Effect of cation substitution on the pseudocapacitive performance of spinel cobaltite MCo₂O₄ (M = Mn, Ni, Cu, and Co)

Liu, Shude,Ni, Dixing,Li, Hai-Feng,Hui, Kwun Nam,Ouyang, Chu-Ying,Jun, Seong Chan The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.23

<P>Cation substitution is a promising strategy for modulating the structural properties and optimizing the electrochemical performance of spinel cobalt oxide (Co3O4); however, the underlying mechanism of this action induced by different cation substitutions has not yet been clearly addressed. Herein, a systematic investigation is performed to elucidate the effect of cation substitution on the pseudocapacitive performance of spinel cobaltite (MCo2O4; M = Mn, Ni, Cu, and Co) mesoporous nanowires grown on nickel foam (NF). Theoretical and experimental analyses reveal that the substitution of Co by transition metals (<I>i.e.</I>, Mn, Ni, and Cu) in the lattice of Co3O4 can simultaneously improve charge transfer and ion diffusion, thereby exhibiting enhanced electrochemical properties. Herein, as a representative example, MnCo2O4 achieves a high specific capacitance of 2146 F g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP>, while 92.1% of its initial capacitance is retained after 5000 cycles. An asymmetric supercapacitor with MnCo2O4 as the positive material and activated carbon (AC) as the negative material delivers a high energy density of 56.1 W h kg<SUP>−1</SUP> at a power density of 800 W kg<SUP>−1</SUP>, and a favorable energy density of 29.3 W h kg<SUP>−1</SUP> at a power density as high as 8000 W kg<SUP>−1</SUP>.</P>

An asymmetric supercapacitor with excellent cycling performance realized by hierarchical porous NiGa₂O₄ nanosheets

Liu, Shude,Hui, Kwan San,Hui, Kwun Nam,Li, Hai-Feng,Ng, Kar Wei,Xu, Jincheng,Tang, Zikang,Jun, Seong Chan The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.36

<▼1><P>Cycling stability of an asymmetric supercapacitor is enhanced using hierarchical porous NiGa2O4 nanosheets as cathode electrode.</P></▼1><▼2><P>Rational design of the composition and electrochemically favorable structural configuration of electrode materials are highly required to develop high-performance supercapacitors. Here, we report our findings on the design of interconnected NiGa2O4 nanosheets as advanced cathode electrodes for supercapacitors. Rietveld refinement analysis demonstrates that the incorporation of Ga into NiO leads to a larger cubic lattice parameter that promotes faster charge-transfer kinetics, enabling significantly improved electrochemical performance. The NiGa2O4 electrode delivers a specific capacitance of 1508 F g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP> with a capacitance retention of 63.7% at 20 A g<SUP>−1</SUP>, together with excellent cycling stability after 10 000 charge–discharge cycles (capacitance retention of 102.4%). An asymmetric supercapacitor device was assembled by using NiGa2O4 and Fe2O3 as cathode and anode electrodes, respectively. The ASC delivers a high energy density of 45.2 W h kg<SUP>−1</SUP> at a power density of 1600 W kg<SUP>−1</SUP> with exceptional cycling stability (94.3% cell capacitance retention after 10 000 cycles). These results suggest that NiGa2O4 can serve as a new class cathode material for advanced electrochemical energy storage applications.</P></▼2>

Hierarchical manganese cobalt sulfide core–shell nanostructures for high-performance asymmetric supercapacitors

