This isn't close to the record for dragsters; if they can increase the energy density per unit mass there are traction and downforce improvements that can be used to improve this. It's very hard to beat chemical energy like detonating gasoline or nitromethane - you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery - especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard.
I suspect that traction control for an electric motor may someday allow electric vehicles to exceed the records held by internal (well, mostly internal) combustion engines. You could keep the tire at exactly the right amount of slip for maximum acceleration, rather than trying to balance centrifugal clutches to get just the right amount of power at the right time.
I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy.
Edit: I think the most interesting category here is the typical friction-propelled, human-carrying vehicle of either chemical or electric power sources. Railguns, rockets, fan cars (using active downforce), and vehicles which engage the ground by rack and pinion are qualitatively different. When the question is accelerating your own mass forwards using the friction developed by your own mass being pulled down by gravity, there's an interesting optimization problem trading off weight and power.