Urea-Mediated Monoliths Made of Nitrogen-Enriched Mesoporous Carbon Nanosheets for High-Performance Aqueous Zinc Ion Hybrid Capacitors.

Aqueous zinc ion hybrid capacitors (aZHCs) are of great potential for large-scale energy storage and flexible wearable devices, of which the specific capacity and energy density need to be further enhanced for practical applications. Herein, a urea-mediated foaming strategy is reported for the efficient synthesis of monoliths consisting of nitrogen-enriched mesoporous carbon nanosheets (NPCNs) by prefoaming drying a solution made of polyvinylpyrrolidone, zinc nitrate, and urea at low temperatures, foaming and annealing at high temperatures, and subsequent acid etching. NPCNs have a large lateral size of ≈40 µm, thin thickness of ≈55 nm, abundant micropores and mesopores (≈3.8 nm), and a high N-doping value of 9.7 at.%. The NPCNs as the cathode in aZHCs provide abundant zinc storage sites involving both physical and chemical adsorption/desorption of Zn2+  ions, and deliver high specific capacities of 262 and 115 mAh g-1 at 0.2 and 10 A g-1 , and a remarkable areal capacity of ≈0.5 mAh cm-2  with a mass loading of 5.3 mg cm-2 , outperforming most carbon cathodes reported thus far. Moreover, safe and flexible NPCNs based quasi-solid-state devices are fabricated, which can withstand drilling and mechanical bending, suggesting their potential applications in wearable devices.

A Two-Dimensional Mesoporous Polypyrrole-Graphene Oxide Heterostructure as a Dual-Functional Ion Redistributor for Dendrite-Free Lithium Metal Anodes.

Guiding the lithium ion (Li-ion) transport for homogeneous, dispersive distribution is crucial for dendrite-free Li anodes with high current density and long-term cyclability, but remains challenging for the unavailable well-designed nanostructures. Herein, we propose a two-dimensional (2D) heterostructure composed of defective graphene oxide (GO) clipped on mesoporous polypyrrole (mPPy) as a dual-functional Li-ion redistributor to regulate the stepwise Li-ion distribution and Li deposition for extremely stable, dendrite-free Li anodes. Owing to the synergy between the Li-ion transport nanochannels of mPPy and the Li-ion nanosieves of defective GO, the 2D mPPy-GO heterostructure achieves ultralong cycling stability (1000 cycles), even tests at 0 and 50 °C, and an ultralow overpotential of 70 mV at a high current density of 10.0 mA cm-2 , outperforming most reported Li anodes. Furthermore, mPPy-GO-Li/LiCoO2 full batteries demonstrate remarkably enhanced performance with a capacity retention of >90 % after 450 cycles. Therefore, this work opens many opportunities for creating 2D heterostructures for high-energy-density Li metal batteries.

Telmisartan Mitigates TNF-α-Induced Type II Collagen Reduction by Upregulating SOX-9.

The proinflammatory cytokine tumor necrosis factor-α (TNF-α)-induced degradation of extracellular matrix (ECM), such as type II collagen in chondrocytes, plays an important role in the development of osteoarthritis (OA). Telmisartan, an angiotensin II (Ang-II) receptor blocker, is a licensed drug used for the treatment of hypertension. However, the effects of Telmisartan in tumor necrosis factor-α (TNF-α)-induced damage to chondrocytes and the progression of OA are unknown. In this study, we found that treatment with Telmisartan attenuated TNF-α-induced oxidative stress by reducing the levels of mitochondrial reactive oxygen species (ROS) and the production of protein carbonyl in human C28/I2 chondrocytes. Interestingly, Telmisartan inhibited TNF-α-induced expression and secretions of proinflammatory mediators such as interleukin-1ß (IL-1ß), interleukin-6 (IL-6), and monocyte chemotactic protein 1 (MCP-1). Notably, stimulation with TNF-α reduced the levels of type II collagen at both the mRNA and the protein levels, which was rescued by the treatment with Telmisartan. Mechanistically, we found that Telmisartan restored TNF-α-induced reduction of SOX-9. Silencing of SOX-9 blocked the inhibitory effects of Telmisartan against TNF-α-induced degradation of type II collagen. These findings suggest that Telmisartan might be a potential and promising agent for the treatment of OA.

