Ethylene Carbonate Research Articles

Identification and Quantification of Lithium Ion Battery Electrolyte Residues in Blackmass Via Headspace-GC-MS/FID

Due to the increasing demand for lithium-ion batteries (LIBs) in recent years, the demand for resources has also risen. As a result, the amount of LIBs that have reached the end of their life is increasing, leading to stricter guidelines that require certain proportions of recycled materials in the production of new LIBs. Typical recycling strategies start by deactivating, dismantling and shredding LIBs, thereby generating blackmass consisting of active and inactive materials (e.g. Li, Mn, Ni, Co, Cu and organic carbonates). However, black mass is a non-standardized resource, and its composition and purity vary depending on the respective process. 1,2 Therefore, it is essential to characterize and quantify its composition in order to make use of this highly variable resource stream while maintaining quality and safety.This work aims to identify and quantify organic electrolyte residues in black mass without further sample preparation. To achieve this, the samples were agitated using a headspace sampler and then analyzed by gas chromatography-mass spectrometry (GC-MS) and flame ionization detector (FID). Linear and cyclic carbonates such as dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate, as well as aging products such as 2,5-dioxahexanedioic acid dimethyl ester (DMDOHC), were detected. The identification results were compared to those achieved by thermodesorption and solid-phase microextraction.Overall, this study demonstrates a method for identifying and quantifying organic electrolyte residues in black mass, which can aid in the development of more efficient and sustainable recycling processes for LIBs.References(1) Peschel, C.; van Wickeren, S.; Preibisch, Y.; Naber, V.; Werner, D.; Frankenstein, L.; Horsthemke, F.; Peuker, U.; Winter, M.; Nowak, S. Comprehensive Characterization of Shredded Lithium-Ion Battery Recycling Material. Chemistry (Weinheim an der Bergstrasse, Germany) 2022, 28, e202200485.(2) Neumann, J.; Petranikova, M.; Meeus, M.; Gamarra, J. D.; Younesi, R.; Winter, M.; Nowak, S. Recycling of Lithium‐Ion Batteries—Current State of the Art, Circular Economy, and Next Generation Recycling. Advanced Energy Materials 2022, 761, 2102917.

Exploring the Efficiency of Lithium Stripping/Plating in Solid Polymer Anode-Free Lithium Cells

Traditional Li-ion batteries (LIBs) are widely used in various electronic devices due to their advantages in energy storage applications. However, finding ways to push the energy densities even higher would be highly desirable for the further rapid development of electric vehicles and electromobility. Li metal batteries and anode-free batteries (AFBs) – where the Li metal is plated in situ from Li+ ions taken from the cathode – have received extensive attention and research due to their very high specific capacity.[1] However, Li ions are unevenly deposited on the surface of anodes to form Li dendrite during the charging and discharging process, which severely deteriorates their electrochemical performance and battery safety.[2] To solve this problem, many researchers choose solid polymer electrolytes (SPEs) instead of liquid electrolytes in the batteries, because of the stability of SPEs towards Li metal.Long-term cycling of AFBs requires high-efficiency Li metal stripping and plating, which in a solid polymer cell is highly dependent on the polymer electrolyte system used, so finding appropriate host materials and salts to for the SPEs is very necessary. Poly(ethylene oxide) (PEO)-based SPEs are one of the most popular host materials for SPEs, due to their excellent chemical stability. Poly(ε-caprolactone) (PCL)-based SPEs have higher ionic conductivity and can be cycled at room temperature.[3] Poly(trimethylene carbonate) (PTMC)-based SPEs have high lithium transference number and better mechanical properties.[4] Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) is one of the most popular salts used for SPEs. Recently, lithium difluoro(oxalate)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) have been considered a promising alternative as electrolyte because they can passivate electrode surfaces and protect electrode materials.[5] Combinations of these materials are all potentially relvant for application in AFBs.In this work, three different polymer host materials, PEO, PTMC, and PCL, were explored as polymer electrolytes together with LiTFSI salt for their performance in anode-less cell setups, testing the plating/striping coulombic efficiency (CE) in Cu || Li cells. The results reveal clear issues for the CE of cycling in the PEO:LiTFSI system, while low-concentration PTMC:LiTFSI instead shows much more promising results. Changing the LiTFSI salt for LiBOB or LiDFOB also improves the CE of the cells.[1] Beyene, T. T., Jote, B. A., Wondimkun, Z. T., Olbassa, B. W., Huang, C. J., Thirumalraj, B., Wang C. H., Su W. N., Dai H., Hwang B. J., Effects of concentrated salt and resting protocol on solid electrolyte interface formation for improved cycle stability of anode-free lithium metal batteries, ACS applied materials & interfaces, 2019, 11(35), 31962.[2] Huang W. Z., Zhao C. Z., Wu P., Yuan H., Feng W. E., Liu Z. Y., Lu Y., Sun S., Fu Z. H., Hu J. K., Yang S. J., Anode‐Free Solid‐State Lithium Batteries: A Review, Advanced Energy Materials, 2022, 12(26), 2201044.[3] Chiu, C. Y., Chen, H. W., Kuo, S. W., Huang, C. F., Chang, F. C., Investigating the effect of miscibility on the ionic conductivity of LiClO4/PEO/PCL ternary blends. Macromolecules, 2004, 37(22), 8424.[4] Li Z., Mogensen R., Mindemark J., Bowden T., Brandell D., Tominaga Y., Ion‐conductive and thermal properties of a synergistic poly (ethylene carbonate)/poly (trimethylene carbonate) blend electrolyte. Macromolecular rapid communications, 2018, 39(14):1800146.[5] Shkrob, I. A., Zhu, Y., Marin, T. W., Abraham, D. P., Mechanistic Insight into the Protective Action of Bis (oxalato) borate and Difluoro (oxalate) borate Anions in Li-Ion Batteries, The Journal of Physical Chemistry C, 2013, 117(45), 23750.

