Flexible Paper Electrodes for Li-Ion Batteries Using Low Amount of TEMPO-Oxidized Cellulose Nanofibrils as Binder

Abstract

Flexible Li-ion batteries attract increasing interest for applications in bendable and wearable electronic devices. TEMPO-oxidized cellulose nanofibrils (TOCNF), a renewable material, is a promising candidate as binder for flexible Li-ion batteries with good mechanical properties. Paper batteries can be produced using a water-based paper making process, avoiding the use of toxic solvents. In this work, finely dispersed TOCNF was used and showed good binding properties at concentrations as low as 4 wt %. The TOCNF was characterized using atomic force microscopy and found to be well dispersed with fibrils of average widths of about 2.7 nm and lengths of approximately 0.1-1 μm. Traces of moisture, trapped in the hygroscopic cellulose, is a concern when the material is used in Li-ion batteries. The low amount of binder reduces possible moisture and also increases the capacity of the electrodes, based on total weight. Effects of moisture on electrochemical battery performance were studied on electrodes dried at 110 °C in a vacuum for varying periods. It was found that increased drying time slightly increased the specific capacities of the LiFePO4 electrodes, whereas the capacities of the graphite electrodes decreased. The Coulombic efficiencies of the electrodes were not much affected by the varying drying times. Drying the electrodes for 1 h was enough to achieve good electrochemical performance. Addition of vinylene carbonate to the electrolyte had a positive effect on cycling for both graphite and LiFePO4. A failure mechanism observed at high TOCNF concentrations is the formation of compact films in the electrodes.

Thickness difference induced pore structure variations in cellulosic separators for lithium-ion batteries

“…A bacterial cellulose based separator composed of a cross-linked three dimensional network exhibiting good performance in a battery has likewise been demonstrated (Jiang et al 2015). Since cellulose often contains significant amounts of water it is, however, very important to choose a type of cellulose that contains as little water as possible (Lu et al 2016). We have recently shown that separators made from Cladophora cellulose (CC) are particularly well-suited due to the low water content of this type of cellulose (Pan et al 2016).…”

Flexible and Lightweight Lithium-Ion Batteries Based on Cellulose Nanofibrils and Carbon Fibers

“…Since the rate performance is good (see below), these are sufficient conductivities for usage without additional current collectors. The conductivities can be compared to our previous work, where an LFP/SPC/CNF electrode exhibited a conductivity of around 0.1-1 S m −1 , depending on the component ratios [24]. Even with as much as 11 wt% SPC, the conductivity was no higher than 1.14 S m −1 .…”

“…2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized CNF was synthesized following a procedure reported elsewhere [24,29]. The charge density of the CNF was~626 µeq g −1 .…”

“…In our previous work, we have shown that flexible electrodes can be fabricated using a low amount (4 wt%) of CNF [24]. In the present work we have developed this concept further by incorporating lightweight CF current collectors and producing a full battery cell with a high degree of carbon based materials: CF current collectors; CF as active negative electrode material; and CNF as binder.…”

“…In addition, using PVDF as a binder limits the flexibility of the electrodes. 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].…”