Three dimensional Ti3C2 MXene nanoribbon frameworks with uniform potassiophilic sites for the dendrite-free potassium metal anodes.

Potassium (K) metal batteries hold great promise as an advanced electrochemical energy storage system because of their high theoretical capacity and cost efficiency. However, the practical application of K metal anodes has been limited by their poor cycling life caused by dendrite growth and large volume changes during the plating/stripping process. Herein, three-dimensional (3D) alkalized Ti3C2 (a-Ti3C2) MXene nanoribbon frameworks were demonstrated as advanced scaffolds for dendrite-free K metal anodes. Benefiting from the 3D interconnected porous structure for sufficient K accommodation, improved surface area for low local current density, preintercalated K in expanded interlayer spacing, and abundant functional groups as potassiophilic nuleation sites for uniform K plating/stripping, the as-formed a-Ti3C2 frameworks successfully suppressed the K dendrites and volume changes at both high capacity and current density. As a result, the a-Ti3C2 based electrodes exhibited an ultrahigh coulombic efficiency of 99.4% at a current density of 3 mA cm-2 with long lifespan up to 300 cycles, and excellent stability for 700 h even at an ultrahigh plating capacity of 10 mA h cm-2. When matched with K2Ti4O9 cathodes, the resulting a-Ti3C2-K//K2Ti4O9 full batteries offered a greatly enhanced rate capacity of 82.9 mA h g-1 at 500 mA g-1 and an excellent cycling stability with high capacity retention (77.7% after 600 cycles) at 200 mA g-1, demonstrative of the great potential of a-Ti3C2 for advanced K-metal batteries.

3D Flexible, Conductive, and Recyclable Ti3C2Tx MXene-Melamine Foam for High-Areal-Capacity and Long-Lifetime Alkali-Metal Anode.

Alkali metals are ideal anodes for high-energy-density rechargeable batteries, while seriously hampered by limited cycle life and low areal capacities. To this end, rationally designed frameworks for dendrite-free and volume-changeless alkali-metal deposition at both high current densities and capacities are urgently required. Herein, a general 3D conductive Ti3C2TX MXene-melamine foam (MXene-MF) is demonstrated as an elastic scaffold for dendrite-free, high-areal-capacity alkali anodes (Li, Na, K). Owing to the lithiophilic nature of F-terminated MXene, conductive macroporous network, and excellent mechanical toughness, the constructed MXene-MF synchronously achieves a high current density of 50 mA cm-2 for Li plating, high areal capacity (50 mAh cm-2) with high Coulombic efficiency (99%), and long lifetime (3800 h), surpassing the Li anodes reported recently. Meanwhile, MXene-MF shows flat voltage profiles for 720 h at 10 mA cm-2 for the Na anode and 800 h at 5 mA cm-2 for the K anode, indicative of the wide applicability. Notably, the high current density of 20 mA cm-2 for 20 mAh cm-2 for the Na anode, accompanying good recyclability was rarely achieved before. When coupled with sulfur or Na3V2(PO4)3 cathodes, the assembled MXene-MF alkali (Li, Na)-based full batteries showcase enhanced rate capability and cycling stability, demonstrating the potential of MXene-MF for advanced alkali-metal batteries.

Conducting and Lithiophilic MXene/Graphene Framework for High-Capacity, Dendrite-Free Lithium-Metal Anodes.

Li-metal anode is widely acknowledged as the ideal anode for high-energy-density batteries, but seriously hindered by the uncontrollable dendrite growth and infinite volume change. Toward this goal, suitable stable scaffolds for dendrite-free Li anodes with large current density (>5 mA cm-2) and high Li loading (>90%) are highly in demand. Herein, a conductive and lithiophilic three-dimensional (3D) MXene/graphene (MG) framework is demonstrated for a dendrite-free Li-metal anode. Benefiting from its high surface area (259 m2 g-1) and lightweight nature with uniformly dispersed lithiophilic MXene nanosheets as Li nucleation sites, the as-formed 3D MG scaffold showcases an ultrahigh Li content (∼92% of the theoretical capacity), as well as strong capabilities in suppressing the Li-dendrite formation and accommodating the volume changes. Consequently, the MG-based electrode exhibits high Coulombic efficiencies (∼99%) with a record lifespan up to 2700 h and is stable for 230 cycles at an ultrahigh current density of 20 mA cm-2. When coupled with Li4Ti5O12 or sulfur, the MG-Li/Li4Ti5O12 full-cell offers an enhanced capacity of 142 mAh g-1 after 450 cycles, while the MG-Li/sulfur cell delivers an improved rate performance, implying the great potential of this 3D MG framework for building long-lifetime, high-energy-density batteries.

