Using Three-Dimensional Carbon and Boron Nitride to Improve the Properties of Polyethylene Oxide-Based Solid-State Electrolytes for Li Ion Batteries

Abstract

Polyethylene oxide (PEO)-based solid-state electrolyte (SSE) is attractive due to its excellent adhesion with electrodes and good processability. However, lithium dendrites easily penetrate PEO because of their soft nature, which results in inferior battery performance and safety issues. In this talk, we will discuss the development of 3D (insulating) amorphous carbon and 3D amorphous BN to improve the properties of polyethylene oxide (PEO)-based solid-state electrolytes for Li ion batteries.For the 3D amorphous carbon, we developed a novel self-healing PEO-based SSE is prepared by incorporating 2 wt% amorphous three-dimensional carbon (3DC). This SSE possesses suitably low electronic conductivity for battery applications (on the order of 10^−9 S/cm), which is five orders of magnitude lower than its ionic conductivity (10−4 S/cm) at 60 °C. In addition, the improved fluidity and strong adhesion between the 3DC and the PEO matrix contribute to the self-healing ability of SSE, which will repair the cracks of SSE formed during battery cycling. Moreover, this SSE shows enhanced ionic and thermal conductivities and mechanical strength, suppressing the formation and growth of lithium dendrites. As a result, this SSE exhibits excellent electrochemical stability, achieving 5000 h of stable cycles in lithium symmetric cell (0.1 mA cm−2, 0.1 mAh cm−2) and 850 long-term stable cycles for the LFP//Li full cell at 1 C (0.31 mA cm−2).For the 3D amorphous BN, we have developed the first synthesis of powdery hexagonal boron nitride (h-BN). This synthesis introduces a novel NaCl-glucose assisted strategy to synthesize micron-sized 3D h-BN with a honeycomb-like structure. When incorporated into polyethylene oxide-based electrolytes for Li-ion batteries, 5 wt% of 3D h-BN significantly enhances ionic conductivity and mechanical strength. Consequently, this composite electrolyte demonstrates superior electrochemical stability; it delivers 300 h of stable cycles in the lithium symmetric cell at 0.1 mA cm-2 and retains 89 % of discharge capacity (138.9 mAh/g) after 100 cycles at 1 C in the LFP//Li full cell.These two approaches reveal that 3DC and 3D h-BN can be used to improve the properties of PEO-based electrolytes of Li-ion batteries.