Cladophora Cellulose-based Separators for Lithium Batteries

Abstract: The development of lithium-ion batteries (LIBs) has been focused on exploring and improving the electrode materials and electrolytes in the past decades. An indispensable component, the separator, is however not studied as extensively. In general, a separator has two functions, i.e. preventing the direct contact between the cathode and anode and providing the ionic transport pathways. Commercial separators for LIBs are usually made of polyolefin materials, which often have low thermal stabilities and poor electrolyte wettabilities.In this thesis, a new type of material, i.e. Cladophora cellulose, is used to manufacture separators for LIBs and lithium-metal batteries (LMBs). The separators, made with Cladophora cellulose fibers via a straightforward paper making method, possess several advantages compared to conventional polyolefin separators regarding, e.g. ionic conductivity, thermal stability, electrolyte wettability and pore distribution, providing promising alternatives for battery separators.Apart from studying the two basic functions mentioned above, two types of advanced separator functionalities have been studied, i.e. redox-activity and the attainment of a homogeneous current distribution, in conjunction with proposals for new separator designs.Two types of redox-active separators have been devised for the first time in the separator field, based on the use of a redox-active conducting polymer, polypyrrole (PPy) and a natural polymer, polydopamine (PDA). Based on their redox-active potentials, the PPy-based redox-active separator was designed to contribute capacity to the cathode of a LIB, while the PDA-based redox-active separator was proposed to be used on the anode side.It is known that a homogeneous current distribution is beneficial for the battery performance. Therefore, two new types of separators with homogenous pore distributions have been manufactured to study the influence of the pore distribution on the Li deposition/stripping behavior and composite cathode utilization in LMBs. With the knowledge obtained from the study, a stable, long lifetime paper-based LMB was designed.