Koichi Kagesawa

Synthesis of LiNi0.5Mn1.5O4 and 0.5Li2MnO3–0.5LiNi1/3Co1/3Mn1/3O2 hollow nanowires by electrospinning

Hollow wires with thin nanowalls constructed from two-dimensionally connected, highly crystalline nanoparticles were fabricated by electrospinning to create electrode active materials of LiNi0.5Mn1.5O4 (5 V spinel) and 0.5Li2MnO3–0.5LiNi1/3Co1/3Mn1/3O2 (solid-solution type). The resultant materials show large-energy-density properties suitable for use as cathode materials in Li-ion batteries.

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.

VGCF-core@LiMn0.4Fe0.6PO4-sheath heterostructure nanowire for high rate Li-ion batteries

Vapor Grown Carbon Fiber (VGCF)-core@LiMn0.4Fe0.6PO4-sheath heterostructure nanowire was successfully fabricated by an electrospinning method for high rate Li-ion batteries. The fabricated heterostructure has both the electronic conduction path (VGCF-core) and large reaction surface area with high crystallinity (LiMn0.4Fe0.6PO4-sheath), which enables the high charge–discharge rate capability.

Progress of Multi Functional Properties of Organic-Inorganic Hybrid System, A[FeIIFeIIIX3] (A = (n-CnH2n+1)4N, Spiropyran; X = C2O2S2, C2OS3, C2O3S)

In the case of mixed-valence systems whose spin states are situated in the spin crossover region, new types of conjugated phenomena coupled with spin and charge are expected. From this viewpoint, we have investigated the multifunctional properties coupled with spin, charge and photon for the organic-inorganic hybrid system, A[FeIIFeIIIX3](A = (n-CnH2n+1)4N, spiropyran; X = dto(C2O2S2), tto(C2OS3), mto(C2O3S)). A[FeIIFeIII(dto)3] and A[FeIIFeIII(tto)3] undergo the ferromagnetic phase transitions, while A[FeIIFeIII(mto)3] undergoes a ferrimagnetic transition. In (n-CnH2n+1)4N [FeIIFeIII(dto)3](n = 3,4), a new type of phase transition called charge transfer phase transition (CTPT) takes place around 120 K, where the thermally induced charge transfer between FeII and FeIII occurs reversibly. At the CTPT, the iron valence state dynamically fluctuated with a frequency of about 0.1 MHz, which was confirmed by means of muon spin relaxation. The charge transfer phase transition and the ferromagnetic transition for (n-CnH2n+1)4N[FeIIFeIII(dto)3] remarkably depend on the size of intercalated cation. In the case of (SP)[FeIIFeIII(dto)3](SP = spiropyran), the photoinduced isomerization of SP under UV irradiation induces the charge transfer phase transition in the [FeIIFeIII(dto)3] layer and the remarkable change of the ferromagnetic transition temperature. In the case of (n-CnH2n+1)4N[FeIIFeIII(mto)3](mto = C2O3S), a rapid spin equilibrium between the high-spin state (S = 5/2) and the low-spin state (S = 1/2) at the FeIIIO3S3 site takes place in a wide temperature range, which induces the valence fluctuation of the FeS3O3 and FeO6 sites through the ferromagnetic coupling between the low spin state (S = 1/2) of the FeIIIS3O3 site and the high spin state (S = 2) of the FeIIO6 site.

Linkage-isomerization and charge-transfer in the formation of iron mixed valence complexes, (n-C3H7)4N[FeIIFeIII(dto)3] (dto = C2O2S2) and (n-C4H9)4N[FeIIFeIII(mto)3] (mto = C2O3S)

In iron mixed-valence complex, (n-C3H7)4N[FeIIFeIII(dto)3] (dto = C2O2S2), the linkage isomerisation and charge-transfer between FeII FeIII occur in the precipitation process. We succeeded the suppression of linkage-isomerization and charge-transfer in the formation process of (n-C3H7)4N[FeIIFeIII(dto)3] by the synthesis on low temperature condition and the selection of solvent. Moreover, we have found that the charge transfer occurs in the formation of (n-C4H9)4N[FeIIFeIII(mto)3] (mto = C2O3S) without linkage-isomerization.