Microstructure Evolution And Underlying Mechanism Of Composite Li-B Based Li Metal Batteries Anode

Lithium metal batteries（LMBs）are attracting much attentions due to their high energy densities.Nevertheless,the uncontrollable Li electrostripping and plating process that results in dendritic Li growth and huge volume change of Li anode limits the practicality of Li metal batteries（LMBs）.To simultaneously address these issues,designing threedimensional（3D）,lithiophilic and mechanically robust electrodes seems to be one of the cost-effective strategies.This paper focuses on the design of 3D Li-B based composite anode and its morphology evolution mechanism,and the following research targets have been achieved:（1）Three types of Li-B-Mg composite anodes are fabricated.Due to the various content of B,3D skeletons with different microstructures are formed in situ inside the electrodes.The electrochemical characterization and 3D synchrotron X-ray computed tomography（SX-CT）technique have been employed on analyzing three composite anodes comprehensively.The 70Li-B-Mg composite anode can maintain electrode structure and induce the uniform Li deposition/dissolution process during long-term electrochemical cycling.On the contrary,the 8 3Li-B-Mg and 88.5Li-B-Mg composite anodes show half of the 70Li-B-Mg cells’ lifespan due to the collapsed 3D skeleton after cycled.Furthermore,when the 70Li-B-Mg composite anode pairs with the commercial lithium iron phosphate（LiFePO₄）or high nickel ternary（NCM）cathode materials,it can obtain more than 90%capacity retention in full cell testing.In Li-O2 battery system,70Li-B-Mg composite anode can effectively reduce the formation of inert porous transition layer（PTL）on the anode surface,prolonging the cycle life over 100 cycles.（2）Based on the composition design of Li-B-Mg composite anode,herein,a new 3D Li-B-C-Al composite anode is designed and fabricated.The prepared 3D composite anode exhibits not only superior lithiophilicity that facilitates uniform Li nucleation and growth but also sufficient mechanical stability that maintains its structural integrity.Superior performance of the prepared 3D composite anode is demonstrated through comprehensive electrochemical tests,which can cycle above 1000h.In addition,non-destructive and 3D SX-CT technique is employed to investigate the underlying working mechanisms of the prepared composite anode.A unique twofold Li electrostripping and plating mechanism under different electrochemical cycling conditions is revealed.Lastly,improved performance more than 200h of the full cells built with the 3D composite anode and LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）cathode corroborate its potential application capability.Overall,the current work in this paper not only showcases the superiority of the 3D Li-B composite anode as potential anode material for LMBs but also provides fundamental insights into its underlying working mechanisms that may further propel its research and development.