Ultra-small Co-doped Mn3O4 nanoparticles tiled on multilayer graphene with enhanced performance for lithium ion battery anodes

Uniform Fe2 O3 Nanospheres Anchored on Multilayer Graphene as Anode Materials for High-Rate Ni-Fe Batteries

Ni-Fe battery is one of prospective aqueous alkaline batteries due to its high safety, eco-friendliness and cost-effectiveness. However, the electrochemical performance of Fe-based anodes is limited due to the particle aggregation and low electric conductivity. In this work, iron powder is used as a precursor in a chemical bath deposition method. By optimizing the concentration of HNO3 , a balanced dissolution-crystallization process is achieved to obtain uniform Fe2 O3 nanospheres in size between 60 and 90 nm, which are separately anchored on ultrasonically prepared multilayer graphene (MLG). This composite delivers specific discharge capacities of 191.1 and 160.8 mAh g-1 at the current densities of 2 and 10 A g-1 , respectively. A Ni-Fe battery with the as-prepared Fe2 O3 /MLG as anode and Ni(OH)2 /MLG as cathode exhibits an energy density of 69.5 Wh kg-1 at a high power density of 3931.6 W kg-1 .

Nanowires-Assembled TiO2 Nanorods Anchored on Multilayer Graphene for High-Performance Anodes of Lithium-Ion Batteries

Multilayer graphene (MLG) prepared via ultrasonic exfoliation has many advantages such as its low-cost and defect-free nature, high electronic conductivity, and large specific surface area, which make it an apt conductive substrate for TiO₂ composites. To synthesize graphene/TiO₂ hybrids, traditional methods that greatly depend on the chemical bond of oxygen-containing functional groups on graphene with titanium cations are not applicable due to the absence of these functional groups on MLG. In this work, a facile chemical method is developed to directly deposit TiO₂ on the MLG surface without the introduction of chemically active groups. With this method, four types of TiO₂ materials, that is pure anatase TiO₂ nanoparticles, a mixture of anatase TiO₂ nanoparticles and rutile TiO₂ nanoflowers, pure rutile TiO₂ nanoflowers, and pure rutile TiO₂ nanorods, are homogeneously anchored on the MLG surface by controlling the amount of HCl in the reactant. Interestingly, the rutile TiO₂ nanorods in the TiO₂/MLG composite are assembled by many TiO₂ nanowires with an ultra-small diameter and ultra-long length, which provides a better synergetic effect for high performances as LIB anodes than other composites. A specific capacity of 631.4 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1 is delivered, indicating it to be a valuable LIB anode material with low cost and high electrochemical performances.

Standing and Lying Ni(OH)2 Nanosheets on Multilayer Graphene for High-Performance Supercapacitors

For conventional synthesis of Ni(OH)₂/graphene hybrids, oxygen-containing functional groups should be firstly introduced on graphene to serve as active sites for the anchoring of Ni(OH)₂. In this work, a method for growing Ni(OH)₂ nanosheets on multilayer graphene (MLG) with molecular connection is developed which does not need any pre-activation treatments. Moreover, Ni(OH)₂ nanosheets can be controlled to stand or lie on the surface of MLG. The prepared hybrids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The growth processes are suggested according to their morphologies at different growth stages. The enhanced electrochemical performances as supercapacitor electrode materials were confirmed by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. Ni(OH)₂ nanosheets standing and lying on MLG show specific capacities of 204.4 mAh g⁻¹ and 131.7 mAh g⁻¹, respectively, at 1 A g⁻¹ based on the total mass of the hybrids and 81.5% and 92.8% capacity retention at a high current density of 10 A g⁻¹, respectively. Hybrid supercapacitors with as-prepared hybrids as cathodes and activated carbon as anode were fabricated and tested.