All-solid secondary battery and method of preparing all-solid secondary battery

An all-solid secondary battery including: a positive electrode layer including a positive active material; a negative electrode layer including a negative electrode current collector and a first negative active material layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, the solid electrolyte including a solid electrolyte, wherein the first negative active material layer is adjacent to the solid electrolyte layer, the first negative active material layer includes a multi-component metal composite including M1, M2, M3, and X, an atomic ratio of M2M3X to M1M2M3X in the multi-component metal composite is in a range of about 0.5 to about 0.85, and an atomic ratio of M2M3X to M1 ion is in a range of about 1 to about 5.51.