A Facile Method to Improve the High Rate Capability of Co_(3)O_(4)Nanowire Array Electrodes

The capability of fast charge and fast discharge is highly desirable for the electrode materials used in supercapacitors and lithium ion batteries.In this article,we report a simple strategy to considerably improve the high rate capability of Co_(3)O_(4)nanowire array electrodes by uniformly loading Ag nanoparticles onto the surfaces of the Co_(3)O_(4)nanowires via the silver-mirror reaction.The highly electrically conductive silver nanoparticles function as a network for the facile transport of electrons between the current collectors(Ti substrates)and the Co_(3)O_(4)active materials.High capacity as well as remarkable rate capability has been achieved through this simple approach.Such novel Co_(3)O_(4)-Ag composite nanowire array electrodes have great potential for practical applications in pseudo-type supercapacitors as well as in lithium ion batteries.

Three-dimensional ordered hierarchically porous carbon materials for high performance Li-Se battery

Developing host materials with high specific surface area, good electron conductivity, and fast ion transportation channel is critical for high performance lithium-selenium(Li-Se) batteries. Herein, a series of three dimensional ordered hierarchically porous carbon(3D OHPC) materials with micro/meso/macropores are designed and synthesized for Li-Se battery. The porous structure is tuned by following the concept of the generalized Murray’s law to facilitate the mass diffusion and reduce ion transport resistance.The optimized 3D Se/OHPC cathode exhibits a very high 2 nd discharge capacity of 651 m Ah/g and retains 361 m Ah/g after 200 cycles at 0.2 C. Even at a high current rate of 5 C, the battery still shows a discharge capacity as high as 155 m Ah/g. The improved electrochemical performance is attributed to the synergy effect of the interconnected and well-designed micro, meso and macroporosity while shortened ions diffusion pathways of such Murray materials accelerate its ionic and electronic conductivities leading to the enhanced electrochemical reaction. The diffusivity coefficient in Se/OHPC can reach a very high value of 1.3 × 10^(-11)cm^(2)/s, much higher than those in single pore size carbon hosts. Their effective volume expansion accommodation capability and reduced dissolution of polyselenides ensure the high stability of the battery. This work, for the first time, established the clear relationship between textural properties of cathode materials and their performance and demonstrates that the concept of the generalized Murray’s law can be used as efficient guidance for the rational design and synthesis of advanced hierarchically porous materials and the great potential of 3D OHPC materials as a practical high performance cathode material for Li-Se batteries.

Metal organic framework-combustion: A one-pot strategy to NiO nanoparticles with excellent anode properties for lithium ion batteries

NiO nanoparticles with average particles size of 30 nm are synthesized using a one-pot metal–organic framework-combustion（MOF-C） technique, for use as an anode material in rechargeable lithium ion batteries（LIBs）. The structural and electronic properties of these nanoparticles are studied using various techniques, including powder X-ray diffraction（PXRD）, transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, X-ray photoelectron spectroscopy（XPS）, and N_2 adsorption/desorption studies. The as-synthesized NiO nanoparticles sustained reversible stable capacities of 748 and 410 mAh/g at applied current densities of 500 and 1000 m A/g, respectively, after 100 cycles. Furthermore, the anode displays a notable rate capability, achieving a stable capacity of ~200 mAh/g at a high current density of10 A/g. These results indicate that the size of the NiO nanoparticles and their high surface area influence their electrochemical properties. Specifically, this combustion strategy is clearly favorable for improving the cyclability and rate capability of various metal oxides in rechargeable battery electrodes.

