Achievement of high-cyclability and high-voltage Li-metal batteries by heterogeneous SEI film with internal ionic conductivity/external electronic insulativity hybrid structure

Abstract

Establishing electronic hinder/ionic transfer pathway in SEI film is key issue for high-performance Li-metal anodes (LMA), which requires the SEI with high ionic conductivity to enable fast Li+ diffusion and regulated Li deposition behavior, and poor electronic conductivity to block the electrolyte consumption. Herein, we propose a strategy to construct heterogeneous SEI via selective reduction of electrolytes components to improve Li stability and suppress dendrite growth. The inner N-rich sub-layer of SEI film enables fast Li+ transportation for nodule-like Li deposition while the outer C-rich sub-layer of SEI film exhibits an electronic insulation property to block electrolyte decomposition. This hybrid SEI endows the LMA with high Coulombic efficiency (99.0%), long lifespan, and dendrite suppression. Theoretical calculations, XPS and AFM were employed to examine the heterogeneous SEI structure and clarify its formation mechanism. A high-capacity retention of 91.6% after 160 cycles at 0.5 C in LiCoO2/Li pouch cells with ultra-thin Li anodes (25 μm) and low N/P ratio (1.67), and an excellent performance with 85.7% capacity retention after 300 cycles at higher charge potential (4.5 V) was also obtained. The insight in heterogeneous SEI formation provides new opportunities for rational electronic/ionic transfer pathway construction for achieving high-performance Li-metal batteries.