Article

Recycled Graphite for Sustainable Lithium-Ion Batteries

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Abstract

Graphite – natural or synthetic – is the most dominant active material used for LIB anodes [1] . Natural graphite, however, is considered a critical material within the EU [2] , while synthetic graphite is obtained from coke [3] – a carbon precursor produced from coal or petroleum. Therefore, efficient recycling and reuse of graphite are essential towards sustainability and resource preservation [4] . Herein, we report a novel and highly efficient process to recover high-quality graphite from spent LIBs. Following a comprehensive physicochemical characterization of the materials obtained, we conducted an extensive electrochemical characterization in half-cells and graphite‖NMC 532 full-cells and compared the results with the data obtained for half-cells and full-cells using pristine commercial graphite. In half-cells, the recycled graphite shows remarkably high reversible specific capacities (e.g., 350 mAh g ⁻ ¹ at C/20) and very stable cycling for several hundred cycles at 1C. The graphite‖NMC 532 full-cells also show excellent cycling stability, with a capacity retention of 80% after about 1,000 cycles. Particularly, the comparison with the pristine graphite comprising full-cells reveals very comparable performance, highlighting the great promise of recycled and reused graphite as a pivotal step towards truly sustainable LIBs and the great goal of a circular economy. References [1] J. Asenbauer, T. Eisenmann, M. Kuenzel, A. Kazzazi, Z. Chen, and D. Bresser, “The success story of graphite as a lithium-ion anode material – fundamentals, remaining challenges, and recent developments including silicon (oxide) composites,” Sustain. Energy Fuels , 2020. [2] Comisión Europea, European Commission, Report on Critical Raw Materials and the Circular Economy, 2018 . 2018. [3] S. Richard, W. Ralf, H. Gerhard, P. Tobias, and W. Martin, “Performance and cost of materials for lithium-based rechargeable automotive batteries,” Nat. Energy , vol. 3, no. Li, pp. 267–278, 2018. [4] A. Vanderbruggen, E. Gugala, R. Blannin, K. Bachmann, R. Serna-Guerrero, and M. Rudolph, “Automated mineralogy as a novel approach for the compositional and textural characterization of spent lithium-ion batteries,” Miner. Eng. , vol. 169, p. 106924, 2021.

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... Some studies have revealed that recovered GA could be regenerated as anode materials for energy storage devices after some retreatments. [103][104][105][106] Low-cost regeneration of GA from spent LIBs is of great significance to solve the problem of waste graphite utilization and pollution. Comparing with the fresh graphite, the directly recycled GA (with coating, SEI layer and other Impurities) exhibits lower initial discharge capacity, which are 354.2 and 298.7 mAh/g respectively. ...
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There is growing production for lithium‐ion batteries (LIBs) to satisfy the booming development renewable energy storage systems. Meanwhile, amounts of spent LIBs have been generated and will become more soon. Therefore, the proper disposal of these spent LIBs is of significant importance. Graphite is the dominant anode in most commercial LIBs. This review specifically focuses on the recent advances in the recycling of graphite anode (GA) from spent LIBs. It covers the significance of GA recycling from spent LIBs, the introduction of the GA aging mechanisms in LIBs, the summary of the developed GA recovery strategies, and the highlight of reclaimed GA for potential applications. In addition, the prospect related to the future challenges of GA recycling is given at the end. It is expected that this review will provide practical guidance for researchers engaged in the field of spent LIBs recycling. image
... As a result, Western countries are actively searching for strategies to develop their own graphite supply chain for battery production, including plans to integrate recycled graphite. 7 During typical LIB recycling processes, a comminution stage is used as a first stage to separate electrode particles from their current collectors, producing foils in the coarse size fraction and active particles in the fine fraction. This is possible since electrode foils present a ductile behavior and, as reported by Schubert,8 ductile materials can be liberated through shear, cutting, and tearing stresses. ...
