Hollow nanotubular clay composited comb-like methoxy poly(ethylene glycol) acrylate polymer as solid polymer electrolyte for lithium metal 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.

Earth-Abundant Kaolinite Nanoplatelet Gel Electrolytes for Solid-State Lithium Metal Batteries

Lithium-ion batteries are the leading energy storage technology for portable electronics and vehicle electrification. However, demands for enhanced energy density, safety, and scalability necessitate solid-state alternatives to traditional liquid electrolytes. Moreover, the rapidly increasing utilization of lithium-ion batteries further requires that next-generation electrolytes are derived from earth-abundant raw materials in order to minimize supply chain and environmental concerns. Toward these ends, clay-based nanocomposite electrolytes hold significant promise since they utilize earth-abundant materials that possess superlative mechanical, thermal, and electrochemical stability, which suggests their compatibility with energy-dense lithium metal anodes. Despite these advantages, nanocomposite electrolytes rarely employ kaolinite, the most abundant variety of clay, due to strong interlayer interactions that have historically precluded efficient exfoliation of kaolinite. Overcoming this limitation, here we demonstrate a scalable liquid-phase exfoliation process that produces kaolinite nanoplatelets (KNPs) with high gravimetric surface area, thus enabling the formation of mechanically robust nanocomposites. In particular, KNPs are combined with a succinonitrile (SN) liquid electrolyte to form a nanocomposite gel electrolyte with high room-temperature ionic conductivity (1 mS cm-1), stiff storage modulus (>10 MPa), wide electrochemical stability window (4.5 V vs Li/Li+), and excellent thermal stability (>100 °C). The resulting KNP-SN nanocomposite gel electrolyte is shown to be suitable for high-rate rechargeable lithium metal batteries that employ high-voltage LiNi0.8Co0.15Al0.05O2 (NCA) cathodes. While the primary focus here is on solid-state batteries, our strategy for kaolinite liquid-phase exfoliation can serve as a scalable manufacturing platform for a wide variety of other kaolinite-based nanocomposite applications.

Grafting Polyethyleneimine-Poly(ethylene glycol) Gel onto a Heat-Resistant Polyimide Nanofiber Separator for Improving Lithium-Ion Transporting Ability in Lithium-Ion Batteries

To improve the lithium-ion transporting ability in lithium-ion batteries, a high-performance polyimide-based lithium-ion battery separator (PI-mod) was prepared by chemically grafting poly(ethylene glycol) (PEG) onto the surface of a heat-resistant polyimide nanofiber matrix with the assistance of amino-rich polyethyleneimine (PEI). The resulted PEI-PEG polymer coating exhibited unique gel-like properties with an electrolyte uptake rate of 168%, an area resistance as low as 2.60 Ω·cm², and an ionic conductivity up to 2.33 mS·cm^-1, which are 3.5, 0.10, and 12.3 times that of the commercial separator Celgard 2320, respectively. Meanwhile, the heat-resistant polyimide skeleton can effectively avoid thermal shrinkage of the modified separator even after 200 °C treatment for 0.5 h, which ensures the safety of the battery working under extreme conditions. The modified PI separator possessed a high electrochemical stability window of 4.5 V. Compared with the batteries from the commercial separator Celgard 2320 and the pure polyimide matrix, the assembled coin cell with the PI-mod separator showed much better rate capabilities and capacity retention due to the high electrolyte affinity of the PEI-PEG polymer coating. The developed strategy of using the electrolyte-swollen polymer to modify the thermal-resistant separator network provides an efficient way for establishing high-power lithium-ion batteries with good safety performance.

Advanced Composite Solid Electrolytes for Lithium Batteries: Filler Dimensional Design and Ion Path Optimization

Composite solid electrolytes are considered to be the crucial components of all-solid-state lithium batteries, which are viewed as the next-generation energy storage devices for high energy density and long working life. Numerous studies have shown that fillers in composite solid electrolytes can effectively improve the ion-transport behavior, the essence of which lies in the optimization of the ion-transport path in the electrolyte. The performance is closely related to the structure of the fillers and the interaction between fillers and other electrolyte components including polymer matrices and lithium salts. In this review, the dimensional design of fillers in advanced composite solid electrolytes involving 0D-2D nanofillers, and 3D continuous frameworks are focused on. The ion-transport mechanism and the interaction between fillers and other electrolyte components are highlighted. In addition, sandwich-structured composite solid electrolytes with fillers are also discussed. Strategies for the design of composite solid electrolytes with high room temperature ionic conductivity are summarized, aiming to assist target-oriented research for high-performance composite solid electrolytes.

Functionalized Halloysite Scaffold Controls Sodium Dendrite Growth

Sodium metal is one of the most promising anodes for the prospective low-cost rechargeable batteries. Nevertheless, the commercialization of Na metal anodes remains restricted by sodium dendrite growth. Herein, halloysite nanotubes (HNTs) were chosen as the insulated scaffolds, and Ag nanoparticles were introduced as sodiophilic sites to achieve uniform sodium deposition from bottom to top under the synergistic effect. Density functional theory (DFT) calculation results demonstrated that the presence of Ag greatly increased the binding energy of sodium on HNTs/Ag (-2.85 eV) vs HNTs (-0.85 eV). Meanwhile, thanks to the opposite charges on the inner and outer surfaces of HNTs, faster Na⁺ transfer kinetics and selective adsorption of SO₃CF₃^- on the inner surface of HNTs were achieved, thus avoiding the formation of space charge. Accordingly, the coordination between HNTs and Ag afforded a high Coulombic efficiency (about 99.6% at 2 mA cm^-2), long lifespan in a symmetric battery (for over 3500 h at 1 mA cm^-2), and remarkable cycle stability in Na metal full batteries. This work offers a novel strategy to design a sodiophilic scaffold by nanoclay for dendrite-free Na metal anodes.

