Cation-Doped Nasicon-Type Electrolyte for Lithium-Ion Batteries

Abstract

In response to the global challenge of climate change, scientists are actively engaged in developing diverse energy storage solutions. Among these, lithium-ion batteries (LIBs) remain the most prevalent due to their high energy density and reliable cycling performance. Nonetheless, the liquid electrolytes utilized in LIBs pose safety concerns, including the risk of combustion and explosion. To address these issues, extensive efforts have been directed towards the development of solid electrolytes, which offer enhanced thermal stability, thereby improving safety during usage. However, solid electrolytes face challenges such as low ionic conductivity and suboptimal contact with electrodes. Li 1.3 Al 0.3 Ti 1.7 (PO4) 3 (LATP) stands out as a promising lithium-ion solid electrolyte, characterized by relatively high ionic conductivity and chemical stability in atmospheric conditions. This study first optimized the stoichiometric ratio and heat treatment during LATP synthesis. The resulting LATP exhibited an ionic conductivity of approximately 4 × 10 -4 S/cm at room temperature. Additionally, efforts were made to substitute Ti 4+ with another element in the lattice sites, inducing slight lattice distortion and promoting the segregation of a Li-ion-conductive second phase at grain boundaries. Consequently, the ionic conductivity of cation-doped LATP was successfully enhanced to 8 × 10 -4 S/cm at room temperature. Nevertheless, an inherent challenge faced by LATP involves its reactivity with lithium metal, posing a significant threat to the cycle life of LIBs. To mitigate direct contact between LATP and lithium metal, a protective layer composed of Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane was introduced. This not only prevented direct contact but also substantially improved the contact resistance. The culmination of these advancements led to the assembly of an all-solid-state lithium-ion battery (ASSLIBs) comprising PVDF-HFP, cation-doped LATP ceramic pellet, LiFePO4 cathode, and Li anode.