Li cells maintain relatively stable and low voltage hysteresis of～26 m V for 2600 h at 1 mA cm^-2.Ag@TNTAs/Ti-Li|LFP full cell shows an initial discharge specific capacity of is 155.2 mAh g^-1 with77.3%capacity retention after 200 cycles at 0.5 C.