Optimized Thermal Treatment of Lithium-Ion Battery Components as a Basis for Sustainable Pyrometallurgy

www.chemsuschem.org Optimized Thermal Treatment of Lithium-Ion Battery Components as a Basis for Sustainable Pyrometallurgy Anna Pražanová,* Jan Koˇcí, JonášUˇriˇcáˇr, Dominik Pilnaj, Daniel-Ioan Stroe, and Vaclav Knap The escalating global demand for lithium-ion batteries necessitates efficient and sustainable end-of-life management. Major recycling routes such as pyrometallurgy and hydrometallurgy offer promising paths for metal recovery, but their efficiency often depends on the pretreatment of spent batteries. However, optimizing low-temperature pretreatment for complete organic removal while preserving active material integrity remains challenging. This study investigated thermal decomposition and surface changes of key battery components—lithium nickel manganese cobalt oxide (NMC622) cathode, graphite anode, and polymeric separator—from 100 to 800 °C, focusing on the 400–650 °C industrial interval. Material responses were characterized using thermo-gravimetric analysis coupled with mass spectrometry, isothermal mass loss, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. A 500 °C treatment was identified as optimal, enabling complete organic carbon removal within 1 h without compromising the NMC spinel structure or current collector degradation. This precise control reduces energy consumption and mitigates hazardous gas release, enhancing environmental sustainability and providing a practical, scalable, and cost-effective strategy for improving battery recycling. These findings help to define the parameters for efficient electroactive material separation. This work advances the understanding of low-temperature thermal pretreatment for battery recycling, supporting a circular economy for critical materials. 1. Introduction The escalating global demand for lithium-ion batteries (LIBs), especially in electric vehicles (EVs), necessitates efficient and sustainable end-of-life (EOL) management strategies. [1,2] In parallel, growing environmental concerns and the limited availability of critical raw materials such as lithium, cobalt, and nickel underscore the importance of developing circular economy solutions that support resource security and industrial resilience. [3,4] Regardless of the final metallurgical recovery route, the recycling of spent LIBs typically begins with a series of pretreatment steps, among which thermal treatment is critical for handling the organic components [5–7] This step is foundational for both major recycling pathways. For hydrometallurgical processes, a controlled low-temperature treatment (typically up to 800 °C) is employed to decompose the organic binders (e.g., polyvinylidene fluoride - PVDF) and polymeric separators. This liberates the active materials from the current collectors, making them accessible for efficient downstream chemical leaching [8–10] For pyrometallurgical processes, this low-temperature stage serves a similar purpose of removing volatile and flammable organic materials to ensure safer and more stable operation of the subsequent high-temperature smelting (1500–1800 °C) for metal recovery. [11,12] It should be noted, however, that some industrial pyrometallurgical operations perform direct smelting of battery packs without a separate low-temperature pretreatment step. [13,14] Our work focuses on optimizing the separate, lowtemperature pretreatment, as this approach offers better control over organic degradation and preserves the integrity of active materials, enhancing the efficiency and sustainability of the overall recycling chain. The first stage conditions the internal electrode–separator assembly and mitigates safety hazards from residual electrolytes and flammable materials. [15] This step is often decoupled from metallurgical recovery to control organic degradation better, preserve active materials’integrity, and facilitate delamination for downstream recovery. However, decomposition involves overlapping reactions with specific onset temperatures, requiring precise process control. Among various chemistries, lithium nickel manganese cobalt oxide (NMC) is widely studied due to its prevalence in high-energy cells and complex thermochemical behavior. [16] Industrially, external casings (polymer-laminated aluminum (Al) A. Pražanová, J. Koˇcí, J. Uˇriˇcáˇr, D. Pilnaj, V. Knap Department of Electrotechnology Faculty of Electrical Engineering Czech Technical University in Prague Prague 16000, Czech Republic E-mail: [email protected] J. Koˇcí Department of Glass and Ceramics University of Chemistry and Technology Prague Technická 5, 166 28 Prague, Czech Republic J. Uˇriˇcáˇr Department of Polymers University of Chemistry and Technology Prague 16628 Prague, Czech Republic D.