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There is an undeclared competition for better, more efficient batteries which pushes researchers to continue developing new methods for extracting and synthesising electrodic materials.

Recovery of lithium as battery grade material

Lithium (Li) is a key component in batteries and scientists involved in the RHINOCEROS Project have been exploring ways to extract it from recycled materials from used batteries known as “black mass” (BM). But one of the challenges scientists are facing is the reduction of fluoride content in extracted Li. Researchers at KIT tested their mechanochemical process for extracting Li from various BM samples provided by partners ACC and TES. Their experiments engaging reactive milling coupled with various reactive agents aimed to reduce the fluoride content of the aqueous solution. These tests showed that using magnesium as a reactive agent yielded most promising results for Li extraction.

Progress in Lithium-Manganese battery materials and Advancements in Reduced Graphene Oxide production

Research team at Sapienza Univ. of Rome (UoS) has been making progress in developing lithium-manganese-rich materials for battery applications. These materials were produced using an integrated hydrometallurgical process, which includes the production of reduced graphene oxide and a co-precipitation method that leads to the formation of lithium-manganese-rich cathodes. The resulting cathode materials are currently undergoing extensive physicochemical and electrochemical characterizations.

For the synthesis of reduced graphene oxide, the researchers compared two methodologies and observed differences in productivity. These differences are now being investigated to determine whether they are influenced by the thermal pre-treatment of the graphite or by the role of metals present in different oxidation states. The use of mechano-chemically treated powder has demonstrated remarkable productivity, reaching approximately 80%.

Enhanced solvometallurgical processes

As evoked by its name, solvometallurgy uses solvents to extract metals. Researchers at TEC have been optimising the process, using additives as copper (Cu) or hydrogen peroxide (H₂O₂) when necessary, achieving a high recovery rate of >95%. However, the process also increased the dissolved Cu content, which required additional steps to reduce it. Researchers are now exploring methods like cementation or electrodeposition to recover and reuse the dissolved Cu. The deep eutectic solvents (DES) were already regenerated and reused, result which could bring a positive impact on the process sustainability assessment.

Direct recovery of battery materials

The Gas-Diffusion Electrocrystallisation (GDEx) technology allows the one-step recovery of metals and synthesis of new materials with high added value. In the framework of the RHINOCEROS project, the research team at VITO has been focusing on optimising the GDEx technology to achieve the selective recovery of nickel (Ni), manganese (Mn), and cobalt (Co), contained in leachates from black mass and achieved 90 % extraction of Ni, Mn and Co. This two-step GDEx process facilitated the removal of all the impurities such as Cu, Fe from the leachate solution. Using the GDEx process, VITO researchers have successfully synthesised Layered Double Hydroxide (LDH) materials and spinel-type nanostructures from the synthetic solutions. The LDH materials were lithiated and LiNi_0.8Mn_0.1Co_0.1O₂ (LNMCO811) was synthesised, which could be used as a cathode active material for lithium-ion batteries (LiBs).  The results obtained with synthetic solutions portray the potential of the method to obtain relevant active cathode materials out of leachate solutions.

Recovery of materials from low concentration waste streams

Aiming towards a zero-waste strategy for the recovery of metals from battery refining waste waters, LEITAT is working on the development and evaluation of novel polymer inclusion membranes (PIM). PIMs are a type of liquid membrane in which the liquid phase, the extractant, is held within a polymeric network. The interest in these membranes has been growing exponentially over the past few years as an alternative separation technique to conventional solvent extraction.

During the previous six months, the team at LEITAT have been investigating two types of membranes that have shown high selectivity, recovering manganese (Mn) and cobalt (Co) from mixed metal solutions. In their future research, LEITAT will use these membranes in combination to ensure increased selectivity of targeted metals.

Optimising lithium carbonate recovery

Lithium carbonate(Li₂CO₃) is another critical material for batteries, and researchers at TEC and LEITAT are working to optimise its recovery from various solutions. This involves fine-tuning the conditions for Li₂CO₃ precipitation, including the influence of pH and the presence of other cations. Tests are currently conducted with both synthetic solutions and real leachates to ensure the effectiveness of the process. Additionally, efforts are underway to automate the recovery process, which includes assembling elements for pH monitoring and CO₂ bubbling systems.

Bringing innovations to market

To bring these innovations to market, researchers are preparing to scale up their processes. This involves a selective process based on data collection, life cycle assessment (LCA) and life cycle cost (LCC) analysis, to ensure the best technological routes are chosen to be further upscaled and meet the production demands.

Author: KIT

During the third semester, researchers from KIT further studied and improved the conditions for the mechanochemical transformation of black mass (BM) into metallic black mass (MBM). Since BM supplied by ACC is already in a reduced state, they focused on reducing BM supplied by TES. This BM consists mostly of NMC (lithium nickel manganese cobalt oxides) cathode material and graphite, which was found to slow down the reaction kinetics. The reduction of the cathode active material by the metallic reducing agent result in the formation of the transition metals along with lithium oxide (Li₂O) and the oxide of the respective reducing agent, which can be monitored by X-ray diffraction.

In contrast to the previous two semesters, researchers switched from shaker mills to planetary mills, which enable control of the rotation speed and larger volumes that can be processed. Various parameters such as ball-to-sample ratio (BSR), ball size, total load and rotation speed were investigated to optimise for a short reaction time.

Main take-aways

In general, the higher the BSR, the more mechanical energy can be transferred per gram of powder which results in a more intense milling and a faster reaction; however, this limits the throughput. Larger balls, on the one hand, lead to higher kinetic energies. On the other hand, fewer balls are used to keep the BSR constant resulting in a lower collision frequency. The maximum rotation speed is lower to prevent damage to the grinding media.

