Influence of Ni/Cu ratio in nickel copper carbonate hydroxide on the phase and electrochemical properties

Abstract

Transition metal compounds containing nickel and copper have been investigated as electrode materials for energy storage. (Ni,Cu)(OH)2CO3 and α-Ni(OH)2 with different Ni/Cu ratios are synthesized by a simple hydrothermal method. All the samples show the similar dandelion-like morphology. It is demonstrated that the mole ratio of Ni to Cu is a key factor to influence the phase and electrochemical performances of the products. Carbonate anions will be intercalated into nickel copper layered double hydroxides with a hydrotalcite structure when the sample is nickel-rich, which will lead to much better electrochemical properties compared with the copper-rich samples with crystalline (Ni,Cu)(OH)2CO3 structure. Among all the materials, sample (Ni0.89Cu0.11)2(OH)2CO3 can deliver the highest specific capacitance of 1017.3 F g−1 at 1 A g−1 and retain 68.5% of the original value after 4000 cycles at 5 A g−1. Meanwhile, an asymmetric capacitor which is assembled by using the optimized material as a positive electrode and activated carbon as a negative electrode exhibits a high energy density of 38.56 Wh kg−1 at a power density of 850.01 W kg−1 and a high power density of 8407.4 W kg−1 at an energy density of 21.7 Wh kg−1. Based on the above results, nickel copper carbonate hydroxides are of potential application for energy storage.