Synthesis of triaxial LiFePO4 nanowire with a VGCF core column and a carbon shell through the electrospinning method

Advanced Matrixes for Binder-Free Nanostructured Electrodes in Lithium-Ion Batteries

Commercial lithium-ion batteries (LIBs), limited by their insufficient reversible capacity, short cyclability, and high cost, are facing ever-growing requirements for further increases in power capability, energy density, lifespan, and flexibility. The presence of insulating and electrochemically inactive binders in commercial LIB electrodes causes uneven active material distribution and poor contact of these materials with substrates, reducing battery performance. Thus, nanostructured electrodes with binder-free designs are developed and have numerous advantages including large surface area, robust adhesion to substrates, high areal/specific capacity, fast electron/ion transfer, and free space for alleviating volume expansion, leading to superior battery performance. Herein, recent progress on different kinds of supporting matrixes including metals, carbonaceous materials, and polymers as well as other substrates for binder-free nanostructured electrodes in LIBs are summarized systematically. Furthermore, the potential applications of these binder-free nanostructured electrodes in practical full-cell-configuration LIBs, in particular fully flexible/stretchable LIBs, are outlined in detail. Finally, the future opportunities and challenges for such full-cell LIBs based on binder-free nanostructured electrodes are discussed.

Large Charge-Transfer Energy in LiFePO4 Revealed by Full-Multiplet Calculation for the Fe L3 -edge Soft X-ray Emission Spectra

We analyzed the Fe 3d electronic structure in LiFePO₄ /FePO₄ (LFP/FP) nanowire with a high cyclability by using soft X-ray emission spectroscopy (XES) combined with configuration-interaction full-multiplet (CIFM) calculation. The ex situ Fe L_2,3 -edge resonant XES (RXES) spectra for LFP and FP are ascribed to oxidation states of Fe²⁺ and Fe³⁺ , respectively. CIFM calculations for Fe²⁺ and Fe³⁺ states reproduced the Fe L₃ RXES spectra for LFP and FP, respectively. In the calculations for both states, the charge-transfer energy was considerably larger than those for typical iron oxides, indicating very little electron transfer from the O 2p to Fe 3d orbitals and a weak hybridization on the Fe-O bond during the charge-discharge reactions.

Li4 Ti5 O12 Anode: Structural Design from Material to Electrode and the Construction of Energy Storage Devices

Spinel Li₄ Ti₅ O₁₂ , known as a zero-strain material, is capable to be a competent anode material for promising applications in state-of-art electrochemical energy storage devices (EESDs). Compared with commercial graphite, spinel Li₄ Ti₅ O₁₂ offers a high operating potential of ∼1.55 V vs Li/Li⁺ , negligible volume expansion during Li⁺ intercalation process and excellent thermal stability, leading to high safety and favorable cyclability. Despite the merits of Li₄ Ti₅ O₁₂ been presented, there still remains the issue of Li₄ Ti₅ O₁₂ suffering from poor electronic conductivity, manifesting disadvantageous rate performance. Typically, a material modification process of Li₄ Ti₅ O₁₂ will be proposed to overcome such an issue. However, the previous reports have made few investigations and achievements to analyze the subsequent processes after a material modification process. In this review, we attempt to put considerable interest in complete device design and assembly process with its material structure design (or modification process), electrode structure design and device construction design. Moreover, we have systematically concluded a series of representative design schemes, which can be divided into three major categories involving: (1) nanostructures design, conductive material coating process and doping process on material level; (2) self-supporting or flexible electrode structure design on electrode level; (3) rational assembling of lithium ion full cell or lithium ion capacitor on device level. We believe that these rational designs can give an advanced performance for Li₄ Ti₅ O₁₂ -based energy storage device and deliver a deep inspiration.

Nanosized sustained-release drug depots fabricated using modified tri-axial electrospinning

Nanoscale drug depots, comprising a drug reservoir surrounded by a carrier membrane, are much sought after in contemporary pharmaceutical research. Using cellulose acetate (CA) as a filament-forming polymeric matrix and ferulic acid (FA) as a model drug, nanoscale drug depots in the form of core-shell fibers were designed and fabricated using a modified tri-axial electrospinning process. This employed a solvent mixture as the outer working fluid, as a result of which a robust and continuous preparation process could be achieved. The fiber-based depots had a linear morphology, smooth surfaces, and an average diameter of 0.62±0.07μm. Electron microscopy data showed them to have clear core-shell structures, with the FA encapsulated inside a CA shell. X-ray diffraction and IR spectroscopy results verified that FA was present in the crystalline physical form. In vitro dissolution tests revealed that the fibers were able to provide close to zero-order release over 36h, with no initial burst release and minimal tailing-off. The release properties of the depot systems were much improved over monolithic CA/FA fibers, which exhibited a significant burst release and also considerable tailing-off at the end of the release experiment. Here we thus demonstrate the concept of using modified tri-axial electrospinning to design and develop new types of heterogeneous nanoscale biomaterials.

