**1. Introduction**

Since the development of lithium-ion batteries (LIBs) in the 1970s, and due to the exclusive attributes of a long lifespan and high energy capacity, LIBs have grown to be important in the field of portable electronic devices [1,2]. In 2015, at least 5.6 billion LIB cells were traded globally [3,4], and the market size of LIBs has been predicted to grow by another 12% from 2016 to 2024, achieving a market value of USD 56 billion by 2024 [3]. Due to their significantly higher energy density, economic, and ecological advantages over other cell technologies, LIBs are particularly suitable as traction batteries, and therefore are predestined to be used in electric vehicles. The shift from internal combustion engines (ICEs) to e-mobility is expected to lead to even greater increases in registrations of electrically powered vehicles in the coming years. Kosai et al. claimed that, by 2050, up to 56 million battery electric vehicles (BEVs) are expected to be registered, 28 times as many as in 2016, which increases the demand for LIBs significantly [5].

After reaching their end of life (EOL), because they become hazardous materials in the waste stream of the environment, EOL LIBs need to be managed responsibly [6,7]. In Europe, between the years 2013 and 2014, the LIB market reported a total consumption of 65,500 tons of LIBs [8], while only about 1900 tons was recycled in the same period [3].

**Citation:** Kurz, L.; Faryadras, M.; Klugius, I.; Reichert, F.; Scheibe, A.; Schmidt, M.; Wörner, R. Global Warming Potential of a New Waterjet-Based Recycling Process for Cathode Materials of Lithium-Ion Batteries. *Batteries* **2021**, *7*, 29. https://doi.org/10.3390/ batteries7020029

Academic Editor: Kai Peter Birke

Received: 1 April 2021 Accepted: 20 April 2021 Published: 1 May 2021

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In another report, Wang et al. [9] claimed that the number of waste LIBs in vehicles that would need to be recycled, in an optimistic case, would be 6.76 million in 2035. Through a combination of innovations in recycling technologies and proactive regulations regarding collection and disposal of spent batteries, a significant fraction of the materials required for production of new LIBs could be supplied by EOL LIBs [10]. With the recently published proposal concerning batteries and waste batteries, the European Union (EU) aims to boost the circular economy of the battery value chain to reduce the environmental impact of batteries. To achieve this, the EU is striving for directives that set minimum rates for the recycling of EOL batteries and usage of recyclate within the production of new batteries for the EU market [11]. Therefore, the development of applicable technologies for LIB recycling, to recover particularly the elements that are low in the earth crust, are necessary [9]. Another aim of recycling LIBs is to keep hazardous materials from entering landfills [12] and to close the loop of raw materials utilized in LIBs for long-term sustainability and resource conservation [13]. In other words, since recycling processes enable internal material flows, it is considered to be a fundamental aspect of the circular economy [3].

Apart from reusing the batteries, recycling of LIBs can be categorized into the following three different technologies [9], used alone or in combination—namely, hydrometallurgy (e.g., retrieve technologies); pyrometallurgy (e.g., Umicore); and direct recycling (example—On to tech) [10,14,15], as shown in Figure 1. The pretreatment process includes discharging by immersing in a salt solution (e.g., NaCl), dismantling, which must be done in a sealed environment for safety reasons, and separating of damaged spent LIBs [9]. The hydrometallurgy route involves the leaching of valuable elements from a solid matrix into ions formed in a solution of inorganic or organic acid [16] and, subsequently, recovery of these metals by selective separation, electrochemical deposition, solvent extraction [16] into mono-metal material, or a precursor for the fabrication of new electrode materials [9,17]. Before hydrometallurgical treatment, the spent LIBs usually get shredded for an easier leaching procedure. The pyrometallurgical route is a smelting process which concentrates metal species such as Co, Cu, and Ni in the molten phase, while other constituents such as Li, Al, Si, Ca, and some Fe in the slag phase [9,14]. In order to obtain pure metals or metal salts, the slags are processed using the hydrometallurgical technique. In direct recycling, battery material is recovered without breaking it down into its components [6,18]. The aim is to reuse this material in new cells with minimal effort and without additional processes [6]. The most important battery material for direct recycling is considered to be the cathode material, as it is usually the most valuable component of an LIB cell with 33% of the total cost [19]. The most important question, however, is whether the recovered material can have comparable quality properties to virgin material [6]. While recovered material from direct recycling methods might not perform the same as primary material, however, compared to the hydrometallurgy and pyrometallurgy, direct recycling methods appear to be more environmentally friendly with lower amounts of emissions and energy consumption [10].

