Gravity is not a traditional force, it’s a distortion of space-time.
Magnetism is a force but has no energy on its own.. it is a good way to convert energy from one form to another i.e. motion to electrical current.
If you could create a sheet of material that could block gravity or magnetism then you would have a perpetual motion machine... it just ain’t possible. It is as silly as the notion of pulling yourself up by the bootstraps...lol
As an aside, the best vehicle that can possibly be made given the current state of technology is a diesel-electric.
Purely battery powered cars await a breakthrough in battery technology that is not yet in sight (compact super-capacitor batteries of small size/weight with enormous capacity and rapid charge times)
A small, clean diesel drives an efficient generator to charge the batteries. The batteries drive the brushless motors in the wheel hubs. No normal braking system required as magnetic braking is excellent, no transmission needed, massive acceleration possible for short durations... no problems running a heater in winter or air conditioning in summer. No waiting to charge your car, it charges itself. You can drive on electric only for quite a few miles to cut pollution inside cities. Diesel is far safer in an accident compared to gasoline - much less danger of fire... i.e. The gas powered Sherman tank was a burning joke compared to German diesel tanks of WW2