Reaction of Li1.3Al0.3Ti1.7(PO4)3 and LiNi0.6Co0.2Mn0.2O2 in Co-Sintered Composite Cathodes for Solid-State Batteries

All solid-state batteries offer the possibility of increased safety at potentially higher energy densities compared to conventional lithium-ion batteries. In an all-ceramic oxide battery, the composite cathode consists of at least one ion-conducting solid electrolyte and an active material, which are typically densified by sintering. In this study, the reaction of the solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) and the active material LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) is investigated by cosintering at temperatures between 550 and 650 °C. The characterization of the composites and the reaction layer is performed by optical dilatometry, X-ray diffractometry, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, as well as scanning transmission electron microscopy (STEM). Even at low sintering temperatures, elemental diffusion occurs between the two phases, which leads to the formation of secondary phases and decomposition reactions of the active material and the solid electrolyte. As a result, the densification of the composite is prevented and ion-conducting paths between individual particles cannot be formed. Based on the experimental results, a mechanism of the reactions in cosintered LATP and NCM622 oxide composite cathodes is suggested.

Mitigating the Interfacial Degradation in Cathodes for High-Performance Oxide-Based Solid-State Lithium Batteries

Solid-state lithium batteries (SSLBs) are the promising next-generation energy storage systems because of their attractive advantages in terms of energy density and safety. However, the interfacial engineering and battery building are of huge challenges, especially for stiff oxide-based electrolytes. Herein, we construct SSLBs by a cosintering method using Li₃BO₃ as a sintering agent to bind the cathode materials LiNi_0.6Mn_0.2Co_0.2O₂ (NMC) and solid-state electrolytes Li_6.4La₃Zr_1.4Ta_0.6O₁₂. Small NMC primary particles are compared with large secondary particles to study the effects on interfacial adhesion, mechanical retention, internal resistance evolution, and electrochemical performance. Our results reveal that the interfacial resistance decreases during charging and increases during discharging, resulting in an overall increase in the interfacial resistance after one cycle. The main reason is attributed to the microcracks induced by the volumetric changes of NMC during the electrochemical process. The mechanical degradations at the interfaces accumulated upon cycling can cause capacity decay and low Coulombic efficiency. The SSLB constructed from small NMC primary particles shows regulation of particle distribution, mitigation in local volumetric change, and alleviation in mechanical degradation at the interfaces, leading to smaller resistance change and better electrochemical performance. The findings shed lights on designing SSLBs with good mechanical retention and electrochemical performance.