Modification of network structure induced by glass former composition and its correlation to the conductivity in lithium borophosphate glass for solid state electrolyte

The xLi2O–(1 − x)(yB2O3–(1 − y)P2O5) glasses system is one of the parent compositions for chemically and electrochemically stable solid state electrolyte applicable to thin film battery. The purpose of this study was to seek an optimum composition maximizing the ionic conductivity for the deposition of thin film electrolytes. xLi2O–(1 − x)(yB2O3–(1 − y)P2O5) glasses were prepared with wide range of composition, i.e. x = 0.40–0.47 and B2O3/(B2O3 + P2O5) ratio was 0.17–0.67 (y = xx ∼ xx). The structural variation of the oxide Li2O–B2O3–P2O5 system was investigated by Raman spectroscopy to find out the correlation with the electrical conductivity. It was shown that under 40 mol% of Li2O the ionic conductivity monotonically increased with increasing of B2O3, while over the 40 mol% of Li2O it exhibited a maximum at a specific B2O3/(B2O3 + P2O5) ratio, typically ∼ 0.5. The structural investigation indicated that the variation in conductivity was closely correlated to the variation of 4-coordinated boron groups.