A Multiscale Hollow Spherical LATP Active Filler Improves Conductivity and Mechanical Strength in Composite Solid Electrolytes for Li Batteries

Polymer-based electrolytes would be ideal for all-solid-state Li metal batteries due to the superior processability of polymers and their ability to make good interfaces with electrode materials. However, polymer electrolytes have lower room temperature Li+ conductivities than desired. Composite solid electrolytes (CSEs) containing both polymer and ceramic filler have far greater conductivity than the polymer alone, and it is believed this is due to conduction paths along the polymer–ceramic interface. A strategy often pursued for increasing conductivity has been to engineer the filler with a high aspect ratio shape, such as nanorods or interconnected nanofibers. In this work we employ a multiscale hollow spherical filler, which is not directional but achieves similar conductivity to those with fibrous morphologies. The hollow spherical shape avoids agglomeration and provides continuous Li+ transfer channels. We fabricated multiscale hollow spherical ceramic Li1.3Al0.3Ti1.7(PO4)3 (LATP) nanoparticles for use in a poly(ethylene oxide) (PEO) matrix. This network also provided structural support and enhanced the mechanical properties of the polymer matrix, which is important for a battery electrolyte. The resulting CSE membrane had room temperature ionic conductivity of 1.64 × 10–4 S/cm. Li/Li symmetric cells using this CSE showed no short circuits for 500 h cycling at a current density 0.1 mA cm–2. Control cells using standard LATP powder showed higher overpotential and dendrite failure, as did the polymer membrane with no LATP.