All-solid-state rechargeable lithium batteries have attracted much attention because of their high safety, large energy density, long-cycle performance, and versatile geometry. Sulfide solid electrolytes having high lithium-ion conductivity of over 10-2 S cm-1 have been developed, and the conductivity of inorganic lithium ion conductors has already reached to the same level of the conductivity of organic liquid electrolytes applied to commercially available lithium-ion batteries. We have studied sulfide glass-ceramic electrolytes and crystalline Li7P3S11 with superionic conduction was successfully precipitated as a metastable phase by careful heat-treatment of a mother Li7P3S11 glass. In addition, sulfide electrolytes have a unity of lithium-transference number and a wide electrochemical window of 5 V, which are difficult to achieve in organic liquid electrolytes. Mechanical properties such as good formability and appropriate Young’s modulus are also important to secure charge-discharge cycling in all-solid-state batteries. The sulfide electrolytes have a good formability and thus a favorable electrode-electrolyte interface is formed by only cold press without sintering at high temperatures. Formation of favorable and large contact areas between electrode and electrolyte is achieved by electrolyte coating on electrode particles via gas-phase or liquid-phase techniques. The electrolyte coatings have a merit of reducing the amount of electrolyte in the electrode layer, which results in an increase of energy density of the batteries. We have also reported all-solid-state rechargeable sodium batteries with sulfide electrolytes operated at room temperature. Glass-ceramic electrolytes with cubic Na3PS4 showed a high conductivity of over 10-4 S cm-1, and the value was increased to 7.4 x 10-4 S cm-1 by partial substitution of Si for P in cubic Na3PS4. All-solid-state sodium-sulfur batteries have been developed by using sulfide glass-ceramic electrolytes. Recent development of glass-ceramic electrolytes and several approaches to form solid-solid interfaces will be demonstrated.

Development of glass-ceramic solid electrolytes for all-solid-state rechargeable Li or Na batteries

252nd National Meeting (2016)

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