Preparation And Electrochemical Properties Of All-solid-state Supercapacitors With Nickel-Cobalt Transition Metal Oxide/Sulphide

The spinel phase Ni Co₂O₄ was obtained by annealing the precursors grown on nickel foam(NF)substrates by hydrothermal method.Co and Ni elements mainly exist in the form of Co³⁺and Ni²⁺in Ni Co₂O₄ structure.The crystallinity,specific surface area and mesoporous volume of the as-prepared samples increase with the increase of annealing time and temperature,and are not effected significantly by the hydrothermal reaction temperature.The T100-NCO/NF electrode with the largest specific surface area(126m²?g^-1)and mesoporous volume(0.44 cm³?g^-1)shows the high specific capacitance with1076 F?g^-1 at current density of 0.5 A?g^-1.The T100-NCO/NF electrode also shows excellent rate performance with 61%capacitive retention at the current density of 20 A?g^-1and better cyclic stability which the specific capacity is 14%higher than that of the beginning after 1000 cycles at current density of 10 A?g^-1.The all-solid-state symmetrical supercapacitor(SSC)assembled with the T100-NCO/NF electrodes as the positive and negative electrodes delivers a high energy density of 31 w?h?kg^-1 at a power density of 750w?kg^-1 and good cycle stability which the specific capacitance is 86%of the initial specific capacitance at the current density of 2 A?g^-1 after 500 cycles.The LED lamps in parallel can be powered at least 10 min by the two SSC devices in series with a working voltage of 3 V.Ni Co₂S₄ electrode material was grown on NF substrate by hydrothermal method at the different reaction temperature and time.The as-prepared samples display the spinel phase Ni Co₂S₄ structure with impure phase(Ni₃S₂),in which Co and Ni elements mainly exist in the form of Co³⁺and Ni²⁺.The NCS-150/NF electrode prepared by hydrothermal reaction at 150?for 9 hours exhibits the high specific capacitance with 3378 F?g^-1 at current density of 1 A?g^-1 and better rate performance with 52%capacitive retention at the current density of 20 A?g^-1.The NCS-150/NF electrode also shows excellent cyclic stability which the specific capacity is about 21%less than that of the beginning after 1000 cycles at current density of 10 A?g^-1.The SSC device assembled with the NCS-150/NF electrodes as the positive and negative electrodes also exhibits the higher energy density than that of the SSC device based on the T100-NCO electrodes.The energy density is enhanced to 49.5w?h?kg^-1 at a power density of 800 w?kg^-1.The specific capacitance is 68%of the initial specific capacitance at the current density of 5 A?g^-1 after 500 cycles,.The LED lamps in parallel can be powered at least 15 min by the two SSC devices in series with a working voltage of 3 V.The spinel phase Ni Co₂O₄ was obtained by annealing the precursors grown on nickel foam(NF)substrates by hydrothermal method,and then the surface of as-prepared Ni Co₂O₄ was treated using thiourea through the hydrothermal method to obtain the spinel phase Ni Co₂O₄@Ni Co₂S₄ composite.Co and Ni elements are mainly in the form of Co³⁺and Ni²⁺,and S and O are in the form of S²⁺and O²⁺in the composite.The crystallinity of the as-prepared sample decrease with the increase of sulfuration time.However,the specific surface area and mesoporous volume increase firstly and then decrease.The NCO@NCS-2 sampledispalys the large specific surface area(96 m²?g^-1)and mesoporous volume(0.43 cm³?g^-1).The electrochemical performance results show that NCO@NCS-6/NF electrode exhibit the highest specific capacitance and NCO@NCS-2/NF electrode display the best ratio performance and cycle stability.The specific capacitance of NCO@NCS-2/NF electrode is 2236 F?g^-1 at the current density of 1 A?g^-1,which keeps 78%capacitance at the current density of 20 A?g^-1.The specific capacity of NCO@NCS-2/NF electrode is only 5%less than that of the original specific capacity after 1000 cycles at current density of 10 A?g^-1.The SSC device assembled with the NCO@NCS-2/NF electrodes as the positive and negative electrodes exhibits the higher energy density than that of the SSC device based on the T100-NCO electrodes.The energy density is enhanced to 37 w?h?kg^-1 at a power density of 800 w?kg^-1.Meantime,the SSC device based on NCO@NCS-2/NF electrodes as the positive and negative electrodes also exhibits excellent cycle stability than those of the T100-NCO and NCS-150/NF electrodes.The specific capacitance is 93%of the initial specific capacitance at the current density of 5 A?g^-1 after500 cycles,the T100-NCO and NCS-150/NF electrodes are 86 and 68%,respectively.The LED lamps in parallel can be powered at least 12 min by the two SSC devices in series with a working voltage of 3 V.The above results show that the NCO/NF electrode displays the good ratio performance and cycle stability,and the NCS/NF electrode exhibits the super high specific capacitance.The NCO@NCS/NF composite electrode take advantage of the both electrodes to improve obviously the electrochemical properities of the NCO@NCS/NF electrode.Also,the electrochemical performance of the SSC device based on NCO@NCS/NF electrode as the positive and negative electrodes are enhance dramatically.The mechanism of the improved electrochemical performance of NCO@NCS/NF composite electrode is discussed.