Lingyun Guo

Pineapple-shaped ZnCo2O4 microspheres as anode materials for lithium ion batteries with prominent rate performance

Pineapple-shaped ZnCo2O4 (ZCO) microspheres with a porous nanostructure are synthesized by a typical hydrothermal method and used as high performance anodes in Li-ion batteries. The microspheres show excellent cycling and rate performance. The initial discharge capacity of 1596.2 mA h g−1 and the reversible discharge capacity of 1132 mA h g−1 can be maintained after 120 cycles at a current density of 100 mA g−1. More interestingly, the reversible capacity as high as 800 mA h g−1 can be retained at a high current density of 1000 mA g−1 after 200 cycles. Surprisingly, the pineapple-shaped ZCO electrode exhibits a prominent rate performance, a reversible specific capacity of 1237 mA h g−1 and 505 mA h g−1 at current densities of 500 mA g−1 and 6000 mA g−1 respectively. In addition, the influence of distilled water and urea on the phase and morphology of the material is investigated by SEM and EDS. The results indicate that adding distilled water into the solvent could ensure the high purity of products with no loss of the Zn element. At the same time, the cycle performance can be effectively improved because of the more regular surface and the more stable structure of the microspheres with urea-assistance.

Three-dimensional NiCo2O4 nanowire arrays: preparation and storage behavior for flexible lithium-ion and sodium-ion batteries with improved electrochemical performance

The growth of three-dimensional (3D) porous NiCo2O4 nanowire arrays on a carbon fiber cloth (denoted as NCO@CFC) via a facile low-cost solution method combined with a subsequent annealing treatment is reported. The structure and morphology of the materials were characterized by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. Owing to the unique 3D hierarchical architecture, the NCO@CFC nanowires as a flexible electrode material for lithium-ion batteries exhibit a stable cycling performance (92.3% retention after 100 cycles), a fairly high rate capacity (507 mA h g−1 at 4000 mA g−1), and an enhanced lithium storage capacity. When employed as an electrode material for sodium-ion batteries, the NCO@CFC is investigated in comparison with a 3D ordered array structure and exhibits similar charge/discharge characteristics and a feasible electrochemical performance. The greatly improved electrochemical performance could be ascribed to the 3D porous nanostructure of the NCO@CFC nanowire arrays together with a novel carbon skeleton, which provides enough space to allow volume expansion during the Li+/Na+ insertion/extraction process and facilitates rapid transport of ions and electrons.

Mesoporous ZnCo2O4 microspheres as an anode material for high-performance secondary lithium ion batteries

Herein, we report mesoporous ZnCo2O4 microspheres fabricated by a facile hydrothermal method followed by pyrolysis of a Zn0.33Co0.67CO3 precursor. The obtained ZnCo2O4 microspheres were made up of closely packed primary nanoparticles with a diameter of about 30 nm and a large number of pores that were sized between 10 to 40 nm, which results in a high BET surface area of 39.52 m2 g−1. The large surface area permits a high interfacial contact area with the electrolyte and provides more locations and channels for fast Li+ insertion/extraction into the electrode material. The porous structure may not only be beneficial for Li+ ions to diffuse efficiently to active material with less resistance but also to buffer the volume expansion during the discharging/charging processes. When used as an anode material, the specific capacity was maintained at a high value of 1256 mA h g−1 after 100 cycles at a current density of 100 mA g−1, which is about 3.4 times larger than that of the commercial graphite electrode (372 mA h g−1). More interestingly, a reversible capacity as high as 774 mA h g−1 could be retained at a high current density of 1000 mA g−1 after 200 cycles, which indicates that the mesoporous ZnCo2O4 microspheres had excellent cycling performance at a high current density for use as anode materials for lithium-ion batteries (LIBs).

The design and synthesis of porous NiCo2O4 ellipsoids supported by flexile carbon nanotubes with enhanced lithium-storage properties for lithium-ion batteries

Porous NiCo2O4 ellipsoids supported by flexile carbon nanotubes (denoted as NCO/CNTs) were successfully synthesized by a facile hydrothermal method followed by subsequent annealing in air. The structure and morphology of the materials were characterized by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. When evaluated as anode materials for lithium-ion batteries (LIBs), the NCO/CNTs composites exhibit a high and stable reversible capacity (1273.8 mA h g−1 at 500 mA g−1), excellent rate capability (593.0 mA h g−1 at 4000 mA g−1), and long cycling stability (no capacity fade over 200 cycles). The improved performance of these LIBs can be attributed to the unique 3D porous NCO/CNTs composite frameworks, which will enhance electrical conductivity of the materials, facilitate fast ion/electron transport through the electrode, and accommodate massive volume expansion/contraction during cycling. Furthermore, the synthetic strategy is simple but very effective, it can be easily extended to prepare many other metal oxides with the CNTs acting as the conductive network and used as promising anode materials for high-performance LIBs.