Irreversible phase transformation of layered structure into spinel structure is considered detrimental for most of the layered structure cathode materials. Here we report that this presumably irreversible phase transformation can be rendered to be reversible in sodium birnessite (Na x MnO 2 · y H 2 O) as a basic structural unit. This layered structure contains crystal water, which facilitates the formation of a metastable spinel-like phase and the unusual reversal back to layered structure. The mechanism of this phase reversibility was elucidated by combined soft and hard X-ray absorption spectroscopy with X-ray diffraction, corroborated by first-principle calculations and kinetics investigation. These results show that the reversibility, modulated by the crystal water content between the layered and spinel-like phases during the electrochemical reaction, could activate new cation sites, enhance ion diffusion kinetics and improve its structural stability. This work thus provides in-depth insights into the intercalating materials capable of reversible framework changes, thereby setting the precedent for alternative approaches to the development of cathode materials for next-generation rechargeable batteries.

Electrochemical performance of phosphorus/carbon composite was unprecedentedly enhanced by reduced graphene oxide (rGO) encapsulation.

Recently, Na ion battery systems came to the fore again because of their high cost-effectiveness compared to the widely used Li ion battery systems. However, representative Li ion battery anode materials such as graphite and silicon cannot adapt to Na ion battery. So, many researchers have tried to find new anode materials for Na ion battery, and phosphorus has emerged as one of the promising materials. Phosphorus is a prospective anode material substitute for silicon as a high capacity material in Na ion battery. But similar to silicon, poor intrinsic electric conductivity and high volume expansion ratio of phosphorus makes it challenging to be applied as an anode material. To overcome the problems, numerous synthesis processes such as mechanical milling of phosphorus with carbon or other metals, and insertion of phosphorus inside the active carbon by evaporating process have been conducted. However, cyclability and coulombic efficiency of previous materials still needs to be improved in order to make NIB commercially viable. In this study, we encapsulated mechanically milled P/C composite into reduced graphene oxide (rGO) by simple spray-drying to prevent deterioration of the P/C composite. Specifically, we tried to reduce the surface side reaction and volume expansion problem by our design strategy which was helpful to solve the problem due to the outstanding mechanical strength and electric conductivity of rGO. Consequently, rGO encapsulated P/C composite shows improved performance by rGO coating effect in terms of cyclability, rate capability and coulombic efficiency.

Review: such as x-ray and neutron diffraction, x-ray absorption spectroscopy, and microscopy; 222 refs.

Transition metal oxides are very promising electrode materials for lithium-ion batteries that operate through conversion reactions. Energy densities for conversion reactions are higher than for intercalation reactions, but most of transition metal oxides show poor cycling performance and reversibility due to the pulverization of active materials and subsequent volume changes. We here report a facile and scalable synthesis for realizing Li4Ti5O12-coated Fe/Fe3O4 hybrid nanocomposites in the form of one-dimensional nanofibers (C@Fe-Fe3O4/Li4Ti5O12 hybrid NFs). This is a new class of highly-reversible and safe anode material that can significantly reduce the lithium-ion diffusion length and improve strain tolerance during Li ion insertion/extraction. Its oxidation state was also impressively controlled through a carbothermal reaction during annealing. The precise oxidation state control of C@Fe-Fe3O4/Li4Ti5O12 hybrid NFs simultaneously enabled high capacity due to the conversion reaction of Fe3O4 as well as high reversibility and stability resulting from zero-strain characteristics and superb kinetics of Li4Ti5O12. This new electrode material appears promising for not only future energy systems but also various electronic devices.

The surface framework of LiCoO2 is modified through a surface treatment called phosphidation, which suppressed the unwanted phase transition occurring above 4.2 V. The surface instability of LiCoO2 toward organic electrolytes is simultaneously improved by changing its surface structure from an O2‐based framework to a PO4‐based framework that can protect against HF attack during cycling. Phosphidated LiCoO2 is successfully synthesized that showed greater stability in its bulk and surface structures. The phosphidated form enables faster Li+ diffusion and prevents irreversible phase transitions, especially when charged above 4.2 V, and consequently demonstrates excellent cycling performance and rate capabilities. The improved kinetics and stability resulting from phosphidation make LiCoO2 highly suitable as a high‐voltage cathode material for use in lithium ion batteries.

