Review on composite polymer electrolytes for lithium batteries

Polymer-Ion Interaction Prompted Quasi-Solid Electrolyte for Room-Temperature High-Performance Lithium-Ion Batteries

Lithium-ion batteries using quasi-solid gel electrolytes (QSEs) have gained increasing interest due to their enhanced safety features. However, their commercial viability is hindered by low ionic conductivity and poor solid-solid contact interfaces. In this study, a QSE synthesized by in situ polymerizing methyl methacrylate (MMA) in 1,2-dimethoxyethane (DME)-based electrolyte is introduced, which exhibits remarkable performance in high-loading graphite||LiNi0.8Co0.1Mn0.1O2 (NCM811) pouch cells. Owing to the unique solvent-lacking solvation structure, the graphite exfoliation caused by the well-known solvent co-intercalation is prohibited, and this unprecedented phenomenon is found to be universal for other graphite-unfriendly solvents. The high ionic conductivity and great interfacial contact provided by DME enable the quasi-solid graphite||NCM811 pouch cell to demonstrate superior C-rate capability even at a high cathode mass loading (17.5 mg cm-2), surpassing liquid carbonate electrolyte cells. Meanwhile, the optimized QSE based on carbonates exhibits excellent cycle life (92.4% capacity retention after 1700 cycles at 0.5C/0.5C) and reliable safety under harsh conditions. It also outperforms liquid electrolytes in other high-energy-density batteries with larger volume change. These findings elucidate the polymer's pivotal role in QSEs, offering new insights for advancing quasi-solid-state battery commercialization.

Effect of a Polypropylene Separator with a Thin Electrospun Ceramic/Polymer Coating on the Thermal and Electrochemical Properties of Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are well known for their energy efficiency and environmental benefits. However, increasing their energy density compromises their safety. This study introduces a novel ceramic-coated separator to enhance the performance and safety of LIBs. Electrospinning was used to apply a coating consisting of an alumina (Al2O3) ceramic and polyacrylic acid (PAA) binder to a polypropylene (PP) separator to significantly improve the mechanical properties of the PP separator and, ultimately, the electrochemical properties of the battery cell. Tests with 2032-coin cells showed that the efficiency of cells containing separators coated with 0.5 g PAA/Al2O3 was approximately 10.2% higher at high current rates (C-rates) compared to cells with the bare PP separator. Open circuit voltage (OCV) tests revealed superior thermal safety, with bare PP separators maintaining stability for 453 s, whereas the cells equipped with PP separators coated with 4 g PAA/Al2O3 remained stable for 937 s. The elongation increased from 88.3% (bare PP separator) to 129.1% (PP separator coated with 4 g PAA/Al2O3), and thermal shrinkage decreased from 58.2% to 34.9%. These findings suggest that ceramic/PAA-coated separators significantly contribute to enhancing the thermal safety and capacity retention of high-energy-density LIBs.

Advancements in Polyethylene Oxide (PEO)-Active Filler Composite Polymer Electrolytes for Lithium-Ion Batteries: A Comprehensive Review and Prospects

Polyethylene oxide (PEO) has become a highly sought-after polymer electrolyte for lithium-ion batteries (LIBs) due to its high ionic conductivity, strong mechanical properties, and broad electrochemical stability range. However, its usefulness is hindered by its limited ionic conductivity at typical temperatures (<60 °C). Many researchers have delved into the integration of active fillers into the PEO matrix to improve the ionic conductivity and overall efficiency of composite polymer electrolytes (CPEs) for LIBs. This review delves deeply into the latest developments and insights in CPEs for LIBs, focusing on the role of PEO-active filler composites. It explores the impact of different types and morphologies of active fillers on the electrochemical behavior of CPEs. Additionally, it explores the mechanisms that contribute to the improved ionic conductivity and Li-ion transport in PEO-based CPEs. This paper also emphasizes the present obstacles and prospects in the advancement of CPEs containing PEO-active filler composites for LIBs. It serves as a valuable reference for scientists and engineers engaged in the domain of advanced energy storage systems, offering insights for the forthcoming development and enhancement of CPEs to achieve superior performance in LIBs.

Research Progress on the Composite Methods of Composite Electrolytes for Solid-State Lithium Batteries

In the current challenging energy storage and conversion landscape, solid-state lithium metal batteries with high energy conversion efficiency, high energy density, and high safety stand out. Due to the limitations of material properties, it is difficult to achieve the ideal requirements of solid electrolytes with a single-phase electrolyte. A composite solid electrolyte is composed of two or more different materials. Composite electrolytes can simultaneously offer the advantages of multiple materials. Through different composite methods, the merits of various materials can be incorporated into the most essential part of the battery in a specific form. Currently, more and more researchers are focusing on composite methods for combining components in composite electrolytes. The ion transport capacity, interface stability, machinability, and safety of electrolytes can be significantly improved by selecting appropriate composite methods. This review summarizes the composite methods used for the components of composite electrolytes, such as filler blending, embedded framework, and multilayer bonding. It also discusses the future development trends of all-solid-state lithium batteries (ASSLBs).

Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

Building Smarter Aqueous Batteries

Amidst the global trend of advancing renewable energies toward carbon neutrality, energy storage becomes increasingly critical due to the intermittency of renewables. As an alternative to lithium-ion batteries (LIBs), aqueous batteries have received growing attention for large-scale energy storage due to their economical and safe features. Despite the fruitful achievements at the material level, the reliability and lifetime of aqueous batteries are still far from satisfactory. Alike LIBs, integrating smartness is essential for more reliable and long-life aqueous batteries via operando monitoring and automatic response to extreme abuses. In this review, recent advances in sensing techniques and multifunctional battery-sensor systems together with self-healing methods in aqueous batteries is summarized. The significant role of artificial intelligence in designing and optimizing aqueous batteries with high efficiency is also highlighted. Ultimately, it is extrapolated toward the future and present the humble perspective for building smarter aqueous batteries.

Self-reporting and Biodegradable Thermosetting Solid Polymer Electrolyte

To date, significant efforts have been dedicated to improve their ionic conductivity, thermal stability, and mechanical strength of solid polymer electrolytes (SPEs). However, direct monitoring of physical and chemical changes in SPEs is still lacking. Moreover, existing thermosetting SPEs are hardly degradable. Herein, by overcoming the limitation predicted by Flory theory, self-reporting and biodegradable thermosetting hyperbranched poly(β-amino ester)-based SPEs (HPAE-SPEs) are reported. HPAE is successfully synthesized through a well-controlled "A2+B4" Michael addition strategy and then crosslinked it in situ to produce HPAE-SPEs. The multiple tertiary aliphatic amines at the branching sites confer multicolour luminescence to HPAE-SPEs, enabling direct observation of its physical and chemical damage. After use, HPAE-SPEs can be rapidly hydrolysed into non-hazardous β-amino acids and polyols via self-catalysis. Optimized HPAE-SPE exhibits an ionic conductivity of 1.3×10-4  S/cm at 60 °C, a Na+ transference number (t N a + ${{t}_{Na}^{+}}$ ) of 0.67, a highly stable sodium plating-stripping behaviour and a low overpotential of ≈190 mV. This study establishes a new paradigm for developing SPEs by engineering multifunctional polymers. The self-reporting and biodegradable properties would greatly expand the scope of applications for SPEs.

Revealing the role of hydrogen bond coupling structure for enhanced performance of the solid-state electrolyte

Achieving practical applications of PEO-based composite solid electrolyte (CPE) batteries requires the precise design of filler structures at the molecular level to form stable composite interfacial phases, which in turn improve the conductivity of Li+ and inhibit the nucleation growth of lithium dendrites. Some functional fillers suffer from severe agglomeration due to poor compatibility with the polymer base or grain boundary migration, resulting in limited improvement in cell performance. In this paper, ILs@KAP1 is reported as a filler to enhance the performance of PEO-based batteries. Thereinto, the hypercrosslinked phosphorus ligand polymer-containing KAP1, designed at the molecular level, has an abundant porous structure, hydrogen bonding network, and a rigid skeleton structure of benzene rings. These can be used both to improve the flammability with PEO-based and to reduce the crystallinity of the polymer electrolyte. Ionic liquids (ILs) are encapsulated in the nanochannels of KAP1, and thus a 3D Li+ conducting framework could be formed. In this case, it could not only facilitate the wettability of the contact interface with the electrode, significantly promoting its compatibility and providing a fast Li+ transport path, but also facilitate the formation of LiF, Li3N and Li2O rich SEI components, further fostering the uniform deposition/exfoliation of lithium. The LFP||CPE||Li battery assembled with ILs@KAP1-PEO-CPE has a high initial discharge specific capacity about 156 mAh/g at 1C and a remaining capacity about 121.8 mAh/g after 300 cycles (capacity retention of 78.07%).

Targeted release of soybean peptide from CMC/PVA hydrogels in simulated intestinal fluid and their pharmacokinetics

Carboxymethyl cellulose (CMC)/polyvinyl alcohol (PVA) hydrogels loaded with soybean peptide (SPE) were fabricated via a freeze-thaw method. These hydrogels conquer barriers in simulated gastric fluid (SGF), and then release SPE in simulated intestinal fluid (SIF). The results of in vitro SPE release from these hydrogels showed that in SGF only a little of the SPE released, but in SIF the SPE was completely released. The released SPE had scavenging rates for DPPH and ABTS free radicals of 41.68 and 31.43 %. The pharmacokinetic model of SPE release from the hydrogels in SIF was studied. When the hydrogels are moved from SGF to SIF, the sorption of the shrinkage hydrogel network is entirely controlled by stress-induced relaxations. There are swollen and shrunken regions during SPE release. For SPE release into the SIF, SPE has to be freed from the weak bonds in the swollen regions by changes in the conformation of CMC and PVA. The release rate of SPE was found to be governed by the diffusion and swelling rate of the shrinkage hydrogel network. The Korsmeyer-Peppas equation diffusion exponents (n) for SPE release from the hydrogels are >2.063, indicating a super case II transport. These data demonstrate CMC/PVA hydrogels have potential applications in oral peptide delivery.

