Carbonate doped nickel-cobalt layered double hydroxide for high performance asymmetric supercapacitors

In this work, a facile chemical co-precipitation method to prepare nickel-cobalt layered double hydroxide (Ni, Co-LDH) is reported. Through the addition of NaHCO3, carbonate ions (CO32-) are introduced into the LDH in a controlled way. The doping of CO32- causes the original nanosheet structure to bend and interconnect, which increases the contact area between the electrode and the electrolyte, enhancing the energy storage characteristics of materials. Appropriate CO32- doping effectively increases the specific capacity of Ni, Co-LDH. When the doping ratio of carbonate is 5% (Ni, Co-LDH/CO3-5%), the specific capacity is improved from 1432 F g-1 (undoped) to 1970 F g-1 at 1 A g-1. Furthermore, the electrode exhibits satisfactory rate capability, retaining 82.8% of the specific capacity at 20 A g-1. Moreover, an asymmetric supercapacitor (ASC), assembled with Ni, Co-LDH/CO3-5% as the positive electrode and activated carbon as the negative electrode, possesses a high energy density of 54.8 Wh kg-1 at a power density of 374.9 W kg-1 and remains 80.8% after 10000 cycles at 10 A g-1, demonstrating excellent cyclic stability.