3D-honeycomb carbons for high performance electrical double layer capacitors electrodes

Sodium fulvic acid based hierarchical porous carbons(SFA-HPCs) with a specific surface area of 1919 m^2·g^(–1) and total volume of 1.7 cm^3·g^(–1) has been synthesized by a simple self-template method. The carbon skeleton can be formatted by the decomposition process of sodium fulvic acid(SFA) in a N_2 atmosphere. The sodium compund in SFA is used as a self-template to create the hierarchical porous structure. The unique hierarchical structure of SFA-HPCs provides an efficient pathway for electrolyte ions to be diffused into the internal surfaces of bulk electrode particles. It results in a high charge storage capacitance of 186 F·g^(–1) at current load of 40 A·g^(–1). The capacitance of 230 F·g^(–1) at 0.05 A·g^(–1) and 186 F·g^(–1) at 40 A·g^(–1) show its good rate capability. Besides, it also achieves desirable cycling stability, 99.4% capacitance remained after 10000 cycles at 40 A·g^(–1).

Secondary Activation of Commercial Activated Carbon and its Application in Electric Double Layer Capacitor

The cheap commercial activated carbon (AC) was improved through the secondary activation under steam in the presence of FeCl2 catalyst in the temperature range of 800-950℃ and its application in electric double layer capacitors (EDLCs) with organic electrolyte was studied. The re-activation of AC results in the increases in both specific capacitance and high rate capability of EDLCs. For AC treated under optimized conditions, its discharge specific capacitance increases up to 55.65 F/g, an increase of about 33% as compared to the original AC, and the high rate capability was increased significantly. The good performances of EDLC with improved AC were correlated to the increasing mesoporous ratio.

Carbon spheres with rational designed surface and secondary particle-piled structures for fast and stable sodium storage

The electrochemical performance of hard carbon in sodium storage is still limited by its poor cycling stability and rate capability because of the sluggish kinetics process.In this study,we use a simple and effective method to accelerate the kinetics process by engineering the structure of the electrode to promote its surface and near-surface reactions.This goal is realized by the use of slightly aggregated ultra-small carbon spheres.The large specific surface area formed by the small spheres can provide abundant active sites for electrochemical reactions.The abundant mesopores and macropores derived from the secondary particle piled structure of the carbon spheres could facilitate the transport of electrolytes,shorten the diffusion distance of Na^(+)and accommodate the volume expansion during cycling.Benefiting from these unique structure features,PG700-3(carbon spheres with the diameters of 40-60 nm carbonized at 700℃)exhibits high performance for sodium storage.A high reversible capacity of 163 mAh g^(-1) could be delivered at a current density of 1.0 A g^(-1) after 100 cycles.Interestingly,at a current density of 10.0 A g^(-1),the specific capacity of PG700-3 gradually increases to 140 mAh g^(-1) after 10000 cycles,corresponding to a capacity retention of 112%.Given the enhanced kinetics of SIBs reactions,PG700-3 exhibits an excellent rate capability,i.e.,230 and 138 mAh g^(-1) at 0.1 and 5.0 A g^(-1),respectively.This study provides a facile method to attain high performance anode materials for SIBs.The design strategy and improvement mechanism could be extended to other materials for high rate applications.

Enhanced Capacitive Characteristics of Activated Carbon by Secondary Activation

The effect of the improvement of commercial activated carbon(AC) on its specific capacitance and high rate capability of double layer(dl) charging/discharging process has been studied. The improvement of AC was carried out \%via\% a secondary activation under steam in the presence of catalyst NiCl\-2, and the suitable condition was found to be a heat treatment at about 875 ℃ for 1 h. Under those conditions, the discharge specific capacitance of the improved AC increases up to 53.67 F/g, showing an increase of about 25% as compared with that of as-received AC. The good rectangular-shaped voltammograms and A.C. impedance spectra prove that the high rate capability of the capacitor made of the improved AC is enhanced significantly. The capacitance resistance(RC) time constant of the capacitor containing the improved AC is 1\^74 s, which is much lower than that of the one containing as-received AC(an RC value of 4.73 s). It is noted that both kinds of AC samples show a similar specific surface area and pore size distribution, but some changes have taken place in the carbon surface groups, especially a decrease in the concentration of surface carbonyl groups after the improvement, which have been verified by means of X-photoelectron spectroscopy. Accordingly, it is suggested that the decrease in the concentration of surface carbonyl groups for the improved AC is beneficial to the organic electrolyte ion penetrating into the pores, thus leading to the increase in both the specific capacitance and high rate capability of the supercapacitor.

