Hierarchical self-assembly of tannic acid/diethylenetriamine on polypropylene for high-performance separator

In lithium-ion batteries (LIBs), separator is used to provide a barrier between the anode and cathode and provide freedom for the transport of lithium-ions, which serves a key function in inhibiting internal short circuit and improving the battery safety. The limited wettability of commercial polyolefin separators in electrolytes restricts its utilization in extreme environmental conditions. In our work, we choose polypropylene (PP) as the precursor and can address the issue of poor wettability through suitable modification methods. Tannic acid (TA) and diethylenetriamine (DETA) were utilized to coat PP separator via hierarchical self-assembly approach, and the coating is further stabilized by taking advantage of the specific oxidizing properties of sodium periodate. This method scarcely increases the separator thickness or sacrifices the microporous structure of the original separator. The improved separator not only exhibits outstanding wetting capability and relatively high ion conductivity (1.24 mS cm-1), but also has the highest lithium-ion migration number of 0.74. This indicates that when the modified separator is applied to LIBs, its electrochemical performance is significantly enhanced. The enhancement in electrochemical performance of LIBs is attributed to the strong absorption and retention ability of the coating on the separator. The reversible capacity of Li/PP-TD2 separator/LiFePO4 battery is 144.3 mAh g-1 at 2C, which is higher than that of PP separator (117.1 mAh g-1) under the same current density. Even after 200 cycles, the PP-TD2 separator with two-layer assembly modification still maintains a higher coulombic efficiency of 97.55% and a discharge capacity of 96.6%. This hierarchical self-assembly modification of PP provides an effective approach for fabricating high-performance separator. Battery rate performance of different separators. image