Single-ion Conducting Polymer Electrolytes Research Articles

Boron-containing cross-linker assisted single-ion conducting polymer electrolytes for high-performance and dendrite-free Li-metal batteries

Nowadays, single-ion conducting polymer electrolytes for high efficiency, stable, safe and dendrite-free Li-metal batteries are in great need to protect lithium metal anode. In this work, a boron-containing single-ion polymer electrolyte (BSPE), prepared by the copolymerization of allyl diglycol carbonate (ADC), lithium bis((trifluoromethyl)sulfonyl)amide (LiTFSI), and diisopropyl allylboronate (DPAB). The weak coordination interaction between Li+ and polar carbonate enhances Li+ transport ability. Further, the boron-containing cross-linker fixes the counter anions on the polymer backbones, limiting the movement of the anions and promoting the rapid and uniform Li+ transference. The BSPE with 3 wt% DPAB exhibits higher Li+ transference number (t+ = 0.77) and better ionic conductivity (1.36 × 10−4 S cm−1 at 25 °C) compared with that without DPAB. The wider electrochemical window (5.6 V vs. Li+/Li), stable polarization and suppressed lithium dendrites during the plating/stripping cycle at a current density of 0.2 mAcm−2 for 600 h provide the metal-lithium batteries with better safety and higher efficiency. In addition, the initial discharge capacity of LiFePO4/BSPE/Li is 140.7 mAh g−1 with 95.2 % coulombic efficiency, and the capacity retention still remains 98.7 % after 200 cycles at 0.1C. The excellent performance endows the BSPE with the potential application in high-performance lithium metal batteries.

Lithiated Nafion membrane as a single-ion conducting polymer electrolyte in lithium batteries

AbstractSingle lithium-ion conducting polymer electrolytes are promising candidates for next generation safer lithium batteries. In this work, Li+-conducting Nafion membranes have been synthesized by using a novel single-step procedure. The Li-Nafion membranes were characterized by means of small-wide angle X-ray scattering, infrared spectroscopy and thermal analysis, for validating the proposed lithiation method. The obtained membranes were swollen in different organic aprotic solvent mixtures and characterized in terms of ionic conductivity, electrochemical stability window, lithium stripping-deposition ability and their interface properties versus lithium metal. The membrane swollen in ethylene carbonate:propylene carbonate (EC:PC, 1:1 w/w) displays good temperature-activated ionic conductivities (σ ≈ 5.5 × 10–4 S cm−1 at 60 °C) and a more stable Li-electrolyte interface with respect to the other samples. This Li-Nafion membrane was tested in a lithium-metal cell adopting LiFePO4 as cathode material. A specific capacity of 140 mAhg−1, after 50 cycles, was achieved at 30 °C, demonstrating the feasibility of the proposed Li-Nafion membrane.

Structure Optimization of Some Single-Ion Conducting Polymer Electrolytes with Increased Conductivity Used in "Beyond Lithium-Ion" Batteries.

Simulation techniques implemented with the HFSS program were used for structure optimization from the point of view of increasing the conductivity of the batteries' electrolytes. Our analysis was focused on reliable "beyond lithium-ion" batteries, using single-ion conducting polymer electrolytes, in a gel variant. Their conductivity can be increased by tuning and correlating the internal parameters of the structure. Materials in the battery system were modeled at the nanoscale with HFSS: electrodes-electrolyte-moving ions. Some new materials reported in the literature were studied, like poly(ethylene glycol) dimethacrylate-x-styrene sulfonate (PEGDMA-SS) or PU-TFMSI for the electrolyte; p-dopable polytriphenyl amine for cathodes in Na-ion batteries or sulfur cathodes in Mg-ion or Al-ion batteries. The coarse-grained molecular dynamics model combined with the atomistic model were both considered for structural simulation at the molecular level. Issues like interaction forces at the nanoscopic scale, charge carrier mobility, conductivity in the cell, and energy density of the electrodes were implied in the analysis. The results were compared to the reported experimental data, to confirm the method and for error analysis. For the real structures of gel polymer electrolytes, this method can indicate that their conductivity increases up to 15%, and even up to 26% in the resonant cases, via parameter correlation. The tuning and control of material properties becomes a problem of structure optimization, solved with non-invasive simulation methods, in agreement with the experiment.