-I. Stroe Department of Energy Aalborg University Aalborg 9220, Denmark © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. ChemSusChem 2025,00, e202501753 (1 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 or nickel) are removed before thermal treatment, so research focuses on the internal stack: cathode, anode, and separator. [15,17] NMC cathodes are generally thermally stable relative to organic compounds, but their behavior depends on delithiation and residual binders or salts. [18] While the spinel structure may persist up to 800 °C, [19] side reactions involving lithium salts (e.g., lithium hexafluorophosphate, LiPF 6 ; lithium fluoride, LiF; lithium carbonate, Li 2 CO 3 ) can lead to the release of carbon dioxide (CO 2 ) or hydrogen fluoride (HF) and phosphorus-containing gases. [20,21] Furthermore, the Al current collector, with a melting point of ≈660 °C, may melt and encapsulate active material if temperatures exceed this threshold, [22,23] compromising downstream separation and material quality. [12,24,25] Therefore, precise temperature control is critical to remove organic compounds while preserving cathode integrity. [26] Graphite anodes exhibit high thermal stability under inert atmospheres but oxidize in air above ≈500 °C, resulting in significant CO 2 release and mass loss. [27] Complete combustion typically occurs between 600 and 700 °C, depending on oxygen content in the atmosphere, heating rate, and surface area [27–29] Residual surface compounds, such as lithium alkyl carbonates or Li 2 CO 3 , originating from solid electrolyte interphase layer degradation, may also affect the oxidation pathway and initiate earlier decomposition. [30] Polymeric separators, typically made of polyethylene (PE) or polypropylene (PP), begin to degrade below 200 °C. This involves initial melting followed by decomposition into hydrocarbon species [31–33] Polyvinylidene fluoride (PVDF), commonly used as a binder, decomposes between 350 and 500 °C, releasing HF, water, and low-molecular-weight fragments. [34] Above 500 °C, remaining residues are mostly converted into stable inorganic phases; for example, alumina-coated separators may yield aluminum oxide (Al 2 O 3 ) after treatment. [33] Given the complexity of multicomponent battery architectures, most studies on low-temperature pyrometallurgical pretreatment have focused on achieving efficient organic removal while preserving valuable materials, as both are essential for scalable LIB recycling [35–38] Thermal exposure between 500 and 600 °C is widely regarded as a critical step for decomposing polymeric binders and evaporating electrolyte residues, thereby improving the efficiency of mechanical comminution and downstream metal recovery. [37] However, temperatures above 600 °C can lead to the embrittlement or melting of Al foils, complicating their separation. In parallel, elevated temperatures also promote the carbothermic reduction of active materials, such as LiCoO 2 , which begins decomposing around 700 °C and affects both mass loss and lithium recovery yields. Although reviews of pretreatment strategies confirm that calcination between 150 and 650 °C efficiently removes conductive carbon and organic compounds, reducing binder adhesion and enhancing separability, they also emphasize challenges related to high energy demands and the release of hazardous gases, including toxic fluorinated species. [35,37] While several studies have explored high-temperature pyrometallurgy, a comprehensive insight into low-temperature pretreatment effects on cathode and separator integrity remains limited. Therefore, a detailed, component-specific understanding of thermal degradation, particularly how controlled heating influences the structure, surface chemistry, and separability of individual active materials and polymeric separators, is crucial for the development of energy-efficient, scalable recycling processes. Such processes must not only ensure effective organic removal but also minimize unwanted side reactions and preserve material functionality. [38,39] While several studies have explored high-temperature pyrometallurgy, a comprehensive insight into low-temperature pretreatment effects on cathode and separator integrity remains limited. Therefore, the primary aim of this work is to systematically investigate the thermal degradation and surface evolution of individual critical components—the NMC622 cathode, graphite anode, and polymeric separator—to identify an optimal pretreatment temperature. The novelty of this study lies in its integrated analytical approach. We combine dynamic analysis via thermogravimetric analysis coupled with mass spectrometry, static isothermal mass loss studies, and detailed surface characterization using scanning electron microscopy with energydispersive X-ray spectroscopy. This allows us to bridge the gap between simple mass loss, and a deeper understanding of how controlled heating influences the structural integrity, surface chemistry, and separability of materials. By defining a precise, energy-efficient temperature (500 °C) that ensures complete organic removal while preserving the valuable inorganic components, this work provides practical, foundational data for designing and scaling up sustainable pretreatment processes applicable to any subsequent metallurgical recovery, with a particular focus on its role as a basis for sustainable pyrometallurgy. 