ling Xiao

Facile Shape Control of Co3O4 and the Effect of the Crystal Plane on Electrochemical Performance

Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and {001} planes, and octahedra with exposed {111}planes - is synthesized using a very simple one-step hydrothermal method. The three kinds of Co(3)O(4) exhibit significantly different electrochemical performances and the effect of different exposed crystal planes on the electrochemical performance of Co(3)O(4) is comprehensively studied.

LiCoO2 nanoplates with exposed (001) planes and high rate capability for lithium-ion batteries

AbstractWe report the synthesis of near-uniform LiCoO2 nanoplates by a two-step approach in which β-Co(OH)2 nanoplates are synthesized by co-precipitation and then transformed into LiCoO2 nanoplates by solid state reaction at 750 °C for 3 hours. Characterization by high-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED) reveal that the as-prepared LiCoO2 nanoplates are covered with many cracks and have exposed (001) planes. The electrochemical performance of the LiCoO2 nanoplates was investigated by galvanostatic tests. The capacity of LiCoO2 nanoplates stabilized at 123 mA·h/g at a rate of 100 mA/g and 113 mA·h/g at a rate of 1000 mA/g after 100 cycles. The excellent rate capability of the LiCoO2 nanoplates results from cracks which are perpendicular to the (001) plane and favor fast Li+ transportation. In addition, compared with other methods of synthesis of LiCoO2 the time of the solid reaction state is significantly shorter even at relatively low temperatures, which means the energy consumption in preparing LiCoO2 is greatly decreased. The controllable synthesis of LiCoO2 nanoplates with exposed (001) plane paves an effective way to develop layered cathode materials with high rate capabilities for use in Li-ion batteries.

Facile synthesis of LiCoO2 nanowires with high electrochemical performance

AbstractCobalt precursor Co(CO3)0.35Cl0.2(OH)1.1 nanowire bunches have been synthesized by a hydrothermal method and transformed into Co3O4 nanowires by calcination at 500 °C for 3 h. The Co3O4 nanowires were then mixed with LiOH and formed the LiCoO2 nanowires by calcination at 750 °C. High resolution transmission electron microscopy revealed that the LiCoO2 nanowires were composed of nanoparticles with most of the nanoparticles having exposed (010) planes. The electrochemical performance of the LiCoO2 nanowires was thoroughly investigated by galvanostatic tests. The as-prepared LiCoO2 nanowires exhibited excellent rate capability and satisfactory cycle stability, where the charge and discharge capacity still stabilized at 100 mA·h/g at a rate of 1000 mA/g after 100 cycles. The favorable electrochemical performance of the LiCoO2 nanowires may result from their one-dimensional nanostructure and the exposure of (010) planes, since the (010) plane is electrochemically active for layered LiCoO2 with the α-NaFeO2 structure and favors fast Li+ transportation.

Single-crystal CeO2 nanocubes used for the direct electron transfer and electrocatalysis of horseradish peroxidase.

A new horseradish peroxidase (HRP) third-generation electrochemical biosensor based on ceria nanocubes (CeO(2)-NCs) and chitosan (Chit) was developed. The single-crystalline, uniform and size-controlled CeO(2)-NCs have been synthesized by hydrothermal method. HRP was immobilized in CeO(2)-NCs and Chit film on the glass carbon electrode (HRP/CeO(2)/Chit/GCE). Compared with HRP-chitosan modified electrode (HRP/Chit/GCE), HRP/CeO(2)/Chit/GCE exhibited a pair of more obvious redox peaks at -0.348 V (versus Ag/AgCl). Experimental results indicate CeO(2)-NCs greatly promoted the electron transfer between HRP and GCE. The immobilized HRP exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide (H(2)O(2)). The resulting biosensor showed a linear range of 1-150 microM and a detection limit of 0.26 microM estimated at a signal-to-noise ratio of 3. Stability and reproducibility of the biosensor were also studied. The biological activity of HRP immobilizing in the composite film was characterized by UV-vis and FTIR spectra.

Preparation of hexagonal ultrathin WO3 nano-ribbons and their electrochemical performance as an anode material in lithium ion batteries

Hexagonal ultrathin WO3 nano-ribbons (HUWNRs) of subnanometer thicknesses, 2–5 nm widths, and lengths of up to several micrometers were prepared by a solvothermal method. The as-prepared HUWNRs grow along the [001] direction, and the main exposed facet is the (120) crystal plane. The HUWNRs exhibit good electrochemical performance as an anode material in lithium ion batteries because of their unique structure. It is believed that these unique materials may be applied in many fields.

A Versatile Coating Strategy to Highly Improve the Electrochemical Properties of Layered Oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3)

This work provides a convenient, effective and highly versatile coating strategy for the layered oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3). Here, layered oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3) has been successfully coated with ion conductor of Li2SiO3 by in situ hydrolysis of tetraethyl orthosilicate (TEOS) followed by the lithiation process. The discharge capacity, cycle stability, rate capability, and some other electrochemical performances of layered cathode materials LiMO2 can be highly enhanced through surface-modification by coating appropriate content of Li2SiO3. Particularly, the 3 mol % Li2SiO3 coated LiNi1/3Mn1/3Co1/3O2 exhibits approximately a discharge capacity of 111 mAh/g after 300 cycles at the current density of 800 mA/g (5 C). Potentiostatic intermittent titration technique (PITT) test was carried out to investigate the mechanism of the improvement in the electrochemical properties. The diffusion coefficient of Li(+)-ion (D(Li)) of Li2SiO3 coated layered oxide materials has been greatly increased. We believe our methodology provides a convenient, effective and highly versatile coating strategy, which can be expected to open the way to ameliorate the electrochemical properties of electrode materials for lithium ion batteries.

