3) Cost
To attain a practical energy density (> 350 W h kg-1), the cathode capacity should be above 3–4 mA h cm-2 and a thin Li anode (N/P ratio < 2) is a prerequisite.[4,64] To meet these criteria, a Li metal anode of 15–20 µm should be employed. In general, the calendaring process to produce ultrathin Li foil significantly increases production costs (Li <20 μm – $13 m-2, Li 20 – 50 μm – $9.6 m-2, Li >50 μm – $8 m-2).[61] Figure 1C represents the stack cost per energy estimation of the cells. Interestingly, LMBs with thinner Li anodes (2 mA h cm-2) are more expensive than those with thicker Li anodes (4 mA h cm-2), although less Li is utilized because of the high cost of the Li calendaring process. Meanwhile, it is possible to dramatically reduce the production cost while increasing the energy density, as AFLMBs do not require excess Li. In addition to excluding the price of the Li processing process, less labor is required, and the convenience of the process is increased because highly reactive Li metal is excluded from all manufacturing processes. Furthermore, there is no need to make new investments in manufacturing facilities because of its compatibility with the LIBs fabrication process.[61,65]