2. Experimental Section 2.1. Material The LIB pouch cells used in this study possess a nominal voltage of 3.65 V and a rated capacity of 78 Ah. These cells were previously characterized in our previous work by Pražanová et al. [40] Each cell comprises 36 stacked layers comprising NMC622 cathode materials, where the numbers indicate the molar ratio of Ni:Mn:Co, a polymer separator, and graphite-based anode layers. The electrolyte consists of LiPF 6 in an organic solvent, and the entire assembly was encapsulated in a flexible polymer– aluminum laminated pouch. The module was sourced from an electric vehicle at its EOL, representing a realistic feedstock for recycling. It had a nominal voltage of 29.36 V and a total energy capacity of 6.85 kWh. While the precise State of Health (SOH) was not determined, it was assumed to be in the typical 70%–80% range for an EOL battery. Critically, for safety reasons, before disassembly, the module was deeply discharged to ≈0 V. This process subjects the cell components to harsh conditions known to induce further irreversible degradation, thus positioning our samples as a challenging but representative case for thermal treatment. It could be postulated that a process proven effective on this degraded material will be equally or more successful on less degraded batteries (higher SOH). To access the internal cells, the module’s casing ChemSusChem 2025,00, e202501753 (2 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License was carefully milled open, and the adhesive bonding was weakened by applying alcohol to facilitate their separation. Subsequently, the cells were manually extracted from the opened module. The open structure of the module, individual battery cells, their opening procedure, and specimen preparation and characterization are shown in Figure 1. 2.2. Methods 2.2.1. Specimen Preparation A set of samples consisting of the active material coated on its native current collector was prepared for analysis. This configuration was intentionally maintained because a primary objective of the study is to optimize a thermal process that facilitates the separation (delamination) of the active material from the foil by decomposing the binder. Analyzing the isolated powder without the foil would therefore not align with the study’s practical, recycling-oriented goals. To ensure statistical validity and reproducibility, all measurements were conducted in five independent replicates. The battery cell was carefully disassembled using a ceramic knife, and individual components, specifically the cathode enclosed within the separator pouch and the anode, were isolated. All procedures were conducted inside a laboratory fume hood. Following disassembly, as described in Figure 1, intact electrodes and the separator layers were predried at ambient temperature to evaporate the carbonates. The predried layers were subsequently sectioned into 25 25 mm square samples using a precision paper cutter. Afterwards, the sections were dried at 60 °C until no further decreases in mass were observed (approximately 1 week). The final samples were weighed in porcelain crucibles using an analytical balance. The specimens were classified into three groups according to their functional role within the cell: cathode, anode, and separator. In addition, a fourth reference group was prepared, consisting of the cathode layer covered by a separator on both sides, to control potential interfacial effects. This configuration deviates from the standard architecture, in which separators on both sides typically enclose the cathode. Five independent replicates were measured for each sample category to ensure statistical validity. For the thermal degradation analyzes, circular samples with a diameter of 5 mm were punched from an unopened battery cell using a manual puncher. These specimens comprised the entire cross-section of the battery cell, including spinel, separator, and graphite layers, and are hereinafter referred to as “crosssection samples.”In addition to the full cross-section samples, a separate specimen of cathode, anode, and the cathode with a two-sided separator was explicitly prepared for TGA-MS measurements. Figure 1. Overview of the experimental workflow: opening of the battery module, extraction and disassembly of pouch cells, preparation of specimens of battery materials, and subsequent morphological and elemental analyzes (SEM; energy-dispersive X-ray spectroscopy, EDS) followed by thermal analyzes (thermogravimetric analysis, TGA; thermogravimetric analysis coupled with mass spectrometry, TGA-MS). ChemSusChem 2025,00, e202501753 (3 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2.2.2. Material Characterization Methods 2.2.2.1. Thermogravimetric Analysis Thermal degradation in dynamic mode was assessed using a thermogravimetric analyzer (Discovery TGA550 Auto Advanced, TA Instruments, USA). A cross-section specimen, including all electrochemically active layers with a weight of ≈25 mg, was subjected to heating from room temperature (24 °C) to 1000 °C at a constant heating rate of 10 °C min 1 in an air atmosphere with a flow rate of 65 mL min 1 . 2.2.2.2. Thermogravimetric Analysis –Mass Spectrometry The chemical composition of degradation products was investigated using coupled TGA-MS. The following sample types were analyzed: cross-section, anode, cathode, and cathode with one-sided separator. Measurements were performed on a TG-DTA Setsys Evolution system (Setaram, France) coupled to an OmniStar quadrupole mass spectrometer (Pfeiffer Vacuum, Germany). Before thermal treatment, all samples were stabilized at 30 °C for 30 min. Subsequently, the samples were heated in an air atmosphere at a constant heating rate of 10 °C min 1 . After the heating and thermogravimetric data acquisition were completed, the samples were allowed to cool under ambient conditions, while mass spectrometric data acquisition continued for an additional 50 min. Mass spectra were recorded up to 150 m z 1 (mass-to-charge ratio) with a resolution of 1 m z 1 ; each spectrum was acquired over 8 s, corresponding to a dwell time of 53 milliseconds per m/z unit. The data obtained from TGA and MS were synchronously aligned, processed, annotated, and visualized using OriginPro software. Representative ions corresponding to specific compounds or chemical groups were selected based on the NIST17 library of electron ionization spectra. 