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Recycling is a potential solution to narrow the gap between the supply and demand of raw materials for lithium-ion batteries (LIBs). However, the efficient separation of the active components and their recovery from battery waste remains a challenge. This paper evaluates the influence of three potential routes for the liberation of LIB components (namely mechanical, thermomechanical, and electrohydraulic fragmentation) on the recovery of lithium metal oxides (LMOs) and spheroidized graphite particles using froth flotation. The products of the three liberation routes were characterized using SEM-based automated image analysis. It was found that the mechanical process enabled the delamination of active materials from the foils, which remained intact at coarser sizes along with the casing and separator. However, binder preservation hinders active material liberation, as indicated by their aggregation. The electrohydraulic fragmentation route resulted in liberated active materials with a minor impact on morphology. The coarse fractions thus produced consist of the electrode foils, casing, and separator. Notwithstanding, it has the disadvantage of forming heterogeneous agglomerates containing liberated active particles. This was attributed to the dissolution of the anode binder and its rehardening after drying, capturing previously liberated particles. Finally, the thermomechanical process showed a preferential liberation of individual anode active particles and thus was considered the preferred upstream route for flotation. However, the thermal treatment oxidized Al foils, rendering them brittle and resulting in their distribution in all size fractions. Among the three, the thermomechanical black mass showed the highest flotation selectivity due to the removal of the binder, resulting in a product recovery of 94.4% graphite in the overflow and 89.4% LMOs in the underflow product.
... As a result, Western countries are actively searching for strategies to develop their own graphite supply chain for battery production, including plans to integrate recycled graphite. 7 During typical LIB recycling processes, a comminution stage is used as a first stage to separate electrode particles from their current collectors, producing foils in the coarse size fraction and active particles in the fine fraction. This is possible since electrode foils present a ductile behavior and, as reported by Schubert,8 ductile materials can be liberated through shear, cutting, and tearing stresses. ...
Thesis
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With the constant growth in portable electronic devices and the expected market growth for electric vehicles, the demand for lithium-ion batteries (LIBs) is booming. The raw materials production with a combination of mining and recycling will be essential and unavoidable to meet the upcoming demand for LIBs. Consequently, the European authority is updating the regulations demanding higher recovery efficiencies, 70 % by 2030. However, most of the state-of-the-art recycling technologies for LIBs focus on the recovery of components that have high economic value such as Co and Ni. The fine fraction resulting from the mechanical pre-treatment containing the lithium metal oxides (LMOs) and graphite particles, commonly referred to as "Black Mass" (BM), is generally used as a starting point for metals recovery by metallurgical means. Indeed, in industry, this BM is usually not further sorted and is directly fed to pyro- and/or hydrometallurgical processing routes to extract metals from LMOs, at the expense of graphite not being recovered. Recent studies, however, have convincingly illustrated that froth flotation can be applied to the BM to efficiently generate two valuable products, therefore increasing the overall efficiency of LIB recycling significantly. The work presented in this thesis aims to increase the overall materials recovery from LIBs by improving the BM beneficiation through froth flotation. The research work hereby presented offers a systematic study of the influence of the recycling pre-treatment processes on the liberation of the LIB components and the potential flotation mechanisms of active particles. The first part of this thesis is focused on the liberation analysis of the LIB components, which cannot be determined by conventional bulk characterization techniques such as X-ray fluorescence. In this thesis, a new approach for the BM characterization using automated mineralogy has been developed. With this particle-based technique, information on the chemical composition, morphology and degree of liberation of LIB components was acquired, helping to understand how the particles behaved during the process. The second part is focused on BM beneficiation on the basis of flotation. The use of flotation has recently gained interest as a method to separate LMOs and graphite particles. However, the flotation mechanisms of LMOs have not been paid sufficient attention. Therefore, this work provides the first fundamental study on the flotation mechanisms of active particles, with the aim of properly identifying the challenges to overcome in order to drive selectivity in flotation separation. To understand the flotation behavior, an industrial BM from pyrolyzed LIBs was compared to a model BM, comprising fully liberated LMOs and graphite particles. In addition, ultrafine hydrophilic particles were added to the flotation feed as an entrainment tracer, showing that the LMOs recovery in overflow products is a combination of entrainment and true flotation mechanisms. Ultimately, the findings of this thesis indicate the possibility of recovering and reusing graphite into new batteries.
