Cation-Disorder-Assisted Reversible Topotactic Phase Transition between Antifluorite and Rocksalt Toward High-Capacity Lithium-Ion Batteries.

Multielectron reaction electrode materials using partial oxygen redox can be potentially used as cathodes in lithium-ion batteries, as they offer numerous advantages, including high reversible capacity and energy density and low cost. Here, a reversible three-electron reaction is demonstrated utilizing topotactic phase transition between antifluorite and rocksalt in a cation-disordered antifluorite-type cubic Li6CoO4 cathode. This cubic phase is synthesized by a simple mechanochemical treatment of conventionally prepared tetragonal Li6CoO4. It displays a reversible capacity of 487 mAh g-1, a high value because of a reversible three-electron reaction using Co2+/Co3+, Co3+/Co4+, and O2-/O22- redox, occurring without O2 gas evolution. The mechanochemical treatment is assumed to reduce its lattice distortion by cation-disordering and facilitate a reversible topotactic phase transition between antifluorite and rocksalt structures via a dynamic cation pushing mechanism.

Crystalline Grain Interior Configuration Affects Lithium Migration Kinetics in Li-Rich Layered Oxide.

The electrode kinetics of Li-ion batteries, which are important for battery utilization in electric vehicles, are affected by the grain size, crystal orientation, and surface structure of electrode materials. However, the kinetic influences of the grain interior structure and element segregation are poorly understood, especially for Li-rich layered oxides with complex crystalline structures and unclear electrochemical phenomena. In this work, cross-sectional thin transmission electron microscopy specimens are "anatomized" from pristine Li1.2Mn0.567Ni0.167Co0.067O2 powders using a new argon ion slicer technique. Utilizing advanced microscopy techniques, the interior configuration of a single grain, multiple monocrystal-like domains, and nickel-segregated domain boundaries are clearly revealed; furthermore, a randomly distributed atomic-resolution Li2MnO3-like with an intergrown LiTMO2 (TM = transitional metals) "twin domain" is demonstrated to exist in each domain. Further theoretical calculations based on the Li2MnO3-like crystal domain boundary model reveal that Li(+) migration in the Li2MnO3-like structure with domain boundaries is sluggish, especially when the nickel is segregated in domain boundaries. Our work uncovers the complex configuration of the crystalline grain interior and provides a conceptual advance in our understanding of the electrochemical performance of several compounds for Li-ion batteries.

A new sealed lithium-peroxide battery with a co-doped Li2O cathode in a superconcentrated lithium bis(fluorosulfonyl)amide electrolyte.

We propose a new sealed battery operating on a redox reaction between an oxide (O(2-)) and a peroxide (O2(2-)) with its theoretical specific energy of 2570 Wh kg(-1) (897 mAh g(-1), 2.87 V) and demonstrate that a Co-doped Li2O cathode exhibits a reversible capacity over 190 mAh g(-1), a high rate capability, and a good cyclability with a superconcentrated lithium bis(fluorosulfonyl)amide electrolyte in acetonitrile. The reversible capacity is largely dominated by the O(2-)/O2(2-) redox reaction between oxide and peroxide with some contribution of the Co(2+)/Co(3+) redox reaction.

A new rechargeable sodium battery utilizing reversible topotactic oxygen extraction/insertion of CaFeO(z) (2.5 ≤ z ≤ 3) in an organic electrolyte.

At present, significant research efforts are being devoted both to identifying means of upgrading existing batteries, including lithium ion types, and also to developing alternate technologies, such as sodium ion, metal-air, and lithium-sulfur batteries. In addition, new battery systems incorporating novel electrode reactions are being identified. One such system utilizes the reaction of electrolyte ions with oxygen atoms reversibly extracted and reinserted topotactically from cathode materials. Batteries based on this system allow the use of various anode materials, such as lithium and sodium, without the requirement to develop new cathode intercalation materials. In the present study, this concept is employed and a new battery based on a CaFeO3 cathode with a sodium anode is demonstrated.

Direct atomic-resolution observation of two phases in the Li(1.2)Mn(0.567)Ni(0.166)Co(0.067)O2 cathode material for lithium-ion batteries.

About phase: The coexistence of rhombohedral LiTMO2 (TM=Ni, Co, or Mn) and monoclinic Li2MnO3-like structures inside Li1.2Mn0.567Ni0.166Co0.067O2 is revealed directly at atomic resolution. The hetero-interface along the [001]rh/[103]mon zone axis direction is demonstrated, indicating the two-phase nature of these lithium-rich cathode materials (green Li, blue Mn, red O, cyan TM).

Reversible solid state redox of an octacyanometallate-bridged coordination polymer by electrochemical ion insertion/extraction.

