Single-Ion Block Copoly(ionic liquid)s as Electrolytes for All-Solid State Lithium Batteries

A Zwitterion Coupled All-Solid-State Single Ion Conducting Polymer Electrolyte via Photoinitiated Thiol-Ene Click Polymerization

The all-solid-state single ion conducting polymer electrolyte has a bottleneck in ionic conductivity even though it can prevent concentration polarization. Here, lithium 3,3'-(diallylammonio)bis(propane-1-sulfonyl(trifluoromethyl sulfonyl)imide) (LiDAA(PSI)2) with a symmetrical "one positive, two negative" structure and unsaturated double bonds for propagation, is synthesized. LiDAA(PSI)2 is copolymerized with 1,2-ethanedithiol and poly(ethylene glycol) diacrylate via photoinitiated thiol-ene click polymerization and forms a random copolymer, SPZ for short. For comparison, lithium 3-(diallylamino)propane-1-sulfonyl(trifluoromethyl sulfonyl)imide) (LiDAAPSI) and corresponding copolymer SP are synthesized. The 7Li resonance peak position of LiDAA(PSI)2 shifts to a low-field compared to that of LiDAAPSI, indicating a weaker electrostatic attraction. The symmetrical "one positive, two negative" structure is responsible for the low-field shift, taking effect of charge conjugation. Unsurprisingly, the ionic conductivity of SPZ is 1.69e-5 S cm-1 at 60 °C, which is 1.9 times that of SP. Lithium electroplating and stripping at 0.0125 mA cm-2@0.05 mAh cm-2 at 60 °C are performed. An all-solid-state single ion conducting lithium metal secondary battery is demonstrated. Zwitterion coupled LiDAA(PSI)2 possesses a symmetrical "one positive, two negative" structure, charge conjugation to weaken electrostatic interaction, and unsaturated double bonds for propagation, which inspires the design and synthesis of single ion conducting polymer electrolytes with zwitterion effect.

The Sustainable Potential of Single-Ion Conducting Polymers

Energy storage technologies are critical for sustainable development, with electrolyte materials playing a decisive role in performance and safety. Single-ion conducting polymers (SICPs) represent a distinct materials class characterized by selective ion transport through immobilized ionic groups. While their potential for battery applications is recognized, an analysis of their sustainability implications and pathways to practical implementation has been lacking. This work demonstrates how strategic design of SICPs can contribute to sustainable energy storage through both materials' development and device integration. Recent advances in lithium borate-based systems and CO2-derived polycarbonate architectures have achieved ionic conductivities exceeding 10-4 S cm-1 at room temperature through scalable synthesis routes. In lithium-metal batteries, their high transference numbers and viscoelastic properties enable stable cycling with industrial-relevant cathode loadings, while as electrode binders, they enable aqueous processing and enhanced interfacial stability. Their versatility extends to sustainable chemistries, including sodium and zinc systems. Analysis reveals that while SICPs can enhance energy storage sustainability through improved performance, processability, and potential recyclability, opportunities remain in investigating end-of-life management. This work highlights frameworks for advancing SICP sustainability while maintaining the performance requirements for practical implementation in next-generation energy storage.

Protective Coating for Stable Cycling of Li-Metal Batteries Based on Cellulose and Single-Ion Conducting Polymer

The thermodynamically unstable interface between metallic lithium and electrolyte poses a major problem for the massive commercialization of Li-metal batteries. In this study, we propose the use of a multicomponent protective coating based on cellulose modified with dimethylthexylsilyl group (TDMSC), single-ion conducting polymer P(LiMTFSI), and LiNO3 (TDMSC-P(LiMTFSI)-LiNO3, namely PTL). The coating shows its positive effect by increasing the Coulombic efficiency in Li || Cu cells from 95.9 and 98.6% for bare Li, to >99.3% for Li coated (Li@PTL), with 1 M LiFSI in FEC:DEC and 1 M LiFSI in DME electrolyte, respectively. Symmetrical Li || Li PTL-coated cells exhibit a much more prolonged and stable cycling with a slower increase in overpotential compared to bare Li cells. Li@PTL anodes enable improved cycling of Li@PTL/LFP cells compared to noncoated cells in liquid electrolytes. In this respect, inhibition of high surface area lithium growth is confirmed through postcycling scanning electron microscopy. Remarkably, dendrite-free galvanostatic cycling is demonstrated in laboratory-scale solid-state battery cells assembled with LFP composite cathode (catholyte configuration with PEO + LiTFSI as ionically conducting binder) and a cross-linked PEO-based solid polymer electrolyte. The PTL protective coating enables improved stability of Li metal batteries in combination with smooth transport of Li+ at the electrode-electrolyte interface and homogeneous lithium coating, highlighting its promising prospects in enhancing the performance and safety of lithium metal batteries by properly tuning the synergy between the coating components.

Solid-State Lithium Batteries with In Situ Polymerized Acrylate-Based Electrolytes Capable of Electrochemically Stable Operation at 100 °C

