High-power Electrodes Research Articles

High Rate Performance of Dual-Substituted LiFePO4 Based on Controlling Metastable Intermediate Phase

High rate capability is one of the most important properties in Li-ion batteries for electric vehicle and/or energy grid use. Herein, a high-power electrode material consisting of dual-substituted LiFePO4 by zirconium and silicon, Li(Fe0.95Zr0.05)(P0.9Si0.1)O4, was developed as it exhibits small lattice volume change between Li-rich and Li-poor phases. The dual-substituted cathode exhibited 1.1–4.4 times larger charge/discharge capacities for upper 10 C rates than that of the undoped material. Time-resolved XRD measurements at the high rate of 10 C revealed the formation of a metastable intermediate phase during the Li intercalation/deintercalation processes which triggers the continuous phase transition in Li(Fe0.95Zr0.05)(P0.9Si0.1)O4 with moderation of the lattice mismatch. Controlling the lattice volume change between the initial and end phase of the intercalation materials is key to achieving high rate capabilities.

Facile Synthesis of Porous Coralline LiVO3 as High‐Performance Li‐Ion Battery Cathodes

AbstractA facile and easily scaled‐up polymer‐pyrolysis method is developed to synthesize porous coralline LiVO3 as cathodes for lithium‐ion batteries (LIBs). Polyacrylates of Li and V are used as the precursor compounds. The nanostructured LiVO3 delivers a high specific capacity of 307.6 mAh g−1 with a remarkable capacity retention of 80.6% after 100 cycles. In addition, a high energy density close to 800 Wh kg−1 as well as a competitive power density of ∼4500 W kg−1 are attained. Such excellent lithium storage performance derives from its porous nanoarchitecture, which not only supplies numerous active sites for electrochemical reactions, and shortens Li‐ions diffusion distance, but also provides enough void space to buffer the volume change during lithium intercalation and deintercalation. Therefore, the porous coralline LiVO3 justifies its potential practical application as an alternative to high energy and high power electrode materials for lithium‐ion batteries. The simple approach opens up a new way to fabricate other types of porous coralline energy storage materials.

A synergistic vertical graphene skeleton and S–C shell to construct high-performance TiNb2O7-based core/shell arrays

Binder-free VG/TiNb2O7@S–C electrodes prepared via a powerful solvothermal-electrodeposition (ST-ED) method show good high-rate performance (241 mA h g−1/70 °C at 160C) and long high-temperature lifespan (>5000 cycles) at medium–high temperatures.

A Density Functional Theory Study of New Boron Nanotubes

Abstract Using first-principles calculations, a series of new boron nanotubes (BNTs), which show various electronic properties, were theoretically predicted. Stable nanotubes with various chiral vectors and diameters can be formed by rolling up the boron sheet with relative stability [H. Tang and S. I. Beigi, Phys. Rev. B 82, 115412 (2010).]. By increasing the diameter for BNT, the stability is enhanced. The calculated density of states and band structures demonstrate that all the predicted BNTs are metallic, regardless of their diameter and chirality. The multicentre chemical bonds of the relatively stable boron sheet and BNTs are analysed using the deformation electron density. Within our study, the BNTs all have metallic conductive characteristics, in addition to having a low effective quality and high carrier concentration, which are very good nanoconductive material properties and could be combined to form high-power electrodes for lithium-ion batteries such as those used in many modern electronics.

Conformal Vanadium Oxides Beyond Crystalline V2O5 As High Energy Density 3D Thin-Film Electrodes for Lithium-Ion Batteries