An All-in-one Free-Standing Single-Ion Conducting Semi-Solid Polymer Electrolyte for High-Performance Practical Li Metal Batteries

Single-ion conducting polymer electrolytes, characterized by effective Li+ transport and dendrite mitigation, are emerging as promising candidates for the highly demanded lithium metal batteries. However, despite the promise, their current...

Solvent-free single-ion conducting polymer electrolyte for lithium-metal batteries synthesized via a unique donor–acceptor copolymerization

Unique donor–acceptor copolymerization of an ionic vinyl ether and a poly(ethylene glycol) containing maleate leads to a solvent-free single-ion conducting polymer electrolyte, which shows excellent performance in lithium metal batteries.

Sodium 4-styrenesulfonyl(trifluoromethanesulfonyl)imide-based single-ion conducting polymer electrolyte incorporating molecular transporters for quasi-solid-state sodium batteries

A sodium salt monomer-based single-ion polymer electrolyte was designed, and as proof of concept, a quasi-solid-state sodium–metal cell, using Prussian White cathode, was manufactured, which delivers a capacity of 147 mA h g−1.

Synthesis of a Conceptual New Single-Ion Conducting Polymer Electrolyte for All-Solid-State Batteries

The increasing global population and the rapid change in climatic conditions strengthens the demand for a more efficient handling of energy consumption and energy storage technologies. In this context, all-solid-state batteries (ASSBs) as next-generation rechargeable lithium-ion batteries offer an improved energy and power density based on the integration of novel separators and electrode materials. In comparison to their liquid representatives, ASSBs provide a higher intrinsic safety via non-flammable components and in addition greater long-term durability. In relation to common electrolyte classes, solid polymers stand out due to their good mechanical flexibility, easy film-formation ability, good contact supply between cell components, and lower production costs, favoring the application as electrolytes, protective coatings, as well as additives in cathode composites. Among a variety of polymers, poly(ethylene oxide) (PEO) is a well-studied and established host polymer due to its great ability to dissolve lithium salts like LiBH4, LiPF6 or LiTFSI. Based on a low glass transition temperature (Tg) of about - 60 to - 50 °C, PEO shows a high degree of polymer chain flexibility which facilitates the migration of the lithium cations through the solid electrolyte. Nevertheless, its semi-crystalline character often leads to low conductivities below its melting point (Tm) of around 60 °C, making pure PEO unattractive as solid electrolyte. Copolymerization, the addition of a small amount of solvent to produce so called gel polymer electrolytes, the addition of some plasticizers, or the interplay of polymer and inorganic fillers try to counteract this trend. The synthetical concept behind this work is aiming to benefit from the flexible nature of PEO, and at the same time to improve the ionic conductivities and especially the lithium migration by structural realignment away from a dual-ion towards a single-ion conducting polymer electrolyte (SICPE). The polar PEO-backbone ensures polymer chain mobility, whereas a rigid aromatic structure unit as side chain bears the fixed anionic group. The immobilization of the anionic charges on the polyether backbone tends to guide the electrolyte to higher lithium transference numbers, fewer polarization effects, and the suppression of dendrite growth, resulting in an overall improved cell performance. Synthesis steps via the novel SICPE are characterized with the help of nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Thermal analyses of the homopolymer already show the positive influence of the flexible PEO-backbone by lowering the Tg from 100 to 150 °C for related aliphatic derivatives down to 60 to 80 °C in our case. On the basis of electrochemical impedance spectroscopy (EIS) measurements, the interplay of chemical, thermal, and electrochemical key properties is investigated. The gained results tend to open a discussion panel concerning occurring challenges for solid-state polymer electrolytes and the interdependencies between electrolyte constitution and polymer characteristics.

