Single-ion Polymer Electrolytes Research Articles

Artificial SEI Layer Combined with Single-Ion Polymer Electrolytes to Prevent Dendrite Growth in Lithium Metal Batteries

Li-metal batteries have the potential to become the next generation of batteries since they can provide an increased energy density vs. Li-ion batteries. However, the safety issue caused by the inhomogeneous Li deposition and Li dendrite growth greatly limits their commercial application. Several methods have been proposed to address this issue. On the one hand, when Li ions are released from one electrode and consumed at the other electrode, it causes a salt concentration gradient. Besides, the electrical migration of anions in the opposite direction aggravates the concentration of gradient since anions do not react at the electrodes. Fast dendritic growth then occurs when the current is high enough to fully deplete the Li+ ion at the anode during charge. Thus, suppressing concentration gradient by immobilizing the anions would in principle solve the fast dendritic growth issue. On the other hand, the Solid Electrolyte Interphase (SEI) plays a crucial role in the operation of Li metal batteries since it prevents further reduction and continuous electrolyte reaction. SEI derives from the passivation layer formed onto the surface of Li metal under dry air during lithium foil extrusion and then evolves further in contact with the electrolytes and during subsequent electrochemical Li stripping/plating. The SEI is inhomogeneous and since it contains lower resistance pathways for Li+ transport, it favors inhomogeneous deposition at any current. Thus, SEI engineering, in order to favor the homogeneity of current density and enhanced mechanical properties to confine lithium could, in principle, improve the performance of Li metal batteries.Thus, we studied the use of single-ion conducting polymers with high cationic transference numbers (tLi+ close to 1) as artificial SEIs (art-SEIs) since they include immobile anions and thus prevent Li+ depletion during charge and, at the same time, improve lithium metal confinement and the homogeneity of current density. Our results show much improved homogeneity of Li deposition and cycling stability after single-ion art-SEI coating using an ether-based liquid electrolyte combined with a separator. Nevertheless, it could not enable long-term cycling as the separator does not enable homogeneous pressure and current density onto the lithium anode. Thus, the use of a single-ion conducting solid polymer electrolyte was combined with a single-ion conducting art-SEI (as illustrated in Figure 1). This strategy allows the suppression of salt concentration gradients, inhomogeneous pressure and current density, thus enables homogeneous Li deposition and long-term cycling of Li metal anode. Figure 1

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 Polymer Electrolyte Based on Lithium-Rich Imidazole Anionic Porous Aromatic Framework for High Performance Lithium-Ion Batteries.

The low ionic conductivity and Li+ transference number ( ) of solid polymer electrolytes (SPEs) seriously hinder their application in lithium-ion batteries (LIBs). In this study, a novel single-ion lithium-rich imidazole anionic porous aromatic framework (PAF-220-Li) is designed. The abundant pores in PAF-220-Li are conducive to the Li+ transfer. Imidazole anion haslow binding force with Li+ . The conjugation of imidazole and benzene ring can further reduce the binding energy between Li+ and anions. Thus, only Li+ moved freely in the SPEs, remarkably reducing the concentration polarization and inhibiting lithium dendrite growth. PAF-220-quasi-solid polymer electrolyte (PAF-220-QSPE) is prepared through solution casting of Bis(trifluoromethane)sulfonimide lithium (LiTFSI) infused PAF-220-Li and Poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP), and possessed excellent electrochemical performance. The electrochemical property are further improved by preparing all-solid polymer electrolyte (PAF-220-ASPE) via pressing-disc method, which has a high Li+ conductivity of 0.501mScm-1 and of 0.93. The discharge specific capacity at 0.2C of Li//PAF-220-ASPE//LFP reached 164mAhg-1 , and the capacity retention rate is 90% after 180 cycles. This study provided a promising strategy for SPE with single-ion PAFs to achieve high-performance solid-state LIBs.

