Abstract
Flexible, low-weight electrodes with integrated current collectors based on chopped polyacrylonitrile carbon fibers (CF) were produced using an easy, aqueous fabrication process, where only 4 wt% of TEMPO-oxidized cellulose nanofibrils (CNF) were used as the binder. A flexible full cell was assembled based on a LiFePO4 (LFP) positive electrode with a CF current collector and a current collector-free CF negative electrode. The cell exhibited a stable specific capacity of 121 mAh g−1 based on the LFP weight. The CF in the negative electrode acted simultaneously as active material and current collector, which has a significant positive impact on energy density. Stable specific capacities of the CF/CNF negative electrode of 267 mAh g−1 at 0.1 C and 150 mAh g−1 at 1 C are demonstrated. The LFP/CNF with CF/CNF, as the current collector positive electrode (LFP-CF), exhibited a good rate performance with a capacity of ~150 mAh g−1 at 0.1 C and 133 mAh g−1 at 1 C. The polarization of the LFP-CF electrode was similar to that of a commercial Quallion LFP electrode, while much lower compared to a flexible LFP/CNF electrode with Al foil as the current collector. This is ascribed to good contact between the CF and the active material.
Highlights
The demand for flexible electronic devices, such as flexible displays [1], flexible radio frequency identification (RFID) tags [2], wearable electronics and implantable devices [3,4], is rapidly growing.Flexible lithium-ion batteries (LIB) have gained considerable attention as a promising energy storage solution for such applications [5,6,7,8,9,10,11,12,13]
We report the successful fabrication of a flexible, lightweight, current collector-free Carbon fibers (CF) negative electrode, and an LFP with carbon fibers as a current collector positive electrode (LFP-CF)
The conductivities of both electrodes were high enough to be used without additional metallic current collectors, 143 S m−1 for the CF/Super-P carbon (SPC)/cellulose nanofibrils (CNF) negative electrode and 95 S m−1 for the LFP-CF positive electrode
Summary
The demand for flexible electronic devices, such as flexible displays [1], flexible radio frequency identification (RFID) tags [2], wearable electronics and implantable devices [3,4], is rapidly growing. Yoon et al reported that carbon nanotube films as negative electrodes for flexible LIB had high flexibility, good mechanical properties, and high electrical conductivity [17]. These nanostructured current collectors and carbon-based materials are relatively expensive and require complex preparation processes. Cellulose-based materials, including cellulose fibers, or cellulose nanofibrils (CNF) produced from wood in a sustainable way have gained considerable interest as a promising alternative binder for flexible paper electrodes due to excellent mechanical properties, low cost, and environmental friendliness [9,11,24,25]. This work demonstrates a facile fabrication process of lightweight and flexible electrodes with integrated current collectors, which is very beneficial from environmental and industrial perspectives
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