Toward Solid-State 3D-Microbatteries Using Functionalized Polycarbonate-Based Polymer Electrolytes

3D microbatteries (3D-MBs) impose new demands for the selection, fabrication, and compatibility of the different battery components. Herein, solid polymer electrolytes (SPEs) based on poly(trimethylene carbonate) (PTMC) have been implemented in 3D-MB systems. 3D electrodes of two different architectures, LiFePO₄-coated carbon foams and Cu₂O-coated Cu nanopillars, have been coated with SPEs and used in Li cells. Functionalized PTMC with hydroxyl end groups was found to enable uniform and well-covering coatings on LiFePO₄-coated carbon foams, which was difficult to achieve for nonfunctionalized polymers, but the cell cycling performance was limited. By employing a SPE prepared from a copolymer of TMC and caprolactone (CL), with higher ionic conductivity, Li cells composed of Cu₂O-coated Cu nanopillars were constructed and tested both at ambient temperature and 60 °C. The footprint areal capacity of the cells was ca. 0.02 mAh cm^-2 for an area gain factor (AF) of 2.5, and 0.2 mAh cm^-2 for a relatively dense nanopillar-array (AF = 25) at a current density of 0.008 mA cm^-2 under ambient temperature (22 ± 1 °C). These results provide new routes toward the realization of all-solid-state 3D-MBs.