Fabrication of Polymer Electrolytes for 3D-Microbatteries

Abstract: Pressing demands on electrical energy storage require high power and high energy density rechargeable batteries with improved safety, reliable performance and low cost. This has led to reconsiderations in the choice of battery chemistry and battery design. Practical concerns originating from the use of flammable liquid electrolytes has renewed the interests in using solvent-free polymer electrolytes as flexible solid ionic conductors. At the same time, the limitations of conventional planar battery designs have seen the utilization of these materials in novel battery designs, such as three-dimensional microbatteries (3DMBs).In this work, solvent-free polymer electrolytes have been tailored for 3DMB applications, due to their beneficial properties of non-flammability and dimensional stability. Polymer electrolytes based on functionalized poly(propylene glycol) triamine (PEA)-based oligomer have been developed via different synthetic routes, their potential use in 3DMBs has been demonstrated, and also their applicability for batteries of conventional dimensions. By tailoring the functionality in PEA oligomer, the electrolyte can be self-assembled and in-situ polymerized onto semi-3D (e.g., LiFePO4 composite) and 3D electrodes (e.g., 3D Cu-nanopillar) using in-situ UV-initiated polymerization or electropolymerization. The obtained conformal and uniform coatings, with thicknesses down to micro- and nano-dimensions, display useful ionic conductivity and stability for 3DMB applications.Moreover, high molecular weight poly(trimethylene carbonate) (PTMC), serving as a polymer host material alternative to the conventional polyethers, was investigated for Li-ion batteries and potential implementation in 3DMBs. Polymer electrolytes with useful electrochemical stability and flexibility have been tested in LiFePO4 half-cells and demonstrate promising cycling performance comparable to liquid electrolyte-based counterparts at elevated temperature.