A battery is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the negative end) and a cathode (the positive end). Collectively the anode and the cathode are called the electrodes. What is positive and what is the negative terminal? It would be great to simply say that the anode is negative and the cathode is positive, however, that is not always the case. Sometimes the opposite is true depending on battery technology.
In between the 18650 battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte, which can be either liquid or solid. This battery consisting of two electrodes is called a voltaic cell.
Therefore batteries in effect create electrochemical energy. In order to convert chemical energy into electrical energy there is a chain of events that have to occur prior to the creation of electrical energy. Key to the creation of electrochemical energy in NiMH batteries is that electrical energy is injected into two chemicals in a solution. Electricity is introduced into a battery via a charger. The charger acts as a conduit of the pushing electrons that are forcing their way into the chemical lithium. This charge process involves intercalation: the joining of a molecule (or molecule group) between two other molecules (or groups). Intercalation is the process of ions being pushed by electrical current into solid lithium compounds. Lithium is one of the chemical components used to create electrical energy in batteries. Polymer Lithium ion Battery compounds have minuscule spaces between the crystallized planes for small ions to insert themselves from a force of current. Ionizing lithium loads the crystal planes to the point where they are forced into a current flow. Intercalation replenishes, in effect, lithium but the net result of ionization is the ultimate depletion of the lithium reactive property. You could say if you use it you will lose it.