Chang-An Wang

Optimizing Li+ conductivity in a garnet framework

The garnet-related oxides with the general formula Li7−xLa3Zr2−xTaxO12 (0 ≤ x ≤ 1) were prepared by conventional solid-state reaction. X-ray diffraction (XRD), neutron diffraction and AC impedance were used to determine phase formation and the lithium-ion conductivity. The lattice parameter of Li7−xLa3Zr2−xTaxO12 decreased linearly with increasing x. Optimum Li-ion conductivity in the Li-ion garnets Li7−xLa3Zr2−xTaxO12 is found in the range 0.4 ≤ x ≤ 0.6 for samples fired at 1140 °C in an alumina crucible. A room-temperature σLi ≈ 1.0 × 10−3 S cm−1 for x = 0.6 with an activation energy of 0.35 eV in the temperature range of 298–430 K makes this Li-ion solid electrolyte attractive for a new family of Li-ion rechargeable batteries.

High-rate aluminium yolk-shell nanoparticle anode for Li-ion battery with long cycle life and ultrahigh capacity

Alloy-type anodes such as silicon and tin are gaining popularity in rechargeable Li-ion batteries, but their rate/cycling capabilities should be improved. Here by making yolk-shell nanocomposite of aluminium core (30 nm in diameter) and TiO2 shell (∼3 nm in thickness), with a tunable interspace, we achieve 10 C charge/discharge rate with reversible capacity exceeding 650 mAh g−1 after 500 cycles, with a 3 mg cm−2 loading. At 1 C, the capacity is approximately 1,200 mAh g−1 after 500 cycles. Our one-pot synthesis route is simple and industrially scalable. This result may reverse the lagging status of aluminium among high-theoretical-capacity anodes.

Design and Preparation of MnO2/CeO2–MnO2 Double-Shelled Binary Oxide Hollow Spheres and Their Application in CO Oxidation

Herein, we designed an extremely facile method to prepare well-defined MnO2@CeO2-MnO2 ball-in-ball binary oxide hollow spheres by employing carbon spheres (CSs) as sacrificial templates. The synthesis process involves a novel self-assembled approach to prepare core-shell CSs@CeO2 precursor, which would directly react with KMnO4 aqueous solution to form yolk-shell CSs@MnO2/CeO2-MnO2 precursor in the following step. Well-dispersed Ce-Mn binary oxide with double-shelled hollow sphere structure could be achieved after annealing the precursor in air. The evolution process and formation mechanism of this novel structure were thoroughly studied in this paper. Especially the as-prepared double-shell MnO2/CeO2-MnO2 hollow spheres exhibited enhanced catalytic activity for CO oxidation compared with the pure MnO2 hollow spheres and pure CeO2 hollow spheres. We believe the high surface area, hierarchical porous structures, and strong synergistic interaction between CeO2 and MnO2 contribute to the excellent catalytic activity. Most importantly, this method could be extended to prepare other transition metal oxides. As an example, triple-shelled Co-Mn composite hollow spheres assembled by ultrathin nanoplates were successfully prepared.

A soft non-porous separator and its effectiveness in stabilizing Li metal anodes cycling at 10 mA cm−2 observed in situ in a capillary cell

While lithium metal anodes have the highest theoretical capacity for rechargeable batteries, they are plagued by the growth of lithium dendrites, side reactions, and a moving contact interface with the electrolyte during cycling. Here, we synthesize a non-porous, elastomeric solid–electrolyte separator, which not only blocks dendritic growth more effectively than traditional polyolefin separators at large current densities, but also accommodates the large volume change of lithium metal by elastic deformation and conformal interfacial motion. Specially designed transparent capillary cells were assembled to observe the dynamics of the lithium/rubber interface in situ. Further experiments in coin cells at a current density of 10 mA cm−2 and an areal capacity of 10 mA h cm−2 show improved cycling stability with this new rubber separator.

Li-Ion Conduction and Stability of Perovskite Li3/8Sr7/16Hf1/4Ta3/4O3.

A solid Li-ion conductor with a high room temperature Li-ion conductivity and small interfacial resistance is required for its application in next-generation Li-ion batteries. Here, we prepared a cubic perovskite-related oxide with the general formula Li3/8Sr7/16Hf1/4Ta3/4O3 (LSHT) by a conventional solid-state reaction method, which was studied by X-ray diffraction, electrochemical impedance spectroscopy, and (7)Li MAS NMR. Li3/8Sr7/16Hf1/4Ta3/4O3 has a high Li-ion conductivity of 3.8 × 10(-4) S cm(-1) at 25 °C and a low activation energy of 0.36 eV in the temperature range 298-430 K. It exhibits both high stability and small interfacial resistance with commercial organic liquid electrolytes, which makes it promising as a separator in Li-ion batteries.

Stabilization of Garnet/Liquid Electrolyte Interface Using Superbase Additives for Hybrid Li Batteries

To improve the solid-electrolyte/electrode interface compatibility, we have proposed the concept of hybrid electrolyte by including a small amount of liquid electrolyte in between. In this work, n-BuLi, a superbase, has been found to significantly improve the cycling performance of LiFePO4/Li hybrid cells containing Li7La3Zr1.5Ta0.5O12 (LLZT) and conventional carbonate-based liquid electrolyte. The modified cells have been cycled for 400 cycles at 100 and 200 μA cm-2 at room temperature, indicating excellent solid/liquid electrolyte interface stability. The role of n-BuLi may be 3-fold: to retard the decomposition reaction of LE, to suppress the Li+/H+ exchange, and to lithiate the garnet/LE interface, inhibiting side reactions and enhancing interfacial lithium-ion transport.

Facile synthesis of well-dispersed CeO2–CuOx composite hollow spheres with superior catalytic activity for CO oxidation

Well-dispersed CeO2–CuOx composite hollow spheres have been successfully synthesized through a facile reflux method using carbon spheres as sacrificial templates. The shells of the hollow spheres, ∼40 nm in thickness, consist of self-assembled 10–15 nm sized nanoparticles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to study the structural features of the CeO2–CuOx composite hollow spheres. X-ray photoelectron spectroscopy (XPS) confirmed that most of the copper element is distributed on the surface of the CeO2 shell support. The CeO2–CuOx composite hollow spheres exhibited enhanced catalytic activity for CO oxidation: complete CO conversion could be obtained at 112 °C. The excellent catalytic activity could be ascribed to the hollow structure, high specific surface area and the strong synergistic interaction between CeO2 and CuOx.

A specially designed Li–H2O2 semi-fuel cell: A potential choice for electric vehicle propulsion

A specially designed Li–H2O2 semi-fuel cell based on hybrid electrolytes is proposed. It is a combination of fuel cell and lithium battery. Five “mechanical charge–discharge” cycles (800 hours in total) of the Li–H2O2 semi-fuel cell were conducted. The cell exhibits fast mechanical rechargeability, good stability and high lithium utilization. Output power of the Li–H2O2 semi-fuel cell can be flexibly adjusted by changing H2O2 concentration.