Correlating Nanoscale Structures with Electrochemical Properties of Solid Electrolyte Interphases in Solid-State Battery Electrodes

Here, we investigate the nonlinear relationship between the content of solid electrolytes in composite electrodes and the irreversible capacity via the degree of nanoscale uniformity of the surface morphology and chemical composition of the solid electrolyte interphase (SEI) layer. Using electrochemical strain microscopy (ESM) and X-ray photoelectron spectroscopy (XPS), changes of the chemical composition and morphology (Li and F distribution) in SEI layers on the electrodes as a function of solid electrolyte contents are analyzed. As a result, we find that the solid electrolyte content affects the variation of the SEI layer thickness and chemical distributions of Li and F ions in the SEI layer, which, in turn, influence the Coulombic efficiency. This correlation determines the composition of the composite electrode surface that can maximize the physical and chemical uniformity of the solid electrolyte on the electrode, which is a key parameter to increase electrochemical performance in solid-state batteries.

Recent Development in Topological Polymer Electrolytes for Rechargeable Lithium Batteries

Solid polymer electrolytes (SPEs) are still being considered as a candidate to replace liquid electrolytes for high-safety and flexible lithium batteries due to their superiorities including light-weight, good flexibility, and shape versatility. However, inefficient ion transportation of linear polymer electrolytes is still the biggest challenge. To improve ion transport capacity, developing novel polymer electrolytes are supposed to be an effective strategy. Nonlinear topological structures such as hyperbranched, star-shaped, comb-like, and brush-like types have highly branched features. Compared with linear polymer electrolytes, topological polymer electrolytes possess more functional groups, lower crystallization, glass transition temperature, and better solubility. Especially, a large number of functional groups are beneficial to dissociation of lithium salt for improving the ion conductivity. Furthermore, topological polymers have strong design ability to meet the requirements of comprehensive performances of SPEs. In this review, the recent development in topological polymer electrolytes is summarized and their design thought is analyzed. Outlooks are also provided for the development of future SPEs. It is expected that this review can raise a strong interest in the structural design of advanced polymer electrolyte, which can give inspirations for future research on novel SPEs and promote the development of next-generation high-safety flexible energy storage devices.

Polypropylene carbonate-based electrolytes as model for a different approach towards improved ion transport properties for novel electrolytes

Linear poly(alkylene carbonates) such as polyethylene carbonate (PEC) and polypropylene carbonate (PPC) have gained increasing interest due to their remarkable ion transport properties such as high Li⁺ transference numbers. The cause of these properties is not yet fully understood which makes it challenging to replicate them in other polymer electrolytes. Therefore, it is critical to understand the underlying mechanisms in polycarbonate electrolytes such as PPC. In this work we present insights from impedance spectroscopy, transference number measurements, PFG-NMR, IR and Raman spectroscopy as well as molecular dynamics simulations to address this issue. We find that in addition to plasticization, the lithium ion coordination by the carbonate groups of the polymer is weakened upon gelation, leading to a rapid exhange of the lithium ion solvation shell and consequently a strong increase of the conductivity. Moreover, we study the impact of the anions by employing different conducting salts. Interestingly, while the total conductivity decreases with increasing anion size, the reverse trend can be observed for the lithium ion transference numbers. Via our holistic approach, we demonstrate that this behavior can be attributed to differences in the collective ion dynamics.

A Brief Review of Gel Polymer Electrolytes Using In Situ Polymerization for Lithium-ion Polymer Batteries

Polymer electrolytes (PEs) have been thoroughly investigated due to their advantages that can prevent severe problems of Li-ion batteries, such as electrolyte leakage, flammability, and lithium dendrite growth to enhance thermal and electrochemical stabilities. Gel polymer electrolytes (GPEs) using in situ polymerization are typically prepared by thermal or UV curing methods by initially impregnating liquid precursors inside the electrode. The in situ method can resolve insufficient interfacial problems between electrode and electrolyte compared with the ex situ method, which could led to a poor cycle performance due to high interfacial resistance. In addition to the abovementioned advantage, it can enhance the form factor of bare cells since the precursor can be injected before polymerization prior to the solidification of the desired shapes. These suggest that gel polymer electrolytes prepared by in situ polymerization are a promising material for lithium-ion batteries.

Tailoring Practically Accessible Polymer/Inorganic Composite Electrolytes for All-Solid-State Lithium Metal Batteries: A Review

Highlights

The current issues and recent advances in polymer/inorganic composite electrolytes are reviewed. The molecular interaction between different components in the composite environment is highlighted for designing high-performance polymer/inorganic composite electrolytes. Inorganic filler properties that affect polymer/inorganic composite electrolyte performance are pointed out. Future research directions for polymer/inorganic composite electrolytes compatible with high-voltage lithium metal batteries are outlined.

