Nanosized Electrode Materials Research Articles

Consecutive engineering of anodic graphene supported cobalt monoxide composite and cathodic nanosized lithium cobalt oxide materials with improved lithium-ion storage performances

Downsizing the electrochemically active materials in both cathodic and anodic electrodes commonly brings about enhanced lithium-ion storage performances. It is particularly meaningful to explore simplified and effective strategies for exploiting nanosized electrode materials in the advanced lithium-ion batteries. In this work, the spontaneous reaction between few-layered graphene oxide (GO) and metallic cobalt (Co) foils in mild hydrothermal condition is for the first time employed to synthesize a reduced graphene oxide (RGO) supported nanosized cobalt monoxide (CoO) anode material (CoO@RGO). Furthermore, the CoO@RGO sample is converted to nanosized lithium cobalt oxide cathode material (LiCoO2, LCO) by taking the advantages of the self-templated effect. As a result, both the CoO@RGO anode and the LCO cathode exhibit inspiring lithium-ion storage properties. In half-cells, the CoO@RGO sample maintains a reversible capacity of 740.6 mAh·g−1 after 300 cycles at the current density of 1000 mA·g−1 while the LCO sample delivers a reversible capacity of 109.1 mAh·g−1 after 100 cycles at the current density of 100 mA·g−1. In the CoO@RGO//LCO full-cells, the CoO@RGO sample delivers a reversible capacity of 553.9 mAh·g−1 after 50 cycles at the current density of 200 mA·g−1. The reasons for superior electrochemical behaviors of the samples have been revealed, and the strategy in this work can be considered to be straightforward and effective for engineering both anode and cathode materials for lithium-ion batteries.

A variational method guided confining tip discharge for MOF-derived supercapacitors

Nanosized electrode materials have received wide attention in electrochemistry since their large specific surface areas are the precondition for the excellent performance of electrochemistry, such as supercapacitors, Li-ion batteries, Na-ion batteries, electrocatalysis, photoelectrocatalysis, electrolysis and electrodeposition. However it also leads to the high value of curvature of nanomaterials, causing the unavoidable and non-ignorable leakage currents, and therefore the activity degradation. Here, guided by the variational method, we first theoretically predict that, with giving a certain value of curvature, the paraboloid structure possesses the maximal surface area to greatly reduce the tip-charge, thus guaranteeing the electrochemical performance. Consequently, with using supercapacitors as the model application, this unusual morphological structure was successfully constructed in the metal-organic frameworks (MOFs)-derived Zn-Ni-Co-P@CoP nanowire arrays (ZNCP@CoP NWRs), which largely ensures the ZNCP@CoP NWRs || AC device exhibits an ultralow leakage current of 10.28 μA. The low curvature structure of ZNCP@CoP NWRs also significantly improves the electrochemical performance of supercapacitors with a large specific capacitance of 1483 C g−1 at 1 A g−1 and a high cyclic stability of 80% capacity maintained over 5000 cycles at 5 A g−1. The finding in this work highlights the great potential of the reasonable material design approach for advanced energy applications.

One-pot spray pyrolysis for core–shell structured Sn@SiOC anode nanocomposites that yield stable cycling in lithium-ion batteries

A novel strategy is reported for the synthesis of high-capacity anode materials with good cycling stability for use in lithium-ion batteries. A facile one-pot spray pyrolysis process is conducted using an ethanol solution of Sn acetate and diphenylsilanediol (DPSD). Phase separation between Sn and DPSD leads to the formation of core@shell-structured Sn@DPSD nanoparticles, and subsequent heat-treatment in an inert atmosphere carbonizes the DPSD to form Sn@SiOC nanoparticles (∼50 nm). When applied as an anode material in lithium-ion batteries (LIBs), the Sn core retains its high energy density, while the SiOC shell limits volume expansion of the core and protects it from pulverization and agglomeration. The Sn@SiOC nanoparticles exhibit a reversible capacity of 917 mA h g −1 at 0.1C and stable cycling performance for 200 cycles at 1C. The nanoparticle formation mechanism is investigated by optimizing the Sn acetate/DPSD ratio in the precursor solution, and the origin of the enhanced properties is investigated by comparing the results of Sn@SiOC nanoparticles with those of SiOC nanoparticles and Sn microspheres. SiOC shows considerable promise as a coating material for Sn nanoparticles, which may serve as a milestone in the synthesis of nanosized electrode materials with coatings that can prolong the cycle lives of rechargeable batteries.

