Anything portable needs a battery. We wouldn’t have the cell phones, laptops or other consumer electronic gadgets we use daily without battery technology—the research is ubiquitous. This is especially true of lithium-ion batteries.
The face of battery research has changed since the 1980s where it was considered a “dirty science” and researchers would mix carbon and other elements in their laboratories. Noted as the first generation of lithium-ion batteries, the 1980s gave birth to lithium-metal battery technology, which is now seeing a resurgence today. And, in 1991, when Japan’s Sony first released the lithium-ion battery to power music players and camcorders, they probably didn’t anticipate the crucial impact the technology would have over all society. And they probably didn’t foresee Asia’s dominance in battery technology R&D.
However, now there’s another shift in battery technology happening within transportation and storage on the grid, which are an order-of-magnitude larger than personal electronics. To run electric vehicles and the grid, it will take a bigger battery. And researchers are working on “beyond lithium-ion” solutions to bring battery power to the highest level.
Asia’s dominance in lithium-ion development
In 1991, the world of batteries changed after Sony introduced its first commercial lithium-ion battery. In the 1990s, lithium-ion battery facilities in Japan resembled semiconductor fabs. “Battery development moved from the dark arts to high technology,” says Steven Visco, CEO/CTO of PolyPlus Battery Company in an interview with R&D Magazine. “The bar was raised so significantly due the very complex chemistries, engineering and manufacturing that was put in place. However, sadly, this is where the U.S. dropped the ball.”
Leading up to the time of the first lithium-ion battery development, Asian companies, and in particular Japanese companies, were increasingly funding lithium-related battery research and filing patents. “In the 20-year period leading up to 1991, there was an exponential rise in Japanese patents related to the lithium battery technology,” says Visco. “And the opposite was seen in the U.S.”
Companies like the big three alkaline battery producers at the time—Duracell, Rayovac and Energizer—were basking in the glory of throw-away batteries, and weren’t interested in rechargeable technologies. And, when lithium-ion first hit the market, the U.S. “could only launch an anemic response,” says Visco.
Shortly after, all three companies tried to get into lithium-ion chemistries, but failed. And their excuse, at the time, “was the Japanese had too much lead way,” says Visco. After the Japanese dominance, Korea got into lithium-ion technology, shortly followed by China, leaving the U.S. behind some of our largest technology competition.
“Now there’s a big catchup game, because batteries are changing the global landscape,” says Visco. “It’s such a big business and drives so many technologies that the U.S. needs to be in the space.” So, as a result, the U.S. has invested much R&D money (almost $525 million) to catchup up to our Asian competitors. And through this funding, many battery entrepreneur startups, such as A123 Systems and SolidEnergy System (both out of Massachusetts Institute of Technology), are forming throughout the U.S., especially in Silicon Valley.
“The opportunities are huge, particularly if the U.S. goes the way of electric vehicles,” says Visco. “It’s truly the next trillion dollar industry, and the U.S. can’t afford not to be involved.”
Focus on lithium-ion
The funding for battery technology in the U.S. is slated for $325 million in the FY16 budget. A good portion of this funding will go into lithium-ion battery research, and how researchers can make a gold-standard technology even better.
“The trend here is to make better lithium-ion battery cathodes,” says George Crabtree, Director of the Joint Center for Energy Storage Research in an interview with R&D Magazine. The standard current cathode for lithium-ion batteries is cobalt dioxide. However, to make the next-generation lithium-ion battery, researchers “must make cathodes based on cobalt dioxide, but have it diluted or mixed with other elements, such as manganese and nickel,” says Crabtree.
The key behind this research is voltage. And a mixture of cobalt, nickel and manganese dioxide can lead to a better performing cathode by increasing voltage. “Lithium-ion batteries are typically 4.5 V, but if you can get the voltage up by a few tenths of a volt, somewhere around 4.8 V, then you can increase the energy density,” says Crabtree. And this is what society needs to power the latest electronic devices we crave.
As the lithium-ion battery is 25 years old, researchers know a lot about the technology. And the materials used in a lithium-ion battery are pretty standard and mature. The anode material typically used for lithium-ion batteries is graphite, where the lithium ions intercalate between the layers of graphite. On the cathode side it’s typically cobalt oxide or cobalt dioxide, where the lithium ions can also intercalate between the layers. “There are few other materials lithium-ion batteries use—iron phosphate instead of cobalt oxide, or manganese oxide,” says Crabtree. “There aren’t many materials we can use, and the number of liquid electrolytes we can use for lithium-ion batteries amounts to five or six.” And much research around lithium-ion battery materials also revolves around these electrolytes.
