Aluminum Contamination Blocks Efficient Battery Recycling
Source： eepower
The demand for lithium-ion batteries is soaring as the global push for electrification intensifies. But this boom has brought an urgent question: How do we sustainably manage end-of-life batteries and recover critical materials without perpetuating environmental harm?
Offering a potential answer to that question, Hong Kong University of Science and Technology (HKUST) researchers have uncovered a previously unrecognized atomic-scale mechanism that fundamentally disrupts the efficiency of lithium-ion battery recycling.
The study in Advanced Science reveals that residual aluminum from battery disassembly infiltrates cathode crystal structures and blocks the release of critical metals such as nickel, cobalt, and manganese during chemical extraction. This breakthrough challenges long-standing assumptions in the field and directly impacts the design of next-generation recycling processes.
Lithium-ion batteries ready for recycling. Image used courtesy of Adobe Stock
A Hidden Chemical Obstruction
In conventional hydrometallurgical recycling, battery cells are shredded or crushed, and the resulting black mass, comprising cathode and anode materials, is chemically leached in solvents to extract valuable metals. However, the research team discovered that during mechanical disassembly, residual aluminum foil undergoes friction-induced infiltration into the cathode’s nickel-cobalt-manganese (NCM) lattice.
Atomic-resolution electron microscopy combined with density functional theory modeling showed that aluminum atoms substitute for cobalt atoms within the NCM structure. This substitution initiates the formation of ultra-stable aluminum-oxygen bonds that alter the lattice energetics and anchor oxygen ions, stabilizing the crystal and rendering it chemically inert during leaching.
This mechanism fundamentally suppresses metal leachability across several solvent systems. Even trace aluminum concentrations drastically inhibited nickel, cobalt, and manganese dissolution in strong acid (e.g., sulfuric acid), weak acid (e.g., formic acid), and green solvents like deep eutectic mixtures.
Solvent-Dependent Behavior and Leaching Kinetics
The extent of aluminum's interference is highly solvent-dependent. In formic acid, aluminum presence slows NCM materials dissolution by stabilizing lattice oxygen and reducing proton attack efficiency. However, the researchers observed enhanced metal extraction in ammonia-based leaching systems, potentially due to ligand substitution or aluminum complexation pathways destabilizing the matrix.
Deep eutectic solvents (DES), considered environmentally friendly alternatives, exhibited mixed behavior. The team speculated that the balance between complexing agents and lattice energetics in DES systems creates variable response profiles depending on the specific solvent composition and temperature.
Critically, the work revealed that conventional recycling approaches, designed under the assumption of chemically pristine cathodes, may be fundamentally miscalibrated when applied to real-world battery waste contaminated with embedded aluminum.
Beyond leaching resistance, aluminum contamination alters the cathode’s fundamental electrochemical behavior. Substituting aluminum for cobalt reduces the d-band electron availability, lowers crystal symmetry, and inhibits redox activity, which in turn diminishes the structural breakdown required for metal release during hydrometallurgical processing.
The resulting structural passivation has both a thermodynamic and kinetic impact: the Gibbs free energy of dissolution increases, and reaction rates decrease, reducing recovery yields and requiring harsher process conditions (e.g., higher acid concentrations or elevated temperatures), which undercut environmental and economic goals.
Graphite-Assisted Thermal Decomposition
To circumvent the problem, the HKUST team proposed a parallel strategy involving synchronous thermal decomposition aided by residual graphite from the battery’s anode. By activating interfacial carbon-oxygen bonds, the NCM cathode’s thermal breakdown occurs at significantly lower temperatures, enabling efficient lithium carbonate and transition metal oxides recovery.
This graphite-assisted decomposition reduces process energy demand and sidesteps the limitations of aluminum-induced passivation. Lithium is recovered as Li2CO3, while nickel, cobalt, and manganese precipitate as oxides. The implication is that multi-modal recycling approaches, which combine mechanical separation, chemical leaching, and low-temperature thermal treatments, will likely be necessary to address the compositional complexity of spent battery materials.