1) Low reversibility of Li
The absence of excess Li metal brings not only huge advantages but also causes rapid capacity decay of AFLMBs within a few cycles. Owing to the high reactivity of Li metal, active Li is continuously consumed by the reaction with the electrolytes and the formation of dead Li.[35,68] Without excess Li metal, CEs are directly related to the reversibility of the Li stripping/plating process. The correlation between the average CEs (aCEs) and cycle life is shown in Table 1.[41] High aCEs (> 99.978 %) are required for AFLMBs to practically compete with commercial LIBs (> 500 cycles), but this has not yet been achieved. Even when aCEs are highly improved to 99.8%, the cell only exhibits 80% capacity retention after only 100 cycles, which is far below the commercialization. Therefore, even if a high initial energy density is achieved through AFLMBs, it drops rapidly within several cycles.