The Li-Air batteries which convert the electrochemical reactions of lithium and O₂ into electrical energy have high theoretical gravimetric capacity (3861 mAh/g_Li) that is ten times higher than that of lithium ion batteries (372 mAh/g_c).  Its potential to generate high energy density makes it a promising candidate to replace the lithium ion batteries which practically reached the gravimetric energy density limit in the electric vehicle applications.  To meet the requirements of the electric vehicle applications, the Li-Air batteries need to overcome the technical barriers that limit the cycle life such as electrolyte and cathode instability.  Although recent developments have been focused on improving the cycle life (1) and safety (2) of Li-Air battery in efforts to extend its application into the electric vehicle, it is also important to design a cell structure that can achieve the highest possible energy density.  The Li-Air battery uses lithium metal, porous carbon layer, protective layer and gas diffusion layer (GDL).  The properties of lithium metal anode and porous carbon cathode layer are well known, and the cell design will mainly be affected by the mechanical property of the electrolyte, protective layer and GDL. 

Figure 1 shows the schematic of a Li-Air fold cell where the Li metal anode, protective layer, and cathode are folded.  The oxygen can be distributed to the cathode through the GDL which is inserted between the two cathode layers that are formed from folding.  The cell design enables the two layers of the cathode to share one common GDL layer and thus increasing energy density of the cell.  The capacity of the Li-Air fold cell can be controlled by changing the length (L) and the number of folds of the cell.  The width (W) of the cell affects the O₂ distribution in cathode, thus the choice of W is limited.  Figure 2 shows the areal capacity of three Li-Air fold cells which contained polyethylene oxide with LiTFSI as electrolyte in the cathode and protective layer.  The cells were tested in 1 atm O₂ at 60 C.  The capacities of the cells were adjusted by changing the number of folds.  For the cells in Figure 2, the three cells had WxL dimension of 1x5 cm and were folded 1, 10 and 50 times which resulted in the cells with capacity values of 0.02, 0.2 and 1 Ah, respectively.  Figure 2 indicates that the performance of the Li-Air fold cell is reproducible as the number of folds increase.   In the presentation, the effects of cell dimension on cell performance, the technical difficulties of manufacturing Li-Air cells with high energy density as well as the issues that need to be overcome to improve the cycle life will be discussed.

References

1. A. J. Smith, , J. C. Burns, , S. Trussler, , J. R. Dahn , J. Electrochem. Soc. 157, A196−A202 (2010).

2. S. Menkin, D. Golodnitsky,  E. Peled , Electrochem. Commun. 11, 1789−1791 (2009).