An eco-friendly and flame-retardant bio-based fibers separator with fast lithium-ion transport towards high-safety lithium-ion batteries

As one of the most important parts in lithium-ion batteries (LIBs), commercial polyolefin separators suffer from inherent drawbacks such as thermal-dimensional shrinkage, poor electrolyte wettability, and environmental pollution. In this study, a green bio-based composite separator with good flame retardancy and high ion conductivity is designed by a facile paper-making process and subsequently borate salts crosslinking, which consists of marine-derived calcium alginate fibers bridge and land-derived cellulose micro-fibers filler. The composite separator reveals a multi-hierarchical porous structure and homogeneous boron crosslinking, and consequently has a superior liquid electrolyte wettability and high strength. Impressively, the composite separator delivers better flame retardancy and higher lithium-ion transference number (tLi+ = 0.4) and ion conductivity (σ = 1.53 mS cm−1) compared with the commercial polypropylene separator, attributing to the abundant polar groups upon the fibers and the incorporation of sp3 Boron. As a result, the LIBs equipped with composite separator demonstrate excellent interface stability and rate capability. More importantly, the LIBs exhibit greater security at the elevated temperature of 140 °C. Additionally, the composite separator shows a potential degradation in natural environments. This eco-friendly bio-based separator paves a new insight for the design of heat-resistance separator as well as the safe running of LIBs. [Display omitted] •A bio-based fiber separator is designed by a facile paper-making method.•The composite separator exhibits superior flame retardancy.•The composite separator facilitates Li + transport with higher ion conductivity and Li + migration number.•LIBs equipped with the composite separator reveal enhanced safety at elevated temperature.