Enhancing the Performance and Stability of Li-Ion Batteries with Fluorinated Electrolytes: Insights from MD Simulation and Experimental Analysis

The significance of using fluorinated electrolytes, particularly fluorinated ethylene carbonate (FEC) and difluoro ethylene carbonate (DFEC), in the electrolyte system of 1.2 M LiPF6 in dimethyl carbonate (DMC)/fluorinated solvent (FEC/DFEC), was explored using classical molecular dynamic (MD) simulation and density functional theory (DFT) calculation in this work. Various parameters, such as radial distribution function (RDF), integral over RDF, transference number, coordination number, and solvation energy, were analyzed. The study demonstrated that DFEC enhances the reduction in binding energy of the solvation sheath compared to FEC. Additionally, the electrochemical performance of a practical full-cell 18650 of LiNi0.88Co0.10Al0.02O4 (NCA) cathode and graphite anode batteries was examined, confirming that 1.2 M LiPF6 in DMC/FEC/DFEC (4:0.5:0.5 %v) demonstrated the highest capacity retention after 1,000 cycles, surpassing 1.2M LiPF6 in DMC/fluorinated (4:1 %v, FEC and DFEC, respectively) and the previous electrolyte 1.2 M LiPF6 in EC/EMC/DEC/FEC (1:1:1:1.3 %V). Spectroscopy techniques, including DEMS, NMR, and GC-MS, were utilized to investigate the electrolyte decomposition, revealing CO2 and H2 as the main gas products during decomposition. NMR results identified some species, such as HF, H2O, acetal, formaldehyde, and unknown products, while GC-MS confirmed that all the solvents in the electrolyte take part in the decomposition process. This study highlights the potential of fluorinated electrolytes in battery systems and provides insight into their decomposition mechanism, contributing to the development of more efficient and stable battery systems.

Development of polycarbonate-based electrolytes with in situ polymerized electrolyte interlayers for lithium-metal batteries

Solid polymer electrolytes (SPEs), especially polycarbonate-based SPEs, have emerged as promising candidates for next-generation lithium-metal batteries (LMBs) due to their enhanced safety features and suitable mechanical and electrochemical properties. However, the limited interface compatibility between SPEs and electrodes, along with the persistent issue of lithium dendrite formation, hindered the progress of LMBs. In this study, an innovative approach is introduced to address these challenges by incorporating an in situ polymerized poly(vinyl ethylene carbonate) (PVEC) electrolyte interlayer between poly(ethylene carbonate) (PEC)-based SPE and electrode material. Furthermore, lithium nitrate (LiNO3) is incorporated as an additive in the PEC-based SPE to facilitate the formation of a stable and suitable solid electrolyte interphase (SEI) layer, thereby enhancing the cycling stability of LMBs. Notably, the Li||Li symmetric cell, equipped with the in situ PVEC electrolyte interlayer and the LiNO3-additive-containing PEC-based electrolyte, exhibited remarkable stability, maintaining a continuous cycling for 70 h at a current density of 0.1 mA cm−2. Similarly, a Li||LiFePO4 cell demonstrated impressive performance, sustaining 40 charge-discharge cycles at a current density of 0.1C (1C = 170 mA g−1) while maintaining a discharge capacity of approximately 150 mAh g−1. This work showcases a straightforward strategy for enhancing interfacial compatibility through in situ polymerization of the interlayer and the incorporation of electrolyte additives.

Conductivity Improvement of LiBF4 Containing Electrolyte for Enhanced Application in Lithium-Ion Batteries

In view of a possible cost reduction and safety improvement of Lithium-Ion-Batteries (LIBs), the exchangeability of the common electrolyte salt lithium hexafluorophosphate LiPF6 with lithium tetrafluoroborate LiBF4 was investigated.[1,2] Replacement of LiPF6 with LiBF4 was considered due to the salt’s superior thermal stability and moisture stability compared to LiPF6. While LiBF4 was repeatedly studied for application in LIBs, low conductivity compared to analogous electrolyte solutions with LiPF6 is referred to as one of the main drawbacks of LiBF4 electrolytes.[1,3] These differences in electrolyte solution conductivity are usually related to an increased tendency for ion pair formation between the [BF4]– anion and Li+.[1,4] To overcome the strong ion-pairing between Li+ and [BF4]–, the conductivity of a LiBF4 electrolyte solution was improved by introduction of different amounts of 1,2-dimethoxyethane (DME) as bidentate ligand into the commercially available electrolyte solvent L57 (ethyl carbonate : ethylmethyl carbonate, 30 : 70, by wt%). The solvent modification was carried out in consideration of the published superior oxidative stability of lithium associated oligoethers compared to non-associated analogues.[5] All electrolyte solutions were investigated for their electrochemical behavior and their performance in Lithium-Ion-Battery (LIB) cells with commercially available cell components. All results were referred to analogous measurements with LiPF6 and LiBF4 electrolyte solution in the unmodified L57 solvent. Electrochemical characterization was performed by conductivity measurements and cyclic voltammetry. Battery cell experiments were carried out for Lithium-Metal cells with excess of electrolyte solution and Lithium-Ion cells. Lithium nickel cobalt manganese oxide (NCM622) electrodes were implemented as positive electrodes and Lithium-Ion cells were assembled with graphite electrodes as negative electrodes. All battery cells were investigated for their ambient temperature cycle life. Furthermore, ambient temperature C-rate stability of Li-Ion cells was examined. In view of the electrochemical behavior, conductivity of LiBF4 electrolytes significantly increases with the introduction of DME to the chosen electrolyte solvent, which is shown in the figure presenting the temperature dependent conductivities of the investigated electrolyte solutions. This conductivity enhancement is decreasing towards the contribution of more than two equivalents of DME per Li+ ion in the electrolyte solution. Cyclic voltammetry experiments of the electrolyte solutions show negligible effects on reductive stability of the electrolyte solution system, while the respective oxidative stability distinctly decreases with the addition of DME into the electrolyte solvent. A decreased oxidative stability is considered to induce parasitic reactions at the positive electrode, which presumably can be affected by change of positive electrode material. Despite the differences in conductivity, battery cell experiments present LiBF4 as a comparable electrolyte salt to LiPF6, with a performance difference that could possibly be overcome by utilization of the right electrolyte additive(s). The investigated oligoether containing electrolyte solutions show inferior battery performance compared to the unmodified carbonate-based electrolyte solvent. Since the battery cycling experiments were prepared at the oxidative stability limit of these electrolyte solutions, these electrolyte solutions might still create promising battery cell performance with a change of positive electrode material. In order to further investigate the ion pair association of lithium cations and tetrafluoroborate anions, the utilized system was additionally investigated spectroscopically and with quantum chemical calculations on the basis of density functional theory. Spectroscopic characterization was carried out with help of stimulated spin echo experiments in nuclear magnetic spectroscopy and Raman spectroscopy measurements. Both spectroscopies present changes in the associated structure of lithium cation and tetrafluoroborate anions by addition of DME to the commercial electrolyte solvent. For further conclusions, these results were compared with the calculations prepared for the electrolyte solution system. In summary, spectroscopic characterization and quantum chemical calculations indicate a modification of the associated structures in solution by the addition of DME to the chosen electrolyte solvent. By comparison of all collected results, research concerning the application of LiBF4 electrolytes should be continued with adaption of electrolyte solution additives or positive electrode material, respectively.[1] C. Daniel, J. O. Besenhard (Hrsg.) Handbook of battery materials, Wiley-VCH-Verl., Weinheim, 2011.[2] M. Winter, R. J. Brodd, Chem. Rev. 2004, 104, 4245.[3] R. Korthauer (Hrsg.) Handbuch Lithium-Ionen-Batterien, Springer Vieweg, Berlin, Heidelberg, 2013.[4] H. Tsunekawa, A. Narumi, M. Sano, A. Hiwara, M. Fujita, H. Yokoyama, J. Phys. Chem. B 2003, 107, 10962.[5] K. Yoshida, M. Nakamura, Y. Kazue, N. Tachikawa, S. Tsuzuki, S. Seki, K. Dokko, M. Watanabe, J. Am. Chem. Soc. 2011, 133, 13121. Figure 1

