Improved Route to Linear Triblock Copolymers by Coupling with Glycidyl Ether-Activated Poly(ethylene oxide) Chains

Poly(ethylene oxide) block copolymers (PEO$_z$ BCP) have been demonstrated to exhibit remarkably high lithium ion (Li$^+$) conductivity for Li$^+$ batteries applications. For linear poly(isoprene)-b-poly(styrene)-b-poly(ethylene oxide) triblock copolymers (PI$_x$PS$_y$PEO$_z$), a pronounced maximum ion conductivity was reported for short PEO$_z$ molecular weights around 2 kg mol$^{−1}$. To later enable a systematic exploration of the influence of the PI$_x$ and PS$_y$ block lengths and related morphologies on the ion conductivity, a synthetic method is needed where the short PEO$_z$ block length can be kept constant, while the PI$_x$ and PS$_y$ block lengths could be systematically and independently varied. Here, we introduce a glycidyl ether route that allows covalent attachment of pre-synthesized glycidyl-end functionalized PEO$_z$ chains to terminate PI$_x$PS$_y$ BCPs. The attachment proceeds to full conversion in a simplified and reproducible one-pot polymerization such that PI$_x$PS$_y$PEO$_z$ with narrow chain length distribution and a fixed PEO$_z$ block length of z = 1.9 kg mol$^{−1}$ and a Đ = 1.03 are obtained. The successful quantitative end group modification of the PEO$_z$ block was verified by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). We demonstrate further that with a controlled casting process, ordered microphases with macroscopic long-range directional order can be fabricated, as demonstrated by small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has already been shown in a patent, published by us, that BCPs from the synthesis method presented here exhibit comparable or even higher ionic conductivities than those previously published. Therefore, this PEO$_z$ BCP system is ideally suitable to relate BCP morphology, order and orientation to macroscopic Li$^+$ conductivity in Li$^+$ batteries

Risk factors associated with adverse fetal outcomes in pregnancies affected by Coronavirus disease 2019 (COVID-19): a secondary analysis of the WAPM study on COVID-19.

Objectives To evaluate the strength of association between maternal and pregnancy characteristics and the risk of adverse perinatal outcomes in pregnancies with laboratory confirmed COVID-19. Methods Secondary analysis of a multinational, cohort study on all consecutive pregnant women with laboratory-confirmed COVID-19 from February 1, 2020 to April 30, 2020 from 73 centers from 22 different countries. A confirmed case of COVID-19 was defined as a positive result on real-time reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assay of nasal and pharyngeal swab specimens. The primary outcome was a composite adverse fetal outcome, defined as the presence of either abortion (pregnancy loss before 22 weeks of gestations), stillbirth (intrauterine fetal death after 22 weeks of gestation), neonatal death (death of a live-born infant within the first 28 days of life), and perinatal death (either stillbirth or neonatal death). Logistic regression analysis was performed to evaluate parameters independently associated with the primary outcome. Logistic regression was reported as odds ratio (OR) with 95% confidence interval (CI). Results Mean gestational age at diagnosis was 30.6+/-9.5 weeks, with 8.0% of women being diagnosed in the first, 22.2% in the second and 69.8% in the third trimester of pregnancy. There were six miscarriage (2.3%), six intrauterine device (IUD) (2.3) and 5 (2.0%) neonatal deaths, with an overall rate of perinatal death of 4.2% (11/265), thus resulting into 17 cases experiencing and 226 not experiencing composite adverse fetal outcome. Neither stillbirths nor neonatal deaths had congenital anomalies found at antenatal or postnatal evaluation. Furthermore, none of the cases experiencing IUD had signs of impending demise at arterial or venous Doppler. Neonatal deaths were all considered as prematurity-related adverse events. Of the 250 live-born neonates, one (0.4%) was found positive at RT-PCR pharyngeal swabs performed after delivery. The mother was tested positive during the third trimester of pregnancy. The newborn was asymptomatic and had negative RT-PCR test after 14 days of life. At logistic regression analysis, gestational age at diagnosis (OR: 0.85, 95% CI 0.8-0.9 per week increase; pPeer reviewe