Solid polymer electrolytes (SPEs) typically consist of salts with mobile anions that could cause instabilities and parasitic side reactions in solid-state lithium (Li) batteries. To address this challenge, single-Li-ion conducting (SLIC) SPEs, where anions of Li salts are covalently attached to the polymer backbone, have been utilized to reduce the number of mobile anions. This approach improves the cationic transference number but is accompanied by a loss of ionic conductivity. In this work, we investigate a synergetic approach of using both a polymerizable SLIC salt and a conventional Li salt in a polymer matrix by in situ polymerization of the poly(propylene glycol) acrylate (PPGA) monomer. The synthesized hybrid SPEs show a high ionic conductivity of up to ∼2 × 10-4 S cm-1 and a relatively high Li-ion transference number of ∼0.4. With a significantly reduced fraction of mobile anions in the combined salt SPE, in situ polymerized SPE cells with a LiFePO4 (LFP) cathode achieve a stable performance for over 100 cycles at temperatures as high as 100 °C, which is unattainable with conventional Li salts or electrolytes. Furthermore, solid-state nuclear magnetic resonance spectra provide additional insights into differences in Li nucleus environments and emphasize a reduction in activation energy for hybrid SPEs due to their more open structure. This study opens the path for the fabrication of high-performance solid polymer Li batteries capable of operating at high temperatures using commercial battery fabrication equipment, as in situ polymerized acrylate-based polymers provide drop-in compatibility with conventional battery production, ease of acrylate polymerization, and inexpensive, facile SPE chemistry. We expect that further tuning of the acrylate-based SPE composition may allow further increases in its conductivity without sacrificing its electrochemical stability or mechanical properties.

Fabrication of Single-Ion Conductors Based on Liquid Crystal Polymer Network for Quasi-Solid-State Lithium Ion Batteries

Single-ion conductive polymer electrolytes can improve the safety of lithium ion batteries (LIBs) by increasing the lithium transference number (tLi+) and avoiding the growth of lithium dendrites. Meanwhile, the self-assembled ordered structure of liquid crystal polymer networks (LCNs) can provide specific channels for the ordered transport of Li ions. Herein, single-ion conductive nematic and cholesteric LCN electrolyte membranes (denoted as NLCN-Li and CLCN-Li) were successfully prepared. NLCN-Li was then coated on commercial Celgard 2325 while CLCN-Li was coated on poly(vinylidene fluoride-hexafluoropropylene) film, coupled with plasticizer, to make NLCN-Li/Cel and CLCN-Li/Pv quasi-solid-state electrolyte membranes, respectively. Their electrochemical properties were evaluated, and it was found that they possessed benign thermal stability and electrolyte/electrode compatibility, high tLi+ up to 0.98 and high electrochemical stability window up to 5.2 V. A small amount (0.5M) of extra Li salt added to the plasticizer could improve the ion conductivity from 1.79 × 10-5 to 5.04 × 10-4 S cm-1, while the tLi+ remained 0.85. The assembled LFP|Li batteries also exhibited excellent cycling and rate performances. The orderliness of the LCN layer played an important role in the distribution and movement of Li ions, thereby affecting the Li deposition and growth of Li dendrites. As the first report of nematic and cholesteric LCN single-ion conductors, this work sheds light on the design and fabrication of ordered quasi-solid-state electrolytes for high-performance and safe LIBs.

Dynamic Ion Gels from the Complex Coacervation of Oppositely Charged Poly(ionic liquid)s

A cationic poly(ionic liquid) (PIL) with pendent butyl imidazolium cations and free bis(trifluoromethylsulfonyl)imide (TFSI) anions and an anionic PIL with pendent TFSI anions and free 1-butyl-3-methylimidazolium cations are synthesized by postpolymerization chemical modification and reversible addition-fragmentation chain-transfer radical copolymerization, respectively. Upon mixing solutions of these two PILs in acetone with stoichiometric amounts of ion pairs, ionic exchanges induce coacervation and, after solvent evaporation, lead to the formation of a dynamic ion gel (DIG) and the concomitant release of free [1-methyl-3-butyl imidazolium]TFSI ionic liquid (IL). A comparison of thermal (Tg), ion conducting (σDC), and viscoelastic (elastic moduli (G')) properties for DIGs and their parent polyelectrolytes, as well as extracted and IL-doped DIGs, demonstrates the formation of ionic cross-links and the ability to easily produce polymer electrolytes with enhanced ionic conductivity (σDC up to 4.5 × 10-5 S cm-1 at 30 °C) and higher elastic moduli (G' up to 4 kPa at 25 °C and 1 rad s-1), making them highly desirable in many electrochemical applications, including supercapacitors, soft robotics, electrochromic devices, sensors, and solar cells.

Piperazinium Poly(Ionic Liquid)s as Solid Electrolytes for Lithium Batteries

Poly(ionic liquid)s combine the unique properties of ionic liquids (ILs) within ionic polymers holding significant promise for energy storage applications. It is reported here the synthesis and characterization of a new family of poly(ionic liquid)s synthesized from cationic piperazinium ionic liquid monomers. The cationic poly(acrylamide piperazinium) in combination with sulfonamide anions like bis(trifluoromethanesulfonyl) imide (TFSI) and bis(fluorosulfonyl) imide (FSI) are characterized as solid polymer electrolytes. The polymer electrolytes in combination with pyrrolidonium ILs and LiFSI show high ionic conductivity, 5×10-3 S cm-1 at 100 °C. Piperazinium polymer electrolytes show excellent compatibility with lithium metal reversible plating and stripping at high current density and low temperature 40 °C.

Steric molecular combing effect enables Self-Healing binder for silicon anodes in Lithium-Ion batteries

Silicon is a promising anode material for lithium-ion batteries with its superior capacity. However, the volume change of the silicon anode seriously affects the electrode integrity and cycle stability. The waterborne guar gum (GG) binder has been regarded as one of the most promising binders for Si anodes. Here, a unique steric molecular combing approach based on guar gum, glycerol, and citric acid is proposed to develop a self-healing binder GGC, which would boost the structural stability of electrode materials. The GGC binder is mainly designed to weaken van der Waals' forces between polymers through the plasticizing effect of glycerol, combing and straightening the guar molecular chain of GG, and exposing the guar hydroxyl sites of GG and the carboxyl groups of citric acid. The condensation reaction between the hydroxyl sites of GG and the carboxyl groups of citric acid forms stronger hydrogen bonds, which can help achieve self-healing effect to cope with the severe volume expansion effect of silicone-based materials. Silicon electrode lithium-ion batteries prepared with GGC binders exhibit outstanding electrochemical performance, with a discharge capacity of up to 1579 mAh/g for 1200 cycles at 1 A/g, providing a high capacity retention rate of 96%. This paper demostrates the great potential of GGC binders in realizing electrochemical performance enhancement of silicon anode.

