The development of nano-batteries finally results in the miniaturization of the voltage sources to the dimensions of the other electronic components. The nano-battery is designed so that it can remain in a dormant state for at least 15 years and provide, as soon as it is activated, a burst of high-intensity energy.
Charles Choi, Scientific American
When the transistor was invented, in 1947, it looked like a sloppy jumble of components, a device more than a centimeter tall. Since then, it has shrunk to a device whose components are only a few hundred atoms in size. The electricity output of the batteries, on the other hand, increased during this time at a rate 50 times lower.
Bell Labs, where the first transistor was built, is now busy reinventing the battery. The goal is to apply transistor manufacturing techniques for the mass production of batteries that will be integrated into chips along with the rest of the electrical circuit components. The device, called a nano-battery, minimizes certain components in the electrodes to nanometer dimensions.
The nano-battery is designed so that it can remain in a dormant state for at least 15 years and provide, as soon as it is activated, a burst of high-intensity energy. This way you can be used, for example, as a voltage source for a sensor that monitors radioactivity, or the accumulation of toxic chemicals. From this idea, perhaps the first battery will be developed that can also clean itself - by neutralizing the concoction of toxic chemicals inside it.
Grow nanometer grass
The nano-battery grew out of Bell Labs' previous foray into nanotechnology. In the fall of 2002, Lucent Technologies, the parent corporation of Bell Laboratories, engaged in preparations for the launch of the New Jersey Nanotechnology Consortium together with the state government and the New Jersey Institute of Technology. The idea was to offer nanotechnology practitioners in industry, academia and government the company's services in research, development and construction of prototypes. David Bishop, vice president of nanotechnology research at Bell Labs, began holding seminars with the company's scientists in which they shared ideas about innovative applications arising from their research and which association members could further develop.
One of the scientists from Bell Labs, Tom Krupankin, worked on micro liquid lenses, of the type commonly used in phone cameras today. These lenses are made of small droplets, whose optical focus changes as they change shape in response to an electrical voltage applied to the surface on which they are located. Due to the change in tension, the surface goes from a state where it is extremely hydrophobic (a feature called superhydrophobicity) to a hydrophilic state. This phenomenon is called "electric wetting".
Superhydrophobicity is the property responsible for raindrops rolling off duck feathers and lotus plant leaves. Surface tension causes liquid droplets to condense, but the solid on which they land may exert attractive forces that cause them to spread.
Hydrophilic surfaces, such as glass, cause the water droplets to flatten. But on super-hydrophobic surfaces, the droplets form perfectly and practically avoid any interaction with the surfaces.
Based on this behavior of the droplets on superhydrophobic surfaces, Kropankin proposed using electrowetting to control chemical reactions. His idea was to produce rows of nanometer-wide superhydrophobic pillars capable of electrowetting. Under the microscope, the columns look like a uniformly mowed field of "nanometric grass". This "grass" can now be produced using the methods accepted in the microchip industry, which were developed during decades of working with silicon (silicon). By applying an electrical voltage to the liquid, the scientists could induce a reaction that would cause the pillars to become hydrophilic and pull the droplets down so that they penetrate into the spaces between the nano-pillars. The liquid can then react with any compound found on the bottom. Krupankin realized that the liquid could be used to produce electrical energy in a nanometer battery.
Chemical reaction reactors
Batteries are, in fact, chemical reaction reactors. A disposable battery consists of two electrodes, an anode and a cathode, immersed in an electrolyte solution. The compounds from which the electrodes are made react with each other through the electrolyte and release electrons. But the problem is that these electrochemical reactions occur even when the batteries are not connected to the devices. An average unused battery loses 7 to 10 percent of its capacity per year.
To keep batteries for an extended period, the electrolyte is separated from the electrodes by means of a physical partition until activation. The extremely vigorous electrochemical reactions that occur when the partition is removed provide powerful bursts of energy. The mechanical challenge of preventing contact between the electrolyte and the electrodes means that these batteries are large and bulky, so they are mainly intended for emergency situations, such as in intensive care units or hospital operating rooms, and for military uses, such as night vision goggles or laser lighting.
The invention of the nanometer grass has greatly helped to minimize emergency batteries. Also, Krupankin explains, instead of all the reactants being activated at once, it is now possible to design a battery that will activate only one area of the nanometer lawn at a time.
Bell Labs started looking for buyers for the idea of the nanometer grass. "Lucent is not a battery company, but we would like to revolutionize the field," says Bishop. At a seminar held at Lucent in late 2003, representatives of a company called mPhase heard a lecture about a battery based on nanotechnology. "We walked out of the room saying, 'Wow, that was amazing!'" recalls Steve Simon, mPhase's vice president of engineering, research and development. At that time, mPhase was a company whose main business was DSL components for home broadband and video applications. It spun off from Microphase, a microwave electronics company that worked for the military, aerospace, and communications industries in Norwalk, Connecticut.
As competition intensified in the communications hardware market, Ron Durando, mPhase's Chief Performance Officer, sought to reinvent the company as a nanotechnology supplier. He was looking for a product whose development would not take too long and would not be intended for medical use, so as not to get entangled in the bureaucracy of clinical trials. His preference was given to a product that would serve the needs of the military market that is not deterred by the high price of the nanotechnological devices at the beginning of their journey. "The battery met all three requirements," explains Simon.
In March 2004, mPhase signed a joint development agreement to commercialize the nanometer battery. mPhase checks what the potential customers' requirements are from the battery, in order to create profitable devices, while Lucent donates the technology license in exchange for royalties, use of a clean room that costs 450 million dollars and assistance from scientists with decades of experience in the production of Zorn vehicles.
