Jianming Bai

A zero-strain layered metal oxide as the negative electrode for long-life sodium-ion batteries

Room-temperature sodium-ion batteries have shown great promise in large-scale energy storage applications for renewable energy and smart grid because of the abundant sodium resources and low cost. Although many interesting positive electrode materials with acceptable performance have been proposed, suitable negative electrode materials have not been identified and their development is quite challenging. Here we introduce a layered material, P2-Na0.66[Li0.22Ti0.78]O2, as the negative electrode, which exhibits only ~0.77% volume change during sodium insertion/extraction. The zero-strain characteristics ensure a potentially long cycle life. The electrode material also exhibits an average storage voltage of 0.75 V, a practical usable capacity of ca. 100 mAh g(-1), and an apparent Na(+) diffusion coefficient of 1 × 10(-10) cm(-2) s(-1) as well as the best cyclability for a negative electrode material in a half-cell reported to date. This contribution demonstrates that P2-Na0.66[Li0.22Ti0.78]O2 is a promising negative electrode material for the development of rechargeable long-life sodium-ion batteries.

Amorphous Hierarchical Porous GeOx as High-Capacity Anodes for Li Ion Batteries with Very Long Cycling Life

Many researchers have focused in recent years on resolving the crucial problem of capacity fading in Li ion batteries when carbon anodes are replaced by other group-IV elements (Si, Ge, Sn) with much higher capacities. Some progress was achieved by using different nanostructures (mainly carbon coatings), with which the cycle numbers reached 100-200. However, obtaining longer stability via a simple process remains challenging. Here we demonstrate that a nanostructure of amorphous hierarchical porous GeO(x) whose primary particles are ~3.7 nm diameter has a very stable capacity of ~1250 mA h g(-1) for 600 cycles. Furthermore, we show that a full cell coupled with a Li(NiCoMn)(1/3)O(2) cathode exhibits high performance.

Anomalous Pseudocapacitive Behavior of a Nanostructured, Mixed-Valent Manganese Oxide Film for Electrical Energy Storage

While pseudocapacitors represent a promising option for electrical energy storage, the performance of the existing ones must be dramatically enhanced to meet todays ever-increasing demands for many emerging applications. Here we report a nanostructured, mixed-valent manganese oxide film that exhibits anomalously high specific capacitance (∼2530 F/g of manganese oxide, measured at 0.61 A/g in a two-electrode configuration with loading of active materials ∼0.16 mg/cm(2)) while maintaining excellent power density and cycling life. The dramatic performance enhancement is attributed to its unique mixed-valence state with porous nanoarchitecture, which may facilitate rapid mass transport and enhance surface double-layer capacitance, while promoting facile redox reactions associated with charge storage by both Mn and O sites, as suggested by in situ X-ray absorption spectroscopy (XAS) and density functional theory calculations. The new charge storage mechanisms (in addition to redox reactions of cations) may offer critical insights to rational design of a new-generation energy storage devices.

Promotion of water-mediated carbon removal by nanostructured barium oxide/nickel interfaces in solid oxide fuel cells.

The existing Ni-yttria-stabilized zirconia anodes in solid oxide fuel cells (SOFCs) perform poorly in carbon-containing fuels because of coking and deactivation at desired operating temperatures. Here we report a new anode with nanostructured barium oxide/nickel (BaO/Ni) interfaces for low-cost SOFCs, demonstrating high power density and stability in C3H8, CO and gasified carbon fuels at 750°C. Synchrotron-based X-ray analyses and microscopy reveal that nanosized BaO islands grow on the Ni surface, creating numerous nanostructured BaO/Ni interfaces that readily adsorb water and facilitate water-mediated carbon removal reactions. Density functional theory calculations predict that the dissociated OH from H2O on BaO reacts with C on Ni near the BaO/Ni interface to produce CO and H species, which are then electrochemically oxidized at the triple-phase boundaries of the anode. This anode offers potential for ushering in a new generation of SOFCs for efficient, low-emission conversion of readily available fuels to electricity.

A Size-Dependent Sodium Storage Mechanism in Li4Ti5O12 Investigated by a Novel Characterization Technique Combining in Situ X-ray Diffraction and Chemical Sodiation

A novel characterization technique using the combination of chemical sodiation and synchrotron based in situ X-ray diffraction (XRD) has been detailed illustrated. The power of this novel technique was demonstrated in elucidating the structure evolution of Li4Ti5O12 upon sodium insertion. The sodium insertion behavior into Li4Ti5O12 is strongly size dependent. A solid solution reaction behavior in a wide range has been revealed during sodium insertion into the nanosized Li4Ti5O12 (~44 nm), which is quite different from the well-known two-phase reaction of Li4Ti5O12/Li7Ti5O12 system during lithium insertion, and also has not been fully addressed in the literature so far. On the basis of this in situ experiment, the apparent Na(+) ion diffusion coefficient (DNa+) of Li4Ti5O12 was estimated in the magnitude of 10(-16) cm(2) s(-1), close to the values estimated by electrochemical method, but 5 order of magnitudes smaller than the Li(+) ion diffusion coefficient (D(Li+) ~10(-11) cm(2) s(-1)), indicating a sluggish Na(+) ion diffusion kinetics in Li4Ti5O12 comparing with that of Li(+) ion. Nanosizing the Li4Ti5O12 will be critical to make it a suitable anode material for sodium-ion batteries. The application of this novel in situ chemical sodiation method reported in this work provides a facile way and a new opportunity for in situ structure investigations of various sodium-ion battery materials and other systems.

