Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

International audienceThe use of polymer electrolytes instead of liquid organic systems is considered key for enhancing the safety of lithium batteries and may, in addition, enable the transition to high-energy lithium metal anodes. An intrinsic limitation, however, is their rather low ionic conductivity at ambient temperature. Nonetheless, it has been suggested that this might be overcome by decoupling the ion transport and the segmental relaxation of the coordinating polymer. Here, we provide an overview of the different approaches to achieve such decoupling, including a brief recapitulation of the segmental-relaxation dependent ion conduction mechanism, exemplarily focusing on the archetype of polymer electrolytes – polyethylene oxide (PEO). In fact, while the understanding of the underlying mechanisms has greatly improved within recent years, it remains rather challenging to outperform PEO-based electrolyte systems. Nonetheless, it is not impossible, as highlighted by several examples mentioned herein, especially in consideration of the extremely rich polymer chemistry and with respect to the substantial progress already achieved in designing tailored molecules with well-defined nanostructures

Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

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High temperature (HT) polymer electrolyte membrande fuel cells (PEMFC) - A review

One possible solution of combating issues posed by climate change is the use of the High Temperature (HT) Polymer Electrolyte Membrane (PEM) Fuel Cell (FC) in some applications. The typical HT-PEMFC operating temperatures are in the range of 100e200 o C which allows for co-generation of heat and power, high tolerance to fuel impurities and simpler system design. This paper reviews the current literature concerning the HT-PEMFC, ranging from cell materials to stack and stack testing. Only acid doped PBI membranes meet the US DOE (Department of Energy) targets for high temperature membranes operating under no humidification on both anode and cathode sides (barring the durability). This eliminates the stringent requirement for humidity however, they have many potential drawbacks including increased degradation, leaching of acid and incompatibility with current state-of-the-art fuel cell materials. In this type of fuel cell, the choice of membrane material determines the other fuel cell component material composition, for example when using an acid doped system, the flow field plate material must be carefully selected to take into account the advanced degradation. Novel research is required in all aspects of the fuel cell components in order to ensure that they meet stringent durability requirements for mobile applications.Web of Scienc

PEO: An immobile solvent?

Despite used for half a century as host for salt-polymer complexes, PEO is still not a fossil and due to its availability, remains regularly used as a reference in solvent-free polymer electrolytes and related electrochemical cells. Often qualified as macromolecular solvent or immobile solvent, its drawbacks (crystallinity, mechanical strength) are well identified. On the other hand, its electrolyte conductivity maxima are considered as the best possible in absence of molecular solvents or ionic liquids. The comparison of PEO/LiTFSI based on raw PEO and ultrafiltrated one, shows unambiguously the impact of unentangled oligomers not only on ionic transport but also on mechanical behavior. Conductivity, cationic transference numbers and storage modulus data go in the same direction and the cationic conductivity (O/Li = 30) is divided by 2, following PEO purification.Jean-Yves Sanchez acknowledges the CONEX Programme, funding received from Universidad Carlos III de Madrid, the European Union's Seventh Framework Programme for research, technological development and demonstration (Grant agreement nº 600371), Spanish Ministry of Economy and Competitiveness (COFUND2013-40258) and Banco Santander. Amadou Thiam acknowledges ANR for his fellowship. Yannick Molméret acknowledges KICINNO Energy for the granting of his post-doc fellowship, in the frame of the project PENLiB coordinated by Prof. Jean-Yves Sanchez

Single-ion conducting polymer electrolyte for Li||LiNi0.6_{0.6}Mn0.2_{0.2}Co0.2_{0.2}O2_{2} batteries—impact of the anodic cutoff voltage and ambient temperature

Polymer-based electrolytes potentially enable enhanced safety and increased energy density of lithium-metal batteries employing high capacity, transition metal oxide-positive electrodes. Herein, we report the investigation of lithium-metal battery cells comprising Li[Ni$_{0.6}$Mn$_{0.2}$Co$_{0.2}$]O$_{2}$ as active material for the positive electrode and a poly(arylene ether sulfone)-based single-ion conductor as the electrolyte incorporating ethylene carbonate (EC) as selectively coordinating molecular transporter. The resulting lithium-metal battery cells provide very stable cycling for more than 300 cycles accompanied by excellent average Coulombic efficiency (99.95%) at an anodic cutoff potential of 4.2 V. To further increase the achievable energy density, the stepwise increase to 4.3 V and 4.4 V is herein investigated, highlighting that the polymer electrolyte offers comparable cycling stability, at least, as common liquid organic electrolytes. Moreover, the impact of temperature and the EC content on the rate capability is evaluated, showing that the cells with a higher EC content offer a capacity retention at 2C rate equal to 61% of the capacity recorded at 0.05 C at 60 degrees C