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Lithium cobalt oxide from a wasted lithium ion secondary battery (LIB) is recovered by means of flotation. At first, the wasted LIB was crushed by vertical cutting mill and classified by air table and vibration screen. Referring to the crushing and separating results, wasted LIB is represented by light materials (organic separator of anode and cathode of battery), metallic materials (aluminum & copper foil, aluminum case etc.) and electrode materials (mixture of lithium cobalt oxide (LiCoO2) and graphite).Electrode materials were thermally treated in a muffle furnace at 773K, followed by flotation to separate LiCoO2 and graphite. The fact that the surface of particles was changed from hydrophobic to hydrophilic due to the removal of binder from the surface at 773K.Considering the results, 92% LiCoO2 was recovered from electrode materials, whereas the purity was higher than 93%. The optimum conditions of flotation process were as follows: 0.2 kg/t kerosene as a collector, 0.14 kg/t MIBC as a frother and 10% pulp density.The experimental results suggested that this process by using mineral processing technology, such as crushing, screening, flotation, etc., is feasible to recover LiCoO2 from the wasted LIB representing a new recycling technique.
Article
The lithium-ion exchange rate capability of various commercial graphite materials are evaluated using galvanostatic charge/discharge cycling in a half-cell configuration over a wide range of C-rates (0.1–60C). The results confirm that graphite is capable of de-intercalating stored charge at high rates, but has a poor intercalating rate capability. Decreasing the graphite coating thickness leads to a limited rate performance improvement of the electrode. Reducing the graphite particle size shows enhanced C-rate capability but with increased irreversible capacity loss (ICL). It is demonstrated that the rate of intercalation of lithium-ions into the graphite is significantly limited compared with the corresponding rate of de-intercalation at high C-rates. For the successful utilisation of commercially available conventional graphite as a negative electrode in a lithium-ion capacitor (LIC), its intercalation rate capability needs to be improved or oversized to accommodate high charge rates.
Article
First- and second-order Raman scattering from graphite has been studied. The second-order spectra of single crystals and of highly oriented pyrolytic graphite are continuous and exhibit several well-defined bands which can be attributed to features in the density of vibrational states as determined from current lattice-dynamics models. The density of states deduced from the lattice-dynamics model of Nicklow, Wakabayashi, and Smith provides the best replication of the second-order Raman spectrum, but is nevertheless somewhat deficient in this regard, and in need of improvement. The dependence of the first- and second-order graphite Raman spectra on crystallite size has also been studied for a series of samples with typical dimensions Lc and La as small as 30 Å. With decreasing crystal size the features in the second-order spectrum broaden noticeably and additional broad features appear in both the first- and second-order spectra. The additional first- and second-order features are also attributed to structure in the vibrational density of states and arise from the wave-vector selection-rule relaxation that results from finite-crystal-size effects. Evidence is presented to demonstrate that the above described spectral features are intrinsic and not associated with impurity excitations.
Article
Using lithium/graphite electrochemical cells and in situ x-ray diffraction, we have determined the phase diagram of LixC6 for 0<x<1 and 0 °C<T<70 °C. We find several differences between our results and previous work. For x<0.04, the intercalated Li is randomly distributed throughout the graphite host in a dilute stage-1 phase. As x increases past 0.04, a clear coexistence between this phase and a stage-4 phase is observed. As x increases further at 21 °C, transitions to stage 3, to a ‘‘liquidlike’’ stage-2 phase (denoted 2L), to stage 2, and finally to filled stage 1 occur sequentially as expected on the basis of previous work. We have been able to accurately determine the ranges in x and in T of the single-phase and the coexisting-phase regions. Clear coexisting-phase regions are observed (indicating first-order transitions) for all the transitions except for the stage-4 to -3 transition. We discuss the difference between this transition and the others. The average layer spacing of LixC6 has been measured as a function of x.