All-Solid-State Planar Sodium-Ion Microcapacitors with Multidirectional Fast Ion Diffusion Pathways.

With the relentless development of smart and miniaturized electronics, the worldwide thirst for microscale electrochemical energy storage devices with form factors is launching a new era of competition. Herein, the first prototype planar sodium-ion microcapacitors (NIMCs) are constructed based on the interdigital microelectrodes of urchin-like sodium titanate as faradaic anode and nanoporous activated graphene as non-faradaic cathode along with high-voltage ionogel electrolyte on a single flexible substrate. By effectively coupling with battery-type anode and capacitor-type cathode, the resultant all-solid-state NIMCs working at 3.5 V exhibit a high volumetric energy density of 37.1 mWh cm-3 and an ultralow self-discharge rate of 44 h from V max to 0.6 V max, both of which surpass most reported hybrid micro-supercapacitors. Through tuning graphene layer covered on the top surface of interdigital microelectrodes, the NIMCs unveil remarkably enhanced power density, owing to the establishment of favorable multidirectional fast ion diffusion pathways that significantly reduce the charge transfer resistance. Meanwhile, the as-fabricated NIMCs present excellent mechanical flexibility without capacitance fade under repeated deformation, and electrochemical stability at a high temperature of 80 °C because of using nonflammable ionogel electrolyte and in-plane geometry. Therefore, these flexible planar NIMCs with multidirectional ion diffusion pathways hold tremendous potential for microelectronics.

2D transition metal carbide MXene as a robust biosensing platform for enzyme immobilization and ultrasensitive detection of phenol.

MXene-Ti3C2, as a new class of two-dimensional (2D) transition metal carbides (or nitrides), has been synthesized by exfoliating pristine Ti3AlC2 phases with hydrofluoric acid. The SEM and XRD images show that the resultant MXene possesses a graphene-like 2D nanostructure. and the surface of MXene has been partially terminated with -OH, thus providing a favorable microenvironment for enzyme immobilization and retaining their bioactivity and stability. Considering the unique metallic conductivity, biocompatibility and good dispersion in aqueous phase, the as-prepared MXene was explored as a new matrix to immobilize tyrosinase (a model enzyme) for fabricating a mediator-free biosensor for ultrasensitive and rapid detection of phenol. The varying electrochemical measurements were used to investigate the electrochemical performance of MXene-based tyrosinase biosensors. The results revealed that the direct electron transfer between tyrosinase and electrode could be easily achieved via a surface-controlled electrochemical process. The fabricated MXene-based tyrosinase biosensors exhibited good analytical performance over a wide linear range from 0.05 to 15.5 µmol L-1, with a low detection limit of 12 nmol L-1 and a sensitivity of 414.4 mA M-1. The proposed biosensing approach also demonstrated good repeatability, reproducibility, long-term stability and high recovery for phenol detection in real water samples. With those excellent performances, MXene with graphene-like structure is proved to be a robust and versatile electrochemical biosensing platform for enzyme-based biosensors and biocatalysis, and has wide potential applications in biomedical detection and environmental analysis.

All-MXene-Based Integrated Electrode Constructed by Ti3C2 Nanoribbon Framework Host and Nanosheet Interlayer for High-Energy-Density Li-S Batteries.

