Membrane Separators for Electrochemical Energy Storage Technologies

Abstract

In recent years, extensive efforts have been undertaken to develop advanced membrane separators for electrochemical energy storage devices, in particular, batteries and supercapacitors, for different applications such as portable electronics, electric vehicles, and energy storage for power grids. The membrane separator is a critical component in batteries (lithium–ion and redox flow) and capacitors as it determines the performance as well as the economic viability. The membrane separator prevent cross-mixing of the positive and negative electrolytes, while still allowing the transport of ions to complete the circuit during the passage of current. The performance of these devices is greatly affected by the materials and structure of the membrane separators. Separators for lithium–ion batteries (LIBs) can be classified into (1) microporous polymer membranes, (2) nonwoven fabrics, and (3) inorganic composite membranes. In redox flow batteries, ion-exchange membranes (cation/anion) that conduct positive–negative charged ions are traditionally used as separators. The porous separator membrane that separates the electrodes of supercapacitor allows ions to diffuse across to the opposite electrode, without recombination, when voltage is applied. An ideal membrane separator should have high ionic conductivity, low water intake, and excellent chemical and thermal stability, as well as good ionic exchange capacity to withstand the assembly process.