High-mobility organic mixed conductors with a low synthetic complexity index via direct arylation polymerization

Through direct arylation polymerization, a series of mixed ion-electron conducting polymers with a low synthetic complexity index is synthesized. A thieno[3,2-b]thiophene monomer with oligoether side chains is used in direct arylation polymerization together with a wide range of aryl bromides with varying electronic character from electron-donating thiophene to electron-accepting benzothiadiazole. The obtained polymers are less synthetically complex than other mixed ion-electron conducting polymers due to higher yield, fewer synthetic steps and less toxic reagents. Organic electrochemical transistors (OECTs) based on a newly synthesized copolymer comprising thieno[3,2-b]thiophene with oligoether side chains and bithiophene exhibit excellent device performance. A high charge-carrier mobility of up to μ = 1.8 cm2 V-1 s-1 was observed, obtained by dividing the figure of merit [μC*] from OECT measurements by the volumetric capacitance C* from electrochemical impedance spectroscopy, which reached a value of more than 215 F cm-3.

Correlation between Ionic Conductivity and Mechanical Properties of Solid-like PEO-based Polymer Electrolyte

Poly(ethylene glycol) methyl ether methacrylate polymer networks (PEO-based networks), with or without anionic bis(trifluoromethanesulfonyl)imide (TFSI)-grafted groups, are promising electrolytes for Li-metal all solid-state batteries. Nevertheless, there is a need to enhance our current understanding of the physicochemical characteristics of these polymer networks to meet the mechanical and ionic conductivity property requirements for Li battery electrolyte materials. To address this challenge, our goal is to investigate the impact of the cross-linking density of the PEO-based network and the ethylene oxide/lithium ratio on mechanical properties (such as glass transition temperature and storage modulus) and ionic conductivity. We have synthesized a series of cross-linked PEO-based polymers (si-SPE for single ion solid polymer electrolyte) via solvent-free radical copolymerization. These polymers are synthesized by using commercially available lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate (LiMTFSI), poly(ethylene glycol)methyl ether methacrylate (PEGM), and [poly(ethylene glycol) dimethacrylate] (PEGDM). In addition, we have synthesized a series of cross-linked PEO-based polymers (SPE for solid polymer electrolyte) using LiTFSI as the ionic species. Most of the resulting polymer films are amorphous, self-standing, flexible, homogeneous, and thermally stable. Interestingly, our research has revealed a correlation between ionic conductivity and mechanical properties in both the SPE and si-SPE series. Ionic conductivity increases as glass transition temperature, α relaxation temperature, and storage modulus decrease, suggesting that Li+ transport is influenced by polymer chain flexibility and Li+/EO interaction.

Printable Single-Ion Polymer Nanoparticle Electrolytes for Lithium Batteries

New material solutions are searched for the manufacturing and safety of current batteries. Herein, an extrusion printable polymer separator for lithium batteries based on single-ion polymer electrolytes is presented. The polymer electrolytes are based on methacrylic polymeric nanoparticles (NPs) functionalized with a lithium sulfonamide group combined with different organic plasticizers such as sulfolane and carbonates. The synthesis of the polymer NPs is carried out by emulsion copolymerization of methyl methacrylate and lithium sulfonamide methacrylate in the presence of a crosslinker, resulting in particle sizes of less than 30 nm, as shown by electron microscopy. Then polymer electrolytes are prepared by mixing polymer NPs with varying lithium sulfonamide content and different plasticizers such as carbonates and sulfolane. The polymer electrolytes show ionic conductivities between 2.9 × 10-4 and 2.3 × 10-5 S cm-1 at 85 °C with the highest values for the small-sized NPs with the highest lithium content. As a proof-of-concept application, layer-by-layer printing of a sulfolane-based polymer electrolyte is evaluated via direct ink writing directly onto classic battery electrodes. The electrochemical characterization of the printed solid electrolyte indicates favorable properties, ionic conductivity, lithium transfer number, electrochemical stability window, and cyclability in lithium symmetrical cells, to be used in lithium batteries.

Optimizing the Ion Conductivity and Mechanical Stability of Polymer Electrolyte Membranes Designed for Use in Lithium Ion Batteries: Combining Imidazolium-Containing Poly(ionic liquids) and Poly(propylene carbonate)

State-of-the-art Li batteries suffer from serious safety hazards caused by the reactivity of lithium and the flammable nature of liquid electrolytes. This work develops highly efficient solid-state electrolytes consisting of imidazolium-containing polyionic liquids (PILs) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI). By employing PIL/LiTFSI electrolyte membranes blended with poly(propylene carbonate) (PPC), we addressed the problem of combining ionic conductivity and mechanical properties in one material. It was found that PPC acts as a mechanically reinforcing component that does not reduce but even enhances the ionic conductivity. While pure PILs are liquids, the tricomponent PPC/PIL/LiTFSI blends are rubber-like materials with a Young's modulus in the range of 100 MPa. The high mechanical strength of the material enables fabrication of mechanically robust free-standing membranes. The tricomponent PPC/PIL/LiTFSI membranes have an ionic conductivity of 10-6 S·cm-1 at room temperature, exhibiting conductivity that is two orders of magnitude greater than bicomponent PPC/LiTFSI membranes. At 60 °C, the conductivity of PPC/PIL/LiTFSI membranes increases to 10-5 S·cm-1 and further increases to 10-3 S·cm-1 in the presence of plasticizers. Cyclic voltammetry measurements reveal good electrochemical stability of the tricomponent PIL/PPC/LiTFSI membrane that potentially ranges from 0 to 4.5 V vs. Li/Li+. The mechanically reinforced membranes developed in this work are promising electrolytes for potential applications in solid-state batteries.

