A 3.5 V Lithium–Iodine Hybrid Redox Battery with Vertically Aligned Carbon Nanotube Current Collector

A lithium–iodine (Li–I2) cell using the triiodide/iodide (I3–/I–) redox couple in an aqueous cathode has superior gravimetric and volumetric energy densities (∼ 330 W h kg–1 and ∼650 W h L–1, respectively, from saturated I2 in an aqueous cathode) to the reported aqueous Li-ion batteries and aqueous cathode-type batteries, which provides an opportunity to construct cost-effective and high-performance energy storage. To apply this I3–/I– aqueous cathode for a portable and compact 3.5 V battery, unlike for grid-scale storage as general target of redox flow batteries, we use a three-dimensional and millimeter thick carbon nanotube current collector for the I3–/I– redox reaction, which can shorten the diffusion length of the redox couple and provide rapid electron transport. These endeavors allow the Li–I2 battery to enlarge its specific capacity, cycling retention, and maintain a stable potential, thereby demonstrating a promising candidate for an environmentally benign and reusable portable battery.