Rational Design of Sandwiched Nanofiber Separators with Controllable Surface Porosity and Thermal Shutdown Functions

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Balancing performance and safety in lithium-ion and lithium metal batteries under extreme conditions is critical.
• Advanced separators are needed to prevent thermal runaway and dendrite growth.

Purpose of the Study:

• To fabricate a sandwich-structured nanofiber separator (PPNFs-PI) with tunable surface porosity and integrated thermal shutdown.
• To enhance the safety and performance of lithium-ion batteries.

Main Methods:

• Fabrication of a polyimide (PI) nanofibrous skeleton via electrostatic spinning, sandwiched between polypropylene nanofiber (PPNFs) layers via multilayer coextrusion.
• Characterization of thermal dimensional stability, porosity, electrolyte uptake, and ionic conductivity.
• Electrochemical testing including Li plating/stripping cycling and full cell performance evaluation (NCM811/graphite).

Main Results:

• The PPNFs-PI separator demonstrated excellent thermal dimensional stability (no shrinkage at 180 °C), high porosity (66.4%), superior electrolyte uptake (358%), and high ionic conductivity (1.18 mS cm⁻¹).
• Integrated thermal shutdown function achieved by melting PPNFs layers above 170 °C, blocking ionic transport and preventing combustion.
• Suppressed dendrite growth and uniform Li⁺ flux due to the 3D ion transport network.
• Outstanding interfacial stability over 1000 h of Li plating/stripping.
• Remarkable rate performance (145.96 mAh g⁻¹ at 5C) and cycling stability (90.8% capacity retention after 200 cycles at 1C in NCM811/graphite full cells).

Conclusions:

• The PPNFs-PI separator offers a scalable and cost-effective strategy for designing advanced separators for high-performance lithium-ion batteries.
• The rational design provides enhanced safety through thermal shutdown and improved performance via suppressed dendrite growth and high ionic conductivity.