Liquid Structure and Anti-Corrosion Effect of Super-Concentrated Electrolyte Solution

For realizing sustainable world, Lithium-ion batteries are required to have higher energy density. Aluminum metal have been dominantly used as a current collector of positive electrode. A mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 mol dm-3 Lithium hexafluorophosphate (LiPF6) has been used as an electrolyte solution. Aluminum forms thin passivation layer on its surface, preventing the corrosion. However, aluminum corrosion may occur due to this electrolyte solution under high voltage condition. Recently, super-concentrated electrolyte solution (SCES) [1], which consists of only two or three times as much solvent as lithium salt, has been attracting attention as a new electrolyte solution of high-voltage lithium-ion battery. Motsumoto et al. proposed that aluminum corrosion was remarkably suppressed in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based SCES [2]. To clarify the corrosion-inhibiting factor of SCES, we investigated aluminum corrosion in the several lithium salts based SCESs [3]. And we found that lithium perchlorate (LiClO4)-based SCES could suppress corrosion of Aluminum current collector. Liquid structure of the SCES may plays an important role in corrosion suppression. In the present work, we demonstrated Raman spectroscopy and Quantum chemical calculations to reveal the liquid structure of the LiClO4-based SCES.The LiClO4 based SCES was prepared by dissolving LiClO4 into DMC as the molar ratio of 1 : 2. For comparison, DMC solution containing 1 mol dm-3 LiClO4 and neat DMC was also prepared. Raman spectroscopic experiments were conducted using Laser Raman spectrophotometer (NRS-5100, JASCO) installed a laser at 532 nm. Quantum calculations were performed using the Gaussion 9 program suite (Gaussian, USA). Geometry optimization were conducted at the B3LYP/6-311+G(d,p) level. An intensive peak is observed at approximately 915 cm-1 for neat DMC. When a small amount of LiClO4 is added to DMC (corresponding to 1 mol dm-3 LiClO4 solution), new peak is observed at approximately 932 cm-1. This peak can be assigned to ClO4 - anion. A new peak appears at approximately 950 cm-1 with increasing LiClO4 (corresponding to the SCES). According to the Quantum calculations, the new peak is assigned to aggregate in which the ClO4 - cross-links Li+. In addition, HOMO energy of a contact ion pair (CIP), in which ClO4 - coordinates to Li+, is lower than that of free ClO4 - anion. The oxidative stability of ClO4 - increases by forming CIP and aggregate. The decomposition products of ClO4 - may affect the Aluminum corrosion. The high oxidative stability of LiClO4-based SCES may prevent the Aluminum corrosion.

Nafion-Based Quasi-Solid-State Polymer Electrolyte for Lithium-Sulfur Batteries

Lithium-sulfur batteries are considered a strong contender for next-generation high-energy battery systems given their high gravimetric energy density. However, this battery chemistry is still facing challenges such as the polysulfide shuttle effect caused by the high solubility of long-chain lithium polysulfides (Li2Sn) resulting in active material loss and compromised cycle life. Solid-state polymer electrolytes (SPEs) represent a promising pathway to address this issue by preventing the formation and transport of these undesirable polysulfide intermediates.1,2 Moreover, the application of flexible polymer electrolytes promotes safe high energy batteries for smart textiles.In this study, single lithium-ion conducting solid polymer electrolytes (SLIC-SPEs) based on lithiated Nafion membrane have been investigated, utilizing the chemical and thermal stability of this kind of ionomers. Among others, a mixture of ethylene carbonate (EC) and propylene carbonate (PC) was tested as organic aprotic swelling solvent offering advantageous characteristics such as great chemical stability and high ion mobility while avoiding phase separation issues and undesired leaching.Sulfur-infiltrated ultramicroporous carbon composite cathodes were utilized in combination with the investigated SLIC-SPEs, facilitating a quasi-solid-state lithium-sulfur full cell with carbonate-solvent compatibility and high active material utilization.3 Electrochemical performance of the full cell was investigated elaborately and compared with a reference system using solely the liquid EC:PC solvent. While rapid capacity fading can be observed for the liquid electrolyte cell, an enduring high capacity is found in the lithiated-Nafion system. For better understanding of these effects, cycling analysis was accompanied by implementing impedance spectroscopy upon galvanostatic cycling. The electrochemical characterization indicates the formation of a stable film and high degree of reversibility during cycling of the lithiated-Nafion cell whereas an increased film resistance due to sulfur cross-over and electrolyte decomposition was observed within the liquid electrolyte system.(1) Z. Li, W. Lu, N. Zhang, Q. Pan, Y. Chen, G. Xu, D. Zeng, Y. Zhang, W. Cai, M. Yang, J. Mater. Chem. A 2018, 6 (29), 14330-14338.(2) X. Hao, H. Wenren, X. Wang, X. Xia, J. Tu, J. Colloid Interface sci. 2020, 558, 145-154,(3) M. Nojabaee, B. Sievert, M. Schwan, J. Schettler, F. Warth, N. Wagner, B. Milow, K. A. Friedrich, J. Mater. Chem. A 2021, 9 (10), 6508-6519,