Stretchable self-charging energy integrated device of high storage efficiency

Integrated energy devices consisting of solar cells and rechargeable batteries are in great demand in wearable electronics and low-energy-density applications in fields such as healthcare. However, developing energy-efficient stretchable energy systems is very difficult due to numerous technical limitations. Herein, a stretchable solar module/rechargeable lithium-ion battery-integrated energy device using a zig-zag truncated electrode for energy storage, nano-sized electrode materials and a polymer–metal-island non-woven common substrate for the integration device is presented. This new stretchable device is portable, has a high operation potential (up to 1.8 V), a long life, high self-charging efficiency, and a high rate-capability. Its self-power conversion/storage efficiency is unprecedented at 13.3%. Additionally, an 89.34% retention capacity can be obtained after 100 cycles, and a surprisingly low-capacity decay of 5.7% in the 30% stretched state is observed. The device's stable performance under various current density and stretching conditions paves the way for the development of highly stretchable integrated energy systems.

Structural characterization and electrochemical performance of Ni-doped Co9S8 for Li-ion battery and asymmetric supercapacitor dual applications

Development of nano-sized electrode materials with unique structural and electrical properties is urgently needed due to their vital roles in advanced energy storage systems. Adhering to that.Ni-doped Co9S8 nanoparticles were directly prepared by a facile solvothermal method for implementation as active anodes in rechargeable Li-ion batteries and supercapacitors. X-ray diffraction analysis using Rietveld method revealed a single Co9S8 phase with cubic structure (Fm3‾m), confirming the incorporation of Ni ions into the Co9S8 lattice replacing Co ions mainly at octahedral sites. The particle size and morphology were examined by HRTEM images taken at different magnifications. The XPS measurements verified the presence of Ni ions in the Co9S8 matrix and determined the cations oxidation states. The as-prepared nano-Ni@Co9S8 anode material delivered high discharge and charge capacities ∼764 and 520 mAhg−1, respectively in the initial cycle of Li-ion battery. The fabricated Ni@Co9S8 supercapacitor demonstrated good specific capacitance ∼312 F g−1 with high capacitance retention ∼96% after 700 cycles which decreased to 206 F g−1 after 1600 cycles. Meanwhile, a sharp loss in its capacitance by 36% was happened in the subsequent 900 cycles achieving about 206 F g−1 after 1600 cycles.

Phase boundary propagation mode in nano-sized electrode materials evidenced by potentiostatic current transients analysis: Li-rich LiFePO4 case study

Phase boundary propagation dynamics in phase-transforming battery nanomaterials is widely studied due to high practical relevance of the boundary propagation patterns to the rate performance and degradation of metal-ion batteries. In this work, we decipher the complex interplay between the kinetic limitations in the course of phase boundary movement, which can be controlled by slow diffusion, interfacial charge transfer and nucleation. Employing nanosized Li-rich LiFePO4 materials as model systems, we consistently analyze the effect of each of the possible limiting factors on the evolution of potentiostatic current transients’ shape. Our results conclusively demonstrate that under the experimental conditions all three rate-controlling factors contribute to the rate-limitations of an intercalation material. We used numerical modeling to provide illustrative examples of current transients under different limiting regimes, which can be employed for the rapid and accurate diagnostics of the control factors during phase transformations. The derived conclusions allow rationalizing both the phase-transformation pathways in multiparticle electrodes (particle-by-particle or concurrent intercalation) and phase-growth morphologies (intercalation wave or shrinking core) based on easily accessible experimental estimates of kinetic parameters. These results are of high diagnostic value for the development of physically adequate battery models.

