Kenichiro Kami

Low-temperature growth of spinel-type Li1+xMn2−xO4 crystals using a LiCl–KCl flux and their performance as a positive active material in lithium-ion rechargeable batteries

Low-temperature growth of idiomorphic spinel-type Li1+xMn2−xO4 (x = 0.09, 0.14) crystals was achieved by using a LiCl–KCl flux. The flux growth driven by rapid cooling resulted in truncated octahedral Li1+xMn2−xO4 crystals surrounded by both dominating {111} and minor {100} faces. The chemical compositions, sizes, and shapes of the Li1+xMn2−xO4 crystals could be tuned by simply changing the growth conditions. Among the various products, the crystals grown at a low temperature of 600 °C showed a small average size of 0.2 μm. The small Li1+xMn2−xO4 crystals grown at 600 °C showed better rate properties than the large crystals grown at 900 °C, when used as a positive active material in lithium-ion rechargeable batteries.

Molybdate flux growth of idiomorphic Li(Ni1/3Co1/3Mn1/3)O2 single crystals and characterization of their capabilities as cathode materials for lithium-ion batteries

A Li2MoO4 flux enabled size-tunable idiomorphic Li(Ni1/3Co1/3Mn1/3)O2 (NCM) crystal growth. The crystal size was controlled from 0.26 to 4.4 μm simply by changing the experimental conditions (i.e., solute concentration and reaction temperature). The obtained crystals individually dispersed in both water and N-methylpyrrolidone without unexpected agglomeration; however, Li deficiency and a thin amorphous-like layer formed on the NCM crystal surface during flux removal with water. We found that post-heat-treatment with LiOH significantly improved the discharge capacity of NCM. Recovery of the surface quality of the NCM crystals was primarily responsible for the capacity improvement. The electrodes achieved a high capacity of 81 mA h g−1 under a high current density of 2000 mA g−1, while the electrodes prepared from commercially available NCM showed a maximum of 65 mA h g−1. The rate and cycle performance of the flux-grown NCM crystals was highly dependent on the crystal size. Smaller crystals showed excellent discharge capacities at high C rates, whereas larger crystals showed better cycle performances.

High-voltage capabilities of ultra-thin Nb2O5 nanosheet coated LiNi1/3Co1/3Mn1/3O2 cathodes

In this study, we propose coating the surface of LiNi1/3Co1/3Mn1/3O2 (NCM) electrodes with 1.1 nm Nb2O5 nanosheets as a new way for enhancing their high-voltage capabilities in galvanostatic charge–discharge performances and long-term storage of the charged state at 60 °C. The coatings suppress the oxidative decomposition of the electrolyte and the disordering of the layered structures on the NCM surface, which result in impedance growth. After 100 cycles at voltage ranges 4.6–2.8 V at 1 C rate, more than 70% of the initial discharge capacity was retained in the coated electrodes. In comparison, the discharge capacity completely faded in the bare NCM cathode. Furthermore, the nanosheet coatings stabilize the delithiated NCM lattice charged at 4.6 V and inhibit current generation based on the electrode reactions at 60 °C for 300 h.