Free-standing Anode For Lithium-ion Batteries Research Articles

Fabrication of porous carbon nanofibers by electrospinning as free-standing anodes for lithium-ion batteries

Free-standing anodes composed of porous carbon nanofibers (PCNFs) were fabricated by electrospinning for use in lithium-ion batteries. The use of terephthalic acid (PTA) as the sublimating agent, one-step carbonization at 900 °C for 2 h under vacuum converts the as-prepared samples to have interconnected pores along the PCNFs interior with numerous surface openings. The electrode was characterized using scanning electron microscopy (SEM), surface area analysis (BET), x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and Raman spectra (Raman). This strategy makes the PCNFs with a specific surface area of up to 290 m2 g−1, which is significantly higher than the CNFs with 107 m2 g−1. As a result, electrochemical tests exhibited that the PCNFs have a high discharge capacity of 750 mAh g−1, which is sharply higher than that of the CNFs (234 mAh g−1) at 100 mA g−1. Even at a current density of 3000 mA g−1, the PCNFs still exhibit a very high discharge capacity of 621 mAh g−1. The present study may provide an effective strategy for synthesizing low-cost, binder-free, and environmentally friendly anodes for lithium-ion batteries with outstanding properties.

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.

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.

The fabrication of silicon/dual-network carbon nanofibers/carbon nanotubes as free-standing anodes for lithium-ion batteries.

Silicon, known for its high theoretical capacity and abundant resources, is regarded as one of the most promising anode materials for lithium-ion batteries (LIBs). However, the application of silicon anode materials is limited by huge expansion and poor electricity of silicon. Herein, a novel free-standing Si/C anode (noted as Si/CNFs/CNTs) is synthesized by combining electrospinning and in situ chemical vapor deposition, in which Si nanoparticles are composited with a conducting dual-network composed of carbon nanofibers (CNFs) and in situ deposited carbon nanotubes (CNTs). In situ deposited CNTs surround the surface of CNFs to form an elastic buffer layer on the surface of Si attached to CNFs, which ensures structural integrity. CNTs with excellent conductivity and a large specific surface area shorten Li+ transport pathways. Therefore, Si/CNFs/CNTs exhibits stable cycling performance and maintains a capacity of 639.9 mA h g-1 and a capacity retention rate of 69.9% after 100 cycles at a current density of 0.1 A g-1. This work provides a promising approach for the structural modification of self-supporting Si/C electrodes.

A Free-Standing Polyaniline/Silicon Nanowire Forest as the Anode for Lithium-ion Batteries.

Despite its high theoretical capacity, silicon anode has limited intrinsic conductivity and experiences significant volume changes during charge-discharge. To overcome these issues, facile metal-assisted chemical etching and in-situ polymerization of aniline are employed to produce a dense 1D polyaniline/silicon nanowire forest without noticeable agglomeration as a free-standing anode for lithium-ion batteries. This hybrid electrode possesses high cycling performance, delivering a stable capacity capped at 2 mAh cm-2 for 346 cycles of charge-discharge. Maximum capacity of 2 mAh cm-2 is also achievable at high-rate cell testing of 2 mA cm-2 , which cannot be obtained by the anode with plain silicon wafer and silicon nanowire only. The introduction of polyaniline on the silicon nanowire is shown to reduce the solid electrolyte interface (SEI) resistance, stabilize the SEI layer, further alleviate the effect of volume changes, and boost the conductivity of the hybrid anode, resulting in the high electrochemical performance of the anode.

Encapsulating yolk-shelled Si@Co9S8 particles in carbon fibers to construct a free-standing anode for lithium-ion batteries

Silicon-based (Si-based) materials have aroused extensive attention owing to their ultra-high theoretical specific capacity, while the huge volume expansion and inferior electronic conductivity have impeded their practical application in lithium-ion batteries (LIBs). Rational structural design has been regarded as a fascinating strategy, especially for yolk-shell structures. Herein, Si nanoparticles (Si NPs) were encapsulated in ZIF-67 metal–organic frameworks to obtain Si@ZIF-67 particles, which were wrapped in one-dimensional carbon fibers (CFs) by simple processes of electrospinning, vulcanization and carbonization to obtain a free-standing Si@Co9S8 CF electrode. The yolk-shelled Si@Co9S8 particles could remarkably ameliorate the volume variation of Si materials during the lithiation/de-lithiation cycling and the introduction of CFs endowed an efficient one-dimensional electronic pathway accurately to improve the conductivity of composite materials. In addition, it was not negligible that the as-obtained Si@Co9S8 CF films could be as a self-supporting electrode, which avoided the traditional cumbersome procedure of the electrode preparation. The resulting composite electrodes possess an excellent rate performance and an ultra-stable cycling lifespan. We hope this work can provide some novel insights for the development of the self-supporting Si-based electrode materials.

