Battery cell structure
A battery cell consists of three main components; two electrodes and one electrolyte. The negative electrode is called an anode and the positive electrode is called a cathode. Inside the cell, the anode and cathode are only in contact with each other through the electrolyte: a material that has an ability to conduct ions but not electrons. The electrolyte is usually a liquid e.g. water or an organic solvent with a dissolved salt to increase ion conductivity. There are also battery cells where the electrolyte is in solid or gel-like form.
In addition to the main components, a battery cell usually contains two current conductors connected to the respective electrode as well as a separator, a permeable membrane that allows ion transport but which ensures that the electrodes do not have direct electrical contact with each other.
The characteristics of a battery cell are directly dependent on the main components included. The two electrode materials determine the voltage of the cell and the electrolyte can e.g. affect whether the battery works well at high or low temperatures. The actual design of the cell and the components of the cell can affect whether the cell can withstand high power outputs or if it is more suited to high energy content and long operating time. Differences in battery cell structure and the different properties of the components make different cells suitable for different types of applications.
If the current conductor from anode and cathode is coupled with an external load, for example, a lamp, the anode is actually coupled to cathode. The anode material emits electrons which, due to the electrolyte’s ability to conduct only ions, then migrate through the outer circuit to the cathode.
As the negative electrode releases electrons, the migration of ions from the anode starts through the electrolyte to the cathode. The chemical process in the cell can continue until the electrodes become depleted. The cell has then devoted all its energy. How long this takes depends, among other things, on how much electrode material the cell contains (capacity), how much current (load) the cell is exposed to and whether it is used continuously or intermittently.
When charging a rechargeable battery, it is the cathode that emits electrons that migrate through the outer circuit to the anode while the ions migrate through the electrolyte to the anode. This chemical process, unlike it at discharge, is not spontaneous but requires that it be supplied from outside to happen. The time it takes to recharge a battery depends in part on the size of the power supplied and the electrochemical properties of the battery cell (how fast it can convert electrical energy into chemical energy).
