Self-generated nanoporous metal electrode

A KAIST research team has established new concept of laser processing that grows silver nanoseed, and has shown that numerous nanopores can be self-generated in the microelectrode. The microelectrodes have more surface area than non-porous electrodes, which enables the fabrication of high-performance film-type supercapacitors.

Article  |  Spring 2018

The flexible electronics industry is growing rapidly, and new applications are constantly emerging. Not only flexible displays and RFID tags, but also flexible memories, nerve electrodes, micro-sensors, piezoelectric, and thermoelectric energy harvesting devices are being extensively. However, the essential component for these applications, the flexible energy storage device has developed at a relatively slower rate.

The development of a thin, flexible lithium ion battery has many obstacles since the most common energy storage device, the lithium ion battery, has a multi-layered structure, requiring an anode, a cathode, and a separator, as well as an additional encapsulation process to protect the electrolyte from oxygen in ambient conditions.

Conversely, the film-type supercapacitor, which is called a ‘micro-supercapacitor’, can be fabricated on a single flexible film without a separator. This thin, flexible device has superior power and lifetime compared to those of the lithium ion battery, so they are one of the most ideal power sources for flexible electronic devices. However, the anode and cathode of the device need to be separated to avoid the problem of electrical shorts, and a patterning process for these electrodes is required.

Professor Minyang Yang and his team suggest a solution to these problems: by irradiating a laser on an organometallic solution-coated flexible PI film, they fabricate highly porous silver electrodes. The electrode of a supercapacitor must have high surface area and electrical conductivity, and these highly porous silver microelectrodes, which contain numerous nanopores, are excellent candidates for the electrodes of a supercapacitor.

Laser processing is a simple, one-step, cost-effective fabrication process, and the greatest advantage of this research is that the fabrication of a nanostructured electrode and its patterning can be done in a single process. Since nanostructured electrodes have significantly higher surface area than flat electrodes, the nanostructuring of the electrodes is frequently conducted for the micro-supercapacitor. Unlike previous research, which required high-temperature annealing in the vacuum environments, or complicated chemical/mechanical processes, the present research generates highly porous silver microelectrodes during the pattering process.

The principle generating nanopores inside the silver microelectrodes can be explained by the new concept metal laser processing, which the research team reported, the growth sintering. Mild annealing of silver organometallic solution can generate tiny silver nanoseeds, and the seeds grow by absorbing thermal energy from the irradiated laser. Unlike previous metal nanoparticle-based laser sintering, which requires high-energy lasers to instantly melt the nanoparticle, this process does not require a high amount of laser energy since role of the laser is initiating the growth of the nanoseeds. This is a great advantage for the utilization of the process for the film-type supercapacitor since many films cannot endure high temperatures. Electrodes and current collectors are fabricated in a single processing domain by simply changing the laser scanning rate.

On the highly porous silver electrodes, manganese and iron oxides are electrodeposited and act as the active electrode materials, and LiClO4-PVA solid electrolyte is drop-casted. Owing to the high surface area and electrical conductivity of highly porous silver electrodes, the device shows high volumetric energy and power density compared to previous research and commercial devices.

A video and article on Journal of materials chemistry A:

http://pubs.rsc.org/en/content/articlelanding/2017/ta/c7ta07960e#!divAbstract