Study Of Closed-loop Hydrometallurgical Recycling Of Lithium-ion Battery Cathode Active Materials

Development of electric vehicles powered by lithium-ion batteries(LIBs)is part of the Chinese national strategy,which has been rapidly carried out since a decade ago in China.Survey shows that China's electric vehicle production in 2020 topped 1.367million vehicles,a 29.5%compound annual growth rate(CAGR)from 2015 to 2020.Along with the fast development of electric vehicle industry,the demand of China's LIBs reached to 63.6GWh in 2020,a CAGR of 32.3% from 2015 to 2020.With the early commissioned LIBs starting to reach end of life,the volume of LIBs that need to be decommissioned is growing.In 2020,the amount of LIBs that need to be decommissioned reached to 500,000 tons.Faced with the increasing number of decommissioned lithium-ion batteries,the sustainability of the supply of lithium-ion battery materials,and the reduction of the environmental impact of the spent and discarded lithium-ion batteries,it is essential to recycle and reuse the material of lithium-ion batteries.In addition,the current raw materials for manufacturing lithium-ion battery cathode active materials such as lithium,nickel,cobalt,manganese and other metals are gradually becoming scarce and their prices have risen sharply.It is imperative to regenerate new lithium cathode active materials from material recovered from spent lithium-ion batteries.The existing commercial methods to recycle spent LIBs are pyrometallurgical recycling and hydrometallurgical recycling.The pyrometallurgical recycling process is relatively simple but energy intensive.It also generates toxic exhaust gases.Hydrometallurgical recycling process uses sulfuric acid with hydrogen peroxide to leach valuable metals from spent/waste LIB cathode active materials and then extract them with solvent extraction.The use of hydrogen peroxide results in the recycling system having a large volume of process water that needs to be treated and discharge and the additional process water cannot be fully directed back to the system.In addition,although solvent extraction can extract each metal separately,the organic solvent needs to be treated so that it can be reused or discharged,which will result in a large amount of secondary waste needed to be treated.Therefore,the current hydrometallurgical recycling process is not a closed-loop process,can produce secondary waste,cause environmental burden,and create obstacles for the future development of the electric vehicles-powered by LIBs.This thesis has successfully developed a closed-loop continuous hydrometallurgical process for recycling waste and spent lithium-ion battery cathode active materials,as well as explored and understood the operating mechanism of the process.This closed-loop process uses sulfur dioxide to replace hydrogen peroxide for leaching,lithium hydroxide to replace sodium hydroxide to reduce the sodium ion content in the recovery process,and lithium hydroxide to replace organic solvents to extract metals such as aluminum,nickel,cobalt,and manganese.The process uses electrodialysis to recover lithium and regenerate sulfuric acid and lithium hydroxide.The developed process for recycling and regenerating lithium ion battery cathode active materials reduces the process water produced during the recycling process of lithium ion batteries,allowing the process water to be reused in the system to minimize wastewater treatment procedures.The research in this thesis overcomes the shortcomings of the current hydrometallurgical recycling process and develops a closed-loop hydrometallurgical process for recycling waste and spent lithium-ion battery cathode active materials.Specifically,this thesis covers the following research work:1)A comprehensively reviews on the available hydrometallurgical technologies for recycling spent/waste LIB cathode active materials.The fundamental chemistries of the leaching,precipitation and solvent extraction of various LIB cathode active materials including lithium cobalt oxide,lithium manganese oxide,lithium nickel cobalt aluminum oxide,lithium nickel manganese cobalt oxide,lithium titanate,and lithium iron phosphate are analyzed and summarized.Currently,valuable metal ions such as aluminum,cobalt,lithium,manganese,and nickel can be extracted from the spent/waste LIB cathode active materials through leaching with chemicals such as hydrochloric acid(HCl),nitric acid(HNO₃),sulfuric acid(H₂SO₄),oxalate(H₂C₂O₂),DL-malic acid(C₄H₅O₆),citric acid(C₆H₈O₇),ascorbic acid(C₆H₈O₆),phosphoric acid(H₃PO₄)or acidithiobacillus ferrooxidans.Recovery of cobalt,manganese,and nickel can be achieved through precipitation with sodium hydroxide or solvent extraction.Lithium can be recovered through adding sodium carbonate to precipitate lithium as lithium carbonate.In addition,the technical challenges in recycling LIB cathode active materials are analyzed and perspectives are overseen for facilitating the further research and development of recycling technologies for spent/waste LIB materials.2)Study the theoretical background and technical operation of the instrumental technologies necessary for analyzing LIB cathode active materials compositions and fundamentally understanding the chemical reaction mechanisms in the closed-loop hydrometallurgical recycling technologies.The measurement technologies mainly include the inductively coupled plasma(ICP),scanning electron