LiSn2(PO4)3-based polymer-in-ceramic composite electrolyte with high ionic conductivity for all-solid-state lithium batteries

Abstract

In this work, fabrication and electrochemical behavior of polymer-in-ceramic composite electrolytes based on lithium-ion conducting triclinic LiSn2(PO4)3 (LSP) for all-solid-state batteries are reported. The composite ceramic electrolyte (CCE) was fabricated using polymeric salt (PEO+LiClO4) as a filler to the ceramic compound LSP using a simple hot-press technique. The x-ray diffraction and Fourier transform infrared spectroscopy (FTIR) studies were performed to determine the structure of the composite electrolyte. Composite electrolyte containing 30 wt.% PEO+LiClO4 exhibit the highest conductivity of ~ 3.48 × 10−5 Scm−1 at 27 °C, which improves to ~ 1.18 × 10−4 Scm−1 at 60 °C. The low activation energy calculated to be ~ 0.34 eV results from additional mobile lithium-ion in a composite electrolyte. The field emission scanning electron microscopy (FESEM) and energy-dispersive x-ray spectroscopy (EDX) reveals the Li+ diffusion route along with the 3D inter-connected LSP-(PEO+LiClO4) interfaces and distribution of polymeric salt to LSP. The ionic and Li+ transference numbers calculated by a combination of ac signal and dc polarization were found to be ~ 0.99 and ~ 0.39, respectively. The electrochemical performance of the CCE was tested using the cyclic voltammetry (CV) and galvanostatic charging-discharging (GCD) in symmetric cell employing lithium metal as the electrode. Composite electrolyte exhibited highly reversible lithium stripping/plating behavior at low current density. All-solid-state cells fabricated using LiMn2O4 as the cathode, Li metal as the anode, and the LSP-30 (PEO+LiClO4) as the solid electrolyte deliver a high specific discharge capacity of ~ 103.3 mAhg−1 at a current density of 100 μAcm−2.