Analysis of Transport Properties of Polycarbonate-Based Polymer Electrolytes Containing Lithium (perfluoroalkylsulfonyl)Imides for Possible Application in Lithium-Ion Batteries

The search for safe electrolytes for the use in lithium metal batteries and high energy density batteries has driven the interest in alternative polymer electrolytes with enhanced performance. The central interest focuses on transport properties as good ionic conductivities and on high electrochemical stability towards lithium metal anodes and cathodes for high voltage batteries. To gain insight in the Li-ion movement in polycarbonates, as dry or gel electrolyte, is necessary for understanding how to improve these systems and achieve better performances. In this context, we present a critical study on polycarbonates as alternative to polyethylene oxide (PEO) in salt-in-polymer electrolytes. [1]Polymer electrolytes based on PEO as well as some related with grafted PEO side chains along polymer backbones such as polyphosphazenes, polysiloxanes and others are known to reach ionic conductivities in the range of 10-3 - 10-4 S·cm-1 in a favourable temperature range and typical Li+ transference numbers around 0.2.[2,3] In contrast to that, polycarbonates were reported to exhibit transference numbers up to about 0.5 as well as higher ionic conductivities and electrochemical stability.[4]In this work, the commercially available polycarbonates polyethylene carbonate (PEC) and polypropylene carbonate (PPC) were prepared as flexible self-standing membranes with dissolved fluorinated lithium salts such as LiTFSI and others. With the use of propylene carbonate (PC) novel gel-polymer electrolytes have been fabricated. The ion conducting polymer membranes were examined regarding their electrochemical and transport characteristics with respect to possible battery applications. We studied ionic conductivity and Li-ion transference number as well as the coordination of lithium with different dissolved lithium salts on carefully purified polycarbonate samples. We obtained ionic conductivities in dry state around 10-6 S·cm-1 at room temperature and up to 10-3 in gelled systems. The novel gel systems based on PEC and PPC perform significantly better than the dry alternatives

Polycarbonate-Based Lithium Salt-Containing Electrolytes: New Insights into Thermal Stability

For investigation of the thermal stability of polycarbonate-based lithium salt-containing electrolytes, polycarbonate–salt mixtures [polyethylene carbonate (PEC) and polypropylene carbonate (PPC) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)] were heated to 100 °C and the conductivity was monitored with electrochemical impedance spectroscopy for at least 24 h. At a constant high temperature, the observed rise in conductivity can be correlated to degradation of long-chain polymer units to small-chain polymer units as the viscosity decreases with a shorter chain length. In both cases, degradation can be observed. With PEC–LiTFSI, it takes ≈9 h until total degradation; with PPC–LiTFSI, the process is slower. Additionally, we repeated the experiments with PEC and other Li salts such as lithium trifluoromethanesulfonate (LiOTf), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), and lithium difluoro(oxalato)borate (LiDFOB). These experiments resulted in the degradation being dependent on the electrophilic activation by the lithium salt. With different Li-free salts such as sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), potassium bis(trifluoromethanesulfonyl)imide (KTFSI), and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI), no degradation of the polymer is observable. As a degradation mechanism, we anticipate a depolymerization of PEC at the α-carbon of the carbonate group in the polymer chain in the presence of a lithium salt with a weakly coordinating anion

Ester-Based Battery Solvents in Contact with Metallic Lithium: Effect of Water and Alcohol Impurities

Organic ester-based battery solvents were examined with respect to their reactivity with water and alcohols in contact with metallic lithium. The investigation was focused on monohydric esters (n-propyl acetate, isopropyl acetate), dihydric esters (trimethylene diacetate, 1,2-propylene glycol diacetate), and trihydric esters (triacetin). Experiments with lithium metal, the respective ester and water, and the matching alcohol were done. The resulting reaction solutions were analyzed with 1H NMR spectroscopy and compared to spectra recorded with the anticipated reaction products that were synthesized separately. The study reveals a tandem reaction from ester saponification to a catalytic Claisen condensation. Thus, the products formed during the reaction showed early degradation in cyclic voltammetry measurements in both the anodic and cathodic regions. A reactivity trend could be examined whereupon the trihydric esters were the least reactive followed by the dihydric and monohydric esters. In the absence of water and alcohols, all investigated esters are stable against metallic lithium

