Synthesis And Electrochemical Performance Of Nickel Cobalt Layered Double Hydroxides

As a new type of energy storage component,supercapacitor not only has higher power density than batteries but also possesses higher density than the traditional capacitance.Nickel cobalt layered double hydroxides with ideal electrochemical properties and supercapacitor performance won the extensive research.This thesis mainly studies the preparation of nickel cobalt layered double hydroxides and investigated its pseudocapacitor performance.A facile strategy was developed for synthesis of nickel cobalt layered double hydroxide via a hydrothermal method using methanol and water as a medium.The Ni²⁺and Co²⁺ions in the solvent reacted with OH^-ions which generated underwent a redox reaction of methanol and NO₃^-.The diverse morphologies of nickel cobalt layered double hydroxide are obtained in different solvents by means of adjusting the volume ratio of water to methanol.The results exhibit that the products prepared in defferent synthesis conditions show great difference of morphology and electrochemical performacne.The sample parpred in water and methanol ratio of 1:1 consist of nanosheets,which the formed nanosheets interlace each other to form uniform spherical particles with a size around 8?m.The 3D porous structures of spherical particles assembled with nanosheets possess well-defined pathways to electrolyte access and mechanical stability for supercapacitor electrodes.The electrochemical performance of HC11 showed the highest capacitance of690 F g^-1 at a current densities of 1 A g^-1 and the asymmetrical HC11//AC supercapacitors was researched by two-electrode system with a large potential window?0-1.6 V?and the results showed that it had an excellent energy-power combination of 53.82 Wh kg^-1 at the power density of 160 W kg^-1,and maintains at 43 Wh kg^-1 even the power density reached of 1600 W kg^-1.A facile one-step method for preparing nickel cobalt layered double hydroxide?Ni/Co LDH?compound is presented using the buffer solution of NH₄Cl/NaOH.The buffer solution provides OH^-reacting with Ni²⁺/Co²⁺to generate products.It was found that different reaction temperatures affect not only the size of the microsphere,but also the specific surface area.The Cl^-intercalated nickel cobalt layered double hydroxide with high specific surface area and abundant macroporous was synthesized under the low temperature of 70?C.Ni/Co LDH-70 shows the highest capacitance of 1141.9 F g^-1 at a current density of 0.5A g^-1 and the value still keep 970 F g^-1 at a high current density of 10 A g^-1,which is84.95%of that at 0.5 A g^-1.Furthermore,the asymmetrical Ni/Co LDH-70//activated carbon?AC?two-electrode system possess a wide potential window of 0-1.6 V.The energy density of the Ni/Co LDH-70 can achieve to 58.13 Wh kg^-1 at the power density of 160 W kg^-1.Even at a high discharge current of 2 A g^-1,the energy density can still remain 45.78Wh kg^-1 at a power density of 1600 W kg^-1.