Electrode Materials and Electrolytes for High-Rate Electrochemical Energy Systems: A Review

High-rate electrochemical systems as well as materials and electrolytes for such systems are briefly described. An optimized citrate method is presented for the synthesis of nanosized electrode materials with electrochemical properties comparable to the properties of the best commercial samples. Possible criteria for an ideal electrode material are formulated and the theoretical high-rate limit of such material is estimated. Dynamic criteria are proposed to identify the specific species in the electrolyte solutions and the most efficient charge transfer is shown to be carried out by solvent-separated ion pairs.

Fe2 VO4 Hierarchical Porous Microparticles Prepared via a Facile Surface Solvation Treatment for High-Performance Lithium and Sodium Storage.

Preventing the aggregation of nanosized electrode materials is a key point to fully utilize the advantage of the high capacity. In this work, a facile and low-cost surface solvation treatment is developed to synthesize Fe2 VO4 hierarchical porous microparticles, which efficiently prevents the aggregation of the Fe2 VO4 primary nanoparticles. The reaction between alcohol molecules and surface hydroxy groups is confirmed by density functional theory calculations and Fourier transform infrared spectroscopy. The electrochemical mechanism of Fe2 VO4 as lithium-ion battery anode is characterized by in situ X-ray diffraction for the first time. This electrode material is capable of delivering a high reversible discharge capacity of 799 mA h g-1 at 0.5 A g-1 with a high initial coulombic efficiency of 79%, and the capacity retention is 78% after 500 cycles. Moreover, a remarkable reversible discharge capacity of 679 mA h g-1 is achieved at 5 A g-1 . Furthermore, when tested as sodium-ion battery anode, a high reversible capacity of 382 mA h g-1 can be delivered at the current density of 1 A g-1 , which still retains at 229 mA h g-1 after 1000 cycles. The superior electrochemical performance makes it a potential anode material for high-rate and long-life lithium/sodium-ion batteries.

Impact of the synthesis parameters on the microstructure of nano-structured LTO prepared by glycothermal routes and 7Li NMR structural investigations

The efficient materials for Li-ion battery electrodes require suitable composition, high-crystallinity and appropriate structuration. The last one is important to assure an efficient exchange of Li ions between the anode and electrolyte, thus enhancing the kinetics of electrochemical reactions. Therefore, the synthesis of well-crystallized nano-sized electrode materials exhibiting high surface area is of great interest. Herein, we explore the influence of the glycothermal synthesis variations on the structure and porosity of Li4Ti5O12. The utilized precursors and their concentration have a minor influence on crystallites size, but they could be used to control the porosity of assembled particles. The prepared Li-ion battery anode could be charged at low and high rate reaching the theoretical capacity of Li4Ti5O12. The material retains its peculiar porous structuration even after 1000 cycles at charging/discharging rate of 50C which contributes to the lack of capacity fading. Additionally, 7Li NMR is performed on one of synthesized nano-structured Li4Ti5O12 and compared with commercially available nanosized Li4Ti5O12 to understand the excellent electrochemical performance.

High Power Lithium-ion Battery based on Spinel Cathode and Hard Carbon Anode

Power performance of lithium-ion batteries (LIBs) is generally controlled by the Li+ diffusion within crystalline framework of electrode materials, and thus nano-sized electrode materials with shortened diffusion length have been widely used to build high power LIBs. However, the undesired effects from nano-sized electrode materials, such as low tap density, low thermal stability and increased interface also discount the overall performance of LIBs. Accordingly, it is desired to develop high power LIBs with micro-sized electrode materials. Herein, we demonstrate that hard carbon displays fast Li-storage kinetics which is not controlled by Li+ diffusion in the crystalline framework. Furthermore, it is found that micro-sized spinel LiNi0.5Mn1.5O4 and LiMn2O4 have high rate performance, owing to their three-dimensional channels for Li+ diffusion. Finally, the micro-sized spinel LiNi0.5Mn1.5O4 (or Li1.1Mn2O4) and micro-sized hard carbon are used as cathode and anode, respectively, to fabricate the full cells that exhibit supercapacitor-like high power performance. The achieved results point a way to develop high power LIBs besides nano-sizing electrode materials.

