Soon your floor could charge your electric razor, toothbrush, radio, or even double for solar storage

Researchers at Rice University have developed highly unorthodox batteries that can literally be painted onto a variety of surfaces, including "ceramic bathroom tiles, flexible polymers, glass, stainless steel, and even a beer stein."

I. Designing Paintable Lithium Ion Batteries

The research team, funded by grants from the Advanced Energy Consortium, the National Science Foundation, the U.S. Army Research Laboratories, and Nanoholdings Inc. succeeded in their goal of creating stable batteries, overcoming early issues of the separation layer peeling away from the tile which ruined the battery.

The finished design is capable of putting off 2.4V of power.  Total capacity and current output vary, but the design is lithium based, so it should be in line with the batteries found in today's personal electronics devices.

The design is composed of four layers, much like traditional cells.  

The first step of the process was to paint a cathode current collector material.  Aluminum paints were considered too toxic and reactive, so they were ruled out.  Instead, the researchers use purified single-wall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone for this step.   

The next layer in the painting process is the cathode.  The cathode contains lithium cobalt oxide, carbon, and ultrafine graphite (UFG) powder in a polyvinylidine fluoride (PVDF) "binder" solution in NMP.  PVDF is a low-cost binder that is used in many premium color paints, such as the metal paints used on the Petronas Towers in Malaysia.

II. Separator Posed the Biggest Hurdle

The third layer, which is eventually hydrated with electrolyte and separates the cathode and anode is perhaps the most critical.  Early designs had stable cathodes and anodes, but had the separator layer peel away, ruining the battery.  The issue was that at certain voltages, the separator had a tendency to lose its integrity, hence peeling off.

Researchers eventually found that using Kynar Flex resin, they could accommodate a wider voltage range.  They mixed the KynarFlex with PMMA and silicon dioxide dispersed in an acetone and N,N-Dimethylformamide (DMF) solvent mixture.  That formulation did the trick and kept the layers stably attached.

The fourth layer forms the anode.  It is composed of lithium titanium oxide carbon black, and UFG.  It was turned into a paint using the same PVDF (binder) and NMP (solvent) mixture used in the cathode. Lastly, a copper paint is applied to the anode.

Rice battery airbrushing
The battery is sprayed on in four layers. [Image Source: Jeff Fitlow]

The battery's separator layer is then soaked in electrolyte, allowing the separator to take up the necessary electrolyte.  The finished cell is then sealed using laminated poly(ethylene)-aluminum-poly(ethylene terephthalate) (PE-Al-PET). 

In tests the Rice researchers used a series of nine tiles, powered by a solar panel, to illuminate a series of light-emitting diodes that spelled out "RICE".  

The testing results and a description of the materials/process is published [full-text] in the peer-reviewed open Nature journal Scientific Reports.  

The first author was Neelam Singh, a grad student and the senior author was materials engineering professor Pulickel Ajayan.  

Rice University team
Right to left: Charudatta Galande, Professor Pulickel Ajayan, and lead author Neelam Singh
[Image Source: Jeff Fitlow]

Other co-authors include Charudatta Galande and Akshay Mathkar, alumna Wei Gao, and research scientist Arava Leela Mohana Reddy, all of Rice; Rice Quantum Institute intern Andrea Miranda; and Alexandru Vlad, a former research associate at Rice, now a postdoctoral researcher at the Université Catholique de Louvain, Belgium.

III. Outlook

The chemicals used are not without its downsides -- namely some of the compounds are somewhat toxic and would thus require careful disposal.  In addition to the dangers of lithium, studies have shown that both NMP and DMF can lead to birth defects or reproductive issues.  Additionally, the DMF solvent has been linked to cancer in humans.

Rice battery stein
You might want to be careful drinking from that Stein. [Image Source: Jeff Fitlow]

Likewise, lithium is a scarce resource, primarily controlled by China.  With electric vehicle makers already vying for production, costs for the novel batteries could become increasingly high.

Still the idea of being able to quite literally paint a lithium ion battery onto a wealth of form factors, including ceramic floor tiles could offer a big step forward towards both "smart" houses, and to storage of home-generated solar power.

Rice battery + LEDs
The new battery could help homeowners get "off the grid". [Image Source: Jeff Fitlow]

Rice University and Nanoholdings Inc. are looking to commercialize the process and have filed a patent on it.  Soon people looking to live "off the grid" with solar panel installations may be able to quite literally store their excess daytime solar energy in their floor.

Sources: Scientific Reports, an open Nature journal, Rice [Press Release]

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