Isotopic Labeling of Carbonate Solvents to Understand Gas Generation in Li-Ion Batteries and Gas Reduction by Fluorinated Organosilanes

Battery aging processes from cycling or storage at high temperatures, high voltages, and long times lead to significant degradation of the lithium-ion electrolyte, including decomposition to gaseous species. Gassing in battery pouch cells causes swelling, negatively impacting cell safety and performance. Development of electrolyte formulations that increase stability and reduce gassing is critical for next-generation battery applications and requires a greater understanding of the mechanisms of gas generation and reduction.Fluorinated organosilicon (OS) materials have been developed by Silatronix® to improve high temperature performance with significantly reduced gassing in high Ni battery systems.1 Utilization of a calibrated GC-TCD system allows the specific gas species to be identified and quantified but did not provide information on the mechanisms responsible for producing each species. To provide that information, studies using isotopically labeled carbonate solvents were conducted to identify the source for each gas species using a calibrated GC-MS system.2,3 Beyond identifying the gas species that evolve from particular carbonate solvents, these studies showed that the fluorinated organosilicon (OS) compounds reduce gassing (50-80% reduction depending on the specific OS formulation) by addressing all observed sources of gas during high temperature storage.2,3 The use of isotopically labeled carbonate solvents is extended within this study to provide insight into the origin of gas products and the nature of gas reduction by various OS materials under diverse aging conditions, including high temperature and fast charge cycling, as well as high temperature storage. This investigation includes multiple 13C-labeled electrolyte components including diethyl carbonate (DEC) and dimethyl carbonate (DMC) in addition to ethylene carbonate (EC). Carbonate-only electrolytes are compared to electrolytes containing OS compounds to gain insight into gas reduction mechanisms. Where possible, comparisons are made between different OS structures and popular commercial additives.Overall, this study builds on previous work to detail the origins of gassing from three common commercial carbonate solvents when combined in a complex electrolyte formulation under multiple test conditions and demonstrates that OS materials are highly effective gas-reducing components.

Eutectic Mixtures As Highly Concentrated and Molten Electrolytes with Nearly Single-Ion Conducting Behavior

Today's state-of-the-art liquid electrolytes in lithium ion batteries (LIBs) have a high ionic conductivity and good performance regarding their cycle life. (1) However, they pose a safety risk due to their high vapor pressures and low thermal stability. (1) Furthermore, due to the limited electrochemical stability of the solvent, liquid electrolytes are not suitable for the application in high-voltage LIBs. (2) Molten salts, also called ionic liquids (IL), or highly concentrated electrolytes (HCE) have high lithium ion concentrations, where nearly every solvent molecule is coordinated. Due to this, there are strong ion interactions and the formation of ion clusters that lead to an increased lithium ion transference number of >0.5. (3) Therefore, they can represent an alternative in the field of liquid electrolytes. Additionally, HCE exhibit a higher thermal and electrochemical stability compared to dilute electrolytes and can improve the cycle performance in lithium metal batteries. (4, 5)McOwen et al. reported the coordination of lithium ions and crystalline structures in HCE of the binary mixtures of ethylene carbonate (EC) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) with molar ratio up to 1:1. (6) Based on the concept of melting point depression as known from thermodynamics, room-temperature molten, highly concentrated electrolytes of a carbonate-based solvent with lithium sulfonyl imides were investigated. Instead of EC, the solvent pinacol carbonate (PIC) without acidic α-hydrogen atoms, but four bulky methyl groups was synthesized and used for eutectic mixtures, as the melting point of PIC is with 187 °C far above room-temperature. The physicochemical properties of these electrolytes are studied with respect to the different influence of lithium bis(fluorosulfonyl)imide and LiTFSI despite their same basic molecule structure. The focus will be on the electrochemical analysis by the means of the ionic conductivity, transference number and the electrochemical stability.In comparison to dilute liquid electrolytes the molten electrolytes show extremely high transference numbers, especially for the PIC-LiTFSI mixtures nearly a single-ion conducting behavior (0.9) is observed. This behavior can be explained by the formation of a 2D polymeric network within the HCE electrolyte as determined by crystallographic measurements in the solid state. Combined with the high electrochemical stability, a stable long-term cycling and dendrite suppression in symmetric lithium cells could be shown. Cycling in full cells with high-voltage cathode materials such as LiNi0.6Mn0.2Co0.2O2 (NMC622) or LiMn4O2 (LMO) against lithium metal anodes is applicable. References K. Xu, Chemical Reviews, 104(10), 4303–4417 (2004).J. Li, C. Ma, M. Chi, C. Liang and N. J. Dudney, Advanced Energy Materials, 5(4) (2015).K. M. Diederichsen, E. J. McShane and B. D. McCloskey, ACS ENERGY LETTERS, 2(11), 2563–2575 (2017).G. Jiang, F. Li, H. Wang, M. Wu, S. Qi, X. Liu, S. Yang and J. Ma, Small Struct., 2(5), 2000122 (2021).V. Nilsson, A. Kotronia, M. Lacey, K. Edstrom and P. Johansson, ACS Applied Energy Materials, 3(1), 200–207 (2020).D. W. McOwen, D. M. Seo, O. Borodin, J. Vatamanu, P. D. Boyle and W. A. Henderson, Energy & Environmental science, 7(1), 416–426 (2014).

