A Resilient Sponge‐Like Separator by Confined Microfluid Phase Separation for Stabilizing Lithium‐Metal Anode

Polyolefin separators have achieved great commercial success but face a big challenge in stabilizing electrode interfaces, which is critical for lithium-metal batteries. Here, to address this challenge, a resilient sponge-like separator (RSLS) is fabricated via confined microfluidic phase separation (CMPS) of poly(vinylidene fluoride) solution coated onto a polyolefin-separator. The results show that the sponge-like porous network structure of the separator coating is critical for its functions, which has been well-controlled by the CMPS conditions. The optimized RSLS can significantly improve not only the wettability of various liquid electrolytes, but also the thermal-shrinkage resistance of the polyolefin substrate. Importantly, the unique resilient pore network structures of the RSLS can effectively regulate the lithium deposition and stabilize the lithium-metal anode surface, due to its adaptive contact with the anode surface during the notable volume change induced by lithium deposition and stripping. This capability enables extended cycle life and reduces the polarization voltage in Li|RSLS|Cu half-cells compared to the bare commercial polyolefin-separator. Furthermore, the NCM|RSLS|Li battery also demonstrates higher discharge specific capacity and notably enhanced cycling stability even at a high rate of 1C. This study uncovers the significance of resilient separators for stabilizing the lithium-metal anode.