Free-standing Anode Research Articles

A flexible plane-wire MoO2-anchored carbon nanofiber matrix as freestanding anodes for lithium storage with enhanced cyclability

Inspired by beds of silkworm cocoon, a flexible ″plane-wire″ MoO2-anchored carbon nanofiber matrix has been successfully prepared through electrospinning and subsequent annealing processes. It delivers an initial discharge capacity of 877 mAh g−1 at 200 mA g−1 with a high initial coulombic efficiency of 84.7 % and showcases a high reversible specific capacity of 743 mAh g−1 in the second cycle when employed as free-standing anodes for lithium batteries. It also exhibits good rate performance and superb cyclability, which delivering a specific capacity of 364 mAh g−1 at a high current density of 2 A g−1 and maintains a notable specific capacity of 674 mAh g−1 even after 2000 cycles. It is found that, the carbon nanofiber matrix serves as a robust electronic conductive network to reduce the charge transfer resistance and promote the transportation of Li+, and provides excellent support to buffer volume changes of the MoO2, resulting in enhanced rate performance and cyclability. Moreover, these electrodes are designed to be free-standing, which can improve the flexibility of the electrode and initial coulombic efficiency. It is believed that the as-prepared ″plane-wire″ MoO2-anchored carbon nanofiber matrix is a promising anode material for high-performance LIBs.

Crystalline and amorphous Fe2O3 nanocubes grown on electrospun carbon nanofibers for lithium-ion batteries and lithium-sulfur batteries: A comparative study

Amorphous transition metal oxides have recently received particular research interests in electrochemical energy storage. However, there is still a lack of direct comparisons between amorphous materials and their crystalline counterparts. Here, we demonstrate the rational synthesis of crystalline and amorphous Fe2O3 nanocubes uniformly grown on carbon nanofibers (denoted as CNFs@C-Fe2O3 and CNFs@A-Fe2O3, respectively) for lithium-ion batteries (LIBs) and lithium-sulfur batteries (LSBs). In such a structure, the Fe2O3 nanocubes possess strong interfacial bonding with CNFs, which can ensure rapid electron transportation. Besides, these Fe2O3 nanocubes are highly porous, which can effectively alleviate the volume change, enlarge the surface area, increase active sites and facilitate ion diffusion. When employed as freestanding anode for LIBs, the CNFs@C-Fe2O3 electrode delivers much improved lithium ion storage performance compared to that of CNFs@A-Fe2O3. When evaluated as interlayers for LSBs, instead, the batteries with CNFs@A-Fe2O3 exhibit better rate performance cycling stability than that of with CNFs@C-Fe2O3. Moreover, theoretical calculations elucidate the amorphous Fe2O3 has stronger adsorption ability toward the soluble lithium polysulfides. This work would provide new insights into the reasonably development of crystalline and amorphous transition metal oxides toward electrochemical energy storage.

CNT Sheets Co‐Loaded with Sulfur and Silicon Oxides: Free Standing Anodes for Lithium and Sodium‐Ion Batteries

AbstractSulfur and silicon oxides loaded self‐supporting binder and collector free CNT sheets have been synthesized using floating catalyst chemical vapor deposition technique and investigated for their application as anodes in lithium/sodium ion battery. The CNT sheets have been characterized thoroughly using various microscopic and spectroscopic techniques. The addition of sulfur improves the interplanar spacing in the lattice and also generated abundant defects. The silicon oxides help in enhancing the specific capacity of the CNT sheet via conversion reactions. These features lead to enhanced electrochemical properties and the best performance has been demonstrated by the co‐loaded CNT/S/silicon oxide electrode. As anode in LIB, it delivers 830 mAh g−1 at 1 A g−1 current density after 250 cycles. More importantly, the kinetic analysis confirms that sulfur/silicon oxide co‐loading can improve the Li+ diffusion coefficient in CNT anode and enhance the metal ion storage. The structural modifications also enhance Na+ ion storage and the CNT/S/Silicon oxide anode delivers 368 mAh g−1 after 250 cycles at a current rate of 1 A g−1 with a superior initial coulombic efficiency of 77.5 %.

