Stable Sodium-Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment

Sodiophilic Au-diamane polypropylene separator enabled dendrite-free sodium metal batteries

Sodium metal is considered a promising anode material for sodium metal batteries (SMBs) owing to its high theoretical specific capacity and low electrochemical potential. Nevertheless, its practical application is hindered by the challenge of dendrite formation. To address this issue, a separator modification strategy was adapted to enhance the performance of sodium metal anodes (SMAs) using Au nanoparticle-decorated two-dimensional diamane on a commercial polypropylene substrate (Au-diamane/PP) separator. The sodiophilic Au-diamane/PP separator facilitates improved Na+ ion diffusion kinetics and induces a dendrite-free deposition morphology, effectively suppressing dendrite growth. The dendrite-free deposition behavior was systematically characterized using in situ optical microscopy and ex situ scanning electron microscopy. The symmetric Na||Na cell incorporating the Au-diamane/PP separator exhibits exceptional cycling stability, maintaining operation for more than 2100 h at 2 mA cm-2 with 1 mA h cm-2. The sodiophilicity originates from the in situ formed AuNa2 alloy formed on the surface of diamane during the discharging process. Additionally, a full cell with a Na3V2(PO4)3@C cathode, Au-diamane/PP separator, and Na metal anode delivers a high reversible capacity of 88.4 mA h g-1 even after more than 300 cycles. Our work underscores the potential of the Au-diamane/PP separator in advancing the development of SMBs with extended cycle life and enhanced performance.

Ionic Liquid-Inspired Highly Aligned Fibrous Ionogel for Boosted Thermoelectric Harvesting

Ionogels represent promising materials for thermoelectric generators that efficiently convert low-grade heat into electricity due to their flexibility, stability, nonvolatility, and high thermopower. However, improving their thermoelectric performance presents challenges stemming from the complex interplay between ionic conductivity and thermal conduction. In this study, we developed a highly oriented nanofibrous ionogel membrane through the electrospinning of poly(ethylene oxide) (PEO) blended with a linear CO2-derived polycarbonate oligomer and an ionic liquid, ethylmethylimidazolium dicyanamide. The ionic liquid facilitated the formation of highly aligned nanofiber structures, which demonstrated superior ionic conductivity and reduced thermal conduction compared to the bulk counterparts, primarily due to the size effect inherent in nanofibers. Additionally, the incorporation of CO2-derived polycarbonate can increase the amorphous region of the PEO matrix and strengthen the ion-polymer interaction without compromising the orientation of the nanofibers thanks to its compatibility with PEO and its abundance of electron-withdrawing carbonate groups. This strategy effectively decouples ionic conductivity from thermal conduction, thereby enhancing the thermoelectric efficiency of ionogels. This advancement paves the way for the development of nanofibrous ionogels for use in flexible electronics and energy harvesting applications.

Synergistic Dual-Polar-Functionalized Metal-Organic Framework-Modified Separator for Stable and High-Performance Sodium Metal Batteries

Sodium metal, regarded as an ideal anode material for high-energy-density rechargeable sodium metal batteries (SMBs), faces critical challenges, such as sluggish Na+ transport kinetics and uncontrolled dendritic growth, which severely hinder its cycling stability and practical applications. Herein, the well-designed, multifunctional separator, UFS2@GF, constructed using metal-organic frameworks functionalized with fluorinated (-F) and sulfonic acid (-SO3H) groups, synergistically provides more nucleation sites for Na+ deposition, thereby reducing the nucleation overpotential and achieving uniform deposition. The inorganic-rich solid electrolyte interphase induced by UFS2 facilitates a uniform Na+ flux and enhances charge transfer efficiency. Structural characterization and density functional theory calculations further demonstrate that the introduction of abundant sodiophilic sites provided by -F and -SO3H significantly enhances Na+ transport kinetics by reducing the energy barriers for Na+ migration within the UFS2 framework, leading to a higher Na+ transference number, superior ionic conductivity, and accelerated ion transport. Because of these synergistic effects, the symmetric cell with UFS2@GF achieves stable performance, enabling stable cycling for over 2500 h at 0.25 mA cm-2 while delivering an excellent specific capacity of 87.3 mA h g-1 at 10C in Na∥Na3V2(PO4)3 cells. These results highlight the critical role of synergistic functional group strategies in addressing the limitations of SMBs.