Firefighting Gel Polymer Electrolyte for Non-Flammable Li-Ion Batteries Based on Extremely Low Amount of a Cross-Linkable Polymer

Safety issues of lithium-ion batteries(LIBs) have caught a priority of concerns as the electric vehicle(EV) market expands dramatically and requires higher energy densities. To be free from a variety of unpredictable situations and environments triggering such a safety issue, materials that provide a mechanism to control the factors causing fire and explosion are required to be involved in LIB cells.In this work, we present a gel polymer electrolyte(GPE) characterized by nonflammability and fire-extinguishing capability by radical scavenging(Rs). This GPE was realized within battery cells by in situ crosslinking a small amount of a cross-linkable fluoro-functionalized cyanoethyl polyvinyl alcohol(F7) in conventional carbonate electrolytes having LiPF6. The cyanoethyl functional groups(-CN) is responsible for gelation by cross-linking while the fluorine-containing moiety terminated radical chain reactions triggering thermal runaway by Rs. The strong interaction between the polymer and solvent molecules restricted solvent volatility. The tiny solid content at 2 wt. % in GPE guaranteed a liquid-level ionic conductivity at 9 mS/cm, disallowing battery performances to be sacrificed. Formation of the LiF-dominant solid-electrolyte-interphase(SEI) layer on anodes was encouraged by the fluoro-moiety of F7.In previous research of our group, PVA-CN was used as cross-linkable polymer for enhancement of mechanical property with additional metal-chelating functional group. Hydroxy group of PVA-CN is useful to modify the functional group by DCC coupling mechanism. Herein, as same as previous modification, the Heptafluorobutyric acid(HFB) was used for non-flammability and battery performance. F7 was expected to not only increase thermal stability but also scavenge the radicals. In addition, LiF-rich SEI layers would be made by fluorine groups.First, GPE increase its thermal stability by strong interaction between cross-linked polymer matrix and organic solvents. The binding energy of ethylene carbonate (EC) and hydrogen of cyanoethyl side chain was 0.4 eV which is stronger compared with general hydrogen bond(0.2 eV). Therefore, the flammable gas generation was suppressed by strong interaction between solvents and polymer matrix.In addition, the flash point demonstrated the strong interaction in GPE. The flash point of GPE which contained different polymer contents was decreased as the ratio of polymer content was increased. The composition of the atmosphere in the devices changed into more flammable because of the higher ratio of EMC gas in the atmosphere within enough time to equilibrate. In other words, EC forms a greater number of strong interactions with the polymer matrix while the polymer contents increased. The SET test of 2 wt.% PVA-CN-based GPE(G2)(3.36 s/g) and 5 wt.% PVA-CN-based GPE(G5)(0 s/g) proved that higher contents of PVA-CN in GPE ensure the non-flammability.Second, to overcome the poor electrochemical ability of G5, Rs functionalized F7 was used instead of PVA-CN. Unlike G2, only with 2 wt. % of F7 guaranteed the 0 s/g of SET. Non-flammability of 2 wt.% F7-based GPE(FG2) is due to the fluorine moiety scavenge the O• or H•. In the nail penetration test, only the FG2 was not exploded and maintained charged voltage while the nail penetrates the whole pouch cell vertically because of its elasticity.The Rs capability was demonstrated by cyclic voltammetry(CV) with 2,2’-azobisisobutyronitrile(AIBN) and alpha-tocopherol(α-TOH). After α-TOH react with AIBN radicals at the 70 ℃, the oxidation current decreased because of consumption of α-TOH. The Rs capability was calculated by ratio of current retention of α-TOH oxidation current with a same amount of among scavenger additives. The Rs capability of F7 was 214%.Lastly, our findings suggest sufficient non-flammability without battery performances degradation. The capacity retention of FG2 was higher than LE at the 300th Cycles. This is because the fluorine moiety contributed to make LiF-rich SEI layers. The rigid SEI layers and GPE suppressed volume expansion of graphite. Also, the capacity fade was not observed in FG2 with higher current density. The reason for great rate capability is higher lithium-ion conductivity which is a multiplication of ionic conductivity and lithium-ion transference number(tLi+). FG2has 4.82 of lithium-ion conductivity, while 3.63 in LE. Therefore, the mass transfer resistance was not large on the electrode surface due to the higher lithium-ion mobility in FG2.In this work, the non-flammability and battery performance were successfully demonstrated by thermal stability and Rs capability without any battery performances degradation. The thermal stability was enhanced by strong intermolecular forces between polymer chain and polar organic solvents. The radical chain reaction was terminated by fluorine moiety of GPEs matrix. The capacity retention of FG2 was outstanding compared with LE. Therefore, due to the FG2, the battery will be able to ensure non-flammability without degradation of performance. Figure 1

Solvent-Driven Degradation of Ni-Rich Cathodes Probed by Operando Gas Analysis

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling stability, which is exacerbated by increased cell voltage due to higher interfacial reactivity than their lower Ni-content analogues. Here, we study the pivotal role of electrolyte solvents in determining the interfacial reactivity at charged LiNi0.33Mn0.33Co0.33O2 (NMC111) and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells (1, 2). Operando gas analysis reveals that the solvent-dependent reactivity for Ni-rich cathodes is related to the extent of lattice oxygen release and accompanying electrolyte oxidation. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 is charged above 4.3 V vs Li/Li+ - the observed onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. The gas analysis also reveals the crosstalk effect caused by the products of the nascent oxygen from the NMC811 lattice and the electrolyte solvent, showing anodic reactivity. In contrast, NMC111, which does not release oxygen up to 4.6 V, shows a similar extent of degradation irrespective of the electrolyte. Higher lattice oxygen release with EC-containing electrolytes is coupled with higher interfacial impedance, a thicker oxygen-deficient rock-salt surface reconstruction layer, more electrolyte solvent and salt breakdown. Oxygen loss is suppressed in the EC-free electrolyte, highlighting the incompatibility between Ni-rich cathodes and conventional electrolyte solvents. W. M. Dose et al., Onset Potential for Electrolyte Oxidation and Ni-Rich Cathode Degradation in Lithium-Ion Batteries. ACS Energy Letters 7, 3524-3530 (2022).W. M. Dose et al., Electrolyte Reactivity at the Charged Ni-Rich Cathode Interface and Degradation in Li-Ion Batteries. ACS Applied Materials & Interfaces 14, 13206-13222 (2022). Figure 1