Flashlight treatment for instantaneous structuring of dense MXene film into porous MXene/TiO2 nanocomposite for lithium-ion battery anodes

MXenes, the two-dimensional metal carbides and nitrides, have been considered a new class of electrode materials with their noticeable performance in various energy storage systems. Furthermore, the unique property and morphology allow MXenes to be assembled into freestanding films, which can be applied in energy storage devices with lightweight and high energy density. However, their tendency to restack and aggregate remains a challenge to enhance the electrochemical performance of MXenes. In this study, we propose a facile method to fabricate a porous MXene-TiO2 freestanding anode with the help of a flashlight. Simply heating the MXene films with a flashlight in milliseconds increases the interlayer spacing of the MXenes and simultaneously forms TiO2 on the MXene surface. Along with the widened interlayer and formation of TiO2, improved wettability, easy electrolyte penetration, and reduced electrode resistance were achieved. As a result, this freestanding anode exhibits nearly 50 times higher Li+ storage capacity (148 mAh/g) than pristine MXene film (3 mAh/g) at 0.05 A/g and excellent cycle stability up to 1500 cycles without degradation.

From 0D to 3D: Hierarchical structured high-performance free-standing silicon anodes based on binder-induced topological network architecture

Free-standing silicon anodes with high proportion of active materials have aroused great attention; however, the mechanical stability and electrochemical performance are severely suppressed. Herein, to resolve the appeal issues, a free-standing anode with a “corrugated paper” shape on micro-scale and a topological crosslinking network on the submicron and nano-scale is designed. Essentially, an integrated three-dimensional electrode structure is constructed based on robust carbon nanotubes network with firmly anchored SiNPs via forming interlocking junctions. In which, the hierarchical interlocking structure is achieved by directional induction of the binder, which ensures well integration during cycling so that significantly enhances mechanical stability as well as electronic and ionic conductivity of electrodes. Benefiting from it, this anode exhibits outstanding performance under harsh service conditions including high Si loading, ultrahigh areal capacity (33.2 mA h cm−2), and high/low temperatures (−15–60 °C), which significantly extends its practical prospect. Furthermore, the optimization mechanism of this electrode is explored to verify the crack-healing and structure-integration maintaining along cycling via a unique self-stabilization process. Thus, from both the fundamental and engineering views, this strategy offers a promising path to produce high-performance free-standing electrodes for flexible device applications especially facing volume effect challenges.

Poly (vinyl alcohol) based carbon nanofibers as freestanding anodes for lithium‐ion batteries

AbstractIn this study, we investigated the iodination process for the preparation of water‐soluble polyvinyl alcohol (PVA)‐based carbon nanofibers (CNFs) and their electrochemical properties. Iodinated nanofibers were carbonized at different temperatures (600°C, 800°C) under an argon (Ar) atmosphere. Morphology and physical properties of fiber mats were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA), while electrical conductivity measurements were done using four probes. As a freestanding anode in half‐cell lithium batteries, the CNFs were prepared by electrospinning of PVA and PVA–CNT blend, which was exposed to iodine vapor at various temperatures (60, 80, and 100°C). Iodine vapor treatment at 80°C and subsequent carbonization at 800°C provided a 29% carbon yield. The resulting CNT‐containing optimized CNFs exhibited superior flexibility, electrical conductivity (2.16 S/cm), and handleability, making them a promising, binder‐free environmentally friendly carbon source for lithium‐ion batteries with high capacity (672 mAh/g at 50 mA/g). The study clearly showed that PVA might be an alternative precursor for the production of carbon micro‐ and nanofibers.Highlights Anodic performance of PVA‐based carbon nanofibers was analyzed. PVA precursor offers economic and environmental option for binder‐free electrodes. PVA–CNT composite nanofibers with optimized iodination and carbonization time identified as a promising high carbon yield carbon source for lithium‐ion batteries. CNT‐containing optimized carbon nanofibers exhibited superior flexibility and electrical conductivity (2.16 S/cm). Freestanding fiber anodes exhibited a higher capacity of 672 mAh/g, at 50 mA/g compared to conventional graphite anode (372 mAh/g).