Binding of Li+ to Negatively Charged and Neutral Ligands in Polymer Electrolytes

Conceptually, single-ion polymer electrolytes (SIPE) with the anion bound to the polymer could solve major issues in Li-ion batteries, but their conductivity is too low. Experimentally, weakly interacting anionic groups have the best conductivity. To provide a theoretical basis for this result, density functional theory calculations of the optimized geometries and energies are performed for charged ligands used in SIPE. Comparison is made to neutral ligands found in dual-ion conductors, which demonstrate higher conductivity. The free energy differences between adding and subtracting a ligand are small enough for the neutral ligands to have the conductivity seen experimentally. However, charged ligands have large barriers, implying that lithium transport will coincide with the slow polymer diffusion, as observed in experiments. Overall, SIPE will require additional solvent to achieve a sufficiently high conductivity. Additionally, the binding of mono- and bidentate geometries varies, providing a simple and clear reason that polarizable force fields are required for detailed interactions.

Toward a molecular understanding of the conductivity of lithium-ion conducting polyanion polymer electrolytes by molecular dynamics simulation

With the improved lithium-ion transference number near unity, the low conductivity of single lithium-ion conducting solid polymer electrolytes (SLIC-SPEs) still hinders their application in high-rate batteries. Though some empirical conclusions on the conducting mechanism of SLIC-SPEs have been obtained, a more comprehensive study on the quantitative relationship between the molecular structure factors and ionic conduction performance is expected. In this study, a model structure that contains adjustable main chain and anion groups in the polyethylene oxide (PEO) matrix was used to clarify the influence of molecular structural factors on ionic conductivity and electrochemical stability of SLIC-SPEs. The anionic group was further disassembled into the intermediate group and end group while the main chain structure was distinguished into different degrees of polymerization and various lengths of the spacers between anions. Therefore, a well-defined molecular structure was employed to describe its relationship with ionic conductivity. In addition, the dissociation degree of salts and mobility of ions changing with the molecular structure were also discussed to explore the fundamental causes of conductivity. It can be concluded that the anion group affects the conductivity mainly via the dissociation degree, while the main chain structure impacts the conductivity by both dissociation degree and mobility.

Applications of Polymer Electrolytes in Lithium-Ion Batteries: A Review

Polymer electrolytes, a type of electrolyte used in lithium-ion batteries, combine polymers and ionic salts. Their integration into lithium-ion batteries has resulted in significant advancements in battery technology, including improved safety, increased capacity, and longer cycle life. This review summarizes the mechanisms governing ion transport mechanism, fundamental characteristics, and preparation methods of different types of polymer electrolytes, including solid polymer electrolytes and gel polymer electrolytes. Furthermore, this work explores recent advancements in non-aqueous Li-based battery systems, where polymer electrolytes lead to inherent performance improvements. These battery systems encompass Li-ion polymer batteries, Li-ion solid-state batteries, Li-air batteries, Li-metal batteries, and Li-sulfur batteries. Notably, the advantages of polymer electrolytes extend beyond enhancing safety. This review also highlights the remaining challenges and provides future perspectives, aiming to propose strategies for developing novel polymer electrolytes for high-performance Li-based batteries.

A New Method to Prepare Stable Polyaniline Dispersions for Highly Loaded Cathodes of All-Polymer Li-Ion Batteries

A new method for the preparation of polyaniline (PANI) films that have a 2D structure and can record high active mass loading (up to 30 mg cm^-2) via acid-assisted polymerization in the presence of concentrated formic acid was developed. This new approach represents a simple reaction pathway that proceeds quickly at room temperature in quantitative isolated yield with the absence of any byproducts and leads to the formation of a stable suspension that can be stored for a prolonged time without sedimentation. The observed stability was explained by two factors: (a) the small size of the obtained rod-like particles (50 nm) and (b) the change of the surface of colloidal PANI particles to a positively charged form by protonation with concentrated formic acid. The films cast from the concentrated suspension were composed of amorphous PANI chains assembled into 2D structures with nanofibrillar morphology. Such PANI films demonstrated fast and efficient diffusion of the ions in liquid electrolyte and showed a pair of revisable oxidation and reduction peaks in cyclic voltammetry. Furthermore, owing to the high mass loading, specific morphology, and porosity, the synthesized polyaniline film was impregnated by a single-ion conducting polyelectrolyte-poly(LiM_n-r-PEGM_m) and characterized as a novel lightweight all-polymeric cathode material for solid-state Li batteries by cyclic voltammetry and electrochemical impedance spectroscopy techniques.

Mechanically Robust Poly(ionic liquid) Block Copolymers as Self-Assembling Gating Materials for Single-Walled Carbon-Nanotube-Based Thin-Film Transistors

The proliferation of high-performance thin-film electronics depends on the development of highly conductive solid-state polymeric materials. We report on the synthesis and properties investigation of well-defined cationic and anionic poly(ionic liquid) AB-C type block copolymers, where the AB block was formed by random copolymerization of highly conductive anionic or cationic monomers with poly(ethylene glycol) methyl ether methacrylate, while the C block was obtained by post-polymerization of 2-phenylethyl methacrylate. The resulting ionic block copolymers were found to self-assemble into a lamellar morphology, exhibiting high ionic conductivity (up to 3.6 × 10^-6 S cm^-1 at 25 °C) and sufficient electrochemical stability (up to 3.4 V vs Ag⁺/Ag at 25 °C) as well as enhanced viscoelastic (mechanical) performance (storage modulus up to 3.8 × 10⁵ Pa). The polymers were then tested as separators in two all-solid-state electrochemical devices: parallel plate metal-insulator-metal (MIM) capacitors and thin-film transistors (TFTs). The laboratory-scale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼10³ Hz and high areal capacitance (up to 17.2 μF cm^-2). For solid-state TFTs, low hysteresis was observed at 10 Hz due to the completion of EDL formation and the devices were found to have low threshold voltages of -0.3 and 1.1 V for p-type and n-type operations, respectively.

