Hydrolysis Of Ethylene Carbonate Research Articles

Gas Evolution from Thermal and Electrochemical Side Reactions with Contaminants in Lithium-Ion Batteries

Recently, it was shown that H2O contamination in lithium-ion batteries can cause H2 gassing during the formation of the solid-electrolyte interphase (SEI) on graphite as well as substantial concentrations of CO2 in the battery cell.1 The latter was attributed to the hydrolysis of ethylene carbonate (EC) in the electrolyte by OH- formed through H2O reduction at the anode. The H2O- and OH--driven EC hydrolysis rates were measured at temperatures between 10 and 80°C by adding discrete amounts of H2O or TBAOH•30H2O to the electrolyte and monitoring the associated CO2 evolution by On-line Electrochemical Mass Spectrometry (OEMS).2 Apart from the intrusion of H2O into the battery cell as a trace contaminant, it was recently reported that H2O could be generated from the reaction of carbonate electrolyte with reactive oxygen released from NMC cathodes at high voltage.3 Thus, the often detected formation of POF3 at high-voltage4 could be explained by the reaction of PF5 with in-situ generated H2O to yield POF3 and HF. However, a competing reaction would be the reduction of the generated H2O at the anode (crosstalk5) releasing H2 and OH-, and forming CO2 via the hydrolysis of EC. In this study, we will deconvolute these reactions. First, we present an accurate quantification of POF3 by determining its calibration factor in OEMS using a high-temperature cell and employing the thermal decomposition of LiPF6 to POF3 and PF5, as previously evidenced by TGA-FTIR.6 We further use accelerated tests to determine the thermal reactivity of both, H2O and OH-, with EC in a LiPF6 containing electrolyte, yielding CO2 and POF3. Next, we correlate our accelerated test with the POF3 and CO2 evolution formed by electrochemical side reactions during the SEI formation on graphite in presence and absence of H2O and OH-. For this, we employ our recently presented two-compartment cell in which anode and cathode compartments are separated by a Li+-ion conducting solid electrolyte (Ohara glass) laminated with aluminum and polypropylene foil, so that the gas evolution from side reactions at the graphite electrode can be studied without cross-diffusion of reaction products to the counter-electrode, thereby enabling a more detailed analysis of the reaction pathways.5 This is a major advance over conventional cells, where the gases come from both electrodes, and thus do not allow a deconvolution of the simultaneously occurring reactions from anode and cathode. The study is concluded by discussing the impact of the contaminants, H2O and OH-, on the cycle life of NMC//graphite full-cells at 45°C where both side reactions, the hydrolysis of EC and the decomposition of LiPF6, can play a role. Figure 1 shows an exemplary OEMS measurement with a 1.5 M LiPF6 EC electrolyte containing either H2O (blue) or OH- contamination (green) in an accelerated test to determine the gas evolution from side reactions with these contaminants at various temperatures. References R. Bernhard et al., J. Electrochem. Soc., 162, A1984 (2015).M. Metzger et al., J. Electrochem. Soc., 163, A1219 (2016).R. Jung et al., 231st ECS Meeting, #39, New Orleans, USA (2017).M. Metzger et al., J. Electrochem. Soc., 162, A1227 (2015).M. Metzger et al., J. Electrochem. Soc., 163, A798 (2016).H. Yang et al., J. Power Sources, 161, 573 (2006). Acknowledgement The authors gratefully acknowledge BASF SE for financial support of this research through the framework of its Scientific Network on Electrochemistry and Batteries. Figure 1. Temperature set point (black) and cell temperature (red) vs. time during OEMS measurements (upper panel), and respective CO2 and POF3 evolution (lower panel) for 240 μl of 1.5 M LiPF6 in EC with H2O (blue) or OH- contamination (green). The gray data shows a reference measurement with only the base electrolyte (<20 ppm H2O). Figure 1

Hydrolysis of Ethylene Carbonate with Water and Hydroxide under Battery Operating Conditions

