Recycling of spent rechargeable batteries: A review for the lithium-ion batteries

Recycling of spent rechargeable batteries: A review for the lithium-ion batteries G.G. Papavasileiou, C.S. Psomopoulos *, G.Ch. Ioannidis, S.D. Kaminaris Department of Electrical Engineer, Piraeus University of Applied Science, 12244 Egaleo, Greece *Corresponding author: E-mail: cpsomop@teipir.gr, Tel +30 2105381182 Abstract The large availability of different types of electrodes has promoted the development of various types of batteries having different design, size, capacity, power and energy capabilities. Batteries applications are rapidly growing resulting in boosting resources demand. Battery recycling is a necessity, to relieve the shortage of rare resources and eliminate the pollution of hazardous components. In this paper, the current status of the recycling processes of spent lithium batteries, as well as, some examples of typical combined recycling processes are presented. Also, problems and prospect of some recycling technologies are put forward. Meanwhile, the advantages, disadvantages and prospect of each single process, combined process, as well as industrial recycling processes, are presented. Keywords: rechargeable batteries recycling; metals recovery; industrial recycling processes. 1. INTRODUCTION A battery is an electrochemical device comprising one or more electrochemical cells and has the ability to convert the stored chemical energy into electricity. In the last 100 years, batteries have extremely penetrated on the daily life of man, having a wide range of applications from mobiles up to electric cars in recent years.. The batteries are divided in two categories: primary batteries and rechargeable batteries. Some rechargeable batteries are Nickel-Metal hydride (NiMH) batteries, Nickel-Cadmium (Ni-Cd) batteries, lead-acid batteries and Lithium-ion batteries (LIBS). Comparing rechargeable batteries, it is concluded that the Lithium-ion battery has a higher energy density, power, more recharging cycles, longer life, lower self-discharge and higher cell voltage. Taking all of these into account, it is fully understood why Lithium-ion batteries are the most commonly used compared to other rechargeable batteries [1, 2, 3]. The need for energy storage in combination with increased energy demand for electrical and electronic appliances forced a great increment of the production and consumption of rechargeable batteries. This resulted to a significant increase of the use of metal that have been considered as potential or toxic behavior in live beens. So recycling and recovery of battery waste materials is a vital need as it will significantly reduce the consumption of potentially hazardous metals and raw materials, preventing further environmental pollution. The development of technology on the design of advanced recycling processes is considered to be one of the most important (if not the most important) steps to increase the rate of recycling waste. Even though the lithium-ion batteries are highly used today, their methods used for material recovery during their end of the life are still in laboratory scale [1, 2, 3]. This work is attempting to present the basic methods used for recycling Lithium-ion spent batteries. Physical, chemical, mechanical and combined methods are presented in order to be compared. 2. MATERIALS AND METHODS 2.1 Typical Lithium ion battery The essential parts of a battery are: the anode, the cathode, the electrolyte mixture, and the separator. The main differences between batteries are the materials of which the electrodes and the electrolyte are made, which give also the respective battery properties [5]. Proceedings of the Fifth International Conference on Environmental Management, Engineering, Planning & Economics ISBN: 978-960-6865-87-9, Mykonos island, Greece, June 14-18, 2015 315

The overall reaction: Discharge LiMO2 + 6C Charge Li1-xMO2 + LixC6 (1) The anode is the negative electrode of a primary cell and is always associated with the oxidation or the release of electrons into the external circuit. In a rechargeable cell, the anode is the negative pole during discharge and the positive pole during charge. The standard material used as an anode is carbon. Other materials could be used, but not as usual (such as graphite and petroleum coke), which give different properties, like temperature [4, 2, 6]. The anodic reaction: Discharge xli + + xe- + 6C LixC 6 (2) Charge The cathode is the electrode from which the current leaving the battery. Research on new cathodes for Lithium-ion batteries has been directed towards crystalline metal oxide-based materials, with charge stored by lithium insertion into the material matrix. It is usually made of aluminum plate coated with an active material such as cobalt-based lithium-ion, nickel cobalt aluminum, lithium iron phosphate [4, 2, 7, 8]. The cathodic reaction: Discharge LiMO2 Charge Li1-xMO2 + xli+ + xe- (3) The electrolyte is an organic liquid which helps to become the transport of ions between the electrodes thereby causing the stored chemical energy into electrical. The most common element used is LiPF 6 because of the fact that the voltage of a Li-ion cell ( 3.6 V) is higher than the standard potential of electrolysis of water (1.23 V at 25 C), so a nonaqueous solvent is necessary. Also, the electrolyte should contain lithium salts for higher ionic conductivity. Some other chemicals used for the electrolyte are LiPF 6, LiBF 4, LiCF 3 SO 3, or Li (SO 2 CF 3 ) 2 [2, 8]. The separator is a microporous film which is located between the anode and the cathode to maintain a distance between them (thereby preventing the short circuit of the battery). The standard construction material is polypropylene or polyethylene. Its thickness is 25μm, so ideally, separators are thinner than 25μm. It functions as a safety device of the battery because if it is overheated it melts and comes in contact with both electrodes [4, 9]. 2.2 Recycling processes The procedures for recycling Lithium-ion batteries are divided into two basic categories of simple procedures [which are divided into physical (pretreatment) and chemical (secondary treatment)] and combinatorial processes. On used Li-ion batteries always a small part of power remains. It is not unusual that batteries blow up during the recycling process due to oxidation when lithium is exposed to air due to the significant mechanical shock. For this reason glasses, gloves and gas mask should be used in every step in every process must be used [4, 7]. 316

