Category: EV Technology

Carnegie Mellon University's Venkat Viswanathan and a team of researchers have reduced the problem of sudden death in lithium air batteries through the addition of water, increasing energy storage capacity by five times.

"We could not get all the energy out of these batteries because of sudden death," says Viswanathan, an assistant professor of Mechanical Engineering. "That was the ugly aspect of this battery."

Lithium air batteries are an exciting research frontier because they could store at least twice as much energy as lithium ion batteries, which are currently the most common battery used in many consumer products, ranging from cell phones and laptops to electric vehicles. The potential of lithium air batteries lies in replacing one of the battery materials, the cathode, with air, making lithium air batteries lighter than lithium ion batteries. The lighter the battery, the more energy it can store. In addition, lithium air batteries have the possibility to increase safety.

Viswanathan, IBM researchers Nagaphani B. Aetukuri, Jeannette M. García, and Leslie E. Krupp, University of California, Berkley Assistant Professor Bryan D. McCloskey and Alan C. Luntz of the SLAC National Accelerator Laboratory discovered that adding water to the battery decreases a phenomenon called sudden death, which reduces the battery's storage capacity. They published their results in Nature Chemistry.

Sudden death causes lithium air batteries to die prematurely. The batteries require lithium, oxygen and an electron to move inside the battery to reach the active site where the reaction produces energy. As the battery operates, however, the lithium and oxygen form lithium peroxide films that produces a barrier and prevents electron movement to the active site, resulting in sudden death.

Water selectively dissolves the lithium peroxide, and the dissolved lithium and oxygen move to a toroidal depository in the cathode, removing the barrier to electron movement, before reforming into lithium peroxide.

"This allows for five times the capacity of the original case," says Aetukuri.

While water is a temporary solution, it is eventually consumed and results in parasitic products that reduce battery efficiency. Viswanathan and McCloskey are currently searching for an additive other than water, which will result in increased battery capacity and efficiency. However, the addition of water is a large step forward in lithium air battery technology.

"This additive opens up the opportunity to be able to reach a much higher energy density than a lithium ion battery, and once we perfect the design, we can compete with lithium ion batteries," says Viswanathan.

To read the full Nature Chemistry paper, visit: http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.2132.html

Scientists at Nanyang Technology University (NTU) have developed ultra-fast charging batteries that can be recharged up to 70 per cent in only two minutes.

The new generation batteries also have a long lifespan of over 20 years, more than 10 times compared to existing lithium-ion batteries.

This breakthrough has a wide-ranging impact on all industries, especially for electric vehicles, where consumers are put off by the long recharge times and its limited battery life.

With this new technology by NTU, drivers of electric vehicles could save tens of thousands on battery replacement costs and can recharge their cars in just a matter of minutes.

Commonly used in mobile phones, tablets, and in electric vehicles, rechargeable lithium-ion batteries usually last about 500 recharge cycles. This is equivalent to two to three years of typical use, with each cycle taking about two hours for the battery to be fully charged.

In the new NTU-developed battery, the traditional graphite used for the anode (negative pole) in lithium-ion batteries is replaced with a new gel material made from titanium dioxide.

Titanium dioxide is an abundant, cheap and safe material found in soil. It is commonly used as a food additive or in sunscreen lotions to absorb harmful ultraviolet rays.

Naturally found in spherical shape, the NTU team has found a way to transform the titanium dioxide into tiny nanotubes, which is a thousand times thinner than the diameter of a human hair. This speeds up the chemical reactions taking place in the new battery, allowing for superfast charging.

Invented by Associate Professor Chen Xiaodong from NTU’s School of Materials Science and Engineering, the science behind the formation of the new titanium dioxide gel was published in the latest issue of Advanced Materials, a leading international scientific journal in materials science.

Prof Chen and his team will be applying for a Proof-of-Concept grant to build a large-scale battery prototype. With the help of NTUitive, a wholly-owned subsidiary of NTU set up to support NTU start-ups, the patented technology has already attracted interest from the industry.

The technology is currently being licensed by a company for eventual production. Prof Chen expects that the new generation of fast-charging batteries will hit the market in the next two years. It also has the potential to be a key solution in overcoming longstanding power issues related to electro-mobility.

“Electric cars will be able to increase their range dramatically, with just five minutes of charging, which is on par with the time needed to pump petrol for current cars,” added Prof Chen.

“Equally important, we can now drastically cut down the toxic waste generated by disposed batteries, since our batteries last ten times longer than the current generation of lithium-ion batteries.”

The 10,000-cycle life of the new battery also mean that drivers of electric vehicles would save on the cost of battery replacements, which could cost over US$5,000 each.

Easy to manufacture

According to Frost & Sullivan, a leading growth-consulting firm, the global market of rechargeable lithium-ion batteries is projected to be worth US$23.4 billion in 2016.

