Nanostructured Li Metal Anode to Inhibit Dendrite Growth in Safe Li-Metal Batteries
Authors: Cheng Xin-Bing , Peng Hong-Jie , Huang Jia-Qi , Zhang Rui , Zhao Chen-Zi , Zhang Qiang 
Published: February 2020

Li metal is considered as the “Holy Grail” of energy storage systems due to its extremely high theoretical specific capacity (3860 mAh g−1), low gravimetric density (0.59 g cm−3), and lowest negative redox potential (−3.040 V vs. standard hydrogen electrode). The bright prospects give rise to worldwide interests in the metallic Li for the next generation energy storage systems, including highly considered rechargeable metallic Li batteries such as Li-O2 and Li-sulfur (Li–S) batteries. However, the formation of Li dendrites induced by inhomogeneous distribution of current density on the Li metal anode and the concentration gradient of Li ions at the electrolyte/electrode interface is a crucial issue that hinders the practical demonstration of high-energy-density metallic Li batteries.
A unique nanostructured anode with Li metal distributed in fibrous Li7B6 matrix is proposed as a promising anode to prevent the dendrite growth. The nanostructured anode is with a large specific area, thus rendering a low current density on the Li metal anode. The dendrite growth is effectively inhibited via decreasing the growth velocity of Li deposits and then limiting the final size of deposited Li on the nanostructured matrix, thus leading to the dendrite-free morphology at macroscale. The concentration gradient of Li ions near the anode surface are sharply reduced, because the 3D Li7B6 fibrous structure provides quantities of free space to accommodate electrolyte. To improve the Coulombic efficiency of Li depositing/dissolution, a dual-phase Li metal anode containing polysulfide-induced SEI and nanostructured graphene framework was investigated for Li-S batteries. Free-standing graphene foam provides several promising features as underneath layer for Li anode, including (1) relative larger surface area than 2D substrates to lower the real specific surface current density and the possibility of dendrite growth, (2) interconnected framework to support and recycle dead Li, and (3) good flexibility to sustain the volume fluctuation during repeated incorporation/extraction of Li. The synergy between the LiNO3 and polysulfides provides the feasibility to the formation of robust SEI in an ether-based electrolyte. The efficient in-situ formed SEI-coated graphene structure allows stable Li metal anode with the cycling Coulombic efficiency of ∼97 % with high safety and efficiency performance, which is with a low resistance of 19.65 Ω (29.10 Ω for Cu foil based Li metal anode) and high ion conductivity of 5.42×10-2 mS cm-1 (2.33×10-2 mS cm-1 for Cu foil based Li metal anode). These results indicated that interfacial engineering of nanostructured electrode were a promising strategy to handle the intrinsic problems of Li metal anodes, thus shed a new light toward LMBs, such as Li-S and Li-O2 batteries with high energy density.

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