Smectic solid electrolytes containing lamellar conducting channels for solvent-free lithium-ion batteries with a thermal switch on/off performance

Abstract

Developing electrolytes with desirable electrochemical performance and robust stability remains a huge challenge to meet the efficiency and durability demands of energy storage and conversion devices. Herein, the potential of ionic liquid crystals as high-performance electrolytes is demonstrated. Smectic ionic liquid crystals only consisting of conventional [C14Mim][BF4] and LiBF4 are designed and prepared as electrolytes for solvent-free lithium-ion batteries. [C14Mim][BF4] has good miscibility with LiBF4 to form smectic liquid crystals. LiBF4 is highly concentrated by [C14Mim][BF4] layers in the smectic electrolytes to form dynamic lamellar conducting channels, which enable considerable ion conductivities of 10–4 ∼ 10–3 S cm−1. The smectic electrolytes possess robust cyclic stability and energy conversion efficiency in Li/LiFePO4 batteries, which show a charge/discharge capacity of 154.7 mA h g−1 at a 1 C current density, as well as stable performance after 100 charge/discharge cycles even at 80 ℃. Additionally, the phase transition behavior of the electrolytes can be applied as a smart switch to thermally tune on/off the batteries. The electrolytes show almost no charge/discharge behavior under crystal phase, but automatically operate efficiently with charge/discharge capacities >150 mA h g−1 once entering the smectic phase. The present work sheds new light on developing high-performance and smart electrolytes for solvent-free Li-ion batteries.