Atsuo Yamada 교수

powders were synthesized under various conditions and the performance of the cathodes was evaluated using coin cells. The samples were characterized by X-ray diffraction, scanning electron microscope observations, Brunauer, Emmett, and Teller surface area measurements, particle-size distribution measurements, and Mössbauer spectroscopy. Ab initio calculation was used to confirm the experimental redox potentials and Mössbauer parameters. The choice of a moderate sintering temperature and a homoge

Abstract Efficient energy storage is a driving factor propelling myriads of mobile electronics, electric vehicles and stationary electric grid storage. Li‐ion batteries have realized these goals in a commercially viable manner with ever increasing penetration to different technology sectors across the globe. While these electronic devices are more evident and appealing to consumers, there has been a growing concern for micro‐to‐mega grid storage systems. Overall, the modern world demands energy

A potential 4 V cathode material for lithium batteries was investigated. The crystal chemistry of the olivine-type of (discharged state) and its delithiated form (charged state) were comparatively studied using X-ray diffraction, Mössbauer spectroscopy, and ab initio calculations. A strong oxidizer, nitronium tetrafluoroborate, was used for chemical delithiation of to obtain The strong electron/lattice interaction induced by the trivalent manganese in (charged state) is highlighted as the intrin

Abstract Hard carbon is a standard anode material for Na‐ion batteries. However, its low crystallinity and diverse microstructures make obtaining a full understanding of the sodium storage mechanism challenging. Here, the results of a systematic ex situ small and wide angle X‐ray scattering study of a series of nanostructured hard carbons, which reveal clear evidence of sodium storage in the graphene–graphene interlayers and nanopores, are presented. Particularly, an emergence of a broad peak ar

Extending the pyrophosphate chemistry for rechargeable Na-ion batteries, here we report the synthesis and electrochemical characterization of Na2FeP2O7, a novel Fe-based cathode material for sodium batteries. Prepared by conventional solid-state as well as solution-combustion synthesis (at 600 °C), the Na2FeP2O7 adopts a triclinic structure (space group: P-1) with three-dimensional channels running along [100], [− 110] and [01-1] directions. With no further optimization, the as-synthesized Na2Fe

Pseudocapacitance is a key charge storage mechanism to advanced electrochemical energy storage devices distinguished by the simultaneous achievement of high capacitance and a high charge/discharge rate by using surface redox chemistries. MXene, a family of layered compounds, is a pseudocapacitor‐like electrode material which exhibits charge storage through exceptionally fast ion accessibility to redox sites. Here, the authors demonstrate steric chloride termination in MXene Ti 2 C T x ( T x : su

The room temperature x, y two-dimensional phase diagram of the olivine-type solid-solution, Li x (Mn y Fe 1y )PO 4 (0 x, y 1, orthorhombic, D 2h 16 : Pmnb), is determined. The x-dependent changes in the unit cell dimensions at various fixed Mn contents y are analyzed in detail. The manganese substitution for iron in the octahedral 4c sites induces 1, the two-phase Mn 3 /Mn 2 redox region with a potential of 4.1 V vs. Li/Li ; 2, a partial conversion of the form of the Fe 3 /Fe 2 redox reaction 3.

Abstract State‐of‐the‐art LiFePO 4 technology has now opened the door for lithium ion batteries to take their place in large‐scale applications such as plug‐in hybrid vehicles. A high level of safety, significant cost reduction, and huge power generation are on the verge of being guaranteed for the most advanced energy storage system. The room‐temperature phase diagram is essential to understand the facile electrode reaction of Li x FePO 4 (0 < x < 1), but it has not been fully understood.

The charge-discharge reaction mechanism of the olivine-type a possible 4 V class cathode material for lithium batteries, was investigated using equilibrium voltage measurements, X-ray diffraction, Mössbauer spectroscopy, and X-ray absorption spectroscopy. The flat two-phase region with an open-circuit voltage (OCV) of ca. 4.1 V (region I: and the S-curved single-phase region with (region II: were clearly identified together with the corresponding change in the unit cell dimensions of the orthorh

Larger interlayer distances and defects may account for both the sloping and flat regions of charge–discharge curves of disordered carbons.

Beyond the limited lithium storage capability of the (PO4)3−-based compound, LiFePO4 (170 mAh/g), which is currently recognized as the most promising lithium battery cathode for large-scale application, a compound with the lightest small triangle oxyanion unit (BO3)3−, namely LiFeBO3, exhibits a much larger reversible capacity of ca. 200 mAh/g with surprisingly small volume change of ca. 2%. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such docume

Abstract The quest to explore and to discover novel cathode materials is key to sustaining the progress of Li‐ion rechargeable batteries. It has encouraged materials’ chemists to design and develop a variety of polyanionic compounds. This paper reports and summarizes recent progress in the development of alkali metal pyrophosphate based cathode materials for battery applications. It points out that the pyrophosphate‐based polyanionic‐framework materials offer a rich crystal chemistry, ease of sy