Silicon (Si) has attracted much attention as a promising anode material for Li ion battery because of its high theoretical specific capacity and low working potential. However, Si has shown poor cycling behavior and reversibility, which result from its huge volume change and the following pulverization. In this study, an electrospinning method was adopted to synthesize Pitch-incorporated into Si/Carbon nanofibers (Si/Pitch CNFs), which has high crystalline carbon network compared to other Si/Carbon nanofibers without the carbon matrix obtained from the decomposition of pitch. We demonstrated that this high crystalline carbon network in the form of nanofiber has two kinds of merits: it not only reduced the diffusion length for Li ion transport thanks to its 1D morphology but also helped to tolerate high strain of Si and maintain electron transport throughout the entire electrode. As a result, Si/Pitch CNFs showed a greatly enhanced kinetic performance, even at 10C, thus showing its feasibility as a high-power material for future applications like electric vehicles (EV) and energy storage systems (ESS).

Development of high performance electrode materials for energy storage is one of the most important issues for our future society. However, a lack of clear analytical views limits critical understanding of electrode materials. This review covers useful analytical work using X-ray diffraction, X-ray absorption spectroscopy, microscopy and neutron diffraction for ion storage systems. The in situ observation facilitates comprehending real-time ion storage behaviour while the ion storage system is operating, which help us to understand detailed physical and chemical properties. We will discuss how the tools have been used to reveal detailed reaction mechanisms and underlying properties of electrode materials.

Na3V2(PO4)3 particles partly embedded in carbon nanofibers enabled fast electronic conduction as well as facile Na ion migration simultaneously. As a result, the composite showed excellent electrochemical properties as a cathode material for sodium ion batteries.

Li4Ti5O12 is a promising anode material for rechargeable lithium batteries due to its well-known zero strain and superb kinetic properties. However, Li4Ti5O12 shows low energy density above 1 V vs Li(+)/Li. In order to improve the energy density of Li4Ti5O12, its low-voltage intercalation behavior beyond Li7Ti5O12 has been demonstrated. In this approach, the extended voltage window is accompanied by the decomposition of liquid electrolyte below 1 V, which would lead to an excessive formation of solid electrolyte interphase (SEI) films. We demonstrate an effective method to improve electrochemical performance of Li4Ti5O12 in a wide working voltage range by coating Li4Ti5O12 powder with p-type semiconductor NiOx. Ex situ XRD, XPS, and FTIR results show that the NiOx coating suppresses electrochemical reduction reactions of the organic SEI components to Li2CO3, thereby promoting reversibility of the charge/discharge process. The NiOx coating layer offers a stable SEI film for enhanced rate capability and cyclability.

Transition metal oxides are promising electrode materials for lithium-ion batteries that operate through conversion reactions. Energy densities for conversion reactions are higher than for intercalation reactions, but most transition metal oxides show poor cycling performance and reversibility due to pulverization of active materials and subsequent volume changes. We report a facile, scalable, electrospinning synthesis for fabrication of Li4Ti5O12-coated Fe/Fe3O4 nanocomposites into one-dimensional hybrid nanofibers (C@Fe-Fe3O4/Li4Ti5O12 hybrid NFs). This is a new class of highly-reversible and safe anode material that significantly reduces the lithium-ion diffusion length and improves strain tolerance caused by lithium-ion insertion/extraction. Oxidation state is also impressively controlled through a carbothermal reaction during annealing. The precise oxidation state control of C@Fe-Fe3O4/Li4Ti5O12 hybrid NFs provided high capacity due to the Fe oxide conversion reaction and substantial reversibility and stability resulting from zero-strain characteristics and superb kinetics of Li4Ti5O12. This new electrode material appears promising for future energy systems.

For the purpose of reducing not only the consumption of natural resources, but also the environmental pollution from internal combustion engines, much effort has been dedicated to developing new energy storage systems (ESSs) and electric vehicles (EVs) powered by batteries. There are several stringent requirements, such as high power/energy density, good safety, and high reliability against external environmental abuse. For next-generation batteries to meet these requirements, the development of a new energy conversion system is crucial. Therefore, lithium-oxygen (lithium-O-2) batteries have attracted intensive attention, due to their high theoretical energy density, compared with those of gasoline engines. However, present lithium-O-2 batteries exhibit low round-trip efficiency and cyclic degradation, thus preventing their commercialization as next-generation power sources. This drawback may be attributed to the high thermodynamic stability of discharge products and their intrinsic insulating character, leading to the surge of polarization in oxygen reduction reactions/oxygen evolution reactions (ORRs/OERs). To alleviate cyclic degradation and improve round-trip efficiency, it has been reported that the polarization can be reduced by adopting adequate cathode catalysts, based on their surface structures regulating oxygen adsorption. Here we provide and discuss several design strategies for tailoring catalytic materials from a structural and morphological viewpoint, as well as their effect on discharge products.