Stepwise Optimization of Single-Ion Conducting Polymer Electrolytes for High-Performance Lithium-Metal Batteries

Single-ion conducting polymer electrolytes (SIPEs) are among the most promising candidates for high-energy and high-safety lithium-metal batteries. Nevertheless, their commonly limited ionic conductivity and electrochemical stability hamper their practical application. Herein, three new SIPEs, i.e., poly (1,4-phenylene ether ether sulfone)-Li, polysulfone-Li, and hexafluoropolysulfone-Li, all comprising covalently tethered perfluorinated ionic side chains, were designed, synthesized, and comparatively investigated to unveil the influence of the backbone chemistry and the concentration of the ionic group on their electrochemical properties and the eventual cell performance. In particular, the trifluoromethyl group in the backbone and the concentration of the ionic group turn out to play an important role for the charge transport and electrochemical stability towards oxidation. As a result, the combination of both leads to the best-performing SIPE with a high ionic conductivity of ca. 2.5 × 10-4 S cm-1, an anodic stability of >4.8 V, and the best cycling stability in Li‖LiNi0.6Co0.2Mn0.2O2 cells.

(Invited) Exploiting Organic Materials for Next Generation Batteries

Energy storage plays, undoubtedly, a fundamental role in the process of total decarbonization of the global economy that is expected to take place in the coming decades. The energy transition to a renewable and sustainable generation will be the solution to reduce greenhouse gas emissions and thus achieve the European Commission´s goal of becoming the world´s first decarbonized economy. Our mission is therefore aligned with this goal by improving the industry competitiveness and sustainable development, from a benchmark position in energy research, generating disruptive knowledge in materials and high-tech solutions. Within the electrochemical storage area, and in particular organic hybrid materials group, we work from the synthesis and design of organic molecules and polymeric materials to the understanding of their properties and interfaces with the ultimate goal of developing next generation battery systems.In this talk, a general overview of our core research will be given with a special focus on the design of polymer electrolytes. In recent years we have explored various strategies to meet the requirements of electrolytes: high lithium cation conductivity and stability against high voltage and towards lithium metal (LiM). In this scenario we have synthesized new polymers and lithium salts. Inspired by poly(ethylene oxide), polymers containing ethylene oxide units will be presented, with decreased crystallinity to improve ionic conductivity.1 This improvement generally compromises the mechanical properties. In this respect, different strategies will be shown.2,3 However, it is difficult to design a polymer that meets all properties. In this scope, a bi-layer concept will be described and how salt migration can be addressed using a single-ion conducting polymer electrolyte (SLIC).4,5 Motivated by the bi-layer strategy, within SAFELiMOVE EU project a new solid-state-based technology have been proposed.6 The most relevant work carried out in the framework of the project will be presented.References I. Aldalur et al., J Power Sources, 347, 37–46 (2017).I. Aldalur et al., J Power Sources, 448, 227424 (2020)I. Aldalur, M. Martinez-Ibañez, M. Piszcz, H. Zhang, and M. Armand, Batter Supercaps, 1, 149–159 (2018)M. Arrese-Igor et al., ACS Energy Lett, 7, 1473–1480 (2022)M. Arrese-Igor et al., Energy Storage Mater, 45, 578–585 (2022)https://safelimove.eu/

Towards an in-Depth Understanding of Single-Ion Conducting Polymer Electrolytes for Lithium-Metal Batteries

Recently, we have reported a new polyarylene-based single-ion conducting multi-block copolymer electrolyte providing very high ionic conductivities of about 1 mS cm-1 at ambient temperature and excellent cycling stability of LiNMC811 (LiNi0.8Mn0.1Co0.1O2) cells – even at 0 °C.1–3 Further improvement of this new electrolyte system, however, requires an in-depth understanding of ideally each single functional unit in the polymer.Herein, we present some of our latest results on the experimental and theoretical investigation of stepwise modified copolymers in order to decipher the impact of the different functional groups on the eventual mechanical, thermal, chemical, and electrochemical behavior. This stepwise modification includes, amongst others, the replacement of the biphenyl unit by a series of bisphenol derivatives and the variation of the ionophobic and ionophilic block. The former approach provides the unique opportunity to investigate the influence of the monomer substitution pattern, while the latter unveils some rather unexpected findings concerning the impact of the lithium concentration in the electrolyte. References H.-D. Nguyen et al., Energy Environ. Sci., 11, 3298–3309 (2018).D. Steinle et al., J. Solid State Electrochem., 26, 97–102 (2022).Z. Chen et al., Nano Energy, 77, 105129 (2020).

