The escalating demand for lithium, driven by the rapid growth of electric vehicles, has led to a dramatic price increase. Securing a reliable and cost-effective lithium supply chain is crucial, necessitating exploration of alternative extraction sources beyond the currently dominant brine-based methods. Brine extraction, while currently cost-effective, suffers from drawbacks including large footprints, lengthy extraction times, soil pollution, and geographically limited resources. Lithium-bearing ores, such as spodumene, offer a more geographically diverse alternative, and spodumene is particularly attractive due to its high lithium concentration. Traditional leaching methods involving strong acids or bases at high temperatures are energy-intensive and environmentally impactful. Acid leaching involves proton exchange with Li⁺, while base leaching breaks Si-O bonds to release Li⁺. Both processes present significant drawbacks: high-temperature calcination is needed for acid leaching, increasing energy consumption, and base leaching requires subsequent impurity separation. The development of more sustainable leaching techniques is paramount to meeting the growing demand for lithium while minimizing environmental impact. Electrochemical leaching, which employs an electric field to facilitate metal ion dissolution, offers a promising alternative. This method overcomes the limitations of chemical leaching by reducing reliance on high temperatures and high concentrations of leaching agents, improving sustainability by allowing the use of renewable energy sources. However, challenges remain, including overcoming the heterogeneous nature of the electrochemical reaction, which can lead to large overpotentials, side reactions, and poor Faraday efficiency. The addition of soluble leaching promoters, such as H₂O₂, can improve electron transfer kinetics, but their decomposition and storage present safety concerns. Traditional 2-dimensional current collectors also limit mass transport, hindering high-throughput leaching. This study addresses these challenges by focusing on improving both electron and mass transport to enable large-scale electrochemical lithium extraction.

Existing literature highlights the urgent need for sustainable lithium extraction methods due to increasing demand and limitations of traditional processes. Studies have investigated various approaches, including chemical leaching using strong acids or bases at elevated temperatures. These approaches, however, suffer from high energy consumption (acid leaching requiring high-temperature calcination) or the need for subsequent steps to remove impurities (base leaching). Research on electrochemical leaching of metals from electronic waste and spent lithium-ion batteries has shown promise, but the application to spodumene extraction has been less explored. The use of leaching promoters like H₂O₂ in electrochemical leaching has been investigated, demonstrating improved electron transfer kinetics. However, challenges related to promoter decomposition and mass transport remain. The existing literature underscores the necessity of developing improved electrochemical leaching methods that address these challenges, offering both sustainability and scalability for lithium extraction from spodumene.

This study investigated the electrochemical leaching of lithium directly from α-phase spodumene using a 0.5 M sulfuric acid electrolyte at room temperature. The impact of morphology, crystal structure, and surface chemistry on leaching efficiency were studied using techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The addition of H₂O₂ as a promoter was examined, and its effectiveness was evaluated using thermodynamic calculations and linear sweep voltammetry (LSV). XRD and TEM were employed to analyze the structural changes in spodumene during leaching. The reaction frontier was identified using atomic-resolution TEM imaging with geometric phase analysis (GPA). In-situ Raman spectroscopy was used to confirm the presence of intermediate products like O₂²⁻. A novel 3-dimensional current collector was designed, using a graphene oxide (GO) aerogel with a carbon felt (CF) framework, modified with Au nano-catalysts, to enhance mass transport and achieve high-throughput leaching. Chronoamperometry (CA) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) were employed to monitor the Faradaic and leaching efficiencies. A glassy carbon microelectrode was utilized to measure the H₂O₂ concentration in-situ. The electrochemical tests were conducted using a three-electrode system with a saturated calomel electrode (SCE) as the reference electrode. For the high-throughput experiments, a custom-designed three-electrode setup was used with a silver wire as the counter and reference electrode. The study also included a techno-economic assessment comparing the electrochemical leaching process to traditional methods.

The study demonstrated that the morphology and crystal structure of spodumene significantly influence leaching efficiency. α-phase spodumene has a compact, faceted structure, hindering Li⁺ extraction, while β-phase shows a pulverized structure, facilitating leaching. XPS analysis revealed a Li deficiency on the surface of β-phase spodumene, likely due to evaporation during high-temperature calcination. LSV showed that β-phase spodumene leaches at a lower potential than α-phase. Thermodynamic calculations confirmed the higher leaching potential of α-phase spodumene. The addition of H₂O₂ as a promoter dramatically reduced the leaching potential, shifting the reaction pathway and improving efficiency. XRD analysis showed that α-phase spodumene retains its crystal structure after electrochemical leaching, with only lattice shrinkage, while β-phase undergoes a phase transformation to HAISi₂O₆. TEM imaging with GPA revealed the reaction frontier and showed a 2% reduction in (110) interplanar spacing in α-phase after leaching. XPS confirmed the formation of AlOOH on leached β-phase spodumene, while leached α-phase showed different Al-O bond characteristics. In-situ Raman spectroscopy confirmed the existence of O₂²⁻ as an intermediate product during leaching of α-phase. The newly designed 3-dimensional current collector, modified with Au nano-catalysts, achieved a leaching current of 18 mA and a leaching efficiency of 92.2%, exceeding traditional methods. The optimized leaching potential was 0.95 V vs. SCE, balancing high Faradaic efficiency (71.5%) with high leaching efficiency (92.2%). Techno-economic assessment showed that electrochemical leaching reduced costs by 35.6% and CO₂ emissions by 75.3% compared to traditional methods.

The findings address the research question by demonstrating the feasibility and advantages of electrochemical leaching for direct lithium extraction from α-phase spodumene. The use of H₂O₂ as a promoter alters the reaction pathway, enabling efficient leaching at room temperature and significantly reducing energy consumption. The novel 3-dimensional current collector design further enhances the process's efficiency and scalability. The results highlight the potential of electrochemical leaching as a sustainable and cost-effective alternative to traditional methods. The significant reduction in energy consumption and CO₂ emissions contribute to a greener lithium extraction process, aligning with the global drive towards sustainable resource management. Further research could focus on exploring other suitable promoters and optimizing the current collector design for even higher efficiency and broader applicability.

This study successfully demonstrated a novel electrochemical method for directly extracting lithium from α-phase spodumene at room temperature using dilute sulfuric acid and an H₂O₂ promoter. The method significantly reduces energy consumption and CO₂ emissions compared to traditional methods, and the development of a high-throughput current collector enhances scalability. This approach offers a promising pathway towards a more sustainable and cost-effective lithium supply chain. Future research could focus on optimizing the process parameters and exploring alternative promoters and current collector designs.

While the study achieved high leaching efficiency, the in-situ generation of H₂O₂ using Au catalysts requires further optimization to improve the long-term stability and reduce catalyst consumption. The techno-economic analysis relies on certain assumptions regarding energy sources and costs, and these could vary depending on geographical location and specific operational conditions. The study focuses primarily on α-phase spodumene; further research is needed to determine the applicability of this method to other lithium-bearing ores.