Elsevier

Minerals Engineering

Volume 45, May 2013, Pages 4-17
Minerals Engineering

Adaptation of minerals processing operations for lithium-ion (LiBs) and nickel metal hydride (NiMH) batteries recycling: Critical review

https://doi.org/10.1016/j.mineng.2012.12.005Get rights and content

Abstract

Production of LiBs and NiMH batteries is expected to increase rapidly due to the soaring price of oil and gas which increases interest in renewable energy as well as the introduction of hybrid vehicles (HVs), and electric vehicles (EVs) which used secondary batteries as an effective energy storage device. Development of an efficient recycling scheme to recover the valuable parts and safely dispose the harmful one at batteries end life is a necessity. The challenge, however, is how to recover all the valuable metals without sacrificing the economics of recycling process.

Several LiBs and NiMH batteries recycling processes have been developed in recent years. A review of these processes and their development timeline was presented in this paper. It was found that the major drawback of these recycling processes is the losses of some of batteries valuable parts since these recycling processes are not originally developed for this type of batteries. Also, some of these processes are expensive and designed for specific types of batteries which ignore contamination of recycling stream with impurities and other type of batteries.

Using minerals processing operations such as grinding, sieving, magnetic, electrostatic, and gravity separations to liberate batteries electrodal materials and concentrate valuable metals is critical step in any recycling process. This may be due to the simplicity, efficiency, flexibility, and high throughput of these separation processes. The literature showed that applying these processes reduces the volume of LiBs and NiMH scrap, liberates their valuables, reduces the need for leachate purification in hydrometallurgical process, and facilitates the decomposing of battery’s electrolyte. Based on these results a flowsheet to recycle mixed stream LiBs, and NiMH battery scrap was proposed.

Highlights

► LiBs and NiMH batteries currently share more than 80% of batteries market. ► Recycling of these cells is an environmental and economical necessity. ► Cost, inflexibility, and losses of valuables are the major recycling drawbacks. ► A flowsheet for recycling mixed stream LiBs and NiMH battery scrap was proposed. ► The economic effect of pre-treatment on battery recycling was evaluated.

Introduction

Lithium-ion based batteries (LiBs) and nickel metal hydride (NiMH) batteries are currently dominated the portable electronics as well as hybrid vehicles (HVs) and electric vehicles (EVs) market. LiBs dominate the mobile phone and laptops industry while NiMH still shared large proportion of portable electronics such as camcorders as well as HV and EV. However, in recent years LiBs gradually replaced the NiMH batteries due to their higher volumetric and gravimetric energy density.

As an example, Japan secondary battery market statistics (Fig. 1) shows that LiBs market share increased linearly since its introduction to the market in 1993. In 2002, it had the same share as NiMH (about 30%) but since then it almost dominated the market with more than 65% share. On the other hand, NiMH batteries was representing 7.5% of Japan secondary battery in 1993. A peak value (50%) was reached in 2000 but since then the share decreased drastically leaving it with just 22% in 2011 (Sullivan and Gains, 2010).

The main reasons for such increase can be summarized as follows (Dewulf et al., 2010, Lin et al., 2003, Zhang et al., 1998a):

  • 1.

    Very good electrochemical properties of LiBs such as high energy density (120 W h/kg), high voltage (up to 3–6 V), longevity (500–1000 cycles), wide temperature range (−20 to 60 °C), and minimum memory effect.

  • 2.

    LiBs do not contain hazardous heavy metals such as cadmium and lead.

  • 3.

    Soaring price of oil and gas in recent years increasing the interest in renewable energy, HV, and EV which in turn increased the demand for secondary batteries in general as an effective energy storage device.

Some of batteries components are difficult to degrade. So discarding them after their end life into municipal waste may pollute the soil and underground water while their incineration contaminate the air by releasing toxic gases (Tedjar and Foudraz, 2010). Also, the recent surge in minerals price encouraged battery recycling as a cheaper source of valuable metals (Ruffino et al., 2011). Therefore, the development of an efficient recycling scheme to recover the valuable parts and safely dispose the harmful one is a necessity. This is also encouraged by countries legislations which makes recycling free of charge for end users or by forcing the manufactures to pay for it.

However, the amount of spent batteries available for recycling is small and does not match the large number of secondary cells produced for every year. For example, 97 tons of spent NiMH batteries were recycled in Germany in 2003 which represents only 3% of NiMH batteries produced in that year. According to Muller and Friedrich (2006), this may due to the following reasons:

  • 1.

    Long life time of NiMH batteries (4–7 years) and the behavior of the end users who usually keeps spent batteries for another 2–4 years as “Hoarding time” before disposing them.

  • 2.

    Inefficient spent batteries collection system either due to lack of legislations or public awareness.

Due to the heterogeneity of LiBs and NiMH batteries composition (Sections 2.1 and 2.2) as well as the spent batteries stream available for recycling, number of aspects need to be considered when designing an efficient recycling process. Firstly, designing recycling process for only one specific type of batteries is either technically difficult or economically unpractical. So the favorite choice is to develop a flexible recycling process (Castillo et al., 2002). Secondly, because of toxicity, reactivity, and corrosiveness of some components of these batteries, safe procedures are required during their recycling (Maclaughlin and Adams, 1999).

