Optimization of solid electrolytes for all-solid-state lithium batteries

Solid-state battery is considered as one of the most promising energy storage devices that can significantly improve the safety and environmental friendliness of batteries. However, the large-scale application of solid-state battery is still hindered by the relatively low ionic conductivity of electrolyte and high interfacial resistance between electrolyte and electrode. In this study, the major effort is made in the conductivity improvement and interfacial modification of Li₆·₄La₃Zr_1·4Ta_0·6O₁₂ (LLZTO) ceramic solid electrolyte. To improve the conductivity of the electrolyte pellet, the protocols of LLZTO powder synthesis and pellet preparation are systematically studied. The calcination temperature of LLZTO powder is significantly reduced to 600 ℃ and still maintain good ionic conductivity (1.05 × 10⁻³ S/cm at 30 °C). CO₂ is utilized for the surface treatment of LLZTO particles to in situ generate a Li₂CO₃ layer that can serve as the sintering aid to densify LLZTO pellet. By improving the sinterability of LLZTO powder and avoiding the contaminations during sintering, LLZTO pellets with ideal microstructures are prepared. With interfacial modification using low melting point glass, The LLZTO based full cell achieves a high capacity of 144 mAh/g and high capacity retention of ~96% after 100 cycles. Effort is also made to improve the poly(ethylene oxide) (PEO) based composite solid electrolyte by adding H₂SO₄ treated TiO₂ nanowire in PEO matrix. The high polarity of treated TiO₂ nanowire can dissociate the lithium salt in PEO leading to improved conductivity of ~1.19 × 10⁻⁴ S/cm at 30 °C and improved battery performance of 144 mAh/g with retention of 74.5% after 800 cycles. This study provides new methods to improve the conductivity and reduce interfacial resistance of solid electrolyte which adds new insights into the development of solid-state batteries.