Self-Assembled VS4 Hierarchitectures with Enhanced Capacity and Stability for Sodium Storage

Sodium-ion batteries(SIBs)have become an auspicious candidate for largescale energy storage by cause of low cost,natural abundance,and similar working principle with lithium-ion batteries(LIBs).At present,there is an urgent need to explore superior anode materials with rapid and stable sodiation/desodiation.Herein,3D self-assembled VS4 curly nanosheets hierarchitectures(VS4-CN-Hs)are developed for SIB anodes,where VS4 possesses a large theoretical sodium storage capacity,and the building block of nanosheets has large exposed surface area to the electrolyte as well as the constructed hierarchitectures can provide abundant buffer space to alleviate the volume expansion.As a result,VS4-CN-Hs anode possesses excellent electrochemical performance under a wide voltage window of 0.01–3.0 V,such as high reversible capacity of 863 mA h g^(−1) at 0.1 A g^(−1),marvelous rate feature(444 mA h g^(−1) at 10 A g^(−1)),and extralong cycle stability(386 mA h g^(−1) after 1000 times at 5 A g^(−1)).

Hierarchical porous carbon derived from animal bone as matric to encapsulated selenium for high performance Li-Se battery

Animal bone was employed as raw material to prepare hierarchical porous carbon by KOH activation. Rare metal selenium（Se） was encapsulated into hierarchical porous carbon successfully for the cathode material of Li–Se battery, achieving the transformation of waste into energy,protecting environment and reducing the spread of the disease. Animal bone porous carbon（ABPC） acquires a specific surface area of 1244.7903 m^2·g^-1 and a pore volume of 0.594184 cm^3·g^-1. The composite Se/ABPC with 51 wt%Se was tested as a novel cathode for Li–Se batteries. The results show that Se/ABPC exhibits high specific capacity,good cycling stability and current-rate performance; at 0.1C,the composite Se/ABPC delivers a high reversible capacity of 705 mAh·g^-1 in the second cycle and 591 mAh·g^-1 after 98 cycles. Even at the current density of 2.0C, it can still maintain at a reversible capacity of 485 mAh·g^-1. The excellent electrochemical properties benefit from the high electron conductivity and the carbon with unique hierarchical porous structure. ABPC can be a promising carbon matrix for Li–Se batteries.

新型离子交换法制备具有高倍率和高强度钠离子存储性能的本征赝电容正极材料Na_(0.44)MnO_(2)

钠离子电池因其成本低、资源丰富等优点而成为新一代储能设备.在各种正极中,隧道型Na_(0.44)MnO_(2)因其较大的Na^(+)通道,被认为是快速充电电池的合适正极材料,但仍然存在Na^(+)动力学缓慢等问题.本文首次提出了一种Na_(0.44)MnO_(2)的新型离子交换方法,通过调节合成条件,可以很好地控制K^(+)残余量和Na_(0.44)MnO_(2)的尺寸.结果表明,Na_(0.44)MnO_(2)结构中的残留K^(+)扩大了Na^(+)的输运通道,小颗粒形貌缩短了Na^(+)的迁移距离,且晶体中的带状缺陷界面进一步加速了Na^(+)的输运.获得的Na_(0.44)MnO_(2)具有本征赝电容特性,在2-4 V和20 C电流下有79.0 mA h g^(-1)的优异倍率性能.长期循环测试表明,20 C下1000次循环的保持率为98.1%,0.5 C下200次循环的保持率为96.3%.本工作为用于快速充电储能装置的高倍率、高稳定性Na_(0.44)MnO_(2)正极的大规模生产提供了一条新途径.