Liu, Shude,Jun, Seong Chan Elsevier 2017 Journal of Power Sources Vol.342 No.-

<P><B>Abstract</B></P> <P>High electrical conductivity and rational design of structures are two crucial routes to improving the electrochemical performance of electrode materials. However, highly conductive electrode materials with short ion-transport paths remain a challenge in energy storage. Here, we propose manganese cobalt sulfide (MnCo<SUB>2</SUB>S<SUB>4</SUB>) nanowire wrapping by a flocculent shell layer using a facile hydrothermal method with post-sulfurization treatment. The resultant MnCo<SUB>2</SUB>S<SUB>4</SUB> electrode employed for supercapacitor delivered a remarkable specific capacitance of 2067 F g<SUP>−1</SUP> at the current density of 1 A g<SUP>−1</SUP>, good rate capability, and excellent cycling stability. Moreover, an asymmetric supercapacitor device was successfully assembled using MnCo<SUB>2</SUB>S<SUB>4</SUB> and reduced graphene oxide (rGO) as electrodes, achieving a high energy density of 31.3 W kg<SUP>−1</SUP> at a power density of 800 W kg<SUP>−1</SUP>. With such outstanding electrochemical performance, this asymmetric supercapacitor device holds great potential in developing high-energy-storage applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A formation mechanism of MnCo<SUB>2</SUB>S<SUB>4</SUB> hybrid nanostructure is proposed. </LI> <LI> MnCo<SUB>2</SUB>S<SUB>4</SUB> delivers a superior rate capability and high specific capacitance. </LI> <LI> The assembled MnCo<SUB>2</SUB>S<SUB>4</SUB>//rGO supercapacitor exhibits a high energy and power densities. </LI> </UL> </P>

Nickel hydroxide/chemical vapor deposition-grown graphene/nickel hydroxide/nickel foam hybrid electrode for high performance supercapacitors

Liu, Shude,Yin, Ying,San Hui, Kwan,Hui, Kwun Nam,Lee, Su Chan,Chan Jun, Seong Elsevier 2019 ELECTROCHIMICA ACTA Vol.297 No.-

<P><B>Abstract</B></P> <P>Rational design of electrode structures has been recognized as an effective strategy to improve the electrochemical performance of electrode materials. Herein, we demonstrate an integrated electrode in which nickel hydroxide (Ni(OH)<SUB>2</SUB>) nanosheets are deposited on both sides of chemical vapor deposition-grown graphene on Ni foam, which not only effectively optimizes electrical conductivity of Ni(OH)<SUB>2</SUB>, but also accommodates the structural deformation associated with the large volume change upon cycling. The synthesized Ni(OH)<SUB>2</SUB>/graphene/Ni(OH)<SUB>2</SUB>/Ni foam electrode exhibits a high specific capacity of 991 C g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP>, which is higher than the theoretical specific capacity of additive sum of Ni(OH)<SUB>2</SUB> and graphene, and retains 95.4% of the initial capacity after 5000 cycles. A hybrid supercapacitor is constructed by using Ni(OH)<SUB>2</SUB>/graphene/Ni(OH)<SUB>2</SUB>/Ni foam as the positive electrode and activated carbon on Ni foam as the negative electrode, which achieves a maximum energy density of 49.5 W h kg<SUP>−1</SUP> at a power density of 750 W kg<SUP>−1</SUP>, and excellent cycling lifespans with 89.3% retention after 10000 cycles at 10 A g<SUP>−1</SUP>.</P>

Honeycomb-Like Interconnected Network of Nickel Phosphide Heteronanoparticles with Superior Electrochemical Performance for Supercapacitors

Liu, Shude,Sankar, Kalimuthu Vijaya,Kundu, Aniruddha,Ma, Ming,Kwon, Jang-Yeon,Jun, Seong Chan American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.26

<P>Transition-metal-based heteronanoparticles are attracting extensive attention in electrode material design for supercapacitors owing to their large surface-to-volume ratios and inherent synergies of individual components; however, they still suffer from limited interior capacity and cycling stability due to simple geometric configurations, low electro-chemical activity of the surface, and poor structural integrity. Developing an elaborate architecture that endows a larger surface area, high conductivity, and mechanically robust structure is a pressing need to tackle the existing challenges of electrode materials. This work presents a supercapacitor electrode consisting of honeycomb-like biphasic Ni5P4-Ni2P (NixPy) nanosheets, which are interleaved by large quantities of nanoparticles. The optimized NixPy delivers an ultrahigh specific capacity of 1272 C g(-1) at a current density of 2 A g(-1), high rate capability, and stability. An asymmetric slipercapacitor employing as-synthesized NixPy as the positive electrode and activated carbon as the negative electrode exhibits significantly high power and energy densities (67.2 W h kg(-1) at 0.75 kW kg(-1); 20.4 W h kg(-1) at 15 kW kg(-1)). These results demonstrate that the novel nanostructured NixPy can be potentially applied in highperformance supercapacitors.</P>

BPF-based Grid Voltage Feedforward Control of Grid-connected Converters for Improving Robust Stability

Shude Yang,Xiangqian Tong,Jun Yin,Haiyan Wang,Yaping Deng,Le Liu 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2

Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter’s robust stability against grid impedance variations. The selection method of the BPF’s bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system’s robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