Improved Cycling Stability of Conversion and Alloying Anodes through the Use of Nanomaterials

In order to meet the growing need for portable energy storage future batteries need to provide improved energy densities. One major problem lies in the current use of intercalation based electrode materials which are typically limited to storing one lithium ion per formula unit. Improved energy storage can be achieved through the use of conversion and alloying reactions where it is possible to store multiple lithium ions per formula unit. Even though impressive energy densities can be obtained through the use of conversion and alloying anode materials, only surpassed by the use of lithium metal itself, these systems are typically plagued by capacity fading during cycling. The origin is generally ascribed to irreversible reactions with the electrolyte amplified by major volume expansion, causing the growth of a solid electrolyte interphase (i.e. SEI). One promising strategy to address this issue is through the use of nanosized electrode materials (e.g. Si nanoparticles), as it has been shown that nanoparticles and nanowires show better cycling stability than their bulk counterparts [1, 2]. Large particles (i.e micrometer sized) form cracks during cycling as opposed to smaller particles (i.e. < 150 nm) [3]. Even though the use of nanoparticles can reduce crack formation and the accompanied SEI growth, capacity fading is still observed for these systems. Our work has focused on studying freestanding nanostructured conversion materials (e.g. Cu2O nanowires), which offer in depth analyses of the conversion reactions without disturbance from binders or conducting additives. Contrary to previous understanding nanosized Cu2O thin films and multi-layered nanostructures show an increase in capacity during cycling [4, 5]. This behaviour is caused by improved access to the entire material when using the nanomaterials. The system has also shown improved performance during cycling likely caused by electrochemical milling of the particles thereby consistently reducing the particle size and thus allowing more of the material to be accessible. With the successful use of nanosized conversion materials our research is now focused on addressing the stability problems of alloying materials by studying the effect of nanomaterials.

New Analytical Tool for Electrochemical Interfaces – in Situ Neutron Reflectometry

Interfacial reactions between intercalation electrodes and electrolyte have attracted much attention to achieve high current drain and long-term stability of lithium batteries, fuel cells, and metal-air batteries. However, there is no common strategy for the design of materials produced under an electrochemical potential field. Neutron reflectometry (NR) is a new experimental technique that gives useful information of the concentration gradient of diffusing species from the electrode to the electrolyte on battery operation [1]. Here we have detected a defect-rich phase in the 10–20 nm region from the surface of lithium intercalation electrodes, Li4Ti5O12, LiMn1/3Co1/3Ni1/3O2, and LiFePO4. The defective phase formation has been directly related to the electrochemical activity of nanosized electrode materials. Epitaxial films of each electrode material were grown on Nb:SrTiO3(111) substrates using a pulsed laser deposition apparatus [1-2]. Thicknesses of the films were 25 to 45 nm. NR measurements were performed on SOFIA (BL-16, J-PARC), which is a time-of-flight reflectometer [3]. A deuterated propylene carbonate electrolyte containing 1 M LiPF6 was used as an electrolyte solution to prevent incoherent scattering of 1H. The neutron reflectivity spectra were collected at pristine and at open circuit voltage condition. The models of interfacial structure were refined by the Parratt32 data analysis program using roughness, thickness, and scattering length density (SLD) of each layer as parameters. The SLD in the surface region of Li4Ti5O12(111) increased from the pristine to the cell-construction conditions. As nLi ions have a negative coherent scattering length of -1.9 fm, the increase in the SLD indicated a formation of lithium vacancies in the surface region prior to electrochemical cycling. The lithium vacancy-type (VLi') defect formation was confirmed by lattice contraction observed by surface X-ray diffraction [4]. Similar to Li4Ti5O12, a lithium vacancy-type defect phase was detected for LiMn1/3Co1/3Ni1/3O2(1-18). In contrast, LiFePO4(100) films showed a decrease in the SLD value at the electrochemical interface formation, indicating a defect phase of interstitial lithium type (Lii .). The type of defects generated may be related to the electrochemical potentials of the electrode and the electrolyte. The difference in electrochemical potential causes a gradual change in the structure at the interfacial region to equilibrate the potentials of the two materials. Lithium is the mobile species in these electrodes; therefore, lithium may participate in charge compensation with formation of the defect phase. The defective phase was related to an extremely high lithium storage capacity of nanosized Li4Ti5O12[5] and an isotropic lithium diffusion in nanosized LiFePO4. The results suggest how to create a defect phase at the electrochemical interface and the concept of interfacial defect phase control is extended to nanosize material control for next-generation battery materials. References M. Hirayama, et al., Electrochemistry, 78 (2010) 413.M. Hirayama, et al., Dalton Trans., 40 (2011) 2882.M. Koji et al., J. Phys.: Conf. Ser., 272 (2011) 012017.M. Hirayama, et al., J. Am. Chem. Soc., 132, (2010) 15268; K. Sakamoto, et al., Phys. Chem. Chem. Phys., 12 (2010) 3815; K. Sakamoto, et al., Chem. Mater., 21 (2009) 2632.Wagemaker, et al., J. Am. Chem. Soc., 131 (2009) 17786.

