Dongzhimen station is the only one on Line 13 to have any art whatsoever, and that is almost certainly as a result of the Airport Express Line being built.
As the third line to be built on the Beijing system, and covering as it does the outer northern suburbs, it is clear that artwork for Line 13 took a very low priority, with most stations having a utilitarian feel about them, and having little to commend them visually.
The pillars supporting the hallway in the approaches to Line 13 bear a striking resemblance to the platform artwork of the Airport Express Line at the same station.