Lithium-Ion Battery

A lithium-ion battery is a rechargeable electrochemical cell in which lithium ions move between the two electrodes through a non-aqueous electrolyte and separator. On discharge, lithium ions travel from the negative to the positive electrode while electrons flow through the external circuit; charging reverses the process, driving ions back in a process called intercalation. A single cell has a nominal voltage of about 3.6 to 3.7 volts, fixed by its chemistry, so practical packs wire many cells in series to reach useful voltages. Lithium-ion offers high energy density, roughly 100 to 265 Wh/kg and 250 to 700 Wh/L, with specialty cells reaching higher, and a round-trip efficiency around 80 to 90 percent. This combination of compactness and efficiency makes it dominant wherever storage must be carried around, such as phones, laptops, and electric vehicles. Cycle life is typically several hundred to over a thousand charge cycles. The main hazard is thermal runaway: the flammable organic electrolyte can decompose rapidly when overheated, overcharged, or damaged, leading to fire or explosion (see Thermal Runaway). To manage heat and keep ion-diffusion paths short, cells are built from thin, layered electrodes, often a jelly-roll spool of positive electrode, separator, negative electrode, and separator wound together, rather than thick monolithic material. This is why a large battery is always a pack of small cells rather than one giant cell. Lithium-ion is one of the electrochemical options in Grid Energy Storage, best suited to short-duration applications.