Development Of Porous Separators For Lithium-Ion Batteries Via 3d Printing And Thermally Induced Phase Separation

Additive manufacturing processes allow the development of custom-shape rechargeable batteries, but research in custom filaments for fused deposition modeling (FDM) of battery separators has remained limited until now. This study discusses the development and optimization of a composite thermoplastic filament feedstock to 3D print separator membranes. A number of post-processing steps - leveraging the thermally induced phase separation (TIPS) of the composite filament - are introduced in tandem with FDM to promote microporosity formation through the removal of the sacrificial diluent phase within 3D printed samples. Three distinct compositions of varying polymer/diluent ratios were developed and thoroughly investigated through thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, rate capability cycling testing, linear sweep voltammetry, potentiostatic electrochemical impedance spectroscopy, X-ray micro-computed tomography, and tensile testing to explore the need for a compromise between porosity, electrochemical performance, printability, and mechanical strength. Results revealed a trend where increasing polymer content led to improved tensile strength and printability, but electrochemical performance in coin cell batteries was compromised. These findings introduce a novel process to manufacture porous separator membranes without mechanical post-processing and highlight the promising electrochemical performance of 3D printed separators. Understanding the influence of printing parameters during TIPS enables better control over pore size and distribution, further improving electrochemical performance of 3D printed separators.