Orthorhombic LiMnO2 Research Articles

SYNTHESIS OF ORTHORHOMBIC LiMnO2 BY HYDROTHERMAL PROCESS

This work synthesised layered structural orthorhombic LiMnO2 powder via a hydrothermal process. The influences of hydrothermal temperature (tr°), reaction time (tht), molar concentration of LiOH.H2O in aqueous solutions (CLH), and the ratio of Mn2O3 powder (xr/t) were investigated. A high-purity LiMnO2 powder was successfully synthesised using hydrothermal synthesis at CLH = 4M, tht = 8 h, tr° = 180 °C, and xr/t = 0.9. The synthesis LiMnO2 powders have layer structure, and the planar density calculations indicated that the (021) planes had a lower average planar density than those of (100) and (010) planes, which led to a faster crystal growth on (021) planes. Moreover, single crystals of LiMnO2 were pseudo-hexagonal also due to the lower average planar density of (221) planes compared to that of (021) planes, which made the crystal grow faster on (221) planes.

Isothermal Microcalorimetry Analysis of Li/β-MnO2 Discharge

Despite widespread use over several decades, the lithium/manganese dioxide (Li/MnO2) discharge mechanism is not completely understood owing to the structural complexity of the material. However, an improved understanding could lead to broader adoption as a primary and even secondary cathode material. Here, we examine the discharge of single-phase β-MnO2 using isothermal microcalorimetry for the first time. Equilibrium voltage and entropy changes are characterized over the entire discharge range and used to rationalize the results. These measurements are supplemented by electrochemical impedance and X-ray diffraction data that give the clearest picture of the β-MnO2 lithiation process to date. We find that the first half of discharge is dominated by a two-phase reaction to form Li0.5MnO2 followed by single-phase insertion to a composition of Li1.0MnO2, which confirms prior first-principles calculations. The tetragonal β-MnO2 lattice undergoes asymmetric expansion from Jahn-Teller distorted Mn3+ to form an orthorhombic LiMnO2 phase which retains the 1 × 1 tunnel structure. Microcalorimetry results suggest the presence of parasitic reactions occurring during the second half of discharge, which could arise from decomposition of electrolyte or release and reaction of residual water retained in the structure.

Molten Hydroxide Electrodeposition of Transition Metal Oxide Cathodes for Electrochemical Energy Storage

State-of-the-art synthesis for layered oxide cathodes for Li and Na-ion battery involves prolonged high temperature (>700°C) multistep processing for long reaction times (~24 hours) under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Here, we demonstrate an intermediate temperature (250-350°C) molten hydroxide-based electrodeposition process to grow alkali ion (Li+, Na+) intercalated transition metal oxides across multiple transition metal chemistries of the Li system (from layered LiCoO2 to cobalt-less orthorhombic LiMnO2, layered Li2MnO3, spinel LiNixMn1-xO4, LiMn2O4,) and Na system (O3 and P2 NaxCoO2, O’3 NaxMnO2) in thick film form factors. The highly textured ([110]||ND), dense (>95%) electroplated LiCoO2 cathodes can perform at ultrahigh thickness of ~200 µm (areal capacity ~13.6 mAh/cm2) in comparison to 40-60 µm for state-of-the-art slurry cast cathodes (areal capacity ~3-4 mAh/cm2 with a porosity of ~20%), a fivefold increase in areal capacity and volumetric energy density. We discuss the interplay of bulk crystallographic orientation of the electro-active material (LiCoO2), surface terminating planes interacting with the electrolyte, and electrochemically grown conformal surface protective layers on the electrochemical-chemo-mechanical degradation mechanisms during intercalation and deintercalation for high voltage operation (>4.2 V vs. Li). We also demonstrate electrochemically controllable isovalent transition metal doping and substitution in ceramic oxides (LiCoxMn1-xO2) by electrodeposition. Our findings highlight the influence of the unique molten hydroxide-based solution chemistry platform and electrochemical processing parameters, on regulating the phase assemblage, designing the microstructure, and controlling crystallographic orientation during electrocrystallization.

Atomistic Insights of Irreversible Li+ Intercalation in MnO2 Electrode.