The nearly unmatched conformality of Atomic Layer Deposition (ALD) renders it a powerful deposition technique for applications such as catalysis where high surface areas are critical, or for protective coatings on complex 3D surfaces such as powders or porous materials. In the last decade, ALD for energy storage has come into view. Advances in technology have pushed the requirements of energy storage devices, leading to novel lithium-ion battery (LIB) concepts such as 3D-structured electrodes, thin-film electrode and the combination of both. These concepts enable high-power and high-energy integrateable batteries, but require a conformal deposition technique for the current collectors, electrodes, solid electrolytes and interfacial coatings alike. Besides 3D structuring, materials design of the LIB electrodes is paramount to achieve higher power and higher energy densities, beyond traditional electrode materials such as LiCoO2, and LiMnO2which are limited to volumetric capacities of 550-700mAh/cm³. Traditionally, the main focus of materials development for batteries has been on crystalline compounds. However, several indications exist that higher energy and power density can be found in amorphous materials. ALD is not only excellently suited to deposit conformal films, but also able to grow high-quality amorphous films at low deposition temperatures, enabling the study of amorphous thin-film electrodes. In this work, ALD of vanadium oxides for applications as lithium-ion electrodes is envisioned. Vanadium oxides were amongst the first materials to be studied as LIB cathodes, but were never commercialised. V2O5 is a well-known LIB electrode, but the rather low volumetric energy density (when storing one lithium) or poor cyclability (when storing 2-3 lithium ions) have prevented its large-scale commercialisation in the past. Here, we demonstrate the ALD deposition of amorphous and crystalline V2O5, and two ‘flavours’ of amorphous VO2, from a single vanadium precursor (Tetrakis[ethylmethylamino] vanadium). We demonstrate the crystallisation of these films into crystalline films in the Wadsley series, and are able to unravel the influence of initial ALD process, atmosphere, temperature and substrate on the crystallization and oxidation of the VO2 films. With this in mind, we are able to obtain phase-pure crystalline vanadium oxides in the whole Wadsley series (VO2–V6O13–V4O9–V3O7–V2O5), which show very high energy densities up to more than double that of typical bulk cathodes (1380mAh/cm³ for V4O9). The amorphous initial states (amorphous VO2 and V2O5) are often not considered due to their lack of a clearly defined electrode potential. However, building on the nature of ALD to grow high-purity amorphous films, these were also investigated here. It was found that, besides also having very high capacities, their kinetics are excellent. Finally, the best candidates were examined on an ALD Pt-coated silicon micropillar array as 3D-structured thin-film electrodes. The 20x surface enhancement of the micropillar substrate enhanced the footprint capacity of the 40nm films from approximately 2-5µAh/cm² to 40-100µAh/cm², with the highest capacity for amorphous VO2(>100µAh/cm² for the 40nm film), while at the same time maintaining the excellent thin-film kinetics of the planar films, in effect simultaneously demonstrating the potential of ALD to deposit 3D thin-film electrodes as well as a tool to study amorphous and crystalline films. In conclusion, a wide range of crystalline and amorphous vanadium oxides were demonstrated from a single vanadium-precursor based ALD process. All films were examined as potential lithium-ion battery electrodes, and showed promise of very high volumetric capacities. In particular, the amorphous films and the crystalline VO2 (B) not only displayed very high capacities, but also excellent kinetics, enabling both high-energy and high-power electrodes. Figure 1

In Situ Observation of Single-Phase Lithium Intercalation in Sub-25-nm Nanoparticles.

Many lithium-storage materials operate via first-order phase transformations with slow kinetics largely restricted by the nucleation and growth of a new phase. Due to the energy penalties associated with interfaces between coexisting phases, the tendency for a single-phase solid-solution pathway with exceptional reaction kinetics has been predicted to increase with decreasing particle size. Unfortunately, phase evolutions inside such small particles (tens of nanometers) are often shrouded by electrode-scale inhomogeneous reactions containing millions of particles, leading to intensive debate over the size-dependent microscopic reaction mechanisms. This study provides a generally applicable methodology capable of tracking lithiation pathways in individual nanoparticles and unambiguously reveals that lithiation of anatase TiO2 , previously long believed to be biphasic, converts to a single-phase reaction when particle size reaches ≈25 nm. These results imply the prevalence of such a size-dependent transition in lithiation mechanism among intercalation compounds and provide important guidelines for designing high-power electrodes, especially cathodes.

A hyperaccumulation pathway to three-dimensional hierarchical porous nanocomposites for highly robust high-power electrodes.