Highly conductive and nonflammable boron-based gel type single ion conducting electrolyte membranes toward high-safety and dendrite-free lithium metal batteries

Single-ion conducting polymer electrolytes (SIPEs), having a high Li-ion transference number (tLi+) close to unity, hold great promise for circumventing the lithium dendrite growth of lithium metal batteries (LMBs). However, SIPEs synthesized by a simple method that also simultaneously fulfill the requirements of high ionic conductivity, good thermal stability, and remarkable fire resistance are still quite rare. Herein, a novel single-ion conducting fibrous membrane (es-DDBSB-Li) based on borate anions of single-ion conductors (denoted as DDBSB-Li) and poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) as a binder was prepared via facile electrospinning technology. The introduction of borate anions promotes the homogeneous distribution of highly concentrated Li-ions and accelerates the ionic migration, leading to an enhanced ionic conductivity of 3.75 × 10−4 S cm−1 at 25 °C for DDBSB-Li saturated with organic solvents. Additionally, the thermally stable and nonflammable DDBSB-Li endows the resultant fibrous membranes to possess good high-temperature stability and fire-resistance properties. The Li||Li cell using this electrolyte displays a high tLi+ of 0.91 and effectively mitigates concentration polarization, thereby enabling a remarkably stable cyclic performance over 2000 h at 2.5 mA cm−2 at 25 °C. Also, this gel SIPE-based Li||LiFePO4 battery demonstrates superior rate performances up to 3C and delivers long-term cycling durability over 600 cycles under 1C at 25 °C. We believe this novel gel SIPE-based fibrous membrane has great potential for practical application in high-safety and dendrite-proof LMBs.

Highly conductive and mechanically robust single-ion conducting polymer electrolyte membranes with a high concentration of charge carriers for dendrite-proof lithium metal batteries

Single-ion polymer electrolytes (SIPEs) with high Li-ion transference number (tLi+≈1) are promising candidates for inhibiting the growth of lithium dendrites in lithium metal batteries (LMBs). However, it remains challenging to develop SIPEs applicable to high-performance LMBs due to their relatively low ionic conductivity and poor mechanical strength. Herein, an aromatic single-ion conductor (LiPSBI) with high Li-ion concentration is elaborately designed, yielding porous and mechanically robust SIPE membranes (NSIPM) when mixed with aliphatic poly (vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) binder via “structural self-assembly” method. As expected, the as-prepared NSIPM porous membranes can simultaneously exhibit a high porosity of 41.4%, a considerable organic solvent uptake of 181.0%, and excellent mechanical strength of 20.5 MPa. Notably, the LiPSBI-based gel NSIPM demonstrates an ionic conductivity of 8.15 × 10−5 S cm−1 at 25 °C, which is almost twice that of the single-ion electrolyte with low Li-ion concentration (4.74 × 10−5 S cm−1). Consequently, the Li||LiFePO4 cells using the gel NSIPM display remarkable cycling durability for several hundred cycles while delivering high discharge specific capacities of 148.4 mA h g−1 and 122.9 mA h g−1 at 0.2C and 1 C, respectively. In addition, the Li/Li symmetric cells assembling the gel NSIPM can effectively alleviate concentration polarization and inhibit the lithium dendrites growth, which is responsible for an exceptionally steady striping/plating process with a low overpotential over 1300 h at 2.5 mA cm−1 at 25 °C. This work provides a new strategy to prepare high-performance SIPEs by increasing the concentration of charge carriers.

