De Li

Layered lithium transition metal oxide cathodes towards high energy lithium-ion batteries

Development and discovery of cathode materials with superior performance seem to be tremendous challenges for Li-ion battery scientists. Since the topotactic reaction was first demonstrated in the 1970s, layered Li transition metal oxides (LiMO2, M = Co, Ni, Mn) have been a shining star throughout the research and innovation in intercalation materials due to their appealing merits. Generally the basic LiMO2 with a single kind of transition metal ion suffers from safety concerns and structural instability and can not support high energy Li-ion batteries. Nowadays, Li-stoichiometric mixed metal oxides and Li-excess Mn-based oxides have been considered as the most promising families of cathode materials for large-scale Li-ion batteries with high energy density used for transportation. In the present paper, with the help of a phase diagram tetrahedron, we provide an overview of the major developments in the field of LiMO2 cathode materials. The changes in structure during Li extraction and the phase compatibility of Li mixed metal oxides are highlighted. The latest progress in the research of Li-excess Mn-based oxides is also included.

The water catalysis at oxygen cathodes of lithium-oxygen cells.

Lithium–oxygen cells have attracted extensive interests due to their high theoretical energy densities. The main challenges are the low round-trip efficiency and cycling instability over long time. However, even in the state-of-the-art lithium–oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials. Here we report a reaction mechanism at an oxygen cathode, ruthenium and manganese dioxide nanoparticles supported on carbon black Super P by applying a trace amount of water in electrolytes to catalyse the cathode reactions of lithium–oxygen cells during discharge and charge. This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles. The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium–oxygen cells.

Surface coating of lithium–manganese-rich layered oxides with delaminated MnO2 nanosheets as cathode materials for Li-ion batteries

Lithium–manganese-rich layered oxides are of great importance as cathode materials for rechargeable lithium batteries. In this article, Li1.2Mn0.567Ni0.167Co0.066O2 is prepared by a co-precipitation method, and the delaminated MnO2 nanosheets with different amounts, 1 wt%, 3 wt% and 5 wt%, are introduced for coating this material for the first time. The structure and morphology of these materials have been investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. The results clearly demonstrate that the surface of lithium–manganese-rich layered oxides is covered by continuous delaminated MnO2 nanosheets. The electrochemical properties including the discharge capacity, initial coulombic efficiency, rate capability and cycle stability of these coated materials have been greatly enhanced, which are obviously related to the delaminated MnO2 nanosheet coating with good electrochemical activity and low charge transfer resistance. Moreover, the lithium–manganese-rich layered oxide coated with 3 wt% delaminated MnO2 nanosheets presents the best comprehensive electrochemical properties as well as improves the initial discharge capacity and coulombic efficiency by 299 mA h g−1 and 88% respectively; the capacity retention after 50 cycles also reaches 93%, and the discharge capacity can be 157 mA h g−1 even at a 5 C discharge rate.

High stable post-spinel NaMn2O4 cathode of sodium ion battery

A spinel-type NaMn2O4 based on an inventive manganese and sodium compound has been synthesized under high pressure (4.5 GPa) for use as the cathode of a sodium ion battery. It exhibits a one-step voltage profile, limited polarization and good capacity retention both at room and high temperatures. The capacity retention is 94% after 200 cycles at room temperature. The stable battery performance is due to the high barrier of structure rearrangement and suppressed Jahn–Teller distortions in this post spinel structure.

Exchange of electric and magnetic resonances in multilayered metal/dielectric nanoplates

In this work, we have experimentally demonstrated that in a rectangular multilayered Ag/SiO₂ nanoplate array, electric and magnetic resonances are exchanged at the same frequency simply by changing the polarization of incident light for 90°. Both electric and magnetic resonances originate from localized surface plasmons, and lead to negative permittivity and permeability, respectively. The numerical calculations on electromagnetic fields agree with the experiments. The investigations provide a simple building block for a metamaterial to switch electric and magnetic resonances by external excitation field.

Optical properties of Bi3.15Nd0.85Ti3O12 nanostructures

Ferroelectric materials are widely researched because of their application in electronic devices. A ferroelectric nanotube is important both theoretically and experimentally because of its nonplanar structure. Bi3.15Nd0.85Ti3O12 nanotubes are fabricated utilizing templates of porous anodic aluminum oxide and thin films are synthesized as well for comparison. Atomic force microscopy, scanning electron microscopy, and x-ray diffraction reveal the microstructure of the samples. The optical properties are investigated carefully to reveal the size effect with the decrease in sample dimensionality. The observed shift of the absorption edge for different nanostructures is discussed.

Tunable interference of light behind subwavelength apertures

We demonstrate in this letter that electromagnetic waves passing through the subwavelength apertures on a silver film interfere with each other in the airgap behind the apertures. Depending on the width of the airgap, either constructive or destructive interference occurs. It is shown that constructive interference enhances the extraordinary optical transmission and evidently improves the quality factor, whereas destructive interference weakens the extraordinary optical transmission. We suggest that our results provide a unique approach to construct plasmonic structures and devices.

Promotional recyclable Li-ion batteries by a magnetic binder with anti-vibration and non-fatigue performance

With the exponentially growing utilization of lithium ion batteries (LIBs), their manufacture and recycling technologies with low cost and low pollution emissions are drawing increasing attention. Herein, we proposed an intelligent battery architecture design with a Magnetic-Manipulated Electrode (MME) by exploiting magnetic Fe3O4 particles as binder. It greatly simplifies the LIB fabrication and recycling technologies, and decreases the total cost as well. In addition, a battery equipped with MME shows anti-vibration and non-fatigue performance.

Tunable electric and magnetic resonances in multilayered metal/dielectric nanoplates at optical frequencies

In this work, we investigate electromagnetic responses in multilayered Ag/SiO2 nanoplates at optical frequencies. Electric and magnetic resonances, which originate from localized surface plasmons, are demonstrated by the effective permeability and permittivity, electric and magnetic field distributions, and measured transmission at oblique incidence. Furthermore, electric and magnetic resonances can be tailored by the geometrical parameters of the nanoplates. In a rectangular nanoplate, magnetic resonance only shifts with the width along the incident polarization, and electric resonance shifts obviously as the aspect ratio of the nanoplate changes. The investigation may provide a tunable building block for optical metamaterials.

Omnidirectional transparency induced by matched impedance in disordered metamaterials

In this work, we present an omnidirectional perfect transmission in the photonic band gap of a metamaterial, where positive-index and active negative-index materials are randomly stacked. Due to mismatched impedance, a photonic band gap appears when the metamaterial possesses zero averaged refractive index. By introducing the matched impedance at the expected frequency, a complete tunneling is achieved in the photonic band gap. This kind of transparency is robust against not only incident angles, optical polarization but system disorder as well. The finding is expected to achieve potential applications in optoelectronic devices.