Fluoroethylene Carbonate Research Articles

Toward the Integration of a Silicon/Graphite Anode-Based Lithium-Ion Battery in Photovoltaic Charging Battery Systems.

Solar photovoltaic (PV) energy generation is highly dependent on weather conditions and only applicable when the sun is shining during the daytime, leading to a mismatch between demand and supply. Merging PVs with battery storage is the straightforward route to counteract the intermittent nature of solar generation. Capacity (or energy density), overall efficiency, and stability at elevated temperatures are among key battery performance metrics for an integrated PV–battery system. The performance of high-capacity silicon (Si)/graphite (Gr) anode and LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode cells at room temperature, 45, and 60 °C working temperatures for PV modules are explored. The electrochemical performance of both half and full cells are tested using a specially formulated electrolyte, 1 M LiPF6 in ethylene carbonate: diethyl carbonate, with 5 wt % fluoroethylene carbonate, 2 wt % vinylene carbonate, and 1 wt % (2-cyanoethyl)triethoxysilane. To demonstrate solar charging, perovskite solar cells (PSCs) are coupled to the developed batteries, following the evaluation of each device. An overall efficiency of 8.74% under standard PV test conditions is obtained for the PSC charged lithium-ion battery via the direct-current–direct-current converter, showing the promising applicability of silicon/graphite-based anodes in the PV–battery integrated system.

Enhancing the Interfacial Stability of High‐Energy Si/Graphite||LiNi0.88Co0.09Mn0.03O2 Batteries Employing a Dual‐Anion Ionic Liquid‐based Electrolyte

AbstractThe poorly flammable room‐temperature ionic liquid‐based electrolyte composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and N‐butyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr14FSI) with fluoroethylene carbonate (FEC) as an additive is investigated towards its compatibility with the LiNi0.88Co0.09Mn0.03O2 (NCM88) cathode and a high‐capacity Si/graphite (SiG) anode, revealing a remarkably stable performance in lithium‐ion cells. Interestingly, this dual‐anion electrolyte with FEC additive forms a stable electrode‐electrolyte interphase on both sides, which suppresses the morphological degradation of the electrode materials and continuous electrolyte decomposition. Consequently, lithium‐ion cells using such dual‐anion ionic liquid‐based electrolyte display significantly improved cycling stability compared to conventional carbonate ester‐based electrolyte, achieving a high specific energy of 385 Wh kg−1 (based on both cathode and anode active materials weight) with a capacity retention of 74 % after 200 cycles at 0.2 C, demonstrating the possibility to realize safe and high energy density LIBs.

Assessment on the Stable and High‐Capacity Na−Se Batteries with Carbonate Electrolytes

AbstractFactors affecting proper functioning of Na−Se system are investigated focusing on the polyselenide formation in ether‐ and carbonate‐based electrolytes. To do so, Se cathode is prepared by ball milling with commercial carbon and selenium powders. It is revealed that the soluble polyselenide species form in ether while no signature in carbonates proven by the in‐situ cyclic voltammetry and ex‐situ ultraviolet‐visible spectroscopy measurements as well as monitoring self‐discharge behaviours. Different Se discharge mechanism is also highlighted by staircase potentio electrochemical impedance spectroscopy (SPEIS) that is an impedance measurement applied to each potential step. Volume expansion is targeted using different types of binders in which carboxyl methylcellulose‐styrene butadiene rubber (CMC‐SBR) delivers the highest reversible capacity and the best rate performance resulting from its high adhesion strength. To further improve the performances, fluoroethylene carbonate (FEC) is used as a film forming additive that preserves Na metal integrity proven by the Na−Na symmetric cells and voltage relaxation upon cycling. As a whole, binders and electrolyte compositions are found to be the two crucial factors to obtain stable and high‐capacity Na−Se cells. This study underlines that much effort needs to be put on the strategies to overcome volume expansion than that of Se confinement into porous cathode.