The Effect of Crystal Face of Fe2O3 on the Electrochemical Performance for Lithium-ion Batteries.

Fe2O3 nanorods exposing (001) and (010) plane as well as Fe2O3 nanosheets exposing (001) plane have been successfully synthesized. Fe2O3 nanosheets exhibit better cycle performance and rate capabilities than that of Fe2O3 nanorods. The discharge capacity of Fe2O3 nanosheets can stabilize at 865 mAh/g at the rate of 0.2 C (1C = 1000 mA/g) and 570 mAh/g at the rate of 1.2 C after 80 cycles, which increased by 90% and 79% compared with 456 mAh/g and 318 mAh/g of Fe2O3 nanorods. In comparison with (010) plane, the (001) plane of hematite possesses larger packing density of Fe3+ and O2−, which is responsible for the superior electrochemical performances of Fe2O3 nanosheets than that of Fe2O3 nanorods. In addition, potentiostatic intermittent titration (PITT) results show the diffusion coefficients of Li+ (DLi) of Fe2O3 nanosheets is higher than that of Fe2O3 nanorods. The higher diffusion coefficients of Li+ is favorable for the excellent lithium-storage capabilities and rate capability of Fe2O3 nanosheets. Inspired by our results, we can design and synthesize Fe2O3 or other electrodes with high performances according to their structure features in future.

A study of the structure–activity relationship of the electrochemical performance and Li/Ni mixing of lithium-rich materials by neutron diffraction

0.3Li2MnO3·0.7LiNi0.5−xMn0.5−xM2xO2 (M = Mg or Al, x = 0–0.08) samples have been synthesized by a combination of co-precipitation (CP) and solid-state reaction. Electrochemical measurements show that not only can the charge–discharge capacity of lithium-rich materials be enhanced, but more importantly, the rate capacity can be greatly improved by doping with magnesium and aluminum. At a current density of 400 mA g−1, the 0.3Li2MnO3·0.7LiNi0.46Mn0.46Mg0.08O2 and 0.3Li2MnO3·0.7LiNi0.49Mn0.49Al0.02O2 electrodes deliver discharge capacities of 135 mA h g−1 and 127 mA h g−1, respectively, while the pristine electrode delivers a discharge capacity of only 10 mA h g−1. Through studying the structure of lithium-rich materials, we find that the Li/Ni mixing of lithium-rich materials is reduced by doping with magnesium and aluminum, in turn, the performance of doped lithium-rich materials is improved greatly. Furthermore, compared with Al-doped lithium-rich materials, the Li/Ni mixing of Mg-doped materials is further reduced. So the performance improvement of Mg-doped lithium-rich materials is more obvious than that of Al-doped materials.

Decreasing Li/Ni Disorder and Improving the Electrochemical Performances of Ni-Rich LiNi0.8Co0.1Mn0.1O2 by Ca Doping

Decreasing Li/Ni disorder has been a challenging problem for layered oxide materials, where disorder seriously restricts their electrochemical performances for lithium-ion batteries (LIBs). Element doping is a great strategy that has been widely used to stabilize the structure of the cathode material of an LIB and improve its electrochemical performance. On the basis of the results of previous studies, we hypothesized that the element of Ca, which has a lower valence state and larger radius compared to Ni2+, would be an ideal doping element to decrease the Li/Ni disorder of LiMO2 materials and enhance their electrochemical performances. A Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode material was selected as the bare material, which usually shows severe Li/Ni disorder and serious capacity attenuation at a high cutoff voltage. So, a series of Ca-doped LiNi0.8(1-x)Co0.1Mn0.1Ca0.8xO2 (x = 0-8%) samples were synthesized by a traditional solid-state method. As hypothesized, neutron diffraction showed that Ca-doped LiNi0.8Co0.1Mn0.1O2 possessed a lower degree of Li/Ni disorder, and potentiostatic intermittent titration results showed a faster diffusion coefficient of Li+ compared with that of LiNi0.8Mn0.1Co0.1O2. The Ca-doped LiNi0.8Mn0.1Co0.1O2 samples exhibited higher discharge capacities and better cycle stabilities and rate capabilities, especially under a high cutoff voltage with 4.5 V. In addition, the problems of polarization and voltage reduction of LiNi0.8Mn0.1Co0.1O2 were also alleviated by doping with Ca. More importantly, we infer that it is crucial to choose an appropriate doping element and our findings will help in the research of other layered oxide materials.

New insight into Li/Ni disorder in layered cathode materials for lithium ion batteries: a joint study of neutron diffraction, electrochemical kinetic analysis and first-principles calculations

Although layered cathode materials LiNixMnyCo1−x−yO2 have attracted much attention due to their number of advantages, the issue of Li/Ni disorder seriously restricts their electrochemical properties. It is very important and pivotal for the better optimization of layered cathode materials to clearly explain the detailed relationships among the Li/Ni disorder, Li+ migration resistance, electrochemical kinetics and electrochemical properties. Here we focus on the LiNixMnyCo1−x−yO2 cathode material and report relationships among the crystal structures, Li+ migration resistance, electrochemical kinetics and electrochemical properties by combining neutron diffraction techniques, electrochemical kinetic analysis techniques and first-principles calculation methods. The results suggest that more Li+/Ni2+ ion exchange will shrink the inter-slab space thickness, causing a higher Li+ ion migration barrier and inferior electrochemical kinetics, all of which should be responsible for the limited electrochemical properties.