Natural plants consist of a hierarchical architecture featuring an intricate network of highly interconnected struts and channels that not only ensure extraordinary structural stability, but also allow efficient transport of nutrients and electrolytes throughout the entire plants. Here we show that a hyperaccumulation effect can allow efficient enrichment of selected metal ions (for example, Sn2+, Mn2+) in the halophytic plants, which can then be converted into three-dimensional carbon/metal oxide (3DC/MOx) nanocomposites with both the composition and structure hierarchy. The nanocomposites retain the 3D hierarchical porous network structure, with ultrafine MOx nanoparticles uniformly distributed in multi-layers of carbon derived from the cell wall, cytomembrane and tonoplast. It can simultaneously ensure efficient electron and ion transport and help withstand the mechanical stress during the repeated electrochemical cycles, enabling the active material to combine high specific capacities typical of batteries and the cycling stability of supercapacitors.

(Invited) Atomic Layer Deposition: Eye on the Future of Batteries

Over the past few years, as atomic layer deposition (ALD) has emerged as a promising technique to improve the performance of electrochemical energy storage devices. In conventional battery architectures and chemistries, ALD layers have been used to protect the surface of anodes1 and cathodes,2 resulting in improved electrode stability and enhanced cycling performance. Beyond conventional Li-ion batteries, ALD has allowed fabrication of ultra-high performance 3D nanoheterostructures that combine intimate contact between high electrical conductivity current collectors and thin layers of active material for incredible charge/discharge rate capabilities proportional to the active material surface area. Both anode3 and cathode4 nanoheterostructures exhibit significantly higher charge/discharge rate capabilities over their bulk electrode counterparts in ½ cell geometries. The culmination of this architecture uses the high degree of control inherent in the ALD process to fabricate arrays of opposing cylindrical heterostructures inside a nanoporous template, and can achieve nearly 50% theoretical capacity while charging/discharging at a rate of 150 C.5 However, use of liquid electrolytes present a number of challenges with high power electrodes. High charge/discharge rates, desirable for fast charging of plug-in hybrid vehicles and personal electronic devices exacerbate already present safety issues, particularly that of Li dendrite formation and subsequent cell failure. Increased electrode surface area may mitigate dendrite formation by lowering the local current density, but deleterious electrolyte degradation reactions can consume electrolyte and result in eventual cell failure. Use of solid state electrolytes, previously only suitable for niche applications due to their low inherent ionic conductivity and limitations in fabrication process, can now be expanded to new applications such as the previously described 3D batteries by utilizing ALD processes. A number of suitable ALD process for well-known solid electrolytes have been developed,6,7 allowing deposition of thin, conformal solid electrolyte layers at temperatures as low as 150˚C. The current status of 3D solid state batteries will be discussed, as will remaining challenges. ALD’s capability for very thin solid electrolyte layers opens the door to advanced electrode protection, and and recent results showcasing the utility of ALD solid electrolyte coatings for protection layers on 3D nanoheterostructured electrodes and next-generation Li metal anodes will be discussed. In the case of conversion electrode materials, ALD coatings can prevent electrolyte decomposition and solid electrolyte interphase formation, lowering overpotential required for charge and discharge. Additionally, ALD coatings mechanically constrain conversion electrode particles, preventing volume expansion and fracturing of the coatings upon cycling.8 ALD layers applied to Li metal anodes can prevent electrolyte decomposition and Li dendrite formation by chemical stabilization of the electrode surface, resulting in both higher capacities and longer cycling lifetimes in the case of the Li-S and Li-Air systems.9,10

Pseudocapacitive Negative Electrodes Based on Mxene Ti2CT x for High-Power Li-Ion Batteries