Self-propagating fabrication of SiO x @rGO film with superior cycling stability and rate performance as anode for lithium-ion batteries

With high theoretical capacity and suitable operating potential, SiO x is regarded as one of the most promising anode materials for high-energy density lithium-ion batteries (LIBs), but it suffers from large volume change during charge/discharge and low electronic conductivity, leading to poor cycling stability and rate capability. To overcome these problems, a SiO x @ reduced graphene oxide (rGO) film with porous structure is prepared through vacuum filtration and self-propagation reduction method, which can be directly used as a free-standing anode for LIBs. The self-propagation process of graphene oxide to graphene can be completed rapidly within 1 s, and endows the film with developed pores due to the instantaneous release of substantial gases. The porous structure is beneficial for exposing massive active sites, facilitating fast ion transport and buffering the volume change of the SiO x during charge/discharge. Moreover, the rGO sheets construct a conductive framework for rapid electron transfer in the film. As a result, the SiO x @rGO film exhibits high lithium storage capacity (1189.7 mAh g−1 at 0.1 A g−1), excellent cycling stability (81.1% capacity retention after 100 cycles) and good rate capability (349.2 mAh g−1 at 3.2 A g−1). This study not only provides a high-performance film anode material for LIBs, but also develops a simple and efficient method for constructing porous film electrodes for various energy storage devices.

Porous Si decorated on MXene as free-standing anodes for lithium-ion batteries with enhanced diffusion properties and mechanical stability

Silicon is an ideal anode candidate for next-generation lithium-ion batteries (LIBs) due to its high specific capacity, low working potential and abundant sources. However, its practical application is seriously hindered by its huge volume expansion, which leads to the destruction of the electrode structure and the short cycle life. Herein, we fabricated flexible self-supporting binder-free porous silicon/MXene-2:1 composite film (pSi/MXene-2:1 film) as anode for LIBs by vacuum filtration. The pSi possesses sheet-shape resulting from layered montmorillonite, which is beneficial to shorten ion transport length. Furthermore, the pSi/MXene-2:1 film possesses excellent mechanical flexibility and the voids in the structure can well accommodate the volume expansion during cycling. Benefitting from these advantages, the pSi/MXene-2:1 film anode shows steady cycling performance with 1039.3 mAh/g at 500 mA g−1 after 200 cycles and excellent rate performance with 840.3 mAh/g at 5 A/g. Furthermore, a high reversible capacity of 1201 mAh/g can be obtained at 1 A/g for pSi/MXene-2:1||LiFePO4 full cell. This work provides a strategy to fabricate high-capacity and long-cycle self-supporting silicon-based anodes for flexible LIBs.

MoO2-Mo2C uniformly encapsulated into N, P co-doped carbon nanofibers as a freestanding anode for high and long-term lithium storage

Lithium‐ion batteries (LIBs) have been widely studied and developed as the currently predominant energy storage devices. As anode materials for LIBs, Molybdenum dioxide (MoO2) has attracted many researchers’ attention owing to its high conductivity, theoretical capacity, chemical stability and rich abundance. However, MoO2 bulk materials suffer from sluggish kinetics during lithiation, resulting in their rapid capacity fading and inferior cycling performance. Therefore, we prepare an electrospun electrode evenly encapsulating MoO2-Mo2C nanoparticles into N, P co-doped carbon nanofibers (MoO2-Mo2C@CNFs) composite as a free-standing anode for LIBs. The Mo2C promotes the electrical conductivity of the composite. The N, P co-doped CNFs provide more active sites for lithium storage, faster kinetics for Li+ transport and better mechanical strength for cycling stability. The uniform combination of MoO2-Mo2C and N, P co-doped CNFs ensures the anode to obtain high capacity. When served as the anode for LIBs, MoO2-Mo2C@CNFs exhibits excellent electrochemical performance in terms of its high capacity and long cycle life.