Nanocrystalline cellulose reinforced poly(ethylene oxide) electrolytes for lithium-metal batteries with excellent cycling stability

Polyethylene oxide (PEO) based polymer electrolytes are still the state of the art for commercial lithium-metal batteries (LMBs) despite their remaining challenges such as the limited ionic conductivity at ambient temperature. Accordingly, the realization of thin electrolyte membranes and, thus, higher conductance is even more important, but this requires a sufficiently high mechanical strength. Herein, the incorporation of nanocrystalline cellulose into PEO-based electrolyte membranes is investigated with a specific focus on the electrochemical properties and the compatibility with lithium-metal and LiFePO$_4$-based electrodes. The excellent cycling stability of symmetric Li||Li cells, including the complete stripping of lithium from one electrode to the other, and Li||LiFePO$_4$ cells renders this approach very promising for eventually yielding thin high-performance electrolyte membranes for LMBs

Fluorinated materials in electrochemical storage and conversion devices: assessment of advantages and disadvantages

Electrochemical energy storage and conversion systems, such as rechargeable lithium batteries and fuel cells, are considered to be nexuses that link chemical and electrical energies. To achieve efficient, safe, and sustainable energy storage and conversion, many new materials must be designed, synthesized, and tested. Among these, fluorinated organic and inorganic materials play a key role. The highly electronegative fluorine atoms give these materials exceptional stability against degradation, as well as improved performance in electrochemical processes and the development of next-generation solid-state batteries, PEMFC and electrolyzers. In this article, we provide a brief overview of our recent work on fluorinated materials developed at the Laboratory of Electrochemistry and Physical-Chemistry of Materials and Interfaces (LEPMI, Grenoble). These include new salts, solvents, separators, binders, polymer electrolytes, etc. for batteries and fuel cells. We hope that this article will raise awareness of the importance of fluorinated synthons, molecules and materials in electrochemical energy sources, especially given the serious environmental concerns surrounding PFAS compounds

Simulating competitive egress of noncircular pedestrians

We present a numerical framework to simulate pedestrian dynamics in highly competitive conditions by means of a force-based model implemented with spherocylindrical particles instead of the traditional, symmetric disks. This modification of the individuals' shape allows one to naturally reproduce recent experimental findings of room evacuations through narrow doors in situations where the contact pressure among the pedestrians was rather large. In particular, we obtain a power-law tail distribution of the time lapses between the passage of consecutive individuals. In addition, we show that this improvement leads to new features where the particles' rotation acquires great significance

Pristine and modified porous membranes for zinc slurry–air flow battery

The membrane is a crucial component of Zn slurry–air flow battery since it provides ionic conductivity between the electrodes while avoiding the mixing of the two compartments. Herein, six commercial membranes (Cellophane™ 350PØØ, Zirfon®, Fumatech® PBI, Celgard® 3501, 3401 and 5550) were first characterized in terms of electrolyte uptake, ion conductivity and zincate ion crossover, and tested in Zn slurry–air flow battery. The peak power density of the battery employing the membranes was found to depend on the in-situ cell resistance. Among them, the cell using Celgard® 3501 membrane, with in-situ area resistance of 2 Ω cm$^{2}$ at room temperature displayed the highest peak power density (90 mW cm−2). However, due to the porous nature of most of these membranes, a significant crossover of zincate ions was observed. To address this issue, an ion-selective ionomer containing modified poly(phenylene oxide) (PPO) and N-spirocyclic quaternary ammonium monomer was coated on a Celgard® 3501 membrane and crosslinked via UV irradiation (PPO-3.45 + 3501). Moreover, commercial FAA-3 solutions (FAA, Fumatech) were coated for comparison purpose. The successful impregnation of the membrane with the anion-exchange polymers was confirmed by SEM, FTIR and Hg porosimetry. The PPO-3.45 + 3501 membrane exhibited 18 times lower zincate ions crossover compared to that of the pristine membrane (5.2 × 10$^{-13}$ vs. 9.2 × 10$^{-12}$ m$^{2}$ s$^{-1}$). With low zincate ions crossover and a peak power density of 66 mW cm$^{-2}$, the prepared membrane is a suitable candidate for rechargeable Zn slurry–air flow batteries