Development of rapid charging systems in Li-ion batteries is one of the urgent tasks for the widespread use of environmental-friendly electric vehicles towards a sustainable and green society. However, in spite of numerous efforts devoted to realizing the high-power systems, their power density is not satisfactory, partly due to the poor rate capability of the negative electrodes. A novel family of layered compounds, MXene (M n +1X n T x : M = Ti, V, Nb, etc.; X = C, N; n = 1-3; T = surface termination groups) has attracted increasing attention as negative electrode material with high-rate capability for Li-ion batteries.[1] MXene is the derivative phase of ternary layered compounds, MAX phase (M n AX n : A = Al, Si, S, etc.), first synthesized with concentrated hydrofluoric acid (HF) solution to extract selectively the A element.[2] Due to the tunable compositions and structures in MXene, there are huge choices for the development of the high-power electrode materials. Gogotsi and colleagues have recently discovered that lithium fluoride (LiF) and hydrochloric acid (HCl) solution also selectively extracts the A element from MAX phase, and Ti3C2T x synthesized with the LiF and HCl solution exhibits higher performance as pseudocapactior in aqueous systems than HF-synthesized Ti3C2T x .[3]Therefore, the synthetic method for MXene is a key process to determine its electrochemical property. In this work, we have successfully synthesized Ti2CT x with the LiF and HCl solution. The charge-discharge measurement reveals that the Ti2CT x delivers large reversible capability of 260 mAh/g in 1M LiPF6/EC-DMC (1:1, v:v) electrolyte, which is larger than that of Ti2CT x prepared with concentrated HF solution (180 mAh/g).[4] Reaction mechanism was investigated with combined approach using XANES, XRD, and 7Li-MAS-NMR. We construct the prototype full cell with the Ti2CT x and LiNi1/3Co1/3Mn1/3O2 negative/positive electrodes, and demonstrate that the Ti2CT x is the promising electrode material for the high-power Li-ion batteries. [1] M. R. Lukatskaya, et al. and Y. Gogotsi, Science 341, 1502 (2013). [2] M. Naguib, et al. and M. W. Barsoum, Adv. Mater. 23, 4248 (2011). [3] M. Ghidiu, et al. and Y. Gogotsi, Nature 516, 78 (2014). [4] J. Come, et al. and P. Simon, J. Electrochem. Soc. 159, A1368 (2012). Figure 1. Charge-discharge profile of Ti2CT x in 1M LiPF6/EC-DMC (1:1, v:v) electrolyte and comparison in the rate capability synthesized with different solutions. Figure 1

Nb4N5/Nb2O5/r-GO Composites As Anode Materials for High Power Lithium Ion Batteries

Lithium-ion batteries have been extensively investigated for a range of portable electronic devices, but a major downside to current technology is the slow charging speeds. A potential solution is to utilize pseudocapacitve materials, in which the diffusion length for lithium ions is short. For example, Nb2O5 is a promising anode material with almost no kinetics limitations for solid-state Li+ diffusion due to the facile two-dimensional Li+ transport pathways within the structure. However, it is also a large bandgap semiconductor, with a low bulk electrical conducitivity of ~3.4 x 10-5 S cm-1at 300 K. The low electronic conductivity hinders its high-rate performance, especially for thick electrodes with high mass loadings. Numerous composite structures have been explored to improve the sluggish mobility of electrons in Nb2O5, such as blending with carbon nanotube, graphene composites, and carbon coating. Here we report an Nb4N5/Nb2O5/reduced graphene oxide (rGO) composite structure with improved kinetics prepared via partial nitridation of Nb2O5. Nb4N5 shows excellent metallic conductivity of 2000 S cm-1, which facilitates the interparticle electron conduction pathway in combination with the conductive graphene scaffold. Very high capacity retention at high charging/discharging speed is achieved in these materials, though the high power density comes at some cost of the capacity because the nitride is electrochemically inactive. One important advantage of the niobium oxide/nitride system, compared to pure Nb2O5/carbon composites is improved interface between the electrochemically active material and the conductive coating, since Nb2O5 can transform to Nb4N5 with almost no structural change. The composite also has a high volumetric capacity, since carbon additive is not needed in slurry electrodes. We believe metal oxide/metal nitride composites could provide a new design for high power electrode materials.

Universal roles of hydrogen in electrochemical performance of graphene: high rate capacity and atomistic origins.

Atomic hydrogen exists ubiquitously in graphene materials made by chemical methods. Yet determining the effect of hydrogen on the electrochemical performance of graphene remains a significant challenge. Here we report the experimental observations of high rate capacity in hydrogen-treated 3-dimensional (3D) graphene nanofoam electrodes for lithium ion batteries. Structural and electronic characterization suggests that defect sites and hydrogen play synergistic roles in disrupting sp2 graphene to facilitate fast lithium transport and reversible surface binding, as evidenced by the fast charge-transfer kinetics and increased capacitive contribution in hydrogen-treated 3D graphene. In concert with experiments, multiscale calculations reveal that defect complexes in graphene are prerequisite for low-temperature hydrogenation, and that the hydrogenation of defective or functionalized sites at strained domain boundaries plays a beneficial role in improving rate capacity by opening gaps to facilitate easier Li penetration. Additional reversible capacity is provided by enhanced lithium binding near hydrogen-terminated edge sites. These findings provide qualitative insights in helping the design of graphene-based materials for high-power electrodes.