Tunnel-structured MnO2 represents open-framed electrode materials for reversible energy storage. Its wide application is limited by its poor cycling stability, whose structural origin is unclear. We tracked the structure evolution of β-MnO2 upon Li+ ion insertion/extraction by combining advanced in situ diagnostic tools at both electrode level (synchrotron X-ray scattering) and single-particle level (transmission electron microscopy). The instability is found to originate from a partially reversible phase transition between β-MnO2 and orthorhombic LiMnO2 upon lithiation, causing cycling capacity decay. Moreover, the MnO2 /LiMnO2 interface exhibits multiple arrow-headed disordered regions, which severely chop into the host and undermine its structural integrity. Our findings could account for the cycling instability of tunnel-structured materials, based on which future strategies should focus on tuning the charge transport kinetics toward performance enhancement.

Atomistic Insights of Irreversible Li+ Intercalation in MnO2 Electrode

AbstractTunnel‐structured MnO2 represents open‐framed electrode materials for reversible energy storage. Its wide application is limited by its poor cycling stability, whose structural origin is unclear. We tracked the structure evolution of β‐MnO2 upon Li+ ion insertion/extraction by combining advanced in situ diagnostic tools at both electrode level (synchrotron X‐ray scattering) and single‐particle level (transmission electron microscopy). The instability is found to originate from a partially reversible phase transition between β‐MnO2 and orthorhombic LiMnO2 upon lithiation, causing cycling capacity decay. Moreover, the MnO2/LiMnO2 interface exhibits multiple arrow‐headed disordered regions, which severely chop into the host and undermine its structural integrity. Our findings could account for the cycling instability of tunnel‐structured materials, based on which future strategies should focus on tuning the charge transport kinetics toward performance enhancement.

Electrochemically Grown Crystallographically Controlled Energy and Power Dense Cathodes for Li and Na Ion Batteries

Electrochemical synthesis of materials has contributed to significant breakthroughs in materials processing by replacing high temperature, cost and energy intensive pyrometallurgical processes. Although electrodeposition as a technology for reduction of elements and alloys has been practiced since at least the 1940s, a current key and exciting question is to identify and develop electrodeposition strategies for the growth of secondary battery cathodes. Specifically, we focus on anodic electrolytic deposition methods to grow alkali-ion intercalated, layered/spinel transition metal oxide intercalation cathode systems. State-of-the-art synthesis for layered oxide cathodes for Li and Na-ion battery involves prolonged high temperature (>700°C) processing for long reaction times (~24 hours) under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Here, we demonstrate an intermediate temperature (250-350°C) electrodeposition process to grow alkali ion (Li+, Na+) intercalated transition metal oxides across multiple transition metal chemistries of the Li system (orthorhombic LiMnO2, Li2MnO3, LiNixMn1-xO4, LiMn2O4, LiCoO2) and Na system (O3 and P2 NaxCoO2, O’3 and P2 NaxMnO2) in thick film form factors. Even though our cathodes are electrochemically grown at the lowest reported synthesis temperature and reaction times, they retain the key structural and electrochemical performance of the high temperature bulk synthesized analogues. The key features of this alternate high throughput cathode manufacturing technique include formation of binder-and-additive-free, tens of microns thick, >75% dense, highly textured electrodeposits exhibiting near theoretical gravimetric capacity, low tortuosity, and chemical diffusion coefficient of Li+/Na+ ions. Our findings highlight the influence of the unique molten hydroxide-based solution chemistry platform and electrochemical processing parameters, on regulating the phase assemblage, designing the microstructure, and controlling crystallographic orientation during electrocrystallization.

