We tried to prepare solid-state batteries consisting of TiO 2 anodes and a Li 3 BO 3 −Li 2 SO 4 −Li 2 CO 3 solid electrolyte only by room-temperature pressing without any sintering process. The solid-state batteries successfully operated at 90 °C and showed reversible capacity in the range of 278−331 mA h g −1 in the first cycles at 0.01C. In addition to this, the rate capability was remarkably improved by the doping of Nb or Ta into TiO 2 : the doped TiO 2 electrodes exhibited a capacity of 140 mA h g −1 at 0.1C, whereas the undoped TiO 2 showed only 10 mA h g −1 . The charge-transfer resistance of TiO 2 was reduced by the doping of Nb or Ta. The improvement in the anode performance was attributed to the improved electronic conductivity and the expanded interlayer distance by doping. These results demonstrated for the first time that the oxide anodes can operate in bulk-type oxide-based solid-state batteries prepared only by room-temperature pressing.
Solid electrolytes with high sodium conductivities and favorable formabilities are key materials to improving the performance of all-solid-state sodium-ion batteries. Sulfide electrolytes composed of tetrahedral structural units (PS4 or SbS4)...
Interphase formation at the interface between a solid electrolyte and negative electrode is one of the main factors limiting the practical use of all-solid-state sodium batteries. Sulfide-type solid electrolytes with group 15 elements (P and Sb) exhibit high ductility and ionic conductivity, comparable to those of organic liquid electrolytes. However, the electronically conductive interphase formed at the interface between Na 3 PS 4 and sodium metal increases the cell resistance and deteriorates its electrochemical properties. Contrarily, Na 3 BS 3 , containing boron as an electrochemically inert element, forms an electronically insulating thin passivate interphase, facilitating reversible sodium plating and stripping. Sodium-metal symmetric cells with Na 3 BS 3 exhibit steady operation over 1000 cycles. Thus, reduction-stable solid electrolytes can be developed by substitution with an electrochemically inert element versus sodium.
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