Revolutionizing Inorganic Nanofibers: Bridging Functional Elements to a Future System

The advancement of intelligent ecosystems depends upon not only technological innovation but also a multidimensional understanding of material-world interactions. This theoretical transformation prompts increasing demands for multifunctional materials exhibiting hierarchical organization across multiple length scales. Inorganic nanofibers demonstrate potential in bridging the gap between microscale and macroscale through their three-dimensional architectures. However, their inherent brittleness, primarily resulting from inferior structural integrity poses, significantly limits their current applications. This critical limitation highlights the urgent necessity for developing fabrication strategies that simultaneously enhance the mechanical flexibility and robustness, ensuring reliable performance under extreme operational conditions. This comprehensive review systematically examines brittle mechanism fracture through multiscale analysis including molecular, nanoscale, and microscale dimensions. It presents innovative methodologies integrating simulation-guided structural design with advanced in situ characterization techniques capable of real-time monitoring under a practical stress-strain process. Furthermore, the discussion progresses to address contemporary challenges and emergent solutions in oxide nanofiber engineering, providing strategic insights for developing mechanically robust flexible systems with stable functional properties. Ultimately, this review examines the potential of inorganic nanofibers to overcome the limitations of nano powder materials and achieve their promising real-world applications.

An anisotropic strategy for developing polymer electrolytes endowing lithium metal batteries with electrochemo-mechanically stable interface

Developing versatile solid polymer electrolytes is a reasonable approach to achieving reliable lithium metal batteries but is still challenging due to the nonuniform lithium deposition associated with the sluggish Li+ kinetics and insufficient mechanical strength. Herein, the concept of developing anisotropic solid polymer electrolyte is realized via integrating polymer hosts with highly oriented polyacrylonitrile nanofibers modified by Li6.4La3Zr1.4Ta0.6O12 particles. The oriented composite structure is employed to homogenize Li+ flux, serving as a physical barrier to resist lithium dendrites, retarding the side reaction between the electrolyte and lithium, thus endowing a compatible interface for lithium negative electrode. Correspondingly, the Li | |LiFePO4 cells steadily operate over 1000 cycles, delivering durable capacity retention of 91% at 170 mA g-1. Furthermore, numerical modeling and density functional theory are combined to clarify the multiphysics interplay between the designed solid polymer electrolyte and lithium negative electrode. This work provides a perspective for constructing interface-friendly solid polymer electrolytes at an electrochemo-mechanical level.

Regulating Homogeneous Reactions for Stable Lithium Metal Batteries

Discontinuous and uneven Li+ flux leads to inhomogeneous reactions, accelerating lithium (Li) dendrite growth and reducing the utilization of active materials, which severely impacts the performance of lithium metal batteries (LMBs). To address this challenge, we propose an effective homogeneous reaction design facilitated by an all-aligned nanofibrous architecture, which establishes continuous, uniform, and rapid Li+ pathways throughout the battery. This design enhances Li+ diffusion dynamics and ensures a uniform distribution of current density, hence promoting homogeneous Li nucleation at the anode and efficient Li+ insertion/extraction at the cathode. Moreover, the architecture exhibits superior mechanical strength and flexibility, maintaining structural stability during long-term cycling and suppressing dendrite growth, thereby minimizing the risk of short circuits. As a result, LMBs incorporating this homogeneous reaction design exhibit exceptional electrochemical performance. This work provides valuable insights into the design of homogeneous reactions for high-performance LMBs.