A single ion polymer electrolyte via copolymerization of lithium (4-Styrenesulfonyl)(Trifluoromethanesulfonyl)imide and allyl Poly(Aryl ether Ketone) enables safe lithium ion batteries

Given its capacity to suppress concentration polarization in lithium-ion batteries (LIBs), single-ion polymer electrolytes (SIPEs) have been considered a substitute for the traditional dual-ion electrolyte. However, SIPEs still have challenges such as low ion conductivity. Meanwhile, gel polymer electrolytes (GPEs) have high ionic conductivity and compatibility with electrodes, but are limited by concentration polarization. In this study, a novel poly(aryl ether ketone) (PAEK50) single-ion polymer (PAEK-LiSTFSI) was prepared via the copolymerization of lithium (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide (LiSTFSI) and allyl poly(aryl ether ketone). The obtained PAEK-LiSTFSI was compounded with poly(ethylene oxide) and then immersed in EC/PC to obtain poly(aryl ether ketone) single-ion gel polymer electrolyte (PAEK-SIGPE). The tensile strength and elongation at break of PAEK-SIPE reached 21.4 MPa and 116.7 %, respectively. PAEK-SIGPE exhibited a high ionic conductivity of 7.8 × 10-5 S cm−1 at 30 °C and Li+ transference number of 0.95, which effectively inhibited the growth of lithium dendrites. The LiFePO4(LFP)/PAEK-SIGPE/Li half-cell possessed excellent cycle and rate performance. The discharge capacity of the battery reached 140 mAh g−1, and the capacity retention rate was as high as 95 % at 0.2C even after 400 cycles. These results indicated that the novel PAEK-SIGPE can be applied to next-generation LIBs.

Engineered networking in a family of solvent-free single-ion conducting borate network polymer electrolytes for Li-metal battery applications

As the state-of-the-art energy storage technology, lithium-ion batteries have been attracting lots of attention, but their finite energy densities cannot satisfy the overwhelming demand for large energy storage and commercial flammable liquid electrolytes are also plagued by safety concerns. Solvent-free single-ion polymer electrolytes with excellent electrochemical properties are expected to solve these issues and enhance the energy density of the next-generation batteries technology. Here, we engineered the networking of a series of solvent-free anionic network polymer electrolytes to improve ionic transport for Li-metal battery applications. The anionic network polymers formed as a diamondoid structure consisting of borate anions bridged by branched ethylene glycol linkers of differing stoichiometric ratios, enabling the controlled segmental mobility of network polymers. The increasing segmental mobility offered an elevated ionic conductivity, revealing ionic transport was mostly controlled by engineering the segmental mobilities of polymers, especially at the given interanionic distance. However, there was a restricted ionic transport in fast segmental dynamics of the network polymers featuring free branches, implying that the branching would less contribute to ionic transport compared to the interanionic distance likely due to the frustration in changing the coordination site. Standout network polymer exhibited notable ion selectivity in Li+ cation transport and high oxidative stability. Galvanostatic cycling reveals outstanding resistance to dendrite growth, suggesting that the solvent-free network polymer can serve as a powerful electrolyte for Li-metal batteries.

A flexible and highly conductive quasi-solid single-ion polymer electrolyte for high performance Li-metal batteries

A series of flexible and highly conductive quasi-solid single-ion polymer electrolytes (abbreviated as PU-TFMSI) based on lithium sulfonimide are presented. Owing to the crosslinked structure with three types of segments (hard segment, soft segment and Li rich segment), PU-TFMSI displays a stretchability of 1350% and toughness of 13.6 MJ m−3. These PU-TFMSI single-ion electrolytes deliver high ionic conductivity over 1.3 × 10−4 S cm−1 at ambient temperature, a wide electrochemical stability window (up to 5.0 V vs Li+/Li), a high lithium transfer number (LTN ∼ 0.9), and good compatibility with electrodes. The LiFePO4/PU-TFMSI-2/Li coin cell exhibits stable cycling with an average Coulombic efficiency of 99.58% and superior rate performance. Furthermore, the LiFePO4//Li soft pouch cell with PU-TFMSI-2 single-ion electrolyte maintains functionality under bending. The flexible single-ion polymer electrolytes designed in this study have the potential to be applied in flexible devices and stretchable batteries.

A Flexible Single-Ion Gel Electrolyte with a Multiscale Channel for the High-Performance Lithium Metal Batteries

Single-ion polymer electrolytes (SIPEs) have attracted attention due to their unique advantage in suppressing lithium dendrite growth. However, the low ionic conductivity seriously restricts the development of SIPEs. Herein, an aerogel-based SIPE with multiscale Li+ conducting channels is proposed for the first time. The microscale Li+ transport channel is constructed through the self-assembly of cyclodextrins and Li+ containing polymer, while the macroscale channel is formed via a unidirectional freeze-drying process. The obtained aerogel exhibits high thermal stability, good wettability, and outstanding mechanical properties (78% stretchability and 50% compression resilience). The aerogel electrolyte exhibits high oxidative stability (∼4.7 V), good ionic conductivity at room temperature (2.5 × 10–4 S cm–1), and high Li+ transference number (∼0.96). The Li||LiFePO4 cells deliver outstanding rate performance and long cycle life (98% capacity retention after 200 cycles at 0.2 C). This work provides new insight toward mechanically flexible and highly performing single-ion polymer electrolytes for Li metal batteries.

