Highly conductive NiSe₂ nanostructures for all-solid-state battery–supercapacitor hybrid devices

We have developed a facile one-step hydrothermal strategy to synthesize pyramid-like NiSe₂ nanostructures, serving as electrode materials for battery–supercapacitor hybrid (BSH) devices. The NiSe₂ nanopyramid electrode exhibits superior electrochemical performances, including a high specific capacity of 240.83 mAh g⁻¹ at current density of 1 A g⁻¹ and a low internal resistance of 0.85 Ω. The all-solid-state hybrid devices have been assembled with NiSe₂ as the battery-type electrode and activated carbon as the capacitor-type electrode. The hybrid device exhibits a high energy density of 0.196 mWh cm⁻² at power density of 1.60 mW cm⁻². The internal resistance of 1.52 Ω further reveals the nature of low resistance and high conductivity for the hybrid devices. Connecting two hybrid devices in series is able to drive a red LED for more than 3 min after charging for 9 s. This work has demonstrated that the pyramid-like NiSe₂ nanostructure is expected to be an ideal high specific capacity electrode for BSH devices, especially for all-solid-state energy storage devices and portable electronic devices.