Ultrathin separator with efficient ion transport and superior stability prepared from cotton cellulose for advanced supercapacitors

The thickness of separators has a great influence on electrochemical performance and battery safety. However, the solution for the inevitable trade-off between separators thickness and their performance still remains a great challenge. Herein, we report novel strategy for manufacturing ultrathin cellulose membrane as separator for high-performance supercapacitors (SCs) via a low-cost and scalable solution-phase inversion technique. The ultrathin cellulose separator with a thickness of 15 µm possessed excellent physical performances, including higher tensile strength (74.5 MPa) and porosity (66.7%), ensuring safety during assembly and operation of the device. Simultaneously benefiting from the substantial polar hydroxyl groups (–OH) and inter- and intra-molecular hydrogen bonds in the cellulose structure, cellulose separator directly realized better electrolyte affinity, thermal stability, and chemical stability in contrast with commercial separators. The ultrathin construction of the separator shortened ion transport pathways, reduced the internal resistance and increased the ion conductivity, which would facilitate fast ion transport for the practical application of separator. Our methods provided a much-needed strategy for fabrication of ultrathin separators and might promote the development of portable energy storage devices.