Abstract
A bilayered cellulose‐based separator design is presented that can enhance the electrochemical performance of lithium‐ion batteries (LIBs) via the inclusion of a porous redox‐active layer. The proposed flexible redox‐active separator consists of a mesoporous, insulating nanocellulose fiber layer that provides the necessary insulation between the electrodes and a porous, conductive, and redox‐active polypyrrole‐nanocellulose layer. The latter layer provides mechanical support to the nanocellulose layer and adds extra capacity to the LIBs. The redox‐active separator is mechanically flexible, and no internal short circuits are observed during the operation of the LIBs, even when the redox‐active layer is in direct contact with both electrodes in a symmetric lithium–lithium cell. By replacing a conventional polyethylene separator with a redox‐active separator, the capacity of the proof‐of‐concept LIB battery containing a LiFePO4 cathode and a Li metal anode can be increased from 0.16 to 0.276 mA h due to the capacity contribution from the redox‐active separator. As the presented redox‐active separator concept can be used to increase the capacities of electrochemical energy storage systems, this approach may pave the way for new types of functional separators.
Highlights
A bilayered cellulose-based separator design is presented that can enhance has received particular attention, since the capacities of the LIBs generally are the electrochemical performance of lithium-ion batteries (LIBs) via the limited by the capacities of the cathodes
Scanning electron microscopy (SEM) studies indicated the presence of an open mesoporous structure in both the nanocellulose fibers (NCFs) and the PPy-containing layer (Figure 2c–e), some differences could be seen at the micro- and nanoscales
The results have demonstrated that the present proof-of-concept redox-active separator, which contains a mesoporous insulating NCF layer and a redox-active PPy-containing support layer, can be used to enhance the capacity of LIBs
Summary
The flexible, redox-active separators were fabricated from nanocellulose using a straightforward paper-making approach. This effect can be explained by the fact that PPy is reduced to its electronically insulating state upon contact with the anode This “automatic fuse effect,” which would clearly not be seen for a conventional electronic conducting material, enables the use of a thin NCF and a thicker redox-active layer without increasing the risk of short-circuits. This effect is in good agreement with the long-time cycling results obtained with a symmetric Li/Li cell containing a PPy-NCF membrane (Figure S3, Supporting Information) as well as by the cycling of a Li/LFP cell described in the section below
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