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