A Thermally Robust Biopolymeric Separator Conveys K+ Transport and Interfacial Chemistry for Longevous Potassium Metal Batteries

Potassium metal batteries (KMBs) hold promise for stationary energy storage with certain cost and resource merits. Nevertheless, their practicability is greatly handicapped by dendrite-related anodes, and the target design of specialized separators to boost anode safety is in its nascent stage. Here, we develop a thermally robust biopolymeric separator customized via a solvent-exchange and amino-siloxane decoration strategy to render durable and safe KMBs. Through experimental investigation and theoretical computation, we reveal that the optimized porosity and surface functionalization could manage ion transport and interfacial chemistry, thereby enabling efficient K+ diffusion and a favorable solid electrolyte interphase to achieve prolonged cycling stability (over 3000 h). The thus-assembled full cell retains 80% of its initial capacity after 400 cycles at 0.5 A g-1. The heat-proof property of the designed separator is further demonstrated. Our biopolymeric separator, affording multifunctional features, provides an appealing solution to circumvent instability and safety issues associated with potassium metal batteries.

Simultaneous Regulation of Organic and Inorganic Components in Interphase by Fiber Separator for High-Stable Sodium Metal Batteries

Uncontrollable side reactions at the metal interface have been identified as the root cause of the formation of a fragile solid electrolyte interphase, leading to irreversible sodium loss in sodium metal batteries. Here, we proposed an interface engineering strategy that employed a carboxyl functionalized cellulose separator to provide strong dipole moments and induce the cleavage of P-F bond to construct a solid electrolyte interphase (SEI) rich in NaF. In addition, we employed nuclear magnetic resonance technology confirmed that the separator with strong dipole moments prevented the reduction of organic solvents by attracting electrons, thereby inhibiting the formation of organic oligomers. SEI with high NaF content and few oligomers is smooth and robust, obviously decreasing the interface impedance of the Na anode. The symmetric Na||Na cells, equipped with the functionalized separator, efficiently operated for 1400 hours with a stable 72 mV overpotential at 0.25 mA cm-2, exhibiting low energy barrier and fast ion transport kinetics. The Na||Na3V2(PO4)3 cell also showed stable cycling performance, with the capacity remaining at 94.83 % of the initial capacity after 1000 cycles at 1C. The proposed separator could control the formation and composition of SEI, paving the way for the development of long-life sodium metal batteries.

Dendrite-Free Lithium Batteries Enabled by an Artificial High-Dielectric Biopolymer Interface Layer

Lithium (Li) metal batteries face challenges, such as dendrite growth and electrolyte interface instability. Artificial interface layers alleviate these issues. Here, cellulose nanocrystal (CNC) nanomembranes, with excellent mechanical properties and high specific surface areas, combine with polyvinylidene-hexafluoropropylene (PVDF-HFP) porous membranes to form an artificial solid electrolyte interphase (SEI) layer. The porous structure of PVDF-HFP equalizes the electric field near metallic lithium surfaces. The high mechanical modulus of CNC (6.2 GPa) effectively inhibits dendrite growth, ensures the uniform flow of lithium ions to the lithium metal electrode, and inhibits the growth of lithium dendrites during cycling. The synergy of high polarity β-phase poly(vinylidene fluoride) (PVDF) and CNC provides over 1000 h of stability for Li//Li batteries. Moreover, Li//LiFePO4 (LFP) full cells with this artificial protective layer perform well at 5 C, showcasing the potential of this film in lithium metal batteries.

Electrospun PVDF-Based Polymers for Lithium-Ion Battery Separators: A Review

Lithium-ion batteries (LIBs) have been widely applied in electronic communication, transportation, aerospace, and other fields, among which separators are vital for their electrochemical stability and safety. Electrospun polyvinylidene fluoride (PVDF)-based separators have a large specific surface area, high porosity, and remarkable thermal stability, which significantly enhances the electrochemistry and safety of LIBs. First, this paper reviewed recent research hotspots and processes of electrospun PVDF-based LIB separators; then, their pivotal parameters influencing morphology, structures, and properties of separators, especially in the process of electrospinning solution preparation, electrospinning process, and post-treatment methods were summarized. Finally, the challenges of PVDF-based LIB separators were proposed and discussed, which paved the way for the application of electrospun PVDF-based separators in LIBs and the development of LIBs with high electrochemistry and security.