While much is known about lithium-ion batteries, there have been some recent spectacular lithium-ion battery fires caused by the electrolyte material—most noted is the Boeing Dreamliner. With more and more electric vehicles on the road, lithium-ion batteries contain liquids in their electrolyte material, and those liquids are flammable. “If those liquids are overheated or an electric car were to crash, it could lead to an amazing fire,” says Visco. “So there is a push to develop safer lithium-ion battery electrolytes.”
The key thing with lithium-ion battery safety is as the energy density increase, safety becomes an issue. “There are many challenges to safety, but you can typically mitigate them through cell design and the module system design through a battery management system,” says Patrick Hurley, CTO, A123 Systems in an interview with R&D Magazine. A battery management system allows for monitoring of the cells, and if one gets out of line, it can be shut down.
On the anode side, carbon is a relatively heavy material, and with the push to go to smaller electronics, researchers are moving to materials other than carbon that will allow a drop in the weight and size of the battery. “There are two school of thought here,” says Visco. “One is silicon-based. And the other is lithium metal. With lithium-metal you can’t get much better.”
SolidEnergy Systems, a Waltham, Mass.-based company, is working on developing anodes and electrolytes for lithium-metal batteries. The company’s technology, the Solid Polymer Ionic Liquid (SPIL) rechargeable lithium battery, which won a R&D 100 Award in 2014, consists of a cathode, electrolyte and anode. “The cathode is a high-voltage and high-energy-density metal oxide material with lithium-ion storage capacity ranging from 155 to 300 mAh/g,” says Qichao Hu, Founder and CEO of SolidEnergy Systems. “The electrolyte consists of a dual-layer design with ionic liquid-based electrolyte on the cathode side and solid polymer electrolyte coating on the anode side.”
The ionic liquid-based electrolyte consists of a room temperature ionic liquid that’s a molten salt at room temperature, has high lithium-ion conductivity and is completely non-flammable and non-volatile. “The push to lithium-metal batteries is the high energy density,” says Hu. “It has a much higher energy density than any lithium-ion battery.” SolidEnergy Systems prototype battery, according to Hu, has a higher energy density than conventional lithium-ion batteries, by 50% compared to graphite anodes, and 30% compared to silicon-based anodes. The battery also reduces cost by eliminating the separator at the cell level and simplifying the cooling system at the battery pack level.
With the push to the grid and electric vehicles, battery technology beyond lithium-ion is needed. This is shown in the funding for electric drive vehicle at the DOE’s Vehicle Technology Office at $125 million. And also the $54 million in funding related to advanced materials for battery technology research. This also poses more challenging, because unlike with lithium-ion batteries where you are fine-tuning one component, the cathode, researchers must discover all three materials: anode, cathode and electrolyte.
Lithium-air is an example of beyond lithium-ion that’s gotten a lot of play over the past 10 years because it could store several times the energy of a lithium-ion battery in the same space. This is enough to power cars and to deploy grid backup like wind or solar farms.
PolyPlus Battery Company, a spinout from Lawrence Berkeley National Laboratory, around 2000, invented the water stable lithium electrode, “which is much like an oxymoron, because people don’t expect lithium to work with anything close to water,” says Visco. “You think of lithium and water as being mutually exclusive. But, actually, we have invented a structure where we surround the lithium-metal electrode with a ceramic electrolyte, and it’s called a protected lithium electrode (PLe), because it’s protected from the external environment.”
With the discovery, and the patents PolyPlus ensued, the company went on to develop water-based lithium-air and lithium-sulfur batteries. The batteries are based on the PLEs. “At a nominal potential of about 3 V, the theoretical specific energy for a lithium-air battery is over 3,300 Wh/kg for the reaction forming LiOH and 11,000 Wh/kg for the reaction of lithium with dissolved oxygen in seawater, rivaling the energy density for hydrocarbon fuel cells and far exceeding lithium-ion battery chemistry that has a theoretical specific energy of about 400 Wh/kg,” says Visco. PolyPlus is currently developing an aqueous lithium-sulfur battery with a projected performance of 600 Wh/l and 400 Wh/kg. The company’s Li-Air and Li-S technology is currently the most advanced in the field.
Other companies such as Toyota Motor Corp. and BMW are also working on lithium-air technology for use in hybrid and electric vehicles. Currently, Toyota is using lithium-ion batteries in its Prius plug-in hybrid, some Prius v and the eQ electric car. However, a lithium-air’s anode is filled with lithium, and the cathode with air, allowing for the battery to generate and store more electricity than lithium-ion battery technology. The research is ongoing with the hopes of a functional battery in the next two to three years.