Abstract

Solid-state electrolytes (SSEs) are widely considered the essential components for upcoming rechargeable lithium-ion batteries owing to the potential for great safety and energy density. Among them, polymer solid-state electrolytes (PSEs) are competitive candidates for replacing commercial liquid electrolytes due to their flexibility, shape versatility and easy machinability. Despite the rapid development of PSEs, their practical application still faces obstacles including poor ionic conductivity, narrow electrochemical stable window and inferior mechanical strength. Polymer/inorganic composite electrolytes (PIEs) formed by adding ceramic fillers in PSEs merge the benefits of PSEs and inorganic solid-state electrolytes (ISEs), exhibiting appreciable comprehensive properties due to the abundant interfaces with unique characteristics. Some PIEs are highly compatible with high-voltage cathode and lithium metal anode, which offer desirable access to obtaining lithium metal batteries with high energy density. This review elucidates the current issues and recent advances in PIEs. The performance of PIEs was remarkably influenced by the characteristics of the fillers including type, content, morphology, arrangement and surface groups. We focus on the molecular interaction between different components in the composite environment for designing high-performance PIEs. Finally, the obstacles and opportunities for creating high-performance PIEs are outlined. This review aims to provide some theoretical guidance and direction for the development of PIEs.

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.

Ceramic-in-Polymer Hybrid Electrolytes with Enhanced Electrochemical Performance

Polymer electrolytes are attractive candidates to boost the application of rechargeable lithium metal batteries. Single-ion conducting polymers may reduce polarization and lithium dendrite growth, though these materials could be mechanically overly rigid, thus requiring ion mobilizers such as organic solvents to foster transport of Li ions. An inhomogeneous mobilizer distribution and occurrence of preferential Li transport pathways eventually yield favored spots for Li plating, thereby imposing additional mechanical stress and even premature cell short circuits. In this work, we explored ceramic-in-polymer hybrid electrolytes consisting of polymer blends of single-ion conducting polymer and PVdF-HFP, including EC/PC as swelling agents and silane-functionalized LATP particles. The hybrid electrolyte features an oxide-rich layer that notably stabilizes the interphase toward Li metal, enabling single-side lithium deposition for over 700 h at a current density of 0.1 mA cm^-2. The incorporated oxide particles significantly reduce the natural solvent uptake from 140 to 38 wt % despite maintaining reasonably high ionic conductivities. Its electrochemical performance was evaluated in LiNi_0.6Co_0.2Mn_0.2O₂ (NMC622)||Li metal cells, exhibiting impressive capacity retention over 300 cycles. Notably, very thin LiNbO₃ coating of the cathode material further boosts the cycling stability, resulting in an overall capacity retention of 78% over more than 600 cycles, clearly highlighting the potential of hybrid electrolyte concepts.

Tough, Self-Healing, and Conductive Elastomer ─Ionic PEGgel

Ionically conductive elastomers are necessary for realizing human-machine interfaces, bioelectronic applications, or durable wearable sensors. Current design strategies, however, often suffer from solvent leakage and evaporation, or from poor mechanical properties. Here, we report a strategy to fabricate ionic elastomers (IHPs) demonstrating high conductivity (0.04 S m-1), excellent electrochemical stability (>60,000 cycles), ultra-stretchability (up to 1400%), high toughness (7.16 MJ m-3), and fast self-healing properties, enabling the restoration of ionic conductivity within seconds, as well as no solvent leakage. The ionic elastomer is composed of in situ formed physically cross-linked poly(2-hydroxyethyl methacrylate) networks and poly(ethylene glycol) (PEG). The long molecular chains of PEG serve as a solvent for dissolving electrolytes, improve its long-term stability, reduce solvent leakage, and ensure the outstanding mechanical properties of the IHP. Surprisingly, the incorporation of ions into PEG simultaneously enhances the strength and toughness of the elastomer. The strengthening and toughening mechanisms were further revealed by molecular simulation. We demonstrate an application of the IHPs as (a) flexible sensors for strain or temperature sensing, (b) skin electrodes for recording electrocardiograms, and (c) a tough and sensing material for pneumatic artificial muscles. The proposed strategy is simple and easily scalable and can further inspire the design of novel ionic elastomers for ionotronics applications.

High-Rate Solid Polymer Electrolyte Based Flexible All-Solid-State Lithium Metal Batteries

A flexible poly(vinylidene fluoride)-polyetherimide@poly(ethylene glycol) (PVDF-PEI@PEG) solid composite polymer electrolyte is prepared by an in situ thermal curing approach. The homogeneous PVDF-PEI composite porous membrane with an optimized PVDF and PEI weight ratio increases the amorphous phase, while the fast lithium ion transport channels are formed through the filled PEG electrolytes. The optimized polymer electrolyte exhibits high ionic conductivity of 2.36 × 10^-4 S cm^-1 at 60 °C and lithium ion transference number of 0.578 as well as excellent electrochemical stability window of 5.5 V. Moreover, the superior stability toward lithium metal anode enables over 3600 h cycling of the Li//Li symmetric cell at 0.1 mA cm^-2. In particular, the LiFePO₄//Li battery delivers high specific capacities of 132.4 and 111.5 mAh g^-1 with a retention of 86.6% and 85.9% after 200 cycles at 2 C and 100 cycles at 3 C rate under 60 °C, respectively, demonstrating the feasibility as an energy storage device with high rate capability.