Natural Silkworm Cocoon-Derived Separator with Na-Ion De-Solvated Function for Sodium Metal Batteries

The commercialization of sodium batteries faces many challenges, one of which is the lack of suitable high-quality separators. Herein, we presented a novel natural silkworm cocoon-derived separator (SCS) obtained from the cocoon inner membrane after a simple degumming process. A Na||Na symmetric cell assembled with this separator can be stably cycled for over 400 h under test conditions of 0.5 mA cm-2-0.5 mAh cm-2. Moreover, the Na||SCS||Na3V2(PO4)3 full cell exhibits an initial capacity of 79.3 mAh g-1 at 10 C and a capacity retention of 93.6% after 1000 cycles, which far exceeded the 57.5 mAh g-1 and 42.1% of the full cell using a commercial glass fiber separator (GFS). The structural origin of this excellent electrochemical performance lies in the fact that cationic functional groups (such as amino groups) on silkworm proteins can de-solvate Na-ions by anchoring the ClO4- solvent sheath, thereby enhancing the transference number, transport kinetics and deposition/dissolution properties of Na-ions. In addition, the SCS has significantly better mechanical properties and thinness indexes than the commercial GFS, and, coupled with the advantages of being natural, cheap, non-polluting and degradable, it is expected to be used as a commercialized sodium battery separator material.

Synergetic Dual-Additive Electrolyte Enables Highly Stable Performance in Sodium Metal Batteries

Sodium (Na)-metal batteries (SMBs) are considered one of the most promising candidates for the large-scale energy storage market owing to their high theoretical capacity (1,166 mAh g-1) and the abundance of Na raw material. However, the limited stability of electrolytes still hindered the application of SMBs. Herein, sulfolane (Sul) and vinylene carbonate (VC) are identified as effective dual additives that can largely stabilize propylene carbonate (PC)-based electrolytes, prevent dendrite growth, and extend the cycle life of SMBs. The cycling stability of the Na/NaNi0.68Mn0.22Co0.1O2 (NaNMC) cell with this dual-additive electrolyte is remarkably enhanced, with a capacity retention of 94% and a Coulombic efficiency (CE) of 99.9% over 600 cycles at a 5 C (750 mA g-1) rate. The superior cycling performance of the cells can be attributed to the homogenous, dense, and thin hybrid solid electrolyte interphase consisting of F- and S-containing species on the surface of both the Na metal anode and the NaNMC cathode by adding dual additives. Such unique interphases can effectively facilitate Na-ion transport kinetics and avoid electrolyte depletion during repeated cycling at a very high rate of 5 C. This electrolyte design is believed to result in further improvements in the performance of SMBs.

Stable anode/separator interface enabled by graft modification of polypropylene separator via electron beam irradiation technique toward high-performance sodium metal batteries

Sodium metal batteries (SMBs) are considered as strong alternatives to lithium-ion batteries (LIBs), due to the inherent merits of sodium metal anodes (SMAs) including low redox potential (-2.71 V vs. SHE), high theoretical capacity (1166 mAh g-1), and abundant resources. However, the uncontrollable Na dendrite growth has significantly impeded the practical deployment of SMBs. Separator modification has emerged as an effective strategy for substantially enhancing the performance of SMAs. Herein, for the first time, we present the successful grafting polyacrylic acid (PAA) onto polypropylene (PP) separators (denoted as PP-g-PAA) using highly efficient electron beam (EB) irradiation to improve the cyclability of SMAs. The polar carboxyl groups of PAA can facilitate the electrolyte wetting and provide ample mechanical strength to resist dendrite penetration. Consequently, the regulation of Na+ ion flux enables uniform Na+ deposition with dendrite-free morphology, facilitated by the favorable anode/separator interface. The PP-g-PAA separator significantly enhances the cyclability of fabricated cells. Notably, the lifespan of Na||Na symmetric cells can be extended up to 5519 h at 1 mA cm-2 and 1 mAh cm-2. The stable design of the anode/separator interface achieved through polyolefin separator modification presented in this study holds promise for the further advancement of next-generation advanced battery systems.