With Calcium as the reducing agent, no reaction was achieved at all. An unfavorable combination of ductility and size of the calcium pieces seems to resist further size reduction, which is required for the reaction.

Aluminium has the advantage of being used as a current collector and is already present in the black mass. However, during the reaction, LiAlO₂ is formed, which is limiting the subsequent Li extraction efficiency in WP5. This problem can be avoided when magnesium is used as the reducing agent, which proved to be more reactive than aluminium but doesn’t form other lithium compounds than Li₂O.

Compared to the shaker mill, a higher reaction rate was observed in the planetary mill. Researcher from KIT achieved a complete conversion of the lithium transition metal oxide in the planetary mill within 3 h using Mg as the reducing agent. In a larger version of the mill, the required milling time increases to 8 hours. Here, further investigations are planned for the next months.

Read previous article on the pre-treatment operations: Pre-treatment operations: Reactive milling for the production of metallic black mass

© Photo: Adobe

The modified Black Mass (BM) obtained in Task 4.4 – Reactive milling for the production of metallic black mass (MBM), as well as the BM supplied by partner ACCUREC (ACC) were leached under different conditions to extract lithium (Li) salt.

The BM provided by ACC consists of graphite, as well as transition metals such as nickel (Ni), manganese (Mn), cobalt (Co), along with their respective oxides and impurities – copper (Cu), iron (Fe), and few fluorinated compounds. Li is present in the form of lithium carbonate [Li₂CO₃] and lithium aluminium oxide [LiAlO₂ ]. However, breaking off LiAlO₂ to a soluble Li-salt and removing fluoride contamination is a challenging process. To overcome this, the BM was heated with calcium hydroxide in deionised water for one hour and then filtered.

Illustrated in the next figure, LiAlO₂ decomposes during heating and transforms into insoluble calcium aluminium hydroxide. Dissolved fluoride anions are caught by Ca²⁺ ions and precipitate as calcium fluoride. The soluble part only contains Li- and Ca-salts. The latter can be transformed into calcium carbonate and removed with a second filtration step.

X-ray diffraction patterns of leaching and purification process. a) black mass supplied by ACC and treated with calcium hydroxide. b) aluminium system of modified black mass

The second BM from partner TES, obtained after ball milling, consists of graphite, the metallic composite, lithium oxide and the oxidized reducing agent, along with some impurities like Fe and fluorinated compounds.

Lithium extraction after ball milling

In the aluminium system, the extraction of lithium salt poses certain challenges. Due to the tendency of residual aluminium powder to ignite when in contact with air, this requires cautious handling. During milling lithium aluminium oxide is formed, and in the basic solution, a significant amount of aluminium hydroxide dissolves and reacts with lithium hydroxide and CO₂, resulting in the formation of a poorly soluble compound called LACHH. To address this problem, the suspension is heated to 90°C to reinforce the reaction between aluminium hydroxide and lithium hydroxide. The LACHH formed can be decomposed at 350°C into insoluble aluminium oxide and soluble lithium carbonate, which can be separated through filtration.

Lithium extraction in the calcium system, on the other hand, is a relatively straightforward process. The milled powder shows low reactivity towards both oxygen and water. Scientists successfully extracted 98% of lithium from the black mass; however, calcium hydroxide was also dissolved in the process. Subsequent purification steps led to the isolation of lithium carbonate with a purity of 93% in a yield of 75%. The main impurities are shown in the figure displayed below.

In the upcoming months, researchers will work to improve the leaching conditions towards a lower reagent and water consumption, while obtaining a higher purity of resulting lithium salt and lower lithium loses during purification steps.

Impurity cations in isolated lithium carbonate from the calcium system of modified black mass

Focusing on mechanochemical (MC) processing, the chemical transformation of the black masses (BMs) supplied by partners ACCUREC and TES, is planned to be carried out within Work package 4. 

Before MC processing, the black masses were analysed using a combination of different analytical techniques. Both quantitative and qualitative analysis were undertaken to determine the Lithium and transition metals yield of the developing recycling process. 

Using different reducing agents such as Al, Ca, and their mixtures, researchers carried out preliminary investigations of the MC processing of BMs. Within this task, different aspects, such as the role of the ball milling conditions, the ball milling time, presence of other nonreactive components, and nature of the reducing material were investigated. The analysis led to the conclusion that the kinetics of the MC-induced reduction reaction is sensitive to multiple processing parameters, as shown in the featured image: 

XRD patterns of the as-received BMs and products of their reduction after MC processing with Al and Ca as reducing agents: left-TES material; right-ACC material

The upcoming research will focus on improving the reduction reaction kinetics and eliminating the possible safety hazards of fine powder materials. Once finalised, this work will determine the optimal ball milling conditions to be scaled up. 

Recovery of Lithium as battery grade materials

The process described in Task 4.4 leads to the chemical transformation of the black masses (BMs) into ferromagnetic Co-, Ni- and Mn-containing products, which will be separated from other by-products. Lithium will be extracted from the rest of the solid products in the subsequent aqueous leaching process to be further transformed into battery-grade lithium carbonate (Li₂CO₃) salt. 

Within the M1-M6 period, aqueous leaching of the ball-milled samples using Al and Ca as reducing agents (RA) was carried out. At a preliminary stage of investigations, researchers noticed the resulted Li₂CO₃ materials presented small amount of impurities. 

To increase the yield of lithium recycling, in the upcoming period, the research work will target the improvement of the leaching conditions and the purification process.  

X-ray diffraction patterns of the as-milled BM obtained from TES, products of their reduction reactions after MC processing with Al (left) and Ca (right) as RA, and obtained Li salts after aqueous leaching