Self-ignition of spent NiMH batteries when they crushed due to the short circuit caused by moisture contact with hydrogen alloy powder is one aspect of safety risks. On the other hand, LiBs electrolyte (lithium phosphohexa fluorite, LiPF6) may react with water and produce toxic gases such as pentafluoro arsenic, pentafluoro phosphate, and hydrogen fluoride (Nan et al., 2006). Although LiBs used lithium ions instead of metallic lithium to reduce the risk of fire and releasing hydrogen gas, metallic lithium can be deposited on LiBs current collectors due to overcharging and discharging (Lin et al., 2003).

LiBs and NiMH batteries valuable or harmful components are tightly enclosed within battery case which usually made of steel, aluminum, plastics or nickel alloys. So, dismantling the outer shell by crushing and sieving removes the outer iron and plastic shell and facilitate the access to the valuable/harmful materials inside spent batteries. This step is also reduces the scrap volume and improving the subsequent recycling processes such as fine grinding and magnetic separation. Once, the electrodal materials were exposed, ferrous and non-ferrous components can be extracted by pyrometallurgical or hydrometallurgical processes while plastics and papers can be either recycled or incinerated to generate power (Nan et al., 2006).

The aim of this paper is to review the use of physical separation processes such as crushing, grinding, classification, magnetic, electrostatic, and gravity separation in LiBs and NiMH batteries recycling. These processes are already established in minerals processing industry and they are characterized by their relatively low cost and flexibility to treat variable ores characteristics. Using such methods as a pretreatment step before using more expensive hydrometallurgical or pyrometallurgical processes will reduces the amount of impurities in these processes inputs which in turn reduces their cost and increases their selectivity.

In the first section, we gave a brief introduction about the structure of LiBs and NiMH batteries emphasizing the amount of valuable metals they contain while in the second section, a summary of the current recycling processes were given showing their advantages and timeline since their introduction to the market in early 1990s. Physical treatment of LiBs and NiMH batteries were thoroughly investigated in the third section. Data from literature was reanalyzed in order to attenuate the role of physical treatment on the liberation and separation efficiency of each component of LiBs and NiMH batteries. Economics of battery recycling were discussed in the fourth section while our conclusions and recommendations were presented in the fifth section.

Section snippets

LiBs

Different manufactures produce LiBs with variable components. So receiving variable spent LiBs structure is inevitable. This may affect the efficiency and cost of the current hydro-pyrometallurgical based recycling processes.

In general, LiBs consist of positive and negative electrode, separator, electrolyte, and a stainless steel shell. Approximate percentage of each LiBs component is given in Fig. 2. The positive electrode consists of graphite coated on copper foil while the negative electrode

The importance of LiBs and NiMH batteries recycling

Besides the environmental benefits of LiBs and NiMH batteries recycling, they become possible cheaper source for metals due to the recent surge in minerals prices. As shown in Fig. 4, the main metals in LiBs scrap are cobalt, nickel, lithium, copper, manganese, and iron/steel while NiMH batteries contain nickel, cobalt, zinc, manganese, iron/steel as well as REE such as lanthanum, neodymium, cerium, praseodymium, and samarium. Usually, metals are recovered in their metallic form while lithium

Drawbacks of current recycling technologies

In view of previous discussions, the main concerns of secondary battery recycling are safety and cost. Lithium ion batteries may blow up during recycling due to the rapid oxidation of lithium metallic which may be deposited due to battery overcharging. Therefore, pretreatment of this type of batteries either thermally or cryogenically is a necessity for safety reasons (Shin et al., 2005). Also, LiBs contains toxic LiPF6 electrolyte while NiMH batteries contains corrosive alkaline electrolyte,

Mechanical treatment of LiBs and NiMH batteries

In minerals processing, grinding is a necessary step prior to any separation process aiming at liberating valuable particles from gangue. Spent batteries, therefore, require crushing and grinding in order to liberate electrodal materials which are encapsulated in iron and plastic case. Many researchers emphasized the importance of mechanical treatments of spent batteries as a prerequisite for hydrometallurgical process. Mechanical treatment is characterized by its simplicity, efficiency,

Economics of battery recycling

In order to evaluate the economic advantage of using mechanical processing in battery scrap recycling, a comparison between two scenarios were conducted; the first scenario is when battery scrap is firstly incinerated then extracting valuable metals by hydrometallurgy, while the second scenario consists of using crushing and sieving to classify the scrap to coarse and fine part and only the coarse part is smelted while the valuable metals were extracted from the fine part by hydrometallurgy.

As

Proposed flowsheet for recycling mixed LiBs and NiMH batteries

The importance of using mechanical processing as a prerequisite for more expensive hydrometallurgical and pyrometallurgical processes was highlighted in previous discussions. Therefore, we proposed a flowsheet (Fig. 13) which is a combination of minerals processing operations; this will ensure proper liberation of battery scrap valuable metals in order to separate as much as possible of battery scrap constituents to reduce the interference of these impurities with

Summary and conclusions

Based on previous discussion, the following conclusions can be drawn:

  • 1.

    LiBs and NiMH batteries currently share more than 80% of rechargeable batteries market. Production of these cells is expected to increase rapidly due to the soaring price of oil and gas which increases interest in renewable energy as well as the introduction of HV, and EV which used secondary batteries as an effective energy storage device.

  • 2.

    Safe disposal of these batteries at their end life is an environmental necessity since

Acknowledgments

The authors would like to thank Japan Society for Promotion of Science (JSPS) for their generous fellowship to the first author. Also, Dr. Salah sincerely thanks Prof. Nakamura and his laboratory staff for their warm welcome and support during his stay in the Institute of Multidisciplinary research for advanced materials (IMRAM), Tohoku University, Japan.

References (43)

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