A Solid-State Electrolyte Based on Li_0.95 Na_0.05 FePO₄ for Lithium Metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Solid-state electrolytes (SSEs) are critical for developing safe and high-energy-density lithium metal batteries (LMBs).
• Achieving practical application of LMBs hinges on identifying SSEs with superior comprehensive performance.
• Current limitations in SSEs necessitate exploration of novel materials for improved safety and energy density.

Purpose of the Study:

• To investigate the potential of Li$_{0.95}$ Na$_{0.05}$ FePO$_{4}$ (LNFP) as an ideal SSE for LMBs.
• To enhance electronic insulation and interface stability using LNFP-based composite solid electrolytes (CSEs).
• To evaluate the electrochemical performance of LMBs utilizing the developed CSEs.

Main Methods:

• Synthesis and characterization of Li$_{0.95}$ Na$_{0.05}$ FePO$_{4}$ (LNFP) as a solid-state electrolyte.
• Preparation of LNFP-based composite solid electrolytes (CSEs), specifically LNFP50 (50 wt% LNFP).
• Electrochemical testing of LNFP50 in Li|LNFP50|LiFePO$_{4}$ and Li|LNFP50|Li[Ni$_{0.8}$ Co$_{0.1}$ Mn$_{0.1}$ ]O$_{2}$ battery configurations.

Main Results:

• LNFP exhibits enhanced ionic conductivity and stable interface with lithium metal anodes.
• The LNFP50 CSE shows high ionic conductivity (3.58 × 10$^{-4}$ S cm$^{-1}$ at 25 °C) and good compatibility.
• Li|LNFP50|LiFePO$_{4}$ cells achieved 151.5 mAh g$^{-1}$ over 500 cycles with 96.5% retention.
• Li|LNFP50|Li[Ni$_{0.8}$ Co$_{0.1}$ Mn$_{0.1}$ ]O$_{2}$ cells maintained 80% capacity after 170 cycles, surpassing liquid electrolytes.

Conclusions:

• Li$_{0.95}$ Na$_{0.05}$ FePO$_{4}$ (LNFP) is a promising SSE material for high-performance LMBs.
• LNFP-based CSEs offer improved safety, stability, and electrochemical performance compared to liquid electrolytes.
• This work presents a viable strategy for commercializing advanced SSEs for next-generation batteries.