Chemical energy storage using batteries will become increasingly important for future environmentally friendly ('green') societies. The lithium-ion battery is the most advanced energy storage system, but its application has been limited to portable electronics devices owing to cost and safety issues. State-of-the-art LiFePO4 technology as a new cathode material with surprisingly high charge-discharge rate capability has opened the door for large-scale application of lithium-ion batteries such as in plug-in hybrid vehicles. The scientific community has raised the important question of why a facile redox reaction is possible in the insulating material. Geometric information on lithium diffusion is essential to understand the facile electrode reaction of LixFePO4 (0

State‐of‐the‐art LiFePO4 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 LixFePO4 (0 < x < 1), but it has not been fully understood. Here, intermediate solid solution phases close to x = 0 and x = 1 have been isolated at room temperature. Size‐dependent modification of the phase diagram, as well as the systematic variation of lattice parameters inside the solid‐solution compositional domain closely related to the electrochemical redox potential, are demonstrated. These experimental results reveal that the excess capacity that has been observed above and below the two‐phase equilibrium potential is largely due to the bulk solid solution, and thus support the size‐dependent miscibility gap model.

A variety of proton (H(+))-conducting oxides are known, including those used in electrochemical devices such as fuel cells. In contrast, pure H(-) conduction, not mixed with electron conduction, has not been demonstrated for oxide-based materials. Considering that hydride ions have an ionic size appropriate for fast transport and also a strong reducing ability suitable for high-energy storage and conversion devices, we prepared a series of K2NiF4-type oxyhydrides, La(2-x-y)Sr(x + y)LiH(1-x + y)O(3-y), in the hope of observing such H(-) conductors. The performance of an all-solid-state TiH2/o-La2LiHO3 (x = y = 0, o: orthorhombic)/Ti cell provided conclusive evidence of pure H(-) conduction.

The impact of ambient air exposure on LiFePO 4 /C nanocomposites has been investigated. A pristine sample was prepared without any exposure to ambient air through the whole process of synthesis and characterization and compared to the exposed samples. A small amount of lithium deintercalates from the olivine structure during exposure, a majority of which can be electrochemically reintercalated. This phenomenon changes the initial surface and bulk properties and should be taken into account when diminishing the particle size of LiFePO 4 . Keeping nanocomposites away from oxidative moisture atmosphere could be a solution to minimize these side reactions.

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