Caixia Chi

Rational selection of amorphous or crystalline V2O5 cathode for sodium-ion batteries

Vanadium oxide (V2O5), as a potential positive electrode for sodium ion batteries (SIBs), has attracted considerable attention from researchers. Herein, amorphous and crystalline V2O5 cathodes on a graphite paper without a binder and conductive additives have been synthesized via facile anodic electrochemical deposition following different heat treatments. Both the amorphous V2O5 (a-V2O5) cathode and crystalline V2O5 (c-V2O5) cathode show good rate cycling performance and long cycling life. After five rate cycles, the reversible capacities of both the cathodes were almost unchanged at different current densities from 40 to 5120 mA g-1. Long cycling tests with 10 000 cycles were carried out and the two cathodes exhibit excellent cycling stability. The c-V2O5 cathode retains a high specific capacity of 54 mA h g-1 after 10 000 cycles at 2560 mA g-1 and can be charged within 80 s. Interestingly, the a-V2O5 cathode possesses higher reversible capacities than the c-V2O5 cathode at low current densities, whereas it is inversed at high current densities. The c-V2O5 cathode shows faster capacity recovery from 5120 to 40 mA g-1 than the a-V2O5 cathode. When discharged at 80 mA g-1 (long discharge time of 140 min) and charged at 640 mA g-1 (short charge time of 17 min), the a-V2O5 cathode shows a higher discharge capacity than its c-V2O5 counterpart. The different electrochemical performance of a-V2O5 and c-V2O5 cathodes during various electrochemical processes can provide a rational selection of amorphous or crystalline V2O5 cathode materials for SIBs in their practical applications to meet the variable requirements.

Improved cycling stability of MoS2-coated carbon nanotubes on graphene foam as flexible anodes for lithium-ion batteries

Achieving appropriate cycling stability for metal sulfides used as anodes in Li-ion batteries remains highly challenging because of structural collapse or low conductivity. Herein, a novel composite was designed as an anode material for Li-ion batteries. This unique architecture has the advantages of a large interface area, numerous channels for Li+ and electron transport, and a porous structure that facilitates electrolyte infiltration and buffers the volume expansion. As expected, this composite exhibits good cycling stability, high reversible capacity, and high rate capability, delivering a high discharge capacity of 1511.6 mA h g−1 and a high first columbic efficiency of 83.27%. The reversible capacities of graphitic-carbon network material (GCNM) electrodes are 1112 mA h g−1 at a current density of 0.1 A g−1 after 100 cycles, and they show superior rate capabilities. This GCNM composite demonstrates great potential for applications in power sources for flexible and lightweight electronic devices.

Three dimensional hierarchically porous crystalline MnO2 structure design for a high rate performance lithium-ion battery anode

A reasonably designed anode of hierarchically porous crystalline manganese dioxide on nickel foam has been successfully synthesized by facile anodic electrochemical deposition in combination with heat treatment. The three dimensional structure avoids the application of binder and conductive additives. The Ni foam provides a highly electronically conductive network in conjunction with a large surface area to support well contacted MnO2 nanoparticles and effectively increases the mechanical strength of the MnO2 anode as well as suppresses the aggregation of MnO2 nanoparticles during discharge/charge processes. The hierarchical pores composed of a large amount of macropores and mesopores can not only accommodate the volume change of MnO2 nanoparticles during Li ion insertion/extraction, but also accelerate the penetration of electrolyte and promise fast transport and intercalation kinetics of Li ions. The crystalline MnO2 anode exhibits a higher electrochemical performance than the amorphous one. As a result, the hierarchically porous crystalline MnO2 anode shows a long cycling life of 778.0 mA h g−1 after 200 cycles at a current density of 0.4 A g−1 and high-rate capability of up to 82% capacity retention even after the current density increases 20 times from 0.1 to 2.0 A g−1.

