Composite solid electrolyte, thermal battery comprising same, and manufacturing method therefor

A thermal battery comprising:

• a negative electrode current collector;
• a negative electrode layer placed on an upper portion of the negative electrode current collector;
• a composite solid electrolyte layer placed on an upper portion of the negative electrode layer;
• a positive electrode layer placed on an upper portion of the solid electrolyte layer;
• and
• a heat source placed on an upper portion of the positive electrode layer, wherein the composite solid electrolyte layer is formed by mixing a precursor mixture and a molten salt to form a molten salt-precursor mixture, calcining the molten salt-precursor mixture to form a solid electrolyte mixture coated with the molten salt, pulverizing the solid electrolyte mixture coated with the molten salt to obtain a composite solid electrolyte powder, and pelletizing the powder.