The Impact of Polymer Electrolyte Properties on Lithium-Ion Batteries

In recent decades, the enhancement of the properties of electrolytes and electrodes resulted in the development of efficient electrochemical energy storage devices. We herein reported the impact of the different polymer electrolytes in terms of physicochemical, thermal, electrical, and mechanical properties of lithium-ion batteries (LIBs). Since LIBs use many groups of electrolytes, such as liquid electrolytes, quasi-solid electrolytes, and solid electrolytes, the efficiency of the full device relies on the type of electrolyte used. A good electrolyte is the one that, when used in Li-ion batteries, exhibits high Li+ diffusion between electrodes, the lowest resistance during cycling at the interfaces, a high capacity of retention, a very good cycle-life, high thermal stability, high specific capacitance, and high energy density. The impact of various polymer electrolytes and their components has been reported in this work, which helps to understand their effect on battery performance. Although, single-electrolyte material cannot be sufficient to fulfill the requirements of a good LIB. This review is aimed to lead toward an appropriate choice of polymer electrolyte for LIBs.

Phase-Field Simulation and Machine Learning Study of the Effects of Elastic and Plastic Properties of Electrodes and Solid Polymer Electrolytes on the Suppression of Li Dendrite Growth

Lithium (Li) dendrite growth in Li batteries is a long-standing problem, which causes critical safety concerns and severely limits the advancement of rechargeable Li batteries. Replacing a conventional liquid electrolyte with a solid electrolyte of high mechanical strength and rigidity has become a potential approach to inhibiting the Li dendrite growth. However, there still lacks an accurate understanding of the role of the mechanical properties of the metal electrode and the solid electrolyte in the Li dendrite growth. In this work, we develop a phase-field model coupled with the elastoplastic deformation to investigate the Li dendrite growth and its inhibition in the cell. Different mechanical properties, including the elastic modulus and the initial yield strength of both the metal electrode and the solid electrolyte, are explored to understand their independent roles in the inhibition of Li dendrite growth. High-throughput phase-field simulations are performed to establish a database of relationships between the aforementioned mechanical properties and the Li dendrite morphology, based on which a compressed-sensing machine learning model is trained to derive interpretable analytical correlations between the key material parameters and the dendrite morphology, as described by the dendrite length and area ratio. It is revealed that the Li dendrite can be effectively inhibited by electrolytes of high elastic moduli and initial yield strengths. Meanwhile, the role of the yield strength of the Li metal is also critical when the yield strength of the electrolyte becomes low. This work provides a fundamental understanding of the dendrite inhibition by mechanical suppression and demonstrates a computational data-driven methodology to potentially guide the electrode and electrolyte material selection for better inhibition of the dendrite growth.

New insights on the origin of chemical instabilities between poly(carbonate)-based polymer and Li-containing inorganic materials

Composites electrolytes, owing to their potential to combine both polymeric and ceramic properties, are promising candidates for Solid-State-Batteries (SSBs). Here, we assessed the effect of ceramic fillers (Li1+xAlxTi2-xP3O12, Li6.55Ga0.15La3Zr2O12, Al2O3) in a poly(ethylene oxide carbonate)-LiTFSI. First, the role of filler chemistry on thermal and electrochemical properties is evaluated: the polymer crystallinity is reduced, resulting in a gain of ionic conductivity at low temperatures; and the ionic conductivity at low temperature (<30 °C) is boosted for LLZO filler particles. This behaviour is commonly attributed to new conduction pathways generated within the fillers; however, here we demonstrate that a polymer degradation induced by the filler chemistry modifies the polymer chemistry in poly(ethylene glycol), initiated by LiOH that can be found on the LLZO surface. The electrolyte containing LATP or Al2O3 does not under any degradation. Hence, special attention must be paid to surface impurities, as instability/degradation may occur.

Green Polymer Electrolytes Based on Polycaprolactones for Solid-State High-Voltage Lithium Metal Batteries

Solid polymer electrolytes (SPEs) have attracted considerable attention for high energy solid-state lithium metal batteries (LMBs). In this work, potentially ecofriendly, solid-state poly(ε-caprolactone) (PCL)-based star polymer electrolytes with cross-linked structures (xBt-PCL) are introduced that robustly cycle against LiNi_0.6 Mn_0.2 Co_0.2 O₂ (NMC622) composite cathodes, affording long-term stability even at higher current densities. Their superior features allow for sufficient suppression of dendritic lithium deposits, as monitored by ⁷ Li solid-state NMR. Advantageous electrolyte|electrode interfacial properties derived from cathode impregnation with 1.5 wt% PCL enable decent cell performance until up to 500 cycles at rates of 1C (60 °C), illustrating the high potential of PCL-based SPEs for application in high-voltage LMBs.