Electrochemically Grown Energy and Power Dense Cathodes for Li and Na Ion Batteries

Electrochemical synthesis of materials has contributed to significant breakthroughs in materials processing by replacing high temperature, cost and energy intensive pyrometallurgical processes. Although electrodeposition as a technology for reduction of elements and alloys has been practiced since at least the 1940s, a current key and exciting question is to identify and develop electrodeposition strategies for the growth of secondary battery cathodes. Specifically, we focus on anodic electrolytic deposition methods to grow alkali-ion intercalated, layered/spinel transition metal oxide intercalation cathode systems. State-of-the-art synthesis for layered oxide cathodes for Li and Na-ion battery involves prolonged high temperature (>700°C) processing for long reaction times (~24 hours) under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Here, we demonstrate an intermediate temperature (250-350°C) electrodeposition process to grow alkali ion (Li+, Na+) intercalated transition metal oxides across multiple transition metal chemistries of the Li system (orthorhombic LiMnO2, Li2MnO3, LiNixMn1-xO4, LiMn2O4, LiCoO2) and Na system (O3 and P2 NaxCoO2, O’3 NaxMnO2) in thick film form factors. Even though our cathodes are electrochemically grown at the lowest reported synthesis temperature and reaction times, they retain the key structural and electrochemical performance of the high temperature bulk synthesized analogues. The key features of this alternate high throughput cathode manufacturing technique include formation of binder-and-additive-free, tens of microns thick, >75% dense electrodeposits exhibiting near theoretical gravimetric capacity, low tortuosity, and chemical diffusion coefficient of Li+/Na+ ions. Our findings highlight the influence of the unique molten hydroxide-based solution chemistry platform and electrochemical processing parameters, on regulating the phase assemblage, designing the microstructure, and controlling crystallographic orientation during electrocrystallization.

Appearance of the 4 V signal without transformation to spinel-related oxides from loose-crystalline rock-salt LiMnO2

Manganese (Mn)-based positive electrode materials have attracted significant attention because of their low-risk resources, high valence ranges, and their ability to form polymorphs. Loose-crystalline rock-salt LiMnO2 (LCRS-LMO) synthesized via a mechanochemical method exhibited a capacity of ca. 190 mAh g−1 with a potential range of 5.0–2.0 V. The potential curve of LCRS-LMO after 11 charge/discharge cycles exhibited a characteristic 4 V signal, which is similar to the 4 V plateau observed in the transition from layered LiMnO2 or orthorhombic LiMnO2 to the spinel Li-Mn oxide. However, no diffraction peaks corresponding to a spinel-related structure were detected by X-ray diffraction (XRD) measurements of the bulk structure. Furthermore, in situ XRD revealed for the first time that the lattice size of LCRS-LMO approached that of the spinel-related oxide as the charge/discharge process progressed. The local structural changes of LCRS-LMO examined by in situ X-ray absorption fine structure measurements suggest that the local structure around the manganese ions tends to be aligned toward the spinel-related lattice.

A one-step dynamic hydrothermal method for the synthesis of orthorhombic LiMnO2/CNTs nanocomposites networks for Li-ion batteries

Orthorhombic LiMnO2 (o-LiMnO2) is considered as a potential cathode material for lithium ion batteries due to its high theoretical capacity and low cost. However, the irreversible phase transformation to spinel LiMn2O4 and sluggish lithium ion diffusion kinetics result in low practical specific capacity and poor cycling stability. In this work, conductive o-LiMnO2/carbon nanotubes (CNTs) composites frameworks were constructed via an ingenious one-step dynamic hydrothermal method. The obtained o-LiMnO2/CNTs composites achieved outstanding electrochemical performance upon adjustment of the CNTs content. The results demonstrated either physical introduction of 1 wt% CNTs into o-LiMnO2 or in-situ formed o-LiMnO2/CNTs composite with 0.5 wt% CNTs could improve electrochemical performance effectively compared with pristine o-LiMnO2. However, when the content of CNTs increased to 1 wt% in in-situ formed o-LiMnO2/CNTs, the specific capacity reached 194.4 mAh g−1 and retention rate was 93.7% after 50 cycles at 0.1C. Moreover, the in-situ formed composite with 5 wt% CNTs led to the optimum specific capacity of 204.9 mAh g−1 and a high capacity retention rate (97.7% after 50 cycles at 0.1C). Galvanostatic intermittent titration technique (GITT) measurement also demonstrated that 5 wt% CNTs in o-LiMnO2/CNTs composite drastically improved the slowest Li+ diffusion step by a factor 100 times after 30 cycles as compared to the pristine counterpart. This behaviour demonstrated an accelerated diffusion of lithium through this new approach and improved reversibility of charging-discharging.

