Lithium-Ion Batteries Fabricated Entirely with Additive Manufacturing

Abstract

Lithium-ion Batteries Fabricated Entirely with Additive Manufacturing Craig Milroy1,2, Tim Phillips1, Abhimanyu Bhat1,3, David Bourell1, Joseph Beaman1 1Department of Mechanical Engineering, University of Texas, Austin; 2Texas Research Institute, Austin; 3Evonik/Structured Polymers, Inc.There is an immediate need for disruptive battery manufacturing technologies that enable novel architectures and improve energy density by reducing packaging, interconnect, and integration requirements. Most conventional batteries are packaged in rigid metal containers with a restricted range of cell geometries and form factors; this poses major challenges for minimizing footprint and integrating batteries into small spaces. Additive manufacturing (AM) methods fabricate parts layer-by-layer by precisely assembling materials according to digitized instructions, and offer a means for simplified, top-down battery production, which provides enormous freedom to create innovative two-dimensional (2D) and 3D electrode architectural designs, customize battery form factor, and enable on-demand manufacturing. As such, AM offers a paradigm shift in electrochemical device design and manufacturing to accommodate novel geometries, improve energy density, and reduce costs. However, AM is still an emerging field, and while there have been numerous reports describing the use of AM techniques to produce components for batteries and supercapacitors, the vast majority of these efforts have focused on single components (typically the electrodes), rather than on complete systems comprising printed electrodes, separators, and cases.In this presentation, we describe methods to fabricate all necessary components of coin and pouch cells for functional prototype lithium-ion (Li-ion) batteries, using a variety of AM techniques. For example, functional graphite anodes, and cathodes based on nickel-manganese-cobalt oxide (NMC) and lithium iron phosphate (LFP), were fabricated with pneumatic extrusion, screen printing, and selective laser sintering (SLS); polymeric separators were fabricated with SLS; cases/enclosures were fabricated with SLS and direct metal laser sintering (DMLS), and metal components (e.g., foils and tabs) were fabricated with DMLS.We also utilized AM as a rapid-prototyping tool to implement novel component design approaches that improve battery performance, for example:(1) we identified improved electrode configurations by fabricating a wide range of free-standing anodes and cathodes (i.e., electrodes that do not contain or require a metal current collector) using a range of SLS fabrication parameters, then quantified the internal electrode structure/porosity with X-ray computed tomography (XCT) analyses, and used the XCT data to investigate the relationship between AM build parameters and electrochemical performance;(2) we fabricated separators with SLS using a variety of materials (i.e., polypropylene, aluminum oxide, polypropylene-polyethylene copolymer, polyether ether ketone (PEEK), polyester, and blends of these materials). SLS is well-suited to producing porous films, since spherical particles can be lightly melted to create a continuous object with ample void space, minimal membrane thickness, and maximum planar uniformity by preconditioning the printing powders (to prevent clumping), and using a machined build-plate to limit powder depth.The cycle performance of NMC-based cathodes fabricated with extrusion/direct-write and screen-printing was essentially identical to tape-cast (control) cathodes; however, the extrusion-printed cathodes exhibited more pronounced capacity-fade, and there was evidence of electrode-maturation processes, indicating the need for further optimization. The electrochemical performance of LFP-based cathodes fabricated with SLS was found to depend strongly on build setpoints and discharge rate, but exhibited robust extended cycle performance for > 300 cycles.The capacity of graphite-based anodes increased steadily over the first ~20 cycles, and strongly depended on post-SLS processing methods and the charge/discharge rate. We attribute this to the properties of the binder used in the SLS process, and to electrode maturation processes.Printed separators were tested with either tape-cast NMC-based cathodes or additively manufactured anodes/cathodes, and were cycled continuously at rates between C/5 and 2C. Specific capacity was stable and consistent at all rates, and remained above 100 mAh g-1 with no observable capacity fade for any of the rates below 2C. Extended cycling at C/1.5 stable (or even increasing) capacity for approximately 85 cycles, at which point slight capacity fade began.We evaluated the cooperative functionality of printed components (i.e., printed electrodes and separators) in both half-cell and full cell configurations (this work is ongoing). Cells containing an SLS-fabricated separator and a screen-printed NMC cathode charged at C/10 and discharged at C/5 delivered reversible capacity ~160 mAh g-1 for 100 cycles.We will also present ongoing work that uses additive manufacturing to produce flexible batteries and batteries with conformal form-factors. Figure 1