Low-Temperature Sintering of NASICON-Type LAGP Its Application to All-Solid-State Batteries

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All-solid-state batteries (ASSBs) are one of the next-generation batteries towards carbon neutral societies. While sulfide-based ASSBs are on the stage for their practical application, oxide-based ones are still under the feasibility studies, mainly because of their interfacial issues: interphases and/or contact areas that would limit the energy and the power of the ASSBs. These issues are more severe for the full-inorganic ASSBs without any organic electrolytes, although they would extend the application fields of the next-generation batteries: high voltage batteries and batteries for severer environment (vacuum, high temperature, etc.). In this study, materials and processes of NASICON-type solid electrolytes are developed to prepare the electrochemically active interfaces between the solid electrolytes and the active materials. For the NASICON ASSBs, Li1.5Al0.5Ge1.5(PO4)3 (LAGP) was prepared by a solution method using oxalic acid as a chelate. LAGP obtained by sintering the precursor at 600°C exhibited rather high total conductivity of 2 × 10−5 S/cm, which was further increased to 1.6 × 10−4 S/cm by mild-hot-pressing at 10 MPa. The NASICON ASSBs fabricated with TiO2 anode (2.5 mg/cm2) and LiCoPO4 cathode exhibited an initial discharge capacity of 66 mAh/g (0.17 mAh/cm2).The study demonstrated that 3V-class ASSBs worked at room temperature, although the ASSB has not been optimized yet. The performance of the NASICON-based ASSBs would be further improved by optimizing materials/processes/architecture towards novel batteries. Figure 1