Influence of Cyclic Alkyl Carbonate Ring-Opening Processes on Electrode/Electrolyte Interphase Formation in Li-Ion Batteries

Cyclic alkyl carbonates, such as ethylene and vinylene carbonate (EC and VC), form solid electrolyte interphases (SEI) suppressing continuous solvent reduction at the graphite anode. There is a consensus that the choice of carbonate clearly affects SEI performance. VC has been observed to polymerize, forming poly(VC), but also to release major amounts of CO2,1,2 which are two seemingly contradictory processes. In this work, we present a detailed study of reaction pathways of EC and VC in typical Li-ion battery electrolytes. The rate of the decomposition reactions of these carbonates in presence of hydroxide is monitored using an injection cell coupled mass spectrometer at varying temperatures ranging from 30°C to 60°C. The activation energies from the Arrhenius relationship between the CO2 evolution rate and the cell temperature confirms that VC hydrolysis is autocatalytic rather than stoichiometric. Direct quantifications and comparisons of the solubilized reaction products will be done over varying times and temperatures with the help of in-situ nuclear magnetic resonance (NMR) and Raman spectroscopy that will help in clarifying the individual steps in the reaction process. The kinetic studies of EC and VC hydrolysis in model systems like this is an important step towards improving our understanding towards carbonates as there is always some trace amounts of hydroxides present in the cells. The complex interconversions and equilibria of these organic alkyl carbonates and oxides investigated herein, will add to the knowledge of interphase formation processes, and support the tailoring of electrolyte formulations in order to enhance performance of future Li-ion batteries.

Multiple Diffusion Processes in Lithium-Ion Battery Electrolytes

Numerical simulations are a powerful tool for the development and improvement of Li-ion batteries[1]. Modelling the mass transport of the involved electrolytic solutions requires precise determination of the corresponding electrolyte parameter. However, the determination methods are still controversially discussed.In this work, we attempt to measure the complete set of electrolyte parameter for a system of 0.5 M LiPF6 dissolved in a blend of ethylene carbonate and ethyl methyl carbonate (EC:EMC, 3:7 weight) at 20°C and 50°C. In order to determine the conductivity, the diffusion coefficient, the transference number and the thermodynamic factor we conduct a combination of concentration cell measurements, galvanostatic polarization experiments and electrochemical impedance spectroscopy[2].While the conductivity and concentration cell measurements show comparable results to the literature, we find the potential response in the polarization experiments deviating from theoretical expectations. Applying galvanostatic polarization experiments to symmetrical metal Li | electrolyte + separator | Li metal cells result in slower, impeded diffusion processes. This indicates the presence of additional, undesired porous structures on the Li electrodes, preventing a reliable evaluation of the electrolyte parameters[3]. To spectrally resolve the diffusive processes, we conduct very low frequency impedance spectroscopy in an attempt to identify the impedance for the sole diffusion through the separator[4].1. Max Schammer et al 2021 J. Electrochem. Soc. 168 0265112. Johannes Landesfeind and Hubert A. Gasteiger 2019 J. Electrochem. Soc. 166 A30793. Talian et al. The Journal of Physical Chemistry C 2019 123 (46), 27997-280074. F. Wohde et al 2016 J. Electrochem. Soc. 163 A714Figure 1: VLF-IS measurements with amplitudes of 60µA, 500µA and 10µA together wit the corresponding equivalent circuits, fits and Kramers-Kronig transformations at 20° C and 50°C respectively Figure 1

(Invited) Advanced Photoelectron Spectroscopy on Battery Materials: Lessons Learnt on Silicon- Containing Electrodes

While Silicon (Si) is being incorporated more and more as an active material in commercial lithium-ion batteries, it is still a topic of intense research and the motivation for these research efforts remains unchanged: Silicon’s large volume expansion during cycling leads rapid capacity fading largely associated with changes in the Si surface chemistry and unstable solid electrolyte interphase (SEI). Using advanced photoelectron spectroscopy (PES) characterization, we have investigated crucial interfaces on Si model systems and Si-containing negative electrodes for Li-ion batteries. Here, we focus on two approaches to influence the SEI composition intrinsically: Binders and electrolytes.Starting with pristine Si powders, we studied the effect of carboxylic acids as electrode slurry additives on the Si surface chemistry before and after electrochemical cycling [1] using synchrotron PES depth profiling. Further, we used photoelectron spectroscopy to confirm cross-linking in poly-acrylic acid-based binder for Si electrodes and showed that the cross-linking agent pentaerythritol had no negative effect on the SEI thus attributing improved cycling performance to increased binder cross-linking [2].In silicon/graphite negative electrodes, we used PES to elucidate the influence of fluoroethylene carbonate (FEC) on the degradation phenomena in electrodes with varying silicon content [3]. Finally, photoelectron spectroscopy provided insights into what happens to the SEI on Si-containing electrodes if we replace the classical electrolyte solvent ethylene carbonate with either FEC or glyoxylic acetal-based alternatives [4, 5].[1] F. Jeschull, H.Q. Pham, A. Ghamlouche, P.K. Thakur, S. Trabesinger, J. Maibach, J. Phys. Energy 2023, 5 (2), 025002. https://doi.org/10.1088/2515-7655/acbbee.[2] J. He, C. Das, F. Yang, J. Maibach, Electrochimica Acta 2022, 411, 140038. https://doi.org/10.1016/j.electacta.2022.140038.[3] A. Ghamlouche, M. Müller, F. Jeschull, J. Maibach, J. Electrochem. Soc. 2022. https://doi.org/10.1149/1945-7111/ac4cd3.[4] L. Gehrlein, C. Njel, F. Jeschull, J. Maibach, ACS Appl. Energy Mater. 2022, 5 (9), 10710–10720. https://doi.org/10.1021/acsaem.2c01454.[5] L. Gehrlein, C. Leibing, K. Pfeifer, F. Jeschull, A. Balducci, J. Maibach, Electrochimica Acta 2022, 140642–140642. https://doi.org/10.1016/j.electacta.2022.140642.