EDTA-2Na assisted dynamic hydrothermal synthesis of orthorhombic LiMnO2 for lithium ion battery

Herein, pure orthorhombic LiMnO2 (o-LiMnO2) was prepared via a one-step and short time EDTA-2Na assisted dynamic hydrothermal method, in which the electrolytic MnO2 and C4H6MnO4·4H2O were used as manganese source. The effects of EDTA-2Na concentration, hydrothermal temperature and stirring rate on the purity of o-LiMnO2 were investigated. EDTA-2Na served as both chelating reagent and reductant, the oxidation of Mn2+ before reaction and the formation of Li2MnO3 by residual oxygen in reaction system were suppressed due to coordination and reduction effects of EDTA-2Na, respectively. Furthermore, the solid-liquid reaction kinetics could be accelerated by stirring, then final expected pure phase o-LiMnO2 was generated in short time and a low alkali concentration. The obtained product showed high crystallinity with an average diameter of 200–500 nm. When utilized as a lithium ion battery cathode material, the o-LiMnO2 could deliver a high capacity of 166.1 mAh g−1 at 0.1 C at the voltage range of 2.0–4.5 V.

Structural and electrochemical characteristics of o-LiMnO2-MWCNTs nanocomposites

This paper reports the structural and electrochemical studies of the composite made up of orthorhombic LiMnO2 (o-LiMnO2) and oxidized MWCNTs in various percentages where CNTs replaced the carbon black (CB) as an additive material. X-ray diffraction (XRD) patterns confirmed the formation of distorted orthorhombic phase of the space group with Pmnm. Raman spectra showed eight visible Raman modes of LiMnO2. A blue shift (~7 cm−1) in the Raman mode associated with Mn–O bond of composite materials was observed, which was due to mechanical stresses. The EIS measurement indicated the low charge transfer resistance (105 kΩ) for o-LiMnO2/CNTs composites compared to o-LiMnO2/CB composites (195 kΩ). The CV results confirmed the reduction in potential gap between redox peaks with the addition of CNTs, which decreased from 2.02 V to 1.76 V. CNTs provided a network of conducting channel for Li ions as well as resulted in reduction of polarization of redox potentials.

Highly Lithium Adsorption Capacities of H1.6Mn1.6O4 Ion‐Sieve by Ordered Array Structure

AbstractSpinel‐structured Li1.6Mn1.6O4 (LMO) has received wide attention as ion sieve for the recovery of lithium from aqueous lithium resources. In this work, the branched‐like LMO particles were prepared via calcinating orthorhombic LiMnO2. After extracting of Li+ in hydrochloric acid, the branched‐like H1.6Mn1.6O4 (HMO) was obtained. During the preparing process, the structure, morphologies of LMO and HMO were characterized by XRD and SEM. The results indicated that HMO maintained the spinel and ordered array structure, which was beneficial to the lithium uptake behavior. Compared to normal HMO nanoparticles, the Li+ adsorption capacity of HMO by order array branched‐like structure can reach to 43.8 mg/g while rod‐like was 35 mg/g (CLi: 150 mg/L, pH 11, T: 25°C). The adsorption behaviors were well simulated by the pseudo‐second‐order and the Langmuir models. The reusability of the HMO implies that the branched‐like HMO is a potential adsorbent for Li+ recovery from aqueous lithium resources.

Synthesis of mesoporous orthorhombic LiMnO2 cathode materials via a one-step flux method for high performance lithium-ion batteries

Mesoporous orthorhombic LiMnO2 has been directly fabricated by a one-step flux method in this work. Benefiting from the unique mesoporous structure, the orthorhombic LiMnO2 prepared through calcinating the mixture of flux LiOH · H2O and Mn2O3 with various Li/Mn molar ratios shows enhanced lithium storage properties. When used as the cathode for lithium ion battery, the mesoporous orthorhombic LiMnO2 has been found to exhibit a maximum discharge capacity of 191.5 mAh g−1 and a high reversible capacity of 162.6 mAh g−1 (84.9% retention) after 50 cycles at a current density of 0.1 C rate. These results demonstrate its potential application in high performance lithium-ion batteries.

