The disclosure provides a freezing device for freezing a liquid mixture and a method using the same. The freezing device includes a container and a tray removably disposed in the container. The tray has a tray plate disposed above a container bottom wall and has a plurality of spaced-apart receptacles for receiving the liquid mixture. When liquid nitrogen is introduced into a region between the tray plate and a container bottom wall, the liquid mixture received in the receptacles is solidified by the liquid nitrogen and is formed into shaped solid coolant pieces.