Facile premixed flame synthesis C@Fe2O3/SWCNT as superior free-standing anode for lithium-ion batteries

Premixed flame configuration is considered as an effective method for the synthesis of carbon materials. In this work, flexible single-walled carbon nanotube network decorated by carbon-encapsulated Fe2O3 nanoparticles (C@Fe2O3/SWCNT) membrane was in-situ fabricated via a facile floating catalyst premixed ethanol flame method, and followed by annealing treatment. In this process, low-cost ethanol and ferrocene were used as carbon source and catalyst precursor for the synthesis of C@Fe2O3/SWCNT, respectively. Benefiting from the interconnected conductive network, the as-fabricated C@Fe2O3/SWCNT membrane was used as a free-standing anode for lithium-ion batteries. Structural characterization revealed that the ultrafine Fe2O3 nanoparticles homogeneously anchored on the SWCNT network, which facilitates the fast diffusion for electron. Furthermore, the carbon layers uniformly enwrap on Fe2O3 can effectively suppress the aggregation and buffer the volume change of Fe2O3 during the lithiation/delithiation process. Consequently, this material delivered an excellent lithium storage performance with a high reversible capacity of 1294.7 mAh g−1 at 50 mA g−1, and an excellent cyclability of 82.5% retention is obtained after cycles at 2 A g−1. This study provides a novel low-cost and fast method for preparing flexible advanced electrode for next-generation rechargeable batteries.

Nitrogen, Oxygen-Codoped Vertical Graphene Arrays Coated 3D Flexible Carbon Nanofibers with High Silicon Content as an Ultrastable Anode for Superior Lithium Storage.

Free‐standing and foldable electrodes with high energy density and long lifespan have recently elicited attention on the development of lithium‐ion batteries (LIBs) for flexible electronic devices. However, both low energy density and slow kinetics in cycling impede their practical applications. In this work, a free‐standing and binder‐free N, O‐codoped 3D vertical graphene carbon nanofibers electrode with ultra‐high silicon content (VGAs@Si@CNFs) is developed via electrospinning, subsequent thermal treatment, and chemical vapor deposition processes. The as‐prepared VGAs@Si@CNFs electrode exhibits excellent conductivity and flexibility because of the high graphitized carbon nanofiber network and abundant vertical graphene arrays. Such 3D all‐carbon architecture can be fabulous for providing a conductive and mechanically robust network, further improving the kinetics and restraining the volume expansion of Si NPs, especially with an ultra‐high Si content (>90 wt%). As a result, the VGAs@Si@CNFs composite demonstrates a superior specific capacity (3619.5 mAh g−1 at 0.05 A g−1), ultralong lifespan, and outstanding rate capability (1093.1 mAh g−1 after 1500 cycles at 8 A g−1) as a free‐standing anode for LIBs. It is believed that this work offers an exciting method for developing free‐standing and high‐energy‐density electrodes for other energy storage devices.

Polyimide-derived carbon nanofiber membranes as free-standing anodes for lithium-ion batteries.

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies. The influence of carbonization temperature on the physical-chemical characteristics of CNMs was investigated in detail. The electrochemical performances of CNMs as free-standing electrodes without any binder or conducting materials for lithium-ion batteries were also discussed. Furthermore, the surface state and internal carbon structure had an important effect on the nitrogen state, electrical conductivity, and wettability of CNMs, and then further affected the electrochemical performances. The CNMs/Li metal half-cells exhibited a satisfying charge–discharge cycle performance and excellent rate performance. They showed that the reversible specific capacity of CNMs carbonized at 700 °C could reach as high as 430 mA h g−1 at 50 mA g−1, and the value of the specific capacity remained at 206 mA h g−1 after 500 cycles at a high current density of 1 A g−1. Overall, the newly developed carbon nanofiber membranes will be a promising candidate for flexible electrodes used in high-power lithium-ion batteries, supercapacitors and sodium-ion batteries.

Porous Si Decorated on Mxene as Free-Standing Anodes for Lithium-Ion Batteries with Enhanced Diffusion Properties and Mechanical Stability

Porous Si Decorated on Mxene as Free-Standing Anodes for Lithium-Ion Batteries with Enhanced Diffusion Properties and Mechanical Stability

Metal–organic-framework derived Co@CN modified horizontally aligned graphene oxide array as free-standing anode for lithium-ion batteries

A metal–organic-framework derived Co@CN modified horizontally aligned graphene oxide (HAGO/Co@CN) anode with optimized ion/electron transport and a stable structure was fabricated to obtain stable cycling at high areal capacity (5 mA h cm−2).