A Series of Polyhydric Esters As Novel Candidates for Battery Solvents in Lithium Metal Cells: Electrochemical Investigations and Influences of Moisture and Alcohol Residues in Contact with Lithium Metal

In recent years, the lithium metal anode has aroused great interest, not at least through the development of the lithium//sulfur and the lithium//air battery technologies, in all-solid-state batteries. However, the application of lithium metal anodes is limited by safety issues and several failure mechanisms, including, dendrite growth and direct chemical reactions with electrolyte components like battery solvents, which leads to fast capacity losses.In this context, a new series of polyhydric propyl-based esters were investigated, namely n-propyl acetate, isopropyl acetate (monohydric esters), trimethylene diacetate, 1,2-propylene glycol diacetate (dihydric esters) and triacetin (trihydric ester) as attractive and environmental friendly candidates for electrolyte solvents in lithium metal battery applications.The above mentioned organic esters were examined in respect to their reactivity in contact with lithium metal, influenced by water or alcohol impurities. The resulting reaction products were analyzed and determined via 1H-NMR spectroscopy. Additional experiments were performed and the resulting products compared to anticipated reaction products which were prepared separately, to evidence possible reaction mechanisms like the occurrence of a CLAISEN-condensation.Furthermore, the here mentioned propyl-based esters and the reaction products were analyzed by cyclic voltammetry against copper, platinum and aluminum as working electrode to evaluate the anodic and cathodic stability, as well as possible anodic dissolution reactions in the presence of LiTFSI as conducting salt.In both cases, the reactivity in contact with lithium metal and the anodic dissolution of aluminum, a reactivity could be observed whereupon the trihydric esters were least reactive followed by the dihydric and monohydric esters.In absence of water and alcohols all investigated esters show no detectable reaction with lithium metal

New Insights into the Behavior of Polycarbonate-Based Lithium Salt Containing Electrolytes Regarding Thermal Long-Term and Electrochemical Stability

For lithium ion batteries solid-state electrolytes like polymers gained more and more attention in the last years, especially due to safety reasons. Polyethylene oxide (PEO) based systems are still state of the art. One of its major drawbacks is the highly crystalline structure, which inhibits fast migration of lithium ions and results in a low transference number and low conductivity [1]. Recently, polycarbonate based polymer electrolytes gained some interest [2,3]. Polycarbonates were assumed to show weaker ion-dipole interactions in contrast to PEO, given rise to higher transference numbers [2]. With suitable additives and high salt concentrations, higher ionic conductivities were reported at moderate temperatures (>60 °C) [3].Nevertheless, there is still a lack of knowledge concerning long-term performance of the polycarbonate-salt-mixtures as electrolytes in terms of thermal stability in the temperature range of solid-state batteries. Therefore, we prepared lithium salt containing polycarbonate samples using either solution casting with additional removal of the solvent or the hot press method. We examined the behavior of polycarbonate salt mixtures over a period of time at given temperatures. Investigation methods such as differential scanning calorimetry (DSC), nuclear magnetic resonance spectroscopy (NMR) and electrochemical impedance spectroscopy (EIS) were used. The results of the experiments indicate that e. g. the mixture LiTFSI in polyethylene carbonate (PEC) suffers from a salt catalyzed decomposition for longer times whereas polypropylene carbonate (PPC) is stable.Furthermore, candidates with good thermal long-term stability (e. g. PPC/LiTFSI) were analyzed concerning their ionic conductivity and their electrochemical stability window. If necessary, improvements were made to increase the electrochemical stability (e. g. down to lithium stripping / plating) or the conductivity by use of different additives, e.g. plasticizers and SEI additives