Split up the IP (everyone can use it for their own thing) and go your separate ways. If he's not putting in his time he won't do anything with it. Whatever you build from this point onwards to make it a product would be your IP anyways.

The long of it:

A startup is a baby. Don't feed it time and resources, it doesn't grow.

Ideas are worthless. Execution is the only thing that has value.

What you have is a broken marriage. Unfortunately, partnerships are harder than marriage. Getting on the same page and staying on the same page is very hard.

Based on that, one option you might want to consider:

Every project needs a driver. To make decisions one way or the other. Design and development by committee is lethal to productivity, clarity and progress. Usually with good co-founders they defer to each other where they aren't strong.

There's no sense in belabouring negotiations or trying to convince each other of who or what is right or how it's best to move forward.

Good luck, and share what you end up doing here!