Vertically Aligned n-Type Silicon Nanowire Array as a Free-Standing Anode for Lithium-Ion Batteries.

Due to its high theoretical specific capacity, a silicon anode is one of the candidates for realizing high energy density lithium-ion batteries (LIBs). However, problems related to bulk silicon (e.g., low intrinsic conductivity and massive volume expansion) limit the performance of silicon anodes. In this work, to improve the performance of silicon anodes, a vertically aligned n-type silicon nanowire array (n-SiNW) was fabricated using a well-controlled, top-down nano-machining technique by combining photolithography and inductively coupled plasma reactive ion etching (ICP-RIE) at a cryogenic temperature. The array of nanowires ~1 µm in diameter and with the aspect ratio of ~10 was successfully prepared from commercial n-type silicon wafer. The half-cell LIB with free-standing n-SiNW electrode exhibited an initial Coulombic efficiency of 91.1%, which was higher than the battery with a blank n-silicon wafer electrode (i.e., 67.5%). Upon 100 cycles of stability testing at 0.06 mA cm−2, the battery with the n-SiNW electrode retained 85.9% of its 0.50 mAh cm−2 capacity after the pre-lithiation step, whereas its counterpart, the blank n-silicon wafer electrode, only maintained 61.4% of 0.21 mAh cm−2 capacity. Furthermore, 76.7% capacity retention can be obtained at a current density of 0.2 mA cm−2, showing the potential of n-SiNW anodes for high current density applications. This work presents an alternative method for facile, high precision, and high throughput patterning on a wafer-scale to obtain a high aspect ratio n-SiNW, and its application in LIBs.

N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites as free-standing anodes for lithium-ion batteries

Abstract Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity. To mitigate these issues, free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites (Si/C-ZIF-8/CNFs) are designed and synthesized by electrospinning and carbonization methods, which present greatly enhanced electrochemical properties for lithium-ion battery anodes. This particular structure alleviates the volume variation, promotes the formation of stable solid electrolyte interphase (SEI) film, and improves the electrical conductivity. As a result, the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mA h g−1 at 0.2 A g−1 with a capacity retention of 64% for 150 cycles, and exhibits a reversible capacity of 538.6 mA h g−1 at 0.5 A g−1 over 500 cycles. Moreover, the full cell composed of a free-standing Si/C-ZIF-8/CNFs anode and commercial LiNi1/3Co1/3Mn1/3O2 (NCM) cathode shows a capacity of 63.4 mA h g−1 after 100 cycles at 0.2 C, which corresponds to a capacity retention of 60%. This rational design could provide a new path for the development of high-performance Si-based anodes.

Nano-silicon @ soft carbon embedded in graphene scaffold: High-performance 3D free-standing anode for lithium-ion batteries

Herein, the three-dimensional free-standing nano-silicon @ soft carbon embedded in graphene scaffold composite is prepared to boost the lithium storage property of the silicon anode. For the aspect of “single”, the own volume expansion is relieved by the encapsulated soft carbon layer and the soft carbon layer can suppress the repeated formation of solid electrolyte interface films onto the “single” silicon nanoparticle (SNP). Moreover, the soft carbon layer possesses alternating amorphous and crystalline regions to provide the rapid lithium-ion diffusion channel. On the side of “monolithic”, the 3D free-standing graphene-scaffold loading with evenly distributed SNPs eliminates collisions between SNPs during the charging/discharging cycles, and endows the ‘monolithic’ electrode with excellent electronic conductivity, fast lithium-ion diffusion pathway and high SNPs content. Thus, the above composite anode exhibits superior specific capacity, cycling performance and rate performance, such as around 2600 mA h g−1 (8.34 mA h cm−2) of specific capacity at a current density of 0.2 A/g and almost no capacity attenuation after 100 cycles. The design thinking (from ‘single’ to ‘monolithic’) paves a new avenue towards high-performance anodes of silicon and transition metal oxides.

