Recent advances in robust and ultra-thin Li metal anode Zheng Luo, Yang Cao, Guobao Xu, Wenrui Sun, Xuhuan Xiao, Hui Liu, Shanshan Wang Abstract: Li metal batteries have been widely expected to break the energy-density limits of current Li-ion batteries, showing impressive prospects for the next-generation electrochemical energy storage system. Although much progress has been achieved in stabilizing the Li metal anode, the current Li electrode still lacks efficiency and safety. Moreover, a practical Li metal battery requires a thickness-controllable Li electrode to maximally balance the energy density and stability. However, due to the stickiness and fragile nature of Li metal, manufacturing Li ingot into thin electrodes from conventional approaches has historically remained challenging, limiting the sufficient utilization of energy density in Li metal batteries. Aiming at the practical application of Li metal anode, the current issues and their initiation mechanism are comprehensively summarized from the stability and processability perspectives. Recent advances in robust and ultra-thin Li metal anode are outlined from methodology innovation to provide an overall insight. Finally, challenges and prospective developments regarding this burgeoning field are critically discussed to afford future outlooks. With the development of advanced processing and modification technology, we are optimistic that a truly great leap will be achieved in the foreseeable future toward the industrial application of Li metal batteries. Keywords: energy density, Li dendrite, side reaction, ultra-thin Li anode Introduction: Lithium-ion battery (LIB) has rapidly occupied the secondary battery market due to high energy density and prolonged cycling stability, which nowadays become the dominant power source for electric vehicles, electronic products, and even grid-scale energy storage systems. During the past several decades of development, the energy density of graphite-anode-based LIB has been upgraded from the initial 80 Wh/kg to the present 230 Wh/kg, almost approaching its theoretical limits (280 Wh/kg), but still far from satisfying the ever-growing energy density demands. According to the "Made in China 2025" plan led by the Chinese government, the energy density of power batteries should reach the goal of 400 Wh/kg in 2025 and 500 Wh/kg in 2030, which is far beyond the theoretical limits of LIB and a novel battery system is therefore highly expected. Unlike intercalation chemistry-based anode, Li metal anode based on reversible metal electrochemical deposition/stripping possesses the highest theoretical capacity (3860 mAh/g) and the lowest electrochemical potential (-3.04 vs. Standard Hydrogen Electrode), which is reputed as the "Holy Grail" electrode in Li-based battery. As previously demonstrated, when replacing graphite anode with Li metal, the estimated energy density could be improved to 440 Wh/kg. Moreover, the Li metal anode is indispensable to the multi-electron conversion chemistryRecent advances in robust and ultra-thin Li metal anode Zheng Luo, Yang Cao, Guobao Xu, Wenrui Sun, Xuhuan Xiao, Hui Liu, Shanshan Wang Abstract: Li metal batteries have been widely expected to break the energy-density limits of current Li-ion batteries, showing impressive prospects for the next-generation electrochemical energy storage system. Although much progress has been achieved in stabilizing the Li metal anode, the current Li electrode still lacks efficiency and safety. Moreover, a practical Li metal battery requires a thickness-controllable Li electrode to maximally balance the energy density and stability. However, due to the stickiness and fragile nature of Li metal, manufacturing Li ingot into thin electrodes from conventional approaches has historically remained challenging, limiting the sufficient utilization of energy density in Li metal batteries. Aiming at the practical application of Li metal anode, the current issues and their initiation mechanism are comprehensively summarized from the stability and processability perspectives. Recent advances in robust and ultra-thin Li metal anode are outlined from methodology innovation to provide an overall insight. Finally, challenges and prospective developments regarding this burgeoning field are critically discussed to afford future outlooks. With the development of advanced processing and modification technology, we are optimistic that a truly great leap will be achieved in the foreseeable future toward the industrial application of Li metal batteries. Keywords: energy density, Li dendrite, side reaction, ultra-thin Li anode Introduction: Lithium-ion battery (LIB) has rapidly occupied the secondary battery market due to high energy density and prolonged cycling stability, which nowadays become the dominant power source for electric vehicles, electronic products, and even grid-scale energy storage systems. During the past several decades of development, the energy density of graphite-anode-based LIB has been upgraded from the initial 80 Wh/kg to the present 230 Wh/kg, almost approaching its theoretical limits (280 Wh/kg), but still far from satisfying the ever-growing energy density demands. According to the "Made in China 2025" plan led by the Chinese government, the energy density of power batteries should reach the goal of 400 Wh/kg in 2025 and 500 Wh/kg in 2030, which is far beyond the theoretical limits of LIB and a novel battery system is therefore highly expected. Unlike intercalation chemistry-based anode, Li metal anode based on reversible metal electrochemical deposition/stripping possesses the highest theoretical capacity (3860 mAh/g) and the lowest electrochemical potential (-3.04 vs. Standard Hydrogen Electrode), which is reputed as the "Holy Grail" electrode in Li-based battery. As previously demonstrated, when replacing graphite anode with Li metal, the estimated energy density could be improved to 440 Wh/kg. Moreover, the Li metal anode is indispensable to the multi-electron conversion chemistry