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

PEO-Based Block Copolymer Electrolytes Containing Double Conductive Phases with Improved Mechanical and Electrochemical Properties

In this work, the advanced all solid-state block copolymer electrolytes (SBCPEs) for lithium-ion batteries with double conductive phases, poly(ethylene oxide)-b-poly(trimethyl-N-((2-(dimethylamino)ethyl methacrylate)-7-propyl)-ammonium bis(trifluoromethanesulfonyl) imide) (PEO-b-PDM-dTFSI)/LiTFSI, were fabricated, in which the charged PDM-dTFSI block contained double quaternary ammonium cations and the PEO block was doped with LiTFSI. The disordered (DIS) and ordered lamellae (LAM) phase structures were achieved by adjusting the composition of the block copolymer and the doping ratio r. In addition, the presence of the hard PDM-dTFSI block and the formation of the LAM phase structure resulted in a good mechanical strength of the solid PEO-b-PDM-dTFSI/LiTFSI electrolyte, and it could maintain a high level of 10⁴ Pa at 100 °C, which was around 10,000 times stronger than that of the PEO/LiTFSI electrolyte. Based on the good mechanical and electrochemical properties, the PEO-b-PDM-dTFSI/LiTFSI SBCPE exhibited excellent long-term galvanostatic cycle performance, indicating the strong ability to suppress lithium dendrites.

Electrochemical and Ion Transport Studies of Li+ Ion-Conducting MC-Based Biopolymer Blend Electrolytes

A facile methodology system for synthesizing solid polymer electrolytes (SPEs) based on methylcellulose, dextran, lithium perchlorate (as ionic sources), and glycerol (such as a plasticizer) (MC:Dex:LiClO₄:Glycerol) has been implemented. Fourier transform infrared spectroscopy (FTIR) and two imperative electrochemical techniques, including linear sweep voltammetry (LSV) and electrical impedance spectroscopy (EIS), were performed on the films to analyze their structural and electrical properties. The FTIR spectra verify the interactions between the electrolyte components. Following this, a further calculation was performed to determine free ions (FI) and contact ion pairs (CIP) from the deconvolution of the peak associated with the anion. It is verified that the electrolyte containing the highest amount of glycerol plasticizer (MDLG3) has shown a maximum conductivity of 1.45 × 10⁻³ S cm⁻¹. Moreover, for other transport parameters, the mobility (μ), number density (n), and diffusion coefficient (D) of ions were enhanced effectively. The transference number measurement (TNM) of electrons (t_el) was 0.024 and 0.976 corresponding to ions (t_ion). One of the prepared samples (MDLG3) had 3.0 V as the voltage stability of the electrolyte.

Phase behavior of binary and ternary fluoropolymer (PVDF-HFP) solutions for single-ion conductors

A fluoropolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) has a dielectric constant of ∼11, providing charge screening effects. Hence, this highly polar PVDF-HFP material has been employed as a matrix for solid polymer electrolytes (SPEs). In this study, the phase behavior of binary PVDF-HFP solutions was analyzed using the Flory-Huggins theory, in which ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, and acetone were employed as model solvents. In particular, for the binary PVDF-HFP/acetone system, the solid-liquid and liquid-liquid phase transitions were qualitatively described. Then, the phase diagram for ternary acetone/PVDF-HFP/polyphenolate systems was constructed, in which the binodal, spinodal, tie-line, and critical point were included. Finally, when a polyelectrolyte lithium polyphenolate was mixed with the PVDF-HFP matrix, it formed a single-ion conductor with a Li⁺ transference number of 0.8 at 23 °C. In the case of ionic conductivity, it was ∼10^-5 S cm^-1 in solid state and ∼10^-4 S cm^-1 in gel state, respectively.

Combining Organic Plastic Salts with a Bicontinuous Electrospun PVDF-HFP/Li7La3Zr2O12 Membrane: LiF-Rich Solid-Electrolyte Interphase Enabling Stable Solid-State Lithium Metal Batteries

Solid-state electrolytes can guarantee the safe operation of high-energy density lithium metal batteries (LMBs). However, major challenges still persist with LMBs due to the use of solid electrolytes, that is, poor ionic conductivity and poor compatibility at the electrolyte/electrode interface, which reduces the operational stability of solid-state LMBs. Herein, a novel fiber-network-reinforced composite polymer electrolyte (CPE) was designed by combining an organic plastic salt (OPS) with a bicontinuous electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/Li₇La₃Zr₂O₁₂ (LLZO) membrane. The presence of LLZO in the composite helps to promote the dissociation of FSI^- from OPSs. Subsequently, the dissociated FSI^- is then involved in the formation of a LiF-rich solid electrolyte interphase (SEI) layer on the lithium anode via a reductive decomposition reaction, which was affirmed by theoretical calculations and experimental results. Due to the LiF-rich SEI layer, the Li/Li symmetric cell was able to demonstrate a long cyclic life of over 2600 h at a current density of 0.1 mA cm^-2. More importantly, the as-prepared CPE achieved a high ionic conductivity of 2.8 × 10^-4 S cm^-1 at 25 °C, and the Li/LiFePO₄ cell based on the CPE exhibited a high discharge capacity and 83.3% capacity retention after 500 cycles at 1.0 C. Thus, the strategy proposed in this work can inspire the future development of highly conductive solid electrolytes and compatible interface designs toward high-energy density solid-state LMBs.

