Hideyuki Morimoto

New lithium ion conducting glass-ceramics prepared from mechanochemical Li2S-P2S5 glasses

Amorphous solid electrolytes in the system Li 2 S-P 2 S 5 were prepared from a mixture of crystalline Li 2 S and P 2 S 5 using a mechanical milling technique at room temperature. In the composition range x≤87.5 of xLi 2 S(100-x)P 2 S 5 , conductivities of the glassy powders mechanically milled for 20 h were as high as 10 -4 S cm -1 at room temperature. The heat treatment of the 80Li 2 S.20P 2 S 5 glassy powders at around 220 °C produced dense glass-ceramics with high conductivity around 10 -3 S cm -1 at room temperature. The crystallization of conductive phases of Li 7 PS 6 , Li 3 PS 4 and unknown crystals from the glass matrix and the decrease of grain boundaries by the softening of the glassy powders are simultaneously achieved at relatively low temperatures, around 220 °C.

Solid state lithium secondary batteries using an amorphous solid electrolyte in the system (100-x)(0.6Li2S.0.4SiS2).xLi4SiO4 obtained by mechanochemical synthesis

Abstract Electrochemical cells were constructed using amorphous materials in the system (100− x )(0.6Li 2 S·0.4SiS 2 )· x Li 4 SiO 4 , obtained by mechanochemical synthesis, as an electrolyte, LiCoO 2 as a positive electrode and indium as a negative electrode. Charge and discharge behaviors of the cells at a constant current were investigated to see the possibility for utilization as secondary batteries. Charge–discharge efficiency at the 1st cycle was more than 75% in the cells using the solid electrolytes synthesized by mechanical milling (MM) for more than 5 h. Charge–discharge curves of the cells using the amorphous materials milled for more than 10 h, were similar to those of the cells using the corresponding melt-quenched glass samples. The charge–discharge capacity decreased gradually from 90 to 70 mA h/g till about the 10th cycle, and became stable after the 10th cycle. The Coulombic efficiency of the cell showed almost 100%, except for the 1st and 2nd cycles. The amorphous materials synthesized by MM were concluded to work as the electrolyte for solid state lithium secondary batteries.

Preparation of amorphous solid electrolytes in the system Li2S–SiS2–Li4SiO4 by mechanical milling

Abstract Amorphous solid electrolytes in the system Li2S–SiS2–Li4SiO4 were successfully prepared from a mixture of Li2S, SiS2 and Li4SiO4 crystals using a mechanical milling technique at room temperature. In the composition range 0≤x≤5 of (100−x)(0.6Li2S·0.4SiS2)·xLi4SiO4, conductivities of the oxysulfide powders mechanically milled for 20 h were as high as 10−4 S cm−1 at room temperature, which are comparable to the values of the corresponding composition of melt-quenched glasses. As the period of mechanical milling treatment was increased from 0 to 20 h, the structure of milled powders became similar to that of the glasses prepared by melt quenching. Such a structure change brought about a large conductivity increase in the resultant powders from 10−9 to 10−4 S cm−1.

Amorphous solid electrolytes in the system Li2S-Al2S3-SiS2 prepared by mechanical milling

Amorphous solid electrolytes in the ternary system Li2S-Al2S3-SiS2 were successfully prepared by mechanical milling. The ambient temperature conductivity of the 60Li2S·10AlS1.5·30SiS2 (mol%) sample reached over 10−4 S cm−1 with amorphization by mechanical milling for 40 h. The binary Li2S-Al2S3 amorphous electrolytes, which have not been synthesized by a conventional melt-quenching technique, were also obtained by mechanical milling. The 60Li2S·40AlS1.5 (mol%) amorphous electrolyte exhibited lower conductivity and higher activation energy for conduction than the 60Li2S·40SiS2 (mol%) amorphous electrolyte. The addition of SiS2 to Li2S-Al2S3 system monotonically increased electrical conductivity and decreased activation energy for conduction. The amorphous 60Li2S·10AlS1.5·30SiS2 material showed favorable features as a solid electrolyte such as unity of lithium ion transport number and wide electrochemical window.

Mechanochemical synthesis of SnO-B2O3 glassy anode materials for rechargeable lithium batteries

The xSnO·(100 − x)B2O3 (0 ≦ x ≦ 80) glasses were successfully prepared by a mechanical milling technique. The glass with 40 mol% SnO showed the maximum glass transition temperature of 347°C. The SnO-B2O3 milled glasses consisted of both BO3 and BO4 units, and the fraction of BO4 units was maximized at the composition of 50 mol% SnO. The electrochemical properties of the milled glasses were examined using a simple three electrodes cell with a conventional liquid electrolyte. The glasses with high SnO content exhibited high charge capacities more than 1100 mAh g−1 and discharge capacities more than 700 mAh g−1 at the first cycle. The SnO-B2O3 milled glasses proved to work as anode materials for rechargeable lithium batteries.