Controllably regulating ion transport in lithium metal batteries via pore effect of metal–organic framework-based separators

Abstract

Lithium Metal batteries (LMBs) are considered as excellent energy storage systems due to their ultra-high energy density. However, the growth of Li dendrites resulting from irregular transport of ions during cycling seriously limits their further development and application. Therefore, it is urgent and important to regulate the ion transport and inhibit the formation of Li dendrites. In this paper, a Metal-Organic Framework (MOF, UiO-66-NH2) coating is proposed to functionalize a conventional commercial polypropylene (PP) separator to regulate ion transport in liquid electrolytes. Grafted NH2 groups in the MOF act by hydrogen bonding to immobilize anions in the electrolyte, which in turn facilitates cation transport. Compared with the PP separator, the Li ion transfer number (tLi+) of PP-UiO-66-NH2 (PUN) separator increases from 0.45 to 0.68. The Li/Li symmetric cell with PUN separator has an ultra-stable Li plating/stripping cycle of up to 400 h, during which time no lithium dendrite growth. In addition, the LiFePO4/Li and LiNi0.8Co0.1Mn0.1O2/Li batteries with the PUN separator exhibit excellent performance. The new strategy is controllable and universal and can be used for the preparation of various separators with outstanding performances by accurately tuning of MOF structure.