Ethylene Carbonate Free Electrolytes with High Oxidative Stability for High Voltage Lnmo Spinel Cathode in Li-Ion Cells

The increasing implementation of lithium-ion batteries (LIBs) for the fast growing electric vehicle market calls for further improvements in energy density and drives research and innovation to investigate beyond state-of-the-art cell chemistries [1]. Currently, the capacity of the commonly employed transition metal oxide cathodes (NMC series) is approaching their theoretical limit. Thus, to further promote the energy density of LIBs, the most promising strategies are the adoption of a high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode in combination with a high energy density anode. While commercial grades of LNMO are now available, the main challenge toward their implementation is the identification of suitable electrolyte systems with high oxidative stability enabling safe operation of LNMO cathodes at voltages beyond 4.7 V vs Li/Li+, which are also compatible with advanced anode materials operating at low potential. Indeed, electrolytes represent a crucial component in LIBs, and hence a great deal of research has been focusing on the next generation electrolyte systems. These should present a wide electrochemical stability window, high ion conductivity over a wide range of temperature, good thermal stability, and the ability to form stable interphases.[2] In this work we present results on a range of novel electrolytes, based on previous publications [3-5] including super concentrated systems with unconventional solvents to improve the anodic stability, beyond LiPF6 salts to mitigate transition metal dissolution at the cathode, and phosphorous and boron-based additives to improve the stability of the solid/electrolyte interphase (SEI) at the anode. The electrolytes are comprehensively characterised in terms of ionic conductivity over a range of temperatures (see Fig. 1a), viscosity, and thermal stability. Electrochemical impedance spectra (EIS) has been carried out in symmetrical lithium // lithium cells to investigate the interphase stability evolution upon time. Linear sweep voltammetry has been conducted to investigate the anodic stability (see Fig. 1b). The systems have been then investigated in combination with high voltage LNMO cathode, graphite anodes as well as a novel silicon/graphite composite anode. The results will highlight the results achieved so far toward the identification of suitable electrolytes for high energy density Li-ion cells, while discussing the remaining challenges and strategies to mitigate them.[1] Energies 2017, 10(9), 1314, G. Berckmans, M. Messagie, J. Smekens, N. Omar, L. Vanhaverbeke, J. V. Mierlo.[2] Chem. Soc. Rev., 2021, 50, 10486, X. Fan, C. Wang.[3] J. Am. Chem. Soc., 136 (2014) p. 5039, Y. Yamada, K. Furukawa, K. Sodeyama, K. Kikuchi, M. Yaegashi, Y. Takeyama & A. Yamada.[4] Nature Communications, 7 (2016) 12032, J. Wang, Y. Yamada, K. Sodeyama, C. H. Chiang, Y. Tateyama & A. Yamada[5] J. Mater. Sci: Mat. Elec. , 30 (2019) p. 5098, H. Zhou, B. Liu, D. Xia, C. Yin & J. Li Figure 1

Improving the Performance of Flame-Retarding Sodium Bis(Oxalato)Borate in Triethyl Phosphate Electrolyte for Sodium Ion Batteries

An ever-growing demand for energy storage has highlighted potential future resource constraints for Li-ion batteries (LIBs), in particular with respect to Li.1-3 With this in mind Na-ion batteries (NIBs) hold promise as a complementary technology to LIBs, particularly for stationary energy storage.4 To be competitive with LIBs, NIBs need to become fully competitive on cost and on capacity density.5-7 NIBs can however offer more than simply a cost competitive option to LIBs, with potential to offer improvements on both safety and sustainability. A number of cathode materials exist that can avoid many of the unanswered question around the sustainability of state-of-the-art LIB cathodes.3 However, to address safety concerns of LIBs it is impossible to ignore the electrolyte. State of the art electrolyte in LIBs, regularly LiPF6 in a mix of carbonates, is both toxic (by virtue of LiPF6 and to a limited extent ethylene carbonate) and flammable (by virtue of the electrolyte solvents). Importing the Na analogue of state-of-the-art LIB electrolytes (i.e. NaPF6 in carbonates) creates the same problems of flammability and toxicity currently seen in LIBs (albeit the toxicity of NaPF6 is lower than that of LiPF6).Recently Mogensen et al.8 proposed sodium bis(oxalato)borate (NaBOB) in trimethyl phosphate (TMP) electrolyte that overcame the flammability concerns of NaPF6 in carbonate electrolytes. In addition to non-flammability, the use of NaBOB instead of NaPF6 allowed for higher temperatures to be used and produced an electrolyte that was halogen free. Switching from TMP to triethyl phosphate (TEP) allowed for a relatively less-toxic electrolyte (NaBOB and TEP are listed by the European Chemical Agency as ‘harmful if swallowed’ in comparison to ‘harmful if swallowed, in contact with skin or inhaled’ for NaPF6 in carbonates, although limited research has been conducted on the toxicity of NaBOB and so this should be received with limited certainty) without sacrificing cell performance.9 However, hurdles remain for NaBOB in organophosphate electrolytes. Principal amongst these has been the poor solubility of NaBOB in most solvents and the difficulties transferring promising low mass-loading full cell results to higher mass-loading full cells. The low solubility of NaBOB limits the concentration of NaBOB in organophosphate electrolytes to < 0.4 M, producing electrolytes with relatively low conductivities (for NaBOB in TMP, 4.5 mS/cm, and in TEP, 5 mS/cm). N-methyl pyrrolidone (NMP) has previously been shown to increase the solubility of NaBOB when used as a cosolvent with TMP, with conductivity improved to 6.5 mS/cm without sacrificing non-flammability and promising cycling shown in low mass-loading full-cells.10 A range of alternative cosolvents were here investigated to increase the solubility of NaBOB in TEP. Of these, NMP, N,N-dimethyl formamide (DMF) and N,N-dimethyl acetamide (DMAc) were evaluated as cosolvents with TEP for near-commercial mass loading full-cells (Prussian white||hard carbon at ~ 2 mAh/cm2). To maintain non-flammable characteristics, the cosolvents had to be kept below 40% (v/v) for DMAc and DMF and below 60% (v/v) for NMP, resulting in electrolyte conductivities of 5.7, 6.9 and 6.0 mS/cm respectively. These nearly doubled the conductivity we observed for NaBOB in TEP of 3.5 mS/cm. However, all electrolytes examined showed large polarisation, suspected to be due a thick, resistive SEI. A range of strategies have been employed in order to reduce this polarisation, with particular focus on improved formation protocols (studying the effects of temperature, current density and electrochemical method of formation) and their use in concert with film forming additives. Future work will aim to understand the interplay between formation conditions, the resultant SEI formation and the cell polarization in an effort to translate promising low mass-loading full cell results to near-commercial mass-loading full cells.

