The recovery of cobalt from lithium cobalt oxide (LCO) cathodes is a critical process in battery recycling due to the high economic value of cobalt and its importance in cathode manufacturing. LCO cathodes, commonly used in consumer electronics, contain approximately 60% cobalt by weight, making them a prime target for reclamation. Three primary methods dominate cobalt recovery from LCO: direct recycling, re-lithiation, and acid leaching. Each approach has distinct advantages and challenges in terms of efficiency, cost, and material purity.

Direct recycling focuses on preserving the cathode structure while recovering cobalt in its oxide form. This method involves mechanical separation of the cathode material from aluminum foil current collectors, followed by thermal or chemical treatment to remove residual binders and electrolytes. Thermal annealing at temperatures between 500°C and 800°C in an oxygen-rich environment decomposes organic components while restoring the LCO crystal structure. The process avoids breaking down the cathode into its constituent elements, reducing energy consumption compared to traditional pyrometallurgy. However, direct recycling requires precise control of annealing conditions to prevent lithium loss or cobalt oxidation state changes, which can degrade electrochemical performance. The recovered LCO powder can be directly reused in new cathodes after particle size adjustment and surface treatment.

Re-lithiation addresses one of the key challenges in direct recycling: lithium loss during battery cycling and recycling. LCO cathodes degrade over time due to lithium depletion, resulting in Li1-xCoO2, where x increases with cycling. Re-lithiation involves reintroducing lithium into the structure through solid-state reactions or solution-based methods. In solid-state re-lithiation, a lithium source such as Li2CO3 or LiOH is mixed with degraded LCO and heated to 600–800°C. The process restores the original LiCoO2 stoichiometry but requires careful temperature control to avoid cobalt reduction to metallic form. Solution-based re-lithiation uses lithium-containing solutions at lower temperatures, typically below 200°C, reducing energy consumption. The effectiveness of re-lithiation depends on the initial degree of delithiation, with heavily degraded cathodes requiring more aggressive conditions. Re-lithiated LCO typically achieves 90–95% of its original capacity, making it suitable for less demanding applications.

Acid leaching is the most widely used industrial method for cobalt recovery from LCO due to its high extraction efficiency and scalability. The process involves dissolving cathode material in acidic solutions, typically sulfuric acid (H2SO4) or hydrochloric acid (HCl), at concentrations of 1–4 mol/L. Reductants such as hydrogen peroxide (H2O2) are added to accelerate dissolution by reducing Co3+ to more soluble Co2+. Optimal leaching occurs at 60–90°C with solid-to-liquid ratios of 20–50 g/L, achieving cobalt extraction rates above 98%. The leachate contains cobalt ions along with aluminum, copper, and lithium impurities, which require subsequent purification steps. A key advantage of acid leaching is its ability to process heavily degraded or contaminated cathodes that cannot be directly recycled. However, the method generates acidic waste streams that require neutralization and treatment, adding to operational costs.

Following leaching, cobalt is separated from the solution through precipitation or solvent extraction. Precipitation involves adjusting the pH to selectively deposit cobalt as hydroxide or carbonate. At pH 7–8, cobalt hydroxide (Co(OH)2) forms while most aluminum and lithium remain in solution. Sodium hydroxide (NaOH) or sodium carbonate (Na2CO3) are common precipitating agents. Solvent extraction offers higher purity by using organic extractants like di-(2-ethylhexyl) phosphoric acid (D2EHPA) or Cyanex 272 to selectively transfer cobalt ions from the aqueous phase to an organic phase. The extracted cobalt is then stripped back into an acidic solution for further processing. Both methods produce cobalt intermediates that can be converted to battery-grade cobalt sulfate (CoSO4) or cobalt oxide (Co3O4) through additional refining steps.

The choice between these methods depends on economic and environmental factors. Direct recycling and re-lithiation offer lower energy consumption and higher value retention but are limited to cathodes with minimal degradation. Acid leaching provides universal applicability but requires more extensive downstream processing. Industrial operations often combine approaches, using direct recycling for high-quality scrap and leaching for heavily degraded material. Advances in separation technologies and process optimization continue to improve the efficiency and sustainability of cobalt reclamation from LCO cathodes, supporting the circular economy for battery materials.

Material balance considerations are critical in all three methods. For every ton of LCO cathode material processed, approximately 600 kg of cobalt can be recovered through efficient leaching and purification. Direct recycling yields higher material retention but requires nearly intact cathode structures. Energy consumption varies significantly, with acid leaching consuming 5–10 kWh per kg of recovered cobalt, while direct recycling consumes 2–4 kWh per kg. These metrics underscore the trade-offs between material recovery rates and process intensity.

Emerging developments in cobalt reclamation focus on reducing chemical usage and improving selectivity. Organic acids such as citric acid and ascorbic acid are being investigated as environmentally friendly alternatives to mineral acids. Electrochemical methods for direct cobalt recovery from leachates are also gaining attention, potentially eliminating the need for precipitation or solvent extraction. These innovations aim to lower the environmental footprint of cobalt recycling while maintaining high recovery rates and material purity.

The successful reclamation of cobalt from LCO cathodes ensures a stable supply of this critical material while reducing reliance on primary mining. As battery demand grows, efficient recycling processes will become increasingly important for sustainable battery production. Continued research into improved separation techniques and process integration will further enhance the viability of cobalt recovery from spent LCO cathodes.