Battery Recycling Technologies – Part 2: Recycling Lead-Acid and Li-ion

Lead-Acid Batteries (LABs)

LABs can be used in various applications and are very common in the market. Since different applications have different battery requirements, manufacturers must provide diverse LAB designs and approaches. For example, the automotive sector uses starter batteries that provide short power bursts but not a prolonged power supply. On the other hand, solar applications require deep-cycle LABs that have more lead material.

The dominant part of the LAB is lead and lead-oxide (approximately 65%), and sulfuric acid (10-15%). Lead is a highly toxic heavy metal with hazardous health effects. It can cause damage to the brain and kidneys. The sulfuric acid is also dangerous as it can cause skin burns and damage the eyes. However, LABs in operation are quite safe with a low risk of fire.

Since lead is an expensive material and LABs have high lead content, used LAB waste (lead-scrap) is successfully recycled all over the world. LABs are fully recycled, and each part of old batteries is used for manufacturing new batteries.

LAB recycling is still known to be a severe environmental hot spot. Nevertheless, high environmental standards are applied to minimize lead and sulfur emissions. The recycling process must be performed in accordance to relevant standards. There are several health and emissions risks:

• Uncontrolled drainage and disposal of battery acid
• Emission of lead particles and acid caused by inappropriate battery breaking processes
• Inappropriate disposal of hazardous furnace slags
• Hygiene and hazardous working conditions in the factory.

LAB recycling requires a pre-recycling procedure, including breaking of the batteries and separating the electrolyte, lead-scrap and plastics. Non-LABs should be separated because the recycling process for LABs differs from that for other battery types. Damaged and swollen batteries should also be removed during this process.  

LAB Recycling Process

After the initial inspection, LABs undergo an automated process starting with a battery cutting machine with rotating hammers typically powered by an asynchronous motor. The acid is released and collected, and the resulting mix is separated through a sink-float tank-type process, separating the lead and lead paste from the other materials—Polypropylene-PP, Polyvinyl chloride-PVC and Acrylonitrile butadiene styrene-ABS. The lead and heavy materials fall to the bottom and the plastic floats. The collected lead, plastic, acid and other materials are then recycled separately. 

Plastic is washed, dried and melted together in the plastic recycler. The molten plastic is processed through a granulator that produces a uniform particle with a final size suitable for reuse.

Lead parts—lead grids, lead oxide and others—are cleaned and heated inside smelting furnaces at a temperature from 1,000 to 1,250°C. Sodium hydrogen carbonate can be added in liquid form for supplementary purification from metal residuals. The molten lead is then poured into ingot molds where the impurities float to the top and are scraped away. When the ingots cool, they are transported to battery manufacturers where they can be re-melted and used for new batteries.

Battery sulfuric acid can be neutralized or recycled. Neutralization is the process of turning the acid into water by using an industrial base compound. The water needs to be cleaned and tested. Recycling converts the acid to sodium sulfate, which can be used as white powder for laundry detergent and glass and textile production.

Lithium-ion Battery (LIB) Recycling

The rise of LIBs, especially for electric vehicles (EVs), presents a serious waste-management challenge for battery recyclers.

There are several different types of LIBs:

-       Lithium-nickel-manganese-cobalt-oxide (linimncoo2)

-       Lithium-cobalt-oxide (licoo2)

-       Lithium-cobalt-aluminum-oxide (licoalo2)

-       Lithium-manganese-oxide (limn2o4)

-       Lithium-iron-phosphate (lifepo4)

-       Lithium-titanate (Li4Ti5O12)

Cobalt-containing LIBs have high energy-density and are more expensive. This type is usually used in mobile and EVs applications where the energy density is a crucial parameter. Stationary uses, such as off-grid solar plants, mostly use the cheaper LiMn2O4 and LiFePO4 batteries. Li4Ti5O12 batteries have low energy density and, while more expensive, have an advantage in terms of fire safety.

The toxicity and hazard potential of LIBs is significantly lower than LABs. However, LABs are recycled to a far greater extent than LIBs. LIBs contain heavy metals and other parts with potentially negative human and environmental effects. LIBs are also associated with safety risks under certain conditions. For example, overcharging, high temperatures and physical stress can cause thermal runaway, which destroys the battery and can cause fire and explosions. One burning cell can cause problems and thermal runaways in neighboring cells. Deep-battery discharging can cause battery fires as well.

LIB recycling is still a new technological approach and currently provided just by a few plants in the world.

Umicore’s facility in Hoboken, Belgium, is a plant with the largest recycling capacity of approximately 7,000 tons of batteries per year, which is around 250 million cellphone batteries or 35,000 EV batteries (source: Umicore 2018). The focus of the recycling facility is on the recovery of nickel, copper and cobalt because they are rare earth elements. Lithium is recycled from the slag phase. Other materials, such as iron, graphite and phosphor, are not recycled. The profitability of LIB recycling is mostly influenced by the concentrations of cobalt and nickel.

