You seem to be talking more about an external short, and a fuse should work in the case of an external short, but it could still fail because something could short the fuse (cross the distance between the ends of the fuse, or even jump the distance through some other medium, like air, water, etc.). OK, this is very unlikely, but it could happen.
However, one failure mode of Li-ion cells is an internal short. The positive and negative electrodes of cells are very close together where the cell is closed, where the header and can are sealed together. Usually there is an insulator of polymer or glass or something like that. That can possibly degrade, be over compressed, or for some other reason fail and allow an internal short. No fuse will prevent this, unless it is inside the cell, in the tabs used to connect the cell can and header to the internal electrodes foils.
Also, an internal short can happen when foreign contaminants (metals bits, shavings, chunks of electrode coating, etc.) stick through the insulating separator materials between the rolled up electrodes, or if anode crystals (copper or Lithium) grow through the separator materials. Then a fuse cannot help you. The cell will still short.
Not all cells have fuses anyway. The fuses are usually between cells in the battery pack. Some cells have PTC headers that are not really fuses, but when they heat up or have a lot of current pass through them they increase in resistance rapidly. They are typically made with a carbon conductor material in a polymer matrix. When the polymer heats up it expands and the carbon particles separate cutting off the current. It doesn't actually cut it off completely but it makes it very small.
So a fuse is not a safety panacea for a high energy low resistance cell.
Finally, almost everything you add to the cell and battery pack will increase resistance and reduce the power output of the battery and increase the heat generation of the battery and cells. Heat is not good. If you want to charge up very fast you need higher current and lower resistance. Adding a fuse is counter to this need to keep resistance low.
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You seem to be talking more about an external short, and a fuse should work in the case of an external short, but it could still fail because something could short the fuse (cross the distance between the ends of the fuse, or even jump the distance through some other medium, like air, water, etc.). OK, this is very unlikely, but it could happen.
However, one failure mode of Li-ion cells is an internal short. The positive and negative electrodes of cells are very close together where the cell is closed, where the header and can are sealed together. Usually there is an insulator of polymer or glass or something like that. That can possibly degrade, be over compressed, or for some other reason fail and allow an internal short. No fuse will prevent this, unless it is inside the cell, in the tabs used to connect the cell can and header to the internal electrodes foils.
Also, an internal short can happen when foreign contaminants (metals bits, shavings, chunks of electrode coating, etc.) stick through the insulating separator materials between the rolled up electrodes, or if anode crystals (copper or Lithium) grow through the separator materials. Then a fuse cannot help you. The cell will still short.
Not all cells have fuses anyway. The fuses are usually between cells in the battery pack. Some cells have PTC headers that are not really fuses, but when they heat up or have a lot of current pass through them they increase in resistance rapidly. They are typically made with a carbon conductor material in a polymer matrix. When the polymer heats up it expands and the carbon particles separate cutting off the current. It doesn't actually cut it off completely but it makes it very small.
So a fuse is not a safety panacea for a high energy low resistance cell.
Finally, almost everything you add to the cell and battery pack will increase resistance and reduce the power output of the battery and increase the heat generation of the battery and cells. Heat is not good. If you want to charge up very fast you need higher current and lower resistance. Adding a fuse is counter to this need to keep resistance low.