Separator engineering: Assisting lithium salt dissociation and constructing LiF-rich solid electrolyte interphases...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium metal batteries (LMBs) face limitations in energy density due to lithium dendrite growth and dead lithium formation, especially at high current densities.
• Developing advanced separators is crucial for stable LMB operation and enhanced safety.
• Existing separators often struggle to manage lithium deposition and electrolyte decomposition.

Purpose of the Study:

• To engineer a novel separator, CA@2500, using cellulose acetate (CA) coating on a 2500 separator to mitigate lithium dendrite issues in LMBs.
• To investigate the mechanism by which the CA coating enhances the solid electrolyte interphase (SEI) formation and lithium-ion transport.
• To evaluate the electrochemical performance and cycling stability of LMBs utilizing the CA@2500 separator.

Main Methods:

• Fabrication of the CA@2500 separator with a cellulose acetate coating.
• Characterization of the separator's surface chemistry and physical properties, including functional groups and hydrophilicity.
• Electrochemical testing of lithium symmetric cells and full pouch cell (LPF) batteries with the CA@2500 separator.
• Analysis of SEI composition and lithium-ion transport properties.

Main Results:

• The CA@2500 separator effectively suppressed lithium dendrite nucleation and propagation.
• CO functional groups in CA promoted LiTFSI decomposition, forming a robust LiF-rich SEI layer.
• Enhanced hydrophilic properties of CA facilitated uniform Li+ flux and efficient lithium migration, resulting in a high ion transfer number (0.88).
• Lithium symmetric cells demonstrated stable cycling for over 5500 hours at 10 mA cm-2 and 10 mAh cm-2.
• LPF batteries exhibited excellent capacity retention, with an average decay of 0.055% per cycle at 0.2 C and 0.027% per cycle at 5 C after 500 cycles.

Conclusions:

• The CA@2500 separator significantly enhances the stability and performance of lithium metal batteries.
• Simplified engineering of separators can overcome critical challenges in LMB technology.
• This approach offers a promising pathway for developing high-energy-density and long-lasting LMBs.