Metallic Sodium Anodes for Advanced Sodium Metal Batteries: Progress, Challenges and Perspective

Sodium (Na)-based batteries, as the ideal choice of large-scale and low-cost energy storage, have attracted much attention. Na metal anodes with high theoretical specific capacity and low potential are considered to be one of the most promising anodes for next-generation Na-based batteries. However, the high reactivity of Na metal anodes makes the electrode/electrolyte phase unstable, resulting in formation of Na dendrites, short cycle life and safety problems. Herein, the contribution outlines the latest development of Na metal anodes for Na metal batteries. The design strategies for high efficiency utilization of Na metal anodes are elucidated, including sophisticated electrode construction, liquid electrolyte optimization, electrode/electrolyte interface stabilization, and solid electrolyte adaptation. Finally, the future research direction and existing problems are proposed.

Ionic Association in CH3-(CH2-CF2) n -CH3(PVDF)-Li+-(CF3SO2)2N- for n = 1, 4: A Computational Approach

The ionic conductivity of solid polymer electrolytes is governed by the ionic association caused by the polymer···Li+ and the anion···Li+ interactions. We performed the density functional calculation to analyze the molecular interactions in the CH3-(CH2-CF2) n -CH3-Li+-(CF3SO2)2N- for n = 1,4 systems. The gauche conformation is predicted in the lowest energy conformer of pure polymer except for n = 1. The lithium coordination number with the polymer is changed from 3 to 2 in the presence of anion for n = 2, 4 systems. The consequences of the Li+ ion and Li+-(CF3SO2)2N- to the vibrational spectrum are studied to understand the ionic association at the molecular level.

Does Cell Polarization Matter in Single-Ion Conducting Electrolytes?

Single-ion conducting polymer electrolytes (SIPE) are particularly promising electrolyte materials in lithium metal-based batteries since theoretical considerations suggest that the immobilization of anions avoids polarization phenomena at electrode|electrolyte interfaces. SIPE in principle could allow for fast charging while preventing cell failure induced by short circuits arising from the growth of inhomogeneous Li depositions provided that SIPE membranes possess sufficient mechanical stability. To date, different chemical structures are developed for SIPE, where new compounds are often reported through electrochemical characterization at low current rates. Experimental counterparts to model-based assumptions and determination of system limitations by correlating both models and experiments are rare in the literature. Herein, Chazalviel's model, which is derived from ion concentration gradients, is applied to theoretically determine the limiting current density (J_Lim) of a SIPE. Comparison with the experimentally obtained J_Lim reveals a large deviation between the theoretical and practical values. Beyond that, charge-discharge profiles show a distinct arcing behavior at moderate current densities (0.5 to 1 mA cm^-2), indicating polarization of the cell, which is not so far reported for SIPE. In this context, by application of various electrochemical and physiochemical methods, the details of cell polarization and the role of the solid electrolyte interphase in producing arcing behavior in the voltage profiles in stripping/plating experiments are revealed, which eventually also elucidate the inconsistency of J_Lim.

Improved Performance of All-Solid-State Lithium Metal Batteries via Physical and Chemical Interfacial Control

Lithium metal batteries (LMBs) show several limitations, such as high flammability and Li dendrite growth. All-solid-state LMBs (ASSLMBs) are promising alternatives to conventional liquid electrolyte (LE)-based LMBs. However, it is challenging to prepare a solid electrolyte with both high ionic conductivity and low electrode-electrolyte interfacial resistance. In this study, to overcome these problems, a solid composite electrolyte (SCE) consisting of Li6.25 La3 Zr2 Al0.25 O12 and polyvinylidene fluoride-co-hexafluoropropylene is used, which has attracted considerable attention in recent years as a solid-state electrolyte. To operate LMBs without an LE, optimization of the electrode-solid-electrolyte interface is crucial. To achieve this, physical and chemical treatments are performed, i.e., direct growth of each layer by drop casting and thermal evaporation, and plasma treatment before the Li evaporation process, respectively. The optimized ASSLMB (amorphous V2 O5- x (1 µm)/SCE (30 µm)/Li film (10 µm)) has a high discharge capacity of 136.13 mAh g-1 (at 50 °C and 5 C), which is 90% of that of an LMB with an LE. It also shows good cycling performance (>99%) over 1000 cycles. Thus, the proposed design minimizes the electrode-solid-electrolyte interfacial resistance, and is expected to be suitable for integration with existing commercial processes.

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.

High-Performance Room Temperature Lithium-Ion Battery Solid Polymer Electrolytes Based on Poly(vinylidene fluoride-co-hexafluoropropylene) Combining Ionic Liquid and Zeolite

The demand for more efficient energy storage devices has led to the exponential growth of lithium-ion batteries. To overcome the limitations of these systems in terms of safety and to reduce environmental impact, solid-state technology emerges as a suitable approach. This work reports on a three-component solid polymer electrolyte system based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), and clinoptilolite zeolite (CPT). The influences of the preparation method and of the dopants on the electrolyte stability, ionic conductivity, and battery performance were studied. The developed electrolytes show an improved room temperature ionic conductivity (1.9 × 10^-4 S cm^-1), thermal stability (up to 300 °C), and mechanical stability. The corresponding batteries exhibit an outstanding room temperature performance of 160.3 mAh g^-1 at a C/15-rate, with a capacity retention of 76% after 50 cycles. These results represent a step forward in a promising technology aiming the widespread implementation of solid-state batteries.

