Lithium-ion batteries typically come in two shapes: cylindrical and prismatic. Internally, they employ a spiral winding structure, with a very fine and highly permeable polyethylene film separating the positive and negative electrodes. The positive electrode consists of a current-collecting electrode made of lithium cobalt oxide (or lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, etc.) and aluminum foil. The negative electrode consists of a current-collecting electrode made of graphitized carbon material and copper foil. The battery is filled with an organic electrolyte solution. It also includes a safety valve and a PTC element (used in some cylindrical batteries) to protect the battery from damage in abnormal conditions and short circuits.
A single lithium-ion battery has a voltage of 3.7V (3.2V for lithium iron phosphate positive electrodes), and its capacity cannot be infinitely large. Therefore, single lithium-ion batteries are often connected in series or parallel to meet the requirements of different applications.