Lithium-ion batteries usually use additives to bind the electrodes to the anode, which affects the speed in which electrons and ions can transfer in and out of the batteries.

However, Prof Chen’s new cross-linked titanium dioxide nanotube-based electrodes eliminates the need for these additives and can pack more energy into the same amount of space.

Manufacturing this new nanotube gel is very easy. Titanium dioxide and sodium hydroxide are mixed together and stirred under a certain temperature so battery manufacturers will find it easy to integrate the new gel into their current production processes.

Recognised as the next big thing by co-inventor of today’s lithium-ion batteries

NTU professor Rachid Yazami, the co-inventor of the lithium-graphite anode 30 years ago that is used in today’s lithium-ion batteries, said Prof Chen’s invention is the next big leap in battery technology.

“While the cost of lithium-ion batteries has been significantly reduced and its performance improved since Sony commercialised it in 1991, the market is fast expanding towards new applications in electric mobility and energy storage,” said Prof Yazami, who is not involved in Prof Chen’s research project.

Last year, Prof Yazami was awarded the prestigious Draper Prize by The National Academy of Engineering for his ground-breaking work in developing the lithium-ion battery with three other scientists.

“However, there is still room for improvement and one such key area is the power density – how much power can be stored in a certain amount of space – which directly relates to the fast charge ability. Ideally, the charge time for batteries in electric vehicles should be less than 15 minutes, which Prof Chen’s nanostructured anode has proven to do so.”

Prof Yazami is now developing new types of batteries for electric vehicle applications at the Energy Research Institute at NTU (ERI@N).

This battery research project took the team of four scientists three years to complete. It is funded by the National Research Foundation (NRF), Prime Minister's Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) Programme of Nanomaterials for Energy and Water Management.

Venkat Viswanathan, assistant professor of mechanical engineering at Carnegie Mellon University, is developing a search engine that will help researchers and industry experts discover and develop electrolytes for batteries more quickly and efficiently than currently possible.

Viswanathan, who is researching new types of lithium batteries for electric vehicles, realized how slow and inefficient it is to search for specific information on the different components. "You have to go read through multiple charts or go through handbooks to get to that information, and then try to discover something that will actually work," Viswanathan says.

Viswanathan was inspired to find a solution to this problem by President Barack Obama's first announcement of the Materials Genome Initiative. Making the announcement at Carnegie Mellon in 2011, he called upon scientists and engineers to help discover and produce new materials faster and in more cost-effective ways by creating and using a massive database of information on industry materials.

While the Materials Genome Initiative is intended for a broad spectrum of industry applications, Viswanathan is currently focused on developing a data genome for electrolytes. Electrolytes consist of salt and a solvent, and are essential in lithium ion batteries because they serve as the channel that moves the lithium ions, which store the energy. Charged ions must be moved from one side of the battery, and when they are charged, back to the other side, where they can be consumed. Finding electrolytes that work is currently one of the major barriers to developing more energy-dense storage solutions for consumer use.

Using a search engine similar to social networking sites Facebook and Yelp, scientists and researchers can use the electrolyte genome to enter the beginning of queries and receive suggestions about what they might mean, similarly to how when you type "Sara" into your Facebook search, the people named Sara who are your friends are the top suggestions. It also can handle queries with "and," such as if you type in "Sara" AND "Boston" to discover Saras who live in Boston. While this sounds common for everyday users, it is novel for very technical organic chemistry searches.

The search engine is robust enough to help users come up with ideas, such as if a researcher is trying to think of a certain set of desired attributes for a solvent but cannot quite precisely state it — like how you might be trying to think of a word on the tip of your tongue, but can only remember it starts with a certain letter and means something similar to another word.

In the future, users will be able to seamlessly merge data graphically to get more complex information such as correlations between various properties of solvents or between different solvents. This is similar to the search engine Wolfram Alpha, which, should a user type in "GDP of China and India," will provide the users not only with the countries' current GDPs but also with a graph detailing how their GDPs have increased over time, among other relevant facts.

The ability to access this in-depth level of information would result in faster and more successful testing of new materials, ultimately allowing researchers and businesses to get products from concept to marketplace more quickly.

Viswanathan's electrolyte genome project is tailored for expert users who are looking for complex information, such as electrochemical and chemical properties, and highest occupied molecule orbital (HOMO) level of solvents, but he hopes to eventually expand the project to be accessible to the general public and to other kind of solvents beyond organic solvents. The data genome search engine would support a wide range of querying options, from complicated searches by experts to simple searches by general users who are looking for information unavailable outside of print materials or who just want to see the capability of the data genome.

To test Viswanathan's electrolyte genome project, visit: http://www.andrew.cmu.edu/user/venkatv/SEED.html.