2.2.1 Simple processes The metal parts may be collected through different procedures which are divided into two categories: physical processes (pretreatment) and chemical processes (secondary treatment): A. Physical Processes (Pretreatment) Mechanical Separation process The mechanical separation process used to separate the outer casing and the cells from the metallic fraction which used for a hydrometallurgical or pyrometallurgical recycling process. It includes two stages of crushing and sieving, to reach sufficient separation of metals from waste. At first, crushing and sieving is applied to separate metals and then magnetic separation is applied to remove the steel casing. Finally, in order to remove the last pieces of foil, again crushing and sieving is applied. [8]. Dissolution Process The dissolution process is in laboratory-scale. The battery is treated with N-methylpyrrolidone at 100 o C for 1 hour. LiCoO2 can be separated and recovered without separation of the cathode electrode from the anode. Also, copper and aluminum can be recovered in metallic form [8, 10]. Thermal Process For the thermal process several temperatures can be used while duration depends on the secondary treatment. For example, spent battery can be put in a furnace at 500 o C for 2 hours to remove carbon and organic compounds, since it is dissolved into solution HNO 3. Otherwise separation of LiCiO 2 from spent lithium-ion batteries can be reached by shredding and thermal treatment at 150-500 o C for 1 hour [8, 10]. Mechanochemical Process In this process Co and Li from spent Lithium-ion batteries could be recovered. After grinding LiCoO 2 with polyvinyl chloride (PVC) in a ball mill, Co and Li are extracted when leached with water. About 30 minutes of grinding is enough so that the lithium and cobalt recovery to be reached 90-100%. Finally, 90% of the chlorine in PVC has been converted into inorganic chloride. The purpose of this process is to recycle useful materials from the spent battery and from PVC [8]. Pyrometallaurgical Process It is the process by which battery materials are decomposed by heating at high temperatures under pressure. For the pyrometallurgical process strict filtering standards for air pollution from toxic gases has to be followed [5, 10]. B. Chemical Processes Hydrothermal Process The LiCoO 2 can be separated from the electrodes in a LiOH solution with a temperature increase rate of 3 C / min up to 200 o C without prior scraping process. The solution is not pressurized nor we add some gas so the LiCoO 2 from the cathode can be obtained [4]. Ultrasonic Process Ultrasonic process is used for the separation of the cathode materials from the Al foils. This happens because when the agitation is used alone, a lot of cathodic materials are stucked to the foils. So, an ultrasonic washing is used during the agitation for better separation. The ultrasonic process may be used as an adjunctive procedure [4]. Bioleaching Process Due to the high performance and the lower cost as well as the few industrial requirements, the 317