The binder-free Ca2Ge7O16 nanosheet/carbon nanotube composite as a high-capacity anode for Li-ion batteries with long cycling life

We report a facile one-step route to synthesize a Ca2Ge7O16 nanosheet (NS)/carbon nanotube (CNT) anode for the first time. The Ca2Ge7O16 NS/CNT composites are uniformly grown on the surface of three-dimensional Ni foam used as the conductive current collector. The Ca2Ge7O16 NS/CNT composite is used as a binder-free anode for lithium-ion batteries, which delivers a reversible capacity of 998.5 mA h g−1 at a current rate of 0.5 A g−1 and exhibits excellent cycle performance (87% retention of its 2nd cycle reversible capacity after 1000 cycles). Furthermore, a binder free full cell is fabricated, which shows excellent cycle performance with 96% retention of its 10th cycle capacity after 100 cycles. The superior cycling performance is attributed to the synergetic effect of small diffusion lengths in NS, sufficient void space to buffer the volume expansion, the CNT for charge transport and a continuous 3D electronic path of the Ni foam.

Enhanced storage capability by biomass-derived porous carbon for lithium-ion and sodium-ion battery anodes

Efficient electrodes with impressive storage capability and fast ion transfer rate are urgently needed to meet the demand for higher energy/power densities and longer life cycles and large rate powering devices. Through a simple freeze-drying and annealing process, nitrogen-containing porous carbon materials with a hierarchical porous structure and enlarged lattice spacing between graphene layers are synthesized. Benefiting from an improvement in the electrochemical activity, porosity, conductive network and mechanical stability, the porous carbon used as anodes for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) exhibits an excellent storage capability, rate performance, and cyclability. Apple carbon exhibits a high capacity of 1050 mA h g−1, and celery carbon shows the reversible capacities of 990 mA h g−1 at 0.1 A g−1 after the 200th cycle as LIBs anodes. For SIBs, a high capacity of 438 mA h g−1 is obtained after 200 cycles for apple carbon and 451 mA h g−1 for celery carbon. It is noteworthy that celery carbon shows a capacity retention of 94% between the 50th to 200th cycling. Further analysis on the structure characterization and charging curves reveal that celery carbon has a high N content, dilated intergraphene spacing, and an intrinsically hierarchical porous structure, which are capable of reversibly accumulating sodium ions through surface adsorption and sodium intercalation. Also, the electrochemical impedance spectroscopy (EIS) reveals that celery carbon has a low charge-transfer resistance, the enhanced cyclability and rate performance might be attributed to convenient ion diffusion in the electrode.

Template-free growth of coral-like Ge nanorod bundles via UV-assisted ionic liquid electrodeposition

Germanium (Ge) is an important semiconductor material in optoelectronic devices and is being researched in energy storage fields. Ge nanostructure materials with different morphologies may lead to distinctly different application performances. In this work, Ge nanorod architectures were successfully template-free electrodeposited on ITO substrate from the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([Emim]Tf2N) containing dissolved GeCl4 with the assistance of UV light. The UV irradiation influences the conformation of imidazolium rings of [Emim]+ adsorbed during the deposition process. A solution template has been formed on the surface of the electrode which inhibited the lateral growth of Ge nuclei and promoted the growth of Ge nanorod structures. Consequently, the coral-like Ge nanorod bundles (NRBs) has been obtained. This method provides attractive prospects for the other semiconductor nanorod structures.

UV-assisted, template-free electrodeposition of germanium nanowire cluster arrays from an ionic liquid for anodes in lithium-ion batteries

Germanium has emerged as a promising Li ion battery anode material due to its high theoretical capacity. The in situ growth of Ge nanowires on current collectors (binder-free electrodes) has attracted much attention owing to their good electrical contact, excellent strain accommodation ability, promising material durability and short Li ion diffusion distance. Herein, we report a facile and efficient technique to synthesize Ge nanowire cluster arrays (Ge NWCAs) on nickel foam through an ultraviolet light (UV) assisted, template-free electrodeposition process from 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([Emim]Tf2N). As a binder-free anode material, a Ge NWCA electrode exhibits a specific capacity of 1612 mA h g−1 and retains 740 mA h g−1 up to 200 cycles at a current rate of 0.2C. The Ge NWCA electrode affords excellent rate capacity at 0.1C–2C and retains specific capacity as high as 959 mA h g−1 at 2C. Furthermore, the specific capacity well recovers to 998 mA h g−1 when the rate is reduced from 2C to 0.1C. UV assisted ionic liquid electrodeposition might open up a new avenue for the synthesis of semiconductor nanostructures.