Cation effect on ionic liquid-involved polymer electrolytes for solid-state lithium metal batteries

The effect of ionic liquids with varied cations on the electrochemical performance of Li/LiFePO4 batteries is investigated in terms of cationic solvation.

Poly(ethylene glycol) Diacrylate Iongel Membranes Reinforced with Nanoclays for CO2 Separation

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to improve the mechanical properties of iongel membranes, which consists in the incorporation of montmorillonite (MMT) nanoclay, from 0.2 to 7.5 wt%, into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) network containing 60 wt% of the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][TFSI]). The iongels were prepared by a simple one-pot method using ultraviolet (UV) initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) and characterized by several techniques to assess their physico-chemical properties. The thermal stability of the iongels was influenced by the addition of higher MMT contents (>5 wt%). It was possible to improve both puncture strength and elongation at break with MMT contents up to 1 wt%. Furthermore, the highest ideal gas selectivities were achieved for iongels containing 0.5 wt% MMT, while the highest CO2 permeability was observed at 7.5 wt% MMT content, due to an increase in diffusivity. Remarkably, this strategy allowed for the preparation and gas permeation of self-standing iongel containing 80 wt% IL, which had not been possible up until now.

Single-Ion Lithium Conducting Polymers with High Ionic Conductivity Based on Borate Pendant Groups

A family of single‐ion lithium conducting polymer electrolytes based on highly delocalized borate groups is reported. The effect of the nature of the substituents on the boron atom on the ionic conductivity of the resultant methacrylic polymers was analyzed. To the best of our knowledge the lithium borate polymers endowed with flexible and electron‐withdrawing substituents presents the highest ionic conductivity reported for a lithium single‐ion conducting homopolymer (1.65×10⁻⁴ S cm⁻¹ at 60 °C). This together with its high lithium transference number tLi+ =0.93 and electrochemical stability window of 4.2 V vs Li⁰/Li⁺ show promise for application in lithium batteries. To illustrate this, a lithium borate monomer was integrated into a single‐ion gel polymer electrolyte which showed good performance on lithium symmetrical cells (<0.85 V at ±0.2 mA cm⁻² for 175 h).

Ionic Covalent Organic Frameworks for Energy Devices

Covalent organic frameworks (COFs) are a class of porous crystalline materials whose facile preparation, functionality, and modularity have led to their becoming powerful platforms for the development of molecular devices in many fields of (bio)engineering, such as energy storage, environmental remediation, drug delivery, and catalysis. In particular, ionic COFs (iCOFs) are highly useful for constructing energy devices, as their ionic functional groups can transport ions efficiently, and the nonlabile and highly ordered all-covalent pore structures of their backbones provide ideal pathways for long-term ionic transport under harsh electrochemical conditions. Here, current research progress on the use of iCOFs for energy devices, specifically lithium-based batteries and fuel cells, is reviewed in terms of iCOF backbone-design strategies, synthetic approaches, properties, engineering techniques, and applications. iCOFs are categorized as anionic COFs or cationic COFs, and how each of these types of iCOFs transport lithium ions, protons, or hydroxides is illustrated. Finally, the current challenges to and future opportunities for the utilization of iCOFs in energy devices are described. This review will therefore serve as a useful reference on state-of-the-art iCOF design and application strategies focusing on energy devices.

Development and Progression of Polymer Electrolytes for Batteries: Influence of Structure and Chemistry

Polymer electrolytes continue to offer the opportunity for safer, high-performing next-generation battery technology. The benefits of a polymeric electrolyte system lie in its ease of processing and flexibility, while ion transport and mechanical strength have been highlighted for improvement. This report discusses how factors, specifically the chemistry and structure of the polymers, have driven the progression of these materials from the early days of PEO. The introduction of ionic polymers has led to advances in ionic conductivity while the use of block copolymers has also increased the mechanical properties and provided more flexibility in solid polymer electrolyte development. The combination of these two, ionic block copolymer materials, are still in their early stages but offer exciting possibilities for the future of this field.

Block copolymers as (single-ion conducting) lithium battery electrolytes

Solid-state batteries are considered the next big step towards the realization of intrinsically safer high-energy lithium batteries for the steadily increasing implementation of this technology in electronic devices and particularly, electric vehicles. However, so far only electrolytes based on poly(ethylene oxide) have been successfully commercialized despite their limited stability towards oxidation and low ionic conductivity at room temperature. Block copolymer (BCP) electrolytes are believed to provide significant advantages thanks to their tailorable properties. Thus, research activities in this field have been continuously expanding in recent years with great progress to enhance their performance and deepen the understanding towards the interplay between their chemistry, structure, electrochemical properties, and charge transport mechanism. Herein, we review this progress with a specific focus on the block-copolymer nanostructure and ionic conductivity, the latest works, as well as the early studies that are fr"equently overlooked by researchers newly entering this field. Moreover, we discuss the impact of adding a lithium salt in comparison to single-ion conducting BCP electrolytes along with the encouraging features of these materials and the remaining challenges that are yet to be solved.