Applications of carbon nanotubes in high performance lithium ion batteries

The development of lithium ion batteries (LIBs) relies on the improvement in the performance of electrode materials with higher capacity, higher rate capability, and longer cycle life. In this review article, the recent advances in Carbon nanotube (CNT) anodes, CNT-based composite electrodes, and CNT current collectors for high performance LIBs are concerned. CNT has received considerable attentions as a candidate material for the LIB applications. In addition to a possible choice for anode, CNT has been recognized as a solution in improving the performance of the state-of-the-art electrode materials. The CNT-based composite electrodes can be fabricated by mechanical or chemical approaches. Owing to the large aspect ratio and the high electrical conductivity, CNTs at very low loading can lead to an efficient conductive network. The excellent mechanical strength suggests the great potential in forming a structure scaffold to accommodate nano-sized electrode materials. Accordingly, the incorporation of CNTs will enhance the conductivity of the composite electrodes, mitigate the agglomeration problem, decrease the dependence on inactive binders, and improve the electrochemical properties of both anode and cathode materials remarkably. Freestanding CNT network can be used as lightweight current collectors to increase the overall energy density of LIBs. Finally, research perspectives for exploiting CNTs in high-performance LIBs are discussed.

Immobilization of nanosized LiFePO4 spheres by 3D coralloid carbon structure with large pore volume and thin walls for high power lithium-ion batteries

A novel LiFePO4/C composite, including 85.4 wt% of spherical LiFePO4 nanocrystallites with the size of 22 nm is fabricated by using 3D coralloid nitrogen-containing carbon with large pore volume (4.68 cm3 g−1) and thin walls (2–3 nm) as interpenetrating conductive framework. Based on the whole composite, the LiFePO4/C cathode material exhibits a stable and high reversible capacity of 144.6 mA h g−1 at 0.1 C and 60.4 mA h g−1 at 20 C (based on the weight of LiFePO4, it can deliver a high capacity of 155.8 mA h g−1 at 0.1 C and 85.3 mA h g−1 at 20 C). The cell retains 96.7% of its initial capacity at 10 C over 1000 cycles with an ultrahigh specific power of 5114 W kg−1 and the coulombic efficiency is >99%. The excellent performance is ascribed to the facile lithium-ion diffusion within the LiFePO4 nanocrystallites and high conductivity through the 3D continuous network. This coralloid carbon not only provides sufficient space for LiFePO4 hosting to further assist in energy storage, but also acts as a rigid nano-confinement support that prevents agglomeration of LiFePO4 during calcinations, which might be extended for the fabrication of other nano-sized electrode materials.

