# Feasible Energy Density Pushes of Li-Metal vs. Li-Ion Cells
## 7 Summary  
A significant improvement in the energy density of rechargeable lithium batteries is needed to meet future requirements, especially for e-mobility. In order to design a high-technology battery it is important to understand the limitations of both current and next-generation battery systems. The energy density of a battery is mainly limited by two elements of a battery cell: the cathode and anode materials. Cell performances can be significantly enhanced through the selection and matching of electrode materials. Conventional Li-ion batteries are accepted as a very mature technology, however they are far behind future breakthroughs. Even though there are associated technical challenges with Li-metal anodes, they are still regarded as key elements for next generation battery systems due to their high capacity and fast charging compatibility. Many studies have increased the energy density of lab-scale Li-metal batteries simply by using a thick Li-metal foil as an anode material. Although utilizing large amount of excess lithium appears to be a straightforward solution, it is clear that it cannot be a practical solution in the long term. Within the scope of this paper, we have described basic parameters such as Coulombic efficiency, excess lithium, and cycle life for Li-metal anodes. It is clear that limited excess lithium brings higher energy density but unfortunately for a reduced number of cycles. From this perspective, one can ask the key question: Do the next generation Li-metal batteries have to completely replace conventional ones? Or is there a compromise? The last section of this paper demonstrates clearly that Li-metal anodes can be an attractive material for large capacity batteries (>100 kWh) since significantly lower cycles are required for the EoL driving distance. These lower cycle numbers enable a Li-metal battery design with a feasible CE. Lower capacity batteries (<100 kWh) can still use conventional LIBs. It should be noted that use of excess liquid electrolyte in LMBs may be an option to extend the life of the cells. However, in our experience, only those amounts of excess electrolyte which can be physically bound in the separator and the positive electrode are a good option, this electrolyte excess is at most around 10-20%. However, compared to LIB cells, about 25-30% of electrolyte can be subtracted, since the graphite anode does not exist and bare Li-metal cannot absorb any electrolyte. Recalculation for the entire cell means that although excess electrolyte can be applied, assuming the CE is high enough, there is an additional gain in gravimetric energy density of around 10-20% because electrolyte can be saved. In fact, this will increase rather than decrease the energy density of true lithium metal cells. If a liquid electrolyte is replaced by a solid electrolyte the gravimetric energy density decreases about 5-10% since solid electrolytes are heavier than liquid electrolytes. Last but not least, it is very challenging to develop a battery technology with high energy density and low manufacturing cost at the same time. Cost reduction may be achieved by choosing non-critical raw materials, new cell design and easy manufacturing processes. At the moment, however, there is no mass production of Li-metal and/or solid-state cells, and as a result the costs are disproportionately high. Additionally, use of thin Li-metal foil will increase the cell cost as cells with thinner electrodes are more expensive to manufacture due to difficulties in the processability [49]. Therefore, anode-free (zero-excess) cell configuration and obtaining Li metal on the anode side through in situ Li deposition may be a promising cell design. This type of cell will both save on the cost of thin Li-metal foil and the cost of the manufacturing process as there won't be a need for an expensive gas protected environment or a clean room. To conclude, the variety in the battery market may allow for cost reduction, easier and different recycling strategies, and more sustainability.