2D Silicate Materials for Composite Polymer Electrolytes

Two-dimensional (2D) silicate materials have become one of the promising candidates for constructing composite polymer electrolytes due to their advantages of low cost, high stability, good mechanical property, high ionic conductivity and potential to inhibit the growth of lithium dendrites. However, the application of 2D silicate materials in composite polymer electrolytes (CPEs) is still at the infancy stage and facing a lot of challenges. In this minireview, we summarize the structures and properties of 2D silicate materials that have been applied in CPEs, the processing methods of composite electrolytes based on 2D silicates, and the recent process of 2D silicate materials in CPEs. We hope this review could present a general overview of the 2D silicates for CPEs and promote the further study for potential applications.

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.

Natural Clay-Based Materials for Energy Storage and Conversion Applications

Among various energy storage and conversion materials, functionalized natural clays display significant potentials as electrodes, electrolytes, separators, and nanofillers in energy storage and conversion devices. Natural clays have porous structures, tunable specific surface areas, remarkable thermal and mechanical stabilities, abundant reserves, and cost-effectiveness. In addition, natural clays deliver the advantages of high ionic conductivity and hydrophilicity, which are beneficial properties for solid-state electrolytes. This review article provides an overview toward the recent advancements in natural clay-based energy materials. First, it comprehensively summarizes the structure, classification, and chemical modification methods of natural clays to make them suitable in energy storage and conversion devices. Then, the particular attention is focused on the application of clays in the fields of lithium-ion batteries, lithium-sulfur batteries, zinc-ion batteries, chloride-ion batteries, supercapacitors, solar cells, and fuel cells. Finally, the possible future research directions are provided for natural clays as energy materials. This review aims at facilitating the rapid developments of natural clay-based energy materials through a fruitful discussion from inorganic and materials chemistry aspects, and also promotes the broad sphere of clay-based materials for other utilization, such as effluent treatment, heavy metal removal, and environmental remediation.

Solvent-Free Synthesis of the Polymer Electrolyte via Photo-Controlled Radical Polymerization: Toward Ultrafast In-Built Fabrication of Solid-State Batteries under Visible Light

Thin solid polymer electrolytes (SPEs) with good processability, improved room-temperature ionic conductivity, and better interfacial compatibility are urgently needed to develop solid-state batteries without safety and leakage issues. In-built electrolyte polymerization has emerged as a novel and effective platform to obtain such electrolytes. However, existing in-built methods usually involve heat, UV, γ irradiation, and so forth to initiate the polymerization and often require the addition of solvents to avoid the concentrated active propagating species, which inevitably afford solvent residues that persist in the electrolyte matrix, leading to complex SPE preparation processes, safety hazards, and side reactions with the electrodes. Herein, a simple solvent-free preparation of the poly(mPEGAA)-based electrolyte film was achieved via the photo-controlled radical polymerization under visible light irradiation via an in-built manner, which resulted in 99% monomer conversion within 5 min to obtain the polymer electrolytes with a controlled molecular weight distribution. Thanks to the mild and green conditions, a thin, solvent-free, and cross-linked SPE electrolyte film was obtained efficiently yet in a well-regulated manner, which gave rise to good interfacial compatibility and an improved room-temperature ionic conductivity of 1.5 × 10^-4 S cm^-1 at 25 °C. As-prepared solid-state LiFePO₄|Li batteries based on the in-built thin SPE exhibited a high discharge areal capacity of 1.7 mA h cm^-2 (164.6 mA h g^-1) at an ambient temperature. Furthermore, the system displayed lithium dendrite suppression behavior and good long-term charge-discharge cycling in the Li symmetric battery for over 270 h, representing enhanced stability and capacities compared with ex-built systems.

Solid Polymer Electrolytes with Flexible Framework of SiO2 Nanofibers for Highly Safe Solid Lithium Batteries

Composite electrolytes consisting of polymers and three-dimensional (3D) fillers are considered to be promising electrolytes for solid lithium batteries owing to their virtues of continuous lithium-ion pathways and good mechanical properties. In the present study, an electrolyte with polyethylene oxide-lithium (bis trifluoromethyl) sulfate-succinonitrile (PLS) and frameworks of three-dimensional SiO₂ nanofibers (3D SiO₂ NFs) was prepared. Taking advantage of the highly conductive interfaces between 3D SiO₂ NFs and PLS, the total conductivity of the electrolyte at 30 °C was approximately 9.32 × 10^-5 S cm^-1. With a thickness of 27 μm and a tensile strength of 7.4 MPa, the electrolyte achieved an area specific resistance of 29.0 Ω cm². Moreover, such a 3D configuration could homogenize the electrical field, which was beneficial for suppressing dendrite growth. Consequently, Li/LiFePO₄ cells assembled with PLS and 3D SiO₂ NFs (PLS/3D SiO₂ NFs), which delivered an original specific capacity of 167.9 mAh g^-1, only suffered 3.28% capacity degradation after 100 cycles. In particular, these cells automatically shut down when PLS was decomposed above 400 °C, and the electrodes were separated by the solid framework of 3D SiO₂ NFs. Therefore, the solid lithium batteries based on composite electrolytes reported here offer high safety at elevated temperatures.