(Invited) Tailoring Polymer Structure and Composition for High-Power and High-Charge Capacity Redox Electrodes

Conventional batteries are efficient at delivering a continuous supply of power; however, limited discharge rates prevent their use in high power applications. Many energy systems require sources that can repetitively supply high power bursts, which include electric transportation, utilization of renewable energy sources, and portable electronics. This demand can be addressed using advanced Li-ion batteries and supercapacitors, devices that combine the high power, rapid switching, and exceptional cycle life of a capacitor with the high energy density of a battery. Electroactive conducting polymers are suitable candidates for high-power energy storage, but they are currently limited by i) the lack of nano/micro-structure control over large areas, ii) relatively low charge-capacity, and iii) material stability. In this presentation, we will discuss our group’s recent progress on engineering high-energy and high-power electrode materials for energy storage, including scalable synthesis of nano/micro-structured polymer electrodes and integrating high-charge capacity redox polymers. To increase power, redox polymer microtubes with nanometer thickness are synthesized on large area substrates by controlling gas nucleation density, which guides to formation of nanostructured electrodes. Nanostructured electrodes exhibit superior performance at high charge/discharge rates relative to planar electrodes. To increase electrode charge capacity, redox molecules and polymer are incorporated into conducting polymer electrodes during electrochemical synthesis. The capacitance of polypyrrole electrodes can be increased from 249 F/g to 550 F/g using hydroquinone dopants, and up to 400 F/g using naturally abundant Alkali lignin. We show that the conditions for electrode synthesis, along with the type (and molecular composition) of lignin, exhibit strong correlations with electrode performance.

Bioinspired Synthesis of Hierarchical Porous Graphitic Carbon Spheres with Outstanding High-Rate Performance in Lithium-Ion Batteries

Inspired by the biomineralization of unicellular diatoms, a biomimetic approach based on template (pluronic F127 micelle cluster)-induced self-assembly of α-cyclodextrin is developed to create hierarchical porous graphitic carbon spheres via hydrothermal treatment followed by pyrolysis. The as-obtained carbon spheres combine the features required for high-power electrode materials in lithium-ion batteries (LIBs), such as high degree of graphitization, large surface area with hierarchically distributed pore sizes as well as doping with heteroatoms, which synergistically contribute to their impressive electrochemical properties. When applied as an anode for LIBs, the carbon spheres exhibit high reversible capacity (ca. 700 mA h g–1 at 50 mA g–1), good cycling stability, and remarkably outstanding high-rate performance (ca. 600, 450, and 290 mA h g–1 obtained at a current density of 1, 10, and 30 A g–1, respectively), which is among the best of present pure carbon materials for LIBs applications. The fabrica...

Interconnected porous carbon with tunable pore size as a model substrate to confine LiFePO4 cathode material for energy storage

LiFePO4/C composites with tunable particle size and loading content have been prepared using the porous carbon with large pore volume and controllable pore size as an interconnected conductive framework and rigid nano-confinement matrix. The large pore volume of carbon provides sufficient space for LiFePO4 hosting and the controllable pore size of carbon restricts the growth of LiFePO4 crystals to further improve the rate performance. When used as the cathode materials for lithium-ion batteries, they exhibit a stable and high reversible capacity of 161mAhg−1 at 0.1C, 106mAhg−1 at 20C and 50mAhg−1 at 50C. The cell retains 94% of its initial capacity at 20C over 200 cycles with an ultrahigh specific power of 10,446Wkg−1. The high rate performance and good cycle stability can be ascribed to the small nano-sized LiFePO4 confined in the nanopores of the carbon matrix with suitable loading content and good contact between LiFePO4 and the continuous conductive carbon framework, thus allowing fast lithium-ion diffusion and electrons transfer. This structure model may be valid for better understanding the rate performance and might be extended for fabrication of other high power electrode materials.

