A low-toxicity and high-efficiency deep eutectic solvent for the separation of aluminum foil and cathode materials from spent lithium-ion batteries

High-value utilization of graphite electrodes in spent lithium-ion batteries: From 3D waste graphite to 2D graphene oxide

The graphite electrodes of spent lithium-ion batteries (LIBs) have a good crystalline composition and layered structure, and the recovery potential is promising. However, the internal and external surfaces of the waste graphite are often polluted with various organic and inorganic impurities, which seriously restrict its high-value utilization. Herein, the microstructure and surface analysis of waste graphite at variable scales were carried out systematically to reveal the types and occurrence status of impurities and their influence on the preparation of graphene oxide (GO) using a modified Hummers method. The results show that the graphite surface contaminants are polyvinylidene fluoride binder, LiPF₆ electrolyte and LiF residue from the solid electrolyte interface, while residual lithium (Li₂CO₃) and CuO were found to have invaded the crystal structure of graphite. Fortunately, the modified Hummers method can effectively remove these complicated associated impurities and prevent their re-contamination on the GO surface. More importantly, the modified Hummers method can not only destroy the longitudinal molecular bonds between graphite layers, but also splice them horizontally to form 2D GO, which is verified by high-resolution transmission electron microscope (HR-TEM) images. This paper provides theoretical support and practical guidance for the high-value utilization of waste graphite in spent LIBs.

Pyrolysis characteristics of cathode from spent lithium-ion batteries using advanced TG-FTIR-GC/MS analysis

Thermal treatment offers an alternative method for the separation of Al foil and cathode materials during spent lithium-ion batteries (LIBs) recycling. In this work, the pyrolysis behavior of cathode from spent LIBs was investigated using advanced thermogravimetric Fourier transformed infrared spectroscopy coupled with gas chromatography-mass spectrometer (TG-FTIR-GC/MS) method. The fate of fluorine present in spent batteries was probed as well. TG analysis showed that the cathode decomposition displayed a three-stage process. The temperatures of maximum mass loss rate were located at 470 °C and 599 °C, respectively. FTIR analysis revealed that the release of CO₂ increased as the temperature rose from 195 to 928 °C. However, the evolution of H₂O showed a decreasing trend when the temperature increased to above 599 °C. The release of fluoride derivatives also exhibited a decreasing trend, and they were not detected after temperatures increasing to above 470 °C. GC-MS analysis indicated that the release of H₂O and CO displayed a similar trend, with larger releasing intensity at the first two stages. The evolution of 1,4-difluorobenzene and 1,3,5-trifluorobenzene also displayed a similar trend-larger releasing intensity at the first two stages. However, the release of CO₂ showed a different trend, with the largest release intensity at the third stage, as did the release of 1,2,4-trifluorobenzene, with the release mainly focused at the temperature of 300-400 °C. The release intensities of 1,2,4-trifluorobenzene and 1,3,5-trifluorobenzene were comparable, although smaller than that of 1,4-difluorobenzene. This study will offer practical support for the large-scale recycling of spent LIBs.

Deep Eutectic Solvent Based on Lithium Bis[(trifluoromethyl)sulfonyl] Imide (LiTFSI) and 2,2,2-Trifluoroacetamide (TFA) as a Promising Electrolyte for a High Voltage Lithium-Ion Battery with a LiMn2O4 Cathode

To design safe and electrochemically stable electrolytes for lithium-ion batteries, this study describes the synthesis and the utilization of new deep eutectic solvents (DESs) based on the mixture of 2,2,2-trifluoroacetamide (TFA) with a lithium salt (LiTFSI, lithium bis[(trifluoromethane)sulfonyl]imide). These prepared DESs were characterized in terms of thermal properties, ionic conductivity, viscosity, and electrochemical properties. Based on the appearance of the product and DSC measurements, it appears that this system is liquid at room temperature for LiTFSI mole fraction ranging from 0.25 to 0.5. At χLiTFSI = 0.25, DESs exhibited favorable electrolyte properties, such as thermal stability (up to 148 °C), relatively low viscosity (42.2 mPa.s at 30 °C), high ionic conductivity (1.5 mS.cm-1 at 30 °C), and quite large electrochemical stability window up to 4.9-5.3 V. With these interesting properties, selected DES was diluted with slight amount of ethylene carbonate (EC). Different amounts of EC (x = 0-30 %wt) were used to form hybrid electrolytes for battery testing with high voltage LiMn2O4 cathode and Li anode. The addition of the EC solvent into DES expectedly aims at enhancing the battery cycling performance at room temperature due to reducing the viscosity. Preliminary results tests clearly show that LiTFSI-based DES can be successfully introduced as an electrolyte in the lithium-ion batteries cell with a LiMn2O4 cathode material. Among all of the studied electrolytes, DES (LiTFSI: TFA = 4:1 + 10 %wt EC) is the most promising. The EC-based system exhibited a good specific capacity of 102 mAh.g-1 at C/10 with the theoretical capacity of 148 mAh.g-1 and a good cycling behavior maintaining at 84% after 50 cycles.

Challenges to Future Development of Spent Lithium Ion Batteries Recovery from Environmental and Technological Perspectives

Spent lithium ion battery (LIB) recovery is becoming quite urgent for environmental protection and social needs due to the rapid progress in LIB industries. However, recycling technologies cannot keep up with the exaltation of the LIB market. Technological improvement of processing spent batteries is necessary for industrial application. In this paper, spent LIB recovery processes are classified into three steps for discussion: gathering electrode materials, separating metal elements, and recycling separated metals. Detailed discussion and analysis are conducted in every step to provide beneficial advice for environmental protection and technology improvement of spent LIB recovery. Besides, the practical industrial recycling processes are introduced according to their advantages and disadvantages. And some recommendations are provided for existing problems. Based on current recycling technologies, the challenges for spent LIB recovery are summarized and discussed from technological and environmental perspectives. Furthermore, great effort should be made to promote the development of spent LIB recovery in future research as follows: (1) gathering high-purity electrode materials by mechanical pretreatment; (2) green metals leaching from electrode materials; (3) targeted extraction of metals from electrode materials.