We’re increasingly dependent upon our batteries, so finding ways of building ones with enhanced lifetimes would make a lot of people happy. Research on batteries has ranged from trying new materials to changing the configuration of key components. Now, researchers have managed to restructure the materials in a nano-battery, then bundle lots of these individual batteries into a larger device.
Batteries rely on two electrodes to create separate currents of electrons and ions, generating electricity. Nanostructured electrodes have useful properties, such as large surface area and short ion transport time, which enables a high storage capacity and enhanced lifetimes—these batteries hold charge longer and can undergo more charge-discharge cycles. 3-D connectivity and organization of nanostructured electrodes could further improve these devices.
Previously, researchers had developed 3-D nanostructured batteries by placing two electrodes within a nanopore (made of anodic aluminum oxide) and using ultrathin electrical insulating material to separate them. While this system had improved power and energy density, use of such thin electrical insulators limits charge retention and requires complex circuits to shift current between them—it's difficult to retain the benefits of the 3-D nano-architecture due to spatial constraints of the material.
Instead of using wired circuits, liquid solutions of electrically conductive ions (electrolytes) have been used to connect battery circuits. However, nano-batteries that use electrolytes have shown low charge storage; moreover, when used in conjunction with 3-D structures, uneven ion concentration gradients resulted in uneven current densities. Recently, researchers have overcome these limitations through the design of a battery that more effectively combines several components.
The new battery is composed of a parallel array of nanobatteries, each an individual nanotube containing electrodes and a liquid electrolyte confined within nanopores made of anodic aluminum oxide. Each nanotube was comprised of a current collector formed by an outer nanotube of Ru and an inner nanotube of V2O5 as the energy storage material. Each end of the nanopore was coated with either V2O5 or a chemically modified form of V2O5, to serve as the electrodes—the cathode and anode, respectively.
The performance of both individual electrodes was determined (called a half-cell configuration), as was the full-battery construct containing both electrodes, in full-cell configuration. Both configurations showed excellent electrical storage retention and a long charge-discharge cycle lifetime. Electrical storage retention was ~80 mAh/g (a bit less than existing lithium batteries) with more than 80 percent of initial energy storage retained after 1000 cycles. Compared to previous nanowire battery devices using the same material, this nanopore battery has triple the electrical storage capacity and an order of magnitude longer cycle life.
Researchers attribute the superior cycle lifetime to the coaxial tubular structure. The influence of this structure was investigated by comparing electrical storage obtained with the V2O5/Ru nanotube configuration to that obtained with a V2O5/planar Au arrangement. The nanotube configuration was found to have a much higher electrical storage potential than the planar arrangement.
These researchers have demonstrated that properly scaled nanostructures are a viable option for improved battery constructs. An enhanced discharge lifetime and cycle lifetime could make this particular construct an option for future portable devices including phones, tablets, and more.
