Direct Ink Writing of Polymer Batteries

In the recent year, the fabrication of rechargeable batteries via three-dimensional (3D) printing has drawn considerable interest due to the advanced performances that arise from 3D design of rechargeable battery architectures as compared to the conventionally fabricated ones. However, challenges with the 3D printing of electrolytes for rechargeable batteries still remain. Additional processing steps such as solvent evaporation were required for earlier studies of electrolyte fabrication, which hindered the simultaneous production of electrode and electrolyte in an all-3D-printed battery. We demonstrate a novel method to fabricate hybrid solid-state electrolytes using an elevated-temperature direct ink writing technique without any additional processing steps. The hybrid solid-state electrolyte consists of solid Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) matrices and a Li+ conducting ionic liquid electrolyte. The ink was modified by adding nano-sized ceramic fillers to achieve the desired rheological properties. Interestingly, a continuous, thin, and dense layer was discovered to form between the porous electrolyte layer and the electrode, which effectively reduced the interfacial resistance of the solid-state battery. Compared to the traditional methods of solid-state battery assembly, our directly printed electrolyte helps to achieve higher capacities and a better rate performance. The direct fabrication of electrolyte from printable inks at an elevated temperature will shed new light on design of all-3D-printed batteries for next-generation electronic devices. Proper distribution of thermally-conductive nanomaterials in polymer batteries offers new opportunities to mitigate performance degradations associated with local hot spots and battery safety concerns. We utilized direct ink writing (DIW) method to fabricate solvent-free polyethylene oxide (PEO) composite polymers electrolytes (CPE) embedded with silane-treated hexagonal boron nitride (S-hBN) platelets. It was observed that the S-hBN platelets were well aligned in the printed CPE during the DIW process. The in-plane thermal conductivity of the printed CPE with the aligned S-hBN platelets is higher than the pristine CPE with the randomly dispersed S-hBN platelets. Thermal imaging showed that the peak temperature of the printed electrolytes is lower than that of the CPE without S-hBN and the CPE with the randomly dispersed S-hBN, indicating a better thermal transport property. Lithium-ion half-cells made with this printed CPE and LiFePO4 cathode displayed high specific discharge capacity and stable Coulombic efficiency at room temperature. This work facilitates the development of thermally-conductive solid-state batteries enabled by printing techniques.