The recovery of lithium from battery black mass has traditionally relied on hydrometallurgical processes involving acid leaching, solvent extraction, and precipitation. However, these methods face challenges such as high chemical consumption, wastewater generation, and complex purification steps. Alternative approaches that bypass conventional leaching are gaining attention for their potential to improve efficiency, reduce environmental impact, and enhance lithium recovery rates. Among these, mechanochemical activation, chlorination roasting, and other thermal or physical separation techniques offer promising pathways for direct lithium extraction.

Mechanochemical activation leverages mechanical energy to induce chemical reactions in black mass without extensive use of liquid reagents. This process involves high-energy ball milling, where mechanical forces break down the crystal structure of lithium-containing compounds, increasing their reactivity. The activated material can then undergo thermal treatment or react with low-cost reagents like sodium carbonate or aluminum chloride to convert lithium into soluble or volatile forms. Studies indicate that mechanochemical processing can achieve lithium recovery rates exceeding 90% while reducing acid consumption by up to 80% compared to traditional leaching. The energy input for milling varies but typically ranges between 50 and 150 kWh per ton of black mass, depending on the target particle size and reactivity. A key advantage is the ability to process mixed cathode chemistries, including lithium cobalt oxide, lithium nickel manganese cobalt oxide, and lithium iron phosphate, without extensive pre-sorting.

Chlorination roasting is another emerging method that selectively extracts lithium as lithium chloride through high-temperature reactions. In this process, black mass is mixed with a chlorinating agent such as calcium chloride or ammonium chloride and heated to temperatures between 800°C and 1100°C. The lithium compounds react to form volatile lithium chloride, which sublimes and can be condensed separately from other metals. This approach achieves lithium recovery rates of 85–95% with purity levels exceeding 99%. The remaining residue, containing nickel, cobalt, and manganese, can be processed through conventional methods. Chlorination roasting requires significant thermal energy, with estimates suggesting 500–700 kWh per ton of black mass, but it eliminates the need for acid leaching and reduces secondary waste generation. One limitation is the potential corrosion of equipment due to chlorine gas release, necessitating specialized reactor materials.

Other thermal separation techniques include carbothermal reduction and sulfation roasting. Carbothermal reduction involves heating black mass with a carbon source to convert lithium oxides into lithium carbonate or metallic lithium, which can then be separated via sublimation or dissolution. Sulfation roasting uses sulfate salts to transform lithium into water-soluble lithium sulfate while leaving transition metals as insoluble oxides. These methods can achieve lithium recoveries of 80–90% but require precise control of temperature and gas atmosphere to prevent unwanted side reactions. The energy demand for these processes ranges from 400 to 600 kWh per ton, comparable to chlorination roasting.

Physical separation methods, such as froth flotation and electrostatic separation, are also being explored for pre-concentrating lithium-bearing phases before further treatment. Froth flotation exploits differences in surface hydrophobicity to separate lithium-containing particles from other metals, while electrostatic separation relies on conductivity differences. These techniques are less energy-intensive, typically below 50 kWh per ton, but often require finely ground feed material and may not achieve high lithium purity alone. They are best suited as preliminary steps before thermal or chemical processing.

Purity requirements for recovered lithium depend on the intended application. Battery-grade lithium compounds must meet stringent specifications, such as lithium carbonate with less than 0.1% impurities or lithium hydroxide with less than 0.5% contaminants. Thermal methods like chlorination roasting can meet these standards with additional purification steps, such as recrystallization or ion exchange. Mechanochemical routes may require supplementary refining due to residual reagents or co-extracted impurities. In contrast, hydrometallurgical processes traditionally achieve high purity but at the cost of multiple purification stages and higher reagent use.

Energy intensity is a critical factor in evaluating commercial viability. Hydrometallurgical routes typically consume 200–400 kWh per ton of black mass for leaching and precipitation, excluding additional energy for wastewater treatment and solvent recovery. Thermal methods, while more energy-intensive upfront, often streamline downstream processing and reduce chemical consumption. For example, chlorination roasting may have higher thermal energy demands but avoids the need for acid regeneration and neutralization steps. Mechanochemical activation offers a middle ground, with moderate energy use and reduced chemical dependency.

Commercial adoption of these alternative methods depends on scalability, operational costs, and integration with existing recycling infrastructure. Pilot-scale trials of mechanochemical and chlorination processes have demonstrated technical feasibility, but broader implementation requires optimization for varying feed compositions and larger throughputs. Capital costs for thermal systems are generally higher than for hydrometallurgical plants due to the need for high-temperature reactors and gas handling systems. However, operational savings from reduced chemical use and waste treatment can offset these costs over time.

Compared to hydrometallurgical routes, direct extraction methods offer distinct advantages in sustainability and simplicity. They minimize liquid waste generation, reduce reliance on corrosive acids, and often yield higher lithium recovery rates. However, challenges remain in scaling these technologies, ensuring consistent product quality, and managing energy consumption. Ongoing research focuses on hybrid approaches that combine the strengths of thermal, mechanical, and minimal-chemical processes to optimize lithium recovery from black mass. As battery recycling demand grows, these innovative extraction methods may play a pivotal role in establishing a more efficient and sustainable lithium supply chain.