Investigation of structural and electronic properties of graphene oxide

The local atomic structure of graphene oxide has been probed using synchrotron radiations. Detailed investigations of recently proposed simplistic model of graphene oxide using x-ray absorption near edge spectroscopy have been performed. X-ray diffraction measurements and calculations indicate loss of coherence between graphene-like layers. However, larger in-plane structural coherence is understood to be present. Selected area electron diffraction measurements indicate the presence of graphitic regions in graphene oxide which is expected to produce interesting confinement effects in graphene oxide which could be important for the development of tunable electronic and photonic devices.

Direct visualization of the Jahn–Teller effect coupled to Na ordering in Na5/8MnO2

The cooperative Jahn-Teller effect (CJTE) refers to the correlation of distortions arising from individual Jahn-Teller centres in complex compounds. The effect usually induces strong coupling between the static or dynamic charge, orbital and magnetic ordering, which has been related to many important phenomena such as colossal magnetoresistance and superconductivity. Here we report a Na5/8MnO2 superstructure with a pronounced static CJTE that is coupled to an unusual Na vacancy ordering. We visualize this coupled distortion and Na ordering down to the atomic scale. The Mn planes are periodically distorted by a charge modulation on the Mn stripes, which in turn drives an unusually large displacement of some Na ions through long-ranged Na-O-Mn(3+)-O-Na interactions into a highly distorted octahedral site. At lower temperatures, magnetic order appears, in which Mn atomic stripes with different magnetic couplings are interwoven with each other. Our work demonstrates the strong interaction between alkali ordering, displacement, and electronic and magnetic structure, and underlines the important role that structural details play in determining electronic behaviour.

Nanospheres of a New Intermetallic FeSn5 Phase: Synthesis, Magnetic Properties and Anode Performance in Li-ion Batteries

We synthesized monodisperse nanospheres of an intermetallic FeSn(5) phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe(0.74)Sn(5) of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement. Importantly, FeSn(5), which is not yet established in the Fe-Sn phase diagram, exhibits a quasi-one dimensional crystal structure along the c-axis, thus leading to interesting anisotropic thermal expansion and magnetic properties. Magnetization measurements indicate that nanospheres are superparamagnetic above the blocking temperature T(B) = 300 K, which is associated with the higher magnetocrystalline anisotropy constant K = 3.33 kJ m(-3). The combination of the magnetization measurements and first-principles density functional theory calculations reveals the canted antiferromagnetic nature with significant spin fluctuation in lattice a-b plane. The low Fe concentration also leads Fe(0.74)Sn(5) to enhanced capacity as an anode in Li ion batteries.

Investigation of the structural changes in Li1−xFePO4 upon charging by synchrotron radiation techniques

A systematic study on a LiFePO4 sample with 600 nm particle size was carried out to investigate the electronic and crystal structure changes during charge and their relationships with the charging curve. In situX-ray diffraction data collected at 0.1C rate during first charge shows that the crystal FePO4 is observed at x = 0.3 in Li1−xFePO4, with significant delay than the beginning of the charge plateau. On the other hand, in situ X-ray absorption spectra for the Fe K-edge collected at 0.1C during first charge show that the average oxidation of Fe2+ to Fe3+ almost synchronized with the charging curve. In addition, the ex-situ soft X-ray absorption data for the Fe LII–III edges using surface sensitive partial electron yield detection mode show that the lithium content changes at the surface of the sample particles synchronized or ahead to the charge curve, while the data collected at the same time using bulk sensitive fluorescence yield detection mode show that the lithium content changes in the bulk of the particles lag behind the charging curve. The contents of FePO4 and LiFePO4 calculated from in situXRD in relating to the charge curve are quite different than those calculated from in situXAS and ex-situ soft X-ray absorption data. This tells us that cautious need to be taken when using XRD data alone to track the state of charge of LiFePO4 samples, significant delay in observing the new crystal phase formation could occur, especially at relatively high charging rate.

Phase transition behavior of NaCrO2 during sodium extraction studied by synchrotron-based X-ray diffraction and absorption spectroscopy

The structural evolution of layered NaCrO2 cathodes for sodium-ion batteries during charge was investigated using synchrotron-based in situ X-ray diffraction and ex situ X-ray absorption spectroscopy. Three solid solution phases with expanding ‘c’ and contracting ‘a’/‘b’ lattice parameters were observed. The coordination changes of Cr and Na during sodium extraction were also studied.