A Single-Ion Polymer Composite Electrolyte Via In Situ Polymerization of Electrolyte Monomers into a Porous MOF-Based Fibrous Membrane for Lithium Metal Batteries

Single-ion polymer electrolytes have received considerable attention in the development of high-safety and high-energy-density lithium metal batteries due to their high lithium ion transference number, good interfacial compatibility with lithium metal anode, and suppression of lithium dendrite benefits from the immobilization of anions. In this work, we develop a novel single-ion polymer composite electrolyte (SIPCE) by an in situ photoinitiated polymerization of single-ion polymer monomers into porous metal–organic frameworks (MOF)/polymer electrospun fibrous membrane. Experimental results demonstrate that the received SIPCE-MOF exhibits a high lithium ion transference number of 0.80, a wide electrochemical stability window up to 5.68 V, and the remarkable ionic conductivity of 1.14 × 10–5 and 2.23 × 10–5 S cm–1 at 30 and 60 °C, respectively. In addition, the lithium symmetrical battery with such SIPCE-MOF shows a polarization voltage of 120 mV at a current density of 2 mA cm–2 and a stable cycling time of more than 2200 h, implying the excellent long-term lithium plating/stripping performance. As a result, the solid-state LiFePO4/SIPCE-MOF/Li battery achieves an unparalleled rate performance (105 mAh g–1 at 2 C) and maintains 98.3% of its initial capacity after 120 cycles with a superhigh Coulombic efficiency of 99% at 0.5 C. These excellent properties provide great potential for the application of single-ion polymer composite electrolytes in solid-state lithium metal batteries.

Photo-Cross-Linked Single-Ion Conducting Polymer Electrolyte for Lithium-Metal Batteries.

Polymer electrolytes are considered potential key enablers for lithium-metal batteries due to their compatibility with the lithium-metal negative electrode. Herein, cross-linked self-standing single-ion conducting polymer electrolytes are obtained via a facile UV-initiated radical polymerization using pentaerythritol tetraacrylate as the cross-linker and lithium (3-methacryloyloxypropylsulfonyl)-(trifluoromethylsulfonyl)imide as the ionic functional group. Incorporating propylene carbonate as charge-transport supporting additive allowed for achieving single-ion conductivities of 0.21mScm-1 at 20°C and 0.40mScm-1 at 40°C, while maintaining a suitable electrochemical stability window for 4V-class positive electrodes (cathodes). As a result, this single-ion polymer electrolyte featured good cycling stability and rate capability in Li||LiFePO4 and Li||LiNi0.6 Mn0.2 Co0.2 O2 cells. These results render this polymer electrolyte as potential alternative to liquid electrolytes for high-energy lithium-metal batteries.

(Invited) High Performance Single Conducting Polymer Electrolytes for Lithium Metal Batteries

