Contemporary Amperex Technology Co., Limited (CATL), the largest battery manufacturer in the world with a 38% share of the global market, has just announced some fairly significant breakthroughs in battery tech that aren't just theoretical; they're already hitting the market.
It doesn’t need to be, high voltage transmission lines can run 1000s of MW then you can use a transformer to step the voltage to what you need and then use a rectifier bridge to convert to DC.
The problem I see is the effect of trying to turn on and off 1MW power from a grid could cause problems so the battery could work a bit as an expansion tank to smooth out grid power, so that you always charge it at 100KW and if you need to increase supply you can slowly increase your power draw without shocking the grid.
At the end of the day I personally think 1MW charging is overkill and a 10 minute charge time is a perfectly reasonable goal
Why not use a large capacitor as a buffer. Would give peak power at the beginning of the charging cycle which is what you want anyway for quick turnaround.