Island-Like Heterogeneous Interface Generating Tandem Toroidal Built-In Electric Field for Efficient Potassium Ions Diffusion

For large-size potassium accommodation, heterostructure usually suffers severe delamination and exfoliation at the interfaces due to different volume expansion of two-phase during charge/discharge process, resulting in the deconstruction of heterostructures and shortened lifespan of batteries. Here, an innovative strategy is proposed through constructing a microscopic heterostructure system containing copper quantum dots (Cu QDs) highly dispersed in the triphenyl-substituted triazine graphdiyne (TPTG) substrates (TPTG@CuQDs) to solve this problem. The copper quantum dots are uniformly anchored on TPTG substrates, generating a myriad of island-like heterogeneous structures, together with tandem toroidal built-in electric field (BIEF) between every micro heterointerface. The island-like heterostructure endows both benefits of exposed contact interface and robust architecture. Generated tandem toroidal BIEF provides efficient transport pathways with lower energy barriers, reducing the diffusion resistance and facilitating the reaction kinetics of potassium ions. When used as anode, the TPTG@CuQDs exhibit highly reversible capacity and low-capacity degradation (≈0.01% over 5560 cycles at 1 A g-1). Moreover, the TPTG@CuQDs-based full cell delivers an outstanding reversible capacity of ≈110 mAh g-1 over 800 cycles at 1 A g-1. This quantum-scale heterointerface construction strategy offers a new approach toward stable heterostructure design for the application of metal ion batteries.

Achieving highly stable sodium metal batteries with self-adapting and high-ionic-mobility ceramic fiber membranes

Tough issues like sodium (Na) dendrite growth and poor anode reversibility hinder the practical application of sodium metal batteries (SMBs) with moderate liquid electrolytes. To settle these problems, using a smart self-adapting Al2SiO5 ceramic fiber (CF) membrane is demonstrated to enable homogeneous Na depositions and inhibit the dendritic growth. This inorganic membrane itself has superb thermal stability, high ionic mobility (Na+ transference number: 0.65) and electrolyte wettability over traditional glass fiber (GF) or polymeric ones, guaranteeing the low voltage polarization (14 mV) and long-cyclic lifetime (over 600 h) in symmetric cells testing. Notably, aluminous components in CF membranes would interact with F-based molecules in the electrolyte phase, thereby releasing some Al3+ species that can be electrochemically deposited onto the anodic interface. The packed (+)Na3V2(PO4)3|CF|Na(-) full SMBs exhibit far superior cyclic stability (capacity retention over 78.7 % after 600 cycles at 1C) than other counterparts. The in-situ detection/postmortem analysis reveal that Al/F-based inorganics formed in as-built SEI layers play a vital role in Na metal anode protection. This work may provide a viable strategy to overcome the constraints of high-energy SMBs in practical applications.

Molecular Engineering toward Robust Solid Electrolyte Interphase for Lithium Metal Batteries

Lithium-metal batteries (LMBs) with high energy density are becoming increasingly important in global sustainability initiatives. However, uncontrollable dendrite seeds, inscrutable interfacial chemistry, and repetitively formed solid electrolyte interphase (SEI) have severely hindered the advancement of LMBs. Organic molecules have been ingeniously engineered to construct targeted SEI and effectively minimize the above issues. In this review, multiple organic molecules, including polymer, fluorinated molecules, and organosulfur, are comprehensively summarized and insights into how to construct the corresponding elastic, fluorine-rich, and organosulfur-containing SEIs are provided. A variety of meticulously selected cases are analyzed in depth to support the arguments of molecular design in SEI. Specifically, the evolution of organic molecules-derived SEI is discussed and corresponding design principles are proposed, which are beneficial in guiding researchers to understand and architect SEI based on organic molecules. This review provides a design guideline for constructing organic molecule-derived SEI and will inspire more researchers to concentrate on the exploitation of LMBs.

