Thin Lithium Metal Foil Technology for Advanced Battery Manufacturing

Abstract

Lithium metal anode is regarded as the holy grail for the next generation battery materials due to its high theoretical specific capacity which is 10 times higher than that of graphite1. Currently, the most advanced lithium-ion battery cells have energy density of ~300 Wh/kg. Whereas, lithium metal batteries with liquid or semi solid electrolyte from Solidenergy2 and Sion Power3 have demonstrated record specific energy density of over 400 Wh/kg. Solid-state batteries use non-flammable solid electrolytes instead of liquid and, therefore, offer improved safety. The 20 Ah multi-layer all solid-state cells made by Solid Power have achieved 330 Wh/kg.4 However, solid state batteries can exceed the energy density of today's lithium-ion batteries only when the thin lithium metal foil (<20 um thickness) is used as anode enabling a pathway to beyond 400Wh/kg.Industrial scale thin Lithium metal foil is produced by hydraulic extrusion followed by a rolling process. This process usually requires a delicate balance between the pressure and tension created by both extruder and winder, so that the resulting foil is not torn or stretched, retaining all the dimensional characteristics required. This process can be extremely challenging when making lithium metal films with thickness less 20 µm due to the poor mechanical properties of lithium metal.5 Moreover, the cost of making these foils dramatically increases as the thickness decreases. Livent has recently developed Printable Lithium Technology (PLT), which incorporates stabilized lithium metal powder (SLMP®) into a stable printable formulation. This presentation will cover thin lithium foil manufacturing processes and highlight advantages and disadvantages of our approach. The electrochemical performance results will be presented.Figure 1A compares the 50 μm commercially available lithium foil (left) and 20 μm printed lithium foil (right) laminated to copper current collector. Figure 1A shows that a uniform film made from printable lithium formulation is consistent across the application area. Figure 1B and figure 1C are the optical microscope images of 50 μm commercially available lithium foil and 20 μm printed lithium foil, respectively. Figure 1B shows commercial foil made with conventional extrusion and rolling process has rough and scratched surface. Figure 1C shows that printed lithium foil preserves the shape of precursor particles and boundaries are formed creating higher surface area that potentially can mitigate dendrite growth by distributing current over a wider area. Figure 1D and 1E show the SEM and EDS images of the printed Lithium foil after lamination. Figure 1D and 1E show the clear presence of oxygen at the boundaries. Figure 1F shows the microscope image of printed lithium foil before calendering which is a monolayer. Figure 1G compares lithium plating and stripping properties of testing conducted in a symmetric pouch cell format with a current collector coated with 20 um printed lithium foil vs. 50 um commercially available lithium foil. Figure 1G shows that the cell containing the printed lithium foil, with lower thickness, has exceptional cycling stability with negligible potential increases during the first 70 cycles, indicating that the growth of dendritic lithium has been significantly mitigated.Figure Captions: Figure 1A. Image of 50 μm commercially available lithium foil (left) and 20 μm printed lithium foil (right) on a copper current collector. Figure 1B. Microscope (200x) image of the Printed Lithium Foil before lamination. Figure 1C. SEM Image (500x) of the Printed Lithium Foil after lamination. Figure 1D Microscope image of 50 μm commercially available lithium foil. Figure 1E. Microscope image of 20 μm printed lithium foil. Figure 1F. EDS surface mapping of oxygen for the printed foil. FIG. 1G. Lithium plating and stripping properties tested in a pouch cell with a copper current collector coated with 20 μm printable lithium formulation compared to 50 μm commercially available lithium foil. Cycling voltage is between -0.5V and 0.5 V and a current density is 0.5 C for 1h. References D. Lin, Y. Liu, and Y. Cui, Nature Nanotechnology, 12, 194–206 (2017) http://dx.doi.org/10.1038/nnano.2017.16.Q, Hu, Y. Matulevich and Y, Tang, Solidenergy Systems, US Patent No. 16/308,023, June 08th, 2016https://sionpower.com/2021/sion-power-announces-licerion-ev-targeting-electric-vehicles-with-a-large-format-17-ah-400-wh-kg-cell/https://www.greencarcongress.com/2020/12/20201216-solidpower.htmlO. Mashtalir, M. Nguyen, E. Bodoin, L. Swonger, and S. P. O’Brien, ACS Omega, 3, 181–187 (2018).Shu-Hua Wang et al., Nat. Commun.2019,10,4930 Figure 1