Fluoroacetonitrile‑Based Gel Polymer Electrolytes for Fast‑Charging Lithium Metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Gel polymer electrolytes (GPEs) offer advantages for lithium metal batteries (LMBs) like improved safety and interfacial contact.
• However, GPEs face challenges including interfacial instability with lithium metal anodes (LMAs) and low lithium-ion transference numbers (tLi+), hindering fast-charging capabilities.

Purpose of the Study:

• To develop a fast-charging GPE (GPE-FN) that overcomes interfacial instability and enhances lithium-ion transport in LMBs.
• To investigate the role of fluoroacetonitrile (FAN) solvent, fluoroethylene carbonate (FEC), and LiNO3 additives in forming a stable solid electrolyte interphase (SEI).

Main Methods:

• Formulation of a novel GPE-FN electrolyte using FAN as the solvent, with FEC and LiNO3 as reduction additives.
• Characterization of the electrolyte's ionic conductivity and lithium-ion transference number.
• Electrochemical testing of LiFePO4 (LFP)||Li and LiNi0.8Co0.1Mn0.1O2 (NCM811)||Li cells to evaluate cycling performance and capacity retention at high charge rates (5C).

Main Results:

• The GPE-FN electrolyte exhibited high ionic conductivity (1.66 mS cm-1) and a high tLi+ (0.848) at 25°C.
• A stable SEI layer formed on the LMA, preventing FAN consumption and enhancing interfacial Li+ transport.
• LFP||Li and NCM811||Li cells demonstrated excellent fast-charging performance, achieving 4100 cycles with 80.3% retention and 800 cycles with 79.5% retention at 5C, respectively.
• Full cells with high-loading cathodes showed stable cycling.

Conclusions:

• The developed GPE-FN electrolyte effectively addresses interfacial instability and enhances ion transport in LMBs.
• The GPE-FN shows significant promise for enabling high-performance, fast-charging lithium metal batteries.
• The strategy of using specific solvent and additive combinations to form a stable SEI layer is crucial for advancing LMB technology.