Building Stable Anodes for High-Rate Na-Metal Batteries

Due to low cost and high energy density, sodium metal batteries (SMBs) have attracted growing interest, with great potential to power future electric vehicles (EVs) and mobile electronics, which require rapid charge/discharge capability. However, the development of high-rate SMBs has been impeded by the sluggish Na+ ion kinetics, particularly at the sodium metal anode (SMA). The high-rate operation severely threatens the SMA stability, due to the unstable solid-electrolyte interface (SEI), the Na dendrite growth, and large volume changes during Na plating-stripping cycles, leading to rapid electrochemical performance degradations. This review surveys key challenges faced by high-rate SMAs, and highlights representative stabilization strategies, including the general modification of SMB components (including the host, Na metal surface, electrolyte, separator, and cathode), and emerging solutions with the development of solid-state SMBs and liquid metal anodes; the working principle, performance, and application of these strategies are elaborated, to reduce the Na nucleation energy barriers and promote Na+ ion transfer kinetics for stable high-rate Na metal anodes. This review will inspire further efforts to stabilize SMAs and other metal (e.g., Li, K, Mg, Zn) anodes, promoting high-rate applications of high-energy metal batteries towards a more sustainable society.

Conformal 3D Li/Li13Sn5 Scaffolds Anodes for High-Areal Energy Density Flexible Lithium Metal Batteries

Achieving a high depth of discharge (DOD) in lithium metal anodes (LMAs) is crucial for developing high areal energy density batteries suitable for wearable electronics. Yet, the persistent growth of dendrites compromises battery performance, and the significant lithium consumption during pre-lithiation obstructs their broad application. Herein, A flexible 3D Li13Sn5 scaffold is designed by allowing molten lithium to infiltrate carbon cloth adorned with SnO2 nanocrystals. This design markedly curbs the troublesome dendrite growth, thanks to the uniform electric field distribution and swift Li+ diffusion dynamics. Additionally, with a minimal SnO2 nanocrystals loading (2 wt.%), only 0.6 wt.% of lithium is consumed during pre-lithiation. Insights from in situ optical microscope observations and COMSOL simulations reveal that lithium remains securely anchored within the scaffold, a result of the rapid mass/charge transfer and uniform electric field distribution. Consequently, this electrode achieves a remarkable DOD of 87.1% at 10 mA cm-2 for 40 mAh cm-2. Notably, when coupled with a polysulfide cathode, the constructed flexible Li/Li13Sn5@CC||Li2S6/SnO2@CC pouch cell delivers a high-areal capacity of 5.04 mAh cm-2 and an impressive areal-energy density of 10.6 mWh cm-2. The findings pave the way toward the development of high-performance LMAs, ideal for long-lasting wearable electronics.

Multifunctional Separator Enables High-Performance Sodium Metal Batteries in Carbonate-Based Electrolytes

Sodium metal has become one of the most promising anodes for next-generation cheap and high-energy-density metal batteries; however, challenges caused by the uncontrollable sodium dendrite growth and fragile solid electrolyte interphase (SEI) restrict their large-scale practical applications in low-cost and wide-voltage-window carbonate electrolytes. Herein, a novel multifunctional separator with lightweight and high thinness is proposed, assembled by the cobalt-based metal-organic framework nanowires (Co-NWS), to replace the widely applied thick and heavy glass fiber separator. Benefitting from its abundant sodiophilic functional groups and densely stacked nanowires, Co-NWS not only exhibits outstanding electrolyte wettability and effectively induces uniform Na+ ion flux as a strong ion redistributor but also favors constructing the robust N,F-rich SEI layer. Satisfactorily, with 10 µL carbonate electrolyte, a Na|Co-NWS|Cu half-cell delivers stable cycling (over 260 cycles) with a high average Coulombic efficiency of 98%, and the symmetric cell shows a long cycle life of more than 500 h. Remarkably, the full cell shows a long-term life span (over 1500 cycles with 92% capacity retention) at high current density in the carbonate electrolyte. This work opens up a strategy for developing dendrite-free, low-cost, and long-life-span sodium metal batteries in carbonate-based electrolytes.

