The US Department of Energy’s (DOE) Argonne National Laboratory has developed a new dual gradient cathode design that improves the performance and reduces the costs of lithium-ion batteries. A paper on the dual gradient work is published in Nature Energy.

Cathodes for next-generation batteries are pressed for higher voltage operation (≥4.5V) to achieve high capacity with long cyclability and thermal tolerance. Current cathodes fail to meet these requirements owing to structural and electrochemical strains at high voltages, leading to fast capacity fading. Here we present a cathode with a coherent architecture ranging from ordered to disordered frameworks with concentration gradient and controllable Ni oxidation activities, which can overcome voltage ceilings imposed by existing cathodes. This design enables simultaneous high-capacity and high-voltage operation at 4.5V without capacity fading, and up to 4.7 V with negligible capacity decay.

Multiscale diffraction and imaging techniques reveal the disordered surface is electrochemically and structurally indestructible, preventing surface parasitic reactions and phase transitions. Structural coherence from ordering to disordering limits lattice parameter changes, mitigating lattice strain and enhancing morphological integrity. The dual-gradient design also notably improves thermal stability, driving the advancement of high-performance cathode materials.

—Liu et al.

This latest discovery continues Argonne’s decades-long history of leadership and innovation in battery research.

In 2012, Argonne researchers advanced the state-of-the-art for lithium-ion batteries with a novel cathode material that significantly increased energy density and durability. The team fine-tuned the composition of nickel, manganese and cobalt in cathode particles to harness optimally the beneficial characteristics of these metals.

Nickel can increase energy density but also make the surface of the particles too reactive. In Argonne’s design, called a composition gradient, the nickel concentration gradually decreases from the particle core to surface. The idea was to maximize energy density at high-voltage battery operation and minimize reactivity. The high energy density enables the production of smaller, lower-cost batteries.

The Argonne design has been patented and licensed to battery and materials manufacturers. Even with the great success of the design, the Argonne team recently began exploring ways to improve it further.

High-voltage operation tends to cause cathode particles with layered, ordered structures to crack and react more with the battery’s electrolyte. Electrolytes move lithium ions between a battery’s two electrodes, converting stored energy into electricity. This quickly degrades the cathodes, reducing the battery’s capacity and lifetime while increasing safety concerns.

The team’s solution was to add another wrinkle to its composition—gradient cathode design. This involved fabricating cathode particles in which the structure gradually transitions from disordered material on the surface to ordered, layered material in the core.

The particles still possess a concentration gradient involving nickel, manganese and cobalt. The main difference is that the surface is enriched in cobalt and the interior nearly cobalt-free.

The idea behind this approach was to combine the best aspects of different compositions and structures into a single particle. The disordered particle surface would suppress cracking and reactivity while the ordered core would maximize ion transport. In this way, the cathode can potentially achieve high capacity and stability while operating at high voltages.

The team performed a series of X-ray, electron and imaging experiments to characterize the new cathode material at rest and while operating. Together, these tests assessed the material at the cathode, particle and atomic levels. The aim was to provide a comprehensive picture of composition, structure and performance. These analyses were carried out at the Advanced Photon Source and Center for Nanoscale Materials at Argonne, as well as the National Synchrotron Light Source II at DOE’s Brookhaven National Laboratory. These are all DOE Office of Science user facilities.

The tests confirmed that the fabrication successfully produced cathode particles with the above structure and composition gradients. Importantly, they showed that the particles remained structurally and chemically stable during high-voltage operation.

We proved that the disordered particle surface is indestructible, with virtually no reactivity or structural strain.

—Tongchao Liu, lead autho

The dual-gradient particles were much more durable than the original Argonne design. After charging and discharging the material 500 times, it lost only about 2% of its storage capacity. Based on this finding, the team expects that the material can support a much longer battery lifetime.

The design reduced the overall amount of cobalt in the cathode material. This is important because cobalt is a scarce, costly material and its extraction can have adverse environmental impacts. Composition measurements revealed that most of the cobalt was on the particle surface. The cobalt concentration in the particle’s interior was less than 2% —down from 10-20% in the original design.

The team also found that the design enhanced the cathode’s ability to withstand

heat. Heat tolerance is crucial to ensure safe operations at high voltage.

The study marks the first time that composition and structure gradients have been combined in a single cathode particle. It is expected to inspire new lines of research on cathodes that integrate different structures and compositions to enhance battery performance.

This breakthrough material represents an across-the-board improvement for batteries. It features higher storage capacity, robust stability and heat tolerance at high voltages, and longer lifetimes. Its high energy density enables production of smaller, lower-cost batteries, supporting widespread adoption of EVs and grid batteries. Our patented design and fabrication process is ready to be licensed by industry.

— Khalil Amine, Argonne Distinguished Fellow and leader of Argonne’s Advanced Battery Technology team

This research was supported by DOE’s Vehicle Technologies Office.

Resources

• Liu, T., Yu, L., Liu, J. et al. Ultrastable cathodes enabled by compositional and structural dual-gradient design. Nat Energy 9, 1252–1263 (2024). doi: 10.1038/s41560-024-01605-8