Coordination polymers have significant potential for new functionality paradigms due to the intrinsic tunability of both their electronic and structural properties. In particular, octacyanometallate-bridged coordination polymers have the extended structural and magnetic diversity to achieve novel functionalities. We demonstrate that [Mn(H2O)][Mn(HCOO)(2/3)(H2O)(2/3)](3/4)[Mo(CN)8]·H2O can exhibit electrochemical alkali-ion insertion/extraction with high durability. The high durability is explained by the small lattice change of less than 1% during the reaction, as evidenced by ex situ X-ray diffraction analysis. The ex situ X-ray absorption spectroscopy revealed reversible redox of the octacyanometallate. Furthermore, the solid state redox of the paramagnetic [Mo(V)(CN)8](3-)/diamagnetic[Mo(IV)(CN)8](4-) couple realizes magnetic switching.

Precise electrochemical control of ferromagnetism in a cyanide-bridged bimetallic coordination polymer.

Magnetic coordination polymers can exhibit controllable magnetism by introducing responsiveness to external stimuli. This report describes the precise control of magnetism of a cyanide-bridged bimetallic coordination polymer (Prussian blue analogue: PBA) through use of an electrochemical quantitative Li ion titration technique, i.e., the galvanostatic intermittent titration technique (GITT). K(0.2)Ni[Fe(CN)(6)](0.7)·4.7H(2)O (NiFe-PBA) shows Li ion insertion/extraction reversibly accompanied with reversible Fe(3+)/Fe(2+) reduction/oxidation. When Li ion is inserted quantitatively into NiFe-PBA, the ferromagnetic transition temperature T(C) gradually decreases due to reduction of paramagnetic Fe(3+) to diamagnetic Fe(2+), and the ferromagnetic transition is completely suppressed for Li(0.6)(NiFe-PBA). On the other hand, T(C) increases continuously as Li ion is extracted due to oxidation of diamagnetic Fe(2+) to paramagnetic Fe(3+), and the ferromagnetic transition is nearly recovered for Li(0)(NiFe-PBA). Furthermore, the plots of T(C) as a function of the amount of inserted/extracted Li ion x are well consistent with the theoretical values calculated by the molecular-field approximation.

Oxygen rocking aqueous batteries utilizing reversible topotactic oxygen insertion/extraction in iron-based perovskite oxides Ca(1-x)La(x)FeO(3-δ).

Developments of large-scale energy storages with not only low cost and high safety but also abundant metals are significantly demanded. While lithium ion batteries are the most successful method, they cannot satisfy all conditions. Here we show the principle of novel lithium-free secondary oxygen rocking aqueous batteries, in which oxygen shuttles between the cathode and anode composed of iron-based perovskite-related oxides Ca(0.5)La(0.5)FeO(z) (2.5 ≤ z ≤ 2.75 and 2.75 ≤ z ≤ 3.0). Compound Ca(0.5)La(0.5)FeO(z) can undergo two kinds of reduction and reoxidation of Fe(4+)/Fe(3+) and Fe(3+)/Fe(2+), that are accompanied by reversible and repeatable topotactic oxygen extraction and reinsertion during discharge and charge processes.

Rapid one-pot synthesis of LiMPO4 (M = Fe, Mn) colloidal nanocrystals by supercritical ethanol process.

We report a rapid one-pot supercritical fluid approach to prepare the desired size and morphology controlled LiMPO(4) nanocrystals, using oleylamine as both capping and reducing agent.

Synthesis of triaxial LiFePO4 nanowire with a VGCF core column and a carbon shell through the electrospinning method.

A triaxial LiFePO4 nanowire with a multi wall carbon nanotube (VGCF:Vapor-grown carbon fiber) core column and an outer shell of amorphous carbon was successfully synthesized through the electrospinning method. The carbon nanotube core oriented in the direction of the wire played an important role in the conduction of electrons during the charge-discharge process, whereas the outer amorphous carbon shell suppressed the oxidation of Fe2+. An electrode with uniformly dispersed carbon and active materials was easily fabricated via a single process by heating after the electrospinning method is applied. Mossbauer spectroscopy for the nanowire showed a broadening of the line width, indicating a disordered coordination environment of the Fe ion near the surface. The electrospinning method was proven to be suitable for the fabrication of a triaxial nanostructure.

Fast Li-Ion insertion into nanosized LiMn(2)O(4) without domain boundaries.

The effect of crystallite size on Li-ion insertion in electrode materials is of great interest recently because of the need for nanoelectrodes in higher-power Li-ion rechargeable batteries. We present a systematic study of the effect of size on the electrochemical properties of LiMn(2)O(4). Accurate size control of nanocrystalline LiMn(2)O(4), which is realized by a hydrothermal method, significantly alters the phase diagram as well as Li-ion insertion voltage. Nanocrystalline LiMn(2)O(4) with extremely small crystallite size of 15 nm cannot accommodate domain boundaries between Li-rich and Li-poor phases due to interface energy, and therefore lithiation proceeds via solid solution state without domain boundaries, enabling fast Li-ion insertion during the entire discharge process.

Determination of activation energy for Li ion diffusion in electrodes.