Tuning wettability of gallium-based liquid metal anode for lithium-ion battery via a metal mixing strategy

Exploring highly stable alloy-type anodes for rechargeable lithium batteries is urgent with the ever-increasing demands for high energy density batteries. The liquid metal (LM)-based anodes demonstrate great potential in advanced lithium-ion batteries due to their high energy densities and self-healing performance. However, its high surface tension leads to poor wettability towards the current collector and higher interfacial contact resistance. In this study, we developed a new free-standing LM-based anode LM-W10/Cu foil with good wettability and machinability by mixing high-melting-point tungsten (W) nanoparticles. It greatly improves the inherent defects of poor interfacial contact and lithium diffusion kinetics between the LM and current collectors, reduces the tedious and costly electrode manufacturing process, and regulates lithium deposition behaviors. And this metal mixing strategy has a negligible effect on the self-healing nature of LM. Symmetric cells of LM-W10/Cu foil anodes displayed a low overpotential (~13 mV) and cycled stably for more than 8,000 h (4,000 cycles) at 0.5 or 1 mA/cm2; full cells coupled with LiFePO4 cathode showed a high capacity retention of 95.15% after 150 cycles.

Flexible carbon nanofibers with multichannel and porous structure as freestanding anode for excellent sodium storage

Hard carbon is the most commonly used anode material for sodium-ion batteries (SIBs). However, it has the drawback of having inferior capacity at high rates due to low ion-diffusion kinetics. Rational design of hard carbon with a hierarchical pore structure and multichannel structure can address this issue. Herein, we introduced an electrospinning method for preparing flexible carbon nanofibers as a freestanding anode for SIBs. The pore structure can be modified by adjusting the amount of Pluronic F-127 (F127) added to the spinning solution. This strategy results in the formation of numerous micropores and mesopores, along with pore-derived defects, effectively increasing the number of sites available for sodium storage. The existence of multichannel facilitates the migration of sodium ions. PCNF-1 possesses an appropriate pore structure with the least amount of added pore-forming agent exhibits exceptional electrochemical performance. It delivers a reversible capacity of 286 mA h g−1 at a current density of 50 mA g−1 with an initial Coulombic efficiency (ICE) of 82 %. At 5 A g−1, it delivers a capacity of 211 mAh g−1. Furthermore, it demonstrates a high retention rate of 79 % at 1 A g−1 even after 1000 cycles. Notably, in full-cell tests, PCNF-1, when paired with a Na3V2(PO4)3 cathode, achieved a specific capacity of 253 mA h g−1 in the second cycle and maintained a retention rate of 51 % after 200 cycles at a current density of 1 A g−1.

Sphere-Confined Reversible Zn Deposition for Stable Alkaline Aqueous Batteries.

The practical applications of alkaline zinc-based batteries are challenged by poor rechargeability with an insufficient zinc utilization ratio. Herein, a sphere-confined reversible zinc deposition behavior from a free-standing Zn anode is reported, which is composed of bi-continuous ZnO-protected interconnected and hollowed Zn microspheres by theKirkendall effect. The cross-linked Zn network with in situ formed outer ZnO shell and inner hollow space not only inhibits side reactions but also ensures long-range conductivity and accommodates shape change, which induces preferential reversible zinc dissolution-deposition process in the inner space and maintains structural integrity even under high zinc utilization ratio. As a result, the Zn electrode can be stably cycled for 390h at a high current density of 20mA cm-2 (60% depth of discharge), outperforming previously reported alkaline Zn anodes. A stable zinc-nickel oxide hydroxide battery with a high cumulative capacity of 8532 mAh cm-2 at 60% depth of discharge is also demonstrated.

A comparative study on morphology dependent performance of neodymium – graphene as an anode material in lithium-ion batteries

The use of rare earth (RE) materials in various applications is gaining significant attention due to their unique electronic configurations. Neodymium (Nd), with its electronic configuration of 4f4 6s2, is one such RE material of interest. However, fabricating low-dimensional forms of RE materials presents a challenge. Additionally, achieving the synthesis of nanoscale RE morphologies on graphene surfaces adds another level of difficulty to the process. In this work, the fabrication of various nanoscale morphologies of neodymium (Nd) on graphene‑nickel foam (Gr-Ni) substrates is demonstrated. This is achieved using a double-heating zone chemical vapor deposition technique, where each heating zone reaches temperatures as high as 1500°C. The resulting Nd-Gr-Ni samples are grown under similar conditions and serve as free-standing additive free anode for direct application in lithium-ion batteries. Among the different nanoscale morphologies obtained, the fiber-like morphology shows the most promising performance. Compared to the ball-like and pyramided-like morphologies, the fiber-like morphology exhibits enhanced cyclic performance with 99% Columbic efficiency and high-capacity retention. Furthermore, the fiber-like anode material demonstrates stable rate performance within a current density range of approximately 0.1–0.5 mAcm−2. The mechanical stability of the Nd-Gr-Ni composites makes them suitable to produce practical LIBs.

