Thin lamellar Li7La3Zr2O12 solid electrolyte with g-C3N4 as grain boundary modifier for high-performance all-solid-state lithium battery

Abstract

Inorganic superionic conductors hold great promise for all-solid-state lithium battery. However, the ionic conductivity of developed inorganic solid electrolytes (ISEs) is often insufficient owing to the enormous grain boundary resistance and large thickness. Herein, a 30 μm-thick Li7La3Zr2O12 (LLZO) lamellar inorganic solid electrolyte (LLZO/CN LISE) is fabricated by assembling LLZO nanosheets into lamellar framework, followed by in-situ growing g-C3N4 in the interlayer spacing. Based on the regular and unambiguous lamellar structure, g-C3N4 is found to be an ideal grain boundary modifier, and the Li-ion transfer process at grain boundary is thus investigated in detail. We demonstrate that this LLZO/CN LISE achieves an ultralow grain boundary resistance (<12.3 Ω cm2vs. 1608 Ω cm2 for LLZO pellet) and hence high ionic conduction properties (the ionic conductivity is 2.50 × 10−4 S cm−1 and the ionic conductance is 167 mS at 25 °C). The assembled Li symmetrical cell can stably cycle over 1500 h at 0.2 mA cm−2 and 60 °C. The assembled LiFePO4|Li cell also exhibits excellent cycling performances with a discharge capacity of 147.7 mAh g−1 at 0.5C and 60 °C after 150 cycles. This insight should present new opportunities in designing and developing high-performance ISEs.