Composite membrane with ultra-thin ion exchangeable functional layer: a new separator choice for manganese-based cathode material in lithium ion batteriesElectronic supplementary information (ESI) available: XPS spectra of the composite separator (Fig. S1); the atomic concentration of the composite separator determined by XPS (Table S1); the Nyquist plots of the Nf-PP-Li separator before and after the ion exchange process (Fig. S2); the Nyquist plots of the Nafion membrane (Fig. S3); the dischar

A composite membrane with an ultra-thin ion exchangeable layer is specially designed as a separator in lithium ion batteries with manganese-based cathode materials. The composite membrane features a Mn 2+ capture function which originates from the ion exchanging process, especially at high temperature, and is proven to help to alleviate the capacity decay of lithium ion batteries effectively. The enhanced thermal stability, improved wettability and higher lithium ion transference number of the composite membrane further suggest its promising application in lithium ion batteries. A composite separator with an ultra-thin ion exchangeable layer was developed to alleviate severe capacity decay of lithium ion batteries.