A freestanding nitrogen-doped carbon nanofiber/MoS2 nanoflowers with expanded interlayer for long cycle-life lithium-ion batteries

In this work, a 3D flexible freestanding nitrogen-doped carbon nanofiber/MoS2 nanoflowers (NCNFs/MoS2) network with expanded interlayer spacing is fabricated by facile electrospinning and hydrothermal synthesis method, which is employed as flexible free-standing anodes for lithium-ion batteries (LIBs) without any additives. A poly(acrylonitrile-co-β-methylhydrogen itaconate) copolymer is synthesized and uses as a precursor to improve the conductivity and flexibility of NCNFs. The three-dimensional open structure of NCNFs/MoS2 provides a highly conductive pathway for fast transfer of charge and electron, and expanded interlayer spacing of MoS2 nanoflowers can increase available surface active sites for Li-ion and reduce the obstacle of Li-ion migration during lithiation/delithiation process. Moreover, it can relieve large internal stress and accommodates volume change during cycling. The NCNFs/MoS2 composite delivers a high capacity of 1168.6 mA h g−1 at a current density of 5A g−1 and an excellent reversible capacity retention of 94.49% after 1000 cycles (only 0.055‰ decay per cycle), which makes it one of the highest capacities and best cycling stability ever reported to date. It also exhibits a superior rate capacity of 909.5 mA h g−1 at current densities 10A g−1, indicating the 3D flexible freestanding NCNFs/MoS2 composite network has potential application in high-performance lithium-ion batteries.

Self-healing liquid metal nanoparticles encapsulated in hollow carbon fibers as a free-standing anode for lithium-ion batteries

As a novel self-healing material, room-temperature liquid metal (LM) composed of Ga and Sn is a promising anode in lithium-ion batteries (LIBs). Although there is no structural pulverization of the anode material with self-healing ability, the volume change during cycling may cause cracks in the supporting structure, such as binders or conductive additives, and thus significantly limits the cycling stability and high capacity for lithium-alloy electrodes. Here, novel self-healing core-shell fibers, with liquid metal nanoparticles as the core coated with a carbon shell (denoted as LMNPs@CS fibers), were synthesized by facile coaxial electrospinning and a carbonization process. The as-prepared fibers, which encapsulated nanosized self-healing LM particles with a well-designed inner void space of the shell, served as free-standing anodes for LIBs. Such anodes offered a reversible capacity of 603.9 mAh g−1 at 1000 mA g−1, excellent rate capability, and a highly stable cycling performance with a discharge capacity of 552 mAh g−1 after 1500 cycles at 1000 mA g−1. The superior electrochemical performance can be attributed to (1) the self-healing ability of the LMNPs, which ensured the superior cycling performance of the electrode, (2) the unique core-shell structure with a well-designed void space, which alleviated the volume changes of LMNPs during the lithiation/delithiation processes, and (3) the self-healing LMNPs, composed of Ga and Sn, possessed high theoretical capacities. These promising strategies and associated opportunities demonstrate great potential for fabricating advanced self-healing anode materials for LIBs.

Strong covalent interaction Fe2O3/nitrogen-doped porous carbon fiber hybrids as free-standing anodes for lithium-ion batteries

A simple and novel method that combines the electrospinning technology with nonaqueous sol–gel method is developed to incorporate Fe2O3 nanoparticles into ZIF-8-derived nitrogen-doped highly porous carbon fibers (NPCFs). The size of Fe2O3 nanoparticles is about 5 nm. The interfacial interaction between Fe2O3 and NPCFs is investigated by thermogravimetric analysis, Raman spectrum and X-ray photoelectron energy spectrum. We found that Fe2O3 nanoparticles are anchored strongly in the NPCFs through the Fe–O–C covalent bond. The impact of the Fe2O3 content in the composites on electrochemical performance is also studied. When served as the flexible and free-standing anode of lithium-ion batteries (LIBs), the Fe2O3/NPCFs-66.9% exhibits superior electrochemical performance with the high discharge capacity of 1351 mA h g−1 at 50 mA g−1, remarkable rate capability (337 mA h g−1 even at 5000 mA g−1), and stable cycling performance (1106 mA h g−1 after 100 cycles at 100 mA g−1). The excellent anodic property can be ascribed to the ultra-small size of Fe2O3 nanoparticles, and the one-dimensional (1D) structure combined with the excellent electrical conductivity of NPCFs matrix. Moreover, the robust interfacial interaction Fe–O–C bond can restrain the aggregation of Fe2O3 nanoparticles and accommodate the volume change. This can effectively maintain the integrity of the whole electrode during the long-term cycles. The results show that the composite may be considered as a promising anode material for advanced LIBs.