A battery works on the basic principle that electrons tend to move from where they are abundant, or in excess, to where they are scarce. This can happen, if there is a medium that will allow the movement of these electrons.
The part of battery with too many electrons is called the anode which means it is the negative electrode (remember, the charge of an electron is negative). The part of the battery where electrons are scarce is called the cathode, which means it is the positive electrode, which means, there is net positive charge there.
Let’s present Anode and Cathode characteristics as lists, to make things more understandable:
Anode:
• Abundance of electrons
• Negatively charged
• Chemical reaction during discharge: Oxidation
• Material example: Zinc
Cathode:
• Scarcity of electrons
• Positively charged
• Chemical reaction during discharge: Reduction
• Material example: Manganese Dioxide (MnO2)
Between anode and cathode is a barrier material which prevents their direct contact but still allows passing of ions. If this direct contact was not prevented, there would be a short circuit in the battery and it would deplete very rapidly and be useless.
And there is the electrolyte material, such as an alkaline Potassium Hydroxide (KOH) in an alkaline battery.
An ion is an atom where the number of electrons and protons are not equal, therefore it is an atom with a net electrical charge. If electrons are more than protons, it is a negative ion, and if protons are more than electrons it is a positive ion.
When the battery is not in use, there is no flow of electrons. But when an external circuit is connected to the battery, the electrons are released from anode (i.e. Zinc), which travel through the external circuit, does its work in the circuit (such as turning a motor, illuminating a lamp, making a microprocessor work and so on…), and then they arrive at the cathode, which is able to accept those electrons as it was positively charged. But this is not all. For current to keep flowing, the loop of flow must continue, in other words, be closed. This means, inside the battery, there must also be a path to complete this loop. This is where the electrolyte material comes in which serves as this path. It makes possible for ions (see description above) to travel between cathode and anode, in order to complete this loop and keep the current running. Through this electrolyte inside the battery, positive ions travel from anode to cathode (so that cathode can keep being positive and continue to accept electrons when they arrive from external circuit), and negative ions travel from cathode to anode (so that it can keep sending electrons to the external circuit).
The figure above illustrates this process. This is how a battery works. In the figure, electrons traveling inside the battery electrolyte actually represent the free electrons of the negative ions that move from cathode to anode. And for clarity of the figure, positive ions that go from anode to cathode were not shown.
