Huajun Guo

Enhanced electrochemical properties of lithium-reactive V2O5 coated on the LiNi0.8Co0.1Mn0.1O2 cathode material for lithium ion batteries at 60 °C

The cycling performance of a lithium-reactive V2O5 coated LiNi0.8Co0.1Mn0.1O2 material at 60 °C is substantially improved by a wet-coating process. The V2O5-coated materials are obtained from drying a mixture consisting of NH4VO3 and LiNi0.8Co0.1Mn0.1O2 powders dispersed in ethanol at 85 °C followed by firing at 300 °C for 5 h. The morphology of the V2O5-coated LiNi0.8Co0.1Mn0.1O2 particle synthesized by this coating process is characterized by SEM, TEM and EDX analysis. The V2O5 layer is homogeneously coated onto the particle and the coating thickness was found to be approximately 10–30 nm. The capacity improvement at 60 °C is related to the fact that the highly distributed V2O5 near the surface diminishes the side reactions between the cathode and electrolyte. Moreover, the improvements may also benefit from the unique structure and properties of V2O5.

A novel NiCo2O4 anode morphology for lithium-ion batteries

Spray pyrolysis typically produces spherical particles. In this work, dried plum-like NiCo2O4 particles are synthesized as anode materials for lithium-ion batteries via a facile one-pot spray pyrolysis process using acetate precursors. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the concentration of the precursor solution strongly influences the morphology of the prepared NiCo2O4 particles and this results in different electrochemical performances. It is demonstrated that the special morphological features of the NiCo2O4 particles including the wrinkled structure and the resulting dimples on the surface exert significant effects on the electrochemical performances.

Petal-like Li4Ti5O12–TiO2 nanosheets as high-performance anode materials for Li-ion batteries

A petal-like nanostructured Li4Ti5O12-TiO2 composite has been synthesized by a novel, simple, ultrafast, low-cost, and environmentally benign process and investigated as an anode material for Li-ion batteries. This work introduces a special solution system not slurry to synthesize a spherical flower-like Li4Ti5O12-TiO2 composite by boiling followed by solid-state calcination at a low temperature of 500 °C for 3 h. Well-crystallized Li4Ti5O12-TiO2 with relatively larger amounts (18.80 weight%) of anatase TiO2 can be obtained, which is different from conventional carbon coating, metal doping and trace TiO2 coating. Owing to the relatively low calcined temperature, the flower-like shape of the precursor powder is maintained after post-treatment. Because of the rough and porous nanostructured particles and mutually complementary intrinsic advantages between Li4Ti5O12 and TiO2, the Li4Ti5O12-TiO2 composite obtained at a relatively low calcined temperature shows excellent electrochemical performance. There are two pairs of long and flat voltage plateaus during charge and discharge at 0.1 C rate, which are not shown in other Li4Ti5O12-TiO2 composites. The initial discharge capacities are 185.5, 177.2, 167.3, 145.8, 137.7, 127.5 and 112.5 mA h g(-1) at the 0.1, 0.5, 1, 2, 5, 10 and 20 C rates, respectively. After 100 cycles, the prepared Li4Ti5O12 retains 99.6%, 98.0%, 98.2% and 97.1% of its initial discharge capacities at the 2, 5, 10 and 20 C rates, respectively. After total 450 cycles at 1, 2, 5, 10 and 20 C rates, the cell returns to C/10 and still exhibits a remarkably high discharge capacity of 175.8 mA h g(-1) which is 94.8% of the initial discharge capacity at 0.1 C rate.

Accurate construction of a hierarchical nickel–cobalt oxide multishell yolk–shell structure with large and ultrafast lithium storage capability

Novel hierarchical nickel–cobalt oxide microspheres with a multishell yolk–shell structure have been accurately synthesized via a facile and scalable method. The multishell yolk–shell powder shows a significantly improved electrochemical performance in terms of high reversible capacity, good rate capability and excellent cycling performance.

Hydrogen titanate and TiO2 nanowires as anode materials for lithium-ion batteries

We demonstrate a simple and rapid approach to the synthesis of hydrogen titanate and TiO2 nanowires. The as-prepared materials are characterized by XRD, SEM, TG-DTA, ICP, EDS and electrochemical measurements. SEM images show that the precursor and as-prepared materials are chestnut-like morphology composed of aggregations of nanowires. XRD patterns of the precursor and as-prepared materials indicate that we can get different nanostructured materials by calcining the precursor at the different temperature. Owing to the novel, special and open layered nanostructure, the obtained lepidocrocite hydrogen titanate nanowires show the best cycling capacities and high-rate cycling stability. The initial discharge capacities are 781, 440, 405, 319, 282 and 194 mA h g−1 at the current densities of 20, 100, 200, 400, 1000 and 2000 mA g−1, respectively. After 50 cycles, the as-prepared hydrogen titanate nanowires electrodes retain 103.54% and 97.82% of its initial charge capacities at the current densities of 1000 and 2000 mA g−1, respectively.