2.2.2.3. Static Thermal Mass Loss Analysis Samples were placed in a CLASIC laboratory furnace with a frontopening design for static thermogravimetric measurements. Heating was performed at 5 °C min 1 to target temperatures of 100, 200, 300, 400, 500, 600, 700, and 800 °C, each followed by a 1h isothermal hold, then cooled to room temperature by natural convection overnight. The relatively high heating rate and short exposure time were chosen to reduce the required time to effectively obtain the studied materials, which corresponds to the study’s objectives and the economic demands of industrial use. This approach is relevant for pyrometallurgical pretreatment in battery recycling, where energy efficiency and time optimization are critical. Temperatures were selected to identify the minimum effective recycling threshold under economic constraints, focusing in detail on the 400 to 650 °C range, with measurements at 400, 450, 500, 550, 600, and 650 °C. After cooling to ambient temperature under natural conditions, gravimetric measurements were performed using a calibrated KERN analytical balance to evaluate mass loss resulting from thermal exposure. Each sample type was measured in five independent replicates, and the mass was recorded to four decimal places to ensure high precision. This methodology enabled a comprehensive assessment of thermally induced mass changes, enhancing understanding of material decomposition behavior across various temperature conditions. 2.2.2.4. Scanning Electron Microscopy Following thermal exposure, the samples were subjected to structural and compositional analyzes to assess changes induced by heat treatment. SEM was employed to examine modifications in surface morphology using a TESCAN VEGA 3 LMU scanning electron microscope. Imaging was conducted at an accelerating voltage of 20 kV, a working distance of 15 mm, and a beam intensity of 15 nA, utilizing both secondary and backscattered electrons at a magnification of 2000 . To complement the morphological investigation, EDS was performed to determine alterations in elemental composition. Measurements were conducted using an OXFORD Instruments INCA 350 EDS analyzer, enabling precise chemical microanalysis of the observed samples. Data were processed using AZtec software (version 4.4), with composition measurements taken over an area of 0.005 mm 2 , yielding an accuracy of 0.1 % for each measured point. Micro-X-ray elemental mapping was also carried out to visualize the spatial distribution of elements across the sample surface. 3. Results and Discussion 3.1. Dynamic Thermal Degradation Analysis The thermal degradation of the cross-section sample in an air atmosphere is a complex process involving multiple decomposition steps. While residual weight at a given temperature is observable, a static thermal weight loss test on a larger scale was also performed due to the dynamic nature of the measurement and the small sample size. The distinct decomposition steps are visible in the temperature-weight derivative curve shown in Figure 2a. The first significant weight loss, characterized by a peak around 120 °C, is followed by a double peak with maxima around 250 °C and 350 °C. A further small weight loss peak was observed around 450 °C. The most intensive weight loss occurred between 550 and 750 °C. High-temperature weight loss (above 900 °C) was also observed, which might be connected to fluorine release, as described in work by Ross et al. [41] While TGA provides valuable insight into the thermal degradation behavior of materials, it is insufficient to identify decomposition products. Therefore, TGA-MS was used to detect and identify evolved gases. The results in Figure 2b include the TGA temperature profile, followed by the weight loss curve and its first derivative in the second row. The subsequent rows display MS signal intensities for selected mass-to-charge (m/z) ChemSusChem 2025,00, e202501753 (4 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ratios: 15, 18, 20, 29, and 44, chosen for their relevance to degradation pathways and evolved moieties. Ion 15 corresponds to the methyl moiety, 18 to water, 20 to HF (though it may also arise from water containing the 18 O isotope), 29 to ethyl, formyl, or carbon monoxide, and 44 to CO 2 . Water, HF, and CO 2 were selected as indicative degradation products of the PVDF binder. [41,42] HF also originates from the thermal breakdown of the LiPF 6 electrolyte. Methyl and ethyl groups are typically associated with carbonate-based electrolyte solvents or with the thermal degradation of the PE separator. Additionally, CO 2 is a known oxidative degradation product of graphite. However, due to the mass spectrometric