High-energy-density lithium-sulfur (Li-S) batteries hold promise for next-generation portable electronic devices, but are facing great challenges in rational construction of high-performance flexible electrodes and innovative cell configurations for actual applications. Here we demonstrated an all-MXene-based flexible and integrated sulfur cathode, enabled by three-dimensional alkalized Ti3C2 MXene nanoribbon (a-Ti3C2 MNR) frameworks as a S/polysulfides host (a-Ti3C2-S) and two-dimensional delaminated Ti3C2 MXene (d-Ti3C2) nanosheets as interlayer on a polypropylene (PP) separator, for high-energy and long-cycle Li-S batteries. Notably, an a-Ti3C2 MNR framework with open interconnected macropores and an exposed surface area guarantees high S loading and fast ionic diffusion for prompt lithiation/delithiation kinetics, and the 2D d-Ti3C2 MXene interlayer remarkably prevents the shuttle effect of lithium polysulfides via both chemical absorption and physical blocking. As a result, the integrated a-Ti3C2-S/d-Ti3C2/PP electrode was directly used for Li-S batteries, without the requirement of a metal current collector, and exhibited a high reversible capacity of 1062 mAh g-1 at 0.2 C and enhanced capacity of 632 mAh g-1 after 50 cycles at 0.5 C, outperforming the a-Ti3C2-S/PP electrode (547 mAh g-1) and conventional a-Ti3C2-S on an Al current collector (a-Ti3C2-S/Al) (597 mAh g-1). Furthermore, the all-MXene-based integrated cathode displayed outstanding rate capacity of 288 mAh g-1 at 10 C and long-life cyclability. Therefore, this proposed strategy of constructing an all-MXene-based cathode can be readily extended to assemble a large number of MXene-derived materials, from a group of 60+ MAX phases, for applications such as various batteries and supercapacitors.

Graphene: a promising 2D material for electrochemical energy storage.

Graphene, with unique two-dimensional form and numerous appealing properties, promises to remarkably increase the energy density and power density of electrochemical energy storage devices (EESDs), ranging from the popular lithium ion batteries and supercapacitors to next-generation high-energy batteries. Here, we review the recent advances of the state-of-the-art graphene-based materials for EESDs, including lithium ion batteries, supercapacitors, micro-supercapacitors, high-energy lithium-air and lithium-sulfur batteries, and discuss the importance of the pore, doping, assembly, hybridization and functionalization of different nano-architectures in improving electrochemical performance. The major roles of graphene are highlighted as (1) a superior active material, (2) ultrathin 2D flexible support, and (3) an inactive yet electrically conductive additive. Furthermore, we address the enormous potential of graphene for constructing new-concept emerging graphene-enabled EESDs with multiple functionalities of lightweight, ultra-flexibility, thinness, and novel cell configurations. Finally, future perspectives and challenges of graphene-based EESDs are briefly discussed.

Investigation of the effect of phlomisoside F on complete Freund's adjuvant-induced arthritis.

Phlomis younghusbandii Mukerjee (Labiatae) has been reported to be effective in the treatment of rheumatoid arthritis (RA). In the present study, the anti-inflammatory and anti-arthritic effects of phlomisoside F (PF), isolated from P. younghusbandii Mukerjee (Labiatae), were investigated in male Wistar rats subjected to carrageen-induced paw edema and complete Freund's adjuvant (CFA)-induced arthritis. Arthritis scores were evaluated by a 5-point ordinal scale (scores 0-4). Expression levels of TNF-α, IL-1ß, IL-6, IL-10, COX-2 and 5-LOX were determined via ELISA and western blot assays. Subsequent to establishing the edema and arthritis models, oral administration of PF (5, 10 and 20 mg/kg) significantly inhibited mean edema rate, compared with the control group in carrageenan-induced paw edema assay. In addition, administration of PF (5, 10 and 20 mg/kg/day) for 28 days markedly exhibited an anti-arthritic activity by offsetting the body weight loss, inhibiting the paw edema, reducing the arthritis scores and the indices of thymus and spleen, inhibiting the expression levels of TNF-α, IL-1ß, IL-6, COX-2 and 5-LOX, and increasing the expression of IL-10, when compared with the respective control group in CFA-induced arthritis assay. In conclusion, PF is a valuable anti-arthritic constituent of P. younghusbandii, and the present study results suggest that this herb may be used in the treatment of RA.

Flexible Paper-like Free-Standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-Performance Sodium Ion Batteries.