Silicon-coated multi-walled carbon nanotube (MWCNT) tissues as flexible free-standing anodes for advanced Li-ion batteries

Silicon-coated multi-walled carbon nanotube (MWCNT) tissues as flexible free-standing anodes for advanced Li-ion batteries

3D binder-free nanoarchitecture design of porous silicon/graphene fibers for ultrastable lithium storage

Enhancing the stability and fast-charging capability of battery electrodes is of paramount importance in the field of battery technology. Silicon (Si), renowned for its high specific capacity, has emerged as a promising candidate for anodes. However, the limited structural stability and electron/ion conductivity of silicon-based anodes have raised significant concerns, including fractures and the continuous formation of unstable solid-electrolyte interphase (SEI) layers, leading to rapid capacity decay. In this study, we introduce a comprehensive approach to fabricating a binder-free and free-standing anode electrode paper using a combination technique of employing electrospinning, magnetron sputtering, and chemical vapor deposition (CVD) techniques. This developed paper electrode incorporates a 3D interconnected network of nitrogen-doped vertical graphene nanosheets (VGs) that connect porous carbon fibers (PCFs) with uniformly distributed Si nanoparticles (VGs@Si@PCFs). The as-fabricated VGs@Si@PCFs paper effectively addresses the mechanical and chemical stability issues commonly associated with Si anodes. The VGs@Si@PCFs anode demonstrates a remarkable reversible capacity of 2205 mAh g-1 at 0.1 A g-1 and exhibits exceptional cycling performance with 83.5% capacity retention at 1.0 A g-1 after 3000 cycles. This design leverages the nanoporous carbon fibers and nitrogen-doped vertical graphene nanosheets as flexible and conductive supports, enhancing the robustness and flexibility of the electrode. Additionally, mechanical modeling reveals that the overall Mises strain in the porous VGs@Si@PCFs structure is significantly lower compared to nonporous cases, potentially minimizing low-cycle fatigue. Our free-standing Si/C composite anode introduces a new class of low-strain Si-based materials, showcasing significantly improved stabilities and fast-charging capabilities.

Ti3C2Tx constrained Sb2S3 composite biomass-derived carbon ribbon film achieves stable sodium storage for flexible quasi-solid full-battery

Optimizing electrode structure, reducing the proportion of inactive substances, and fabricating a flexible free-standing electrode without fluid collection are desirable to enhance the energy density, fast charging, and cycling stability of flexible batteries. In this study, we utilized the biological characteristics of Aspergillus niger to synthesize one-dimensional (1D) Sb2S3 nanoparticle composite N-doped C ribbons. Subsequently, vacuum filtration was employed to blend and assemble these 1D composite C ribbons with Ti3C2Tx nanosheets into a free-standing flexible anode for Sodium-ion batteries (SIBs). Using 1D C ribbons can effectively inhibit the stacking of 2D MXenes, thereby facilitating the penetration of Na+ into Sb2S3@NCR through the interlamellar pores. Ex-situ X-ray photoelectron spectroscopy analyses indicated that the MXene layers were not only physically confined but also effectively suppressed polysulfide diffusion through chemical confinement. Consequently, the energy density and cycling stability of the Sb2S3@NCR composite electrode were enhanced. The Sb2S3@NCR/MXene||CGPFE||NVP@CNF full battery, consisting of an Sb2S3@NCR/MXene anode, free standing NVP@CNF cathode, and PVDF-HFP fiber quasi-solid-state polymer electrolyte prepared via electrospinning, achieved 1,000 stable cycles at a current density of 1 Ag−1. Additionally, the flexible quasi-solid-state bag-type battery could power an LED lamp at a bending angle of 0°–180°.

