有效地回收废弃锂离子电池中的宝贵资源外文文献

Contents lists available at ScienceDirect Journal of Power Sources journal homepage Efficient recycling of valuable resources from discarded lithium ion batteries Chang Heum Jo Seung Taek Myung Department of Nano Technology and Advanced Materials Engineering li thium resources from ores approximately 34 of total lithium production are mostly used for the glass and ceramics industry Fig 1a 19 Because of the limited lithium resources available in brine the unit cost of lithium for LIBs is continuously increasing 20 Therefore recyclingofraw materialsis criticaltoreduce the https doi org 10 1016 j jpowsour 2019 04 048 Received 5 January 2019 Received in revised form 8 March 2019 Accepted 10 April 2019 Corresponding author E mail address smyung sejong ac kr S T Myung Journal of Power Sources 426 2019 259 265 Available online 17 April 2019 0378 7753 2019 Elsevier B V All rights reserved T environmental impact and for economic reasons The cost of extracting resources from brine and hard rock is about 1800 ton 1and 5000 ton 1 respectively while the cost of obtaining resources in battery recycling is about 1130 ton 1 21 Although total quantity of lithium resources obtained from recycling process is still in small scale com pared to the amount obtained from natural sources recycling of bat teries should be further extended due to the finite of lithium resources and the environmental problems of the extracting process 22 There have been many attempts to recycle metals from several types of sec ondary batteries and recycled raw materials are gradually being re applied in new battery products Fig 1b i e in lead acid batteries almost 100 of the lead is recycled material 23 As demonstrated by the successful recovery of lead by recycling the recycling of lithium and cobalt for LIBs rather than the use of mined raw materials can con siderably reduce the production cost and reduce the environmental impact Secondary batteries can be recycled using 1 pyrometallurgical processes 2 intermediate hydrometallurgical processes and 3 direct physical processes In the simple pyrometallurgical processes all of the components of the waste LIBs are melted however extraction and se paration of several elements may require complicated additional treatments More importantly recycling of lithium element would be difficult because of the low melting point of lithium relative to that of cobalt and copper 24 26 Intermediate hydrometallurgy processes which were developed than pyrometallurgical methods completely isolate the metal resources in solution The process requires mechanical crushing and grinding of waste LIBs piece by piece Less energy is consumed relative to the pyrometallurgical process and lithium can be recovered via a low temperature process however environmental is sues pertaining to the recycling process remain to be resolved 27 29 In contrast direct physical processes progress via disassembly of the discarded batteries Insufficient lithium is added more in the cathode however the remaining lithium is completely removed from the anode namely both the cathode and anode are reused for the fabrication of new LIBs This method is thus advantageous from both economic and environmental perspectives However scale up to a commercial scale is still needed and the inferior battery performance needs to be resolved 30 31 A comparison of the three processes is presented in Fig S1a In this work we combined the advantages of the intermediate and direct physical processes In earlier works the intermediate process has only been used to efficiently leach metal resources or to separate metal resources using an expensive reagent Thus separation of lithium and metal was often unclear and expensive chemical reagents were generally used in this process which may not be feasible in practice Table S1 In this study recycling of the materials making up the cathode from discarded LIBs is performed to reduce the environmental and economic burdens of LIB manufacture The objectives of this work are 1 opti mization of the recycling process using a combination of intermediate and physical processes 2 minimization of the environmental burden during processing 3 separation and refining to achieve battery grade performance of the main materials with the least loss and 4 verifica tion of the physical and electrochemical properties of the cathode materials synthesized using the recycled materials We suggest an ef ficient process to recycle high purity raw