Hongwei Tang

Bubble-template-assisted synthesis of hollow fullerene-like MoS2 nanocages as a lithium ion battery anode material

Inorganic fullerene (IF)-like structured materials have attracted considerable attention for electrochemical energy storage and conversion. In this report, we describe a facile method of synthesizing IF-MoS2 hollow structures with a diameter of ∼100 nm by a facile solution-phase reduction process to obtain a hollow MoSx precursor under ambient pressures before subsequent annealing of the material at high temperatures to form IF-MoS2 nanocages. TEM images at different reaction stages reveal the hollow structure spontaneously arising in the novel “close-edge” nanocages under the assistance of an ammonia cation bubble template. When evaluated as an anode material for lithium ion batteries, ex situ characterization indicates that these IF-MoS2 hollow nanocages can provide large expandable spaces for volume changes occurring during the cycles. Such a highly desired structure offers remarkably improved lithium storage performance including high reversible capacity and good cycling behavior and high rate capability.

Facile and Nonradiation Pretreated Membrane as a High Conductive Separator for Li-Ion Batteries.

Polyolefin membranes are widely used as separators in commercialized Li-ion batteries. They have less polarized surfaces compared with polarized molecules of electrolyte, leading to a poor wetting state for separators. Radiation pretreatments are often adopted to solve such a problem. Unfortunately, they can only activate several nanometers deep from the surface, which limits the performance improvement. Here we report a facile and scalable method to polarize polyolefin membranes via a chemical oxidation route. On the surfaces of pretreated membrane, layers of poly(ethylene oxide) and poly(acrylic acid) can easily be coated, thus resulting in a high Li-ion conductivity of the membrane. Assembled with this decorated separator in button cells, both high-voltage (Li1.2Mn0.54Co0.13Ni0.13O2) and moderate-voltage (LiFePO4) cathode materials show better electrochemical performances than those assembled with pristine polyolefin separators.

Synthesis of high-purity LiMn2O4 with enhanced electrical properties from electrolytic manganese dioxide treated by sulfuric acid-assisted hydrothermal method

Using sulfuric acid-assisted hydrothermal treatment, β-MnO2 particles were obtained from the electrolytic manganese dioxide (EMD). Via high-temperature solid-phase reactions, spinel lithium manganese oxides (LiMn2O4) were produced using the obtained β-MnO2 particles as precursor mixed with LiOH·H2O for the lithium-ion battery cathodes. Atomic absorption (AAS) shows that after the hydrothermal treatment, the contents of impurity ions, such as Na+, K+, Ca2+, and Mg2+, caused by the limitation of preparation technology of EMD are greatly reduced. X-ray diffraction and scanning electron microscopy show that β-MnO2 is highly alloyed consisting of nano sticks. Spinel lithium manganese (LiMn2O4) synthesized by the β-MnO2 precursor has high crystallinity with a well 111 face grow and presents a regular and micron-sized octagonal crystal. When used as cathode materials for lithium-ion batteries, LiMn2O4 synthesized by the β-MnO2 precursor has greater discharge capacity, better cycle performance, and better high-rate capability when compared with LiMn2O4 synthesized by the EMD precursor. Cyclic voltammetry and electrochemical impedance spectroscopy indicate that LiMn2O4 synthesized by the β-MnO2 precursor has better electrochemical reaction reversibility, greater peak current, higher lithium-ion diffusion coefficient, and lower electrochemical impedance.

Li-rich layered Li1.2Mn0.54Ni0.13Co0.13O2 derived from transition metal carbonate with a micro–nanostructure as a cathode material for high-performance Li-ion batteries

Compared to commercialized cathode materials, Li-rich layered oxide exhibits a superior mass energy density. However, owing to its low tap/press density, the advantage of its volume energy density is not as obvious as that of its mass energy density, which limits its applications in some volume-constrained fields. It has been shown that the morphology of the precursor is critical to the performances of the final product. Here, solvothermal and co-precipitation methods were adopted to synthesize transition metal carbonate balls with micro-size particles to obtain high-density Li-rich layered oxides. The solvothermal synthesized carbonate showed a micro–nano hierarchical structure composed of nanoplates as subunits, and the co-precipitated synthesized carbonate just presents a micrometer quasi-ball morphology. The Li1.2Mn0.54Ni0.13Co0.13O2 derived from the above solvothermal synthesized carbonate (ST-LMNCO) demonstrated an improved volume density of ∼14% compared to the one derived from the co-precipitated synthesized carbonate (CP-LMNCO). As for electrochemical performances, the ST-LMNCO exhibited a higher discharge specific capacitance (296.6 mA h g−1 for the first discharge), a better rate performance (201.6 mA h g−1 at 1C rate) and a better capacity retention capability (86.2% after 80 cycles) than the CP-LMNCO. The morphologies of the transition metal carbonates as starting materials significantly impacted the morphologies of the derived Li1.2Mn0.54Ni0.13Co0.13O2 particles. Therefore, the carbonate with a hierarchical micro–nanostructure obtained from the solvothermal method is a promising precursor for high performance Li1.2Mn0.54Ni0.13Co0.13O2.

Highly [010]-oriented self-assembled LiCoPO4/C nanoflakes as high-performance cathode for lithium ion batteries

In this article, highly [010]-oriented self-assembled LiCoPO4/C nanoflakes were prepared through simple and facile solution-phase strategies at low temperature and ambient pressure. The formation of 5-hydroxylmethylfurfural and levoglucosan via the dehydration of glucose during the reaction played a key role in mediating the morphology and structure of the resulting products. LiCoPO4 highly oriented along the (010)-facets exposed Li+ ion transport channels, facilitating ultrafast lithium ion transportation. In turn, the unique assembled mesoporous structure and the flake-like morphology of the prepared products benefit lithium ion batteries constructed using two-dimensional (2D) LiCoPO4/C nanoflakes self-assembles as cathodes and commercial Li4Ti5O12 as anodes. The tested batteries provide high capacities of 154.6 mA·h·g−1 at 0.1 C (based on the LiCoPO4 weight of 1 C = 167 mA·h·g−1) and stable cycling with 93.1% capacity retention after 100 cycles, which is outstanding compared to other recently developed LiCoPO4 cathodes.

Tin-based materials supported on nitrogen-doped reduced graphene oxide towards their application in lithium-ion batteries

Recently, nitrogen-doped graphene has attracted significant attention for application as an anode in lithium-ion batteries due to effective modulation of the electronic properties of graphene. Herein, we report a facile route to successfully synthesize a series of tin-based materials (including Sn, SnO2, and SnS2) supported on N-doped reduced graphene oxide (N-rGO). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images indicated that the Sn-based materials were uniformly and tightly dispersed on the surface of N-rGO. When used as an anode in LIBs, the electrochemical performances of the proposed electrodes were systematically investigated and compared. The results show that among these electrodes, SnS2/N-rGO with a matched layered structure delivers the best performance with not only high specific capability but also excellent cycling stability.