A lithium-ion battery is a rechargeable battery in which lithium ions move between positive and negative electrodes during charging and discharging. It stores energy chemically and releases it as electricity through an external circuit. The term describes a family of technologies rather than a single chemical composition. Their combination of relatively low weight, rechargeable operation, and substantial energy storage supports applications ranging from portable electronics to electric vehicles and stationary storage. Conventional lithium-ion batteries generally store lithium within electrode materials rather than using a bulk lithium-metal negative electrode. (nobelprize.org)
Operating principle
A cell contains two electrodes, an electrolyte, and a separator. During discharge, lithium ions leave the negative electrode and travel through the electrolyte toward the positive electrode. Simultaneously, electrons flow through the external circuit, supplying electrical power. Charging uses an external power source to drive these processes in reverse. The separator prevents direct electronic contact between the electrodes while permitting ionic transport through its electrolyte-filled pores. (energy.gov)
Many electrode materials store lithium by intercalation: ions enter spaces within a host structure and can subsequently leave it. In graphite, a common negative-electrode material, lithium occupies positions between carbon layers. This reversible storage mechanism allows repeated cycling, although unwanted side reactions gradually change the cell. Other electrode materials, including silicon-containing materials, can store lithium through different mechanisms. (aps.anl.gov)
Battery literature commonly calls the negative electrode the anode and the positive electrode the cathode, following their discharge functions. Strict electrochemical terminology defines these names by oxidation and reduction, so their reaction roles reverse during charging. (nobelprize.org)
Materials and construction
The electrolyte in a conventional cell usually contains a lithium salt dissolved in organic carbonate solvents. It must conduct ions while remaining compatible with both electrode surfaces. A porous polymer separator lies between the electrodes; metallic current collectors carry electrons between the active materials and the terminals. Electrode layers are stacked or wound inside cylindrical cans, rigid prismatic housings, or flexible laminated pouches. These shapes describe packaging, not the underlying electrode chemistry. (publications.anl.gov)
Positive-electrode materials substantially influence voltage, capacity, cost, and thermal behavior. Important families include lithium cobalt oxide, lithium nickel manganese cobalt oxide—usually abbreviated NMC—and lithium iron phosphate, or LFP. Cobalt-containing layered oxides can provide high energy storage, while LFP generally offers greater thermal stability and robust cycling at the expense of lower operating voltage and energy density. LFP contains neither nickel nor cobalt in its active cathode material. No composition simultaneously maximizes every performance characteristic. (energy.gov)
A battery pack combines cells with electrical connections, structural supports, monitoring electronics, and, where needed, cooling equipment. Consequently, the performance of an individual cell does not directly equal that of a complete battery system: packaging and supporting components contribute additional mass and volume. (energy.gov)
Historical development
In the 1970s, M. Stanley Whittingham developed a rechargeable lithium battery using a titanium disulfide positive electrode and a lithium-based negative electrode. Its operation demonstrated the usefulness of lithium insertion, but the reactive negative electrode presented safety difficulties. In 1980, John B. Goodenough demonstrated that a lithium-containing cobalt oxide positive electrode could produce substantially higher voltage. (nobelprize.org)
In 1985, Akira Yoshino produced a commercially viable design combining the cobalt oxide electrode with petroleum coke, a carbon material that could accommodate lithium without requiring a lithium-metal negative electrode. Lithium-ion batteries entered the commercial market in 1991. Goodenough, Whittingham, and Yoshino received the 2019 Nobel Prize in Chemistry for their contributions to their development. (nobelprize.org)
Performance and applications
Battery performance requires several distinct measurements. Capacity measures the electrical charge a cell can deliver, commonly in ampere-hours. Stored electrical energy, commonly expressed in watt-hours, also depends on voltage. Energy density describes energy per unit volume; specific energy describes energy per unit mass. Power concerns how rapidly energy can be delivered, rather than how much is stored. These quantities depend on chemistry, construction, and operating conditions. (energy.gov)
Lithium-ion batteries power smartphones, laptop computers, and other portable devices. Larger systems provide traction energy for electric vehicles or store electricity for the electrical grid. Stationary installations can shift electricity generated from renewable energy sources between periods of production and demand. The suitability of a particular battery depends on the required balance of energy, power, lifetime, cost, and safety. (nobelprize.org)
Aging and safety
Aging occurs both through repeated charging and discharging and through time spent in storage. Mechanisms include loss of available lithium, damage to active particles, and changes at electrode–electrolyte interfaces. The solid electrolyte interphase is a surface layer that helps protect the negative electrode from continued electrolyte decomposition. Its growth or repeated disruption can nevertheless consume lithium and contribute to capacity loss. Degradation depends on temperature, operating history, and material composition. (publications.anl.gov)
Mechanical damage, electrical abuse, or excessive heating can initiate thermal runaway, a self-accelerating sequence of heat-producing reactions. Flammable electrolytes and released gases can contribute to fire, and heat from a failing cell may affect neighboring cells. Material selection, thermal management, protective electronics, and pack design therefore form complementary layers of safety engineering. (nrel.gov)
Recycling and further development
Recycling can recover valuable battery materials. Pyrometallurgical processing uses heat to recover metals, while hydrometallurgical processing uses liquid-based leaching and separation. Direct recycling seeks to preserve or restore engineered electrode materials instead of first reducing them to individual constituents. Some used batteries can also be evaluated for repair or repurposing before recycling. (epa.gov)
Research addresses higher-capacity electrodes, more stable electrolytes, improved manufacturing, and reduced dependence on cobalt. Solid-state batteries replace conventional liquid electrolytes with solid ion-conducting materials. Solid-state construction and lithium-ion chemistry are not synonymous: a solid-state design may use an insertion electrode or a lithium-metal negative electrode, with different interfacial and durability challenges. (energy.gov)