So I know I have a misconception in one of these ideas and I would appreciate it if someone could correct me and thoroughly explain my error. Say I have two parallel plates connected to a battery, now there will be an electric field with magnitude, V/d between these plates. Now if I place a negative ion into the field it will move away from the cathodes. I used to think that is because the electrons travel from the cathode to the anode and so make one side , in this case the anode, less negative than the cathode; however; I also recently found out that in order for the electrons to actually escape the metal it usually needs to be heated. Another thought I had was that the electrons simply build up and then simply repulse the ion but that doesn't seem mathematically correct since by that definition the strength would keep increasing over time. So in summary I would greatly appreciate it if someone could thoroughly explain to me what happens at the atomic level between the two plates connected by a battery.