P-n junction built-in electric field and electrochemical in-situ intercalation enabled ultra-stable and high-energy ammonium-ion storage

Ammonium-ion (NH 4 + ) is a promising non-metallic charge carrier in aqueous energy storage with sustainability and environmental benignity. In spite of the unique H-bond mechanism between NH 4 + and host material, the anisotropy caused from tetrahedral structure of NH 4 + essentially limits its diffusion ability in host materials, still resulting in unsatisfied storage behavior. Herein, the built-in electric field (BIEF) mechanism has been first introduced towards NH 4 + hybrid supercapacitor (HSC) by constructing MnO x /MnS 2 p-n junction. The p-n junction BIEF has a reversibly changed field direction and provides extra inside coulombic force to boost the NH 4 + diffusion kinetics, resulting in outstanding capacity of 838.56 F g −1 (186.35 mAh g −1 ) at 1 A g −1 in 0.5 M NH 4 Ac, which simultaneously outperforms than those in metallic cation electrolyte due to the existed H-bond. Besides, an interlayer pillars effect induced by electrochemical in-situ intercalation of NH 4 + stabilizes the layered matrix structure of MnO x /MnS 2 . As a result, the synergistical optimization of ion kinetics and crystal architectonics enables an ultra-stable NH 4 + storage of 96.42 % capacitance retention upon 40000 cycles. The fabricated HSC delivers a high energy density of 79.57 Wh kg −1 at the power density of 850 W kg −1 , of which the pouch-type device further manifests the practical applicability via powering real-life electric product, such as smartphone and ipad. This work provides new insight into improving NH 4 + intercalation chemistry and developing advanced host materials for aqueous energy storage. Rational integration of built-in electric field and electrochemical in-situ intercalaction mechanisms results ultra-stable and high-energy ammonium-ion storage performances. • Built-in electric field was introduced towards NH4 + supercapacitor for the first time. • NH4 + electrochemical in-situ intercalation supports and stabilizes the crystal matrix structure. • Synergistical optimization of kinetics and architectonics enables high-energy and ultra-stable NH4 + storage. • This work provides new insight into improving NH4 + intercalation chemistry.