Electrochemical properties of monoclinic and orthorhombic LiMnO2 synthesized by a one-step hydrothermal method

The controllable synthesis of layered LiMnO2 with orthorhombic (o-LiMnO2), monoclinic (m-LiMnO2), and mixed phase structures (i.e., containing both m-LiMnO2 and o-LiMnO2) was successfully achieved using a one-step hydrothermal method. The effects of temperature, reaction time, Li/Mn molar ratio, and alkaline solution concentration on the synthesis of the monoclinic and orthorhombic phases were studied in detail. The microstructure and composition of the samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The different valence states of manganese in material m-LiMnO2,o-LiMnO2 and mixed phase LiMnO2 were determined by redox titration method. TEM observations confirmed that these differently structured samples exhibit irregular shapes with grain diameters of ∼50–200 nm. Examination of the electrochemical performances of these samples using the galvanostatic method revealed that the as-synthesized m-LiMnO2 exhibited a maximum discharge capacity of 219.8 mAh·g−1 at 0.1C after several cycles, but exhibited poor cycling behavior. In contrast, o-LiMnO2 exhibited the lowest discharge capacity of 180 mAh·g−1, while demonstrating enhanced cycling stability. The mixed phase containing both m-LiMnO2 and o-LiMnO2 exhibited characteristics corresponding to both structures, namely a good cycling stability and a good discharge ability.

Oxygen Vacancies and Stacking Faults Introduced by Low-Temperature Reduction Improve the Electrochemical Properties of Li2MnO3 Nanobelts as Lithium-Ion Battery Cathodes.

Among the Li-rich layered oxides Li2MnO3 has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine Li2MnO3 generally has to be electrochemically activated in the first charge-discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO2 in Li2MnO3. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine Li2MnO3 changes into a Li2MnO3-LiMnO2 (0.71/0.29) composite, and the monoclinic Li2MnO3 changes from Li2.04Mn0.96O3 in the pristine Li2MnO3 (P-Li2MnO3) to Li2.1Mn0.9O2.79 in the reduced Li2MnO3 (R-Li2MnO3), indicating the production of a large amount of oxygen vacancies in the R-Li2MnO3. High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-Li2MnO3 shows much better electrochemical properties than P-Li2MnO3. For example, when charged-discharged galvanostatically at 20 mA·g-1 in a voltage window of 2.0-4.8 V, R-Li2MnO3 has Coulombic efficiency of 77.1% in the first charge-discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g-1 in the 20th and 30th cycles, respectively. In contrast, under the same charge-discharge conditions, P-Li2MnO3 has Coulombic efficiency of 33.6% in the first charge-discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g-1 in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of Li2MnO3 as a cathode material for Li-ion batteries.

Role of the precursor chemistry on the phase composition and electrochemical performance of thin-film LiMn2O4 Li-ion battery cathodes prepared by spray pyrolysis

LiMn2O4-films were prepared by air-blast spray pyrolysis directly onto stainless steel foil substrate. The films were synthesized from various precursor solutions of dissolved nitrates and acetates with and without the addition of polyethylene glycol (PEG). Hereby X-ray diffraction experiments revealed that the phase compositions of the as-prepared and thermally post-treated films were highly dependent on the precursors used, but independent of the addition of PEG. Samples prepared from nitrates yielded phase mixtures of α-Mn2O3, Mn3O4 and LiNO3 as-prepared and LiMn2O4 and α-Mn2O3 after post-thermal treatment. Whereas films sprayed from acetate precursors consisted of LiMn2O4 predominantly before and after heat treatment, as well. Scanning electron microscopy investigations showed that the applied precursor had an effect on the film morphology and the addition of PEG led to film thinning. Galvanostatic cycling tests and post-mortem analyses of the electrochemical cells fabricated from the thermally treated thin layers revealed that the film prepared from acetates and PEG had the highest capacity retention despite the formation of orthorhombic LiMnO2 besides the cubic LiMn2O4 during battery cycling.

