Integrated Battery–Capacitor Electrodes: Pyridinic N‑Doped Porous Carbon-Coated Abundant Oxygen Vacancy Mn–Ni-Layered Double Oxide for Hybrid Supercapacitors

Integrating the battery behavior and supercapacitor behavior in a single electrode to obtain better electrochemical performance has been widely researched. However, there is still a lack of research studies on an integrated battery–capacitor supercapacitor electrode (BatCap electrode). In this work, an integrated BatCap electrode porous carbon-coated Mn–Ni-layered double oxide (Mn–Ni LDO-C) was fabricated successfully using controllable heat treatment of polypyrrole-precoated Mn–Ni-layered double hydroxide (Mn–Ni LDH@PPy). This Mn–Ni LDO-C electrode was grown on Ni foam directly and possessed a hierarchical structure that consisted of a pyridinic N (N-6)-doped porous carbon shell and a Mn–Ni LDO core within abundant oxygen vacancies. Benefiting from the synergistic effect of N-6-doped porous carbon and increased oxygen vacancies, Mn–Ni LDO-C exhibited excellent electrochemical performance. The capacity of Mn–Ni LDO-C reached 2.36 C cm–2 (1478.1 C g–1) at 1 mA cm–2 and remained at 92.1% of the initial capacity after 5000 cycles at a current density of 20 mA cm–2. The aqueous battery–supercapacitor hybrid device Mn–Ni LDO-C//active carbon (Mn–Ni LDO-C//AC) also presented superior cycle stability: it retained 85.3% of the original capacity after 5000 cycles at 2 A g–1. Meanwhile, Mn–Ni LDO-C//AC could work normally under a wider potential window (2.0 V), so that the device held the highest energy density of 78.2 Wh kg–1 at a power density of 499.7 W kg–1 and retained 39.1 Wh kg–1 at the highest power density of 31.3 kW kg–1. Two Mn–Ni LDO-C//AC devices connected in series could light a light-emitting diode (LED) bulb easily and keep the LED brightly illuminated for more than 10 min. In general, this work synthesized an integrated BatCap electrode Mn–Ni LDO-C; the integrated electrode exhibited high electrochemical performance, thus has a promising application prospect in the field of energy storage.