An ultrathin Zn-BDC MOF nanosheets functionalized polyacrylonitrile composite separator with anion immobilization and Li+ redistribution for dendrite-free Li metal battery

Abstract

Uncontrolled lithium dendrite growth and dead Li accumulation will seriously reduce coulombic efficiency, shorten the cycle life and cause great safety hazards, which are the main reason that restricts the further development of lithium metal batteries (LMBs). Herein, an ultrathin Zn-BDC metal-organic framework nanosheets functionalized polyacrylonitrile (Zn-BDC/PAN@PAN) composite separator is prepared via an electrospinning combined with electrospraying technique for inhibiting dendrite growth and achieving high-performance lithium batteries. Introduction of Zn-BDC/PAN skin layer not only immobilizes anions, increases the ionic conductivity and Li+ transfer number (0.68), but also makes pore size distribution uniform and homogenizes Li+ flux. These advantages enable Zn-BDC/PAN@PAN separator to achieve a stable Li plating/stripping behavior over 1000 h at 2 mA cm−2 with a low voltage polarization difference only about 10 mV, and the Li metal after the cycle displays a dense and smooth surface with no obvious dendrite growth, further confirming that the Zn-BDC/PAN@PAN separator can inhibit Li dendrites growth. Furthermore, the assembled Li/LiFePO4 battery also shows stable cycle performance with a discharge capacity of 142.2 mA h g−1 after 300th cycle and high rate capability (121.3 mA h g−1 at 10C), indicating that the promising application of the composite separator in constructing dendrite-free LMBs. This work provides a feasible strategy to enhance the cell performance of LMBs through Li+ flux regulation.