Likely sodium-ion, which is projected to be significantly cheaper due to abundant materials, safer due to its chemistry, more tolerant to hot/cold weather, and it's main drawback of lower energy density isn't a big deal to trains.
a 4000 HP train is ~ 2,000 kWatts. The average diesel-electric locomotive uses 3.5-4 kwh / mile of electricity (according to chatgpt). So to go 500 miles we're looking at 53,000lbs / 26.7 tons of _just_ battery (doubled up weight to account for non lithium). The locomotive itself can weigh 120-220 tons. A freight railcar can weigh about 100tons.
For a yard locomotive where they are just moving things around this could be super useful. For hauling freight around it's a potential? You're basically losing a freight car of cargo per 500 miles.
And I would really want this thing to be NOT made of lithium ion cuz if the train derailed it would be fairly destructive.[
A typical locomotive carries approximately 5,000 gallons of diesel fuel, which at 7lbs a gallon is already 17 tons, not counting the weight of the tanks.
The diesel engines will be even heavier (and they're Diesel Electric, so they already have electric traction motors, and the related electrical equipment).
Train's don't haul just one car, they haul dozens or even hundreds.
25t of batteries and you save all of the hassle and maintenance of combustion.
http://reasonrail.blogspot.com/2015/09/a-cost-to-benefit-ana...
It looks like 22-66 kWh/mile, depending on size of train.