bioleaching process has begun to replace the leaching process. It is used for extracting of cobalt and lithium from spent batteries. For this process metabolites are used to dissolve metals from spent batteries. It is possible to dissolve metals from the cathodic electrode in a spent lithium-ion battery when acidophilic bacteria are used. [4, 8]. Acid Leaching Process The acid leaching process is the most widely used method for separating material from the cathode of the battery. For the leaching of LiCoO 2, inorganic acids such as: sulfuric acid (H2SO4), hydrochloric acid (HCl), and nitric acid (HNO3), and organic acids such as: citric acid and oxalic acid are used [4, 8]. 2.2.2 Typical combined recycling processes Cobalt, aluminum, lithium and manganese are the main metals for recycling but especially cobalt and lithium are of great importance due to their high cost. Many times a combination of recycling processes is needed to be used in order certain metals to be recovered [8]. A. Combination of crushing, acid leaching, heat treatment and chemical precipitation It operates in a dissolution of dilute acid, a chemical and thermal processing of the solid residue. After the first filtering, 100% of lithium and 95% of manganese can be recovered. Subsequent precipitation of hydroxide of manganese with NaOH solution at ph 10, contributes to a better separation of lithium and manganese. In the final stage the remained solid solution is placed in an oven at 500 o C for 2 hours to remove carbon and organic compounds. Also, heat recovery can be achieved at the outlet of the furnace for recovery of the combustion gases [8]. B. Combination of mechanical, thermal, hydrometallurgical and sol-gel steps At the beginning a leach is taken place and then the LiCoO 2 with nitric acid is added in a LiNO 3 solution. Next 1M citric acid is added to prepare a gelatinous precursor which will be calcined at 950 o C for 24h. Then, LiCoO 2 will be successfully obtained. Among the various processes to produce LiCoO 2, the amorphous citric precursor is one of the optimum ways with a lot of applications [8]. C. Combination of dismaltation, acid leaching, chemical precepitation and solvent extraction This process focus on recovery of cobalt and its separation from the moieties metal pieces. It comprises of the following steps: a) Usually Manual or semi automatic dismalting for the separation the parts of a battery (plastics, iron scraps, cobalt and other metals). b) Anode and cathode manual separation in order to separate the lead. c) Leaching with H 2 SO 4 and H 2 O 2 to become an aqueous solution. The 80% of cobalt and 95% of lithium have been obtained. d) Separate the aluminium with a precipitation in a NH 4 OH at ph 5. e) Using cyanex 272, the cobalt separates from lithium and the 85 % of cobalt obtained. The experimental results showed that around 55% of aluminum, 80% of cobalt and 95% of lithium were leached from the cathode when leaching solutions with H 2 SO 4 and H 2 O 2 were carried out [8]. D. Combination of mechanical dismantling and separator, electrochemical and thermal treatment The recycling process consists of five steps: dismantling, discharging, separation, detachment, and recycling. First, unit cells are soaked in brine for security. Then, manual separation of anode, separator, electrolyte, and cathode in the unit cell are applied. The recycling process is carried out at a 40 and 100 o C. When the recycling reaction will be in a progress, the platinum electrode is galvanostatically charged at a current density between 0.001 and 1.00mA cm 2. At the end, 318

recycling reaction consists of the dissolution of the depleted LiCoO 2, the deposition of the dissolved LiCoO 2 on the platinum electrode, the formation of the recovered LiCoO 2 film, as well as the precipitation of the recovered LiCoO 2 powder from the surface of the LiCoO 2 film [8]. E. Combination of dismantling, chemical deposition and solvent extraction This process is under laboratory scale and is designed to separate copper from cobalt in the spent lithium-ion batteries. The recycling process comprises the dismantling of spent lithium-ion batteries, the recovery of cobalt, and lithium using chemical deposition and solvent extraction methods, and the reuse of recovered compounds to synthesize LiCoO 2 cathode material. It is shown that about 90% of the cobalt was deposited as oxalate with less than 0.5% impurities, and Acorga M5640 and Cyanex 272 are efficient and selective for the extraction of copper and cobalt in sulphate solution. Over 98% of the copper and 97% of the cobalt was recovered [8]. 3. RESULTS AND DISCUSSION 3.1 Advantages and disadvantages of recycling processes There are disadvantages and advantages in any process. A disadvantage of the mechanical separation process is that it cannot recover all substances included in a spent Li-ion battery, since the chemical elements have a form very difficult to be separated. Heat treatment has the advantage of being simple operation but it should be chosen specific equipment type to collect certain materials from smoke or gas. The advantage of the dissolving process is that LiCoO 2 can be separated easily from their support substrate and the recovering of cobalt and aluminum in easier. But there is the disadvantage that the solvent N-methylpyrrolidone is very expensive. For the combined process: crushing, acid washing, processing and chemical precipitation heat, it could be said that is safe, low cost and with this process could be recovered a lot of substances from a lithium ion battery. The powder LiCoO 2 created after the combination process of mechanical, thermal, hydrometallurgical and sol-gel steps showed that the cathode from the viewpoint of chargedischarge present better characteristics[8,11]. The materials used for the production of electrodes in Li-batteries are considered as expensive and present toxic behaviour in the environment, making their recovery a necessity. In order to be financial feasible the recycling process should be simple flexible and must not have very long processes and equipment. In many cases both aforementioned procedures are used combined, sometimes, with a pretreatment step such as pyrolysis or mechanical treatment. The disadvantage of all the pyrometallurgical processes is the high energy consumption and the stringent requirements for the cleaning of equipment [8]. 4. CONCLUSIONS Nowadays, all procedures are focused on obtaining lithium, cobalt and cadmium from the electrodes because these metals are very expensive. All methods used for processing the end of life batteries. The dominant procedures are metallurgical ones. There are rare occasions where it is recycled by means of microorganism s procedure made several studies. Future research on recycling technologies will focus not only on the acquisition of useful resources (metals) and whether to reduce the use of harmful materials to the environment. Metals recovered through these processes are potentially toxic and the methods used are under continuous improvement. There are many steps on the way yet but the preservation of environment is the target which is always kept. 319

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