Exploring Trimethyl-Phosphate-Based Electrolytes without a Carbonyl Group for Li-Rich Layered Oxide Positive Electrodes in Lithium-Ion Batteries

Bis(2,2,2-trifluoroethyl) Carbonate As a Fire Suppressant Candidate for Lithium-Ion Batteries

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a fire suppressant candidate for the use of lithium-ion batteries (LIBs). It is known that the electrolyte components in LIBs are highly flammable, making them susceptible to igniting, whether this is due to a manufacturing fault or an abuse of the LIB itself. To address this risk, the efficiency of BtFEC as a fire suppressant was investigated experimentally in a high-temperature combustion environment, allowing for further refinement and validation of the model. Using a shock tube, BtFEC combustion properties were measured experimentally behind a reflected shock wave, capturing OH* chemiluminescence to assess ignition delay times (IDT) as well as CO time-history profiles through the implementation of laser absorption spectroscopy. Both pyrolysis and oxidation conditions were captured with three equivalence ratios (ϕ = 0.5, 1.0, and 1.5) for a temperature range of ∼1200-1650 K at near-atmospheric pressures. In addition, key species measurements were taken using a microflow reactor (MFR) with a controlled temperature profile associated with Fourier transform infrared spectroscopy (FTIR). Key species investigated were BtFEC, CO, CO2, CHF3, CF2O, C2F6, and HF for the temperatures range of 800-1300 K. MFR measurements allowed for a new set of measurements by which to validate the model compared to the previous study [Mathieu et al. Proc. Combust. Inst. 2023, 39, 499] where the first assembly of the model used CO time-history, IDT, and laminar flame speed measurements. Refinement of the model was carried out with new high-level calculations as well as sensitivity, rate-of-production, and reaction pathway analyses using recent reaction rate updates from the literature. The modifications led to improvements in the level of agreement between the kinetic modeling and the new experimental data.

Regulate the Solvation Structure and Interface by Nitrate in Phosphate-Based Electrolytes for 4.5 V-Class Ni-Rich Batteries

Phosphate-based electrolyte propels the advanced battery system with high safety. Unfortunately, restricted by poor electrochemical stability, it is difficult to be compatible with advanced lithium metal anodes and Ni-rich cathodes. To alleviate these issues, the study has developed a phosphate-based localized high-concentration electrolyte with a nitrate-driven solvation structure, and the nitrate-derived N-rich inorganic interface shows excellent performance in stabilizing the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode interface and modulating the lithium deposition morphology on the anode. The results show that the Li|| NCM811 cell has exceptional long-cycle stability of >80% capacity retention after 800 cycles at 4.3 V, 1 C. A more prominent capacity retention rate of 93.3% after 200 cycles can be reached with the high voltage of 4.5 V. While being compatible with the phosphate-based electrolyte with good flame retardancy and the good electrochemical stability of Ni-rich lithium metal battery (LMBs) systems, the present work expands the construction of anion-rich solvation structures, which is expected to promote the development of the high-performance LMBs with safety.

Value-Added Products Derived from Poly(ethylene terephthalate) Glycolysis

Among polymer wastes, poly(ethylene terephthalate) (PET) is the most important commercial thermoplastic polyester. Less than 30% of total PET production is recycled into new products. Therefore, large amounts of waste PET need to be recycled. We describe a feasible approach for the direct application of the glycolysis products of PET (GP-PET), without further purification, for the synthesis of value-added products. It was established that GP-PET is valorized via phosphorylation with phenylphosphonic dichloride (PPD), as well as with trimethyl phosphate (TMP). When PPD is used, a condensation reaction takes place with the evolution of hydrogen chloride. During the interaction between GP-PET and TMP, the following reactions take place simultaneously: a transesterification with the participation of the hydroxyl group of GP-PET and the methoxy group of TMP and an exchange reaction between the ester group of GP-PET and the methyl ester group of TMP. The occurrence of the exchange reaction was confirmed by 1H, 31P, 13C NMR, and GPC analysis. Thermogravimetric analysis (TGA) revealed that the percentage of a carbon residual (CR) implies the possibility of using the end products as flame retardant (FR) additives, especially for polyurethanes as well as thermal stabilizers of polymer materials or Li-ion cells.

Insights from Ab Initio Molecular Dynamics on the Interface Reaction between Electrolyte and Li2MnO3 Cathode during the Charging Process

The complex interface reactions are crucial to the performance of the Li2MnO3 cathode material. Here, the interface reactions between the liquid electrolyte and the typical surfaces of Li2MnO3 during the charging process are systematically investigated by ab initio molecular dynamics (AIMD) simulation and first-principles calculation. The results indicate that these interface reactions lead to the formation of hydroxide radicals, oxygen, carbon dioxide, carbonate radicals, and other products, which are consistent with the experimental findings. These processes primarily result from the conversion of the stable closed-shell O2- into reactive oxygen ions by electron loss. All surfaces exhibit some degree of layered- and spinel-like phase transitions during the AIMD simulations, consistent with the experiment. This is mainly attributed to the decrease in the Mn-O bond strength and the increase in the Li/O ion vacancy concentration. This study offers valuable theoretical insights into the interface reaction between lithium-rich cathode materials and liquid electrolytes.

Tuning Local Structural Configurations to Improve Oxygen-Redox Reversibility of Li-Rich Layered Oxides

Li-rich layered oxides (LLOs) are regarded as one of the most desirable cathode materials due to their high specific capacity. Nevertheless, the irreversible oxygen release associated with low oxygen stability prevents their widespread application. Herein, an improved oxygen redox reversibility was achieved by constructing Ni²⁺-O^2--Ni²⁺ configurations. Superconducting Quantum Interference Device (SQUID) magnetometry measurements are used to track the evolution of the Ni²⁺-O^2--Ni²⁺ configuration during the electrochemical process. The strongest 180° superexchange interaction in the Ni²⁺-O^2--Ni²⁺ configuration, derived from the inevitable Li/Ni mixing in LLOs, regulates the local structure to form the ferrimagnetic (FiM) structural units. Consequently, the FiM structural units prevent the irreversible oxygen release and endow LLOs with high initial Coulombic efficiency (ICE). This work emphasizes the importance of the Ni²⁺-O^2--Ni²⁺ configuration for LLOs with high reversible capacity and proposes a synthesis approach to modulate the amount of FiM structural units.