Nav: Home

Scientists discover path to improving game-changing battery electrode

December 12, 2017

Menlo Park, Calif. -- If you add more lithium to the positive electrode of a lithium-ion battery - overstuff it, in a sense - it can store much more charge in the same amount of space, theoretically powering an electric car 30 to 50 percent farther between charges. But these lithium-rich cathodes quickly lose voltage, and years of research have not been able to pin down why - until now.

After looking at the problem from many angles, researchers from Stanford University, two Department of Energy national labs and the battery manufacturer Samsung created a comprehensive picture of how the same chemical processes that give these cathodes their high capacity are also linked to changes in atomic structure that sap performance.

"This is good news," said William E. Gent, a Stanford University graduate student and Siebel Scholar who led the study. "It gives us a promising new pathway for optimizing the voltage performance of lithium-rich cathodes by controlling the way their atomic structure evolves as a battery charges and discharges."

Michael Toney, a distinguished staff scientist at SLAC National Accelerator Laboratory and a co-author of the paper, added, "It is a huge deal if you can get these lithium-rich electrodes to work because they would be one of the enablers for electric cars with a much longer range. There is enormous interest in the automotive community in developing ways to implement these, and understanding what the technological barriers are may help us solve the problems that are holding them back."

The team's report appears today in Nature Communications.

The researchers studied the cathodes with a variety of X-ray techniques at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL) and Lawrence Berkeley National Laboratory's Advanced Light Source (ALS). Theorists from Berkeley Lab's Molecular Foundry, led by David Prendergast, were also involved, helping the experimenters understand what to look for and explain their results.

The cathodes themselves were made by Samsung Advanced Institute of Technology using commercially relevant processes, and assembled into batteries similar to those in electric vehicles.

"This ensured that our results represented an understanding of a cutting-edge material that would be directly relevant for our industry partners," Gent said. As an ALS doctoral fellow in residence, he was involved in both the experiments and the theoretical modelling for the study.

Like a Bucket Half Empty

Batteries convert electrical energy to chemical energy for storage. They have three basic parts - two electrodes, the cathode and the anode, and the liquid electrolyte between them. As a lithium-ion battery charges and discharges, lithium ions shuttle back and forth between the two electrodes, where they insert themselves into the electrode materials.

The more ions an electrode can absorb and release in relation to its size and weight - a factor known as capacity - the more energy it can store and the smaller and lighter a battery can be, allowing batteries to shrink and electric cars to travel more miles between charges.

"The cathode in today's lithium-ion batteries operates at only about half of its theoretical capacity, which means it should be able to last twice as long per charge," said Stanford Professor William Chueh, an investigator with the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC.

"But you can't charge it all the way full. It's like a bucket you fill with water, but then you can only pour half of the water out. This is one of big challenges in the field right now - how do you get these cathode materials to behave up to their theoretical capacity? That's why people have been so excited about the prospect of storing a lot more energy in lithium-rich cathodes."

Like today's cathodes, lithium-rich cathodes are made of layers of lithium sandwiched between layers of transition metal oxides - elements like nickel, manganese or cobalt combined with oxygen. Adding lithium to the oxide layer increases the cathode's capacity by 30 to 50 percent.

Connecting the Dots

Previous research had shown that several things happen simultaneously when lithium-rich cathodes charge, Chueh said: Lithium ions move out of the cathode into the anode. Some transition metal atoms move in to take their place. Meanwhile, oxygen atoms release some of their electrons, establishing the electrical current and voltage for charging, according to Chueh. When the lithium ions and electrons return to the cathode during discharge, most of the transition metal interlopers return to their original spots, but not all of them and not right away. With each cycle, this back and forth changes the cathode's atomic structure. It's as if the bucket morphs into a smaller and slightly different bucket, Chueh added.

"We knew all these phenomena were probably related, but not how," Chueh said. "Now this suite of experiments at SSRL and ALS shows the mechanism that connects them and how to control it. This is a significant technological discovery that people have not holistically understood."

At SLAC's SSRL, Toney and his colleagues used a variety of X-ray methods to make a careful determination of how the cathode's atomic and chemical structure changed as the battery charged and discharged.

Another important tool was soft X-ray RIXS, or resonant inelastic X-ray scattering, which gleans atomic-scale information about a material's magnetic and electronic properties. An advanced RIXS system that began operation at ALS last year scans samples much faster than before.

"RIXS has mostly been used for fundamental physics," ALS scientist Wanli Yang said. "But with this new ALS system, we wanted to really open up RIXS for practical materials studies, including energy-related materials. Now that its potential for these studies has been partially demonstrated, we could easily extend RIXS to other battery materials and reveal information that was not accessible before."

The team is already working toward using the fundamental knowledge they have gained to design battery materials that can reach their theoretical capacity and not lose voltage over time.
-end-
The research was funded by the DOE Office of Energy Efficiency and Renewable Energy's Vehicle Technologies Office and by Samsung Advanced Institute of Technology Global Research Outreach Program.

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science. To learn more, please visit http://www.slac.stanford.edu.

SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

DOE/SLAC National Accelerator Laboratory

Related Lithium Articles:

Post-lithium technology
Next-generation batteries will probably see the replacement of lithium ions by more abundant and environmentally benign alkali metal or multivalent ions.
An air-stable and waterproof lithium metal anode
The instability of lithium metal anode in air and the dendrite growth limit its applications.
Expanding the temperature range of lithium-ion batteries
Electric cars struggle with extreme temperatures, mainly because of impacts on the electrolyte solutions in their lithium-ion batteries.
Toward a low-cost industrialization of lithium-ion capacitors
Combining two additives instead of one to facilitate the incorporation of lithium within capacitors: that is the solution proposed by researchers from l'Institut des matériaux Jean Rouxel (CNRS/Université de Nantes), in collaboration with Münster Electrochemical Energy Technology, in order to promote the low-cost, simple, and efficient development of the lithium-ion capacitors used to store electrical energy.
A close look at lithium batteries
Batteries with metallic lithium anodes offer enhanced efficiency compared to conventional lithium-ion batteries because of their higher capacity.
Graphene coating could help prevent lithium battery fires
Researchers from the University of Illinois at Chicago College of Engineering report that graphene -- wonder material of the 21st century -- may take the oxygen out of lithium battery fires.
New approach could boost energy capacity of lithium batteries
Researchers at MIT and in China have found a new way to make cathodes for lithium batteries, offering improvements in the amount of power for both a given weight and a given volume.
Lithium-matrix anode protected by a solid electrolyte layer for stable lithium metal batteries
A house-like Li anode was designed. The house matrix was composed of carbon fiber and affords a stable structure to relieve the volume change.
Whiskers, surface growth and dendrites in lithium batteries
Researchers at Washington University in St. Louis take a closer look at lithium metal plating and make some surprising findings that might lead to the next generation of batteries.
3D-printed lithium-ion batteries
Electric vehicles and most electronic devices, such as cell phones and laptop computers, are powered by lithium-ion batteries.
More Lithium News and Lithium Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab