Sub-nanometer-scale fine regulation of interlayer distance in Ni–Co layered double hydroxides leading to high-rate supercapacitors

Ni–Co layered double hydroxides (LDHs) have high theoretical capacities for energy storage by ion intercalation/release but suffer from the sluggish charge transport kinetics, hence are unsuitable for high-power supercapacitors nowadays. Herein, by intercalating the guest multi-carboxylic anions with straight-chain or conjugated-plane configurations, we have realized the sub-nanometer-scale fine regulation of the interlayer distance in Ni–Co LDHs for tuning the charge (ions and electrons) transport kinetics. With increasing the interlayer distance, the equivalent series resistance (RESR) shows the "inverted-volcano" evolution, which is first demonstrated for the anion-intercalated LDHs. With the smallest RESR, the LDH pillared by the conjugated 1,4-benzenedicarboxylic anion achieves the best matching between ion diffusion and electron transfer, and thus presents a high capacitance of 2115 F g−1 at 1 A g−1 and a record-high rate capability for the powder-like LDHs with the capacitance of 410 F g−1 at an ultrahigh current density of 150 A g−1. The corresponding hybrid supercapacitor coupled with activated carbon presents the high energy density of 11.2 Wh kg−1 at the ultrahigh power density of 30.7 kW kg−1, ranking at the top level for the supercapacitors based on the powder-like LDHs active materials. The minimal RESR from the "inverted-volcano" evolution could provide a feasible criterion to explore the high-rate LDH electrodes.