A solid composite electrolyte of 3D framework Li6.25La3Sn1.25Bi0.75O12 for rechargeable solid-state batteries

Abstract

Composite solid electrolytes (CSE) have a wide vista for development in the field of high energy density, safe solid state lithium batteries. This is due to the combination of the flexibility of a polymer combined with the high ionic conductivity of a ceramic. Unfortunately, ceramic fillers distributed arbitrarily in a solid composite electrolyte fail to offer effective continuous, fast Li+ transport channels, but also seriously diminish the high ionic transfer characteristics of a ceramic. Herein, we report on the preparation of a novel, three-dimensional (3D) framework Li6.25La3Sn1.25Bi0.75O12 (LLSBO) garnet-type material embedded in a polymer matrix via the ice-templating method to greatly increase the ionic conductivity of the product. This solid composite electrolyte, relies on the features of continuous channels for good ionic transport and flexibility, which provided an ion conductivity of 1.2 × 10−4 S cm−1 at room temperature. This result was 8.5 times greater than the composite electrolyte with isolated LLSBO particles dispersed in the matrix. Moreover, the Li-ion transference number was measured to be 0.62, greater than most reported solid composite electrolytes. In addition, symmetric Li/electrolyte/Li cell displayed cycle stability for 300 h during the process of repeated electroplating/stripping at 28 °C. The initial discharge capacity of the full cell was 154.92 mAh g−1 and the coulombic efficiency of 98% at 0.3 C, 28 °C, and the capacity retention of the cell was 70% after 150 cycles. These experimental results were attributed to the continuous lithium-ion transmission channels in the electrolyte provided by its 3D framework-based garnet-type LLSBO, which produced higher ion conductivity and the cycle stability in the full cell.