The high areal-energy and power requirements of advanced microelectronic devices favor the choice of a lithium-ion system, since it provides the highest energy density of available battery technologies suitable for a variety of applications. Several attempts have been made to produce primary and secondary thin-film batteries utilizing printing techniques. These technologies are still at an early stage, and most currently-printed batteries exploit printed electrodes sandwiching self-standing commercial polymer membranes, produced by conventional extrusion or papermaking techniques, followed by soaking in non-aqueous liquid electrolytes. In this work, we suggest a novel flexible-battery design and report the initial results of development and characterization of novel 3D printed allsolid-state electrolytes prepared by fused-filament fabrication (FFF). The electrolytes are composed of LiTFSI, polyethylene oxide (PEO), which is a known lithium-ion conductor, and polylactic acid (PLA) for enhanced mechanical properties and high-temperature durability. The 3D printed electrolytes were characterized by means of ESEM imaging, mass spectroscopy, differential scanning calorimetry (DSC) and electrochemical impedance spectroscopy (EIS). TOFSIMS analysis reveals formation of lithium complexes with both polymers. The flexible all-solid LiTFSI-based electrolyte exhibited bulk ionic conductivity of 3 × 10 −5 S/cm at 90°C and 156ohmxcm 2 resistance of the solid electrolyte interphase (SEI). We believe that the coordination mechanism of the lithium cation by the oxygen of the PLA chain is similar to that of PEO and local relaxation motions of PLA chain segments could promote Li-ion hopping between oxygens of adjacent CH-O groups. What is meant by this is that PLA not only improves the mechanical properties of PEO, but also serves as a Li-ion-conducting medium. These results pave the way for a fully printed solid battery, which enables free-form-factor flexible geometries.

In the current research, we developed and printed by fused-filament fabrication polylactide-polyethylene-oxide blended membranes. The influence of relative content of polymers on the ease of extrusion and printing processes was studied. Ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethane-sulfonyl)imide (Pyr14TFSI) with dissolved LiTFSI salt was infused into the membranes to produce free-standing films of quasi-solid polymer electrolytes. The printed membranes were characterized by ESEM, DSC, XPS, NMR and EIS methods. Neat-printed PLA (polylactide) membrane exhibited poor wetting and low uptake of ionic liquid. However, the XPS tests of 3D-printed PLA-PEO membrane infused with LiTFSI solvated ionic liquid show evidence of the interaction between lithium cations with both, PEO (polyethylene oxide) and PLA. The measurements of diffusion coefficients by PGSE-NMR suggest that the Li+ ions are coordinated by the PEO segments in the polymer blend. Increase of the PEO content at the expense of PLA polymer, leads to more than one order of magnitude improvement of bulk conductivity, approaching 0.2 mS cm−1 at 60 ° C .

The focus on shifting towards miniaturized products coupled with the booming demand for consumer electronics are some of the key-driving factors behind the flexible-battery market. In the development of innovative power sources, freeing from design limitation along with the synthesis of reliable electrochemical materials with well-tuned features, is considered to be the most important scientific prerequisite.Two approaches for the fabrication of flexible free form-factor batteries, developed in our group will be presented. The first one is a unique, single-step method for the preparation of a membrane-electrode assembly [1]. Concurrent electrophoretic deposition (EPD) of positive and negative battery electrodes (LFP and LTO) on opposite sides of a commercial nanoporous membrane (Celgard 2325) results in the formation of a three-layer-battery structure. The cell comprising this electrophoretically deposited structure ran for more than 150 cycles with 125-140mAh/g capacity, which approaches the theoretical value of lithium iron phosphate. The electrodes can be deposited either cathodically or anodically by replacing the interchangeable charging agents, like polyethyleneimine and polyacrylic acid. These polyelectrolytes, when adsorbed on the particles of the active material, serve also as the binders. The simultaneous EPD, which we developed, can be used for the simple and low-cost manufacturing of a variety of cathode and anode materials on nanoporous polymer- and ceramic ion-conducting membranes for energy storage devices.The second approach utilizes printing techniques. These technologies are still at an early stage, and most currently-printed batteries exploit printed electrodes sandwiching self‐standing commercial polymer membranes, produced by conventional extrusion or papermaking techniques, followed by soaking in non-aqueous liquid electrolytes. We suggest a novel flexible-battery designs and report the initial results of development and characterization of novel 3D printed all-solid-state electrolytes prepared by fused-filament fabrication (FFF) [2, 3]. The electrolytes are composed of LiTFSI, polyethylene oxide (PEO), which is a known lithium-ion conductor, and polylactic acid (PLA) for enhanced mechanical properties and high-temperature durability. The flexible all-solid LiTFSI-based electrolyte exhibited bulk ionic conductivity of 3×10−5 S/cm at 90oC and 156 ohm/cm2 resistance of the solid electrolyte interphase (SEI). These results pave the way for a fully printed solid battery, which enables free-form-factor flexible geometries. References: Elazar Cohen, Moran Lifshitz, Alexander Gladkikh, Yossi Kamir, Ido Ben-Barak and Diana Golodnitsky, Novel one-step electrophoretic deposition of membrane-electrode assembly for flexible-batteries application Mater. Chem. A, 2020,8, 11391-11398Heftsi Ragones, Svetlana Menkin, Yosi Kamir, Alex Gladkikh, Tzach Mukra, Gabor Kosa and Diana Golodnitsky Towards Smart Free Form-Factor 3D Printable Battery, Sustainable Energy & Fuels, 2018, 2, 1542Heftsi Ragones, Adi Vine...

The increasing demand for multifunctional portable/wearable electronic devices, including wireless sensors and implantable medical devices is continuously growing. Such devices need rechargeable batteries with dimensions on the scale of 1–10 mm3 (few to tens mm2 footprint area of substrate) including all the components and all the associated packing. Thus, in the past decade, along with the developments in battery materials, the focus has been shifting more and more towards innovative fabrication processes, unconventional configurations, and designs with multi-functional components. 3D printing technologies enable a well-controlled creation of functional materials with three-dimensional architectures, representing a promising approach for fabrication of next-generation electrochemical energy storage (EES) devices with high performance due to a higher electrode/electrolyte interfacial area. In this work, we demonstrate a novel design and a novel approach of 3D printing of batteries of different shapes and size by using filaments composed of active electrode materials bound with polymers. The electrodes were printed by fused-filament fabrication (FFF) method. We demonstrated a reversible electrochemical cycling of 3D printed lithium iron phosphate (LFP) and lithium titanate (LTO) composite polymer electrodes vs. lithium metal anode with high performance and capacity in cells containing both conventional non-aqueous and ionic-liquid electrolytes. In addition, the development and fabrication of a novel 3D-printed solid-state or quasi-solid electrolyte by FFF has been accomplished. The electrolytes are composed primarily of polyethylene oxide (PEO) and polyethylene glycol (PEG) which are known ionic conductors, and polylactic acid (PLA) for enhanced mechanical properties and high temperature durability. Our research introduces novel thick-layer 3D batteries, thus reducing cost related to high mass loading per battery footprint of smart 3D structures with the help of low-cost fabrication method. References [1] H. Ragones et al. "Towards smart free form-factor 3D printable batteries." Sustainable Energy & Fuels 2.7 (2018): 1542-1549. [2] H Ragones et al. On the Road to a Multi-Coaxial-Cable Battery: Development of a Novel 3D-Printed Composite Solid Electrolyte Journal of The Electrochemical Society 2019 ,167 (7), 070503.