The shift toward low-cobalt and cobalt-free battery chemistries, particularly high-nickel formulations like NMC 811 or lithium iron phosphate (LFP), presents unique challenges for recycling through hydrometallurgical processes. Traditional hydrometallurgical methods were optimized for cobalt-rich cathodes, where cobalt was the primary economic driver for recovery. However, as battery compositions evolve, recycling techniques must adapt to maintain efficiency, cost-effectiveness, and environmental sustainability. Key challenges include improving leaching selectivity and optimizing nickel-lithium separation, both of which are critical for the economic viability of recycling low-cobalt chemistries.

Hydrometallurgical recycling typically involves leaching, purification, and recovery stages. In cobalt-rich systems, sulfuric acid leaching with hydrogen peroxide as a reducing agent effectively dissolves cobalt, nickel, and manganese, with cobalt often selectively recovered first due to its higher value. However, high-nickel or cobalt-free cathodes alter the dynamics of leaching and downstream processing. The lower cobalt content reduces the economic incentive for its recovery, while the higher nickel concentration introduces complexities in separation, particularly from lithium.

Leaching selectivity becomes a major hurdle when processing high-nickel cathodes. Nickel and lithium exhibit similar leaching behaviors under standard acidic conditions, making their separation more challenging than cobalt-lithium separation. In traditional systems, cobalt could be preferentially extracted using solvents like Cyanex 272, leaving nickel and lithium in the solution. With cobalt absent or minimal, the focus shifts to separating nickel from lithium, which requires alternative solvents or adjusted process parameters. For instance, phosphate-based extractants or mixed solvent systems have shown promise in selectively isolating nickel from lithium-rich solutions. The pH of the leaching solution also plays a critical role; maintaining a lower pH can enhance nickel dissolution but may co-dissolve more lithium, necessitating careful optimization.

Another challenge is the high solubility of lithium in aqueous systems, which complicates its recovery. In cobalt-rich systems, lithium is often recovered from the residual solution after cobalt and nickel extraction, typically as lithium carbonate or phosphate. However, in high-nickel systems, the higher nickel-to-lithium ratio means that even small losses of lithium during nickel removal can significantly impact overall lithium recovery yields. To address this, staged leaching or precipitation techniques can be employed. For example, controlled precipitation of nickel as nickel hydroxide or sulfate at specific pH levels can reduce lithium co-precipitation, though this requires precise control to avoid lithium entrainment.

The choice of leaching agents also needs reevaluation for low-cobalt chemistries. While sulfuric acid remains widely used, alternative lixiviants like hydrochloric acid or organic acids (e.g., citric or oxalic acid) may offer better selectivity for nickel over lithium. Organic acids, in particular, can provide milder leaching conditions, reducing energy consumption and minimizing unwanted side reactions. However, their higher cost and lower leaching kinetics compared to sulfuric acid must be balanced against potential benefits in selectivity and environmental impact.

Innovations in solvent extraction and membrane technologies are also critical for adapting hydrometallurgical processes. Solvent extraction systems tailored for nickel-lithium separation, such as those using synergistic extractants or modified phosphonic acids, are under development. Membrane-based methods, including nanofiltration or electrodialysis, offer potential for continuous, energy-efficient separation of nickel and lithium without the need for extensive chemical additions. These technologies are still in the early stages of deployment but could significantly improve the sustainability of recycling low-cobalt batteries.

Process integration and waste minimization are additional considerations. High-nickel cathodes often contain aluminum current collectors, which can interfere with leaching if not removed beforehand. Pre-treatment steps like mechanical separation or alkaline leaching may be necessary to reduce aluminum contamination, which otherwise consumes acid and complicates downstream purification. Similarly, fluoride impurities from PVDF binders or electrolyte salts must be managed to prevent equipment corrosion and product contamination.

The economic viability of recycling low-cobalt batteries hinges on maximizing the recovery of nickel and lithium while minimizing processing costs. Nickel’s value makes its recovery essential, but lithium recovery cannot be neglected, especially with rising demand for lithium-ion batteries. Process innovations that reduce reagent consumption, energy use, and waste generation will be crucial for maintaining profitability. For instance, closed-loop systems that regenerate leaching agents or recover byproducts like aluminum or fluorides can improve both economics and environmental performance.

Regulatory and industry standards will also influence the adoption of adapted hydrometallurgical processes. As governments impose stricter recycling targets and material recovery requirements, recyclers must demonstrate efficient nickel and lithium recovery from low-cobalt streams. Standardized methods for assessing recovery rates and purity will be necessary to ensure consistency across the industry.

In summary, the transition to low-cobalt and cobalt-free battery chemistries demands significant adjustments to hydrometallurgical recycling processes. Key focus areas include enhancing leaching selectivity, optimizing nickel-lithium separation, and integrating sustainable process innovations. While challenges remain, advances in solvent extraction, membrane technologies, and process design are paving the way for efficient and economically viable recycling of high-nickel and cobalt-free batteries. The success of these adaptations will play a pivotal role in supporting the circular economy for advanced battery materials.