In 2011, Baughman’s group fabricated CNT biscrolled yarns and

In 2011, Baughman’s group fabricated CNT biscrolled yarns and used them as a substrate for preparing cathodes containing LiFePO4 contents of over 95 wt%.58 The [email protected] biscrolled yarns cathodes were produced by filtration-based guest deposition and twist insertion in a liquid bath. Isopropanol was used as the liquid medium for the dispersion of the LiFePO4 before filtration. Before electrochemical characterization, some samples of the obtained cathodes were thermally annealed at 600 °C for 6 hours in argon flow. As-prepared 1 to 2.5 cm long cathode fibers were employed as a complete cathode, without the need for the aluminum substrates and polymer binder. The electrochemical performance of the LiFePO4 biscrolled yarns as a Li ion cathode was evaluated inside an argon-filled glove box using a three-electrode cell, which consisted of a [email protected],6 yarn cathode, a graphite anode, and a lithium foil reference electrode. The electrolyte was 1 M LiPF6 in PC–EC–DMC (1:2:3, v/v). The full batteries were cycled between 2.5 and 4.2 V at different rates. For a 100 mm diameter biscrolled yarn containing 95 wt% LiFePO4 guest, which is weavable and knottable, the reversible charge storage capabilities based on total electrode weight are 115 mA h g?1 at C/3 rate and 99 mA h g?1 at 1 C (1 C = 170 mA h g?1).Recent publications utilizing CNTs thin films as a substrate have focused on half-cell flexible LIBs, and used lithium foil as a counter electrode. Wang, et al., fabricated super-aligned CNTs films (SACNTs) as current collectors.53 The SACNTs arrays with a tube diameter of 20–30 nm and a height of 300 ?m were synthesized on silicon wafers by chemical vapor deposition (CVD) with iron as the catalyst and acetylene as the precursor. 20 layers of the SACNTs films were first cross-stacked onto a glass substrate for use as a current collector. An electrode slurry was prepared by mixing graphite or LiCoO2, carbon black, and PVDF in NMP solvent at a weight ratio of 8:1:1. The electrode slurry was coated on top of the SACNTs current collector. After drying, the flexible and free-standing graphite–CNTs electrodes or LiCoO2–CNTs electrodes were separated from the glass substrate. These electrode sheets were punched into circular discs with a diameter of 10 mm. The weights of graphite and LiCoO2 in each disc were around 3–4.5 mg and 4.5–6.0 mg, respectively. CR 2016 half-cells were assembled with the graphite–CNTs, graphite–Cu, LiCoO2–CNTs, or LiCoO2–Al discs as the working electrodes, and Li metal as the reference electrode. A porous polymer film (Celgard 2400) was used as the separator. A 1 M LiPF6 in 1:1 EC and DEC solution was used as the electrolyte. The comparative study indicated that the LiCoO2–CNTs cathode had the highest capacity. With a LiCoO2 layer thickness of 57 ?m, an energy density of ?478 W h kg?1 (normalized to cathode) was achieved when cycled between 3 and 4.3 V, displaying a 53% improvement over the LiCoO2–Al electrode (312 W h kg?1). Jia, et al., reported a direct-growth method to produce high-performance flexible LiMn2O4–CNTs cathodes.59 The group started with a flexible CNTs network that was mildly pre-oxidized. Spontaneous redox reactions between the CNTs and KMnO4 generated layers of MnO2 wrapping the CNTs. Subsequent hydrothermal treatment in the presence of LiOH converted the MnO2/CNTs composites into LiMn2O4/CNTs composites. Vacuum filtration of the composites created free-standing cathodes that are binder-free and flexible. The produced electrodes had a thickness of 30–40 ?m, with a LiMn2O4 weight ratio of 89% and nanocrystallite sizes between 50 and 100 nm. The electrical energy storage capability of the composite electrodes was examined in a coin-type half cell using lithium as both counter and reference electrodes. At a relatively high current density of 550 mA g?1 with cut-off voltages of 3.2–4.3 V, the composite material still delivered a discharge capacity of 50 mA h g?1 cathode.