Role of Adsorbed Polymers on Nanoparticle Dispersion in Drying Polymer Nanocomposite Films

Polymers adsorbed on nanoparticles (NPs) are important elements that determine the dispersion of NPs in polymer nanocomposite (PNC) films. While previous studies have shown that increasing the number of adsorbed polymers on NPs can improve their dispersion during the drying process, the exact mechanism remained unclear. In this study, we investigated the role of adsorbed polymers in determining the microstructure and dispersion of NPs during the drying process. Investigation of the structural development of NPs using the synchrotron vertical-small-angle X-ray scattering technique revealed that increasing polymer adsorption suppresses bonding between the NPs at later stages of drying, when they approach each other and come in contact. On the particle length scale, NPs with large amounts of adsorbed polymers form loose clusters, whereas those with smaller amounts of adsorbed polymers form dense clusters. On the cluster length scale, loose clusters of NPs with large amounts of adsorbed polymers build densely packed aggregates, while dense clusters of NPs with small amounts of adsorbed polymers become organized into loose aggregates. The potential for the quantitative control of NP dispersion in PNC films via modification of polymer adsorption was established in this study.

Flexible, Mechanically Robust, Solid-State Electrolyte Membrane with Conducting Oxide-Enhanced 3D Nanofiber Networks for Lithium Batteries

Using a three-dimensional (3D) Li-ion conducting ceramic network, such as Li₇La₃Zr₂O₁₂ (LLZO) garnet-type oxide conductor, has proved to be a promising strategy to form continuous Li ion transfer paths in a polymer-based composite. However, the 3D network produced by brittle ceramic conductor nanofibers fails to provide sufficient mechanical adaptability. In this manuscript, we reported a new 3D ion-conducting network, which is synthesized from highly loaded LLZO nanoparticles reinforced conducting polymer nanofibers, by creating a lightweight continuous and interconnected LLZO-enhanced 3D network to outperform conducting heavy and brittle ceramic nanofibers to offer a new design principle of composite electrolyte membrane featuring all-round properties in mechanical robustness, structural flexibility, high ionic conductivity, lightweight, and high surface area. This composite-nanofiber design overcomes the issues of using ceramic-only nanoparticles, nanowires, or nanofibers in polymer composite electrolyte, and our work can be considered as a new generation of composite electrolyte membrane in composite electrolyte development.

Recent Advances and Perspectives on the Polymer Electrolytes for Sodium/Potassium-Ion Batteries

Owing to the low cost of sodium/potassium resources and similar electrochemical properties of Na⁺ /K⁺ to Li⁺ , sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) are regarded as promising alternatives to lithium-ion batteries (LIBs) in large-scale energy storage field. However, traditional organic liquid electrolytes bestow SIBs/KIBs with serious safety concerns. In contrast, quasi-/solid-phase electrolytes including polymer electrolytes (PEs) and inorganic solid electrolytes (ISEs) show great superiority of high safety. However, the poor processibility and relatively low ionic conductivity of Na⁺ and K⁺ ions limit the further practical applications of ISEs. PEs combine some merits of both liquid-phase electrolytes and ISEs, and present great potentials in next-generation energy storage systems. Considerable efforts have been devoted to improving their overall properties. Nevertheless, there is still a lack of an in-depth and comprehensive review to get insights into mechanisms and corresponding design strategies of PEs. Herein, the advantages of different electrolytes, particularly PEs are first minutely reviewed, and the mechanism of PEs for Na⁺ /K⁺ ion transfer is summarized. Then, representative researches and recent progresses of SIBs/KIBs based on PEs are presented. Finally, some suggestions and perspectives are put forward to provide some possible directions for the follow-up researches.

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.

Polymer-mediated interaction between nanoparticles during hydration and dehydration: a small-angle X-ray scattering study

Polymer-mediated interactions such as DNA-protein binding, protein aggregation, and filler reinforcement in polymers play crucial roles in many important biological and industrial processes. In this work, we report a detailed investigation of interactions between nanoparticles in the presence of high volume fractions of an adsorbing polymer. Small-angle X-ray scattering (SAXS) revealed the existence of a stable gel-like structure in the polymer-nanoparticle dispersion, whereby anchored polymer molecules on nanoparticles acted as bridging centres, while basic interactions between nanoparticles remained repulsive. Time-resolved SAXS measurements showed that the local volume fraction of nanoparticles increased during the drying of the dispersion owing to the shrinkage of the gel-like structure. Further, nanoparticle clusters in the dehydrated composite films showed percolated networks of nanoparticles, except for 5% loading that showed a phase-separated morphology as the volume fraction of nanoparticles remained lower than the percolation threshold. A significant restructuring of nanoparticle clusters occurred upon the hydration of nanocomposite films caused by the expansion of polymer networks induced by hydration forces. Temporal evolution of the volume fraction of nanoparticles during dehydration unveiled three distinct stages similar to the logistic growth function and this was attributed to the evaporation of free, intermediate, and bound water in the different stages. A plausible mechanism was elucidated based on the spring action analogy between anchored polymer chains and nanoparticles during hydration and dehydration processes.

