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Paint on power
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Paint on power ENERGY US researchers have developed a lithium-ion rechargeable battery that can be “painted” on to almost any surface. The system comprises spray-on layers that represent the components of a conventional battery but open up the possibility of radically changing the form factor of many electronic devices by removing the size and shape restrictions imposed by block-type batteries [Ajayan et al., Sci Rep(2012)2 482; doi: 10.1038/srep00481]. The researchers formulated different paints representing the five layered components required for a battery - two current collectors, a cathode, an anode and an insulating polymer separator in the middle. They used an airbrush to spray the materials on to ceramic bathroom tiles, flexible polymers, sheets of glass, stainless steel and even a beer stein to see how well they would bond with each substrate. In their proof of principle tests, they painted nine batteries on bathroom tiles and connected them in parallel. The battery could power a set of light-emitting diodes at a steady 2.4 Volts for more than six hours. One of the cells in the battery pack was integrated with cheap silicon solar cells and a white-light source was used to charge it. Sixty chargedischarge cycles led to only a small drop in the cell capacity. The cell capacities of the “tile batteries” were consistent with only a±10 % variation.
The team describes each layer of their painted batteries as “an optimized stew”. The first layer is the positive current collector and is a mixture of purified singlewall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone. The second layer, the cathode carries lithium cobalt oxide, carbon and ultrafine graphite(UFG) powder in a binder solution. The
Layered structure of the paintable battery. Image courtesy of the study authors.
third is the insulating polymer layer, a Kynar Flex resin, poly(methylmethacrylate) and silicon dioxide dispersed in a solvent mixture. The fourth, the anode, is a mixture of lithium titanium oxide and UFG in a binder, and the final layer is the negative current collector, which the team explains is a commercially available conductive copper paint, diluted with ethanol. The nanotube and cathode layers would adhere well to a surface, the team says but the addition of PMMA helped stabilize the separator to prevent peeling. Once painted on to a surface the system is infused with electrolyte and heat sealed ready to be charged. Given that spray painting is a readily scalable industrial process, the technology could move forward very quickly. Moreover, scientists also recently demonstrated a paintable solar cell. The potential synergy between the two technologies is obvious. “The focus of our ongoing research is to develop new battery materials which would not be degraded by air or moisture, non-toxic and safe to handle and use at home by non-experts, and environmentally friendly during use and disposal. The other goal is to develop the paint for packaging the device and seal the device by spraying this moisture barrier film, team member Neelam Singh told Materials Today.
David Bradley
Memory goes ferroelectric ELECTRONIC MATERIALS Ferroelectrics could be used to boost computer memory and allow information to be stored at previously unimagined densities of several terabytes per square centimeter. Now, a team that includes scientists at Brookhaven National Laboratory [Zhu et al., Nature Mater (2012) doi:10.1038/NMAT3371] and their collaborators have made an advance in imaging the atomic structure and behavior of such materials that could take us a step closer to such super memory devices. The team used electron holography to get a snapshot of the electric fields created by atomic displacements in test materials with picometer accuracy. “This kind of detail allows us for the first time to actually see the positions of atoms and link them to local ferroelectricity in nanoparticles,” explains Brookhaven’s Yimei Zhu. “This kind of fundamental insight is not only a technical milestone, but it also opens up new engineering possibilities.” Ferromagnetic materials have intrinsic magnetic dipole
362
moments, whereas their ferroelectric counterparts are characterized by a positive or negative electric charge within their structure. This polarization is manipulated using an external electric field but the tunable characteristics have only now been imaged in terms of internal asymmetry and ordering phenomena using the team’s transmission electron microscopes. This understanding could one day open up ferroelectrics to data storage in which an applied electric field as opposed to a magnetic one allows bits to be switched between two states representing a 1 or a 0 in computer binary code. Zhu explains the benefits of electric over magnetic: “Ferroelectric materials can retain information on a much smaller scale and with higher density than ferromagnetic,” he says. “We’re looking at moving from micrometers down to nanometers.” At this scale, each particle within the ferroelectric material can represent a single bit of data.
SEPTEMBER 2012 | VOLUME 15 | NUMBER 9
Key to developing these materials into viable memory devices lies in understanding how tightly the bits can be packed and ordered without neighbors interfering with each other. The electron holography shows how the various parameters can be ascertained under different electric field strengths and at different temperatures. The technique is an interferometry technique that uses coherent electron waves to induce phase shifts that produce an electron hologram that betrays the inner structure of the individual ferroelectric particles with unprecedented precision. The study revealed that the electric polarity could remain stable for individual ferroelectric materials, meaning that each particle could be a viable data bit. However, there are fringing fields surrounding each particle, which suggests that ferroelectrics need about five nanometers between particles to operate effectively, the team says.
