Addressing the reliance on cobalt is a central aspect of the ongoing development of lithium-ion batteries for the electric vehicle (EV) market. The cathode is a key battery component that determines energy density, cost, and safety. Nickel-rich cathodes offer the high energy density needed for long-range EVs, but their traditional reliance on cobalt has created technical and supply chain issues.
This article discusses the primary technical considerations related to the transition toward low-cobalt and cobalt-free cathode materials.
Why is reducing cobalt a priority for EV batteries?
The effort to reduce or eliminate cobalt from EV cathodes is based on economic, geopolitical, and ethical considerations. As the most costly raw material in the cathode, cobalt’s price volatility creates financial uncertainty for manufacturers. The supply chain is also a key consideration. Approximately 75% of global cobalt is mined in the Democratic Republic of Congo and refined in China. This results in a concentrated supply chain with vulnerabilities related to geopolitical risk and documented human rights issues.
To move away from cobalt without sacrificing performance, the industry has focused on nickel-rich chemistries. The primary reason is energy density. As shown in Figure 1, while other cobalt-free alternatives like iron-based (LFP) or manganese-based (LMO) cathodes offer advantages in cost and safety, they cannot match the high energy density of nickel-based systems.
Therefore, the engineering goal is to improve the weaker metrics of Ni-rich cathodes, such as thermal stability and cycle life, to create a material that combines high energy with safety, durability, and a lower cost.
Figure 1. Performance trade-offs of Ni-based, Fe-based, and Mn-based cathode materials. (Image: ACS Energy Letters)
What happens to the cathode’s stability when cobalt is removed?
In layered-oxide cathodes, cobalt provides essential structural and chemical stability. Removing it without implementing compensatory measures leads to rapid performance degradation through several key mechanisms: cation mixing (where nickel ions block lithium pathways), microcrack formation due to internal stress, and surface instability from parasitic reactions with the electrolyte.
To address these issues, engineers employ materials engineering strategies, primarily compositional doping, to introduce other elements that replicate cobalt’s stabilizing functions.
Key dopants include Aluminum (Al) for suppressing side reactions, Magnesium (Mg) to act as a structural “pillar” preventing lattice collapse, and Tungsten (W) for enhancing long-term stability The most promising among these is NMA (Lithium Nickel Manganese Aluminum Oxide).
Compositions like LiNi0.80Mn0.13Al0.07O2, and LiNi0.85Mn0.09Al0.06O2 use a synergistic combination of manganese and aluminum to provide the necessary stability, enabling high energy density in a cobalt-free system.
How do structural and surface engineering work together to create a better cathode?
Beyond chemical composition, the physical engineering of cathode particles and their surfaces is important for mitigating mechanical stress and improving safety.
Structural Engineering: Conventional cathodes consist of polycrystalline agglomerates, where the grain boundaries serve as initiation sites for microcracks. A strategy to prevent this is synthesizing the cathode as a single crystal. As illustrated in Figure 2, this approach eliminates grain boundaries entirely, creating a more robust particle with an unobstructed pathway for lithium ions, and enhances durability. Another effective strategy is creating core-shell structures, which feature a high-nickel core (for capacity) and a more stable, manganese-rich outer shell.
Figure 2. The Li-ion pathways in polycrystalline versus single-crystal NMC cathodes, illustrating the impact of grain boundaries. (Image: MDPI)
Surface modification: A protective coating provides a final line of defense, isolating the reactive cathode surface from the liquid electrolyte. An ultrathin coating of a material like zirconia, carbon, or LFP acts as a physical barrier that prevents side reactions and improves stability.
As shown by the thermal runaway data in Figure 3, an LFP coating on an NMC cathode significantly enhances thermal safety, delaying catastrophic failure from 796 minutes (at 147° C) to 989 minutes (at 153° C).
Figure 3. Thermal stability comparison of an uncoated NMC cathode (left) and an LFP-coated NMC cathode (right). (Image: MDPI)
What are the related challenges in manufacturing, and the rest of the battery?
The development of advanced cathodes extends beyond material science to include manufacturing and system-level integration. Complex particle morphologies, like single crystals or core-shell structures, require precise synthesis control. In industrial settings, cathode precursors are commonly produced through co-precipitation in large-scale reactors.
A primary consideration in scaling these processes is maintaining batch-to-batch uniformity and the structural integrity required for consistent performance.
A high-performance cathode must also be paired with a compatible anode to optimize cell performance. The increased capacity of nickel-rich cathodes can be limited by traditional graphite anodes, affecting overall cell performance and cycle life. This has prompted research into higher-capacity anode materials, such as silicon composites. However, silicon undergoes significant volume expansion during cycling, which requires specific mitigation strategies.
Finally, sustainability goals for battery production are supported by a circular economy model. In addition to reducing cobalt, the industry is focused on developing efficient recycling processes. Direct recycling methods, for example, aim to regenerate and recycle spent cathode materials.
This approach restores their structure and performance without the energy-intensive process of breaking them down into elemental components, which is beneficial for recovering materials like nickel and lithium and reducing the environmental footprint of battery production.
Summary
Reducing cobalt in EV batteries is driven by cost, supply chain, and ethical concerns, presenting a key materials engineering challenge. The focus is on nickel-rich cathodes for their superior energy density, which is important for long-range performance.
However, removing cobalt compromises cathode stability. To counteract this, an integrated engineering approach is employed, which includes chemical doping, structural design, and surface coatings. This combination of strategies is essential for realizing the high energy potential of nickel-rich systems in a stable, safe, and commercially viable manner for future EVs.
References
- Recent Development of Nickel-Rich and Cobalt-Free Cathode Materials for Lithium-Ion Batteries, Batteries, MDPI
- An overview of various critical aspects of low cobalt/cobalt-free Li-ion battery cathodes, Royal Society of Chemistry
- Can Cobalt Be Eliminated from Lithium-Ion Batteries?, ACS Energy Letters
- The Latest Trends in Electric Vehicles Batteries, Molecules, MDPI
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