Organofluorophosphates As Electrochemical Aging Products in Lithium Ion Battery Electrolytes

The lithium ion battery (LIB) electrolyte is a delicate system susceptible to a manifold of influences both from the outside and inside. Thermal stress and overcharging of the LIB can result in unwanted side reactions such as rapid electrolyte degradation and the so-called thermal runaway, respectively. Here, the degradation of the conducting salt, namely lithium hexafluorophosphate (LiPF6 )poses many risks to the LIB and the environment. Hydrolysis of LiPF6 leads to the formation of hydrofluoric acid (HF) and POF3 which can react with the organic compounds within the electrolyte to form highly toxic organofluorophosphates (OFPs). The formation of OFPs in LIBs due to thermal stress has been covered in literature. In this study the electrochemically induced formation of OFPs is discussed. Electrolytes containing fluoroethylene carbonate (FEC) as a film-forming additive indicated the presence of OFPs forming at operation voltages of 4.8 V in self-assembled LIB coin cells. Cycling of the coin cells with cut-off voltages of 4.8 V gave rise to 15 non-acidic and two acidic OFPs after 10 charge/discharge steps. The quantity of FEC had an impact on the amount of OFPs formed which gives reason to incorporate FEC in the formation pathways proposed in this study. The formation pathway of OFPs through EC-polymerization proposed in literature is evaluated and an alternative mechanism with FEC as the carbonyl-carbon donor is presented. Structure elucidation and separation of the formed OFPs is achieved by utilization of a) hydrophilic interaction liquid chromatography (HILIC) for acidic OFPs and b) reversed-phase (RP) chromatography for non-acidic OFPs hyphenated to a high-resolution ion trap time-of-flight mass spectrometer (IT-TOF-MS). Based on the findings in this study and due to the highly toxic nature of OFPs further investigation of the formation of OFPs in FEC-containing electrolytes is necessary. Further, the impact of the operation voltages needs to be assessed to ensure for safe and efficient LIBs.

Uncovering Unique Interfacial Properties in Different Lithium Fluoride Phases: A First-Principles Prediction

