Interlayer space regulating of NiMn layered double hydroxides for supercapacitors by controlling hydrothermal reaction time

Abstract

Ordinarily from synthesis of precursor to subsequent ion-exchange process, traditional methods to synthesize layered double hydroxides (LDHs) with large interlayer space are time consuming and complicated. In this work, a simple one-step hydrothermal method to regulate the interlayer space of NiMn-LDHs by keeping urea smaller number moles than the stoichiometric ratios and the reaction time controlling was developed for the first time. The research showed that the interlayer spaces increase along with reaction time extension, and double interlayer spaces appear in the samples after 2-hour, 4-hour and 8-hour reaction because of CO32−, NO3− and some water molecules intercalated into interlayers. The suitable and double interlayer spaces are beneficial to attain better rate performance and cyclic stability. Therefore, the sample after 4-hour reaction with double interlayer spaces 7.87 Å and 7.42 Å shows the highest capacity retention 72.1% and 48.3% at 5 Ag−1and 10 Ag−1, the highest capacity retention 79% after 2000 cycles, rather than the sample with the largest interlayer space. The sample after 2-hour reaction with thinner sheets and pure phase obtains the highest specific capacity of 846.5 Cg−1(average capacity of potential 0–0.45 volts:1881 Fg−1) at 1 Ag−1.