resolution of 1 m z 1 unit, coeluting or overlapping signals from other fragments cannot be excluded. For the same reason, CO was omitted from interpretation as its nominal mass is the same as N 2 in the carrier gas. Decomposition of the cross-section sample is first indicated by the emergence of peaks for methyl and ethyl groups around 120 °C, associated with the evaporation of carbonate-based solvents, most likely dimethyl or diethyl carbonate and methyl ethyl carbonate. A broad signal range for methyl, water, hydrogen fluoride, and ethyl between 225 and 450 °C reflects the decomposition of lithium alkyl carbonates. [43] The water signal appears as a doublet, with a second local maximum at ≈375 °C, corresponding to the thermal degradation of the PE separator. This is accompanied by ion 15, indicating CH 3 moieties released during the cleavage of PE chains. Water peak tails extending up to 530 °C are likely attributed to the decomposition of the PVDF binder. At temperatures exceeding 500 °C, a broad CO 2 signal is observed, corresponding to the thermo-oxidative degradation of the graphite anode. Similar TGA–MS measurements were performed on individual anode, cathode, and cathode-with-separator samples. The obtained profiles exhibited comparable trends with samplespecific variations; the cross-section sample profile (see Figure 2b), however, provides a representative overview and serves as the primary reference for interpretation. The anode sample exhibited broad peaks of water, hydrogen fluoride, methyl, and ethyl groups centered around 350 °C, primarily from decomposing lithium alkyl carbonates. [43] The tailing of water and hydrogen fluoride signals, absent for methyl and ethyl ions, is likely associated with the degradation of the PVDF polymeric binder, similarly to what was observed for the cross-section sample. The release of carbon dioxide, attributed to the thermo-oxidative degradation of graphite, began around 500 °C. As pristine graphite is known for its high thermal stability, the observed shift suggests that degradation during battery operation may reduce this stability. Figure 2. Thermal degradation analysis of the cross-section sample: a) TGA profile showing sample weight loss (black) and its temperature derivative (blue). b) Coupled TGA–MS analysis presenting the same thermal profile and mass spectrometric signals for selected degradation products. ChemSusChem 2025,00, e202501753 (5 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License The cathode and cathode-with-separator samples displayed behavior with notable differences from the cross-section and anode specimens. In the cathode-with-separator sample, the signals for methyl and ethyl groups appeared as distinct doublets, with lower-temperature peaks (around 200 °C) attributed to PE degradation. These peaks were less prominent in the cross-section data, likely due to their relatively low intensity and overlap with the end of carbonates evaporation. For the same sample, the water and carbon dioxide intensities peaked around 375 °C and were noticeably elevated, suggesting ongoing degradation of the PE separator. Both cathode-based measurements exhibited broad carbon dioxide peaks around 325 °C and 550 °C, even without graphite. These observations indicate that complex reactions may occur within the cathode layers. [44] Avoiding cathode exposure to temperatures above 500 °C is recommended to minimize these undesirable decomposition processes. 3.2. Static Thermal Mass Loss Analysis Understanding individual LIB components’thermal decomposition behavior and residual mass is crucial for designing efficient and safe recycling processes. Therefore, their thermal degradation patterns were assessed by monitoring mass loss after controlled heating steps. Figure 3 illustrates the components’ comprehensive mass loss profiles across a broad temperature range (0–800 °C). An initial minor mass loss, observed in all samples below 100 °C, is primarily attributed to the evaporation of residual electrolyte. Following this, significant thermal degradation of organic components commences in the separator, predominantly evidenced by mass loss between 100 and 300 °C. This temperature window represents the primary thermal degradation of the separator’s polymer matrix. While the polymer (e.g., polyethylene) decomposes at these lower temperatures, the separator’s alumina coating remains thermally stable throughout the entire process. By ≈500 °C, these organic constituents were almost entirely decomposed, although minor residues of decomposition products persisted, as confirmed in studies by Mouse et al. [45] and Sadeghi and Restuccia. [46] The anode exhibits minimal mass loss up to ≈500 °C, after which a sharp and substantial mass loss is observed, indicative of the decomposition of its organic binders and residual carbonaceous materials. Conversely, the cathode and the cathode with separator demonstrate high intrinsic thermal stability, with low mass loss recorded across the 100–800 °C range. Quantitative analysis of these mass loss profiles provides critical insights into optimal thermal pretreatment strategies for LIB recycling. The pronounced mass loss events observed at specific temperatures correlate strongly with underlying decomposition processes within the battery components. A temperature of ≈500 °C was identified as an optimal upper limit for preserving material integrity and enabling efficient mechanical separation; this temperature balance is crucial for energy-efficient processing and reducing potential hazardous emissions. At this point, the separator is transformed mainly into refractory Al 2 O 3 , which may facilitate targeted surface functionalization, and enhances the efficiency of downstream metal recovery by minimizing impurities. [33,40] Figure 3. Static thermal mass loss analysis of lithium-ion battery cell components (cathode, anode, separator, and cathode with separator) from 0–800 °C, illustrating their distinct thermal stabilities and highlighting key decomposition and processing temperature ranges with standard deviation error bars. Note that data points for the cathode with separator sample at 450, 550, and 650 °C are linearly interpolated for visual trend continuity. ChemSusChem 2025,00, e202501753 (6 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License By defining a precise temperature of 500 °C for pyrometallurgical pretreatment, this study offers a significant advantage over processes operating at higher temperatures. Compared to conventional pyrolysis methods that often require temperatures of 700 °C or higher for complete organic removal, [40] our findings suggest a substantial potential for energy savings and reduced processing time. This approach not only reduces energy consumption but also mitigates the risk of current collector melting and other side reactions that compromise material quality, thereby providing a more efficient and sustainable pathway for battery recycling. To further characterize the precise thermal behavior of key components within the most critical range for pyrometallurgical pretreatment, [45,47] mass loss observations were focused within the 400 to 650 °C temperature range. This window specifically captures the onset and progression of significant mass loss from the anode and the final stages of separator degradation, which are crucial for defining optimal pretreatment conditions. It is important to note that for the ’Cathode with separator’sample, data points at 450, 550, and 650 °C were not experimentally determined, and its trend line in Figure 3 is linearly interpolated for visual continuity. Conversely, exposure to higher temperatures between 600 and 800 °C led to oxidation and structural degradation of metallic components, particularly the Al current collector in NMC cathodes. This degradation was found to reduce material recovery efficiency and compromise the quality of recovered fractions. 3.3. Morphological and Elemental Composition Changes Analysis Building upon the insights from thermal mass loss analysis, further investigation was conducted into the structural and compositional stability of the cathode materials. In line with the recycling objectives that prioritize the recovery of valuable metals found primarily in battery cathodes, [38,48] thermally exposed cathode samples were analyzed to examine their morphological and structural changes using SEM and EDS. Figure 4 illustrates the representative initial condition of the dried cathode before thermal treatment, along with elemental maps depicting both the baseline state and the state after exposure to the highest temperature achieved (800 °C). This approach was employed to evaluate the surface composition of the cathode and to track the compositional changes resulting from heat treatment across a temperature range of 100 to 800 °C, with increments of 100 °C. The comprehensive results for all exposed cathode samples are provided in Figure 5. The findings from SEM imaging confirmed preservation of the spinel structure and particle morphology for the investigated NMC layer even after exposure to temperatures up to 800 °C, indicating its exceptional thermal stability. However, a critical observation was the onset of melting of the Al current collector at 700 °C. This melting event significantly compromises the integrity of the surrounding electroactive material by causing delamination and potential encapsulation, thereby diminishing the quality of the recovered NMC spinel and increasing the complexity for subsequent purification. The ultimate objective of the thermal treatment process is to achieve a temperature regime that maintains the original properties of the valuable electroactive materials while effectively removing all organic components and facilitating their subsequent separation from current collectors, supporting high-value material recovery. Complementing the morphological observations, detailed elemental analysis of the thermally treated cathode surfaces was performed using EDS. The study primarily focused on key electroactive elements (Ni, Mn, Co) and tracking changes in carbon and fluorine residues, as presented in Figure 6. Beyond these primary targets, various other elements originating from auxiliary battery materials were also identified. The detected Al signal is attributed primarily to Al 2 O 3 residues from the separator, [33] which contaminate the cathode surface during disassembly and handling. A minor contribution from the underlying Al current collector foil is also possible in areas where the active material coating is porous or thin. In contrast, Cu was not detected, which is expected as it is