Electrolytes are susceptible to reductive decomposition on the surface of negative electrodes leading to the formation and growth of solid-electrolyte interphase (SEI) layer [1]. Stable SEI can be beneficial as a protective layer, given that it can provide insulation to electron transport from the anode to electrolyte, prevent solvent molecules from reaching the anode, and at the same time allow transport of Li+ [2]. Thus, the SEI can contribute critically to the safety and operability of lithium-ion batteries (LIBs), but its functionality heavily depends on the conditions under which it gets synthesized [3]. This can have a significant effect on battery performance. For instance, nucleation and growth of lithium dendrites during cycling is known to result in continuous electrolyte degradation, destruction of the SEI, agglomeration of so-called “dead lithium”, and short-circuiting of the battery [4]. This greatly affects next-generation electric vehicles (EVs), for which all-solid-state lithium-metal batteries (ASSLMBs) have garnered significant attention due to their superior energy storage capacity and safety over LIBs [5]. However, the considerable interfacial impedance originating from poor physical contact and/or parasitic reactions at the Li/SSE interface hinders the development of ASSLMBs. Alternative approaches towards achieving a stable protective interface have been pursued: like use of electrolyte additives to manipulate the constituents and compositions of SEI or designing artificial protective layers to improve performance. For instance, admixture of optimum amounts of fluorine-rich additives like fluoroethylene carbonate (FEC) to traditional carbonate electrolytes (like EC/DMC) has been seen to generate a robust LiF-rich SEI. However, the intrinsic role of LiF remains a topic of uncertainty. Conventional understanding would posit that dominance of LiF leaves the SEI susceptible to poor lithium-ion transport properties. Previously, theoretical works reported significantly lower ionic conductivities in crystalline LiF when compared to other common inorganic SEI materials like Li2O and Li2CO3. Underwhelming transport properties pose serious rate limitations in its effectiveness as a serious candidate for interfacial protection in ASSLMBs. To potentially overcome such bottleneck, this study systematically investigates different phases of LiF: their structures, stabilities and interfacial properties are described using first principles calculations. Careful analysis of the structural models reveals that unlike the widely studied rock salt ordered counterpart, certain phases of LiF exhibit excellent Li+ transport properties with a high predicted diffusivity at room temperature. Mechanically too, improved interfacial qualities are demonstrated with increased flexibility and fracture resistance, opening up important avenues for structural and compositional stability over cell cycling while maintaining its desirable electron-blocking characteristics. However, it is also important to take a step back and note that the rock salt phase is the most energetically stable among LiF phases, which thereby exhibit a propensity for phase transformation under ambient conditions. To overcome this, a strategy of incorporating hetero dopants as impurities to stabilize the host matrix is discussed. By increasing the dopant concentration up to an optimum amount, relative thermodynamic stability of the interface-friendly phases of LiF is achieved. Our examination of the structure reveals unique lithium-dopant interactions which help sustain such LiF phases in the host matrix. The combination of excellent Li-ion transport properties and electron blocking ability makes such LiF-rich composites an excellent candidate for use as an interfacial protective layer that can effectively suppress electrolyte decomposition and Li dendrite propagation, while simultaneously improving the contact and compatibility of the electrode/electrolyte interface. These unique and exceptional traits make them materials of great promise for protecting critical interfaces in ASSLMBs and LIBs.[1] M. Gauthier, T.J. Carney, A. Grimaud, L. Giordano, N. Pour, H.-H. Chang, D.P. Fenning, S.F. Lux, O. Paschos, C. Bauer, F. Maglia, S. Lupart, P. Lamp, Y. Shao-Horn, Electrode−Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights, J. Phys. Chem. Lett. 6 (2015) 4653−4672. https://doi.org/10.1021/acs.jpclett.5b01727[2] D. Bedrov, O. Borodin, J.B. Hooper, Li+ Transport and Mechanical Properties of Model Solid Electrolyte Interphases (SEI): Insight from Atomistic Molecular Dynamics Simulations, J. Phys. Chem. C 121 (2017) 16098–16109. https://doi.org/10.1021/acs.jpcc.7b04247[3] D. Aurbach, B. Markovsky, I. Weissman, E. Levi, Y. Ein-Eli, On the Correlation Between Surface Chemistry and Performance of Graphite Negative Electrodes for Li Ion Batteries, Electrochim. Acta 45 (1999) 67−86. https://doi.org/10.1016/S0013-4686(99)00194-2[4] W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J.G. Zhang, Lithium Metal Anodes for Rechargeable Batteries, Energy Environ. Sci. 7 (2014) 513−537. https://doi.org/10.1039/C3EE40795K[5] J. G. Kim, B. Son, S. Mukherjee, N. Schuppert, A. Bates, O. Kwon, M. J. Choi, H. Y. Chung, S. Park, A review of lithium and non-lithium based solid state batteries, J. Power Sources 282 (2015) 299−322. https://doi.org/10.1016/j.jpowsour.2015.02.054

Characterization of the structure and chemistry of the solid-electrolyte interface by cryo-EM leads to high-performance solid-state Li-metal batteries.

