Are there coin locker for big suitcase at Dongdan subway station?

I'm afraid there is no luggage-left counter at the MTR station. But you can store your luggage at the nearby supermarkets or hotels.
Generally, you can store your luggage at supermarkets for free. If you store that in a hotel, you may charge hourly. Different hotels charges differently. Well, the most convenient hotel should be Dongdan Hotel, which is within 5min walking distance from the MTR station. Just for reference!