Battery and energy materials
Which statement about sulfide solid electrolytes used in all-solid-state batteries is correct?
- ASome match organic liquid electrolytes in ionic conductivity and densify by pressing alone, but they react with moisture to release hydrogen sulfide
- BTheir ionic conductivity is at least three orders of magnitude lower than organic liquid electrolytes, but they are so stable that they do not react even with moisture in air, so no dry environment is needed
- CThey are hard and hardly deform, so their particles neither bond nor conduct Li⁺ unless they are sintered together at high temperatures well above 1000 °C
Show answer and explanation
Answer: A. Some match organic liquid electrolytes in ionic conductivity and densify by pressing alone, but they react with moisture to release hydrogen sulfide
Some sulfide solid electrolytes, such as Li₁₀GeP₂S₁₂ (LGPS), Li₇P₃S₁₁ and argyrodite-type Li₆PS₅Cl, show room-temperature ionic conductivities of 10⁻³–10⁻² S/cm, comparable to organic liquid electrolytes (about 10⁻² S/cm). Sulfides are soft and deform easily, so another advantage is that simply pressing the powder at room temperature gives good contact between particles and with the electrodes. On the other hand, they tend to react with moisture in the air and release toxic hydrogen sulfide, so they must be handled in a dry environment. Requiring high-temperature sintering to densify is characteristic of oxide electrolytes such as garnet-type Li₇La₃Zr₂O₁₂ (LLZO). LLZO is relatively stable in air and reacts little with lithium metal, but being hard, it is difficult to form interfaces with the electrodes.