Unraveling the Role of Neutral Units for Single-Ion Conducting Polymer Electrolytes

With the cationic transference number close to unity, single-ion conducting polymer electrolytes (SICPEs) are recognized as an advanced electrolyte system with improved energy efficiency for battery application. The relatively low ionic conductivity for most of the SICPEs in comparison with liquid electrolytes remains the major "bottleneck" for their practical applications. Polyethylene oxide (PEO) has been recognized as a benchmark for solid polymer electrolytes due to its high salt solubility and reasonable ionic conductivity. PEO has two advantages: (i) the polar ether groups coordinate well with lithium ions (Li⁺) providing good dissociation from anions, and (ii) the low T_g provides fast segmental dynamics at ambient temperature and assists rapid charge transport. These properties lead to active use of PEO as neutral plasticizing units in SICPEs. Herein, we present a detailed comparison of new SICPEs copolymerized with PEO units vs SICPEs copolymerized with other types of neutral units possessing either flexible or polar structures. The presented analysis revealed that the polarity of side chains has a limited influence on ion dissociation for copolymer-type SICPEs. The Li⁺-ion dissociation seems to be controlled by the charge delocalization on the polymerized anion. With good miscibility between plasticizing neutral units and ionic conductive units, the ambient ionic conductivity of synthesized SICPEs is still mainly controlled by the T_g of the copolymer. This work sheds light on the dominating role of PEO in SICPE systems and provides helpful guidance for designing polymer electrolytes with new functionalities and structures. Furthermore, based on the presented results, we propose that designing polyanions with a highly delocalized charge may be another promising route for achieving sufficient lithium ionic conductivity in solvent-free SICPEs.

Single-ion conducting polymer electrolytes as a key jigsaw piece for next-generation battery applications

As lithium-ion batteries have been the state-of-the-art electrochemical energy storage technology, the overwhelming demand for energy storage on a larger scale has triggered the development of next-generation battery technologies possessing high energy density, longer cycle lives, and enhanced safety. However, commercial liquid electrolytes have been plagued by safety issues due to their flammability and instability in contact with electrodes. Efforts have focused on developing such electrolytes by covalently immobilizing anionic groups onto a polymer backbone, which only allows Li+ cations to be mobile through the polymer matrix. Such ion-selective polymers provide many advantages over binary ionic conductors in battery operation, such as minimization of cell polarization and dendrite growth. In this review, the design, synthesis, fabrication, and class are reviewed to give insight into the physicochemical properties of single-ion conducting polymer electrolytes. The standard characterization method and remarkable electrochemical properties are further highlighted, and perspectives on current challenges and future directions are also discussed.

Lithium-Conducting Branched Polymers: New Paradigm of Solid-State Electrolytes for Batteries

The past decades have witnessed rapid development of lithium-based batteries. Significant research efforts have been progressively diverted from electrodes to electrolytes, particularly polymer electrolytes (PEs), to tackle the safety concern and promote the energy storage capability of batteries. To further increase the ionic conductivity of PEs, various branched polymers (BPs) have been rationally designed and synthesized. Compared with linear polymers, branched architectures effectively increase polymer segmental mobility, restrain crystallization, and reduce chain entanglement, thereby rendering BPs with greatly enhanced lithium transport. In this Mini Review, a diversity of BPs for PEs is summarized by scrutinizing their unique topologies and properties. Subsequently, the design principles for enhancing the physical properties, mechanical properties, and electrochemical performance of BP-based PEs (BP-PEs) are provided in which the ionic conduction is particularly examined in light of the Li⁺ transport mechanism. Finally, the challenges and future prospects of BP-PEs in this rapidly evolving field are outlined.

UV-Cured Cross-Linked Astounding Conductive Polymer Electrolyte for Safe and High-Performance Li-Ion Batteries

UV-cured cross-linked polymer electrolytes are promising electrolytes for safe Li-ion batteries (LIBs) application due to their excellent conduction ability, low glass-transition temperature (T_g), and high discharge capacity. Herein, we have prepared novel fluorosulfonylimide methacrylic-based cross-linked polymer electrolyte membranes for LIBs via UV-curing process, which is a well-known, easy, low-cost, fast, and reliable technique. The synthesized UV-reactive novel methacrylate monomer with directly attached fluorosulfonylimide functional group methacryloylcarbamoyl sulfamoyl fluoride (MACSF) was used as a precursor for UV curing along with poly(ethylene glycol) dimethacrylate (PEGDMA) and lithium bis(fluorosulfonyl)imide (LiFSI). The results demonstrated that the cross-linked membrane with an optimized amount (30 wt %) of MACSF monomer (noted as CPE-3) showed the best performance. The nonflammable fluorosulfonyl group (a hydrophilic group of MACSF monomer) in the polymer matrix formed a wide channel, as a result of which Li ion can migrate easily via forming an ionic linkage. The CPE-3 electrolyte exhibited a low T_g (-79 °C), excellent phase separation, high conductivity (σ) (ca. 3.5 × 10^-4 and 8.50 × 10^-3 S·cm^-1 at 30 and 80 °C, respectively), and high flame retardancy. The battery performance of half-cell (LiFePO₄/CPE-3/Li) and full cell (LiFePO₄/CPE-3/graphite) with CPE-3 electrolyte were attractive: discharge capacities (155 and 152 mAh/g) with the capacity retentions of 96.17 and 95.17% after 500 cycles at 0.1 C rate for half-cell and full-cell LIBs, respectively.

