Development of High-Areal-Capacity Electrodes for Sulfide-Based All-Solid-State Batteries

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All-solid-state batteries using sulfide-based solid electrolytes with high lithium-ion conductivity equivalent to that of organic electrolyte solution are attracting attention as a next-generation battery with excellent safety. The sulfide-based all-solid-state batteries are especially expected to be used as a power source for electric vehicles, and high-capacity batteries are needed to realize such applications. Increasing in the areal capacity of the electrode by increasing the thickness of the electrode is one of the effective approaches to increasing the capacity of the batteries. Coating metal foils with slurry containing binders used in the fabrication of electrodes for the conventional electrolyte-solution-based lithium-ion batteries is effective for mass production processes, but it causes cracking and delamination in the coating layer when the electrode is made too thick. In addition, the addition of binder to the slurry increases the internal resistance of the battery resulting in lower battery performance. In this study, we developed a fabrication technique for the binder-free and a high areal capacity electrode by vacuum filtration of a slurry containing carbon nanotubes (CNTs) in order to realize high-capacity sulfide-based all-solid-state batteries, and evaluated the charge-discharge performance of the cell. Lithium nickel cobalt manganese oxide (LiNi0.5Co0.2Mn0.3O2, NCM) and artificial graphite (Gr) were used as active materials for the cathode and anode, respectively, and a slurry was prepared by mixing them with an argyrodite-type sulfide solid electrolyte (SE, A-SOLiD®, Mitsui Mining & Smelting Co., Ltd.) and CNTs. The slurry was vacuum filtered and then vacuum dried to obtain cathode and anode. The NCM cathode with a high areal capacity of 4 mAh cm-2 without cracking was obtained by vacuum filtration of the CNT-containing slurry, although it contained no binder. As with the cathode, the Gr anode was also crack-free and had a high areal capacity of 5 mAh cm-2. The NCM cathode and Gr anode thus obtained and the solid electrolyte sheets prepared using the argyrodite-type sulfide solid electrolyte were punched to 13 mm and 14 mm diameters, respectively. A full cell of NCM cathode/SE sheet/Gr anode was fabricated by pressing these staked materials, and the cell performance was evaluated in a coin cell (CR2032 type). The full-cell consisting of NCM cathode and Gr anode prepared by vacuum filtration of CNT-containing slurry showed a stable cycling performance of over 50 cycles.