Lithium-based batteries are a key technology for successfully transitioning from depleting fossil fuels to renewable energy sources, particularly in meeting the demands of a highly mobile society. Nevertheless, the commonly employed liquid organic electrolytes are highly flammable and release toxic degradation products[1]. Solid electrolytes are a promising alternative, since they offer an improved safety and potentially suppress dendritic lithium deposition[2]. Among them, due to their flexibility and modularity, solid polymer electrolytes (SPEs) are excellent candidates. For their commercial implementation, however, one must simultaneously ensure acceptable ionic conductivity (>10-4 S cm-1 at 25 °C), high mechanical strength, and an electrochemical stability window of at least 4-5 V. Conventional polymer electrolytes based on poly(ethylene oxide) (PEO) consist of a lithium salt dissolved in the polymer. Frequently, also a plasticizer is added to enhance the segmental relaxation-dependent charge transport by lowering the glass transition temperature (Tg)[3]. The need for a conducting salt, however, results in transference numbers (t+) far below 0.5. This leads to charge concentration gradient and reversed cell polarization issues, which worsen the long-term cycling stability[4]. SPEs with t+ = 1, also known as ‘single-ion polymer electrolytes’ (SIPEs), might overcome these issues. The simplest approach to achieve single-ion conductivity is to covalently tether the anion to the polymer backbone (so-called ‘ionomers’), thus ensuring that the only mobile species is the cation. Nevertheless, the conductivity of these systems is typically very low (10− 8 to 10− 7 S cm− 1 at 25 °C)[5 ] and despite the ten-fold increase achieved through optimizing the ionomer structure by introducing weakly coordinating anionic species (∼10− 6 S cm− 1 at 25 °C)[ 6] or designing block or grafted copolymers, their employment remains unfeasible. Moreover, for most block copolymer-based SIPEs, the anion is tethered to the rigid block, while the Li+ conduction occurs in the microphase-separated PEO block. Consequently, adequate conductivities are achievable only in the disordered state above the melting point of the PEO phase, so that the phase separation and, accordingly, the mechanical properties provided by the rigid block vanish. In this presentation we give SIPE that we recently synthetized[7,8] with very efficient charge transport pathways, high electrochemical stability and an ionic conductivity approaching that of liquid organic electrolytes. Moreover, these SIPEs allowed for lithium stripping/plating for more than 1000 h with a remarkably low overpotential and cycling of NMC811 with high reversible capacity at various temperatures, including 20 °C and even 0 °C, for more than 500 cycles without substantial capacity fading when applying an optimized charging mode. These are very remarkable and original results, since the materials’ properties are nicely tailorable with regard to the ionomer structure, charge carrier density, phase separation, and morphological appearance. The polymer nanostructure and cell performances are correlated. References Hammami, A., Raymond, N. & Armand, M. Nature 424, 635–636 (2003).Aricò, A. S., Bruce, P., Scrosati, B., Tarascon, J.-M. & Van Schalkwijk, W. Mater. 4, 366–377 (2005).Osada, I., De Vries, H., Scrosati, B. & Passerini, S. Chemie - Int. Ed. 55, 500–513 (2016).Tikekar, M. D., Choudhury, S., Tu, Z. & Archer, L. A. Energy 1, 16114 (2016).Shaplov, A. S., Marcilla, R. & Mecerreyes, D. Acta 175, 18–34 (2015).Xu, K. Rev. 114, 11503–11618 (2014).Nguyen h-D, Kim G-K, Shi J, Elie Paillard, Judeinstein P., Lyonnard S., Bresser D., Iojoiu C. Energy & Environmental Science, 11, 3298-3309, (2018).Chen, D. Steinle, H-D. Nguyen, J-K. Kim, A. Mayer, J. Shi, E. Paillard, C. Iojoiu, S. Passerini, D. Bresser, NanoEnergy, 77, 105121, (2020).

A Stretchable and Highly Conductive Sulfonic Pendent Single-Ion Polymer Electrolyte Derived from Multifunctional Tri-Block Polyether

A Stretchable and Highly Conductive Sulfonic Pendent Single-Ion Polymer Electrolyte Derived from Multifunctional Tri-Block Polyether

Novel single-ion conducting electrolytes based on vinylidene fluoride copolymer for lithium metal batteries

A single-ion polymer electrolyte (SIPE) based on PVDF-based random copolymer (Li-PVDF) was synthesized in water from the radical copolymerization of vinylidene fluoride (VDF) with perfluoro-2-methyl-3-oxa-5-sulfonimido[-3-oxa-5-sulfonyl fluoride] vinyl ether (VEPFSIS) initiated by potassium persulfate. The purified polymer, characterized by 1H and 19F NMR spectroscopy, ICP-MS, and size-exclusion chromatography, contains 96 mol% VDF with an average molar mass of 128 kg mol−1. The Li-PVDF was cast into self-standing membranes and then swollen with a 50/50 v/v mixture of ethylene carbonate and propylene carbonate. The membrane was analyzed using DSC, TGA, pulse field gradient (PFG)-NMR and electrochemical methods. The solvent-doped membrane exhibited a lithium ion transport number close to 1 with lithium ion conductivities higher than 10−4 S cm−1 at 30 °C, an electrochemical stability up to 4.3 V vs. Li+/Li and an excellent reversibility upon continuous lithium plating/striping cycles. In addition, prototype Li/NMC battery cells using Li-PVDF as both electrolyte and cathode binder in the NMC based composite cathode showed reversible cycling and good performance at 60 °C. The results demonstrated the promising potential of this new single-ion polymer family in intrinsically safe all solid-state lithium metal based batteries.

High Lithium Conductivity of Miscible Poly(ethylene oxide)/Methacrylic Sulfonamide Anionic Polyelectrolyte Polymer Blends

In this work, we develop novel single-ion polymer electrolytes by mixing poly(lithium 1-[3-(methacryloyloxy) propylsulfonyl]-1-(trifluoromethanesulfonyl) imide) (PLiMTFSI) and poly(ethylene oxide) ...

