High-Temperature Chemical Stability of Li_1.4Al_0.4Ti_1.6(PO₄)₃ Solid Electrolyte with Various Cathode Materials for Solid-State Batteries

Abstract

In a solid-state battery (SSB) system, undesirable electrode−electrolyte interfacial reactions lead to a significant performance degradation. Herein, we performed a systematic study on the chemical stabilities between Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) solid electrolyte and various cathode materials at their adhesion temperatures of 500−900 °C. Quantitative analysis of X-ray diffraction (XRD) data using Rietveld refinement revealed that Li-concentration disparity between LATP and oxide cathode materials (e.g., layered and spinel phases) is the root cause of phase degradation at high temperatures. For example, Li migration from oxide cathodes to LATP produces multiple secondary phases including LiMPO 4 olivine. In contrast, the LiFePO 4 cathode severely reacted with LATP at low temperature (T < 500 °C) and produced an Fe-rich NASICON phase (e.g., Li 3 M 2 (PO 4 ) 3 ). The onset temperature of the phase decomposition varies with chemical compositions and crystal phases of cathodes. Increasing the cathode/electrolyte adhesion temperature offers a trade-off between the specific capacity and cycle life, as exemplified by the LiCoO 2 (LCO) + LATP composite cathodes. The results in this study offer a fundamental understanding of the LATP/cathode reaction mechanism, which will serve as guidance for designing interfaces and controlling the fabrication processes of SSB cells.

Progress in thermal stability of all‐solid‐state‐Li‐ion‐batteries

“…Yu et al 119 revealed more details of the interfacial thermal reactions between LATP and three different‐structured cathodes (layered, spinel, and olivine) through Rietveld refinement of XRD. Layered‐structured cathodes initially decompose into transition‐metal oxides, from which lithium ions diffuse into LATP at the same time.…”

Electrochemical Compatibility of Solid‐State Electrolytes with Cathodes and Anodes for All‐Solid‐State Lithium Batteries: A Review

“…[41] Also, there have been studies using LATP as a surface coating layer for various cathodes to enhance structure stability and to resist electrolyte erosion, and great electrochemical stability has been found even at a high cycling temperature of 150 C. [89,90] However, due to the rigid nature of oxide electrolytes, the LATP/cathode interface still suffers from poor contact. Yu et al studied the high-temperature (500-800 C) chemical stability between LATP and various cathode materials and found that although a thermodynamically stable phase formed at the LATP/LFP interface at a temperature lower than 500 C, the interface between LATP and a layered or spinel cathode can degrade at 600-700 C due to disparity of Li concentrations, [91] which is consistent with the report by Gellert et al that oxide cathodes are highly reactive to LATP at a sintering temperature as low as 500 C. [92] Therefore, research on low-cost, effective LATP/cathode interfacial engineering is still needed.…”

Interfacial Reactions in Inorganic All‐Solid‐State Lithium Batteries

“…XPS provided evidence of a limited interfacial reaction between LMO and LLZO [113] . LiFePO 4 reacts severely with LATP at low temperature (T<500 °C) and produces NASICON Li 3 M 2 (PO 4 ) 3 (M=Fe and others) [114] …”

“…[113] LiFePO 4 reacts severely with LATP at low temperature (T < 500°C) and produces NASICON Li 3 M 2 (PO 4 ) 3 (M=Fe and others). [114] In summary, there are two main sources of interface resistance between the oxide-based SSEs and the cathode materials. One is the reaction between the electrolyte and the cathode material to generate an interface phase.…”