BPF-based Grid Voltage Feedforward Control of Grid-connected Converters for Improving Robust Stability

Yang, Shude,Tong, Xiangqian,Yin, Jun,Wang, Haiyan,Deng, Yaping,Liu, Le The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2

Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter's robust stability against grid impedance variations. The selection method of the BPF's bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system's robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

State-of-charge Estimation for Lithium-ion Batteries Using a Multi-state Closed-loop Observer

Yulan Zhao,Haitao Yun,Shude Liu,Huirong Jiao,Chengzhen Wang 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.5

Lithium-ion batteries are widely used in hybrid and pure electric vehicles. State-of-charge (SOC) estimation is a fundamental issue in vehicle power train control and battery management systems. This study proposes a novel model-based SOC estimation method that applies closed-loop state observer theory and a comprehensive battery model. The state-space model of lithium-ion battery is developed based on a three-order resistor?capacitor equivalent circuit model. The least square algorithm is used to identify model parameters. A multi-state closed-loop state observer is designed to predict the open-circuit voltage (OCV) of a battery based on the battery state-space model. Battery SOC can then be estimated based on the corresponding relationship between battery OCV and SOC. Finally, practical driving tests that use two types of typical driving cycle are performed to verify the proposed SOC estimation method. Test results prove that the proposed estimation method is reasonably accurate and exhibits accuracy in estimating SOC within 2% under different driving cycles.

State-of-charge Estimation for Lithium-ion Batteries Using a Multi-state Closed-loop Observer

Zhao, Yulan,Yun, Haitao,Liu, Shude,Jiao, Huirong,Wang, Chengzhen The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.5

Lithium-ion batteries are widely used in hybrid and pure electric vehicles. State-of-charge (SOC) estimation is a fundamental issue in vehicle power train control and battery management systems. This study proposes a novel model-based SOC estimation method that applies closed-loop state observer theory and a comprehensive battery model. The state-space model of lithium-ion battery is developed based on a three-order resistor-capacitor equivalent circuit model. The least square algorithm is used to identify model parameters. A multi-state closed-loop state observer is designed to predict the open-circuit voltage (OCV) of a battery based on the battery state-space model. Battery SOC can then be estimated based on the corresponding relationship between battery OCV and SOC. Finally, practical driving tests that use two types of typical driving cycle are performed to verify the proposed SOC estimation method. Test results prove that the proposed estimation method is reasonably accurate and exhibits accuracy in estimating SOC within 2% under different driving cycles.

Temperature influenced chemical growth of hydrous copper oxide/hydroxide thin film electrodes for high performance supercapacitors

Patil, U.M.,Nam, Min-Sik,Lee, Su Chan,Liu, Shude,Kang, Shinill,Park, B.H.,Chan Jun, Seong Elsevier 2017 Journal of alloys and compounds Vol.701 No.-

<P><B>Abstract</B></P> <P>A hierarchical nanostructured hydrous copper oxide/hydroxide (CuO/(OH)<SUB>2</SUB>) with tuneable morphologies are grown on stainless steel (SS) as binder free, robust adhesive thin film electrode by chemical bath deposition (CBD) method. The influence of bath temperature on physico-chemical properties and electrochemical properties are studied. The morphology of the yields can be tailored only by controlling the reaction temperature of the bath and has shown prominence for the self-assembled growth leads transformation from hierarchical nano-bricks, nano-leaves to nanobuds nanostructures. Assisting from the distinctive structural characteristics, the resultant copper oxide/hydroxide nano-bricks, leaves and buds show superior electrochemical performance with specific capacitance values from ∼340 to 140 F g<SUP>−1</SUP> at 1 mA cm<SUP>−2</SUP>. The improved electrochemical performance of integrated binder free electrode signposts their potential capability in energy storage applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A facile synthesis of hydrous mixed phased CuO/(OH)<SUB>2</SUB> thin films using chemical bath deposition method. </LI> <LI> Variation in bath temperatures stimuluses the structural and morphological changes from Nano bricks to buds like structure. </LI> <LI> Structural and morphological changes influences the supercapacitive performance. </LI> <LI> The CuO/(OH)<SUB>2</SUB> nano-buds show superior electrochemical performance with notable specific capacitance values (∼340 F g<SUP>−1</SUP>). </LI> </UL> </P>