Etched colloidal LiFePO4 nanoplatelets toward high-rate capable Li-ion battery electrodes.

LiFePO4 has been intensively investigated as a cathode material in Li-ion batteries, as it can in principle enable the development of high power electrodes. LiFePO4, on the other hand, is inherently “plagued” by poor electronic and ionic conductivity. While the problems with low electron conductivity are partially solved by carbon coating and further by doping or by downsizing the active particles to nanoscale dimensions, poor ionic conductivity is still an issue. To develop colloidally synthesized LiFePO4 nanocrystals (NCs) optimized for high rate applications, we propose here a surface treatment of the NCs. The particles as delivered from the synthesis have a surface passivated with long chain organic surfactants, and therefore can be dispersed only in aprotic solvents such as chloroform or toluene. Glucose that is commonly used as carbon source for carbon-coating procedure is not soluble in these solvents, but it can be dissolved in water. In order to make the NCs hydrophilic, we treated them with lithium hexafluorophosphate (LiPF6), which removes the surfactant ligand shell while preserving the structural and morphological properties of the NCs. Only a roughening of the edges of NCs was observed due to a partial etching of their surface. Electrodes prepared from these platelet NCs (after carbon coating) delivered a capacity of ∼155 mAh/g, ∼135 mAh/g, and ∼125 mAh/g, at 1 C, 5 C, and 10 C, respectively, with significant capacity retention and remarkable rate capability. For example, at 61 C (10.3 A/g), a capacity of ∼70 mAh/g was obtained, and at 122 C (20.7 A/g), the capacity was ∼30 mAh/g. The rate capability and the ease of scalability in the preparation of these surface-treated nanoplatelets make them highly suitable as electrodes in Li-ion batteries.

High-Energy and High-Power Electrodes Screened by Microstructure Reconstruction and Model Simulation

Even though it is well-known that high-power and high-energy lithium ion cells require different electrode design rules, conventional analysis methods fail to quantify the key properties of their microstructures. To shed light on the differences between commercial high-power and high-energy cells, their electrode microstructures are analyzed in detail using focused ion beam and micro X-ray tomography. The cells under investigation are a 18650 LiFePO4/graphite power cell and a 18500 LiCoO2/graphite energy cell. A three-dimensional reconstruction of anodes and cathodes allows for specifying their tailor-made microstructural characteristics. Beside the basic structural parameters (a) volume fractions, (b) surface areas, (c) average particle sizes and (d) tortuosity, a more advanced analysis yields additional information such as: (e) particle size distributions, (f) space-resolved tortuosity values (g) a detailed analysis of different secondary-particle classes. Based on this array of microstructural information, the specific characteristics of all electrodes are identified with respect to cell performance. This newly gained insight is backed up by model simulations. These are based on a refined homogenized porous electrode model, which is parameterized with the structural parameters extracted from the reconstructions. This combined approach gives a high-definition picture of tailor-made electrodes and facilitates understanding of rate-limiting mechanisms in high-power and high-energy electrodes. During charging and discharging, the electrochemically active zone spreads out over the entire electrode thickness within the high-power cell. Contrary, it is spatially restricted in both electrodes of the high-energy cell and migrates from the separator towards the current collector. Model simulations show, that this behavior is caused by (i) the lower electrode porosity and (ii) the larger electrode thickness of the high-energy cell. Furthermore, model simulations show, that the maximum discharge current of both cathodes (16C and 4C) is restricted by a depletion limitation of the electrolyte. Figure 1: Three-dimensional reconstructed microstructures of the high-power cell (a, c) and the high-energy cell (b, d). For the anodes (a, b), the graphite phase is shown in blue with the porosity appearing transparent. For the LiFePO4 cathode (c), the two different agglomerate classes are shown in different shades of green, the carbon additive is shown in gray. For the LiCoO2 cathode (d), the active material is also shown in green and the carbon in gray. The porosity in both cathodes appears transparent.

