How Lithium-Ion Batteries Work

Lithium-ion batteries are experiencing rapid growth in the field of secondary batteries, trailing only nickel-cadmium and nickel-hydrogen batteries. These batteries consist of positive and negative active materials that have the ability to reversibly intercalate and extract lithium. Prior to assembly, at least one of the electrode materials is in a lithium intercalation state. For instance, positive electrodes are often made of transition metal oxides like LiCoO2, LiNiO2, or LiMn2O4. On the other hand, negative electrode materials can vary and include carbon materials, metal oxides, alloys, and more. This diverse composition contributes to the versatility and performance of lithium-ion batteries.

Figure 1 illustrates the operational principle of a lithium-ion battery. In this battery, the negative electrode is made of graphite, while the positive electrode consists of LiCoO2. When the battery is being charged, the lithium ions are extracted from the positive electrode material and move towards the negative electrode through the electrolyte. This movement is driven by the electrochemical potential gradient. To maintain charge balance, an equal amount of electrons flows from the positive electrode to the negative electrode through the external circuit. Meanwhile, the lithium ions that receive electrons are regenerated upon reaching the negative electrode, becoming embedded within its lattice structure. On the other hand, during the discharge process, the reverse occurs. The lithium ions depart from the negative electrode's lattice and become embedded in the positive electrode, where they combine to reform LiCoO2.