Try "Mathematical Methods in the Physical Sciences" by Mary Boas. It's doesn't cover only DEs, but it's got some of everything (at an undergrad level). If you have no exposure to differential equations, you should probably focus on just a differential equations textbook without worrying if it's extremely focused on applications.
I'm of the opinion that you should be comfortable with the math needed in a course before the course starts, because it's a whole lot easier to learn the physics behind something than it is to learn the physics behind something while simultaneously trying to learn the language it's represented in. So I'd say any differential equations textbook would do.
Any differential equations techniques that are needed in quantum mechanics that aren't covered in many DE textbooks will likely be covered in the quantum mechanics textbook anyway.