Sergej Rothermel

Dual-graphite cells based on the reversible intercalation of bis(trifluoromethanesulfonyl)imide anions from an ionic liquid electrolyte

Recently, dual-ion cells based on the anion intercalation into a graphite positive electrode have been proposed as electrochemical energy storage devices. For this technology, in particular electrolytes which display a high stability vs. oxidation are required due to the very high operation potentials of the cathode, which may exceed 5 V vs. Li/Li+. In this work, we present highly promising results for the use of graphite as both the anode and cathode material in a so-called “dual-graphite” or “dual-carbon” cell. A major goal for this system is to find suitable electrolyte mixtures which exhibit not only a high oxidative stability at the cathode but also form a stable solid electrolyte interphase (SEI) at the graphite anode. As an electrolyte system, the ionic liquid-based electrolyte mixture Pyr14TFSI-LiTFSI is used in combination with the SEI-forming additive ethylene sulfite (ES) which allows stable and highly reversible Li+ ion and TFSI− anion intercalation/de-intercalation into/from the graphite anode and cathode, respectively. By addition of ES, also the discharge capacity for the anion intercalation can be remarkably increased from 50 mA h g−1 to 97 mA h g−1. X-ray diffraction studies of the anion intercalation into graphite are conducted in order to understand the influence of the electrolyte additive on the graphite structure and on the cell performance.

Investigation of the Storage Behavior of Shredded Lithium‐Ion Batteries from Electric Vehicles for Recycling Purposes

Shredding of the cells is often the first step in lithium-ion battery (LIB) recycling. Thus, LiNi1/3 Mn1/3 Co1/3 O2 (NMC)/graphite lithium-ion cells from a field-tested electric vehicle were shredded and transferred to tinplate or plastic storage containers. The formation of hazardous compounds within, and being released from, these containers was monitored over 20 months. The tinplate cans underwent fast corrosion as a result of either residual charge in the active battery material, which could not fully be discharged because of contact loss to the current collector, or redox reactions between the tinplate surface and metal parts of the shredded material. The headspace compositions of the containers were investigated at room temperature and 150 °C using headspace-gas chromatography-mass spectrometry (HS-GC-MS). Samples of the waste material were also collected using microwave-assisted extraction and the extracts were analyzed over a period of 20 months using ion chromatography-electrospray ionization-mass spectrometry (IC-ESI-MS). LiPF6 was identified as a conducting salt, whereas dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate were the main solvent components. Cyclohexylbenzene was also detected, which is an additive for overcharge protection. Diethyl carbonate, fluoride, difluorophosphate and several ionic and non-ionic alkyl (fluoro)phosphates were also identified. Importantly, dimethyl fluorophosphate (DMFP) and diethyl fluorophosphate (DEFP) were quantified using HS-GC-MS through the use of an internal standard. DMFP, DEFP, and related compounds are known as chemical warfare agents, and the presence of these materials is of great interest. In the case of this study, these hazardous materials are present but in manageable low concentrations. Nonetheless, the presence of such compounds and their potential release during an accident that may occur during shredding or recycling of large amounts of LIB waste should be considered.

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.

Electrolyte Extraction—Sub and Supercritical CO 2

This chapter reports on experiments aimed at investigating the capability of pressurized carbon dioxide to extract the electrolyte from commercial available LIBs on a laboratory scale. Two different phase conditions of carbon dioxide (subcritical and supercritical) and two different extraction (static and dynamic) have been considered and analyzed for their strengths and weaknesses. Furthermore, the addition of co-solvents is examined with regard to their contribution to higher recovery rates. After reporting the optimized extraction method, the extracted electrolyte was analyzed by gas and ionic chromatography methods for potential de-composition products and their relative amount.

The LithoRec Process

The LithoRec projects were funded by the German Federal Ministry of the Environment, Nature Conservation Building and Nuclear Safety and VDI/VDE Innovation+Technik GmbH. The projects aimed to develop a new recycling process for lithium-ion batteries from electric and hybrid electric vehicles with a focus on energy efficiency and a high material recycling rate. The developed process route combines mechanical, mild thermal and hydrometallurgical treatment to regain nearly all materials of a battery system.

Hydrometallurgical Processing and Thermal Treatment of Active Materials

In this chapter, electrodes containing the cathode material Li[Ni0.33Co0.33Mn0.33]O2 (NCM) were recycled in order to test a newly developed recycling concept which is aiming towards commercial application. The possibility of graphite recovery from spent LIBs by means of three different treatment methods is demonstrated.

Potential Dangers During the Handling of Lithium-Ion Batteries

Due to their high voltage, high stored energy, and reactive components, lithium-ion batteries present a specific and significant hazard potential. This especially comes into play during recycling because nearly every safety precaution of a battery system and battery cell needs to be bypassed. Because the project partners of LithoRec II spared a thermal pre-treatment step to deactivate the batteries, the hazard potential and its handling played a major role. This chapter gives an overview of the hazards associated with lithium-ion batteries and describes their role in every process step.