David Bradley
Paint on power ENERGY US researchers have developed a lithium-ion rechargeable battery that can be “painted” on to almost any surface. The system comprises spray-on layers that represent the components of a conventional battery but open up the possibility of radically changing the form factor of many electronic devices by removing the size and shape restrictions imposed by block-type batteries [Ajayan et al., Sci Rep(2012)2 482; doi: 10.1038/srep00481]. The researchers formulated different paints representing the five layered components required for a battery - two current collectors, a cathode, an anode and an insulating polymer separator in the middle. They used an airbrush to spray the materials on to ceramic bathroom tiles, flexible polymers, sheets of glass, stainless steel and even a beer stein to see how well they would bond with each substrate. In their proof of principle tests, they painted nine batteries on bathroom tiles and connected them in parallel. The battery could power a set of light-emitting diodes at a steady 2.4 Volts for more than six hours. One of the cells in the battery pack was integrated with cheap silicon solar cells and a white-light source was used to charge it. Sixty chargedischarge cycles led to only a small drop in the cell capacity. The cell capacities of the “tile batteries” were consistent with only a±10 % variation.
The team describes each layer of their painted batteries as “an optimized stew”. The first layer is the positive current collector and is a mixture of purified singlewall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone. The second layer, the cathode carries lithium cobalt oxide, carbon and ultrafine graphite(UFG) powder in a binder solution. The
Layered structure of the paintable battery. Image courtesy of the study authors.
third is the insulating polymer layer, a Kynar Flex resin, poly(methylmethacrylate) and silicon dioxide dispersed in a solvent mixture. The fourth, the anode, is a mixture of lithium titanium oxide and UFG in a binder, and the final layer is the negative current collector, which the team explains is a commercially available conductive copper paint, diluted with ethanol. The nanotube and cathode layers would adhere well to a surface, the team says but the addition of PMMA helped stabilize the separator to prevent peeling. Once painted on to a surface the system is infused with electrolyte and heat sealed ready to be charged. Given that spray painting is a readily scalable industrial process, the technology could move forward very quickly. Moreover, scientists also recently demonstrated a paintable solar cell. The potential synergy between the two technologies is obvious. “The focus of our ongoing research is to develop new battery materials which would not be degraded by air or moisture, non-toxic and safe to handle and use at home by non-experts, and environmentally friendly during use and disposal. The other goal is to develop the paint for packaging the device and seal the device by spraying this moisture barrier film, team member Neelam Singh told Materials Today.
David Bradley
Memory goes ferroelectric ELECTRONIC MATERIALS Ferroelectrics could be used to boost computer memory and allow information to be stored at previously unimagined densities of several terabytes per square centimeter. Now, a team that includes scientists at Brookhaven National Laboratory [Zhu et al., Nature Mater (2012) doi:10.1038/NMAT3371] and their collaborators have made an advance in imaging the atomic structure and behavior of such materials that could take us a step closer to such super memory devices. The team used electron holography to get a snapshot of the electric fields created by atomic displacements in test materials with picometer accuracy. “This kind of detail allows us for the first time to actually see the positions of atoms and link them to local ferroelectricity in nanoparticles,” explains Brookhaven’s Yimei Zhu. “This kind of fundamental insight is not only a technical milestone, but it also opens up new engineering possibilities.” Ferromagnetic materials have intrinsic magnetic dipole
362
moments, whereas their ferroelectric counterparts are characterized by a positive or negative electric charge within their structure. This polarization is manipulated using an external electric field but the tunable characteristics have only now been imaged in terms of internal asymmetry and ordering phenomena using the team’s transmission electron microscopes. This understanding could one day open up ferroelectrics to data storage in which an applied electric field as opposed to a magnetic one allows bits to be switched between two states representing a 1 or a 0 in computer binary code. Zhu explains the benefits of electric over magnetic: “Ferroelectric materials can retain information on a much smaller scale and with higher density than ferromagnetic,” he says. “We’re looking at moving from micrometers down to nanometers.” At this scale, each particle within the ferroelectric material can represent a single bit of data.
SEPTEMBER 2012 | VOLUME 15 | NUMBER 9
Key to developing these materials into viable memory devices lies in understanding how tightly the bits can be packed and ordered without neighbors interfering with each other. The electron holography shows how the various parameters can be ascertained under different electric field strengths and at different temperatures. The technique is an interferometry technique that uses coherent electron waves to induce phase shifts that produce an electron hologram that betrays the inner structure of the individual ferroelectric particles with unprecedented precision. The study revealed that the electric polarity could remain stable for individual ferroelectric materials, meaning that each particle could be a viable data bit. However, there are fringing fields surrounding each particle, which suggests that ferroelectrics need about five nanometers between particles to operate effectively, the team says.
David Bradley