When CNTs are used as additives to improve the mechanical, thermal, or electrical properties of a polymer, a key to effective incorporation of the CNTs is preventing aggregation of the CNTs and maximizing their interaction with the polymer matrix, which can be done through functionalization of the CNTs. This analysis also highlights the frequent use of metal-organic frameworks (MOFs) in energy storage applications. A recent example of this is the use of a cerium-based MOF / CNT composite separator in a Li-S battery. Here, the CNT structure provides electrical conductivity and is an effective physical barrier for polysulfide shuttling, while the MOF catalyzes the breakdown of larger polysulfides into Li2S. In another example, MWCNTs were used as a template for the growth of NiCo-based MOFs, improving their performance as supercapacitor electrodes. 215