Achieving high ionic conductivity of LATP solid electrolyte via a LiTFSI-assisted cold sintering process

Abstract

NASICON solid electrolyte LATP (Li_1+xAl_xTi_2−x(PO₄)₃) has the advantages of low cost, good thermal stability and stable existence in humid air. This kind of oxide solid electrolyte has a high sintering temperature and long sintering time, which not only causes lithium volatilization but also easily produces a secondary phase. Although the use of sintering additives can reduce the LATP sintering temperature to a certain extent, the reduced temperature is still not enough for practical application. In addition, the introduction of inappropriate sintering additives such as Li₃PO₄ will generate the impurity AlPO₄ with lower ionic conductivity. In this work, the low-temperature sintering of LATP solid electrolyte (CSH-LATP-0.1LiTFSI(650)) with high ionic conductivity and densification was realized through the introduction of LiTFSI and the low-temperature densification technology of cold sintering. It is found that the island structure formed in LATP during cold sintering and the decomposition products of LiTFSI during heat treatment are conducive to Li⁺ transport between the grain boundaries. In addition, this two-step process increases the LATP lattice parameters and the transmission channel of Li⁺. Owing to the high room temperature ionic conductivity (7.85 × 10⁻⁴ S cm⁻¹) and the amorphous layer formed on the LATP surface, the Li|CSH-LATP-0.1LiTFSI(650)|LiFePO₄ solid-state battery can deliver a high initial discharge capacity of 149.7 mA h g⁻¹ and an excellent capacity retention of 85% after 360 cycles.