microscopes(SEM),X-ray diffraction(XRD),and particle size distribution(PSD).3)Research using sulfur dioxide to replace hydroxide peroxide as reducing agent in sulfuric acid leach of commercial LIB cathode active materials including lithium cobalt oxide,lithium nickel manganese cobalt oxide,and lithium nickel cobalt aluminum to extract valuable metals.The leaching conditions are optimized by the bench scale experiments.Develop a novel environmentally-friendlier closed-loop hydrometallurgical process.Two semi-continuous locked-cycle campaigns conducted using lithium cobalt oxide document the dynamics of the recycled streams and yield much useful data.It is found that the behavior of the leached cobalt is strongly affected by sulphate supersaturation and the location of sodium sulphate crystallization,but successful operation can be maintained when the sodium sulphate level is carefully controlled.Experimental results also show that the systems may reach sulfate supersaturation when circulating loads are incorporated,demonstrating the significance of sulphate levels in such systems.Therefore,The solution properties should be the key factors when recycling spent/waste LIB cathode metals using systems based on sulfuric acid and sodium salts.Two closed-loop flowsheets are developed to recover metals,reduce discharges,and minimize p H environmental impact in the recycling of the spent LIB cathode active materials.4)Investigate the separation of two type of waste/spent cathode active materials from aluminum foil.The two types of cathode active material are lithium nickel cobalt aluminum oxide(NCA)and lithium nickel manganese cobalt oxide (NMC).Both NCA and NMC cathode active material can be separated from aluminum foil by immersing spent/waste LIB cathodes into weak H₂SO₄ solution.For spent/waste NCA cathode separation,the weight ratio of the required 98wt% H₂SO₄ to NCA cathode is around 0.95;for spent/waste NMC cathode separation,the weight ratio of the required 98 wt% H₂SO₄ to NMC cathode is around 0.79.Leach both NCA and NMC cathode active materials using sulfuric acid and sulfur dioxide can obtain>99%leaching efficiencies on Ni,Co,Mn,and Li.The optimal leaching conditions obtained is to control leach pH at 1.5,oxidation-reduction potential(ORP)at 550mV,and retention time of 7 hours with 20wt% pulp density.However,leaching with sulfuric acid and sulfur dioxide generates approximately 6.5g/L of S₂O₆^2-,which needs to be monitored very carefully as the concentration of S₂O₆^2-might potentially build up and affect the downstream metal extraction and lithium recovery.Compared with leaching experiments using sulfuric acid and hydrogen peroxide as the reactants,the leaching with sulfuric acid and sulfur dioxide as the reactants can result in 15%less total leachate volume,which reduces the degree of water management needed in the downstream impurity removal,metal extraction,and lithium recovery.5)Research using lithium hydroxide and lithium carbonate to replace sodium hydroxide in impurity removal step and metal extraction steps in the closed-loop hydrometallurgical recycling process for spent/waste LIB cathode active materials.A three-compartment electrodialysis cell is invented to recover lithium as lithium hydroxide and regenerate sulfuric acid.Using lithium hydroxide and electrodialysis cell can avoid the issue of sulfate supersaturation.Three different scales are developed to understand the reaction kinetics:1-litre batch,40-litre batch,and 73-litre continuous batch.With Li OH as a reagent,impurities such as Al and Fe can be removed at pH 4.0–5.5.Metal extraction of Ni,Co,and Mn as carbonates or hydroxides can be achieved at pH 8–10.Up to 0.9M of LiOH can be generated with this three-compartment electrodialysis cell with a 78% current efficiency.The regenerated sulfuric acid and lithium hydroxide can be reused in the leaching process and regenerate lithium cathode active material,realizing a closed-loop process.The developed closed-loop hydrometallurgical process can reduce costs through reagent regeneration and can provide an environmentally-friendlier approach to recycling spent/waste LIB cathode active materials.6)Regenerate lithium cathode active material uses nickel-cobalt-manganese hydroxide and lithium hydroxide recycled from the developed closed-loop recycling process to produce lithium cathode precursor and lithium cathode active material such as LiNi_0.5Co_0.2Mn_0.3O₂ with a commercial-grade purity.The characters of such regenerated lithium cathode precursor and lithium cathode active material are analyzed by ICP,SEM,XRD,and PSD.This material is used to construct cathodes for protocol LIBs and was examined by p Helectrochemical measurements.The resultant LiNi_0.5Co_0.2Mn_0.3O₂ cathode active material exhibits a discharge capacity of 153.95mA·h/g at 1C,better than that of commercial cathode active material(141.30mA·h/g).The regenerated cathode active material also shows remarkable cycling performance.7)Analyzes the material balance,energy consumption,and economy of the proposed closed-loop continuous process for recycling waste and spent lithium-ion battery cathode active materials to regenerate new lithium cathode active material.Furthermore,analyzes the technical and economic challenges of recycling spent/waste LIB cathode active materials,and provides several possible research directions for overcoming the challenges toward technology commercialization.