Higher power Li ion rechargeable batteries are important in many practical applications. Higher power output requires faster charge transfer reactions in the charge/discharge process. Because lower activation energy directly correlates to faster Li ion diffusion, the activation energy for ionic diffusion throughout the electrode materials is of primary importance. In this study, we demonstrate a simple, versatile electrochemical method to determine the activation energy for ionic diffusion in electrode materials via temperature dependent capacitometry. A generalized form of the temperature dependence of the discharge capacity was derived from the diffusion equation. This method yielded activation energy values for Li ion diffusion in LiCoO2 comparable to those obtained from ab initio calculations.

High-ion conducting solidified hybrid electrolytes by the self-assembly of ionic liquids and TiO2.

We have fabricated solidified electrolytes by using an ionic liquid (BMI TFST) and TiO(2); the electrolyte materials exhibit a high conductivity of 10(-2) S cm(-1) at intermediate temperatures due to self-assembled ionic transport channels.

Synthesis of single crystalline spinel LiMn2O4 nanowires for a lithium ion battery with high power density.

How to improve the specific power density of the rechargeable lithium ion battery has recently become one of the most attractive topics of both scientific and industrial interests. The spinel LiMn2O4 is the most promising candidate as a cathode material because of its low cost and nontoxicity compared with commercial LiCoO2. Moreover, nanostructured electrodes have been widely investigated to satisfy such industrial needs. However, the high-temperature sintering process, which is necessary for high-performance cathode materials based on high-quality crystals, leads the large grain size and aggregation of the nanoparticles which gives poor lithium ion battery performance. So there is still a challenge to synthesize a high-quality single-crystal nanostructured electrode. Among all of the nanostructures, a single crystalline nanowire is the most attractive morphology because the nonwoven fabric morphology constructed by the single crystalline nanowire suppresses the aggregation and grain growth at high temperature, and the potential barrier among the nanosize grains can be ignored. However, the reported single crystalline nanowire is almost the metal oxide with an anisotropic crystal structure because the cubic crystal structure such as LiMn2O4 cannot easily grow in the one-dimentional direction. Here we synthesized high-quality single crystalline cubic spinel LiMn2O4 nanowires based on a novel reaction method using Na0.44MnO2 nanowires as a self-template. These single crystalline spinel LiMn2O4 nanowires show high thermal stability because the nanowire structure is maintained after heating to 800 degrees C for 12 h and excellent performance at high rate charge-discharge, such as 20 A/g, with both a relative flat charge-discharge plateau and excellent cycle stability.

Colloidal crystal-derived nanoporous electrode materials of Cut SWNTs-assembly and TiO2/SWNTs nanocomposite.

Relatively ordered macroporous films of a cut single-walled carbon nanotubes (c-SWNTs) assembly and a TiO 2/c-SWNTs nanocomposite were successfully fabricated by colloidal crystal template processes using polystyrene particles. The macroporous TiO2/c-SWNTs nanocomposite film showed excellent rate capability of Li-insertion/extraction. The rate-dependent Li-insertion/extraction capacities were close to theoretical values expected from Li-diffusion in anatase--TiO2 thin layer without blocking electrolyte-ion and electron access.

Large reversible Li storage of graphene nanosheet families for use in rechargeable lithium ion batteries.

The lithium storage properties of graphene nanosheet (GNS) materials as high capacity anode materials for rechargeable lithium secondary batteries (LIB) were investigated. Graphite is a practical anode material used for LIB, because of its capability for reversible lithium ion intercalation in the layered crystals, and the structural similarities of GNS to graphite may provide another type of intercalation anode compound. While the accommodation of lithium in these layered compounds is influenced by the layer spacing between the graphene nanosheets, control of the intergraphene sheet distance through interacting molecules such as carbon nanotubes (CNT) or fullerenes (C60) might be crucial for enhancement of the storage capacity. The specific capacity of GNS was found to be 540 mAh/g, which is much larger than that of graphite, and this was increased up to 730 mAh/g and 784 mAh/g, respectively, by the incorporation of macromolecules of CNT and C60 to the GNS.

Nanosize effect on high-rate Li-ion intercalation in LiCoO2 electrode.

Recently, battery technology has come to require a higher rate capability. The main difficulty in high-rate charge-discharge experiments is kinetic problems due to the slow diffusion of Li-ions in electrodes. Nanosizing is a popular way to achieve a higher surface area and shorter Li-ion diffusion length for fast diffusion. However, while various nanoelectrodes that provide excellent high-rate capability have been synthesized, a size-controlled synthesis and a systematic study of nanocrystalline LiCoO2 have not been carried out because of the difficulty in controlling the size. We have established the size-controlled synthesis of nanocrystalline LiCoO2 through a hydrothermal reaction and, for the first time, clarified the structural and electrochemical properties of this intercalation cathode material. Lattice expansion in nanocrystalline LiCoO2 was found from powder X-ray diffraction measurements and Raman spectroscopy. Electrochemical measurements and theoretical analyses on nanocrystalline LiCoO2 revealed that extreme size reduction below 15 nm was not favorable for most applications. An excellent high-rate capability (65% of the 1 C rate capability at 100 C) was observed in nanocrystalline LiCoO2 with an appropriate particle size of 17 nm.