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UCI and national lab researchers use high-entropy doping for cobalt-free cathodes for Li-ion batteries

Researchers at the University of California, Irvine and four national laboratories have devised a way to make lithium-ion battery cathodes without using cobalt. In a paper published in Nature, the scientists describe how they overcame thermal and chemical-mechanical instabilities of cathodes composed substantially of nickel by mixing in several other metallic elements.

Through a technique we refer to as ‘high-entropy doping,’ we were able to successfully fabricate a cobalt-free layered cathode with extremely high heat tolerance and stability over repeated charge and discharge cycles. This achievement resolves long-standing safety and stability concerns around high-nickel battery materials, paving the way for broad-based commercial applications.

—corresponding author Huolin Xin, UCI professor of physics & astronomy

Cobalt is one of the most significant supply chain risks threatening widespread adoption of electric cars, trucks and other electronic devices requiring batteries, according to the paper’s authors. The mineral, which is chemically suited for the purpose of stabilizing lithium-ion battery cathodes, is mined almost exclusively in the Democratic Republic of Congo under abusive and inhumane conditions.

Electric vehicle manufacturers are eager to curtail the use of cobalt in their battery packs not only for cost reduction but to counter the child labor practices used to mine the mineral. Research has also shown that cobalt can lead to oxygen release at high voltage, causing damage to lithium-ion batteries. All of this points to a need for alternatives.

—Huolin Xin

However, nickel-based cathodes come with their own problems, such as poor heat tolerance, which can lead to oxidization of battery materials, thermal runaway and even explosion. Although high-nickel cathodes accommodate larger capacities, volume strain from repeated expansion and contraction can result in poor stability and safety concerns.

The researchers sought to address these issues through compositionally complex high-entropy doping using HE-LMNO, an amalgamation of transition metals magnesium, titanium, manganese, molybdenum and niobium in the structure’s interior, with a subset of these minerals used on its surface and interface with other battery materials.

Xin and his colleagues employed an array of synchrotron X-ray diffraction, transmission electron microscopy and 3D nanotomography instruments to determine that their zero-cobalt cathode exhibited an unprecedented volumetric change of zero during repeated use. The highly stable structure is capable of withstanding more than 1,000 cycles and high temperatures, which makes it comparable to cathodes with much lower nickel content.

… by using a new compositionally complex (high-entropy) doping strategy, we successfully fabricate a high-Ni, zero-Co layered cathode that has extremely high thermal and cycling stability. Combining X-ray diffraction, transmission electron microscopy and nanotomography, we find that the cathode exhibits nearly zero volumetric change over a wide electrochemical window, resulting in greatly reduced lattice defects and local strain-induced cracks. In-situ heating experiments reveal that the thermal stability of the new cathode is significantly improved, reaching the level of the ultra-stable NMC-532. Owing to the considerably increased thermal stability and the zero volumetric change, it exhibits greatly improved capacity retention.

—Zhang et al.

This project, which was funded by the US Department of Energy Office of Energy Efficiency and Renewable Energy, also involved researchers from Argonne National Laboratory, Pacific Northwest National Laboratory and SLAC National Accelerator Laboratory.

Resources

  • Zhang, R., Wang, C., Zou, P. et al. (2022) “Compositionally complex doping for zero-strain zero-cobalt layered cathodes.” Nature doi: 10.1038/s41586-022-05115-z

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