Study On The Performance Of Cobalt Aluminum Layered Double Hydroxide And Its Composites Prepared By Micro-impinging Stream Reactors

In recent years,supercapacitors have attracted tremendous attention in the field of energy storage due to their outstanding energy and power densities,superior cycle stability and eco-friendly properties.In order to fully exploit the potential of supercapacitors as energy storage devices,researchers have been focusing on improving the electrochemical properties of their electrode materials.Cobalt aluminum layered double hydroxide（Co Al-LDH）is considered to be one of the most promising electrode materials for high-performance supercapacitors due to its multiple redox states,unique layered structure which can provide plenty of electrochemical active sites,and environmental friendliness.However,many cobalt-aluminum based materials prepared by conventional co-precipitation and hydrothermal methods exhibit significant agglomeration,which has a significantly negative impact on their electrochemical performance.In this work,by utilizing the various advantages of the micro-impinging stream reactor（MISR）in enhancing the micromixing,Co Al-LDH and its composites were successfully prepared by MISR co-precipitation method in combination with hydrothermal method with relatively uniform morphology and good electrochemical performance.The main conclusions are as follows:（1）Co Al-LDH material was prepared by the MISR co-precipitation method and the optimum conditions were determined as:a feed flow rate of 120 m L min^-1,a cobalt to aluminum molar ratio of 2:1,an aging time of5 h and a sodium carbonate addition of 8.20 wt%.Under the optimum conditions,the initial specific capacitance of Co Al-LDH electrode material at the current density of 1 A g^-1 was 618.2 F g^-1and it retained 89.2%after2000 charge-discharge cycles.The initial specific capacitance and cycling stability of Co Al-LDH material prepared by the conventional stirred tank reactor（STR）under the same process and test conditions were only 563.6F g^-1 and 50.8%,respectively.（2）Based on the optimum conditions for the preparation of Co Al-LDH by the MISR co-precipitation,the Co Al-LDH was uniformly loaded onto graphene oxide（GO）by MISR,after which the GO was reduced by hydrothermal method to successfully prepare Co Al-LDH/r GO composites.The best electrochemical performance of the Co Al-LDH/r GO composites electrode material was obtained at a hydrothermal temperature of 140℃,a hydrothermal time of 6 h and a GO addition of 0.77 wt%.Under these conditions,the initial specific capacitance of Co Al-LDH/r GO composites electrode material at the current density of 1 A g^-1 was 998.2 F g^-1and it retained 97.9%after 5000 charge-discharge cycles.Subsequently,Co Al-LDH/r GO composites and activated carbon（AC）were used as the positive and negative electrode materials respectively to successfully assemble Co Al-LDH/r GO//AC asymmetric supercapacitor device（ASC）and its electrochemical performance was investigated at a current of 0.5 A g^-1.The ASC device exhibited an initial capacitance value of 36.3 F g^-1 and a capacity retention of 91.5%after 5000 charge-discharge cycles.（3）On the basis of the optimum conditions for the preparation of Co Al-LDH material by the MISR co-precipitation,Ni Co Al-LDH material was prepared by doping nickel element into Co Al-LDH material by MISR and the optimum Ni Co Al molar ratio of 0.667:1.333:1 was determined.With the optimum Ni Co Al molar ratio,the initial specific capacitance of Ni Co Al-LDH electrode material at the current density of 1 A g^-1 was1229.1 F g^-1and it retained 97.0%after 1000 charge-discharge cycles.