New borate glasses for ionics

Many new glasses composed of AgI, Ag₂O and oxides, M_xO_y, where M_xO_y is B₂O₃, SiO₂, GeO₂, P₂O₅, V₂O₅, As₂O₅, CrO₃, SeO₃ or MoO₃, were found. Among these oxides, the B₂O₃-based glasses, that is, the AgI–Ag₂O–B₂O₃ glasses have several unique properties such as (a) very wide glass forming regions, (b) high glass transition temperatures, (c) network structure with BO₃ and BO₄ groups, and (d) high conductivities of 10 –2 to 10 –7 Scm –1 at room temperature. The high temperature form of AgI, α-AgI, was stabilized in the borate glasses in two ways; one was the rapid melt quenching, and the other was the annealing of glasses at a suitable temperature below the α–β transformation temperature (147°C) for AgI. The latter technique is now usefully applied for the development of glass ceramics as the solid electrolytes for all solid state lithium secondary batteries. Tin oxide containing borate and borophosphate glasses were prepared by the mechanical milling technique as well as melt quenching. These new glasses were proved to work as large capacity nega- tive electrodes for Li⁺ ion secondary batteries. The capacities and also the glass transition temperatures were strongly related to the amount of four coordinated boron.