What is the advantage of an all-solid-state battery (ASSB)? The solidification of a battery surely contributed to enhance the safety due to using a non-flammable solid electrolyte; however, the sufficient electrochemical interface is difficult to achieve between solid and solid, unlike between liquid and solid. Thus, the R&D of ASSB always faces on the interfacial issues. Especially in case of oxide-based ASSB, the thermal reaction between an electrode and an electrolyte during co-sintering is also the additional interfacial issue. The thermally reacted interphase formed during co-sintering has been widely studied to optimize the sintering conditions for bulk-type ASSBs with high Li-ion conductive candidates (e.g. perovskite-type conductors, sodium super ionic conductors (NASICONs), and garnet-type conductors). However, the resulting battery performance during operation remains inadequate. Therefore, successful co-sintered ASSBs are currently limited to specific electrode-electrolyte combinations. Previously, we reported the good performance of an oxide-based ASSB due to an impurity-free interface between a layered rock-salt LiMO₂ electrode (e.g. LiCoO₂) and an LISICON-type oxide solid electrolytes (e.g. LGVO; Li_3.5Ge_0.5V_0.5O₄) following co-sintering.¹⁾

In this study, we prepared homogeneous distributed composite texture by actively utilizing the thermodynamic two-phase coexistence stability of aforementioned LiCoO₂-LGVO combinations. Heterogeneity between the electrode particle and solid electrolyte within the electrode layer, such as agglomeration of the electrode particle, causes electrochemical reaction distribution, which affects battery characteristics such as the cycle capacity retention of ASSB.²⁾ We exploited the thermodynamic stability of LiCoO₂ and LGVO to create finely composite composites of these. By applying heat to the formed precursor to cause recrystallization and grain growth, we created a self-assembled electrode texture in which submicron-sized LiCoO₂ particles were relatively uniformly distributed within the LGVO solid electrolyte. We will present on the fabrication method of self-assembled electrode layer, the stability of the LCO/LGVO interface based on thermodynamic calculations, and battery performances such as cycle capacity retention for bulk-type solid-state battery (Au | LiCoO₂-LGVO self-assembled electrode layer | LGVO | dry polymer | Li).