the current collector for the anode, and this analysis focused exclusively on the cathode. Phosphorus (P) was identified as a residue from the decomposition of the LiPF 6 electrolyte salt. [20,21] Furthermore, tungsten (W). The presence of W, detected at ≈1 wt%, is attributed to tungsten oxide (WO 3 ). WO 3 is commonly used by battery manufacturers as a surface coating or stabilizing agent for NMC active materials, particularly for Ni-rich chemistries such as the NMC622 in our study. [49,50] This protective Figure 4. Illustration of a) SEM measurements for the untreated cathode sample using secondary electrons imaging - left, backscattered electrons imaging - right; b) EDS mapping for the untreated cathode sample (T0) compared to the thermally treated cathode sample at 800 °C (T800). ’T’denotes the specific temperature at which the analysis was performed. ChemSusChem 2025,00, e202501753 (7 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License layer is known to enhance structural stability and limit degradation from side reactions with the electrolyte, thereby improving the battery’s operational lifespan and safety [51–53] The amount detected by our surface-sensitive EDS analysis is consistent with levels reported for such functional coatings. Their identification provided insights into potential contamination sources and the completeness of organic removal following thermal treatment. It is important to clarify that Cu was not detected, as it is the current collector for the anode, while this analysis focused exclusively on the cathode. The detected Al signal is attributed primarily to Al 2 O 3 residues from the separator, which contaminate the cathode surface during disassembly and handling. A minor contribution from the underlying Al current collector foil is also possible in areas where the active material coating is porous or thin. A critical compositional shift was observed at ≈400 °C, manifesting as a substantial reduction in organic carbon and fluorine content. These changes led to a relative increase in NMC metal content (Ni, Mn, Co) due to the elimination of organic components, as evident from the graphs showing a significant increase in the relative yield of target elements from 400 °C. Notably, at 500 °C, the carbon signal was absent, confirming complete removal of the organic matrix without observable degradation of the NMC phase. Further investigation into narrower temperature intervals revealed that residual carbon was fully combusted even at 450 °C with 1 h of exposure. However, complete fluorine removal was only achieved at higher temperatures, ≈700 °C, indicating the presence of more thermally stable fluorine-containing compounds at 500 °C. The persistence of these fluorides at 500 °C is a critical consideration, as they can complicate subsequent hydrometallurgical leaching and may contribute to equipment corrosion or lower final product purity. Regarding other elements, residual P from the electrolyte remained unchanged, while oxygen showed an opposite trend, growing at the highest Figure 5. Illustration of SEM measurements for the cathode sample across a temperature range of 100–800 °C, with increments of 100 °C, using secondary electrons imaging - left, backscattered electrons imaging - right. ‘T’denotes the specific temperature at which the analysis was performed. ChemSusChem 2025,00, e202501753 (8 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License temperatures due to high-temperature oxidation. Among the identified contaminants, only refractory Al 2 O 3 and WO 3 persisted throughout the entire heat treatment. Despite the incomplete fluorine removal at 500 °C, this temperature was reaffirmed as optimal for pyrometallurgical pretreatment, as it effectively combines extensive organic purification (especially carbon removal) with excellent preservation of the electroactive material structure before significant current collector degradation. The systematic analysis of electrode materials subjected to high-temperature exposure for 1 h across a range of temperatures from 100 to 800 °C, explicitly focusing on NMC cathodes, graphite anodes, and polymeric separators, has yielded valuable insights into their thermal behavior. The most significant changes in mass and composition were consistently observed between 400 and 650 °C. This comprehensive investigation underscores the suitability of high-temperature pyrometallurgical approaches for recovering and recycling electroactive materials from spent batteries. At 100 °C, electrode materials undergo thorough drying to a constant mass. Subsequent heating to 200 °C initiates the oxidation and browning of PE within the separator, alongside the decomposition of PVDF binder. At 300 °C, the oxidation of the Figure 6. EDS analysis of cathode surface composition after thermal exposure at selected temperatures: a) full range from 0 to 800 °C in 100 °C increments; b) detailed range from 400 to 650 °C in 50 °C increments. ‘T’indicates the specific temperature at which each sample was analyzed. ChemSusChem 2025,00, e202501753 (9 of 12) © 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202501753 1864564x, 0, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202501753 by Cochrane Czech Republic, Wiley Online Library on [06/11/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License