Sheet-membrane Mn-doped nickel hydroxide encapsulated via heterogeneous Ni3S2 nanoparticles for efficient alkaline battery–supercapacitor hybrid devices

Abstract

Efficient, robust and safe energy storage systems occupy a vital position in the development of the electronics industry; they rely strongly on the rational design of electrode materials. In this manuscript, a one-pot hydrothermal route was employed to prepare sheet-membrane Mn-doped nickel hydroxide encapsulated via heterogeneous Ni₃S₂ nanoparticles. The inner large nanosheets, outer ultrathin membranes and encapsulated Ni₃S₂ nanoparticles construct a mechanically robust three-dimensional structure which provides abundant active sites to participate in electrochemical reactions. Density functional theory (DFT) calculations further reveal that the introduction of Ni₃S₂ and Mn-doping in nickel hydroxide obviously decrease the deprotonation energy and shorten the energy gap of Ni(OH)₂, which greatly favors the electrochemical performance of the electrode material. When directly employed in a three-electrode alkaline supercapacitive electrode, NiMn-1 displays excellent capacitance of 385.6 mA h g⁻¹ at 0.68 A g⁻¹, enhanced rate performance (reaching 56.7% retention at 34 A g⁻¹) and outstanding cycling stability (retaining 95.6% after 3000 cycles). Furthermore, a battery–supercapacitor hybrid device was developed based on this electrode material. The device also exhibits excellent capacitance of 59.7 mA h g⁻¹ (at 0.47 A g⁻¹), a high energy density of 51.5 W h kg⁻¹ (at 404 W kg⁻¹) and a suitable service lifespan. Therefore, this high-capacitance electrochemical performance endows the device with further advantages in the energy storage field.