Solid-state lithium-metal (Li0) batteries are gaining traction for electric vehicle applications because they replace flammable liquid electrolytes with a safer, solid-form electrolyte that also offers higher energy density and better resistance against Li dendrite formation. Solid polymer electrolytes (SPEs) are highly promising candidates because of their tuneable mechanical properties and easy manufacturability; however, their electrochemical instability against lithium-metal (Li0), mediocre conductivity and poorly understood Li0/SPE interphases have prevented extensive application in real batteries. In particular, the origin of the low Coulombic efficiency (CE) associated with SPEs remains elusive, as the debate continues as to whether it originates from unfavoured interfacial reactions or lithium dendritic growth and dead lithium formation. In this work, we use state-of-the-art cryo-EM imaging and spectroscopic techniques to characterize the structure and chemistry of the interface between Li0 and a polyacrylate-based SPE. Contradicting the conventional knowledge, we find that no protective interphase forms, owing to the sustained reactions between deposited Li dendrites and polyacrylic backbones and succinonitrile plasticizer. Due to the reaction-induced volume change, large amounts of cracks form inside the Li dendrites with a stress-corrosion-cracking behaviour, indicating that Li0 cannot be passivated in this SPE system. On the basis of this observation, we then introduce additive engineering, leveraging from knowledge of liquid electrolytes, and demonstrate that the Li0 surface can be effectively protected against corrosion using fluoroethylene carbonate, leading to densely packed Li0 domes with conformal and stable solid-electrolyte interphase films. Owing to the high room-temperature ionic conductivity of 1.01 mS cm-1, the high transference number of 0.57 and the stabilized lithium-electrolyte interface, this improved SPE delivers an excellent lithium plating/stripping CE of 99% and 1,800 hours of stable cycling in Li||Li symmetric cells (0.2 mA cm-2, 1 mAh cm-2). This improved cathodic stability, along with the high anodic stability, enables a record high cycle life of >2,000 cycles for Li||LiFePO4 and >400 cycles for Li||LiCoO2 full cells.

Paving Pathways Toward Long‐Life Graphite/LiNi0.5Mn1.5O4 Full Cells: Electrochemical and Interphasial Points of View

AbstractThe high‐voltage spinel cathode LiNi0.5Mn1.5O4 (LNMO) with no cobalt and low nickel content is promising for lithium‐ion batteries due to its high energy and power densities, good thermal stability, and low cost. However, its high operating voltage (≈4.7 V) results in a decomposition of the electrolyte, severe chemical crossover, and deterioration of electrode‐electrolyte interphases (EEIs), hindering its practical viability. It is demonstrated here that by electrochemically pre‐cycling the graphite in an electrolyte containing 30 wt.% fluoroethylene carbonate, a robust LiF‐rich artificial solid electrolyte interphase can be constructed for surface protection; on the other hand, an electrochemical pre‐lithiation of Fe‐doped LNMO serves as a lithium source for graphite at a full‐cell voltage of 2.6 V. As a result, the full cells with the as‐modified electrodes deliver a high capacity of 129 mA h g−1 with an excellent capacity retention of 93% after 200 cycles, vastly outperforming the full cells with fresh electrodes (120 mA h g−1 initial capacity with 78% retention). Finally, pathways toward long‐life graphite||LNMO full cells are pictured based on the inspirations from the electrochemical modifications and in‐depth analyses of the EEIs in this study.

Fluoroethylene carbonate as co-solvent for Li(Ni0.8Mn0.1Co0.1)O2 lithium-ion cells with enhanced high-voltage and safety performance

In the present work, a non-flammable electrolyte using fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) as solvent is investigated for high-voltage lithium-ion cells with Li(Ni0.8Mn0.1Co0.1)O2 cathode. The cells containing 1 M LiPF6 in FEC/DMC (3:7, volume ratio, named FD37) perform significantly better cycling features than those with the traditional electrolyte under high voltages, i.e., 3.0–4.6 V. This may ascribe to the robust cathode electrolyte interphase layer formed by FD37 on the cathode surface, which effectively inhibits the decomposition of electrolytes and improves the stability of the electrode/electrolyte interface at high voltages. Furthermore, the cells addicted with FD37 show superior performance to the traditional electrolyte-based cells during the high-temperature cycling and storage. In addition, more advanced safety features are revealed by FD37 cells in several typical safety tests including as accelerating rate calorimetry (ARC) tests, nail tests, overcharge tests, etc. To summarize, the fluorinated electrolyte presented herein may bring fresh inspiration for the design of high-voltage and high-safety lithium-ion cells, more concern into it is warranted to complete a deeper understanding.

