HETEROJUNCTION FORMATION OF SOLID ELECTROLYTE AND ELECTRODE ACTIVE MATERIALS BY GLASS-FLUX APPROACHES FOR ALL-SOLID-STATE LIBS

摘要

All-solid-state lithium ion rechargeable batteries (LIBs) consisting of solid electrolytes have been desired for higher energy density, long term durability and safety. A great challenge of all-solid state LIBs for practical use is reduction of the interfacial resistance. Effective interface modification techniques have been proposed, however, the interfacial resistance is still large because the charge transfer resistance at the active material/ solid electrolyte interface would be strongly affected by interfacial contact condition. Herein, we propose a new route to prepare smart interfaces for all-solid-state lithium ion batteries (LIBs). Direct growth of electrode active material crystals layer inside of Li ion conductive glass will provide heterojunction formation at their interface. Cross-sectional SEM and HR-TEM observation coupled with EDX-based elemental analysis revealed that the spattered Co layer was completely converted to highly crystalline LiCoO_2 crystals having hexagonal plate-like shape. Note that the each LiCoO_2 crystals were vertically grown from the Pt substrate. The both interfaces between the crystals and the glass matrixes, between the crystal layer and the current collector surface were well-connected without any impurely phase and pinhole formation. We further characterized their LIB properties with metal lithium as a counter electrode. Typical charge-discharge operation at 0.1C based on Li ion intercalation-deintercalation reaction was obviously observed at 150°C, indicating that this was believed to be due to the efficient lithium-ion transportation in the LIB cell. We think the direct formation of the hetero-junction in Li ion conduction glass matrix reduce its interfacial resistance for lithium ion transportation during all-solid-state LIBs operation. Further details of the structural and the LIB characteristics on Li_4Ti_5O_(12) and Li_(7-x)La_3Zn_(2-x)Nb_xO_(12) crystals fabricated directly in Li_3BO_3 glass will present in the NMS-X meeting.