Kang Du,Chang-Zhi Yin,Yan-Bo Guo,Xiao-Chuan Wang,Wen-Zhong Lu,Shi-Wo Ta,Chun-Yuan Hu,Wen Lei
Ca 3 SnSi 2- x Ge x O 9 (0 ≤ x ≤ 0.8) and (1– y ) Ca 3 SnSi 1.6 Ge 0.4 O 9 – y CaSnSiO 5 – 2 wt% LiF ( y = 0.4 and 0.5) microwave dielectric ceramics were prepared by traditional solid-state reaction through sintering at 1250°C–1425°C for 5 h and at 875°C for 2 h, respectively. Ge 4+ replaced Si 4+ , and Ca 3 SnSi 2- x Ge x O 9 (0 ≤ x ≤ 0.4) solid solutions were obtained. At 0.1 ≤ x ≤ 0.4, the Ge 4+ substitution for Si 4+ decreased the sintering temperature of Ca 3 SnSi 2- x Ge x O 9 from 1425 to 1300°C, the SnO 6 octahedral distortions, and the average CaO 7 decahedral distortions, which affected the τ f value. The large average decahedral distortions corresponded with nearer-zero τ f values at Ca 3 SnSi 2- x Ge x O 9 (0.1 ≤ x ≤ 0.4) ceramics. The τ f value and sintering temperature of Ca 3 SnSi 2- x Ge x O 9 ( x = 0.4) ceramic were adjusted to near-zero by CaSnSiO 5 and decreased to 875°C upon the addition of 2 wt% LiF. The (1 – y ) Ca 3 SnSi 1.6 Ge 0.4 O 9 – y CaSnSiO 5 – 2 wt% LiF ( y = 0.5) ceramic sintered at 875°C for 2 h exhibited good microwave dielectric properties: ε r = 10.3, Q × f = 14 300 GHz (at 12.2 GHz), and τ f = ‒5.8 ppm/°C.
Li-containing argyrodites, particularly Li 5.5 PS 4.5 Cl 1.5 , are key ceramic solid electrolytes with high ionic conductivity (∼10 mS cm –1 at room temperature), making them promising candidates for all-solid-state lithium batteries (ASSBs). However, their poor air and electrochemical stability limit their application as electrolytes for ASSBs. This study attempts to address these issues by Ge 4+ substitution involving the forming of Li 5.5+ x (P 1− x Ge x )S 4.5 Cl 1.5 solid solutions (0 ≤ x ≤ 0.10). The optimized composition, Li 5.56 (P 0.9 Ge 0.1 )S 4.5 Cl 1.5 , exhibits improved air and electrochemical stability and a higher ionic conductivity of 13.2 mS cm –1 . When used in a lab-scale ASSB, this electrolyte achieved an initial discharge capacity of 106.4 mAh g –1 , retaining 89.3 mAh g –1 after 100 cycles with 98.9 % cycling efficiency. This work provides insights into the improving air and electrochemical stability of Li 5.5 PS 4.5 Cl 1.5 solid electrolytes for ASSBs.
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