Another example, in the same category of lithium-air, is lithium-sulfur. However, with lithium-sulfur batteries, the biggest challenge is sulfur and how it acts as an insulator. And when sulfur (an insulator) reacts with lithium, the compound formed, Li2S, is also an insulator. “This means it’s difficult to reverse the reaction, leaving it difficult to recharge the battery,” says Crabtree. “It’s pretty easy to discharge the battery when you create this Li2S compound, but it’s hard to apply a voltage, because you can’t make contact with the insulating Li2S since it doesn’t conduct electrons.”
There are various ways to solve this problem. And the major approach is to nanosize the Li2S cathode by shrinking its dimension down to the nanoscale. “The surface you can always access with electrons, and that surface might be 10 to 100 nm thick,” says Crabtree. “But if the entire cathode is thin, such as 10 nm, then suddenly you can access even the interior on those small scales with electron and could reverse the reaction.”
Researchers at the Joint Center for Energy Storage Research are following this research, and currently have two different kinds of batteries for lithium-sulfur in the works. One is the standard compact battery you could put in your car. The other is a so-called flow battery, which you would use for the grid.
In the flow battery researchers replace the crystalline electrodes with a fluid. “We have many ideas with flow batteries that are based on organic active materials,” says Crabtree. In a standard flow battery, where the anode and cathode are replaced with a fluid, suspension or a solution, vanadium is used, as it’s a transition metal with two oxidation states that oscillate between to store and release energy. However, according to the Joint Center for Energy Storage Research, this can be done better with organic active materials instead of vanadium.
“They can sometimes change its vanadium oxidation state by two, and some organic materials can change their oxidation state by three or four, maybe even five or six,” says Crabtree. “So, in principle, they are much better than vanadium.” Another positive about the technology is since the materials are organic, they are cheap. The materials are made of molecules from oxygen, nitrogen, hydrogen, carbon and “one or two other elements,” according to Crabtree. These molecules are very abundant and inexpensive and, “if you break the molecules down to their elements, you can recycle them,” says Crabtree.
The Joint Center for Energy Storage Research has recently innovated a new direction for flow batteries—one instead of having an isolated molecule as the active material, hook the active molecule onto a polymer backbone and make the active material a polymer. “The reason you want do this is you can control the polymer much better than you could control an individual molecule,” says Crabtree.
The second innovation is to cross-link that polymer. “So, instead of a long chain of active materials you cross-link it into a ball of active material, which is much larger than a molecule,” says Crabtree. The advantage of this is researchers can then filter the active material with a porous membrane that can be purchased off-the-shelf for as little as $1.
The other idea for beyond lithium-ion technologies is to use magnesium, which has two charges, in replacement of lithium, which has one. Every time a magnesium ion goes back and forth between the anode and cathode of the battery it stores and releases twice as much energy as a lithium ion would.
With magnesium the problem is a bit different from lithium-air technologies. “Although you get two charges from the magnesium every time it goes back and forth between the anode and cathode, none of the anodes, cathodes and electrolytes that work with lithium, work with magnesium,” says Crabtree. “So, researchers must discover three new sets of materials.”
The Joint Center for Energy Storage Research works on this problem and has recently found electrolytes that work with a magnesium anode. The researchers found a cathode, manganese oxide, a spinel form of it, which accepts magnesium. So, the team can now make a full magnesium battery—with a magnesium anode, the electrolyte and the manganese oxide cathode—that works.
“It’s really early stage, it still isn’t performing anywhere near well enough for commercialization, but we now have a baseline to work with,” says Crabtree.
For battery technology there is another revolution coming just like in 1991, where nobody could predict the impact the lithium-ion battery would have on personal electronics. Overall, the lithium-ion battery changed the paradigm of how we receive information and treat and interact with people.
The new revolution of similar size will come when there is a 50% deployment of electric cars. “We are at a few percentage points now, 2 or maybe 3%,” says Crabtree. “But that will grow.”
The main thing holding this back is the batteries are too expensive and aren’t powerful enough. And the next generation of batteries being sought by commercial companies, academia and government labs could enable this 50% deployment of electric cars that will dramatically change the face of transportation (as they don’t emit any carbon).
Overall, the future of battery technology is very bright and is ripe for innovation. Just like the beginning of the semiconductor revolution, where there were tremendous advancements taking place, the stakes are high for battery development and commercialization.
It’s global race to the finish line, and the U.S. can now compete with our Asian competitors.
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