Article
For graphitic carbons as anode materials in lithium ion batteries, the morphology and chemistry of the graphite surface have a significant impact on the formation of the solid electrolyte interphase (SEI), the corresponding irreversible charge losses, and the overall electrochemical anode performance. In this work the effects of graphite surface modification, induced by an elevated temperature treatment, on the SEI formation are discussed in details. Morphology changes due to burn-off of carbon are investigated by Raman spectroscopy and nitrogen adsorption measurements, which are not only used to calculate the BET specific surface area but also for the estimation of the absolute and relative extents of the basal plane surface area and the "non-basal plane surface" area. In particular, the relation of the first cycle irreversible charge loss to the change of surface morphology, especially to the quantitative amounts of the different types of surfaces is highlighted. (C) 2011 Elsevier B.V. All rights reserved.
Article
The kinetic performance of graphite particles is difficult to deconvolute from half-cell experiments, where the influences of the working electrode porosity and the counter electrode contribute nonlinearly to the electrochemical re-sponse. Therefore, thin-layer electrodes of circa 1 {\mu}m thickness were prepared with standard, highly crystalline graphite particles to evaluate their rate capability. The performance was evaluated based on the different stage transitions. We found that the tran-sitions towards the dense stages 1 and 2 with LiC6 in-plane densi-ty are one of the main rate limitations for charge and discharge. But surprisingly, the transitions towards the dilute stages 2L, 3L, 4L, and 1L progress very fast and can even compensate for the initial diffusion limitations of the dense stage transitions during discharge. We show the existence of a substantial difference between the diffusion coefficients of the liquid-like stages and the dense stages. We also demonstrate that graphite can be charged at a rate of ~6C (10 min) and discharged at 600C (6 s) while maintaining 80 % of the total specific charge for particles of 3.3 {\mu}m median diameter. Based on these findings, we propose a shrinking annuli mechanism which describes the propagation of the different stages in the particle at medium and high rates. Besides the limited applicable overpotential during charge, this mechanism can explain the long-known but as yet unexplained asymmetry between the charge and discharge rate performance of lithium intercalation in graphite.
Article
Surface pre-treatment of graphitic electrode materials for lithium ion cells has recently been shown to significantly reduce the irreversible consumption of material and charge due to the formation of the so-called solid electrolyte interphase (SEI) during battery charging. In this paper, we compare graphite powders and carbon fibres as model materials for X-ray photoemission spectroscopy (XPS) studies of the effects of surface pre-treatments. For carbon fibres, the surface carbon percentage was found to vary from 70–95% depending on the surface treatment, with corresponding changes in the relative proportion of graphitic compared to CO bonds, as determined from C 1s curve fits. In contrast, results from the graphite powders show very little change in surface chemical composition and an essentially constant C 1s lineshape dominated by graphitic carbon. SEM data show the carbon fibre cross-section to be composed of a radial array of layered graphite, leaving a surface consisting largely of prismatic planes, while the graphite powder consists of graphite platelets with the surface area predominantly of basal planes. We conclude that the chemical modification occurs at the prismatic planes, and that the powders are unsuitable as models for XPS studies of electrode surface modification, while the fibres are very well suited.
EU Legislation in progress: new EU regulatory framework for batteries setting sustainability requirements
  • European Parliament
European Parliament. EU Legislation in progress: new EU regulatory framework for batteries setting sustainability requirements. 2021.
Raman spectrum of graphite
  • F Tuinstra
  • J L Koenig
Tuinstra F, Koenig JL. Raman spectrum of graphite. J Chem Phys. 1970;53(3):1126-1130.