This study deals with the decomposition of ethylene carbonate (EC) by H2O in the absence and presence of catalytically active hydroxide ions (OH−) at reaction conditions close to lithium-ion battery operation. We use On-line Electrochemical Mass Spectrometry (OEMS) to quantify the CO2 evolved by these reactions, referred to as H2O-driven and OH−-driven EC hydrolysis. By examining both reactions at various temperatures (10 – 80°C) and water concentrations (<20 ppm or 200, 1000, and 5000 ppm H2O) with or without catalytically active OH− ions in EC with 1.5 M LiClO4, we determine an Arrhenius relationship between the CO2 evolution rate and the cell temperature. While the apparent activation energy for the base electrolyte (<20 ppm H2O) is very large (app. Ea ≈153 kJ/mol), substantially lower values are obtained in the presence of H2O (app. Ea ≈99 ± 3 kJ/mol), which are even further decreased in the presence of catalytically active OH− (app. Ea ≈43 ± 5 kJ/mol). Our data show that OH−-driven EC hydrolysis is relevant already at room temperature, whereas H2O-driven EC hydrolysis (i.e., without catalytically active OH−) is only relevant at elevated temperature (≥40°C), as is the case for the base electrolyte. Thus, catalytic quantities of OH−, e.g., from hydroxide contaminants on the surface of transition metal oxide based active materials, would be expected to lead to considerable CO2 gassing in lithium-ion cells.

Study on the Synthesis of Ethylene Glycol by Catalytic Hydrolyze of Ethylene Carbonate

The process for ethylene glycol (EG) by catalytic hydrolysis of ethylene carbonate (EC) was studied. The influencing factors of the reaction products were studied which include the reaction temperature, the mole ratio of H2O to EC, the mass fraction of the catalyst and the reaction time. The optimal conditions were identified as follows: the reaction temperature is 140-145°C, n (H2O) :n (EC) = 2.0-2.5 : 1, the catalyst of Al2O3is about 2.0wt%, the reaction time is about two hours. Under the above conditions, EC can be completely hydrolyzed and the selectivity of EG is above 98%.

1,3-Dimethylimidazolium-2-carboxylate: a zwitterionic salt for the efficient synthesis of vicinal diols from cyclic carbonates

The development of efficient, cheap and recyclable catalysts for reactions under mild reaction conditions is a very attractive topic in green chemistry. Herein, a series of basic ionic liquids (ILs) were investigated as catalysts for the synthesis of vicinal diols via the hydrolysis of cyclic carbonates in order to improve this kind of synthetic process. The effects of the IL structure, the molar ratio of cyclic carbonate to water, and various reaction parameters on the catalytic performance were investigated in detail. It was found that 1,3-dimethylimidazolium-2-carboxylate, a simple halogen-free zwitterionic catalyst, showed high activity (a space-time yield of 1086 h−1) and excellent selectivity for the preparation of ethylene glycol via the hydrolysis of ethylene carbonate. The catalyst could be reused over six times without obvious loss of catalytic activity. Also, it was applicable to a variety of cyclic carbonates for the production of their corresponding vicinal diols with high yields and selectivities. A possible catalytic cycle for this kind of catalytic process was proposed based on the experimental results, NMR spectroscopy and theoretical calculations. This reaction protocol opens a new possibility for chemical synthesis as a substitution for traditional base or basic ILs.

Development of Highly Selective Process for Mono-Ethylene Glycol Production from Ethylene Oxide via Ethylene Carbonate Using Phosphonium Salt Catalyst

A new process for the production of mono-ethylene glycol (MEG; HOCH2CH2OH) was developed by Mitsubishi Chemical Corporation (MCC) to meet its growing demand in the world. While the MEG selectivity of conventional non-catalyzed process is around 89% under typical conditions, that of the new process exceeds 99%. The key of the high selectivity is the two-step synthesis via ethylene carbonate. The first step reaction is catalyzed by phosphonium salts and generates ethylene carbonate as an intermediate. This is followed by hydrolysis of ethylene carbonate in the second step. Several commercial plants of the new process have already been operated world-wide.

Poly(ethylene carbonate)s, part II : degradation mechanisms and parenteral delivery of bioactive agents

The degradation and drug carrier properties of poly(ethylene carbonate) (PEC) were investigated in vitro and in rats and rabbits. PEC was found to be specifically degraded in vivo and in vitro by superoxide radical anions O 2 −·, which are, in vivo, mostly produced by inflammatory cells. No degradation of PEC was observed in the presence of hydrolases, serum or blood. PEC is biodegraded by surface erosion without significant change in the molecular weight of the residual polymer mass. The non-hydrolytic biodegradation by cells producing O 2 −· is unique among the polymers used as biodegradable drug carriers. The main degradation product of PEC in aqueous systems is ethylene glycol, formed presumably by hydrolysis of ethylene carbonate. The splitting off of a five-membered ring structure from the polymer chain indicates a chain reaction mechanism for the biodegradation. PEC is a suitable drug carrier, particularly for labile drugs. Using human interleukin-3 and octreotide as model drugs, surface erosion of the PEC formulations was indicated by a 1:1 correlation between drug release and polymer mass loss.