STATEMENT OF SIGNIFICANCE

Nanoscale drug depots with a drug reservoir surrounded by a carrier are highly attractive in biomedicine. A cellulose acetate based drug depot was investigated in detail, starting with the design of the nanostructure, and moving through its fabrication using a modified tri-axial electrospinning process and a series of characterizations. The core-shell fiber-based drug depots can provide a more sustained release profile with no initial burst effect and less tailing-off than equivalent monolithic drug-loaded fibers. The drug release mechanisms are also distinct in the two systems. This proof-of-concept work can be further expanded to conceive a series of new structural biomaterials with improved or new functional performance.

Correlation between the O 2p Orbital and Redox Reaction in LiMn0.6 Fe0.4 PO4 Nanowires Studied by Soft X-ray Absorption

The changes in the electronic structure of LiMn_0.6 Fe_0.4 PO₄ nanowires during discharge processes were investigated by using ex situ soft X-ray absorption spectroscopy. The Fe L-edge X-ray absorption spectrum attributes the potential plateau at 3.45 V versus Li/Li⁺ of the discharge curve to a reduction of Fe³⁺ to Fe²⁺ . The Mn L-edge X-ray absorption spectra exhibit the Mn²⁺ multiplet structure throughout the discharge process, and the crystal-field splitting was slightly enhanced upon full discharge. The configuration-interaction full-multiplet calculation for the X-ray absorption spectra reveals that the charge-transfer effect from O 2p to Mn 3d orbitals should be considerably small, unlike that from the O 2p to Fe 3d orbitals. Instead, the O K-edge X-ray absorption spectrum shows a clear spectral change during the discharge process, suggesting that the hybridization of O 2p orbitals with Fe 3d orbitals contributes essentially to the reduction.

Electrospinning of Nanofibers for Energy Applications

With global concerns about the shortage of fossil fuels and environmental issues, the development of efficient and clean energy storage devices has been drastically accelerated. Nanofibers are used widely for energy storage devices due to their high surface areas and porosities. Electrospinning is a versatile and efficient fabrication method for nanofibers. In this review, we mainly focus on the application of electrospun nanofibers on energy storage, such as lithium batteries, fuel cells, dye-sensitized solar cells and supercapacitors. The structure and properties of nanofibers are also summarized systematically. The special morphology of nanofibers prepared by electrospinning is significant to the functional materials for energy storage.

Bicontinuous Structure of Li₃V₂(PO₄)₃ Clustered via Carbon Nanofiber as High-Performance Cathode Material of Li-Ion Batteries

In this work, the composite structure of Li3V2(PO4)3 (LVP) nanoparticles with carbon nanofibers (CNF) is designed. The size and location of LVP particles, and the degree of graphitization and diameter of carbon nanofibers, are optimized by electrospinning and heat treatment. The bicontinuous morphologies of LVP/CNF are dependent on the carbonization of PVP and simultaneous growing of LVP, with the fibers shrunk and the LVP crystals grown toward the outside. LVP nanocystals clustered via carbon nanofibers guarantee improving the diffusion ability of Li(+), and the carbon fiber simultaneously guarantees the effective electron conductivity. Compared with the simple carbon-coated LVP and pure LVP, the particle-clustered structure guarantees high rate capability and long-life cycling stability of NF-LVP as cathode for LIBs. At 20 C rate in the range 3.0-4.3 V, NF-LVP delivers the initial capacity of 122.6 mAh g(-1) close to the theoretical value of 133 mAh g(-1), and maintains 97% of the initial capacity at the 1000th cycle. The bead-like structure of cathode material clustered via carbon nanofibers via electrospinning will be further applied to high-performance LIBs.