Printable and Free-Standing Silicon-Based Anode for Current Collector-Free Lithium-Ion Batteries.

The evolution of Li-ion rechargeable batteries has driven a demand for systems exceeding the energy density and shape diversity of conventional lithium-ion batteries. Silicon (Si)-based materials, suitable for high-energy-density applications, have been restricted in practical use due to their inherent structural instability and poor conductivities upon electrochemical cycling. Here, we propose a fully printable and free-standing anode, composed of hollow SiOx/C (H-SiOx/C) composite material and an MXene conductive binder, exhibiting high specific capacity, structural reliability, and superior ionic conductivity without any current collector. The hollow structure of H-SiOx/C accommodates volume changes during cycling, while the MXene binder forms a three-dimensional interconnected conducting structure for maintaining the structural integrity of electrodes without a current collector. Furthermore, the printability and free-standing nature of the H-SiOx/C/MXene anode are validated in both coin-type full cell and heart-shaped pouch cell configurations through a straightforward stencil printing technique. This work establishes a foundation for advanced Si-based anodes, enhancing performance and design flexibility and potentially contributing to practical printable battery systems.

Electrochemically exfoliated reduced graphene oxide-based freestanding separator-integrated electrode with embedded C-coated SiOx as the current collector-free anode in flexible batteries

We developed a facile, direct approach for the preparation of freestanding separator-integrated anodes with high flexibility and good capacity by mixing electrochemically exfoliated reduced graphene oxide (rGO) and C-coated SiOx (CSO) via vacuum filtration on a glass fiber separator. The type of current density applied during exfoliation significantly affected the electrochemical properties of graphene, and high electrical conductivity was obtained under the optimized conditions. The mixture of rGO and CSO exerted positive synergistic effects, including alleviated volume expansion, high specific capacity, and enhanced electrical conductivity of rGO, on battery performance, which may enable the development of current collector-free flexible Lithium-ion batteries. The optimized separator-integrated flexible anode exhibited a high reversible capacity at the fifth cycle, as well as satisfactory capacity retention over 200 cycles, which illustrates the superior rate capability and structural durability of this device.

Sustainably flexible and free-standing organic carbonyl potassium salt with continuous conductive network as high-performance anode in K-ion batteries

Developing suitable electrode materials with high flexibility, superior cyclic performance and low-cost have been the new topic and difficulty in the up-coming wearable flexible device. Herein, organic potassium terephthalate (K2TP) with MWCNTs and conductive polymer PEDOT:PSS co-coated K2TP/2MWCNTs/PP composite endowing continuous conductive network, was initially developed as a pliable and free-standing anode material for potassium ion batteries. By analyzing the internal microstructure, external topography and varies electrochemical characterization of the prepared samples, the incorporation of reasonable MWCNTs and PEDOT:PSS allows for the construction of a continuous conductive network with a large specific surface area, the creation of an effective electron transfer channel, an improvement in the kinetics of K+ diffusion and the maintenance of structural integrality. A preeminent specific capacity of 154.3 mAh g−1 can be maintained after 100 cycles at the current density of 50 mA g−1, prevailing over the majority of claimed anode materials employed in K-ion batteries. Furthermore, a high-performance all-organic full battery based on flexible anode and cathode material was successfully assembled delivering an extraordinary energy density of 320 Wh Kg−1. These results can put forward the practical application of organic electrode materials in systems for massive-scale energy storage.

Interfacial friction enabling ≤ 20 μm thin free-standing lithium strips for lithium metal batteries

A practical high-specific-energy Li metal battery requires thin (≤20 μm) and free-standing Li metal anodes, but the low melting point and strong diffusion creep of lithium metal impede their scalable processing towards thin-thickness and free-standing architecture. In this paper, thin (5 to 50 μm) and free-standing lithium strips were achieved by mechanical rolling, which is determined by the in situ tribochemical reaction between lithium and zinc dialkyldithiophosphate (ZDDP). A friction-induced organic/inorganic hybrid interface (~450 nm) was formed on Li with an ultra-high hardness (0.84 GPa) and Young’s modulus (25.90 GPa), which not only enables the scalable process mechanics of thin lithium strips but also facilitates dendrite-free lithium metal anodes by inhibiting dendrite growth. The rolled lithium anode exhibits a prolonged cycle lifespan and high-rate cycle stability (in excess of more than 1700 cycles even at 18.0 mA cm−2 and 1.5 mA cm−2 at 25 °C). Meanwhile, the LiFePO4 (with single-sided load 10 mg/cm2) ||Li@ZDDP full cell can last over 350 cycles with a high-capacity retention of 82% after the formation cycles at 5 C (1 C = 170 mA/g) and 25 °C. This work provides a scalable approach concerning tribology design for producing practical thin free-standing lithium metal anodes.