materials from discarded LIBs that can be applied to help minimize the environmental burden while maximizing the economic benefit for the LIB industry 2 Experimental 2 1 Separation of lithium source from transition metal sources The overall recycling process is depicted in Fig S1b To recover valuable metal resources from the used batteries LiCoO2 hereafter referred to as LCO cathodes were collected from used lab scale pouch cells Before disassembling the cells the positive and negative tabs were interdigitated with each other to fully discharge the cells this process causes the migration of residual lithium ions from the anode to the cathode The disassembly process was performed in a dry room and the cathodes were collected Although parts anode separator other than the cathode can also be recycled this work was beyond the scope of the current study We adopt a physical process that the applied active materials readily exfoliates from the current collectors Before the separation process all tabs were removed from the cathode and anode Then the collected cathodes weighed approximately 140g including the current collectors 50 g and cathode composites 90g and dried at 80 C for 1h in an oven to evaporate the residual electrolytic solvent And these com ponents were immersed in an aqueous solution 420g containing 1MH2SO4with 5vol of H2O2 This leaching process was optimal according to our preliminary test results Fig S2 The solution was agitated ultrasonically for 1hat 60 C This pre treatment resulted in exfoliation of the cathode materials from the Al current collectors which is carried out for 5min to prevent dissolution of Al current col lector Fig 2 And the separation of the conducting carbon and PVdF binder from the cathode are described in Fig S3 After the pre Fig 1 a Components of conventional lithium batteries b Circulation of lithium resources C H Jo and S T MyungJournal of Power Sources 426 2019 259 265 260 treatment 2M NaOH aqueous solution was added to the acidic waste solution until the weight ratio of the waste solution and 2M NaOH aqueous solution reached 1 0 5 the solution was further stirred by an impeller at 100rpm for 1h The black colored precipitates presumably metal hydroxide were then filtered and dried in a vacuum oven at 80 C for 3h The metal hydroxide was heated at some temperature to obtain a metal oxide After the filtration the remaining solution was transferred to a hermetically sealed pressurized container and CO2gas was directly purged into the filtered waste solution The solution containing CO2gas was then slowly evaporated at 80 C for 3h the evaporated species were condensed at 25 C and evaporated several times until no powders appeared The obtained powders colored a tone of beige were dried at 80 C in a vacuum oven washed with deionized water at 40 C for 30s to remove any residual water soluble impurities and then filtered The filtered powders were re dried in a vacuum oven at 80 C for 12h 2 2 Physical properties X ray diffraction XRD 6kW X Pert PANalytical and Rietveld re finement were employed to characterize the crystal structure of the produced powders XRD patterns were obtained at 2 10 110 using a step size of 0 03 and count time of 8s The FullProf Rietveld program was used to analyze the powder diffraction patterns Field emission scanning electron microscopy SEM JSM 6400 JEOL and high re solution transmission electron microscopy HR TEM JEM 3010 JEOL were employed to characterize the shape of the prepared powder The chemical compositions of the final powders were determined using inductively coupled plasma atomic emission spectroscopy ICP AES OPTIMA8300 PerkinElmer USA anelementalanalyzer EA Flash2000 Thermo Fisher Scientific Germany and ion chromato graphy IC Dionex ICS 5000 Thermo Fisher Scientific Germany 2 3 Electrochemical characterization The recycled lithium carbonate Li2CO3 and cobalt oxide Co3O4 were intimately mixed and heated at 900 C for 5h in air The resultant LiCoO2was then mixed with conducting carbon a mixture of Super P carbon black Ketjen black at a weight ratio of 1 1 and polyvinylidene fluoride PVDF in a weight ratio of 92 4 4 in N methyl pyrrolidone NMP solution to confirm the availability of recycled Li2CO3and Co3O4for the production of LiCoO2as cathode materials for LIBs The obtained slurry was applied to Al foil and dried first at 80 C to remove the NMP and then at 120 C overnight under vacuum before use Electrochemical cell tests were performed after assembling an R2032 coin