Question

I need help understanding how batteries work.
Inside of the battery, ions can pass from one side to the other but not electricity.
Outside of the battery, electrons can pass from one side to the other, but no Ions?

Answer 1

thats because positive ions are forced to move in a direction against the electric field..

Answer 2

what's the reason for them being forced to move?

Answer 3

Its best understood using Cu Zn battery example.. in this battery.. you have a Cu rod in CuSo4 solution with acid if you want, and Zn rod with ZnSO4 solution.. now from chemistry you shoudl know that,
if u put a Cu rod in its own solution what would happen?.. the Cu2+ ions from the solution like to gain electrons from the rod, and become neutral atoms and deposit on the Cu rod..

so more and more Cu2+ ions keep depositing.. in this process the rod is losing electrons and hence becomes positive charge.. a time comes, where the rod will not allow any more Cu2+ ions to accumulate.. thats where equilibrium is reached.. so you see, the Cu rod is gets positive charge, and the solution becomes negative (cause SO4 2- concentration has increased)

similarly Zinc atoms from the rod lose electrons and go into the solution making Zn rod negative, at equilibrium
now you connect the two solutions using a salt bridge.. what happens? since the concentration of positive and negative are different.. positive ions from Zn solution move to Cu solution

see what we have done?! we have made sure that positive ions go from Zn half cell (which is negative electrod) to Cu half cell (which is positive electrode)..