A flexible and free-standing silicon-based anode with a rational yolk-shell structure for high-performance lithium-ion batteries

Silicon is arousing considerable interest as a potential material for the anode of lithium-ion batteries (LIBs) owing to its proper discharge voltage and outstanding specific capacity. However, the inferior electrical conductivity, enormous volume variation, and slow Li+ propagation kinetics of Si severely hinder its application. Here, a free-standing and flexible silicon/carbon nanofibers composite with a yolk-shell structure (Si@void@CNFs) is designed, which consists of a yolk synthesized by sodiothermic reduction of SiO2 at a comparatively low temperature (450 ºC), a shell generated via electrospinning technique, and a void formed through etching atomic layer deposition (ALD) Al2O3 coating with dilute HCl. The as-prepared Si@void@CNFs anode employed in LIBs displays a large initial discharge capacity of 2828 mAh g−1 with a perfect Coulombic efficiency of 71 % at 0.2 A g−1, significantly improved cycle stability retaining a large specific capacity of 952 mAh g−1 after 200 cycles, and remarkable rate performance (1725, 1567, 1391, 1121, and 719 mAh g−1 at 0.2, 0.5, 1, 2, and 4 A g−1). The superior electrochemical behaviour of the free-standing Si@void@CNFs is imputed to the cooperative effects of the mechanically robust CNFs shell, the porous silicon yolk, and the rational yolk-shell structure.

CuO quantum dots embedded Cu3(BTC)2/CuO sugar gourd-like nanoarrays on copper foil as free-standing anodes for lithium-ion batteries with boosted performance

CuO quantum dots (QDs)-embedded Cu3(BTC)2/CuO sugar gourd-like nanoarrays are successfully assembled on copper foil through a two-step wet-chemical growth method. As a free-standing anode for lithium-ion batteries, the resultant composite (Cu-BTC/QDs/CuO@Cu) delivers a high specific capacity of 813 mAh/g at a current density of 0.2 A/g after 150 cycles, and 452 mAh/g at 1.0 A/g after 500 cycles, demonstrating excellent cycling stability and rate performance. The superior energy storage capability is attributed to a synergistic effect from the individual components including the electro-active organic ligand, porous framework and CuO nanowires/QDs. As an efficient binder-free anode, Cu-BTC/QDs/CuO@Cu can be a promising candidate for the development of high-performance and cost-effective LIBs with exceptional energy density and power density capabilities.

Inner–outer dual space protection of free-standing MoS2 anodes via electrospinning for stable lithium-ion storage

Although significant achievements in improving the stability of MoS2 anodes have been made, the cycling life in most studies is still less than 1000 cycles. This is because MoS2 anodes directly contact the electrolyte and generate byproducts, leading to the loss of active mass and capacity decay. Herein, the inner–outer dual space protection of MoS2 fibers is realized by regulating the surface and interface structure of electrospinning precursors (noted as X-MoS2/CNFs). Inside the fibers, Mo–N covalent bond is constructed to anchor the active material, preventing MoS2 from falling off the matrix after multiple cycles. Simultaneously, surface of the fibers, a stable solid electrolyte interface layer is induced to prevent contact between active materials and electrolytes. In addition, the initial Coulombic efficiency is enhanced as high as 84.4%. The profound investigations of morphological evolution and internal real-time resistance confirm the double structural protection of 800-MoS2/CNFs. As a result, a decent cycling performance (408.9 mAh g−1 at 1000 mA g−1 for 2000 cycles) and the satisfied rate capacities (100–1000 mA g−1) are achieved. This work provides a new idea for the preparation of stable anodes for alkali metal ion secondary batteries.