The development of nano-batteries finally results in the miniaturization of the voltage sources to the dimensions of the other electronic components. The nano-battery is designed so that it can remain in a dormant state for at least 15 years and provide, as soon as it is activated, a burst of high-intensity energy. In September 2004, scientists already had a working model that produced current. To produce the prototype, the team had to produce Zorn pillars with a diameter of 300 nanometers and at intervals of about two microns. To generate electricity, the researchers used compounds used in normal alkaline batteries, with zinc as the anode and manganese dioxide as the cathode. The iron floor on which the columns rest is coated with zinc, and the columns themselves are coated with iron dioxide, which allows the researchers to control the voltage produced by the device. The ends of the columns are coated with a Teflon-like fluorocarbon layer where the electric wetting phenomenon occurs.
"Even if the things are conceptually simple, they are difficult to implement," Krupenkin emphasizes. Deposition of zinc only on the bottom is "a chain of huge challenges," he recalled. The accepted process for metal plating is called electrolytic plating. But it is impossible to perform it on oxides such as nitrogen dioxide found in the nanometer grass device. It was therefore necessary to plan a way to clean the furnace floor from zinc dioxide and allow the zinc to settle on it, and in the process it must be ensured that the furnace pillars themselves remain coated with oxide. The solution was to coat both the bottom and the columns with oxide, but to laminate a thinner layer on the bottom. Then, the oxide was eaten with ionized gas until it was completely removed from the bottom, while the columns remained coated.
But you can't do electrolytic coating on Zorn either. Therefore, the researchers used wet chemistry methods to deposit nickel or titanium on the bottom, as a seed layer on which the zinc will settle during the electrolytic coating. Deposition of the zinc in a uniform layer, so that mounds of zinc would not form next to exposed places, was a tedious mask of trial and error by playing with the temperature, the electric current and the concentration of the chemicals. "When I look back, I'm amazed it only took a year," says Simon.
Once the scientists had a working prototype, they started talking to potential customers. Following these talks, major changes were introduced in the structure of the battery. The initial design was sandwich-like, the cathode was on top, the zinc chloride solution used as an electrolyte, in the middle, the nanometer grass below it, and the anode below. Representatives of the US Army Laboratories from Adelphi, Maryland, expressed concern that the continuous contact between the electrolyte and each of the electrodes would cause unwanted chemical reactions. After a redesign, the electrolyte is now on top, the anode and cathode compounds are in physically separated areas on the bottom, and a barrier of nanometer size is suspended between them. When activated, it allows the electrolyte to penetrate and flood the electrodes.
The team originally used nanometer pillars to separate the electrolyte from the anode, because the pillars take up the least space and provide more surface area for chemical reactions between the electrodes. But the difficulty of producing the nanometer column battery pushed the researchers to instead develop a membrane in the form of a nanometer honeycomb to separate the electrolyte from the electrodes. Creating this electric wetting membrane, which has pores with a diameter of 20 microns and thin and fragile walls with a width of 600 nanometers, was quite a challenge. At first, the scientists used plasma to etch the delicate structure of the honeycomb from silicon wafers coated with silicon dioxide. Next, they grew soot dioxide on the exposed soot walls of the pores by bubbling oxygen into furnaces at a temperature of 1,000 degrees. Finally, coat the entire challah with fluorocarbon.
The researchers developed the first new samples in October 2005. One of the great advantages of the system, according to Simon, is that the team doesn't have to search hard for the exact conditions needed to grow a uniform anode layer inside a forest of nanometer pillars whenever it wants to try a new combination of anode and cathode. . Instead, the scientists simply place the pieces of electrodes on a flat surface. Also, the extensive experience gained in electrochemical coating helps them today to produce the electrodes very easily. Bell Labs and mPhase are currently trying, in collaboration with Rutgers University, to integrate into the system the type of chemical reactions used in the batteries of digital cameras and cell phones.
A more environmentally friendly power source may also grow from the nanometer battery, which will contain compounds that neutralize the electrolyte. "This will prevent it from spilling onto the ground, or, if a soldier carrying a device with a battery is shot, the battery will not spill its scalding contents on him," says Krupankin. It is also possible that nanoscale plastic structures will replace the mold, Simon adds, and pave the way for flexible nanoscale batteries.
The scientists aren't trying to replace the disposable batteries, since the cost of mass-producing those "is a few fractions of a cent for an AA battery," Krupenkin says. They focus on specialized applications, such as sensors that are dropped from military aircraft and are supposed to use their radio transmitters only once or twice, to signal the presence of intruders, for example, or toxins, or radiation. "If the sensor does not pick up anything of interest, it has nothing to transmit, but if it does, it needs a lot of electrical power," Krupankin explains. Another potential use is in devices that monitor environmental changes. These can use the extra voltage to transmit over a greater distance, thus reducing the number of sensors needed. The emergency batteries may also be able to be integrated into medical implants, cell phones or pet collar transmitters.
The team also considered developing a rechargeable version of the device. A pulse of current can pass through the discharged battery and cause heating of the surface on which the electrolyte rests. As a result, a thin layer of liquid will evaporate, and the drop will jump back to the top of the nanometer structure. "Basically, it's possible. In practice, it is very difficult to do," Krupankin fears. For example, mPhase expects to launch product samples to the first potential users in two to three years. A nanometer battery will be an important milestone in joining the power sources to the miniaturization revolution that has been driving the rest of the electronics industry for several decades.
They know nano technology
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