Marco Evertz

Graphite Recycling from Spent Lithium-Ion Batteries.

The present work reports on challenges in utilization of spent lithium-ion batteries (LIBs)-an increasingly important aspect associated with a significantly rising demand for electric vehicles (EVs). In this context, the feasibility of anode recycling in combination with three different electrolyte extraction concepts is investigated. The first method is based on a thermal treatment of graphite without electrolyte recovery. The second method additionally utilizes a subcritical carbon-dioxide (subcritical CO2 )-assisted electrolyte extraction prior to thermal treatment. And the final investigated approach uses supercritical carbon dioxide (scCO2 ) as extractant, subsequently followed by the thermal treatment. It is demonstrated that the best performance of recycled graphite anodes can be achieved when electrolyte extraction is performed using subcritical CO2 . Comparative studies reveal that, in the best case, the electrochemical performance of recycled graphite exceeds the benchmark consisting of a newly synthesized graphite anode. As essential efforts towards electrolyte extraction and cathode recycling have been made in the past, the electrochemical behavior of recycled graphite, demonstrating the best performance, is investigated in combination with a recycled LiNi1/3 Co1/3 Mn1/3 O2 cathode.

Matrix-matched standards for the quantification of elemental lithium ion battery degradation products deposited on carbonaceous negative electrodes using pulsed-glow discharge-sector field-mass spectrometry

In this work an external calibration approach for glow discharge-sector field-mass spectrometry (GD-SF-MS) using matrix-matched self-prepared carbonaceous standards for elemental battery degradation products of LiNi1/3Co1/3Mn1/3O2 (NCM111) positive electrodes like lithium, manganese, cobalt and nickel is adapted. Firstly, the standards were prepared using graphite mixed with increasing contents of NCM111 which was coated on a thin copper foil as a current collector. The homogeneous distribution of NCM111 in the standards was proven via SEM/EDX images and the bulk homogeneity of the electrode sheets was validated via ICP-OES. Afterwards, sufficient linearity could be obtained in a calibration range of 1 mg g−1 to 28 mg g−1 for 7Li with respect to the active material mass. Additionally, the matrix-matched relative sensitivity factors (RSFs) of each element could be calculated. Limits of detection (LODs) ranging from 80 μg g−1 (7Li) up to 393 μg g−1 (58Ni) could be achieved at low (R > 300) and medium (R > 4000) resolutions for the Element GD, respectively. Secondly, we adapted the matrix-matched RSF values in order to investigate cycled electrodes by monitoring the 7Li signal as well as common isotopes from lithium ion batteries – such as 31P and 19F, originating from the conducting salt – and transition metals to conduct depth-resolved analysis. The concentration of transition metals in all of the cycled electrodes was below the LOD of the GD-SF-MS method which was investigated in a previous study, showing a maximum bulk deposition of transition metals of 4.5 mg g−1. As expected, an accumulation of 7Li in the first few minutes (=surface layers) of sputtering was observed in the cycled carbonaceous negative electrodes followed by a decreasing 7Li signal with ongoing sputtering indicating the presence of a solid electrolyte interphase (SEI) passivation layer.

Adaptation and improvement of an elemental mapping method for lithium ion battery electrodes and separators by means of laser ablation-inductively coupled plasma-mass spectrometry

In this study, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was applied to previously aged carbonaceous anodes from lithium ion batteries (LIBs). The electrodes were treated by cyclic aging in a lithium ion cell set-up with LiNi0.5Mn1,5O4 (LNMO) cathodes and hard carbon (HC)/mesocarbon microbead (MCMB) anodes. An inhomogeneous transition metal deposition pattern could be induced by replacing the spacer in a standard coin cell set-up with a washer. The inhomogeneity pattern matched the dimension of the washer depicted by the hole in the center. These transition metal (TM) patterns were used to optimize higher lateral scanning speeds and frequencies on the spatial resolution of the mapping experiments using LA-ICP-MS. Higher scanning speeds had an observable influence on the resolution of the obtained image and an overall saving of 60% with regard to time and gas consumption could be achieved. Additionally, the optimized method was applied to the cathode and separator in order to visualize the distribution and deposition pattern, respectively.