The electronic band structures of pristine and Cr-, Fe-, Ni-or Mg-doped Li 4 Ti 5 O 12 have been calculated by first-principles local-density calculations. Analysis is carried out for the band gaps and density of states of these materials. It is shown that Cr or Mg doping can improve the electronic conduction of Li 4 Ti 5 O 12 , but Ni or Fe doping does not have such an effect. The mechanism for the improved electronic conduction is also proposed.

No abstract

An empirical method based on chemical bond theory for the estimation of the lattice energy for ionic crystals has been proposed. The lattice energy contributions have been partitioned into bond dependent terms. For an individual bond, the lattice energy contribution made by it has been separated into ionic and covalent parts. Our calculated values of lattice energies agree well with available experimental and theoretical values for diverse ionic crystals. This method, which requires detailed crystallographic information and elaborate computation, might be extended and possibly yield further insights with respect to bond properties of materials.

Silicon (Si) has been regarded as a promising high-capacity anode material for developing advanced lithium-ion batteries (LIBs), but the practical application of Si anodes is still unsuccessful mainly due to the insufficient cyclability. To deal with this issue, we propose a new route to construct a dual core-shell structured Si@SiO@C nanocomposite by direct pyrolysis of poly(methyl methacrylate) (PMMA) polymer on the surface of Si nanoparticles. Since the PMMA polymers can be chemically bonded on the nano-Si surface through the interaction between ester group and Si surface group, and thermally decomposed in the subsequent pyrolysis process with their alkyl chains converted to carbon and the residue oxygen recombining with Si to form SiO, the dual core-shell structure can be conveniently formed in a one-step procedure. Benefiting from the strong buffering effect of the SiO interlayer and the efficient blocking action of dense outer carbon layer in preventing electrolyte permeation, the obtained nanocomposite demonstrates a high capacity of 1972 mA h g, a stable cycling performance with a capacity retention of >1030 mA h g over 500 cycles, and particularly a superiorly high Coulombic efficiency of >99.5% upon extended cycling, exhibiting a great promise for practical uses. More importantly, the synthetic method proposed in this work is facile and low cost, making it more suitable for large-scale production of high capacity anode for advanced LIBs.

The electrochemical and thermal performances of commercial LiCoO 2 as cathode material of lithium-ion batteries were improved by soaking the nano-Al 2 O 3 in commercial LiPF 6 /ethylene carbonate/dimethyl carbonate electrolyte. The acidity of the new electrolyte is much higher than that of the original ͑commercial͒ electrolyte. These observations cannot be explained with traditional models of performance improvement by surface coating/modification. A solid superacid model was proposed based on extended and comprehensive analyses. This model disagrees with previous improvement mechanisms and predicts that some other nanocompounds can also be used as additives for improving the performances of LiCoO 2 cathode materials.

A temperature-responsive cathode is developed by coating an ultra-thin layer of poly(3-octylthiophene) in between an Al substrate and cathode-active layer.

Great efforts have been devoted to developing nano-Si anodes for next-generation lithium ion batteries (LIBs); however, the reversible capacity and cycling stability of all Si anodes developed so far still need to be improved for battery applications. In this work, we propose a new strategy to develop a cycling-stable Si anode by embedding nano-Si particles into a Li + -conductive polymer matrix, in which a stable Si/polymer interface is established to avoid the contact of the Si surface with the electrolyte and to buffer the volume change of the Si lattice during cycles, thus promoting the capacity utilization and long cycle life of nano-Si particles. The nano-Si/polybithiophene composite synthesized in this work demonstrates a high Li-storage capacity of >2900 mA h g À1 , a high-rate capability of 12 A g À1 and a long-term cyclability with a capacity retention of >1000 mA h g À1 over 1000 cycles, possibly serving as a high capacity anode for lithium battery applications. In addition, the fabrication technique for this type of composite material is facile, scalable and easily extendable to other Li-storable metals or alloys, opening up a new avenue for developing high capacity and cycling-stable anodes for advanced Li-ion batteries. † Electronic supplementary information (ESI) available: FTIR spectra of the Si/PBT composite, SEM images of PBT and the Si/PBT composite, charge-discharge prole and cycling performance of the coin-type full cells using the Si/PBT as the anode and NCM as the cathode, the electrochemical impedance spectra (EIS) of the Si/PBT electrode at different cycles, XPS spectra of C 1s and O 1s collected from the surface of the Si/PBT electrode at different cycles, the EIS spectra of the PBT electrode at different charge/discharge states, the relationship between Z re and u À0.5 in a low frequency region, and the diffusion coefficient of Li + ions in the PBT electrode at different charge/discharge states. See

Large-area single-crystalline vanadium dioxide nanoflakes were first fabricated via a thermal reduction method in a tube furnace. The sample was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results show that VO2 nanoflakes are single-crystalline with a monoclinic structure. The VO2 nanoflakes have a width of 200–300 nm, a thickness of 50–100 nm, and a length up to 1–2 μm. It is found that single-crystalline VO2 nanoflakes show a novel and complicated 5–7-step Li-storage behavior for an insertion amount of <0.6 mol lithium per mol of VO2.