Iron Phosphate Coated Flexible Carbon Nanotube Fabric as a Multifunctional Cathode for Na-Ion Batteries.

Conventional slurry casted electrodes cannot stand high loads or be repeatedly flexed or bent without being fractured, which inhibits their use in flexible batteries. Carbon nanotube (CNT) fabric exhibits a paramount mechanical stability and, due to its porosity, can additionally accommodate an active material within its structure. While solution-based protocols cannot achieve conformal coatings of active materials, chemical vapor deposition (CVD) gives a unique opportunity to control and vary the thickness and homogeneity of the coating. Herein, a conformal CVD coating of amorphous iron (III) phosphate (a-FePO4 , FP) on flexible CNT fabric and its ability to reversibly accommodate large radius Na ions is reported. The freestanding binder-free CNT@FP electrodes exhibit high-rate capabilities and exceptional cycle stabilities with 98% of retention of initial capacity after 100 cycles. Such electrodes additionally demonstrate high mechanical stability under high loads, remarkable bending characteristics, and modulus of toughness (12 MJ m-3 ) exceeding that of Al. The presented concept of flexible CNT@FePO4 electrodes with high load-bearing characteristics opens new perspectives toward the formation of light-weight, flexible, multifunctional Na-ion battery electrodes based on abundant materials.

Carbon Nanotube-CoF2 Multifunctional Cathode for Lithium Ion Batteries: Effect of Electrolyte on Cycle Stability.

Transition metal fluorides (MFx ) offer remarkably high theoretical energy density. However, the low cycling stability, low electrical and ionic conductivity of metal fluorides have severely limited their applications as conversion-type cathode materials for lithium ion batteries. Here, a scalable and low-cost strategy is reported on the fabrication of multifunctional cobalt fluoride/carbon nanotube nonwoven fabric nanocomposite, which demonstrates a combination of high capacity (near-theoretical, 550mAhgCoF2-1) and excellent mechanical properties. Its strength and modulus of toughness exceed that of many aluminum alloys, cast iron, and other structural materials, fulfilling the use of MFx -based materials in batteries with load-bearing capabilities. In the course of this study, cathode dissolution in conventional electrolytes has been discovered as the main reason that leads to the rapid growth of the solid electrolyte interphase layer and attributes to rapid cell degradation. And such largely overlooked degradation mechanism is overcome by utilizing electrolyte comprising a fluorinated solvent, which forms a protective ionically conductive layer on the cathode and anode surfaces. With this approach, 93% capacity retention is achieved after 200 cycles at the current density of 100 mA g(-1) and over 50% after 10 000 cycles at the current density of 1000 mA g(-1) .