Ethylcellulose-coated polyolefin separators for lithium-ion batteries with improved safety performance.

With the widely use in portable electronic devices and electric vehicles, the safety of lithium-ion battery has raised serious concerns, in which the thermal stability of separator plays an essential role in preventing thermal runaway reactions. The novelty of this work is to coat commercialized polyethylene (PE) separator and trilayer polypropylene/polyethylene/polypropylene (PP/PE/PP) separator with ethylcellulose (EC), a thermally stable and renewable biomass. The formation of the EC layer with high porosity is through a simple dipping and extracting process. The effects of the EC layer on thermal shrinkage, electrolyte wettability and cell performance are investigated. After coating, the thermal shrinkage of PE separator at shutdown and meltdown point is reduced from 20% to 9% and 42% to 23% respectively, while the drop of OCV under increasing temperature is also postponed from 130°C to 160°C. The electrolyte wettability of pristine trilayer PP/PE/PP separator is greatly improved, leading to increased capacity retention from 28% to 99% of the cell.