Er, no. Constant wear and tear on your car's lithium battery would wear your battery pretty quick. The amount of money that they would need to pay you back when you sell to the grid would need to be significant in order to cover the cost of the extremely expensive lithium battery pack. On top of that, the amount of lithium necessary to even remotely cover grid storage would be massive. MEANWHILE you can manufacture molten salt batteries out of sodium and sulfur, two resources with both near limitless quantities and global distribution, and install cheap, large, monolithic batteries to cover grid storage. Japan already does this. The solution to the problem of grid level storage has literally been around for half a century.