Single‐Ion Conducting Polymer Electrolyte for Superior Sodium‐Metal Batteries

AbstractSodium‐metal batteries (SMBs) are considered a potential alternative to high‐energy lithium‐metal batteries (LMBs). However, the high reactivity of metallic sodium towards common liquid organic electrolytes renders such battery technology particularly challenging. Herein, we propose a multi‐block single‐ion conducting polymer electrolyte (SIPE) doped with ethylene carbonate as suitable electrolyte system for SMBs. This novel SIPE provides a very high ionic conductivity (2.6 mS cm−1) and an electrochemical stability window of about 4.1 V at 40 °C, enabling stable sodium stripping and plating and excellent rate capability of Na||Na3V2(PO4)3 cells up to 2 C. Remarkably, such cells provide a capacity retention of about 85 % after 1,000 cycles at 0.2 C thanks to the very high Coulombic efficiency (99.9 %), resulting from an excellent interfacial stability towards sodium metal and the Na3V2(PO4)3 cathode.

Single-Ion Conducting Polymer Electrolyte for Superior Sodium-Metal Batteries.

Sodium-metal batteries (SMBs) are considered a potential alternative to high-energy lithium-metal batteries (LMBs). However, the high reactivity of metallic sodium towards common liquid organic electrolytes renders such battery technology particularly challenging. Herein, we propose a multi-block single-ion conducting polymer electrolyte (SIPE) doped with ethylene carbonate as suitable electrolyte system for SMBs. This novel SIPE provides a very high ionic conductivity (2.6 mS cm-1) and an electrochemical stability window of about 4.1 V at 40 °C, enabling stable sodium stripping and plating and excellent rate capability of Na||Na3V2(PO4)3 cells up to 2C. Remarkably, such cells provide a capacity retention of about 85% after 1,000 cycles at 0.2C thanks to the very high Coulombic efficiency (99.9%), resulting from an excellent interfacial stability towards sodium metal and the Na3V2(PO4)3 cathode.

Ion Transport in Polymer/Inorganic Composite Electrolytes – a Comparison between Broadband Dielectric Spectroscopy and Impedance Spectroscopy

Significant efforts have been made to develop composite electrolytes combining polymer matrix with Li-ion conducting inorganic solids for feasible construction of solid-state batteries. However, the Li-ion transfer kinetics at the interface between polymer/inorganic electrolyte is unfavorable for Li-ion conduction in the composite electrolyte because of the interfacial resistance and the activation energy barrier for interfacial Li-ion transfer. The activation energy barrier for the Li-ion transfer reaction at the interface is correlated with the interaction between Li-ion and polymer matrix in the polymer electrolyte, interaction between Li-ion and anions in inorganic electrolytes and the interaction between polymer and inorganic electrolytes, therefore, the electrolyte composition significantly affects the interfacial charge transfer kinetics in composites.In this work, Li-ion transport properties in the composite electrolytes are investigated by using broadband dielectric spectroscopy (BDS) and impedance spectroscopy (IS). We particularly focus on Li-ion charge transfer at the polymer/inorganic interface from the dual ion conducting polymer to the single ion conducting polymer electrolytes with different Li-ion conducting salts such as LiN(SO2CF3)2 (LiTFSI) and (LiMTFSI) in vinyl ethylene carbonate (VEC) or polymerized vinyl ethylene carbonate (PVEC). The interfacial resistances of inorganic electrolytes Li0.34La0.56TiO3 (LLTO) in polymer electrolytes are elucidated. To further evaluate the polymer/inorganic electrolyte interfaces, various types of cell are assembled in a glove box filled with argon gas and characterized by a series of techniques such as BDS and IS. The Li-ion transfer kinetics at the interface significantly affects the Li-ion flux through the composite electrolytes and will be presented. In addition, we will present a systematic comparison between BDS and IS results in order to build connections between the two communities. Acknowledgements This work was supported as part of the Fast and Cooperative Ion Transport in Polymer-Based Materials (FaCT), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences at Oak Ridge National Laboratory under contract DE-AC05-00OR22725.