All-Solid-State Lithium-Organic Batteries Comprising Single-Ion Polymer Nanoparticle Electrolytes.

Advances in lithium battery technologies necessitate improved energy densities, long cycle lives, fast charging, safe operation, and environmentally friendly components. This study concerns lithium-organic batteries comprising bioinspired poly(4-vinyl catechol) (P4VC) cathode materials and single-ion conducting polymer nanoparticle electrolytes. The controlled synthesis of P4VC results in a two-step redox reaction with voltage plateaus at around 3.1 and 3.5 V, as well as a high initial specific capacity of 352 mAh g-1 . The use of single-ion nanoparticle electrolytes enables high electrochemical stabilities up to 5.5 V, a high lithium transference number of 0.99, high ionic conductivities, ranging from 0.2×10-3 to 10-3 S cm-1 , and stable storage moduli of >10 MPa at 25-90 °C. Lithium cells can deliver 165 mAh g-1 at 39.7 mA g-1 for 100 cycles and stable specific capacities of >100 mAh g-1 at a high current density of 794 mA g-1 for 500 cycles. As the first successful demonstration of solid-state single-ion polymer electrolytes in environmentally benign and cost-effective lithium-organic batteries, this work establishes a future research avenue for advancing lithium battery technologies.

Communication—Lithium Sulfonated Polyoxadiazole as a Novel Single-Ion Polymer Electrolyte in Lithium-Ion Batteries

A single-ion conductor polymer electrolyte was prepared and the effects of the ratio of isophthalic acid (IPA) to 4, 4’-diphenyl ether dicarboxylic acid (DPE) on the structure and electrochemical properties have been investigated. Results show that all the lithium sulfonated polyoxadiazoles (Li-SPODs) have excellent thermal stability (510 °C). The ionic conductivity of the Li-SPOD is 7.2 × 10−4 S cm−1 at room temperature when the IPA/DPE ratio is 6/4. A high Coulombic efficiency of 99.1% for the LiFePO4/6/4 li-SPOD SPEs/Li half-cell could be achieved with a capacity retention of 90.63% at a current density of 0.1 C after 25 cycles.

Lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide based single-ion polymer electrolyte with superior battery performance

A novel single ion conducting polymer electrolyte is synthesized via a facile and efficient one-step ultraviolet initiated thiol-ene click reaction. The monomers of lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide, pentaerythritol tetrakis (2-mercaptoacetate) and pentaerythritol tetraacrylate are polymerized to be a crosslinked network structured polymer within a polypropylene nonwoven fabric supporting membrane by a photo-initiated thiol-ene click reaction. Upon solvent soaking, the obtained single ion conducting polymer electrolyte exhibits high ionic conductivity (0.84 mS cm−1 at room temperature), very high lithium ion transference number of 0.93, wide electrochemical window up to 5.2 V (vs. Li+/Li) and well compatibility with lithium metal anode. The corresponding LiFePO4/Li cell assembled with the prepared polymer electrolyte shows excellent rate capability and prominent cycling performance with the capacity retention rate of 83% after 400 cycles at 1 C. Therefore, the synthesized single ion conducting polymer electrolyte owns great potential for practical application in lithium ion batteries.

Ultrahigh Li-ion conductive single-ion polymer electrolyte containing fluorinated polysulfonamide for quasi-solid-state Li-ion batteries

With the rapid development of electronic devices and electric vehicles, the requirements for their safety issues and service stabilities have become more and more strict.

Design of ionic liquid like monomers towards easy-accessible single-ion conducting polymer electrolytes

The rational design of single-ion polymer electrolytes emerges as a primary strategy for enhancing the performance of lithium ion batteries. With the aim to increase ionic conductivity, four novel ionic liquid monomers were designed and synthesized in high purity. Such monomers differ from the previously reported systems by (1) the presence of a long and flexible spacer between the methacrylate group and chemically bonded anion or (2) by a long perfluorinated side chain. The investigation of their free radical copolymerization with poly(ethylene glycol) methyl ether methacrylate (PEGM) allowed to identify the impact of thei copolymer composition on thermal and ion conducting properties. The copolymer based on lithium 3-[4-(2-(methacryloyloxy)ethoxy)-4-oxobutanoyl)oxy) propylsulfonyl]-1-(trifluoromethylsulfonyl)imide showed the highest ionic conductivity (1.9 × 10−6 and 2 × 10−5 S cm−1 at 25 and 70 °C, respectively) at [EO]/[Li] = 61 ratio, along with a wide electrochemical stability (4.2 V vs. Li+/Li) and high lithium-ion transference number (0.91). The prepared copoly(ionic liquid)s (coPILs) were further applied for the assembly of Li/coPIL/LiFePO4 lithium-metal cells, which were capable to reversibly operate at 70 °C delivering relatively high specific capacity (up to 115 mAh g−1) at medium C/15 current rate.

