Printed Thin Lithium Foil with Flexible Thickness and Width for Industrial Battery Applications
Authors: Xia Jian , Fitch Brian , Watson Andrew , Cabaniss Emory , Black Rebecca , Yakovleva Marina 
Published: December 2020

Lithium metal anodes are attractive for next generation battery technologies due to their high capacity, low voltage potential and light weight.1 The state of the art lithium-ion battery cells have energy density of ~300 Wh/kg. The lithium metal anode has already been used in rechargeable batteries with liquid electrolyte and demonstrated record specific energy density of more than 400 Wh/kg.2
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3 Solid-state batteries use non-flammable solid electrolytes instead of liquid and therefore offer improved safety. However, solid state batteries can exceed the energy density of today's lithium-ion batteries only when the thin lithium metal foil is used as an anode.

The common process to produce thin lithium foils includes extrusion followed by a rolling process. Typically, extruded lithium foil has a thickness of 100 μm or higher and is often made from lithium aluminum or other alloys to improve its mechanical strength. There are inherent difficulties of making extruded and rolled thin lithium metal films with thickness less 50 μm; for example, the control of thickness uniformity over long lengths and impurity levels.4 Moreover, the cost of making these foils increases as the thickness decreases. Thus, thin lithium foils with thickness less than 50 μm haven’t been produced on an industrial scale with the quality requirements necessary for battery applications.

Livent Corporation, formerly FMC Lithium, is one of the top lithium producers in the world and has over 60 years of extensive experience in providing high quality materials to the lithium-ion battery industry. Livent has recent developed Printable Lithium Technology (PLT), which incorporates stabilized lithium metal powder (SLMP®) into a stable printable formulation. PLT enables printing on any substrate, for example a current collector, prefabricated anode or cathode, separator, and even on solid or polymer electrolytes. The thickness of printed lithium foil is mainly controlled by the particle size of SLMP. The technology is easily scalable using industry standard coating and printing equipment. PLT is flexible, battery chemistry agnostic and adaptable to any energy storage device where thin lithium anodes are used.

Figure 1A shows an image comparing the 50 μm commercially available lithium foil (left) and 20 μm printed lithium foil (right) on a copper current collector. Figure 1A shows that a uniform film made from printable lithium formulation is consistent across the entire 50cm×10cm 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 1C shows that printed lithium foil maintains particulate structure of SLMP precursor that potentially can distribute current density over a wider surface area. The thin foil made with printable lithium formulation (PLF) contains rheology and performance modifiers that serve as a 3D skeleton, which can change the lithium surface plating behavior; therefore, mitigating the growth of dendritic lithium and mechanical degradation; thus, improving safety and cycle life of the battery.

Figure 1D compares lithium plating and stripping properties conducted in a symmetric pouch cell with a current collector coated with 20 um printed lithium foil vs. 50 um commercially available lithium foil. The symmetric cell contains two Li/Cu electrodes with Celgard 3501 separator sandwiched in between. Figure 2 shows that cell containing the printed lithium foil, and in spite of its 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.

Fgiure 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 image of 50 μm commercially available lithium foil. Figure 1C. Microscope image of 20 μm printed lithium foil. Figure 1D Lithium plating and stripping properties tested in a pouch cell with a copper current collector coated with 20 μm printed lithium foil versus 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

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