UCLA: El-Kady featured for his contributions to the development of super batteries
A native of Egypt, El-Kady received his Masters of Science degree in Physical Chemistry from Cairo University in 2009 and his Ph.D. in Chemistry from UCLA in 2013. He is currently a postdoctoral researcher in Kaner’s group, and Chief Technology Officer at Nanotech Energy, Inc. where he and Kaner are working on converting their graphene supercapacitors research from the laboratory scale to mass production.
El-Kady has spent more than 10 years studying electrochemistry at the fundamental level with applications in energy storage devices, chemical sensors and biosensors, solar cells, water splitting and hydrogen energy. He has 15 US patents issued and pending and 35 research articles in prestigious journals including Science, Nature Materials, Nature Review Materials and theProceedings of the National Academy of Sciences. He is also featured in a science movie entitled “Nanotechnology: Use and Misuse” with Sir Harold Kroto, the 1996 Nobel Laureate in Chemistry whose work on fullerenes is widely recognized as the beginning of the nanotechnology age. Maher has a long-standing passion for the design and construction of new “smart” materials that will transform our lives.
To learn more about the research, watch a video in which Kaner and El-Kady discuss their carbon-based supercapacitors, which was part of an episode on batteries that aired last year on the PBS science show NOVA.
For more information about ongoing research in the Kaner Lab, visit their website.
From Scientific American the Arabic edition:
High Powered Batteries Are Longer Lasting and Safer
A research team from the University of Cairo and University of California, Los Angeles develop a new and effective method to improve energy storage
By Mohamed Mansour
The development of smartphones with a battery technology that is safer and longer lasting has become an important goal for the users of modern electronic devices around the world. This has triggered tremendous efforts among academic institutes and electronics companies that have allocated considerable funding to make this goal a reality. Unfortunately, current battery technology carry safety risks and sometimes may lead to severe problems. Back in September 2016, Samsung recalled its acclaimed “Galaxy Note 7” due to unusual fire incidents, which opened up a new debate about the need to increase safety in modern electronic devices.
A large number of Note 7 users have reported a serious flaw that causes their devices to overheat during charging, sometimes causing the devices to explode.
More recently, researchers from the University of California and Cairo University have published a new research paper that could be an important step towards overcoming the problems of current batteries. The research focuses on a relatively new energy storage technology, called supercapacitors, that may enable safer and cheaper charge storage for electronic devices.
The new technique uses powerful lasers to drill precise holes in the electrodes to facilitate the movement of ions during charge and discharge, enabling a new generation of supercapacitors that can be fully recharged in a fraction of a second and have the capability to work at extreme temperatures. They are also safer to use within smartphones and laptops.
According to Dr. Maher El-Kady, a researcher at the Department of Chemistry and Department of Materials Science at the University of California, Los Angeles and Cairo University and one of the study authors, the world is about to switch from storing electricity in lithium-ion batteries to storing it in supercapacitors. Unlike traditional batteries that utilize chemical reactions to store electrical energy, supercapacitors store charge in the form of static electricity, making them safer and much faster. “The low internal resistance of supercapacitors prevents overheating and makes them the safest energy storage system that exists in the market”, he added.
So far, lithium-ion batteries dominate the market of portable electronics due to their high charge storage capacity. They store charge via slow chemical reactions and typically take hours to recharge.
The lithium-ion is a special type of rechargeable batteries, consisting of a cathode (the positive electrode) based on metal oxides doped with lithium ions, and an anode (negative electrode), typically made of porous graphitic carbon, separated by a dielectric. The three components are immersed in an electrolyte that provides a medium for lithium ion transport from the cathode to the anode (and vice versa) during charge and discharge processes. There are different forms of lithium ion batteries that can be custom-designed to work for a specific application depending on the type of chemical reaction distinctive to them, and how they perform, price and safety.
However, lithium-ion batteries no longer meet their intended purpose, as the processors in portable electronic devices have become extremely fast, requiring more powerful batteries, quick recharging and controlled discharging. Therefore, scientists strive to develop new energy storage technologies that utilize the advantages of capacitors.
Recently, supercapacitors have experienced significant advances and have become one of the most important electrical energy storage devices in the market. They can be used for virtually unlimited number of charge/discharge cycles on the order of 1 million, compared with a maximum of 1500 cycles in lithium-ion batteries. Supercapacitors can provide up to tens of thousands of Farads—a unit for measuring the amount of electric charge known as capacitance—and extremely low series resistance “ESR”, which makes the voltage drop during discharge miniscule, according to the journal Nature.
Supercapacitors are usually made up of two electrodes, separated by a dielectric, typically a liquid. This liquid contains a salt that breaks apart to positive and negative ions. When the device is connected to a power supply, charge polarization causes ions in the electrolyte to move to the electrode of the opposite charge eventually leading to charge separation. This process is very fast and typically takes no more than a few seconds. During discharge, the process of charge separation is reversed and the stored charge is released in the form of electricity to power the desired device.
