Wanfeng Yang

3D binder-free Cu2O@Cu nanoneedle arrays for high-performance asymmetric supercapacitors

Nanostructured Cu oxides/hydroxides are promising materials for supercapacitors because of their high theoretical capacitance, low cost and friendliness to environment. However, the development of commercially viable Cu oxides/hydroxides with superior capacitive performance is still challenging. Here, 3D binder-free Cu2O@Cu nanoneedle arrays electrode was developed via facile electrochemistry. The electrode exhibits a high capacitance of 862.4 F g−1 and excellent cycling stability (20 000 cycles). Furthermore, we have successfully constructed a Cu2O@Cu//AC asymmetric supercapacitor, which can achieve an energy density of 35.6 W h kg−1 at 0.9 kW kg−1 and excellent stability with a capacitance retention of 92% after 10 000 cycles. After being charged for dozens of seconds, the in-series Cu2O@Cu//AC supercapacitors can light up LED arrays and even charge a mobile phone. These fascinating performances reasonably indicate their potential in commercial applications for energy storage.

NiO nanorod array anchored Ni foam as a binder-free anode for high-rate lithium ion batteries

Here we report the preparation of 3D binder-free NiO nanorod-anchored Ni foam electrodes, and their application as anode materials for rechargeable lithium-ion batteries. By anodization followed by thermal annealing, blooming flower-like NiO arrays were anchored to Ni foam, and were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption experiments. Electrochemical properties were evaluated by cyclic voltammetry (CV) and galvanostatic cycling. Cycling performance shows that after 70 cycles the NiO nanorod-anchored Ni foam electrode can still deliver a stable reversible capacity up to 705.5 mA h g−1 and 548.1 mA h g−1 with a high coulombic efficiency (≥98%) at a constant current density of 1 A g−1 and 2 A g−1, respectively. The superior performance of the NiO electrode can be attributed to its favorable morphology and the excellent electrical contact between NiO and the current collector of Ni foam. The present strategy can be extended to fabricate other self-supported transition metal oxide nanostructures for high-performance lithium-ion batteries.

Ultrathin mesoporous NiO nanosheet-anchored 3D nickel foam as an advanced electrode for supercapacitors

As promising electrode materials for electrochemical supercapacitors, pseudocapacitive transition metal oxides such as NiO possess high theoretical specific capacitance, environmental benignity and good abundance. However their areal capacitance and cycling stability are greatly restricted by their poor electronic conductivity (NiO, 10−2 to 10−3 S cm−1). Here we propose an in situ growth strategy in combination with nanoscale design to construct ultrathin mesoporous NiO nanosheets on a 3D network of nickel foam. The hybrid structures show well enhanced conductivity and ion transfer, giving rise to an ultrahigh specific capacitance of 2504.3 F g−1 which is close to the theoretical value of NiO. The electrodes also exhibit remarkable cycling stability (no degradation of the overall capacitance after 45 000 cycles). The amazing electrochemical performance of such hybrid structures makes them potential electrodes in supercapacitors. The present strategy could be popularized in other transition metal oxides like Co3O4, MnO2, etc. to create electrodes with desirable nanostructures.

Anodization driven synthesis of nickel oxalate nanostructures with excellent performance for asymmetric supercapacitors

Here we report a facile efficient anodization approach to fabricate nickel oxalate nanostructures on nickel foam (NON@NF). The NON@NF electrode exhibits high specific capacitance and excellent cycling performance. Moreover, an assembled asymmetric supercapacitor based upon NON@NF and activated carbon shows excellent performance with high energy/power density and long cycling stability.

Nickel oxide nanopetal-decorated 3D nickel network with enhanced pseudocapacitive properties

Metal oxides possess high theoretical specific capacitance, but their pseudocapacitive properties are restricted by the poor electronic conductivity. Here we present a strategy to synthesize a three-dimensional binder/conducting agent-free nickel oxide (NiO) electrode through the combination of anodization with calcination. The NiO electrode is composed of a 3D conductive nickel network decorated with nanopetal-like NiO arrays. The influence of calcination temperature has been investigated, with respect to the microstructure and pseudocapacitive properties of the NiO electrodes. The NiO electrode demonstrates great electrochemical properties, especially remarkable rate capability (82% retention of the highest value for the 25-fold enhanced current density) and cycling stability (good capacitance retention after 30000 cycles). Moreover, an asymmetric supercapacitor has been assembled using NiO as the positive electrode and activated carbon (AC) as the negative electrode. The NiO//AC supercapacitor presents excellent cycling stability (91.3% retention after 10000 cycles), and could power a mini fan as well as a commercial red LED for more than 270 min.

[001] preferentially-oriented 2D tungsten disulfide nanosheets as anode materials for superior lithium storage

Rechargeable lithium ion batteries (LIBs) have transformed portable electronics and will play a crucial role in transportation, such as electric vehicles. For higher energy storage in LIBs, two issues should be addressed, that is, the fundamental understanding of the chemistry taking place in LIBs and the discovery of new materials. Here we design and fabricate two-dimensional (2D) WS2 nanosheets with preferential [001] orientation and perfect single crystalline structures. Being used as an anode for LIBs, the WS2-nanosheet electrode exhibits a high specific capacity, good cycling performance and excellent rate capability. Considering the controversy in the lithium storage mechanism of WS2, ex-situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses clearly verify that the recharge product (3.0 V vs. Li+/Li) of the WS2 electrode after fully discharging to 0.01 V (vs. Li+/Li) tends to reverse to WS2. More remarkably, the [001] preferentially-oriented 2D WS2 nanosheets are also promising candidates for applications in photocatalysis, water splitting, and so forth.

Tungsten diselenide nanoplates as advanced lithium/sodium ion electrode materials with different storage mechanisms

Transition-metal dichalcogenides (TMDs) exhibit immense potential as lithium/ sodium-ion electrode materials owing to their sandwich-like layered structures. To optimize their lithium/sodium-storage performance, two issues should be addressed: fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs. In this study, WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery (LIB/SIB) electrode materials. For LIBs, the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability, as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g–1. Most importantly, in situ Raman spectroscopy, ex situ X-ray diffraction (XRD), transmission electron microscopy, and electrochemical impedance spectroscopy measurements performed during the discharge–charge process clearly verified the reversible conversion mechanism, which can be summarized as follows: WSe2 + 4Li+ + 4e– ↔ W + 2Li2Se. The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes. Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na+ more easily and thoroughly than with Li+ and converted to Na2Se and tungsten in the 1st sodiated state. The subsequent charging reaction can be expressed as Na2Se → Se + 2Na+ + 2e–, which differs from the traditional conversion mechanism for LIBs. To our knowledge, this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.