Influence of Ti(4+) on the electrochemical performance of Li-rich layered oxides - high power and long cycle life of Li2Ru1-xTixO3 cathodes

Li-rich layered oxides are the most attractive cathodes for lithium-ion batteries due to their high capacity (>250 mAh g(-1)). However, their application in electric vehicles is hampered by low power density and poor cycle life. To address these, layered Li2Ru0.75Ti0.25O3 (LRTO) was synthesized and the influence of electroinactive Ti(4+) on the electrochemical performance of Li2RuO3 was investigated. LRTO exhibited a reversible capacity of 240 mAh g(-1) under 14.3 mA g(-1) with 0.11 mol of Li loss after 100 cycles compared to 0.22 mol of Li for Li2Ru0.75Sn0.25O3. More Li(+) can be extracted from LRTO (0.96 mol of Li) even after 250 cycles at 143 mA g(-1) than Li2RuO3 (0.79 mol of Li). High reversible Li extraction and long cycle life were attributed to structural stability of the LiM2 layer in the presence of Ti(4+), facilitating the lithium diffusion kinetics. The versatility of the Li2MO3 structure may initiate exploration of Ti-based Li-rich layered oxides for vehicular applications.

Effects of morphology on the electrochemical performances of Li3V2(PO4)3 cathode material for lithium ion batteries

The effects of various morphologies on the electrochemical performances of Li₃V₂(PO₄)₃ (LVP) were summarized and discussed.

Simple fabrication of flexible electrodes with high metal-oxide content: electrospun reduced tungsten oxide/carbon nanofibers for lithium ion battery applications

A one-step and mass-production synthetic route for a flexible reduced tungsten oxide-carbon composite nanofiber (WO(x)-C-NF) film is demonstrated via an electrospinning technique. The WO(x)-C-NF film exhibits unprecedented high content of metal-oxides (∼ 80 wt%) and good flexibility (the tensile strength of the specimen was 6.13 MPa) without the use of flexible support materials like CNTs or graphene. The WO(x)-C-NF film is directly used as an anode in a lithium ion battery (LIB). Compared with previously reported tungsten oxide electrodes, the WO(x)-C-NF film exhibits high reversible capacity (481 mA h g(-1)total electrode), stable cycle, and improved rate performance, without the use of additive carbon, a polymeric binder and a current collector. Moreover, control electrodes fabricated by conventional processes support the positive effects of both the freestanding electrode and metal-oxide embedded carbon 1-D nanofiber structure.

Nanoparticles meet electrospinning: recent advances and future prospects

Nanofibres can be fabricated by various methods and perhaps electrospinning is the most facile route. In past years, electrospinning has been used as a synthesis technique and the fibres have been prepared from a variety of starting materials and show various properties. Recently, incorporating functional nanoparticles (NPs) with electrospun fibres has emerged as one of most exciting research topics in the field of electrospinning. When NPs are incorporated, on the one hand the NPs endow the electrospun fibres/mats novel or better performance, on the other hand the electrospun fibres/mats could preserve the NPs from corrosion and/or oxidation, especially for NPs with anisotropic structures. More importantly, electrospinning shows potential applications in self-assembly of nanoscale building blocks for generating new functions, and has some obvious advantages that are not available by other self-assembly methods, i.e., the obtained free-standing hybrid mats are usually flexible and with large area, which is favourable for their commercial applications. In this critical review, we will focus on the fabrication and applications of NPs-electrospun fibre composites and give an overview on this emerging field combining nanoparticles and electrospinning. Firstly, two main strategies for producing NPs-electrospun fibres will be discussed, i.e., one is preparing the NPs-electrospun fibres after electrospinning process that is usually combined with other post-processing methods, and the other is fabricating the composite nanofibres during the electrospinning process. In particular, the NPs in the latter method will be classified and introduced to show the assembling effect of electrospinning on NPs with different anisotropic structures. The subsequent section describes the applications of these NPs-electrospun fibre mats and nanocomposites, and finally a conclusion and perspectives of the future research in this emerging field is given.

Fabrication of carbon nanofibers with Si nanoparticle-stuffed cylindrical multi-channels via coaxial electrospinning and their anodic performance

Si-encapsulated, multi-channeled carbon nanofiber anode, manufactured using coaxial electrospinning, shows improved electrochemical performance.