Full-Field Synchrotron Tomography of Nongraphitic Foam and Laminate Anodes for Lithium-Ion Batteries

Nondestructive methods that allow researchers to gather high-resolution quantitative information on a material's physical properties from inside a working device are increasingly in demand from the scientific community. Synchrotron-based microcomputed X-ray tomography, which enables the fast, full-field interrogation of materials in functional, real-world environments, was used to observe the physical changes of next-generation lithium-ion battery anode materials and architectures. High capacity, nongraphitic anodes were chosen for study because they represent the future direction of the field and one of their recognized limitations is their large volume expansion and contraction upon cycling, which is responsible for their generally poor electrochemical performance. In this work, Cu6Sn5 coated on a three-dimensional copper foam was used to model a high power electrode while laminated silicon particles were used to model a high energy electrode. The electrodes were illuminated in situ and ex situ, respectively, at Sector 2-BM of the Advanced Photon Source. The changes in electrode porosity and surface area were measured and show large differences based on the electrode architecture. This work is one of the first reports of full-field synchrotron tomography on high-capacity battery materials under operating conditions.

Free-standing and binder-free sodium-ion electrodes based on carbon-nanotube decorated Li4Ti5O12 nanoparticles embedded in carbon nanofibers

Free-standing CNT/Li4Ti5O12/C composite nanofibers with uniformly dispersed Li4Ti5O12 nanoparticles and CNTs in a one-dimensional (1D) carbon nanofiber matrix were developed for high-power electrode materials in Na-ion batteries. The carbon nanofibers act as a matrix to enable better dispersion of Li4Ti5O12 and restrict the Li4Ti5O12 particle size at the nanoscale. The CNTs were introduced to construct a three-dimensional (3D) network between Li4Ti5O12 particles and to enhance the conductivity of the electrode, thereby realizing the full potential of the active materials. Free-standing CNT/Li4Ti5O12/C composite nanofibers achieved a discharge capacity of 119 mA h g−1 after 100 cycles at a current density of 100 mA g−1, corresponding to 95.2% of the initial charge capacity (125 mA h g−1) and a better rate capability (77 mA h g−1 at 500 mA g−1). This design could also be further extended to other electrode materials, which promises to promote the development of next-generation Li-ion batteries or Na-ion batteries.

A porous C/LiFePO4/multiwalled carbon nanotubes cathode material for Lithium ion batteries

Three dimensional (3D) porous C/LiFePO4/MWCNTs was synthesized by a hybrid of in situ sol gel strategy and a facile electro-polymerization polyaniline technique and a simultaneous sintering progress. In combined with the 3D hierarchical pore topologies and high electronic conduction facilitating the kinetics of both electron transport and lithium ion diffusion within the particles, the optimized electrodes exhibit an ultrahigh rate capacity, stable charge/discharge cycle ability, and a comparative volume capacity. The synthesized LiFePO4 composite offers a discharge capacity of 169.6mAhg−1 (nearly to its the theoretical capability 170mAhg−1) at the C/10 rate and delivers a good rate performance with a capacity of 141.9mAh g−1 at a high rate of 20C, and stable charge/discharge cycle ability (>95% capacity retention after 200 charge/discharge cycles).This non-organic facile synthesize avenue can be high desirable to prepare high-power electrode materials

C/LiFePO4/multi-walled carbon nanotube cathode material with enhanced electrochemical performance for lithium-ion batteries

C/LiFePO4/multi-walled carbon nanotubes composite is prepared by a hybrid of hydrothermal progress that involves an in-situ multi-walled carbon nanotubes embedding approach and a facile electro-polymerization polyaniline process. The designed material on nanosize with about 100–200 nm in length contains tridimensional networks and uniform-thickness carbon layer, which remarkably enhance its electronic conductivity. The synthesized LiFePO4 composite offers a discharge capacity of 169.8 mAh g−1 at the C/2 rate and high capacity retention at the 5C rate. Meanwhile, the well-crystallized material composed of many densely aggregated nanoparticles and interconnected nanochannels presents a high tap density leading to excellent volumetric Li storage properties at high current rates (>135 mAh cm−3 at 20C), and stable charge/discharge cycle ability (>95% capacity retention after 200 charge/discharge cycles). As such, the prepared material with controllable size and structure yields an enhanced electrochemical performance in terms of charming rate capability, cycling life and capacity retention as a cathode in lithium-ion batteries, this non-organic facile synthesize avenue can be promising to prepare high-power electrode materials.