A Critical Review for an Accurate Electrochemical Stability Window Measurement of Solid Polymer and Composite Electrolytes

All-solid-state lithium batteries (ASSLB) are very promising for the future development of next generation lithium battery systems due to their increased energy density and improved safety. ASSLB employing Solid Polymer Electrolytes (SPE) and Solid Composite Electrolytes (SCE) in particular have attracted significant attention. Among the several expected requirements for a battery system (high ionic conductivity, safety, mechanical stability), increasing the energy density and the cycle life relies on the electrochemical stability window of the SPE or SCE. Most published works target the importance of ionic conductivity (undoubtedly a crucial parameter) and often identify the Electrochemical Stability Window (ESW) of the electrolyte as a secondary parameter. In this review, we first present a summary of recent publications on SPE and SCE with a particular focus on the analysis of their electrochemical stability. The goal of the second part is to propose a review of optimized and improved electrochemical methods, leading to a better understanding and a better evaluation of the ESW of the SPE and the SCE which is, once again, a critical parameter for high stability and high performance ASSLB applications.

Porous Composite Gel Polymer Electrolyte with Interfacial Transport Pathways for Flexible Quasi Solid Lithium-Ion Batteries

The growing demand for safer energy storage devices leads to wide research on solid-state lithium-ion batteries. However, as an important component in the solid-state battery, the solid-state electrolyte often encounters problems, especially the low conductivity at room temperature, inhibiting the development of solid-state batteries. Here, improved electrochemical performances of lithium-ion batteries are obtained by designing a composite gel polymer electrolyte with a sponge-like structure. The porous composite gel polymer electrolyte (PCGPE) is developed by a facile phase inversion process of poly(vinylidiene fluoride-hexafluoropropylene) (PVdF-HFP) and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO). The solid-state nuclear magnetic resonance test proves the continuous porous structure constructs fast Li-ion transport pathways on internal interfaces. As a result, the ionic conductivity of PCGPE is up to 5.45 × 10^-4 S cm^-1 at room temperature. Moreover, an initial capacity of 142.2 mAh g^-1 and 82.6% capacity retention at 1 C after 350 cycles are successfully achieved in flexible LiFPO₄//PCGPE//Li batteries.

XPCS Microrheology and Rheology of Sterically Stabilized Nanoparticle Dispersions in Aprotic Solvents

X-ray photon correlation spectroscopy (XPCS) microrheology and conventional bulk rheology were performed on silica nanoparticle dispersions associated with battery electrolyte applications to probe the properties of these specific complex materials and to explore the utility of XPCS microrheology in characterizing nanoparticle dispersions. Sterically stabilized shear-thickening electrolytes were synthesized by grafting poly(methyl methacrylate) chains onto silica nanoparticles. Coated silica dispersions containing 5-30 wt % nanoparticles dispersed in propylene carbonate were studied. In general, both XPCS microrheology and conventional rheology showed that coated silica dispersions were more viscous at higher concentrations, as expected. The complex viscosity of coated silica dispersions showed shear-thinning behavior over the frequency range probed by XPCS measurements. However, measurements using conventional mechanical rheometry yielded a shear viscosity with weak shear-thickening behavior for dispersions with the highest concentration of 30% particles. Our results indicate that there is a critical concentration needed for shear-thickening behavior, as well as appropriate particle size and surface polymer chain length, for this class of nanoparticle-based electrolytes. The results of this study can provide insights for comparing XPCS microrheology and bulk rheology for related complex fluids and whether XPCS microrheology can capture expected macroscopic rheological properties by probing small-scale particle dynamics.

Hydrogen Bond Interpenetrated Agarose/PVA Network: A Highly Ionic Conductive and Flame-Retardant Gel Polymer Electrolyte

The gel polymer electrolyte (GPE) is the key to assembling high-performance solid-state supercapacitors (SSCs). The commercial poly(vinyl alcohol) (PVA) GPE has developed a reputation due to low ionic conductivity endowed by its high crystallinity and poor water retention capacity. In this work, density functional theory (DFT) calculations first revealed that the high crystallinity of PVA can be greatly disrupted by forming hydrogen bonds with natural agarose macromolecules. The hydrogen bond interpenetrated three-dimensional agarose/PVA network offers high water retention and large amounts of channels for movement of Li⁺ on hydroxyl oxygen atoms. So, an optimized formation of the Li-O coordinate bond (g_Li-O(r) = 8.78) and improved diffusion coefficient of Li⁺ (D_Li⁺) (71 × 10^-6 cm² s^-1) were obtained in the agarose/PVA model. When assembled into SSCs, agarose/PVA-GPE with 2 M LiOAc (AP-GPE) exhibits an outstanding specific capacitance (697.22 mF cm^-2 at 5 mA cm^-2). The high water retention of agarose and large amounts of -OH groups in the agarose macromolecular can generate H₂O by dehydration reaction, reducing the flammability of PVA and greatly enhancing the safety of SSCs.