In-situ formation of quasi-solid polymer electrolyte for improved lithium metal battery performances at low temperatures

Solid-state polymer electrolytes, featuring excellent processability and flexibility, have received considerable attentions. However, the inherent low ionic conductivity, especially at subzero temperatures, limits their widespread application. Herein, quasi-solid polymer electrolyte (QSPE) with high low-temperature ionic conduction ability is prepared by in-situ ring-opening polymerization of 1,3-Dioxlane with fluoroethylene carbonate (FEC) as plasticizer. The in-situ polymerization imparts good interface contact between QSPE and electrode. The addition of FEC improves the chain mobility and facilitates the dissociation of LiTFSI, giving QSPE a remarkable ionic conductivity and Li+ transference number (2.4 × 10−5 S cm−1 at −60 °C and 0.55 at −20 ° C), two orders of magnitude and 2.3 times higher than those of liquid electrolyte, respectively. As a result, the Li/QSPE/Li cell without significant polarization is obtained, which can operate at 0.2 mA cm−2 and 0 °C for 850 h. Moreover, the LiFePO4/Li cell exhibits excellent cycling stability at 0.2 C and 0 °C: its capacity remains 125.2 mAh g−1 at 400th cycle, exceeding most polymer electrolytes. Even at −20 °C, a discharge capacity of 73.3 mAh g−1 is obtained at 100th cycle under 0.2 C.

Stable Sodium-Based Batteries with Advanced Electrolytes and Layered-Oxide Cathodes.

Sodium-ion batteries offer a promising alternative to the more expensive, resource-limited lithium-ion batteries, in particular to accommodate the growing demand for large-scale energy storage. One of the main challenges for sodium-ion batteries, however, is the poor electrolyte stability, which leads to rapid capacity fade during cycling. Recent advances in the lithium-ion-battery field have expanded our understanding of electrolyte compositions and stability, paving the way for better sodium-ion-battery electrolytes. Two of the most promising new classes of electrolytes are evaluated herein with a sodium layered-oxide cathode, for the first time: a localized high-concentration electrolyte (LHCE) composed of sodium bis(fluorosulfonyl)imide, dimethyl ether, and tetrafluoropropyl ether and a "highly fluorinated" electrolyte (HFE) composed of 20% fluoroethylene carbonate with a lithium difluorophosphate additive. With a combination of electrochemical and post-mortem characterization techniques, the stability of each electrolyte is assessed with the O3-type Na(Ni0.3Fe0.4Mn0.3)O2 cathode and sodium metal anode. Both electrolytes significantly improve the surface and bulk stability of the cathode, but only the LHCE has a meaningful improvement on sodium metal stability. For the purpose of developing a long-lasting, sodium-ion full cell, both classes of electrolyte show great promise.

Operating Highly Stable LiCoO2 Cathodes up to 4.6 V by Using an Effective Integration of Surface Engineering and Electrolyte Solutions Selection

AbstractThe need for high power density cathodes for Li‐ion batteries can be fulfilled by application of a high charging voltage above 4.5 V. As lithium cobalt oxide (LCO) remains a dominant commercial cathode material, tremendous efforts are invested to increase its charging potential toward 4.6 V. Yet, the long‐term performance of high voltage LCO cathodes still remains poor. Here, an integrated approach combining the application of an aluminum fluoride coating and the use of electrolyte solutions comprising 1:1:8 mixtures of difluoroethylene:fluoroethylene carbonate:dimethyl carbonate and 1 m LiPF6 is reported. This results in superior behavior of LCO cathodes charged at 4.6 V with high initial capacity of 223 mAh g−1, excellent long‐term performance, and 78% capacity retention after 500 cycles. Impressive stability is also found at 450 °C with an initial capacity of 220 mAh g−1 and around 84% capacity retention after 100 cycles. Systematic post‐mortem analysis of LCO cathodes and Li anodes after prolonged cycling reveals two main degradation routes related to changes at the surface of the cathodes and formation of passivation layers on the anodes. This study demonstrates the importance of appropriate selection of electrolyte solutions and development of effective coatings for improved performance of high voltage LCO‐based Li batteries.