Crystallography and Growth of Epitaxial Oxide Films for Fundamental Studies of Cathode Materials Used in Advanced Li-Ion Batteries

Li-ion battery systems, synthesized as epitaxial thin films, can provide powerful insights into their electrochemical processes. Crystallographic analysis shows that many important cathode oxides have an underlying similarity: their structures can be considered as different ordering schemes of Li and transition metal ions within a pseudo-cubic sublattice of oxygen anions arranged in a face-center cubic (FCC) fashion. This oxygen sublattice is compatible with SrTiO3 and similar perovskite oxides, thus perovskites can be used as supporting substrates for growing epitaxial cathode films. The predicted epitaxial growth and crystallographic relations were experimentally verified for different oxide films deposited by pulsed laser deposition (PLD) on SrTiO3 or SrRuO3/SrTiO3 of different orientations. The results based on cross-sectional high-resolution TEM of the following films are presented in the paper: (a) trigonal LiCoO2; (b) orthorhombic LiMnO2; (c) monoclinic Li2MnO3; (d) compositionally-complex monoclinic Li1.2Mn0.55Ni0.15Co0.1O2. All results demonstrated the feasibility of epitaxial growth for these materials, with the growth following the predicted cube-on-cube orientation relationship between the cubic and pseudo-cubic oxygen sublattices of a substrate and a film, respectively.

Facile synthesis of orthorhombic LiMnO2 nanorods by in-situ carbothermal reduction: Promising cathode material for Li ion batteries

Abstract Orthorhombic LiMnO2 nanorods were prepared via a simple and economical in-situ carbothermal reduction method using nanorod-like MnO2 as both template and manganese precursor. The obtained product showed high purity and excellent electrochemical performance. When used as a cathode material, it exhibited 165.3 mAh g−1 capacity with low capacity loss at 0.1 C. After 40 cycles, only 7.4% of discharge capacity was lost in the cycling process. Moreover, the maximum discharge capacities of 227.5 and 95.3 mAh g−1 could be delivered at low and high rates of 0.05 and 1.0 C, respectively.

Exceptional Flux Growth and Chemical Transformation of Metastable Orthorhombic LiMnO2 Cuboids into Hierarchically-Structured Porous H1.6Mn1.6O4 Rods as Li Ion Sieves

Selective lithium uptake from seawater and lake brine is an important challenge in energy and environmental science. H1.6Mn1.6O4 with pseudospinel-type structure is a highly selective adsorbent for Li ions, but it is difficult to prepare large, highly crystalline H1.6Mn1.6O4 crystals with porous structure due to its thermodynamic metastability. Herein we demonstrate simple chemical processes that transform flux-grown, idiomorphic orthorhombic LiMnO2 (o-LiMnO2) cuboids of micrometer size into hierarchically structured H1.6Mn1.6O4 rods. We have optimized the flux growth conditions such as the Mn source, holding temperature, and solute concentration in order to yield large, single-phase o-LiMnO2 particles. The use of MnO under very low solute concentration (1 mol %) and high temperature (1000 °C) is critical to obtaining the single-phase, idiomorphic o-LiMnO2 cuboids. The metastability of o-LiMnO2 is confirmed by ab initio density functional theory calculation in comparison with other lithium manganates such...

Orthorhombic LiMnO2 nanorods as cathode materials for lithium-ion batteries: Synthesis and electrochemical properties

A simple solid-state process was developed to prepare the orthorhombic LiMnO2 nanorods by using Mn2O3 nanorods as a template, the latter was prepared via a thermal decomposition process. The obtained product showed good rod-shaped morphology and could be indexed to the orthorhombic LiMnO2 with a space group of Pmnm. Electrochemical tests showed that the LiMnO2 nanorods exhibited a discharge capacity of 183.2mAhg−1 with high coulombic efficiency at 0.1C between 2.0 and 4.3V. After 35 cycles, the discharge capacity still reached up to 175.6mAhg−1, which is a high capacity retention. Furthermore, the LiMnO2 nanorods presented excellent rate capability and small charge transfer resistance. Such high performance might be ascribed to the one-dimensional nanostructures with good crystallinity, which could effectively facilitate the charge and electron transport and enhance the electrode-filled ratio.