The ability to make a lithium ion battery (LIB) in an arbitrary shape could enable customization of the form factor of a battery to better fit the shape of a given product. To this end, numerous fabrication methods have been developed to construct LIBs into thin 2D films, various 2D shapes, wires, and interdigitated microbatteries.^1-4 However, to be fully customizable, ideally all the components of the battery, including the anode, cathode, separator, current collector, and case, would be 3D printable. To make this approach widely accessible, it would be beneficial if each part of the battery could be printed with low-cost, fused filament fabrication (FFF) 3D printers. Batteries made in this way could potentially also serve as the structural components of a product.

This presentation will describe how to make complete LIBs with an FFF 3D printer. A key hurdle to creating 3D printable batteries is the ionic conductivity of the polymers typically used for FFF 3D printing are too low. After testing many solvents, we found the ionic conductivity of polylactic acid (PLA), the most common polymer used for 3D printing, could be increased by more than 10 orders of magnitude (from 8.2 x 10⁻¹⁴ S cm⁻¹ to 2.3 x 10⁻⁴ S cm⁻¹)  by infusing the polymer with a mixture of ethyl methyl carbonate, propylene carbonate, and LiClO₄. The ionic conductivity of the infused PLA is comparable to the mixture of LiClO₄ and solvents (9 x 10⁻³ S cm⁻¹). After selecting PLA as the polymer for the filament, it was found that up to 12 volume % of solids could be mixed into the polymer without causing it to clog during 3D printing. Lithium titanate (LTO) and lithium manganese oxide (LMO) were selected for the active materials in the anode and cathode, respectively, and a 90:10 ratio of conductive carbon to active material maximized their charge storage capacity. Testing of carbon black SuperP, nanocarbon, and carbon nanotubes as conductive fillers indicated that the high conductivity enabled by long carbon nanotubes led to the highest charge storage capacity. The relatively low amount of active material in the anode and cathode led to low capacities (< 1 mAh/g) for the fully printed battery. However, this capacity was sufficient to demonstrate the lighting of LEDs with 3D printed batteries integrated into an eyeglasses frame (Figure 1A&B) and a bangle bracelet (Figure1 C&D). Future improvements in the battery might be attainable by finding a way to 3D print a battery composite with a higher loading of active materials and yet retain comparable mechanical properties. In addition, the high ionic conductivity of infused PLA suggests the use of this polymer as an electrolyte may be worth additional study.

References:

1. Liangbing Hu, H. W., Fabio La Mantia, Yuan Yang, and Yi Cui, Thin,FlexibleSecondaryLi-IonPaper Batteries ACS Nano 2010, 4(10), 5843-5848.

2. Kim, S. H.; Choi, K. H.; Cho, S. J.; Choi, S.; Park, S.; Lee, S. Y., Printable Solid-State Lithium-Ion Batteries: A New Route toward Shape-Conformable Power Sources with Aesthetic Versatility for Flexible Electronics. Nano Lett 2015, 15(8), 5168-77.

3. Park, J.; Park, M.; Nam, G.; Lee, J. S.; Cho, J., All-solid-state cable-type flexible zinc-air battery. Adv Mater 2015, 27(8), 1396-401.

4. Sun, K.; Wei, T. S.; Ahn, B. Y.; Seo, J. Y.; Dillon, S. J.; Lewis, J. A., 3D printing of interdigitated Li-ion microbattery architectures. Adv Mater 2013, 25(33), 4539-43.

Figure 1 - 3D Printed Wearable Batteries – A) 3D printed sunglasses with an imbedded LED circuit and a fully-printed LIB on the temple. B) View of the individual battery components inside the temple. C) 3D printed battery bracelet with 2 surface mounted blue LEDs. D) Separated view of the internal 3D printed anode and cathode mounted within the wrist casing.