Synthesis of nanosized materials for lithium-ion batteries by mechanical activation. Studies of their structure and properties

This short review reports on the synthesis of nanosized electrode materials for lithium-ion batteries by mechanical activation (MA) and studies of their properties. Different structural types of compounds were considered, namely, compounds with a layered (LiNi1 − x − y Co x Mn y O2), spinel (LiMn2O4, Li4Ti5O12), and framework (LiFePO4, LiTi2(PO4)3) structures. The compounds also differed in electronegativity, which varied from 10−4 S cm−1 for LiCoO2 to 10−9 S cm−1 for LiFePO4. The preliminary MA of mixtures of reagents in energy intensive mechanoactivators led to the formation of highly reactive precursors, and annealing of the latter formed nanosized products (the mean particle size is 50–200 nm). The local structure of the synthesized compounds and the composition of their surface were studied by spectral methods. An increase in the dispersity and defect concentration, especially in the region of the surface, improved some electrochemical characteristics. It increased the stability during cycling (LiMn2O4, at 3 V) and the regions of the formation of solid solutions during cycling (Li4Ti5O12, LiFePO4), led to growth of surface Li-ion conductivity (LiTi2(PO4)3), etc. The mechanochemical approach was also used for the synthesis of core-shell type composite materials (LiFePO4/C, LiCoO2/MeO x ) and materials based on two active electrode components (LiCoO2/LiMn2O4).

Anisotropic Surface Effect on Electronic Structures and Electrochemical Properties of LiCoO2

Increasing industrial needs for rechargeable batteries delivering higher power has encouraged advanced research on nanosized electrochemically active compounds. Although nanosized electrode materials are expected to possess much higher power output due to short diffusion length, the nanosize effects on electrodes have not been understood well to date. Here, we report that nanosized LiCoO2 as suggested as electrode material for Li-ion rechargeable batteries has anisotropic surface properties affecting electronic structures, which is evidenced by electron energy loss spectroscopy (EELS). EELS spectroscopy reveals the reduced valence state of the cobalt near the surface, especially along the stacking direction of CoO2 layers. The observed anisotropic surface property explains the nanosize effect on the electrochemical properties.

Nanostructured materials for advanced Li-Ion rechargeable batteries

This article reveals how moving from bulk materials to the nanoscale can significantly change device performance for energy storage and conversion. The development of high-performance Li-ion batteries can benefit from the distinct properties of nanomaterials, such as high surface areas, short diffusion paths, and a large quantity of active sites, as well as freedom for volume change during charging or discharging cycles. Among a wide range of synthetic methods in preparing nanomaterials, simple and elegant are soft chemistry routes that involve sol-gel reactions and that frequently use organic molecules as structure-directing templates. Applications of nanotechnology in energy storage are in the stage of research and development. For realization of wide industrial applications, further work is required to achieve controlled and large-scale synthesis of nanostructures, to understand mechanisms of Li storage in nanomaterials and kinetic transport on the interface between electrode and electrolyte. The effects of nanostructures in battery performance are not simple consequences of a reduction in size. The interfacial properties are subtle and critical, considering space-charge effects at the interface between nanosized electrode materials and charge transport between electrode and electrolyte. This challenges researchers worldwide to carry out systematic experimental studies and to develop predictive theoretical tools for better fundamental understanding of relationships between nanostructures and electrochemical characteristics of electrode materials.

Quantitative analysis of X-ray absorption spectra using a 2D map representation

A promising possibility for the quantitative analysis of X-ray absorption near edge structure (XANES) spectra of nanosized electrode materials is demonstrated. We used a 2D map representation technique, which utilizes the values of the first derivatives of the absorbance with respect to the inserted Li + content plotted over the two-dimensional space defined by the inserted Li + content (mole) versus photon energy (eV) as a single map. The technique was applied to XANES spectra of the Li y CoO system in the first Li + insertion reaction for determining the structural and electronic variations associated with the change in Li + content. The obtained show that the intensities of two peaks at 7725 and 7711 eV increased with the Li + content and the difference of intensity change of these two peaks carried out for successive couples of spectra yielded the largest changes at 1.05 and 1.98 mol of Li content. This approach for quantitative analysis of XANES without using conventional simulation techniques enable us to interpret X-ray absorption spectroscopy (XAS) as a quantitative analytical technique with greater confidence.

Electrochemical Properties of Nano-Sized Electrode Materials Prepared by Spray Pyrolysis Deposition

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