Poly(m-phenylene isophthalamide)/chitosan separator with enhanced ion transport and Interface stability via...

Commercial polyolefin separators, due to the insufficient surface functional groups on their surfaces and their inherent low melting points, have led to urgent issues in lithium-ion batteries (LIBs) regarding lithium dendrite proliferation and safety. Herein, a chemically surface-functionalized poly(m-phenylene isophthalamide) (PMIA)/Chitosan (CS) composite separator is proposed. CS is tightly bound to the PMIA separator via the Schiff base reaction with 1,5-pentanedial (GA). Protonated amino groups (NH₃⁺) with a high adsorption energy of 0.3167 a.u. for PF₆^- were introduced onto the PMIA separator surface. Through strong interaction with hexafluorophosphate ions (PF₆^-), the polar groups with lone pairs of electrons disrupted the solvation sheath structure of lithium ions (Li⁺) in the electrolyte (EC-Li), promoting the dissociation of LiPF₆ in the electrolyte and elevate the concentration of free Li⁺ in LIBs. More importantly, it restricted the movement of PF₆^-. Therefore, the contribution of Li⁺ was increased by six times compared with LIBs assembled with PP separators. The increase in cation contribution reduces the interfacial concentration polarization and suppresses the generation of side reactions. The LFP||Li battery assembled with the PMIA/CS composite separator has a smooth and flat lithium anode surface and a discharge specific capacity of 139.3 mAh/g after 100 cycles under the rate of 0.5C at 25 °C, which is 16% higher than PP separator. This study aims to regulate the solvation structure and migration behavior of Li⁺ by designing chemically functionalized membranes, providing new strategies to improve Li⁺ transport efficiency and stabilize electrodes and separators.