# Multilayer Polyethylene Separator with Enhanced Thermal and Electrochemical Performance for Lithium-Ion Batteries

## TL;DR

This paper introduces a new multilayer separator for lithium-ion batteries that improves safety and performance by enhancing thermal stability and electrochemical properties.

## Contribution

A novel multilayer separator is developed using a scalable process to improve thermal shutdown and mechanical strength in lithium-ion batteries.

## Key findings

- The SAPEAS separator shuts down thermally at 105 °C and maintains integrity at 180 °C with minimal shrinkage.
- It achieves high tensile and puncture strength, excellent electrolyte wettability, and superior ionic conductivity.
- In practical cells, it retains 97.9% energy after 1000 cycles and improves overcharge tolerance.

## Abstract

The inherent limitations of conventional polyolefin separators, particularly their poor thermal stability and insufficient mechanical strength, pose significant safety risks for lithium-ion batteries (LIBs) by increasing susceptibility to thermal runaway. In this study, we developed a novel multilayer separator through sequential coating of a commercial polyethylene (PE) substrate with aluminum oxide (Al2O3), para-aramid (PA), and polyethylene wax microspheres (PEWMs) using a scalable micro-gravure process, denoted as SAPEAS, signifying a PE-based asymmetric structure separator with enhanced thermal shutdown and dimensional stability. The SAPEAS separator exhibits an early thermal shutdown capability at 105 °C, maintains structural integrity with negligible shrinkage at 180 °C, and demonstrates comprehensive performance enhancements, including enhanced mechanical strength (tensile strength: 212.3 MPa; puncture strength: 0.64 kgf), excellent electrolyte wettability (contact angle: 12.8°), a high Li+ transference number (0.71), superior ionic conductivity (0.462 mS cm−1), outperforming that of commercial PE separators. In practical LFP|Gr pouch cells with ampere-hour (Ah) level capacity, the SAPEAS separator enables exceptional cycling stability with 97.9% energy retention after 1000 cycles, while significantly improving overcharge tolerance compared to PE. This work provides an effective strategy for simultaneously improving the safety and electrochemical performance of LIBs.