Niobium boosts lithium battery potential
Reduces 20% loss that has long plagued nickel-rich cathodes Metal Tech News – August 11, 2021
Last updated 8/17/2021 at 3:02pm
Niobium, a metal best known for its ability to strengthen steel, may also be the secret ingredient that allows lithium-ion batteries to live up to their full potential.
One problem with the lithium-ion batteries powering electric vehicles, smartphones, laptops, power tools, and thousands of other applications is they lose nearly a fifth of their storage capacity the first time they are charged up.
The reason for this loss is the formation of impurities on the nickel-rich cathodes – the positive side of a battery.
While this problem has long been understood, the solution to this unwanted buildup and power storage loss has not. More than 40 years after first describing the concept of rechargeable lithium-ion batteries, M. Stanley Whittingham is leading research that could unleash the full potential of this world-changing technology.
Whittingham, which shared the 2019 Nobel Prize in Chemistry with fellow lithium-ion battery pioneers John Goodenough and Akira Yoshino, has found that a niobium coating can significantly reduce the first cycle energy loss.
The Whittingham-led research team that included colleagues from the State University of New York at Binghamton and scientists at the Department of Energy's Brookhaven and Oak Ridge national laboratories used x-rays and neutrons to test whether treating a leading cathode material with a lithium-free niobium oxide would lead to a longer-lasting battery.
Lithium batteries have cathodes made of alternating layers of lithium and oxide materials. Because it is relatively inexpensive and helps deliver higher energy density and greater storage capacity at a lower cost than other metals, nickel is often the main ingredient in these cathodes.
Whittingham and his team carried out their tests on NMC 811 cathodes – 80% nickel, 10% manganese, and 10% cobalt – a popular choice for EVs.
"We tested NMC 811 on a layered oxide cathode material after predicting the lithium-free niobium oxide would form a nanosized lithium niobium oxide coating on the surface that would conduct lithium ions and allow them to penetrate into the cathode material," said Whittingham, now a distinguished professor at State University of New York.
Although nickel has a lot of attributes that make it the metal of choice for high-performance lithium-ion batteries, it has one major drawback – it reacts easily with other elements, leaving the cathode surface covered in undesirable impurities that reduce the battery's storage capacity by 10-18% during its first charge-discharge cycle.
Nickel can also cause instability in the interior of the cathode structure, which further reduces storage capacity over extended periods of charging and discharging.
Whittingham's research team found that adding niobium to the NMC 811 cathodes reduced first-cycle capacity loss, and after 250 charge-discharge cycles, these cathodes retained greater than 93% of their original capacity.
"The improvements seen in electrochemical performance and structural stability make niobium-modified NMC 811 a candidate as a cathode material for use in higher energy density applications, such as electric vehicles," said Whittingham.
To understand how the niobium affects nickel-rich cathode materials, the scientists used specialized equipment at the Oak Ridge National Laboratory Spallation Neutron Source to measure the neutron diffraction patterns of pure NMC 811 and niobium-modified samples.
"Neutrons easily penetrated the cathode material to reveal where the niobium and lithium atoms were located, which provided a better understanding of how the niobium modification process works," said Hui Zhou, battery facility manager at the Northeast Center for Chemical Energy Storage, a DOE Energy Frontier Research Center. "The neutron scattering data suggests the niobium atoms stabilize the surface to reduce first-cycle loss, while at higher temperatures the niobium atoms displace some of the manganese atoms deeper inside the cathode material to improve long-term capacity retention."
This indicates that niobium may have a dual role to play in realizing the full potential of lithium-ion batteries with nickel-rich cathodes.
"Combining a niobium coating with the substitution of niobium atoms for manganese atoms may be a better way to increase both initial capacity and long-term capacity retention," said Whittingham. "These modifications can be easily scaled-up using the present multi-step manufacturing processes for NMC materials."
The founding father of lithium-ion batteries says the niobium research supports the objectives of the Battery500 Consortium, a multi-institution program led by the DOE's Pacific Northwest National Laboratory to develop next-generation lithium-metal battery cells that deliver up to 500-watt hours per kilogram versus the current average of about 220-watt hours per kilogram.