In recent decades, lithium-ion batteries have become the most widely used power source for portable electronic devices and hybrid electric vehicles (HEVs) and plug-in HEVs because it can offer high energy and power density. The most representative cathode material for commercial Li-ion batteries is LiCoO2 due to its high capacity and excellent cycle life. LiCoO2 has the hexagonal α-NaFeO2 phase consisting of the layered rock-salt structure with the order of Li+ and Co3+ on alternating (111) planes in its cubic structure. When a Li/Li1-xCoxO2 cell is typically charged within limited composition range (0 < x < 0.5, 4.2V), it shows reasonably good capacity retention. However, the discharge capacity under the cut-off voltage of 4.2 V is around only 140 mAh/g, which is much lower than the theoretical value (274 mAh/g) of LiCoO2. Unfortunately, the practical use of LiCoO2 has been limited because its stability could be rapidly deteriorated at potentials higher than 4.2 V. Some research groups have reported that the poor cycling performance above 4.2 V is caused by structural instability induced by a phase transition from hexagonal phase to a monoclinic phase, which accompanies a volume change of ~2.6 % along the c-axis. To overcome the above problems, many researchers have developed lots of surface modifications that can improve the structural stability of LiCoO2. In this study, we tried to control the interlayer distance variation (lattice parameter c) though the substitution of phosphorus for Li+ sites by a phosphidation process. As a result, the unwanted phase transition could be suppressed by the existence of PO4 framework formed on the surface of LiCoO2 dramatically improving the cycleability and rate capability of LiCoO2 even above 4.5 V. Using this approach, we could easily change the surface O2-framework of LiCoO2 to PO4-framework. Consequently, phosphidated LiCoO2 came to retain very high structural stability and a stable surface film was formed in contact with electrolyte during charging/discharging. Phosphidated LiCoO2 exhibited greater bulk and surface stability compared to pristine LiCoO2 even in high voltage range, suggesting that this methodology will be also promising for other high-voltage cathode materials in lithium ion batteries.

This work demonstrates higher catalytic activity of nitrogen-doped TiO2 nanofibers for lithium-air cells compared to pristine TiO2. Its electrochemical superiority could be ascribed to electronic property changes on the surface.

The sodium battery has the potential to be the next generation battery system which utilizes cheaper and more abundant sodium material but affords nearly the same power as lithium batteries. The key issue to realize such sustainable batteries is to develop suitable organic electrode materials with sufficient redox capacity and cycling stability. Organic molecules are intriguing candidates for electrode materials for use in rechargeable Na ion batteries, organic electrode with aromatic carbonyl derivate structure has gained much attention because of its low cost, no need for rare metals, low safety risks compared to transition metal oxides, and design flexibility at the molecular level. Among possible organic materials, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) with aromatic carbonyl derivate structure is a promising candidate anode material for lithium rechargeable batteries due to its demonstrate that each carbon in a C6 ring can accept a Li ion to form a Li6/C6 additive complex through a reversible electrochemical lithium addition reaction. In contrast, in this case of sodium addition reaction, NTCDA can insert ~7.5 Na ion in the initial discharge process but with poor cyclability. Recently, the substituents on a phenyl ring can affect the thermodynamic and kinetic properties of aromatic carbonyl derivate structure. In this work, we tried to selectively substitution the functional groups of NTCDA by a bromination, and thus we dramatically enhanced the electrochemical performance of NTCDA.

The phase control of spinel LiNi0.5 Mn1.5 O4 was achieved through surface treatment that led to an enhancement of its electrochemical properties. Li(+) diffusion inside spinel LiNi0.5 Mn1.5 O4 could be promoted by modifying the surface structure of LiNi0.5 Mn1.5 O4 through phosphidation into a disordered phase (Fd3m) that allows facile Li(+) transport. Phosphidated LiNi0.5 Mn1.5 O4 showed a significantly enhanced electrochemical performance, even at high rates exceeding 10 C, demonstrating that the improved kinetics (related to the amount of Mn(3+) ) can render LiNi0.5 Mn1.5 O4 competitive as a high-power cathode material for electric vehicles and hybrid electric vehicles.

The polymorphic change of TiO2 nanofiber catalysts from anatase to rutile enabled Li-O-2 cells to have higher round-trip efficiency and lower overpotential followed by a better cyclic retention. This is due to enhanced catalytic activity probably associated with the smaller Li+ chemisorption energy and band gap of the rutile phase compared with the anatase phase.

Pristine and Ru-doped LiNi0.5Mn1.5O4 samples were synthesized using a simple carbon combustion method. Crystallographic analyses combining X-ray diffraction and Rietveld refinement confirmed that formation of the LixNil_O-x-like impurity phase is prevented and that the lattice parameter increases as a result of Ru doping. Furthermore, its structure is partially changed to the more disordered spinel phase (Fd3m). Both this structural change and the disappearance of the impurity phase greatly enhance the rate capability and cyclic retention of LiNi0.5Mn1.5O4. (C) 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.