Rational Screening of High-Voltage Electrolytes and Additives for Use in LiNi0.5Mn1.5O4-Based Li-Ion Batteries.

In the present work, we focus onthe experimental screening of selected electrolytes, which have been reported earlier in different works, as a good choice for high-voltage Li-ion batteries. Twenty-four solutions were studied by means of their high-voltage stability in lithium half-cells with idle electrode (C+PVDF) and the LiNi0.5Mn1.5O4-based composite as a positive electrode. Some of the solutions were based on the standard 1 M LiPF6 in EC:DMC:DEC = 1:1:1 with/without additives, such as fluoroethylene carbonate, lithium bis(oxalate) borate and lithium difluoro(oxalate)borate. More concentrated solutions of LiPF6 in EC:DMC:DEC = 1:1:1 were also studied. In addition, the solutions of LiBF4 and LiPF6 in various solvents, such as sulfolane, adiponitrile and tris(trimethylsilyl) phosphate, atdifferent concentrations were investigated. A complex study, including cyclic voltammetry, galvanostatic cycling, impedance spectroscopy and ex situ PXRD and EDX, was applied for the first time to such a wide range of electrolytesto provide an objective assessment of the stability of the systems under study. We observed a better anodic stability, including a slower capacity fading during the cycling and lower charge transfer resistance, for the concentrated electrolytes and sulfolane-based solutions. Among the studied electrolytes, the concentrated LiPF6 in EC:DEC:DMC = 1:1:1 performed the best, since it provided both low SEI resistance and stability of the LiNi0.5Mn1.5O4 cathode material.

Rational Electrolyte Design toward Cyclability Remedy for Room‐Temperature Sodium–Sulfur Batteries

AbstractRechargeable room‐temperature sodium–sulfur (RT Na–S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all‐fluorinated electrolyte, containing 2,2,2‐trifluoro‐N,N‐dimethylacetamide (FDMA) solvent, 1,1,2,2‐tetrafluoroethyl methyl ether (MTFE) anti‐solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na–S batteries. A NaF‐ and Na3N‐rich cathode electrolyte interphase derived from FDMA and FEC enables a “quasi‐solid‐phase” Na–S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as‐developed RT Na–S batteries deliver a high capacity, long lifespan, and enhanced safety.

Lessons Learned from Long-Term Cycling Experiments with Pouch Cells with Li-Rich and Mn-Rich Positive Electrode Materials

In this work, the performance of commercial (250–300 mAh) Li1.11Ni0.34Mn0.53Al0.02O2/graphite (LNMA) and Li1.167Ni0.183Mn0.558Co0.092O2/graphite (LNMC) pouch cells was evaluated using different cycling drive profiles, temperatures, formation voltages, cycling upper and lower cut-off voltages. A variety of electrolyte additives and additive combinations were tested in the LNMA cells. The best performing electrolyte in high voltage LNMA cells (4.6 V upper cut-off) was Control + 2% fluoroethylene carbonate (FEC) + 1% lithium difluorophosphate (LFO) + 1% lithium difluoro(oxalato)borate (LiDFOB) with 87% capacity retention after 720 cycles. LNMA cells cycled to 4.25 V and LNMC cells cycled to 4.44 V at 40 °C were able to cycle for 1000 cycles before reaching 80% capacity. These materials can have surprisingly good high-voltage performance, but we stress that a fundamental breakthrough that can eliminate the voltage fade that is ubiquitous in Li-rich and Mn-rich materials is necessary to make Li-rich materials competitive with existing cell chemistries. We demonstrate that the high specific capacity of Li-rich materials can be deceptive when making conclusions about the energy density of Li-rich/graphite full cells. Hopefully, these results can set a baseline for other researchers in the Li-rich space.