Single-Ion Conducting Polymer Electrolytes for Sodium Batteries

Sodium-ion batteries have attracted extensive attention recently owing to the announcements of several companies to commercialize this technology in the (very) near future. Just like commercial lithium-ion batteries, though, these batteries are comprising and/or will comprise a liquid electrolyte – with all its advantages and challenges. Thinking one step ahead (as also done by a few companies already), the next step might be the transition to (“zero-excess”) sodium-metal batteries, which will require fundamentally new electrolyte solutions, and just like for lithium-metal batteries, these might be based, e.g., on polymers.Herein, we present our latest results on single-ion conducting polymer electrolytes for sodium-metal batteries. These polymer electrolytes do not only show higher ionic conductivity than its lithium analogues (>2.5 mS cm-1 at 40 °C), but moreover the same beneficial properties in terms of high electrochemical stability towards oxidation, highly reversible sodium plating and stripping, and excellent cycling stability of Na‖Na3V2(PO4)3 cells for more than 500 cycles. The results thus show that single-ion conducting polymer electrolytes are very promising candidates for high-performance sodium batteries.

Zwitterion-doped self-supporting single-ion conducting polymer electrolyte membrane for dendrite-free lithium metal secondary batteries

Zwitterion-doped self-supporting single-ion conducting polymer electrolyte membrane for dendrite-free lithium metal secondary batteries

Thermally Reprocessable Self-Healing Single-Ion Conducting Polymer Electrolytes

Thermally Reprocessable Self-Healing Single-Ion Conducting Polymer Electrolytes

Fast Li+ Transport Polyurethane-Based Single-Ion Conducting Polymer Electrolyte with Sulfonamide Side chains in the Hard Segment for Lithium Metal Batteries.

Single-ion conducting polymer electrolytes (SICPEs) are considered as one of the most promising candidates for achieving lithium metal batteries (LMBs). However, the application of traditional SICPEs is hindered by their low ionic conductivity and poor mechanical stability. Herein, a self-standing and flexible polyurethane-based single-ion conductor membrane was prepared via covalent tethering of the trifluoromethanesulfonamide anion to polyurethane, which was synthesized using a facile reaction of diisocyanates with poly(ethylene oxide) and 3,5-diaminobenzoic acid (or 3,5-dihydroxybenzoic acid). The polymer electrolyte exhibited excellent ionic conductivity, mechanical properties, lithium-ion transference number, thermal stability, and a broad electrochemical window because of the bulky anions and unique two-phase structures with lithium-ion nanochannels in the hard domains. Consequently, the plasticized electrolyte membrane showed exceptional stability and reliability in a Li||Li symmetric battery. The assembled LiFePO4||Li battery exhibited an outstanding capacity (∼180 mA h g-1), Coulombic efficiency (>96%), and capacity retention. This research provides a promising polymer electrolyte for high-performance LMBs.

Dicarbonate acrylate based single-ion conducting polymer electrolytes for lithium batteries

A series of carbonate-based single-ion conducting, solid polymer electrolytes were synthesized via reversible addition-fragmentation transfer copolymerization with anionic monomers. The abundant carbonate groups within the copolymers provide electron-delocalized complexation sites to aid Li+ dissociation from the polymer backbone, and the cyclic carbonates also provide a crosslinking site to improve mechanical properties. A single-ion conducting network polymer electrolyte prepared with dicarbonate acrylate (DCA) and trifluoromethane sulfonimide methacrylate (MTFSI) was UV-cured with a polyethylene oxide crosslinker and plasticized with vinylene carbonate (VC) to produce a high conductivity and high-performance electrolyte. The DCA-based polymer electrolyte had 0.16 mS/cm ionic conductivity at room temperature and transference number of 0.92. The use of VC was compared to a conventional electrolyte, ethylene carbonate and diethyl carbonate. The polymer electrolyte with VC showed excellent compatibility and stability with lithium. A lithium metal/lithium iron phosphate full cell with VC showed higher capacity and cycling stability than a cell with conventional plasticizers.