Unique Carbonate-Based Single Ion Conducting Block Copolymers Enabling High-Voltage, All-Solid-State Lithium Metal Batteries

Safety and high-voltage operation are key metrics for advanced, solid-state energy storage devices to power low- or zero-emission HEV or EV vehicles. In this study, we propose the modification of single-ion conducting polyelectrolytes by designing novel block copolymers, which combine one block responsible for high ionic conductivity and the second block for improved mechanical properties and outstanding electrochemical stability. To synthesize such block copolymers, the ring opening polymerization (ROP) of trimethylene carbonate (TMC) monomer by the RAFT-agent having a terminal hydroxyl group is used. It allows for the preparation of a poly(carbonate) macro-RAFT precursor that is subsequently applied in RAFT copolymerization of lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethylsulfonyl)imide and poly(ethylene glycol) methyl ether methacrylate. The resulting single-ion conducting block copolymers show improved viscoelastic properties, good thermal stability (T onset up to 155 °C), sufficient ionic conductivity (up to 3.7 × 10-6 S cm-1 at 70 °C), and high lithium-ion transference number (0.91) to enable high power. Excellent plating/stripping ability with resistance to dendrite growth and outstanding electrochemical stability window (exceeding 4.8 V vs Li+/Li at 70 °C) are also achieved, along with enhanced compatibility with composite cathodes, both LiNiMnCoO2 - NMC and LiFePO4 - LFP, as well as the lithium metal anode. Lab-scale truly solid-state Li/LFP and Li/NMC lithium-metal cells assembled with the single-ion copolymer electrolyte demonstrate reversible and very stable cycling at 70 °C delivering high specific capacity (up to 145 and 118 mAh g-1, respectively, at a C/20 rate) and proper operation even at a higher current regime. Remarkably, the addition of a little amount of propylene carbonate (∼8 wt %) allows for stable, highly reversible cycling at a higher C-rate. These results represent an excellent achievement for a truly single-ion conducting solid-state polymer electrolyte, placing the obtained ionic block copolymers on top of polyelectrolytes with highest electrochemical stability and potentially enabling safe, practical Li-metal cells operating at high-voltage.

Cation-Assisted Lithium-Ion Transport for High-Performance PEO-based Ternary Solid Polymer Electrolytes

N-alkyl-N-alkyl pyrrolidinium-based ionic liquids (ILs) are promising candidates as non-flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs), but they present limitations in terms of lithium-ion transport, such as a much lower lithium transference number. Thus, a pyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units. We show, by a combination of experimental characterizations and simulations, that the cation's solvating properties allow faster lithium-ion transport than alkyl-substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO, but also by enabling new conduction modes linked to the solvation of lithium by a single IL cation. This, combined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium-metal polymer batteries.

Self-Healable, Recyclable, and Ultrastrong Adhesive Ionogel for Multifunctional Strain Sensor

Flexible electronic materials have aroused significant interest due to the need for flexible electronics in a variety of applications. However, several obstacles such as low mechanical properties, interfacial adhesion problems, and nonreusability hinder their rapid development. Here, an ionogel was developed by a one-step photopolymerization of an ionic liquid (IL) with the C═C bond of 1-vinyl-3-butylimidazolium tetrafluoroborate in another ionic liquid solution of 1-butyl-3-methylimidazolium tetrafluoroborate without a chemical cross-linker. The poly(ionic liquid) and the ionic liquid (PIL/IL) were highly compatible and resulted in an extremely uniform, stable, and optically transparent PIL/IL ionogel. In addition, this method also avoided complicated solvent replacement in the preparation processes of common ionogels. Our experimental and theoretical results showed that the reported ionogel integrated excellent mechanical properties, ultrastrong adhesive, self-healability, and recyclability. These remarkable advantages were benefited from the strong electrostatic force and other noncovalent bond interactions in the ionogel system. The unique ionogel presented in this study is therefore an ideal candidate material for self-adhesive and reusable wearable electronics.

Solid Polymer Electrolytes with High Conductivity and Transference Number of Li Ions for Li-Based Rechargeable Batteries

Smart electronics and wearable devices require batteries with increased energy density, enhanced safety, and improved mechanical flexibility. However, current state-of-the-art Li-based rechargeable batteries (LBRBs) use highly reactive and flowable liquid electrolytes, severely limiting their ability to meet the above requirements. Therefore, solid polymer electrolytes (SPEs) are introduced to tackle the issues of liquid electrolytes. Nevertheless, due to their low Li⁺ conductivity and Li⁺ transference number (LITN) (around 10^-5 S cm^-1 and 0.5, respectively), SPE-based room temperature LBRBs are still in their early stages of development. This paper reviews the principles of Li⁺ conduction inside SPEs and the corresponding strategies to improve the Li⁺ conductivity and LITN of SPEs. Some representative applications of SPEs in high-energy density, safe, and flexible LBRBs are then introduced and prospected.

100th Anniversary of Macromolecular Science Viewpoint: Solid Polymer Electrolytes in Cathode Electrodes for Lithium Batteries. Current Challenges and Future Opportunities

Solid polymer electrolytes (SPEs) are an important class of ion-transporting materials for enabling safe and high-energy-density all-solid lithium batteries. Within the composite cathode electrode (CCE), an SPE plays a critical role as both binder material for mechanical integrity and electrolyte to facilitate ion transport. The inclusion of an SPE within the CCE leads to the formation of distinctive heterogeneous SPE/solid interfaces that are not present in traditional liquid electrolyte-containing CCE. Here, the viewpoint emphasizes the importance of understanding the interfacial behavior of SPEs in all-solid CCEs. Challenges and opportunities are highlighted in achieving and maintaining good interfacial contact, and the role of interfacial dynamics and nanoconfinement on ion transport. Additionally, routes to achieving high-voltage electrochemical stability through stabilization of interfaces and the development of SPEs with inherently higher oxidative stability are discussed. SPEs with high-voltage stability will provide a pathway to using cathode active materials operating at 4.5 V versus Li/Li⁺ and beyond, which are essential to attaining next-generation higher-energy batteries. Overall, the viewpoint clarifies the importance of targeted research and development of SPEs for enabling all-solid CCEs for lithium batteries.