Polydopamine-based redox-active separators for lithium-ion batteries

Abstract

The performance of lithium-ion batteries (LIBs) can be effectively enhanced with functionalized separators. Herein, it is demonstrated that polydopamine-based redox-active (PRA) separators can provide additional capacity to that of typical anode materials, increase the volumetric capacity of the cell, as well as, decrease the cell resistance to yield an improved performance at higher cycling rates. The PRA separators, which are composed of a 2 μm thick electrically insulating nanocellulose fiber (NCF) layer and an 18 μm thick polydopamine (PDA) and carbon nanotube (CNT) containing redox-active layer, are readily produced using a facile paper-making process. The PRA separators are also easily wettable by commonly employed electrolytes (e.g. LP40) and exhibit a high dimensional stability. In addition, the pore structure endows the PRA separator with a high ionic conductivity (i.e. 1.06 mS cm−1) that increases the rate performance of the cells. Due to the presence of the redox-active layer, Li4Ti5O12 (LTO) half-cells containing PRA separator were found to exhibit significantly higher capacities than the corresponding cells containing commercial separators. These results clearly show that the implementation of this type of redox-active separators constitutes a straightforward and effective way to increase the energy and power densities of LIBs.