Recovery Of Valuable Metals From Spent Lithium-Ion Batteries By Air/Steam Roasting And Its Life Cycle Assessment

Recently,lithium-ion batteries（LIBs）are widely used in electronic products,electric vehicles and energy storage with their superior electrochemical performance,showing an exponential growth trend.Consequently,there is an increasing demand for the disposal of spent LIBs in the forthcoming years due to a limited lifetime of 3～5.years.The spent LIBs are rich in heavy metals,electrolytes and other substances.Direct disposal of spent LIBs will pose a huge threat to the ecological environment and human health.But from the perspective of resources,these spent LIBs can be regarded as urban mines,the valuable metals present in the spent LIBs are at very high levels,even higher than those found in concentrate.Therefore,the recycling of spent LIBs is regarded as an extremely important way to prevent environmental pollution and to meet the requirement of sustainable development of the LIB industry.To address the issue of recycling spent LIBs,many processes mainly by using pyrometallurgical or hydrometallurgical approach were developed.Among these recycling methods,the reduction roasting method has the advantages of both the pyrometallurgical and the hydrometallurgical methods,and is regarded as a recycling technology with great development potential.In this method,the reduction roasting step is crucial for the recovery of valuable metals.Therefore,how to achieve low-consumption,high-efficiency,and green recovery of valuable metals in this step is of great significance for realizing the large-scale application of this technology.Unfortunately,the feasibility for the large-scale application of these existing recycling methods have never been assessed.In this thesis,the life cycle assessment（LCA）of several mainstream methods for recovering valuable metals from spent LIBs reported in the literatures was carried out firstly,and the pros and cons of the methods were analyzed.Then,a new method for recycling spent LIBs by incorporation air/steam into roasting process was proposed to solve the problems of low valuable metal recovery and low utilization rate of anode carbon materials in the in-situ reduction roasting method based on the LCA results,and the LCA of this method to recycle LCO and NCM622 LIBs was carried out as well.The main research contents and conclusions of this thesis are as follows:（1）Life cycle assessment of existing recycling technologies for spent LIBs.In this work,an industrial-scaled spent LIB recycling system integrating the emerging recycling methods(i.e.,Ultra-high temperature method（UHT）,Hydrometallurgical method with sulfuric acid（HM-SA）,Hydrometallurgical method with citric acid（HM-CA）,In-situ reduction roasting method in N₂ atmosphere（RR-N₂）and In-situ reduction roasting method in enclosed-vacuum,（RR-Vac）was proposed.The life-cycle impacts（i.e.,energy consumption,material consumption,and greenhouse gas（GHG）emissions）of the emerging recycling methods were quantified by the process-based LCA approach.To our knowledge,this is the first comparative study of these methods by LCA approach.The results indicated that each recycling method has the potential of energy saving and emission reduction comparing with the production of virgin materials in industry.To be specific,the energy consumption reduction rates of UHT,HM-SA,HM-CA,RR-N₂ and RR-Vac were 71%,71%,46%,88%and 87%,respectively,corresponding to 40%,42%,31%,57%and 57%reduction rates in the GHG emissions.Besides,the main contributors of the total energy consumption and total GHG emissions were the conversion and the regeneration phases.The study also found that the contribution of the collection and transportation phase to the total energy consumption will exceed the In-situ reduction roasting recycling process itself when an energy-intensive transportation mode is used for a more than 500 km of transportation.In addition,the system output of each method is sensitive to the changes in the valuable metal recovery rates and the electricity structure.（2）Recovery of spent lithium-ion batteries by incorporation air and steam into roasting process.In this thesis,the air/steam mixture was used as an active atmosphere for in-situ roasting to recycle spent LIBs instead of an oxygen-free one generally used in existing reduction roasting method.The mechanism of the air/steam mixture on the recovering of cathode materials（mainly valuable metals）and the removal of anode materials（mainly carbon）of spent LIBs was studied in this section.Besides,the influence of operating parameters on the valuable metal roasting recovery rate and C removal rate were obtained as well.The results showed that a suitable reaction condition for in-situ roasting were gas molar ratio with O₂/H₂O/C=0.5:3:1,at 800℃for 1h.It can achieve higher metal recovery efficiency and comprehensive carbon removal rate of Co:98%,Li:75%,CRc:82%,respectively.（3）Life cycle assessment of steam,air/steam in-situ reduction roasting methodsA life cycle assessment system for two recycling methods of spent LIBs,named RR-H₂O and RR-Air&H₂O,was established for the first time in this chapter.And a quantitative analysis of the processing of LCO and NCM622 LIBs by these two methods was conducted,and the material and energy flows as well as the GHG emissions of the four recycling processes were obtained.An analysis of the impact of the key sub-process of waste heat recovery on the output of the system was conducted.The results indicated that when a waste heat recovery rate of 50%was considered,the potential energy consumption reduction rates of LCO-RR-H₂O,LCO-RR-Air&H₂O,NCM-RR-H₂O,and NCM-RR-Air&H₂O were 79%,85%,63%and 70%,the corresponding GHG emission reduction rates were 36%,55%,12%and 32%respectively.From the perspective of energy benefits and environmental effects,the feasibility of RR-H₂O and RR-Air&H₂O for LIB recycling was quantitatively verified.The results showed that RR-Air&H₂O showed greater potential for energy conservation and emission reduction comparing to RR-H₂O.