All-Solid-State Lithium-Metal Secondary Battery Based on a Sulfide Type Electrolyte

摘要

Lithium-metal secondary batteries have attracted attention, especially in automotive applications, due to their prospective high theoretical specific capacity and low electrochemical potential. The most notable problem associated with lithium-metal secondary battery is the formation of Li dendrites during charge/discharge cycling, which is the origin of short-circuits. One of the strategies to overcome this problem is to use solid electrolyte in the separator. We have found that sulfide type solid electrolytes is particularly effective for this purpose, we recently demonstrated this fact through the cycle ability of a (pellet size) solid state Li-S cell [1]. In this presentation, we show further capabilities of a sulfide type solid-state system based on Li-NCA cells in our prototype batteries. We have fabricated the cells by a slurry coating method from composite slurries containing polymer binders. Small-size cells (2x2 cm2) are fabricated using a 30□m thick lithium metal foil as anode (Gen-1). The Gen-1 cells are capable of delivering more than 80 % of the initial capacity even at the 5 mAh/cm2 current density. They retain the capacities above 85 % after 300 cycles. Because of the high coulombic efficiency of >99.9%, longer cycle life is expected for the sulfide-type solid electrolyte than a conventional liquid electrolyte system. We fabricated plating-type cells (Gen-2), that is, no lithium metal is present at DOD = 100%, and it is deposited over the anode current corrector at charging. The Gen-2 batteries attain the capacity of 1000 mAh. A 0.5C cycle test of the Gen-2 has been performed at a high loading level above 5 mAh/cm 2 for the cathode, and it has shown no micro short-circuit over 500 cycles. These favorable characteristics are ascribed to the nature of the solid-state electrolyte. Our results demonstrate that the solid-state lithium-metal secondary battery is a promising candidate for the next generation battery.