Rational Electrolyte Design toward Cyclability Remedy for Room-Temperature Sodium-Sulfur Batteries.

Rechargeable room-temperature sodium-sulfur (RT Na-S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all-fluorinated electrolyte, containing 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) solvent, 1,1,2,2-tetrafluoroethyl methyl ether (MTFE) anti-solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na-S batteries. A NaF- and Na3 N-rich cathode electrolyte interphase derived from FDMA and FEC enables a "quasi-solid-phase" Na-S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as-developed RT Na-S batteries deliver a high capacity, long lifespan, and enhanced safety.

Thermal initiation/ultraviolet cross-linking process in polyethylene oxide@Li6·75La3Zr1·75Ta0·25O12-based composite electrolyte with high room-temperature ionic conductivity and long life cycle

Organic-inorganic composite electrolytes (PL-SCEs) based on polyethylene oxide (PEO) and Li6·75La3Zr1·75Ta0·25O12 (LLZTO) are considered to be one of the most promising solid electrolytes. However, the low room-temperature ionic conductivity caused by the inherent high crystallinity of PEO severely hinders its practical application. Herein, a novel PL-SCE is synthesized through a facile thermal induction and ultraviolet crosslinking process, using fluoroethylene carbonate (FEC) and 4-methylbenzophenone as thermal/ultraviolet triggers, and tetraethylene glycol dimethyl ether (TEGDME) as an ion conductive plasticizer. The F atom in the FEC can attack the C–O bond in the PEO chain and abstract the hydrogen attached to the C atom to form an active site, prompt TEGDME and PEO to achieve a higher degree of cross-linking, thus endowing PL-SCE with high Li-ion conductivity of 5.35 × 10−4 S cm−1 at 25 °C. Besides, the obtained PL-SCE exhibits excellent wettability and compatibility with Li metal anodes, the interfacial impedance is only 44 Ω cm2. The LiFePO4||Li full cell based on the proposed PL-SCE exhibits an excellent room-temperature cycling performance with a capacity retention rate up to 88% and the average Coulombic efficiency above 98% upon 450 cycles at 1 C. Prospectively, this work provides a promising alternative method for the practical application of PL-SCEs.

A high-energy dual-ion battery based on chloride-inserted polyviologen cathode and LiCl/DMSO electrolyte

To improve the energy density of dual-ion batteries (DIBs), for the first time we employ a Cl–-insertable p-type polymer, poly(butyl viologen dichloride) (PBV-Cl2), as cathode material, and low-cost LiCl/DMSO (dimethyl sulfoxide) solution as electrochemically favorable electrolyte. Benefiting from the highest reversible capacity of the PBV-Cl2 cathode among all p-type polymers (183 mAh g–1 based on the weight involving anion), and greatly lowered Li+/Li potential (by 0.5 V) in DMSO compared to that in conventional ester solvents, the Li–PBV-Cl2 DIB achieves the highest actual energy density of 470 Wh kg–1. After adding fluoroethylene carbonate (FEC) additive in the electrolyte for better Li anode compatibility, it also exhibits an excellent cycling stability (88% after 300 cycles) and a superior rate capability (75% at 5000 mA g–1). The concepts of Cl– charge carrier, polyviologen cathode, and LiCl-based electrolyte provide significant insights for the development of high-energy, low-cost, and sustainable DIBs.