**Figure 1.** Battery recycling routes [20].

Beside these, recently, there have been other methods for battery recycling reported. These methods, include cathode healing, which combines two simple steps of hydrothermal processing of the spent cathode material followed by heat treatment in a cost-effective way [21], deagglomeration of polyvinylidene fluoride binder from cathode composite, which is based on a degree of surface hydrophobicity using the froth flotation method [14], and an oxalic coprecipitation method, which is a closed-loop regeneration method for LiNi5Co2Mn3O2 material of spent LIBs using mixed acid leaching, oxalate co-precipitation and solid-phase reaction [16].

Sieber et al. [17] claimed that, as we move into the future, resource- and energyinefficient hydrometallurgy and pyrometallurgy recycling methods must be avoided. Since there are no reports on waterjet-based battery recycling processes to the best of our knowledge, the here-presented procedure is new in the field of battery recycling. This new approach involves a waterjet-based direct recycling method (or functional recycling) with minimal use of chemicals and energy for separation of the cathode-coating layer, which contains LiNixMnyCozO2 (NMC), carbon black, and organic binder from the Al substrate foil, while preserving their chemical, physical, and morphological characteristics [17]. This recycling process does not use energy-intensive shredding or melting down of the cells, as is otherwise used in conventional recycling processes for LIBs. Instead, the process focuses on dismantling the battery and the cell itself as far as possible. The separated electrode then goes on a conveyor belt through a water jetting process, whereby the electrode coating is separated from the collector foil by a high-pressure water jet. The intention of this direct (or functional) recycling approach is to add recovered battery-grade cathode material to new NMC active material up to a certain proportion. Doose et al. [22] claimed that recycling processes must be flexible and adaptable to future cell chemistry and production technologies. Whether or not this waterjet-based recycling can meet these criteria, and can be used for production of new cells, must be examined.

In this study, this new waterjet-based direct recycling approach was ecologically evaluated with the help of a life cycle assessment (LCA) to evaluate its potential ecologic performance. The structure of this LCA is divided into four sections according to the standards DIN EN ISO 14040:2006 [23] and ISO 14044:2006 [24]—the objectives and methodology of the study, life cycle inventory (LCI), life cycle impact assessment (LCIA), and life cycle evaluation.

## **2. Objectives and Methodology of the Study**

## *2.1. Objective of the Study*

In November 2019, the joint project "Industrial Disassembly of Battery Modules and E-Motors to Secure Economically Strategic Raw Materials for E-Mobility (DeMoBat)" [25] was approved by the government of Baden-Wuerttemberg in Germany. The aim is, inter alia, to investigate the feasibility of a waterjet-based recycling process for traction batteries (TBs), to explore the limits of possible admixtures and to identify the potentials for reuse in the TB manufacturing process. Part of this project is to assess the environmental impacts of such an approach. Therefore, we modelled a waterjet-based recycling method for TBs to create an LCA, as well as to be able to draw conclusions about the environmental impacts associated with the recovered cathode coating. Furthermore, comparisons with indirect recycling processes should be made where possible, as well as to investigate possible impacts on new cathode coatings through different admixtures. The focus of this study is primarily based on the impact category of the global warming potential (GWP), which represents an excerpt from a complete LCA.