type cell using the fabricated LiCoO2as the cathode and Li metal as the anode in an argon filled glove box A solution of 1M LiPF6in ethylene carbonate dimethyl carbonate 3 7 by volume was used as the electrolyte The cells were charged and discharged between 3 and 4 3 V and the cells for the C rate tests were also charged and discharged by applying different currents at 25 C 3 Results and discussion As illustrated in Fig S1b the recycling process can be separated into the following four steps 1 cathode collection 2 dissolution and se paration of cathode materials 3 refining of transition metal source and 4 purification of lithium resource material Detailed descriptions are provided below 3 1 Cathode collection The collected cathodes from the disassembled cells were ultra sonically agitated in 1MH2SO4aqueous solution containing 5vol of H2O2for 1h at 60 C under ultrasonic agitation Fig 3a The dissolu tion of cathode materials was facilitated by increasing the reaction time using H2O2additive and using additional sonication Fig 3b Complete dissolution occurred within 100min using the reducing H2O2 additive and the solution became a dark red color Fig 3c Sulfuric acid and the cathode materials are likely to react as follow 2LiCoO2 s 3H2SO4 aq H2O 2CoSO4 aq Li2SO4 aq 3H2O 1 2O2 1 Addition of the reducing agent H2O2 increases the reaction rate because it reduces the trivalent cobalt in LiCoO2to its divalent form facilitating the formation of sulfuric cobalt CoSO4 Otherwise more reaction time is required to complete the dissolution of LiCoO2 Fig 3b LiPF6salt is remained in the cathode after drying in an oven and then the cathodes are treated in an aqueous solution 420g containing 1MH2SO4with 5vol of H2O2 agitated ultrasonically for 1hat 60 C It is thought that the LiPF6salt reacts with water sulfuric acid and NaOH as follows LiPF6 H2O LiF POF3 2HF 2 2LiF H2SO4 Li2SO4 2HF 3 Li2SO4 NaOH Na2SO4 LiOH 4 Fig 2 Separation process of cathodes obtained from discarded cells C H Jo and S T MyungJournal of Power Sources 426 2019 259 265 261 Fig 3 a Schematic illustration of leaching process b the efficiency under various conditions c image of fully leached waste solution Fig 4 Separation process for metal resources and actual images for each step C H Jo and S T MyungJournal of Power Sources 426 2019 259 265 262 The residual impurity Na2SO4 can remain in the final purification step of Li2CO3but can be removed readily because of its high solubility in water which will be later mentioned in reactions 6 8 Also carbons as a conducting agent and PVDF binder are included in the cathode Through the acid treatment in containing 1MH2SO4with 5vol of H2O2 we were able to detach the active materials from the Al current collectors and the active materials were completely dissolved in the acidic solution as shown below Fig 2 During the process black carbon powders used as conducting agents floating on top of the so lution were collected and dried The collected powders were heated at 400 C for 2h in the air Fig S3 Next to separate the lithium and transition metal present in the waste solution 2M NaOH solution was added to the dark red colored solution of Fig 3c until the filtered waste solution became completely transparent using the following reaction CoSO4 aq Li2SO4 aq 4NaOH Co OH 2 s 2LiOH aq 2Na2SO4 aq 5 This reaction results in the formation of Co OH 2and LiOH which can be readily separated because of their different solubility 12 8g 100 mL for LiOH and 0 0032g 100mL for Co OH 2at 25 C After filtration of the precipitates the resultant was rinsed with deionized water and dried All the above process are shown in Fig 4 3 2 Refining of lithium resource To purify the lithium source to obtain a battery grade material the filtered transparent solution was first evaporated at 80 C to obtain the dried lithium compounds In this case the added Na2SO4remained in the dried products although the resulting main product was Li2CO3 Fig 5a For this reason the separated waste solution containing li thium sources was purified using the carbonation method Because li thium was present in an ionic state in the solution we anticipated that the incorporation of CO2gas leads to the production of Li2CO3 As shown in Fig 5a and b drying of the solution resulted in a yield of powders of approximately 57 of which Na2SO4of ca 19 present with Li2CO3 thus 38 yield of Li2CO3 as retained from the XRD data Fig S4 The total yield was calculated from the total weight of the obtained solid