T. Fedynyshn, L. Hancock, R. Pawle, M. Plaut, L. Racz
Keywords: additive manufacturing, 3D Printing, lithium ion, battery
Summary:Current fabrication methods for lithium ion batteries involve roll-to-roll processes that limit the available battery geometries to either cylindrical or prismatic shapes. Additive manufacturing, colloquially known as 3D printing, represents an area for improvement in cell manufacturing technology due to its ability to prepare intricate three dimensional objects, but transitioning materials from a roll-to-roll process to a direct-write process remains a challenge. To date, most efforts to prepare lithium ion cells by direct write printing focus on small scale cells and many reports discuss only a single printed electrode combined with conventionally manufactured components.This presentation will highlight efforts to develop materials and processes for direct-write printing of lithium ion cells performed by a partnership between Akita Innovations and MIT Lincoln Laboratory. We will discuss preparation of printable inks for cathode and anode fabrication, along with the associated current collectors, and show their functionality in cells prepared using commercial-off-the-shelf (COTS) materials as the remaining components. We will also discuss sprayable separator formulations that are directly integrable into 3D printing processes. We then discuss the preparation of a full lithium ion cell entirely by 3D printing-favorable methods, fabricating coin cells composed of a cathode-separator-anode stack. Coin cells prepared by printing the electrode inks show promising initial charge/discharge performance, with 4.0 V discharge plateaus, >10 mAh/cm3 discharge areal capacity and >90% discharge efficiency. Scanning electron microscopy of the electrodes shows well dispersed, homogenous materials. As a demonstration of the utility of this approach, we printed full lithium ion cells into an unmanned aerial vehicle (UAV) airfoil template. In preparing the electrode and separator formulations, we used known lithium ion cell materials and conventional electrolytes, combined with novel binder systems to facilitate printing. This work proves the concept of our approach to flexible, additively-manufactured lithium ion batteries for use in confined or oddly-shaped spaces such as UAV airframes and airfoils. To our knowledge, this is the first example of direct printing of conformal cells onto non-flat surfaces. Future work in this area will adjust the ink formulation to decrease the binder content in the electrodes and to increase the ion mobility of the remaining binder in order to optimize the performance of cells prepared by 3D printing.