Interlayer Space Regulating Of Nickel Manganese Hydrotalcite And Its Composites With CeO₂ Application In Energy Storage

Hydrotalcite is hopefully and widely used as supercapacitors electrode material due to its advantages of low cost,no pollution,simple synthesis,adjustable plate ion,exchangeable interlayer ion and high theoretical specific capacity.However,because of easily stacking of hydrotalcite lamellar,the area of electrochemical active sites decrease,the rate of electrochemical reaction reduces,the specific capacity and rate capability descend.And the poor conductivity of hydrotalcite also reduces the rate capability and cycle stability.Therefore,it is very important for the application of hydrotalcite electrode materials to improve the rate performance and cycle stability,by regulating the interlayer space and studying the influence of interlayer space on the structure and electrochemical performance,and by combining hydrotalcite with easily changedvalence CeO2.Firstly,pure and flower-like nickel manganese hydrotalcite with thin lamellar was synthesized by one step hydrothermal method.The composition,structure and electrochemical properties of the samples were studied by XRD,SEM,TEM,XPS,nitrogen isothermal adsorptiondesorption and electrochemical workstation.The optimum synthetic ratio of Ni:Mn:Ulotropine is 3:3:2.Which sample obtains the maximum specific capacity of 1564.9F/g(1A/g),and the capacity retention rate of 62.7%(1000 cycles at 20A/g).Th e assembled hybrid capacitor obtains the maximum energy density of 34.43 Wh/kg and the maximum power density of 25303.2 W/kg,and the capacity retention rate of 116.8%(10A/g,5000 cycles).On the basis of the best synthesis method above,the double-layer spacing and monolayer spacing nickel manganese hydrotalcites are synthesized with sodium dodecyl sulfonate as intercalation agent.The mechanism of layer spacing adjustment is revealed:With the increasing of sodium dodecyl sulfonate,the amount of dodecyl sulfonate in the interlayer is increasing,the double layer spacing structure intercalated by nitrate and sodium dodecyl sulfonate generates at the same time,firstly.The monolayer spacing structure intercalated alone by sodium dodecyl sulfonate generates,secondly.The sample with interlayer spacing 29(?) obtains the maximum specific capacity of 1994.4F/g(1A/g)and 1282.7F/g(20A/g).The hybrid capacitor assembled with the sample obtains the maximum energy density of 46.5 Wh/kg?the maximum power density of 18933.7 W/kg,and the capacity retention of 82.8%(10A/g,5000 cycles)Keeping the amount of precipitant urea lower than stoichiometric ratio,and adjusting the reaction time,the monolayer spacing structure intercalated by carbonate and the double layer spacing structure intercalated by carbonate and nitrate radical simultaneously appeared.The preferential mechanism of anion intercalation with high anion concentration and high charge density is elucidated.The maximum specific capacity 2206.0F/g(1A/g)and the optimum rate performance is obtained in samples with bilayer spacing after 2-hour action and 4-hour action,respectively.The hybrid capacitor assembled with reaction 4 hours sample obtains the maximum energy density of 55.9 Wh/kg and the maximum power density of 20257.5 W/kg,the capacity retention rate of 90.5%(10A/g,5000 cycles).On the basis of the best hydrothermal synthesis method above,nickel manganese hydrotalcite/CeO2 composites with higher specific capacity,rate performance and cycle performance are synthesized by adding cerium nitrate to the reaction system.The sample added cerium nitrate 0.1mmol obtains the maximum specific capacity of 1956.0 F/g(1A/g)and 1261.4F/g(20A/g),the capacity retention rate of 82.7%(1000 cycles at 20A/g?20%higher than nickel-manganese hydrotalcite).The hybrid capacitor assembled with the sample obtains the maximum energy density of 51.8 Wh/kg and the maximum power density of 20820.6 W/kg,respectively,and the capacity retention rate of 96.9%(10A/g,5000 cycles).