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A reduced graphene oxide/Ni(OH)2 composite with excellent supercapacitive performance was synthesized by a facile hydrothermal route without organic solvents or templates used. XRD and SEM results reveal that the nickel hydroxide, which crystallizes into hexagonal β-Ni(OH)2 nanoflakes with a diameter less than 200 nm and a thickness of about 10 nm, is well combined with the reduced graphene oxide sheets. Electrochemical performance of the synthesized composite as an electrode material was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge measurements. Its specific capacitance is determined to be 1672 F/g at a scan rate of 2 mV/s, and 696 F/g at a high scan rate of 50 mV/s. After 2000 cycles at a current density of 10 A/g, the composite exhibits a specific capacitance of 969 F/g, retaining about 86% of its initial capacitance. The composite delivers a high energy density of 83.6 W·h/kg at a power density of 1.0 kW/kg. The excellent supercapacitive performance along with the easy synthesis method allows the synthesized composite to be promising for supercapacitor applications.

Porous nanoparticles-constructed granule LiMn2O4 spinel was achieved by a solid-state reaction at a relatively low temperature of 600 °C, using a highly reactive Mn3O4 as manganese source, prepared by a precipitation-oxidation process. The granule LiMn2O4, well-crystallized with negligible oxygen deficiency, combines the advantages of nano-structured and bulk materials, exhibiting excellent electrochemical performance and a high tap density of 2.05 g cm−3. Importantly, its cycling performance, especially at elevated temperatures, compares favorably with that of the doped or surface-coated LiMn2O4 materials reported. Also, it shows superior rate capability and cycling performance to the dispersive nanoparticle LiMn2O4 synthesized under the same conditions. The granule LiMn2O4 exhibits a discharge capacity of 121 mAh g−1 at a current rate of 1 C (where 1 C = 148 mA g−1), and retains a capacity of 103 mAh g−1 at 15 C, showing 85% capacity retention. After 200 cycles at 1 C and 25 °C, it delivers a capacity of 119 mAh g−1, retaining 98% of its initial capacity. After 100 cycles at 1 C and 55 °C, it shows a capacity of 114 mAh g−1, preserving 95% of its initial capacity. Due to its excellent electrochemical performance and facile synthesis process adopted, the granule LiMn2O4 can serve as a promising cathode for high-performance Li-ion batteries.

A reduced graphene oxide/β-Ni(OH) 2 composite with excellent supercapacitive performance was prepared by a facile chemical precipitation. Reduced graphene oxide was ultrasonically dispersed in a Ni(NO 3 ) 2 solution, forming a suspension. Then let the prepared suspension stand for 0.5 h and 24 h, respectively, followed by stirring and adding NaOH solution into it for obtaining two types of composites. It was found that the standing time notably affected morphology and supercapacitive performance of the resulting composites. The composite derived from the 24 h-standing suspension presented an ideal morphology with nano-sized β-Ni(OH) 2 particles homogeneously growing on the reduced graphene oxide sheets. The composite exhibited ultra-large specific capacitance, high rate capability and good cycling stability in 6 mol L −1 KOH electrolyte. Its maximum specific capacitance was 2134 F g −1 at a scan rate of 2 mV s −1 , and a large specific capacitance of 882 F g −1 was still preserved at a high scan rate of 70 mV s −1 . After 2000 cycles at a current density of 10 A g −1 , the composite delivered a specific capacitance of 1141 F g −1 , retaining about 81% of its initial capacitance. The high performance and the simple synthesis route allowed the obtained composite to be promising for supercapacitor applications.

Ultra-fine Mn–Ni–Cu oxides (MNCO) are obtained by calcining a solid-state coordination derived oxalate Mn 0.68 Ni 0.22 Cu 0.10 C 2 O 4 · n H 2 O at 250–450 °C. The obtained MNCO present micron-sized agglomerates composed of primary particles with a size of ∼200 nm. The 250 °C- and 350 °C-obtained MNCO are poorly crystallized with a structure of α-MnO 2 , while the 450 °C-obtained MNCO contain multiphase oxides with structures of α-MnO 2 , γ-MnO 2 and Mn 2 O 3 . Electrochemical properties are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy in 6 mol L −1 KOH electrolyte. The MNCO electrodes exhibit good supercapacitive performance, superior to that of powder-based MnO 2 electrodes. At a scan rate of 2 mV s −1 , the 250 °C-, 350 °C-, and 450 °C-obtained MNCO electrodes deliver capacitance values of 490, 293 and 205 F g −1 , respectively. At a current density of 1000 mA g −1 , the 250 °C-, 350 °C-, and 450 °C-obtained MNCO symmetrical capacitors exhibit capacitance values of 368, 286, and 135 F g −1 , respectively, retaining about 75, 81 and 87% of their initial capacitance values after 500 cycles, respectively.