Influence of the fluoroethylene carbonate on the electrochemical behavior of Bi3Ge4O12 as Lithium-ion anode

Systematic ex-situ X-ray diffraction (XRD) characterization and electrochemical study revealed the key roles that the cut-off voltage and fluoroethylene carbonate (FEC) additive play on improving electrochemical performance of the Bi3Ge4O12-based (BGO) electrode. The ex-situ XRD analysis revealed that BGO particles suffer multiphase transitions during the (dis)charge reactions, being observed some phases as Bi2O2.33, BiLi3, Li2O, Ge4Li15, Ge2Li7, Ge3Li7, Ge5Li22, Ge4Li9, Bi2O3 and GeO2. The electrochemical evaluation exhibited that the addition of 5 v/v% of FEC in 1.0 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate and diethyl carbonate (EC: DEC) at an applied cut-off voltage (1.5 V vs Li/Li+) improves the specific capacity (29%, delivering 479 mAh g−1), capacity retention (12%) and rate capability (369 mAh g−1 at 1000 mA g−1) of the BGO-based electrode. Also, FEC promotes the formation of a stable solid-electrolyte interface (SEI) layer on the anode at a cut-off voltage of 1.5 V vs Li/Li+. It displays the lowest values of SEI and charge transfer (CT) resistances, and electrode polarization, improving the reversibility of the alloying reactions related to Ge-Li and Bi-Li and maintaining their redox activity after 100 cycles, according to dQ dV−1 data.

Organic-Inorganic Composite Electrolytes Optimized with Fluoroethylene Carbonate Additive for Quasi-Solid-State Lithium-Metal Batteries.

Composite solid electrolytes (CSEs) are considered crucial materials for next-generation solid-state lithium batteries with high energy density and reliable safety, and they make full use of the advantages of both organic and inorganic solid-state electrolytes. However, few CSEs have sufficiently high ionic conductivity at room temperature for practical applications. Here, a traditional CSE consisting of poly(ethylene oxide) (PEO) matrix and Li1.3Al0.3Ti1.7(PO4)3 (LATP) fillers was optimized by introducing a fluoroethylene carbonate (FEC) additive, resulting in an improved high ionic conductivity of 1.99 × 10-4 S cm-1 at 30 °C. The symmetric Li||Li cell assembled with the optimized CSE exhibited a low overpotential and a good cycling stability of more than 1500 h at room temperature. Moreover, the Li||LiFePO4 battery with the optimized CSE delivered a discharge capacity of 132 mAh g-1 at 0.2 C after 300 cycles at room temperature. Comparisons between the LATP-containing CSE and control electrolytes indicated that the enhanced ion conductivity of the former resulted from the synergistic effect of LATP and FEC. Comprehensive characterizations and DFT calculations suggest that with the presence of LATP, FEC additives in the precursor could transform into some other species in the preparation process of CSE. It is believed that these FEC-derived species improve the ion conductivity of the CSEs. The results reported here may open up new approaches to developing composite electrolytes with high ionic conductivity at room temperature by introducing organic additives in the precursor and converting them into species that facilitate ion conduction in the CSE preparation process.

Double-salt electrolyte for Li-ion batteries operated at elevated temperatures

Lithium ion batteries (LIBs) have swept the whole energy storage field. However, the current mainstream lithium batteries are difficult to operate stably at high temperature (>60°C) due to the decomposition of electrolyte and solid electrolyte interphase (SEI), the cathode metal elements dissolution behavior, and potential thermal runaway. Here, We report a double-salt electrolyte with lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluoro(oxalato)borate (LiDFOB) as electrolyte salt, fluoroethylene carbonate (FEC), and tetra(ethylene glycol) dimethyl ether (TEGDME) as cosolvent, which delivers excellent ionic conductivity, high electrochemical stability and satisfactory ability to impede the dissolution of Fe element under elevated temperature (70°C). In addition, the electrolyte is benefited to form a robust and thermal-resistance solid-electrolyte interface (SEI) layer on the surface of graphite (Gr) anode, which shows improved decomposition temperature (86°C). The assembled thermally stable and high-safety 1300 mAh 18650-type LiFePO4|Gr cell shows high Coulombic efficiency (∼99.7%), improved cycling stability with discharge capacity 871.1 mAh after 200 cycles at 0.5 C and 70°C. This work affords a splendid strategy for address the unstable interface at both cathode and anode for safe high-temperature LIBs.