powder after evaporation of the CO2gas contained a transparent solution of Fig 5 It is interesting that the yield of lithium compounds as Li2CO3powders abruptly increased to 85 with the in jection of CO2gas at a flow rate of 500 mLmin 1for 30sat 25 C CO2 gas injection for 10min resulted in a yield close to 99 Again the presence of CO2improved the yield of solidified lithium compounds however it was necessary to remove the Na2SO4to increase the purity of Li2CO3 The carbonation process can be summarized as follows CO2 H2O H2CO3 HCO3 H 6 Li HCO3 LiHCO3 7 2LiHCO3 Li2CO3 H2O CO2 8 Low temperature is favored for reaction 6 because of the high solubility of CO2gas in water at low temperature Fig S5 Once HCO3 was produced LiHCO3solution was spontaneously produced reaction 7 Thermal decomposition was required for the formation of Li2CO3 reaction 8 In this process the formation of high purity Fig 5 a XRD patterns under various conditions of CO2gas injection inset image of 10min carbonized powder and b yield of obtained solid waste as a function of CO2gas injection time red bar Li2CO3and blue bar Na2SO4 c XRD patterns before and after washing of powders obtained from the solution that CO2gas was injected for 10min inset images before and after washing and d Composition of the obtained powder as a function of washing temperature C H Jo and S T MyungJournal of Power Sources 426 2019 259 265 263 LiHCO3was an important factor determining the purity of the final product Li2CO3 The XRD pattern of the product formed after CO2gas injection for 10min confirms the presence of Na2SO4 Fig 5a The color of the powders was a pale yellow tone caused by the presence of remaining Na2SO4as an impurity inset of Fig 5a Because the solu bility of Na2SO4and Li2CO3in water at 40 C are 47 and 1 08 g mL 1 respectively Fig S6 the residual Na2SO4can be removed by washing the carbonized powder thereby producing high purity Li2CO3 Fig 5c and d Hence the carbonized products were washed with water at 80 C for 30s to minimize dissolution of Li2CO3 As expected no trace of Na2SO4remained after the washing followed by drying at 80 C in a vacuum and the resulting XRD pattern was identified as a single phase Li2CO3white powder Fig 5c with a yield of approximately 81 from the powder Fig 5c The washed solution evaporated at 100 C left pale yellow powders which were confirmed to be pure Na2SO4 Fig S7 Finally the produced Li2CO3powders were analyzed and compared with a commercially available product Li2CO3 sigma Aldrich Fig 6 Table S2 The XRD patterns were identical indicating crystallization into the monoclinic zabuyelite structure with C2 c space group Fig 6a In addition there were no significant differences in the powder morphology Fig 6b The impurity contents of the commer cialized and recycled Li2CO3were quantitatively analyzed using ICP AES and an EA Table S2 The final purity of the recycled Li2CO3was also 99 48 For the present cycling process we here used inexpensive agents H2SO4 NaOH 12 35 kg 1in chemical reagent level and the process does not need high temperature process to obtain Li2CO3and Co OH 2 Although direct comparison among recycle processes are not possible at present our method is beneficial to recover expensive me tals economically and eco friendly with high purity from discarded batteries The weight of the cathode composite is approximately 90 g in which the weight of the LiCoO2material was about 76 5g The purified Li2CO3and Co OH 2were approximately 13 0 g and 65 1g respec tively which showed yields of 85 and 90 compared with the the oretical yield Li2CO3 15 3 g Co OH 2 72 3g This high yield ratio is worth mentioning in consideration of the yield from pyrometallurgical method 50 versus the initial material 32 The present process does not crush batteries and employs evaporation at high temperature so that recovery of high purity Li2CO3and Co3O4is possible with high yield Furthermore this work emphasizes how to recycle discarded LIBs economically and eco friendly to raw materials with high purity For Li NiCoMn O2 NCM and Li NiCoAl O2 NCA adopting batteries since all the active materials from discarded batteries are also dissolved in acidic H2SO4solution sophisticated separation of each Ni Co Mn and Al ions is required Due to similarity in pH for formation of hydroxides Fig S8 it is thought that one of possible ways to separate each ions is to mask each ion using membranes varying pH during precipitation as a form of hydroxide We are planning to extend our