Recycling Spent Cylindrical Lithium-ion Batteries – Hydrometallurgy Approach with Pre-treatments

Dessy Amalia

Recycling spent lithium-ion batteries (LiB) is one effort to reduce the negative impact of battery waste on the environment if it is only landfilled, as the number of batteries will exponentially increase because of the electrification of vehicles. LiB recycling also can provide a sustainable metal resource for energy storage as the waste still contains high grades of critical metals. This thesis represents new method series of recycling cylindrical 18650 type of lithium-ion batteries by applying a hydrometallurgical approach with pretreatments to support closed-loop LiB production. The pretreatment process includes discharging the residual capacity of spent LiBs and recovering cathode material by separating the material from unwanted metals from electrode foils (aluminium and copper) and the iron from steel casing. Both processes require further understanding for their application to the hydrometallurgy approach, and only a few studies have reported the results for application. The products of the pretreatments are expected to meet the requirements for the subsequent leaching process. Thus, this thesis also studied an alternative leaching process employing organic reactants on the produced feed from the pretreatment process. Subsequent recovery of cathode material by separating the dissolved iron and aluminium was also conducted to create comprehensive research on LiB recycling. The final product of this thesis is a flowchart of LiB recycling using a safe and green technology to bring it to a functional approach. The first step in the recycling process series is discharging residual charges from the spent LiB to eliminate fire hazards during the subsequent mechanical treatment. Battery submersion in an electrolyte solution is one of the methods to implement the discharging process in bulk-mass waste. Recent studies have used sodium chloride (NaCl) to discharge the LiBs, which can rapidly discharge the batteries. However, the chemical generates toxic chlorine gas during the discharging process, which is toxic and corrosive. The battery was severely corroded at the positive terminal, producing sedimentation of the casing material and requiring further treatment. An alternative electrolyte solution, sodium hydroxide (NaOH), is investigated comparatively with NaCl on discharging performances and their corrosion impact on the battery. The battery discharging process was examined by immersion of the new and spent battery in the two solutions and an indirect battery connection through electrodes dipped in the solution. Visual observation of the battery and solutions, voltage and current measurements, and chemical and physical analysis of solutions are tools to identify the discharging process. The results show that an NaOH solution had less affected on battery corrosion and resulted in non-toxicant gases. Residual battery capacity (mAh) on an NaOH discharged battery was safe for subsequent treatments. The discharged battery was then safely cut-milled to extract the valuable cathode material (Li, Ni, Co and Mn). Binder adhesion on cathode material to the current aluminium collector foil in the layered sandwich structure of the LiB affected the cathode distribution. The nanoparticle size of cathode material was distributed to >38 μm as some particles are still attached to the foil and plastic separator. Some fine cathode material was also agglomerated due to the binder attachment and remained at >180 μm. Secondary crushing/milling/shredding is the general method to free the attachment. However, the process affects the selectivity of the particle size as metal foils and casing steel are also reported to the finer fraction. Attrition with inert scrubbing media, termed semi-autogenous attrition (SAA), was introduced to increase the cathode liberation from contamination of other battery components and agglomeration. The result is compared to wet sieving and attrition with agitation only. The modified attrition method can effectively replace secondary crushing/milling in LiB recycling. Graphite as anode material was also co-extracted with cathode material, and the mixture is termed black mass. Chemical and physical analysis were conducted as data collection to support the finding of the attrition performances. Mayer upgrading curve was used to evaluate the optimum cut-off point separation of elements in the sample relative to the recovery rate of the Co element. This thesis proposed a new flow chart for the downstream process for preparing the leach feed. The black mass (cathode and anode material mixture) produced from the SAA process was then used for the leaching studies. Alkaline pretreatment was employed to investigate the effect of the chemical treatment on the acid-leaching performance. This chapter compared direct acid leaching and acid leaching with alkaline pretreatment. This comparison examined the efficiency of valuable metals (Li, Ni, Co, Mn) and the sample's structural transformation. The cathode material is in oxides, and the oxidation state of the metals increases after the acid leaching. Reductive leaching is preferable for metal extraction, possibly provided by the indirect effect of aluminium content in the sample that produced reductive hydrogen gases. The lowest extraction of Co after alkaline leaching demonstrates that chemical pretreatment is unnecessary before acid leaching on the feed from SAA process. A subsequent reductive leaching study is performed using organic reactant combinations to eliminate the disadvantages of using inorganic reactants. The leaching cathode material study investigated the combination of acetic acid and cane molasses. Being reasonably priced, easily accessed, and environmentally friendly are factors in choosing the reactants. Observations on acid strength, temperature, and solid/liquid ratio were compared to non-reductive and reductive leaching. This study also examined the amount of reductants and two additional times to the leaching system to obtain the optimum leaching efficiency of the valuable metals. The results show that the leaching with acetic acid and cane molasses is selective for Co, Li, Ni and Mn over copper.

Recycling Spent Cylindrical Lithium-ion Batteries – Hydrometallurgy Approach with Pre-treatments

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