The smelting of lithium-ion batteries produces complex metallic alloys and mattes that require extensive downstream refining to achieve the purity levels necessary for battery remanufacturing. These intermediate products typically contain cobalt, nickel, copper, and other valuable metals in varying ratios depending on the original battery chemistry and smelting conditions. The refining process must accommodate this variability while consistently meeting stringent battery-grade specifications, generally requiring metal purities exceeding 99.8% for cathode active materials.

Electrolytic refining serves as a critical step for producing high-purity cobalt and nickel from smelter outputs. The process begins with the dissolution of nickel-cobalt mattes in sulfuric acid, forming a mixed sulfate solution. Impurities such as iron, copper, and manganese are removed through pH-controlled precipitation steps. Iron removal typically occurs at pH 3-3.5 through oxidation and precipitation as jarosite or goethite, while copper is eliminated via sulfide precipitation or solvent extraction. The purified solution then undergoes electrolysis in membrane-divided cells, where cobalt and nickel are deposited on stainless steel cathodes. Modern operations employ advanced potential control to selectively deposit either metal or produce controlled alloys. Cobalt deposits at lower potentials around -0.28V versus SHE, while nickel requires more negative potentials near -0.25V. Some facilities utilize chloride-based electrolytes for improved current efficiency and deposit morphology. The resulting cathode sheets are periodically harvested, washed, and vacuum-dried before size reduction to powder form.

Solvent extraction plays a complementary role in achieving ultra-high purity levels required for battery materials. The process leverages the differential complexation behavior of metal ions with organic extractants in multi-stage mixer-settler systems. For cobalt-nickel separation, phosphinic acid extractants like Cyanex 272 show high selectivity, with pH controlling the separation efficiency. In typical flowsheets, the aqueous feed at pH 5-6 contacts the organic phase, where cobalt preferentially transfers to the organic phase while nickel remains in the raffinate. Stripping the loaded organic phase with dilute sulfuric acid produces a purified cobalt solution with less than 0.1% nickel contamination. For operations processing mixed battery scrap, additional solvent extraction circuits may be incorporated to remove residual lithium, aluminum, and other minor elements. The flexibility of solvent extraction allows processors to adjust flow rates, stage numbers, and pH conditions to accommodate varying feed compositions from different battery smelting campaigns.

Final product forms depend on the intended cathode chemistry and customer specifications. For NMC (nickel-manganese-cobalt) precursor production, the refined nickel and cobalt sulfate solutions are blended in precise stoichiometric ratios with manganese sulfate, then fed to a continuous stirred-tank reactor for coprecipitation with sodium hydroxide and ammonium hydroxide. The resulting mixed hydroxide precipitate is filtered, washed, and spray-dried to form free-flowing powder. Alternatively, some refiners produce metal powders through thermal reduction of purified oxides or carbonyl processes, particularly for nickel. These powders serve as feedstock for cathode manufacturing through solid-state or solution-based synthesis routes. For LCO (lithium cobalt oxide) production, refined cobalt is converted to cobalt oxide or cobalt carbonate through precipitation or thermal decomposition, then mixed with lithium carbonate for high-temperature calcination.

The refining process must continuously adapt to handle compositional variations from battery smelting operations. Lithium-ion battery scrap varies significantly in cobalt-nickel ratios depending on the source, with consumer electronics batteries typically containing higher cobalt content compared to automotive batteries that favor nickel-rich chemistries. Advanced analytical techniques including X-ray fluorescence and inductively coupled plasma optical emission spectroscopy provide real-time feed characterization, enabling rapid adjustment of process parameters. Automated control systems modify reagent dosages, pH setpoints, and flow ratios to maintain product specifications despite feed variations. For operations processing mixed battery feeds, the integration of flexible solvent extraction circuits with buffer storage tanks allows for continuous operation despite discontinuous smelter outputs.

Purity requirements for battery materials continue to tighten, particularly regarding contaminant elements that impact electrochemical performance. Key specifications include limits on sodium, calcium, and magnesium below 10 ppm each, iron below 20 ppm, and sulfur below 100 ppm. Metallic impurities like zinc, copper, and chromium must be kept below 5 ppm due to their detrimental effects on cycle life and safety. The refining processes achieve these levels through multiple purification barriers, with electrolytic refining typically reducing impurities to 100-200 ppm levels, followed by solvent extraction to reach the final specifications. Final product certification involves comprehensive chemical analysis coupled with electrochemical testing in coin cells or small pouch cells to verify performance in actual battery systems.

Environmental considerations shape modern refining operations, particularly in water management and reagent recovery. Closed-loop water systems minimize liquid discharges, while spent electrolytes are regenerated through ion exchange or electrowinning of residual metals. Solvent extraction circuits incorporate advanced organic recovery systems to minimize extractant losses, typically keeping organic entrainment in aqueous streams below 10 ppm. The industry increasingly adopts life cycle assessment methodologies to optimize the environmental footprint of refining processes, balancing energy consumption, chemical usage, and metal recovery efficiency.

The integration of refining operations with upstream smelting and downstream cathode production creates opportunities for process optimization. Some facilities now employ direct solution transfer between refining and precursor production, eliminating intermediate drying steps and reducing energy consumption. Real-time data sharing between process stages enables dynamic adjustment of operating parameters based on final cathode performance requirements. These integrated approaches demonstrate how battery recycling has evolved from simple metal recovery to sophisticated material regeneration tailored for direct reuse in new energy storage devices.