Triaxial electrospun nanofiber membranes for controlled dual release of functional molecules

A novel dual drug delivery system is presented using triaxial structured nanofibers, which provides different release profiles for model drugs separately loaded in either the sheath or the core of the fiber. Homogenous, coaxial and triaxial fibers containing a combination of materials (PCL, polycaprolactone; PVP, polyvinylpyrrolidone) were fabricated. The drug release profiles were simulated using two color dyes (KAB, keyacid blue; KAU, keyacid uranine), whose release in physiological solution was measured using optical absorption as a function of time. To reach the level of 80% release of encapsulated dye from core, triaxial fibers with a PCL intermediate layer exhibited a ~24× slower release than that from coaxial fibers. At the same time, the hygroscopic sheath layer of the triaxial fibers provided an initial burst release (~ 80% within an hour) of a second dye as high as that from conventional single and coaxial fibers. The triaxial fiber membrane provides both a quick release from the outer sheath layer for short-term treatment and a sustained release from the fiber core for long-term treatment. The intermediate layer between inner core and outer sheath acts as a barrier to prevent leaching from the core, which can be especially important when the membranes are used in wet application. The formation of tri/multiaxially electrospun nanofibrous membranes will be greatly beneficial for biomedical applications by enabling different release profiles of two different drugs from a membrane.

Architecturing hierarchical function layers on self-assembled viral templates as 3D nano-array electrodes for integrated Li-ion microbatteries

This work enables an elegant bottom-up solution to engineer 3D microbattery arrays as integral power sources for microelectronics. Thus, multilayers of functional materials were hierarchically architectured over tobacco mosaic virus (TMV) templates that were genetically modified to self-assemble in a vertical manner on current-collectors, so that optimum power and energy densities accompanied with excellent cycle-life could be achieved on a minimum footprint. The resultant microbattery based on self-aligned LiFePO(4) nanoforests of shell-core-shell structure, with precise arrangement of various auxiliary material layers including a central nanometric metal core as direct electronic pathway to current collector, delivers excellent energy density and stable cycling stability only rivaled by the best Li-ion batteries of conventional configurations, while providing rate performance per foot-print and on-site manufacturability unavailable from the latter. This approach could open a new avenue for microelectromechanical systems (MEMS) applications, which would significantly benefit from the concept that electrochemically active components be directly engineered and fabricated as an integral part of the integrated circuit (IC).

Tailored Li4Ti5O12 nanofibers with outstanding kinetics for lithium rechargeable batteries

We report on the synthesis of one-dimensional (1D) Li(4)Ti(5)O(12) nanofibers through electrospinning and their outstanding electrochemical performances. Li(4)Ti(5)O(12) with a spinel structure is a promising candidate anode material for lithium rechargeable batteries due to its well-known zero-strain merits. In order to improve the electronic properties of spinel Li(4)Ti(5)O(12), which are intrinsically poor, we processed the material into a nanofiber type of architecture to shorten the Li(+) and electron transport distance using a versatile electrospinning approach. The electrospun Li(4)Ti(5)O(12) nanofiber showed significantly enhanced discharging/charging properties, even at high rates that exceeded 10 C, demonstrating that the nanofiber offers an attractive architecture for enhanced kinetics.

LiFePO(4) nanocrystals: liquid-phase reduction synthesis and their electrochemical performance

Nanosized LiFePO4 is a kind of promising material for high performance lithium ion batteries; however, the synthesis of nanosized LiFePO4 still has some challenges in forming an orthorhombic phase in atmospheric liquid phase and protecting the LFP nanoparticles from aggregation, etc. In this work, LiFePO4 nanocrystals were synthesized through a high-temperature (350 °C) liquid-phase reduction method. The size and morphology of nanocrystals can be readily controlled by tuning the ratio of solvents, and the size-dependent behavior of lithium storage performance is also observed. After a carbon-coating surface treatment, rhombic-shaped LiFePO4 nanocrystals display excellent lithium storage properties with high reversible capacities and good cycle life (141.0 mAh g(-1) at 0.5 C after 50 cycles etc.). This method can be extended to prepare LiMnPO4 nanorods by substituting iron source with manganese salt.

Rational synthesis of silver vanadium oxides/polyaniline triaxial nanowires with enhanced electrochemical property

We designed and successfully synthesized the silver vanadium oxides/polyaniline (SVO/PANI) triaxial nanowires by combining in situ chemical oxidative polymerization and interfacial redox reaction based on β-AgVO(3) nanowires. The β-AgVO(3) core and two distinct layers can be clearly observed in single triaxial nanowire. Fourier transformed infrared spectroscopic and energy dispersive X-ray spectroscopic investigations indicate that the outermost layer is PANI and the middle layer is Ag(x)VO((2.5+0.5x)) (x < 1), which may result from the redox reaction of Ag(+) and aniline monomers at the interface. The presence of the Ag particle in a transmission electron microscopy image confirms the occurrence of the redox reaction. The triaxial nanowires exhibit enhanced electrochemical performance. This method is shown to be an effective and facile technique for improving the electrochemical performance and stability of nanowire electrodes for applications in Li ion batteries.