There are, however, major issues with supercapacitor technology, including the high cost of electrode materials, which makes a supercapacitor-based battery nearly 10 times more expensive than a lithium-ion battery.
Carbon nanomaterials such as graphene and carbon nanotubes have been widely explored as promising electrode materials for supercapacitors, yet their high cost have so far limited their practical application. Instead, the majority of supercapacitors currently available in the market utilize another form of carbon derived from coconut shells that exists in nature at low cost. While this form of carbon has the high surface area required for capacitive energy storage, their limited pore structure makes their surfaces not easily accessible to the electrolyte ions.
El-Kady says, “Our research provides an effective solution to this challenge and may enable dramatic improvements in the supercapacitor industry that is now expanding on the use of coconut shells as a cost-effective source for carbon. In general, carbon is obtained by burning coconut shells in a limited supply of oxygen followed by chemical activation of the resulting powder to open up precise holes where the positive and negative electrolyte ions can pass through during charge and discharge. These electrolytes are usually made by dissolving ammonium salts in acetonitrile or propylene carbonate. While this allows the operation of supercapacitors at a relatively high voltage of 2.7 V, these electrolytes are flammable and have a fairly low ionic conductivity.
"We are following the same protocol used in industry to produce carbon supercapacitors, but we are adding one step," El-Kady explains to Scientific American. "Our research team uses lasers to drill tiny holes in activated carbon electrodes, increasing the surface area of the material and reducing the distance over which the ions will have to move during charge and discharge. This allows for better interaction between the electrode surfaces and electrolyte ions and enables ions to move within the electrode more quickly. As a result, laser scribed activated carbon electrodes can be recharged 4 times faster and store 8 times more charge than conventional carbon electrodes.
In addition to using lasers to drill tiny holes, the team took this research a step further by changing the composition of the electrolyte. In order to reduce cost and improve safety of carbon supercapacitors, it is necessary to replace propylene carbonate based electrolytes with a less expensive and safer alternative. After long research, the team utilized aqueous electrolytes consisting of water, another commodity chemical called sodium sulfate and a small amount of potassium ferrocyanide that undergoes reversible oxidation and reduction reactions during charge and discharge. This electrolyte improves not only the cycling stability of carbon supercapacitors, but also greatly increases the safety level of the device.
Capacity of Charge Storage
Supercapacitors suffer from another major shortcoming; low energy density. The amount of charge stored in a supercapacitor is 20 times lower than that of ordinary batteries. This way a smartphone powered by an activated carbon supercapacitor will last for only a few minutes compared with several hours for a lithium ion battery of similar size, making it unlikely for supercapacitors to be used in cellphones at the present time.
"The proposed method may in the future enable the use of supercapacitors in a wide range of applications, including mobile phones and other smart devices," said Dr. Min Gu, supercapacitor scientist at the Office of Research and Development and Consultant at the Royal Melbourne Institute of Technology, Australia. “However, more research still needs to be done to improve the energy density of supercapacitors," he said.
"The trend now is to make batteries based on graphene supercapacitors for use in cellphones," he added. "Of course, it is expensive but is safer and more powerful than ordinary batteries," he says. In a statement to Scientific American, Gu added that “the new method suggested in the study could give a strong boost to the use of supercapacitors in electric buses and trains. The technique is simple, yet effective at enhancing the performance of current supercapacitors while maintaining a relatively low cost, but the capacity of charge storage still remains a challenge."
The supercapacitor market is growing very rapidly and has risen to about $568 million in 2015, with a forecast of $2.81 billion in 2022, which is a major driver for the development of new techniques for the manufacture of more powerful supercapacitors.
In order to meet the increasing energy demands of portable electronic devices, scientists from the University of Central Florida developed a promising supercapacitor battery prototype in 2016. This prototype could last for over 20 times longer than a typical lithium ion battery and has superior cycling stability. The new battery maintains the same performance even after being charged and discharged for 30,000 cycles, and the time required for charging is just a few seconds. In the same year, scientists at the University of Surrey in the Netherlands, designed a plastic-based dielectric to reduce the cost of manufacturing batteries based on supercapacitors.
Notably, while supercapacitor sales have risen, Samsung's market value has fallen by about $19 billion as a result of the recall of its Galaxy Note 7 devices. Despite the partial recovery of the company after the launch of its new Samsung S8, the market for batteries are still burdened by explosion hazards. Battery users are waiting for a ‘revolutionary’ technology that can provide a good balance between the price of supercapacitor batteries, their safety and size. According to El-Kady, the near future will witness a major drop in the price of supercapacitor batteries in a very similar way we had a reduction in their size not too long ago. This will allow the integration of supercapacitors into future electronic devices at low cost while improving safety of these consumer products.