This is the novel lithium-ion battery developed by researchers at Georgia Tech. It uses a promising new cathode and electrolyte system that replaces the expensive metals and traditional liquid electrolyte with lower cost transition metal fluorides and a solid polymer electrolyte. Photo: Allison Carter.The growing popularity of lithium-ion batteries in recent years has put a strain on the world's supply of cobalt and nickel – two metals integral to current battery designs – and sent prices surging. In a bid to develop alternative designs for lithium-based batteries that rely less on those scarce metals, researchers at the Georgia Institute of Technology (Georgia Tech) have developed a promising new cathode and electrolyte system that replaces the expensive metals and traditional liquid electrolyte with lower-cost transition metal fluorides and a solid polymer electrolyte.
"Electrodes made from transition metal fluorides have long shown stability problems and rapid failure, leading to significant skepticism about their ability to be used in next generation batteries," said Gleb Yushin, a professor in Georgia Tech's School of Materials Science and Engineering. "But we've shown that when used with a solid polymer electrolyte, the metal fluorides show remarkable stability – even at higher temperatures – which could eventually lead to safer, lighter and cheaper lithium-ion batteries."
In a typical lithium-ion battery, energy is released during the transfer of lithium ions between two electrodes – an anode and a cathode, with the cathode typically comprising lithium and transition metals such as cobalt, nickel and manganese. The ions flow between the two electrodes through a liquid electrolyte.
For this study, which was sponsored by the US Army Research Office and reported in a paper in Nature Materials, the research team fabricated a new type of cathode from an iron fluoride active material and a solid polymer electrolyte nanocomposite. Iron fluorides have more than double the lithium capacity of traditional cobalt- or nickel-based cathodes. In addition, iron is 300 times cheaper than cobalt and 150 times cheaper than nickel.
To produce such a cathode, the researchers developed a process for infiltrating a solid polymer electrolyte into the prefabricated iron fluoride electrode. They then hot pressed the entire structure to increase its density and reduce any voids.
Two central features of the polymer-based electrolyte are its ability to flex and accommodate the swelling of the iron fluoride while cycling, and its ability to form a very stable and flexible interphase with iron fluoride. Swelling and massive side reactions have been key problems with using iron fluoride in previous battery designs.
"Cathodes made from iron fluoride have enormous potential because of their high capacity, low material costs and very broad availability of iron," Yushin said. "But the volume changes during cycling, as well as parasitic side reactions with liquid electrolytes and other degradation issues, have limited their use previously. Using a solid electrolyte with elastic properties solves many of these problems."
The researchers tested several variations of the new solid-state batteries to analyze their performance over more than 300 cycles of charging and discharging at an elevated temperature of 122°F. They found that the batteries outperformed previous designs that used metal fluoride, even when the previous designs were kept cool at room temperatures.
They also found that the key to the enhanced battery performance was the solid polymer electrolyte. In previous attempts to use metal fluorides, it was believed that metallic ions migrated to the surface of the cathode and eventually dissolved into the liquid electrolyte, causing a capacity loss, particularly at elevated temperatures. In addition, the metal fluorides catalyzed the massive decomposition of liquid electrolytes when cells were operating above 100°F. However, at the connection between the solid electrolyte and the iron fluoride cathode, such dissolving doesn't take place and the solid electrolyte remained remarkably stable, preventing such degradations.
"The polymer electrolyte we used was very common, but many other solid electrolytes and other battery or electrode architectures – such as core-shell particle morphologies – should be able to similarly dramatically mitigate or even fully prevent parasitic side reactions and attain stable performance characteristics," said Kostiantyn Turcheniuk, research scientist in Yushin's lab and a co-author of the paper.
In the future, the researchers aim to develop new and improved solid electrolytes to allow fast charging. They also aim to combine solid and liquid electrolytes in new designs that are fully compatible with conventional cell manufacturing technologies employed in large battery factories.
This story is adapted from material from the Georgia Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.