A lithium-ion (Li-Ion) battery is an advanced battery technology that uses lithium-ion as a key component of its electrochemistry. During a discharge cycle, lithium atoms are ionized at the anode and stripped of their electrons. Lithium ions migrate from the anode through the electrolyte to the cathode, where they recombine with their electrons and electrically neutralize each other. The lithium ions are small enough to move through a micro permeable separator between the anode and cathode. Partly due to lithium's small size (second only to hydrogen and helium), lithium-ion batteries are capable of storing very high voltages and charges per unit mass and volume.
Lithium-ion batteries can use several different materials as electrodes. The most common combination is lithium cobalt oxide (cathode) and graphite (anode), which are most commonly found in portable electronics such as cell phones and laptops. Other cathode materials include lithium manganese oxide (used in hybrid electric and electric cars) and lithium iron phosphate. Lithium-ion batteries typically use ethers (a class of organic compounds) as electrolytes.
Compared to other high-quality battery technologies (nickel-cadmium or nickel-metal hydride), lithium-ion batteries have several advantages. They have one of the highest energy densities of all current battery technologies (100-265 Wh/kg or 250-670 Wh/L). In addition, lithium-ion battery cells can deliver up to 3.6 volts, three times more than technologies such as Ni-Cd or Ni-MH. This means they can deliver large amounts of power for high-power applications, using
Li-Ion batteries are also comparatively low maintenance and do not require timed cycling to maintain battery life. Lithium-ion batteries do not have a memory effect, a damaging process whereby repeated partial charge/discharge cycles can cause a battery to "remember" a lower capacity. This is an advantage over Ni-Cd and Ni-MH, which show this effect. Li-ion batteries also have a low self-discharge rate of around 1.5-2% per month. They contain no toxic cadmium, making them easier to dispose of than Ni-Cd batteries.
Because of these advantages, lithium-ion batteries have supplanted Ni-Cd batteries as the market leader in portable electronic devices (e.g. smartphones and laptops). Lithium-ion batteries are also used to power electrical systems for some aerospace applications, particularly on the newer, greener Boeing 787 where weight is a significant cost factor. From a clean energy perspective, much of the promise of lithium-ion technology comes from its potential applications in battery-powered cars. Currently, the best-selling electric cars, the Nissan Leaf and Tesla Model S use lithium-ion batteries as their primary fuel source.