Ultrafine SnS2 nanocrystals-reduced graphene oxide nanoribbon paper (SnS2-RGONRP) has been created by a well-designed process including in situ reduction, evaporation-induced self-assembly, and sulfuration. The as-formed SnS2 nanocrystals possess an average diameter of 2.3 nm and disperse on the surface of RGONRs uniformly. The strong capillary force formed during evaporation leads to a compact assembly of RGONRs to give a flexible paper structure with a high density of 0.94 g cm-3. The as-prepared SnS2-RGONRP composite could be directly used as free-standing electrode for sodium ion batteries. Due to the synergistic effects between the ultrafine SnS2 nanocrystals and the conductive, tightly connected RGONR networks, the composite paper electrode exhibits excellent electrochemical performance. A high volumetric capacity of 508-244 mAh cm-3 was obtained at current densities in the range of 0.1-10 A g-1. Discharge capacities of 334 and 255 mAh cm-3 were still kept, even after 1500 cycles tested at current densities of 1 and 5 A g-1, respectively. This strategy provides insight into a new pathway for the creation of free-standing composite electrodes used in the energy storage and conversion.

Ti3C2 MXene-Derived Sodium/Potassium Titanate Nanoribbons for High-Performance Sodium/Potassium Ion Batteries with Enhanced Capacities.

Sodium and potassium ion batteries hold promise for next-generation energy storage systems due to their rich abundance and low cost, but are facing great challenges in optimum electrode materials for actual applications. Here, ultrathin nanoribbons of sodium titanate (M-NTO, NaTi1.5O8.3) and potassium titanate (M-KTO, K2Ti4O9) were successfully synthesized by a simultaneous oxidation and alkalization process of Ti3C2 MXene. Benefiting from the suitable interlayer spacing (0.90 nm for M-NTO, 0.93 nm for M-KTO), ultrathin thickness (<11 nm), narrow widths of nanoribbons (<60 nm), and open macroporous structures for enhanced ion insertion/extraction kinetics, the resulting M-NTO exhibited a large reversible capacity of 191 mAh g-1 at 200 mA g-1 for sodium storage, higher than those of pristine Ti3C2 (178 mAh g-1) and commercial TiC derivatives (86 mAh g-1). Notably, M-KTO displayed a superior reversible capacity of 151 mAh g-1 at 50 mA g-1 and 88 mAh g-1 at a high rate of 300 mA g-1 and long-term stable cyclability over 900 times, which outperforms other Ti-based layered materials reported to date. Moreover, this strategy is facile and highly flexible and can be extended for preparing a large number of MXene-derived materials, from the 60+ group of MAX phases, for various applications such as supercapacitors, batteries, and electrocatalysts.

High Packing Density Unidirectional Arrays of Vertically Aligned Graphene with Enhanced Areal Capacitance for High-Power Micro-Supercapacitors.

Interfacial integration of a shape-engineered electrode with a strongly bonded current collector is the key for minimizing both ionic and electronic resistance and then developing high-power supercapacitors. Herein, we demonstrated the construction of high-power micro-supercapacitors (VG-MSCs) based on high-density unidirectional arrays of vertically aligned graphene (VG) nanosheets, derived from a thermally decomposed SiC substrate. The as-grown VG arrays showed a standing basal plane orientation grown on a (0001̅) SiC substrate, tailored thickness (3.5-28 µm), high-density structurally ordering alignment of graphene consisting of 1-5 layers, vertically oriented edges, open intersheet channels, high electrical conductivity (192 S cm-1), and strong bonding of the VG edges to the SiC substrate. As a result, the demonstrated VG-MSCs displayed a high areal capacitance of ∼7.3 mF cm-2 and a fast frequency response with a short time constant of 9 ms. Furthermore, VG-MSCs in both an aqueous polymer gel electrolyte and nonaqueous ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate operated well at high scan rates of up to 200 V s-1. More importantly, VG-MSCs offered a high power density of ∼15 W cm-3 in gel electrolyte and ∼61 W cm-3 in ionic liquid. Therefore, this strategy of producing high-density unidirectional VG nanosheets directly bonded on a SiC current collector demonstrated the feasibility of manufacturing high-power compact supercapacitors.

Self-assembled sulfur/reduced graphene oxide nanoribbon paper as a free-standing electrode for high performance lithium-sulfur batteries.

Flexible, interconnected sulfur/reduced graphene oxide nanoribbon paper (S/RGONRP) is synthesized through S2- reduction and evaporation induced self-assembly processes. The in situ formed sulfur atoms chemically bonded with the surface of reduced graphene oxide nanoribbons and were physically trapped by the compact assembly, which make the hybrid a suitable cathode material for lithium-sulfur batteries.

Multifunctional nitrogen-doped graphene nanoribbon aerogels for superior lithium storage and cell culture.

