Takamasa Ohtomo

All-solid-state Li/S batteries with highly conductive glass–ceramic electrolytes

All-solid-state cells using sulfur-based cathode materials and Li2S–P2S5 glass–ceramic electrolytes were successfully prepared and exhibited excellent cycling performance at room temperature. The cathode materials consisting of sulfur and CuS were synthesized by mechanical milling using sulfur and copper crystals as starting materials. The cell performance was influenced by the milling time for the cathode materials and the cell with cathode materials obtained by milling for 15 min retained large capacities over 650 mA h g−1 for 20 cycles. Sulfur as well as CuS in cathode materials proved to be utilized as active materials on charge–discharge processes in the all-solid-state Li/S cells.

Fabrication of electrode–electrolyte interfaces in all-solid-state rechargeable lithium batteries by using a supercooled liquid state of the glassy electrolytes

The softening behavior of a 80Li2S·20P2S5 (mol%) glass electrolyte was investigated and a favorable electrode–electrolyte interface was fabricated by sticking the supercooled liquid state of the 80Li2S·20P2S5 electrolyte on active material particles. A dense pellet of the glass electrolyte without an obvious grain boundary or any voids was prepared by softening the 80Li2S·20P2S5 glass by means of a hot press. The electrical conductivity of the pellet was 8.8 × 10−4 S cm−1 at room temperature. Sticking the solid electrolyte on the Li4Ti5O12 active material particles increased the contact area at the electrode–electrolyte interface and the utilization of the active material was increased in the all-solid-state cells. However, LiCoO2 reacted with the solid electrolyte during the hot press and the electrochemical performance of the cells using hot-pressed LiCoO2 with the glass electrolyte degraded. LiNbO3 coating suppressed the reaction of LiCoO2 with the solid electrolyte. The all-solid-state full-cell Li4Ti5O12/80Li2S·20P2S5 glass/LiNbO3-coated LiCoO2 prepared by hot press showed a larger reversible capacity of 120 mAh g−1 at 0.064 mA cm−2 compared with the full-cell prepared by cold press. The softening of the 80Li2S·20P2S5 glass electrolyte is an effective way for increasing the contact area between the active materials and solid electrolyte.

LiCoO2 Electrode Particles Coated with Li2S – P2S5 Solid Electrolyte for All-Solid-State Batteries

Electrode/electrolyte composite materials for all-solid-state lithium secondary batteries were prepared by coating the 80Li 2 S·20P 2 S 5 (mol %) solid electrolyte onto LiCoO 2 electrode particles using the pulsed laser deposition method. Cross-sectional transmission electron microscopy images showed that the solid electrolyte layer was formed on the LiCo0 2 particles. The all-solid-state cell using the LiCoO 2 particles coated with the solid electrolyte was charged and discharged, and exhibited good cycle performance. This suggests that the electrolyte coatings provide a lithium-ion conduction path to LiCoO 2 , and the technique is effective in the development of all-solid-state cells.

Improvement of chemical stability of Li3PS4 glass electrolytes by adding MxOy (M = Fe, Zn, and Bi) nanoparticles

Sulfide glasses in the system Li2S–P2S5 are attractive as solid electrolytes for all-solid-state lithium batteries because of their high conductivity and high electrochemical stability. In the present study, we have focused on chemical stability in air of the sulfide glass electrolytes and succeeded in suppressing H2S generation by preparing composite electrolytes of the Li3PS4 glass and one of the metal oxides with the formula MxOy (MxOy: Fe2O3, ZnO and Bi2O3). The H2S amounts generated decreased in the order of the composite with Fe2O3, ZnO, and Bi2O3. It is noteworthy that the use of a favorable MxOy with a larger negative Gibbs energy change (ΔG) for the reaction with H2S is effective in improving the chemical stability of sulfide electrolytes. The composite electrolyte of 90Li3PS4·10ZnO (mol%) exhibited a relatively high ionic conductivity of over 10−4 S cm−1, negligible electronic conductivity and a wide electrochemical window over 5 V. The all-solid-state In/LiCoO2 cell using the 90Li3PS4·10ZnO composite electrolyte operated as a lithium secondary battery with excellent cycleability at room temperature.