Unexplored Reaction Pathways of Ethylene Carbonate during Solid Electrolyte Interphase Formation

The solid electrolyte interphase (SEI) keeps eluding our grasp. Fundamental understanding of Li-ion battery performance will not be complete until the major underlying reaction pathways of SEI formation and growth have been described.1 Although the SEI has been observed to be a complex and highly diverse matrix of in-/organic crystalline and amorphous aggregates, likely only few compounds are functional, i.e. passivate the electrode while at the same time sustaining the Li+ transport. The aim of the presentation is to provide experimental evidence for hitherto largely unexplored reaction pathways of several commonly observed SEI compounds (such as lithium ethyl dicarbonate, abbr. LEDC) and prove how the formation of the same can be altered by the choice of electrolyte additives. For instance, Electrochemical Quartz Crystal Microbalance with Dissipation monitoring complemented by Online Electrochemical Mass Spectrometry is demonstrated to separate electrochemical from chemical reactions in a multistep SEI formation process.2-3 Based on our experimental findings, the role and implication of each compound (be it LiOH, Li2O, LEDC, etc.) in the SEI formation process will be discussed.4

Solvent-Triggered Chemical Recycling of Ion-Conductive and Self-Healable Polyurethane Covalent Adaptive Networks.

Given the substantial environmental challenge posed by global plastic waste, recycling technology for thermosetting polymers has become a huge research topic in the polymer industry. Covalent adaptive networks (CANs), which can reversibly dissociate and reconstruct their network structure, represent a key technology for the self-healing, reprocessing, and recycling of thermosetting polymers. In the present study, we introduce a new series of polyurethane CANs whose network structure can dissociate via the self-catalyzed formation of dithiolane from the CANs' polydisulfide linkages when the CANs are treated in N,N-dimethylformamide (DMF) or dimethyl sulfoxide at 60 °C for 1 h. More interestingly, we found that this network dissociation even occurs in tetrahydrofuran-DMF solvent mixtures with low DMF concentrations. This feature enables a reduction in the use of high-boiling, toxic polar aprotic solvents. The dissociated network structure of the CANs was reconstructed under UV light at 365 nm with a high yield via ring-opening polydisulfide linkage formation from dithiolane pendant groups. These CAN films, which were prepared by a sequential organic synthesis and polymerization process, exhibited high thermal stability and good mechanical properties, recyclability, and self-healing performance. When lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt was added to the CAN films, the films exhibited a maximum ion conductivity of 7.48 × 10-4 S cm-1 because of the contribution of the high concentration of the pendant ethylene carbonate group in the CANs. The ion-conducting CAN films also showed excellent recyclability and a self-healing performance.

Synthesis of Ethylene Carbonate by Urea Transesterification Using Zeolitic Imidazolate Framework Derived Fe-Doped ZnO Catalysts.

The development of environmentally friendly and efficient methods for the synthesis of ethylene carbonate (EC) is crucial for advancing carbon capture, utilization, and storage technologies. Herein, we present the synthesis of EC through the transesterification of urea with ethylene glycol (EG) using a zeolitic imidazolate framework (ZIF) derived Fe-doped ZnO catalyst (Fe;ZnO-ZIF). The Fe;ZnO-ZIF catalyst, prepared by incorporating Fe dopant atoms into a ZnO-ZIF template, demonstrates excellent catalytic activity, achieving high conversion of reactants and superior selectivity toward EC at 160 °C for 150 min under an applied vacuum (160 mmHg). Based on the thermogravimetric, X-ray spectroscopic, and temperature-programmed desorption analysis, the simultaneous presence of strong Lewis acidic and basic sites in Fe;ZnO-ZIF enables its excellent catalytic performance toward EC synthesis with high selectivity. Acidic sites activate the carbon center in urea, while basic sites facilitate the nucleophilic attack on urea by deprotonation of EG. This synergistic reaction pathway resulting from the interaction between the strong Lewis acidic and basic sites promotes nucleophilic attacks of EG on urea, leading to significantly higher conversion efficiency and selectivity, compared to the commercial benchmark ZnO. Although the establishment of a continuous reaction system which takes into account cyclability and stability of the catalysts is further required in the future, our research reported herein provides valuable insights into the design of synergistic, localized active sites for EC synthesis and contributes to the development of sustainable carbon utilization technologies for achievement of net-zero emissions.

Experimental and modeling study of the combustion of ethyl methyl carbonate, a battery electrolyte

Ethyl methyl carbonate (EMC) is one of the main constituents of the electrolyte in lithium-ion batteries (LIBs). To understand better fire events involving LIBs and try to prevent them, the combustion of EMC was studied experimentally, and the results were analyzed using modern detailed kinetics models. Shock tubes were used to collect ignition delay times (IDTs) and CO time histories, while laminar flame speeds were measured in a closed vessel. All experiments were carried out near atmospheric pressure. The shock tube experiments were performed for three equivalence ratios (0.5, 1.0, and 2.0) with the IDTs measured with “fuel-air” mixtures and the CO spectroscopic laser measurements in mixtures highly diluted in 99.25% He/Ar. Comparisons with results obtained for other linear carbonates typically found in LIBs, such as dimethyl carbonate and diethyl carbonate, are also presented. Numerical predictions from recent detailed chemical kinetics mechanisms (Takahashi et al., 2022, Grégoire et al., 2023) did not capture well the combustion behavior of EMC in some of our conditions. Sensitivity analyses suggest that EMC decomposition reactions and subsequent combustion chemistry of the formed intermediates, i.e. methanol and ethylene, still need improvement.