End-of-life batteries need to be collected and transported per international regulations on the transport of dangerous goods. Thermal runaway and fire can be avoided if the batteries are fully discharged before transport and embedded in sand.

LIB Recycling Methods

There are several processes for LIB recycling. The pyrometallurgical recovery method uses a high-temperature furnace to smelt the batteries, during which the component metal oxides are reduced to an alloy of cobalt, copper, iron and nickel. The advantage of this method is the ability to use whole cells or modules, skipping a prior passivation step.

The pyrometallurgical process produces a metallic alloy fraction, slag and gases. At temperatures below 150°C gasses containing volatile organics from the electrolyte and binding components are generated. Higher temperatures will burn off the polymers. The resulting metal alloy can be separated in additional hydrometallurgical processes, making the component metals and slag. The slag contains aluminum, manganese, and lithium metals that can be used in other applications, such as the cement industry.

The burning of the electrolytes and plastics produces heat energy (exothermic process), reducing energy consumption. The pyrometallurgical process cannot recycle the electrolytes, plastics or lithium salts. The disadvantage of this process is the production of toxic gases, high-energy requirements and limited materials that can be recycled. However, this method is still commonly used to recycle the highly valued cobalt and nickel.

The physical material separation processes are performed after battery material comminution. Separation processes are based onproperties such as size, density, ferromagnetism and hydrophobicity. The materials are separated using filters, sieves, shakers and magnets. Magnet separation removes magnetic material (steel casings), and density separation separates plastics from foils.

The black mass (the electrode coatings)contains metal oxides and carbon. Froth flotation is used to extract the carbon from metal oxides. Carbon hydrophobicity is used to separate this material from the more hydrophilic metal oxides.

To extract the graphite and metal oxides from the copper and aluminum current collectors, it is necessary to eliminate the polymeric binders from the black mass components. This can be done by using sonication in a solvent (N-methyl-2-pyrrolidoneor dimethyl-formamide) and thermal heat treatment. The process is slow, approximately three hours, and requires high temperatures, up to 100°C. However, new battery designs use alternative binders on the anode, such as carboxymethyl cellulose, which is water-soluble, or styrene-butadiene rubber used as an emulsion, which is not water-soluble but can be easier to remove during battery recycling. Currently, researchers are working on cathode water-based binder systems, but they are still in the laboratory phase [1].

The hydrometallurgical metals reclamation process leaches the corresponding metals from the cathode material. The commonly used reagent is H₂SO₄/H₂O₂. The leaching efficiency is improved by adding H₂O₂.

The shredding process is fast and efficient, but it complicates future steps in the recycling process because the anode and cathode materials get mixed. It would be much simpler if the anode and cathode were separated prior to the shredding. As such, the current battery cell design that includes polyvinylidene fluoride as a binder makes recycling extremely complex.

The direct recycling process is used to remove the cathode or anode material from the electrode. This recycled material is used for LIB remanufacturing. With minimal changes, the mixed metal-oxide cathode materials can be reincorporated into a new cathode electrode. It is necessary to add lithium because of material losses during battery degradation. When the battery is fully discharged with completely lithiated cathodes, the materials cannot be recovered. The advantage of direct recycling is the possibility to recover all battery components and reuse them after further processing without the need for material separators. Also, the direct method does not require long-lasting and expensive purification steps. The method is convenient for lower-value cathodes, such as LiMn2O4 and LiFePO4, where the cathode oxides are the dominant factor for the costs of the cathodes. This recycling process is usually used for laptop and cellphone batteries.

The biological metals recycling process is an emerging technology for recycling metals from LIBs. The process uses bioleaching by using bacteria harnessed to recover metals. The microorganisms process metal oxides from the cathode and produce metal nanoparticles. The method is relatively new, and there are numerous opportunities for further research in this field. Biological metals recycling has so far been used in the mining industry.

Summary

Successful, efficient and cost-effective LIB recycling is a true challenge, mainly due to the complex multi-material structure of LIBs. However, constant research and development in this field is bringing improvements every day.

Currently, conventional pyrometallurgical or hydrometallurgical recycling processes used for high-cobalt cathodes (lithium cobalt oxide) can recover approximately 70% of the cathode materials. The efficiency significantly drops in the case of cathodes with low-value of cobalt chemistries.[2]

The table below gives an overview of the existing recycling methods.

Table 1: Comparison of different LIB recycling methods

[1] Nirmale, T. C., Kale, B. B. & Varma, A. J. A review on cellulose and lignin based binders and electrodes: small steps towards a sustainable lithium ion battery. Int. J. Biol. Macromol. 103, 1032–1043 (2017).

[2] Gaines, L. Lithium-ion battery recycling processes: research towards a sustainable course. Sustain. Mater. Technol. 17, e00068 (2018).