Yes, coin cell lithium batteries are washable, however you must take note of a couple precautions.
You want to be sure that you are using a non-conductive detergent. The use of a conductive detergent causes batteries to discharge, the battery voltage may drop, and the battery performance may deteriorate in other ways.
Be sure to dry batteries only for short periods of time at temperatures below 85°C. The heat produced when the temperature of the battery rises above 85°C can deform the gaskets and can result in the electrolyte leaking from the battery resulting in deteriorated performance of the battery.