Ion Transport Mechanisms in Single Ion Polymer Electrolytes for Application in Lithium Ion Batteries

In order to increase the energy density of lithium ion batteries, lithium metal is an attractive anode material based on its high specific capacity and low electrochemical potential. However, a major drawback of lithium metal anodes comprises dendrite growth due to unstable solid electrolyte interphase (SEI) resulting in severe safety hazards. Polymer electrolytes constitute a viable alternative to commonly utilized liquid electrolytes and are able to suppress or even avoid dendrite growth thereby providing increased safety. In particular, single ion conducting polymer electrolytes are promising for application in lithium ion or lithium metal batteries. In contrast to common dual ion conducting electrolytes, single ion conductors afford high transference numbers, hence significantly reducing polarization effects as only lithium ions are mobile whereas anions are bound at the polymer backbone. In this contribution we present various single ion conducting polymers composed of AB-type alternating block copolymers in which the lithium ions are bound to the backbone (e.g., bis(4-carboxyl benzene sulfonyl)imide moieties). Systematic variation of the constituents can control the achievable properties including the morphology, electrical and electrochemical properties of the resulting polymers. The electrolyte membranes fabricated for application in lithium meatal batteries are blends of single ion conducting aromatic polymers and a flexible linear polymer such as poly(vinylidene fluoride-co -hexafluoropropylene (PVDF-HFP). The appropriate ratio of the polymer blends is evaluated to yield membranes (swollen with thermally stable solvent solutions of ethylene carbonate and propylene carbonate (EC: PC, 1:1, v/v)), with increased ionic conductivity, reduced solvent uptake as well as sufficient flexibility and mechanical stability as well as reduced solvent uptake. We present optimized routes for the synthesis of single ion conducting polymers and suitable membrane compositions. Furthermore, feasible relations of both structural and physicochemical properties of the polymer membranes are discussed, particularly with respect to underlying ion transport properties or transport mechanisms, in this way potentially enabling controlled modification or adjustment of either the chemical structures or electrochemical properties of the polymer membranes. A morphology analysis is performed using small angle X-ray scattering (SAXS), while nuclear magnetic resonance spectroscopy (NMR) and electrochemical data including impedance as well as dielectric loss spectra are combined to unravel the major ion transport mechanisms and ion mobility in addition to ionic conductivity, complex permittivity, self-diffusion coefficients and transference numbers. Both the oxidative and reductive stability as well as cycling performance in NMC/ lithium metal cells are also presented. Profound understanding of the ion transport mechanisms and property relations in single ion conducting polymer electrolyte membranes is essential and will allow to design future electrolyte membranes having desired properties. Thereby, the requirement for different applications can be met and the application of safe and highly performing lithium metal batteries can be enabled.

Highly porous single-ion conductive composite polymer electrolyte for high performance Li-ion batteries

A highly porous polymer electrolyte with good wettability and excellent thermal dimensional stability is of great importance to enable the high performance of lithium ion batteries (LIBs). This study reports a facile in-situ polymerization process to approach molecular mixing level of poly (vinylidene fluoride-hexa-fluoropropylene) (PVDF-HFP) and the fully aromatic single-ion conducting polymer (fa-SIPE). The molecular level mixing is greatly beneficial for promoting both macro and nanophase separation between the flexible aliphatic PVDF-HFP and the aromatic fa-SIPE. These occur because of the poor physical compatibility of the two polymers and leads to a macro/nano porous single-ion polymer electrolyte (SIPE). Filling the porosity with a Li+-ion coordinating solvent enables high Li+-ion mobility, which is favorable for the development of high power and fast charge LIBs. Remarkably, the highly porous SIPE membrane displays high mechanical stability, high electrolyte wettability and strong thermal dimensional stability, all possibly contributing to excellent stability and reliability of LiBs. This study provides an efficient way of fabricating porous, single-ion polymer electrolyte for LIBs application.