Li-ion

A lithium-ion battery stores energy through the movement of lithium ions between two terminals, called the anode and cathode, separated by an electrolyte. When the battery discharges, lithium ions flow from the negative terminal through the electrolyte to the positive terminal, releasing electrons that power a device. Reversing this flow by applying external current recharges the cell. The chemistry is fast, efficient, and repeatable over hundreds of charge cycles, making it the dominant energy storage technology in industrial, commercial, and consumer applications.

Li-ion batteries come in several chemistries, each optimized for different duties. Lithium iron phosphate (LFP) cells offer safety and cycle life, useful in stationary grid storage and electric buses. Nickel-manganese-cobalt (NMC) chemistry balances energy density and power output, favored in electric vehicles and power tools. Lithium polymer (LiPo) cells are thin and flexible, common in portable electronics and drones. The anode is typically graphite, the cathode a metal oxide compound, and the electrolyte is an organic solvent containing dissolved lithium salts.

Failure modes and real-world limits

Li-ion batteries degrade with use. Cycling, temperature extremes, overcharge, and deep discharge all reduce cycle life and capacity. Thermal runaway, a catastrophic chain reaction causing fire, occurs when cell temperature exceeds roughly 150 degrees Celsius due to manufacturing defects, physical damage, electrical shorts, or poor thermal management. Dendrites, needle-like lithium deposits that can form on the anode during charging, risk internal short circuits. Industrial installations require battery management systems to monitor voltage, current, and temperature cell-by-cell, balancing charge and cutting off when limits approach.

Energy density varies by chemistry and form factor. Cylindrical 18650 cells (18 mm diameter, 65 mm height) deliver around 3.6 volt nominal voltage and 2000 to 3500 milliamp-hour capacity. Prismatic and pouch cells allow larger capacities and better thermal contact in packs. An electric vehicle battery pack of 50 to 100 kilowatt-hours contains thousands of individual cells configured in series and parallel strings, with elaborate wiring, fuses, and management electronics.

The name reflects the key active material: lithium metal compounds shuttle between electrodes during charge and discharge, a mechanism discovered in the 1980s and commercialized in the 1990s by Sony and others. Older nickel-cadmium and nickel-metal-hydride batteries lacked this speed and cycle tolerance. Today, Li-ion dominates because no competing chemistry offers the combination of energy density, cycle life, safety margin, and manufacturing scale at comparable cost.