The Structure Design Of High-performance Lithium Metal Batteries

The high theoretical specific capacity(3860 mA h g^-1)and low redox potential?-3.04 V vs.SHE?endow lithium?Li?great promise to be used in the next generation rechargeable batteries.However,the safety issues and cycling degradation caused by dendrite growth and high reactivity of Li hinder its application severely.Dendrite growth results from multiple factors such as heterogeneous distribution of Li ions,high effective current density and concentration polarization.Here,originated from the essential factors of dendrite growth,we design some unique electrode structures to suppress the dendrite growth and side reaction between Li and electrolyte from various aspects.?1?3D structured carbon material is designed to be the scaffold of metallic Li.The3D structure provides carbon with a high specific surface area,which helps to decrease the effective current density of electrode,thus restraining the dendrite growth.Meanwhile,during the lithiation,the carbon is in-situ transformed into LiC₆ at the initial stage.Owing to the lithiophilicity of LiC₆,the Li-ion flow is uniformly dispersed which facilitates the controlled deposition of Li.With the synergistic effects of 3D structure and lithiophilic LiC₆,the 3D carbon material helps to improve the performance of Li metal anode.?2?A self-standing electrode is designed through infusing molten Li into the bismuth oxides coated carbon cloth?BiO_x@CC?.The BiO_x endows CC with lithiophilicity which benefits the infusion of molten Li.Furthermore,the BiO_x reacts with Li and forms as Li₃Bi alloy when they are connected at the high temperature.The adsorption energy of Li on the Li₃Bi surface is larger than the cohesive energy of bulk Li,which enables uniform Li nucleation and deposition.Meanwhile,the high diffusion barrier of Li atom on Li₃Bi prevents the adatoms from migrating to regions of faster growth,that further ensures uniform Li deposition.Combining with the high specific surface area of CC,which decreases the current density of electrode and suppresses dendrite growth,the Li/Li₃Bi@CC electrode attains excellent performance in Li metal batteries.?3?To further restrain the dendrite growth,an artificial protection layer is introduced in designing electrode substrate as well as the 3D structure and lithiophilicity.To fabricate this unique scaffold,a g-C₃N₄ layer is evenly coated on the CC.Then,due to the huge conductivity difference of g-C₃N₄ and CC,the metallic Li will deposit between CC and g-C₃N₄ layer,that is the interlayered Li electrode.The CC scaffold provides high specific surface area,which helps to decrease the current density of electrode and suppresses the dendrite growth,while the g-C₃N₄ layer is lithiophilic benefiting to disperse Li ions and also physically hindering the dendrite growth.This“integrated design”combines multiple functions in one single structure,which efficiently helps to enhance the performance of Li metal batteries.?4?The artificial protection layer can also control the impact of space charge layer around anode electrode.Here,the covalent organic frameworks LZU1?COF-LZU1?is introduced to serve as a protective layer in-between the Li anode and separator.Because of the interaction between bis?trifluoromethanesulonyl?imide?TFSI?anions and aldehyde functional groups in COF-LZU1,TFSI^-ions are immobilized on the COF-LZU1,enhancing the transference number of Li ions and hence suppressing the dendrite growth.Furthermore,the imine-linked COF-LZU1 is lithiophilic and electrolyte wettable,enabling a homogenous Li ions flux distribution and transport.With all these benefits,the COF-LZU1 protected Li enables safe and high power/energy density Li metal batteries.?5?High performance Li metal battery is related to both dendrite growth and parasitic reaction of Li.To comprehensively restrain the dendrite growth and side reactions of Li,hollow carbon sponge?HCS?is designed as the electrolyte reservoir.The lithiophilicity of HCS enables electrolyte stores into its internal hollow structure,which diminishes the side reactions through holding electrolyte and reducing the contact between Li and electrolyte.The carboxyl is preferred to bond with 1,2-dimethoxyethane?DME?through hydrogen bond,thus reducing the amount of DME molecule coordinated with Li cations and enhancing Li ions mobility.Hence,the lithiophilic elements controlling the Li ions flux works together with the carboxyl promoting Li transmission to suppress the dendrite growth effectively.With all these profits,the HCS as electrolyte reservoir helps battery with more stable cycling and higher Coulombic efficiency.