Enhanced electrochemical properties of a LiNiO2-based cathode material by removing lithium residues with (NH4)2HPO4

Lithium residues on the surface of LiNi0.8Co0.1Mn0.1O2 have been removed by adding (NH4)2HPO4 dissolved in ethanol. Upon precipitating the unmeasurable lithium residue with different amounts of (NH4)2HPO4, the performance of the LiNi0.8Co0.1Mn0.1O2 cathode materials show marked changes. Under the optimized condition, the modified materials exhibit enhanced cycling performance, although X-ray powder diffraction and transmission electron microscopy results demonstrate that the precipitated Li3PO4 is not coated on the surface of LiNi0.8Co0.1Mn0.1O2. The modified material exhibits 66.9% retention after 100 cycles at 2 C, while the pristine material shows only 48.1% retention. The results demonstrate that the removal of lithium residues from the surface of LiNiO2-based materials is effective in decreasing side reactions. This property will be valuable for increasing the available choices of coating methods and materials because the enhancement of the coating will be maximized if the lithium residue can be removed after coating.

A new design concept for preparing nickel-foam-supported metal oxide microspheres with superior electrochemical properties

Herein, we introduced a new design concept for fabricating nickel-foam-supported metal oxide microsphere as an anode for lithium-ion batteries (LIBs). Porous metal oxide microspheres were synthesized via spray pyrolysis. A piece of nickel foam was placed at the exit of the reactor to filter the off-gas and thus to obtain the metal oxide powders. A thin layer of porous metal oxide microspheres was uniformly deposited on the nickel foam within ∼20 minutes. The nickel-foam-supported metal oxide microsphere was directly used as a binder-free anode for the LIBs. The electrochemical properties of the nickel-foam-supported Co3O4 microsphere (prepared as the first target material) were investigated. The as-prepared anode retains a reversible capacity of 1085 mA h g−1 after 180 cycles. More strikingly, it manifests excellent rate performance with a capacity of 555 mA h g−1 even at 3200 mA g−1. Compared to the available methods that are typically time-consuming and complicated, this smart strategy described herein is efficient and simple. It is strongly envisioned that this elegant design concept holds great potential for the efficient synthesis of other nickel-foam-supported metal oxides as electrodes for LIBs or supercapacitors.

Preparation and characteristics of Li2FeSiO4/C composite for cathode of lithium ion batteries

Abstract A Li2FeSiO4/C composite cathode for lithium ion batteries was synthesized at 650 °C by solid-state reaction. The effects of carbon sources and carbon content on the properties of the Li2FeSiO4/C composites were investigated. The crystalline structure, morphology, carbon content and charge/discharge performance of Li2FeSiO4/C composites were determined by X-ray diffraction(XRD), scanning electron microscopy(SEM), carbon/sulfur analyzer and electrochemical measurements. As carbon content increases in the range of 5%–20%, the amount of Fe3O4 impurity phase decreases. The SEM micrographs show that the addition of the carbon is favorable for reducing the Li2FeSiO4 grain size. Using sucrose as carbon source, the Li2FeSiO4/C composite with 14.5% carbon synthesized at 650 °C shows good electrochemical performance with an initial discharge capacity of 144.8 mA·h/g and a capacity retention ratio of 94.27% after 13 cycles.

A novel architecture designed for lithium rich layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 oxides for lithium-ion batteries

Lithium rich manganese layered oxides (Li[Li0.2Mn0.54Ni0.13Co0.13]O2) with three kinds of architectures (conventional small particles, solid spherical particles and novel hollow spherical particles) are synthesized by co-precipitation followed by calcination. Their interior architectures have been studied through observation of cross-sections, and electrochemical impedance spectroscopy (EIS) has been utilized to gain insight into their properties. Conventional small particles have a high specific surface area (3.3467 m2 g−1) that may cause corrosion in an electrolyte to more easily happen on its surface. Solid spherical particles show unsatisfactory electrochemical properties that could result from the long diffusion path (can reach 10.1 μm). Hollow spherical particles illustrate a low specific surface area (0.4648 m2 g−1) and short diffusion path (about 1.5 μm) at the same time, which enhanced their performance during the electrode process (271 mA h g−1 of initial discharge capacity). The electrochemical performance of hollow spherical particles is significant in the development of lithium rich manganese layered oxides.

Effect of activated carbon and electrolyte on properties of supercapacitor

Abstract Effect of activated carbon and electrolyte on electrochemical properties of organic supercapacitor was investigated. The results show that specific surface area and mesoporosity of activated carbon influence specific capacitance. If specific surface area is larger and mesoporosity is higher, the specific capacitance will become bigger. Specific surface area influences resistance of carbon electrode and consequently influences power property and pore size distribution. If specific surface area is smaller and mesoporosity is higher, the power property will become better. Ash influences leakage current and electrochemical cycling stability. If ash content is lower, the performance will become better. The properties of supercapacitor highly depend on the electrolyte. The compatibility of electrolyte and activated carbon is a determining factor of supercapacitors working voltage. LiPF 6 /(EC-EMC+DMC) is inappropriate for double layer capacitor. MeEt 3 NPF 4 /PC has higher specific capacitance than Et 4 NPF 4 /PC because methyls electronegativity value is lower than ethyl and MeEt 3 N + has more positive charges and stronger polarizability than Et 4 N + when an ethyl is substituted by methyl.