potential (−3.04 V vs the standard hydrogen electrode). [2] The application of Li metal anode can further boost the specific energy density of next-generation battery systems (such as solid-state cells, Li-S, and Li-air batteries) theoretically by three to six times relative to the current Li-ion batteries. [3] However, notorious safety hazard, low Coulombic efficiency (CE), as well as short lifespan due to the unsteady solid electrolyte interphase (SEI) and dendritic Li deposition impede the practical implementation of Li metal batteries (LMBs) seriously. [4] Many emerging strategies are proposed to protect the Li metal anode, such as interface regulation, [5] modified electrolyte, [6] localized high-concentration electrolytes, [7] and artificial protective layer. [8] Solid-state electrolytes are introduced into LMBs for high safety, [9] and threedimension (3D) lithiophilic hosts are introduced to inhibit the dendrite growth and volume expansion. [10] These strategies render critical progress in understanding Li plating/stripping science and extending cycling life, though it is unsatisfied for practical applications (usually <200 cycles in practical pouch cells). To further enhance the utilization and lifespan of the Li metal anode, it is primarily significant to gain the failure mechanism and electrochemical diagram of the Li metal anode.Recently, considerable efforts have been devoted and many enlightening opinions are released to understand the plating/ stripping behavior and failure mechanism of the Li metal anode. [11] By in situ high-resolution optical images, Wood et al. clearly correlated the cycling voltage and electrode morphology. [12] Xiao and co-workers systematically investigated the nickel cobalt aluminum oxide (NCA)-based LMBs and proposed the accumulation of highly resistive layer composed of "dead" Li was the main reason for the rapid capacity fading instead of the short circuit. [13] Xu and co-workers described the current density for charge (i.e., Li deposition) is identified as a key factor controlling the corrosion of the Li metal anode under high Li capacity utilization. [14] These works update our understanding in a working battery. However, these experiments are conducted at a relatively small current (<3.0 mA cm −2 , 3.0 mA) and low capacity (<4.5 mAh cm −2 , 4.5 mAh) in a coin cell, which are far from the practical conditions in pouch cells. [15] The pouch cell Lithium (Li) metal is regarded as a "Holy Grail" electrode for nextgeneration high-energy-density batteries. However, the electrochemical behavior of the Li anode under a practical working state is poorly understood, leading to a gap in the design strategy and the aim of efficient Li anodes. The electrochemical diagram to reveal failure mechanisms of ultrathin Li in pouch cells is demonstrated. The working mode of the Li metal anode ranging from 1.0 mA cm −2 /1.0 mAh cm −2 (28.0 mA/28.0 mAh) to 10.0 mA cm −2 /10.0 mAh cm −2 (280.0 mA/280.0 mAh) is investigated and divided into three categories: polarization, transition, a...