Enhancement of lithium ion conductivity by doping Li3BO3 in Li2S-P2S5 glass-ceramics electrolytes for all-solid-state batteries

Abstract (100-x) (0.78Li 2 S·0.22P 2 S 5 )·xLi 3 BO 3 (0 ≤ x ≤ 5) solid electrolytes are prepared via mechanical milling and a post heat-treatment process, and the resulting electrochemical properties are investigated in conjunction with structural analysis. Adding of Li 3 BO 3 into the (100-x) (0.78Li 2 S·0.22P 2 S 5 )·xLi 3 BO 3 solid electrolyte is expected to enhance the conductivity and lower the activation energy as a consequence of changing the structural unit in the glass network. It turned out that the doping of Li 3 BO 3 enhances the conductivity by enlarging the glass forming region and promoting precipitation of high lithium ion conductive thio-LISICON II analog. 97 (0.78Li 2 S·0.22P 2 S 5 )·3Li 3 BO 3 (x = 3) glass-ceramics exhibits the highest conductivity (1.03 × 10 −3  S cm −1 ). Structural analysis shows that the samples with Li 3 BO 3 added to the electrolyte are composed of the main structural unit of PS 4 3− with partially-modified structural unit of PO 4 3− , which are believed to effectively enhance the conductivity and decrease the activation energy. In glass-ceramics produced from these materials, the thio-LISICON II phase with higher ionic conductivity tends to be stabilized by the addition of Li 3 BO 3 . Additionally, the formation of space-charge layer is relaxed by Li 3 BO 3 doping. As a result, the all-solid-state cell shows high initial discharge capacity of 156 mAh g −1 , and the capacity is retained to be 149 mAh g −1 for 40 cycles.