Enabling Further Organic Electrolyte Infiltration of Cellulose-Based Separators via Defect-Rich Polypyrrole Modification for High Sodium Ion Transport in Sodium Metal Batteries

Sodium metal batteries (SMBs) have high-density and cost-effective characteristics as one of the energy storage systems, but uncontrollable dendrite growth and poor rate performance still hinder their practical applications. Herein, a nitrogen-rich modified cellulose separator with released abundant ion transport tunnels in organic electrolyte was synthesized by in situ polymerization of polypyrrole, which is based on the high permeability of cellulose in aqueous solution and the interfacial interaction between cellulose and polypyrrole. Meanwhile, the introduction of abundant structural defects such as branch chains, oxygen-containing functional groups, and imine-like structure to disrupt polypyrrole conjugation enables the utilization of conductive polymers in composite separator applications. With the electrolyte affinity surface on, the modified separator exhibits reinforced electrolyte uptake (254%) and extended electrolyte wettability, thereby leading to accelerated ionic conductivity (2.77 mS cm-1) and homogeneous sodium deposition by facilitating the establishment of additional pathways for ion transport. Benefiting from nitrogen-rich groups, the polypyrrole-modified separator demonstrates selective Na+ transport by the data of improved Na+ transference number (0.62). Owing to the above advantages, the battery assembled with the modified separators exhibits outstanding rate performance and prominent capacity retention two times that of the pristine cellulose separator at a high current density under the condition of fluorine-free electrolyte.

Composite Membrane for Sodium Polysulfide Hybrid Redox Flow Batteries

Non-aqueous redox flow batteries (NARFBs) using earth-abundant materials, such as sodium and sulfur, are promising long-duration energy storage technologies. NARFBs utilize organic solvents, which enable higher operating voltages and potentially higher energy densities compared with their aqueous counterparts. Despite exciting progress throughout the past decade, the lack of low-cost membranes with adequate ionic conductivity and selectivity remains as one of the major bottlenecks of NARFBs. Here, we developed a composite membrane composed of a thin (<25 µm) Na+-Nafion coating on a porous polypropylene scaffold. The composite membrane significantly improves the electrochemical stability of Na+-Nafion against sodium metal, exhibiting stable Na symmetric cell performance for over 2300 h, while Na+-Nafion shorted by 445 h. Additionally, the composite membrane demonstrates a higher room temperature storage modulus than the porous polypropylene scaffold and Na+-Nafion separately while maintaining high Na+ conductivity (0.24 mS/cm at 20 °C). Our method shows that a composite membrane utilizing Na+-Nafion is a promising approach for sodium-based hybrid redox flow batteries.

A Sodiophilic Amyloid Fibril Modified Separator for Dendrite-Free Sodium-Metal Batteries

Sodium (Na) batteries are being considered as prospective candidates for the next generation of secondary batteries in contrast to lithium-based batteries, due to their high raw-material abundance, low cost, and sustainability. However, the unfavorable growth of Na-metal deposition and severe interfacial reactions have prevented their large-scale applications. Here, a vacuum filtration strategy, through amyloid-fibril-modified glass-fiber separators, is proposed to address these issues. The modified symmetric cell can be cycled for 1800 h, surpassing the performance of previously reported Na-based electrodes under an ester-based electrolyte. Moreover, the Na/Na3 V2 (PO4 )3 full cell with a sodiophilic amyloid-fibril-modified separator exhibits a capacity retention of 87.13% even after 1000 cycles. Both the experimental and the theoretical results show that the sodiophilic amyloid fibril homogenizes the electric field and Na-ion concentration, fundamentally inhibiting dendrite formation. Simultaneously, the glutamine amino acids in the amyloid fibril have the highest adsorption energy for Na, resulting in the formation of a stable Na3 N- and NaNx Oy -rich solid-electrolyte-interface film on the anode during cycling. This work provides not only a possible pathway to solve the dendrite problem in metal batteries using environmentally friendly biomacromolecular materials, but also a new direction for expanding biomaterial applications.