Nitrogen-doped graphene nanoribbon aerogels (N-GNRAs) are fabricated through the self-assembly of graphene oxide nanoribbons (GONRs) combined with a thermal annealing process. Amino-groups are grafted to the surface of graphene nanoribbons (GNRs) by an epoxy ring-opening reaction. High nitrogen doping level (7.6 atm% as confirmed by elemental analysis) is achieved during thermal treatment resulting from functionalization and the rich edge structures of GNRs. The three dimensional (3D) N-GNRAs feature a hierarchical porous structure. The quasi-one dimensional (1D) GNRs act as the building blocks for the construction of fishnet-like GNR sheets, which further create 3D frameworks with micrometer-scale pores. The edge effect of GNRs combined with nitrogen doping and porosity give rise to good electrical conductivity, superhydrophilic, highly compressible and low density GNRAs. As a result, a high capacity of 910 mA h g(-1) is achieved at a current density of 0.5 A g(-1) when they are tested as anode materials for lithium ion batteries. Further cell culture experiments with the GNRAs as human medulloblastoma DAOY cell scaffolds demonstrate their good biocompatibility, inferring potential applications in the biomedical field.

Carbon-Stabilized Interlayer-Expanded Few-Layer MoSe2 Nanosheets for Sodium Ion Batteries with Enhanced Rate Capability and Cycling Performance.

Sodium ion batteries (SIBs) have been considered as a promising alternative to lithium ion batteries, owing to the abundant reserve and low-cost accessibility of the sodium source. To date, the pursuit of high-performance anode materials remains a great challenge for the SIBs. In this work, carbon-stabilized interlayer-expanded few-layer MoSe2 nanosheets (MoSe2@C) have been fabricated by an oleic acid (OA) functionalized synthesis-polydopamine (PDA) stabilization-carbonization strategy, and their structural, morphological, and electrochemical properties have been carefully characterized and compared with the carbon-free MoSe2. When evaluated as anode for sodium ion half batteries, the MoSe2@C exhibits a remarkably enhanced rate capability of 367 mA h g-1 at 5 A g-1, a high reversible discharge capacity of 445 mA h g-1 at 1 A g-1, and a long-term cycling stability over 100 cycles. To further explore the potential applications, the MoSe2@C is assembled into sodium ion full batteries with Na3V2(PO4)3 (NVP) as cathode materials, showing an impressively high reversible capacity of 421 mA h g-1 at 0.2 A g-1 after 100 cycles. Such results are primarily attributed to the unique carbon-stabilized interlayer-expanded few-layer MoSe2 nanosheets structure, which facilitates the permeation of electrolyte into the inner of MoSe2 nanosheets, promoting charge transfer efficiency among MoSe2 nanosheets, and accommodating the volume change from discharge-charge cycling.

Sulfur-infiltrated graphene-backboned mesoporous carbon nanosheets with a conductive polymer coating for long-life lithium-sulfur batteries.

Sandwich-type, two-dimensional hybrid nanosheets were fabricated by the infiltration of nanosized sulfur into graphene-backboned mesoporous carbon with a PPy nanocoating. They exhibit a high reversible capacity for as long as 400 cycles with an ultra slow decay rate of 0.05% per cycle at the high rate of 1-3 C due to the efficient immobilization of polysulfides.

Dually fixed SnO2 nanoparticles on graphene nanosheets by polyaniline coating for superior lithium storage.

Dually fixed SnO2 nanoparticles (DF-SnO2 NPs) on graphene nanosheets by a polyaniline (Pani) coating was successfully fabricated via two facile wet chemistry processes, including anchoring SnO2 NPs onto graphene nanosheets via reducing graphene oxide by Sn(2+) ion, followed by in situ surface sealing with the Pani coating. Such a configuration is very appealing anode materials in LIBs due to several structural merits: (1) it prevents the aggregation of SnO2 NPs, (2) accommodates the structural expanding of SnO2 NPs during lithiation, (3) ensures the stable as-formed solid electrolyte interface films, and (4) effectively enhances the electronic conductivity of the overall electrode. Therefore, the final DF-SnO2 anode exhibits stable cycle performance, such as a high capacity retention of over 90% for 400 cycles at a current density of 200 mA g(-1) and a long cycle life up to 700 times at a higher current density of 1000 mA g(-1).