Composition - Structure - Property relationship of Li_2.3C_0.7B_0.3O₃ – Li_6.4La₃Zr_1.4Ta_0.6O₁₂ for composite cathodes in all solid-state batteries

Li_2.3C_0.7B_0.3O₃ (LCBO) has been adopted as an additive to improve an adhesion between cathodes and garnet-based electrolytes such as Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT) in composite cathodes for solid-state batteries (SSBs). The LCBO melts at a relatively low temperature and forms a glass interlayer in between the solid electrolyte and the cathode active material particles, which improves Li-ion transport at the interfaces and reduces the contribution of interfacial resistance of a composite cathode (i.e., cathode + LLZT mixture). In this study, we designed and performed a systematic investigation to understand the composition – structure – property relationships in the LCBO – LLZT mixed electrolytes for the composite cathodes. Specimens made with various LCBO and LLZT ratios were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and distribution of relaxation times (DRT) technique. The DRT data of the LCBO – LLZT mixture was referenced to data obtained from pure LCBO and pure LLZT specimens. The specimens with high LCBO content (> 50 vol%) suffers from formation of LCBO-rich colonies which adversely affected the Li-ion conductivity. Among the various compositions examined, addition of 20 vol% LCBO in the mixed electrolytes offered the highest total Li-ion conductivity, while the grain-boundary conductivities were bottlenecks of the total conductivities from all the samples.