Improvement of Li+ conductivity in ball-milled LiI and the local structure analysis by pair distribution function based on X-ray total scattering

The effects of ball milling on the ionic conduction properties of LiI are investigated. It is found that ball milling drastically increased the conductivity of LiI to 1 × 10 −5 S/cm at room temperature. The activation energy for ion conduction is not significantly changed. The local structure of ball-milled LiI is investigated by a pair distribution function ( PDF ) analysis based on the X-ray total scattering measurement. The nearest neighbor distance of Li + and I − is shorter than that in the perfect crystal of LiI. The X-ray absorption measurements suggest that the bonding state of I − is not significantly changed by ball milling. These results indicate that the disordered local structure of Li + around I − is one of the origins of the enhancement of the conductivity of LiI by ball milling. An all-solid-state cell of Li/amorphous Si film (50 nm in thickness) is constructed using ball-milled LiI as the solid electrolyte. The charge–discharge performances are excellent. It is shown that a charge–discharge capacity of approximately 3500 mAh/g can be maintained for 30 cycles with Coulombic efficiencies of over 99%. It should be emphasized that no degradation of the reduction stability is found in the ball-milled LiI with improved conductivity.