First, the unstable plastic separator is replaced by a nanofiber nonwoven reinforced with Kevlar or Twaron for thermal stability.
Next, solid metal foils are replaced with metallized films with enough metal to run the battery, but not enough to support the intense current density that can light it on fire. The energy flow stops. The cell is also lighter and thinner.
With an internal short now isolated, the rest of the cell continues to function. In short… No more FIRE or EXPLOSION!