Inventor/Assignee: Zhenhua Mao, Anaba Anani | Current Assignee: Amperex Technology Ltd
Introduction: A lithium-ion (Li-ion) battery is an advanced battery technology that uses lithium ions as a key component of its electrochemistry. During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions move from the anode and pass through the electrolyte until they reach the cathode, where they recombine with their electrons and electrically neutralize. The lithium ions are small enough to be able to move through a micro-permeable separator between the anode and cathode. In part because of lithium’s small size (third only to hydrogen and helium), Li-ion batteries are capable of having a very high voltage and charge storage per unit mass and unit volume.
- They have one of the highest energy densities of any battery technology today (100-265 Wh/kg or 250-670 Wh/L).
- Li-ion battery cells can deliver up to 3.6 Volts, three times higher than technologies such as Ni-Cd or Ni-MH. This means that they can deliver large amounts of current for high-power applications, which has Li-ion batteries are also comparatively low maintenance, and do not require scheduled cycling to maintain their battery life.
- Li-ion batteries have no memory effect, a detrimental process where repeated partial discharge/charge cycles can cause a battery to ‘remember’ a lower capacity.
- Li-ion batteries have a tendency to overheat, and can be damaged at high voltages.
- Li-ion batteries require safety mechanisms to limit voltage and internal pressures, which can increase weight and limit performance in some cases.
- Li-ion batteries are also subject to aging, meaning that they can lose capacity and frequently fail after a number of years.
- Another factor limiting their widespread adoption is their cost, which is around 40% higher than Ni-Cd.
Performance: As lithium-ion batteries can have a variety of positive and negative electrode materials, the energy density and voltage vary accordingly.
Batteries with lithium iron phosphate positive and graphite negative electrodes have a nominal open-circuit voltage of 3.2 V, and a typical charging voltage of 3.6 V. Lithium nickel manganese cobalt (NMC) oxide positives with graphite negatives have a 3.7 V nominal voltage with a 4.2 V maximum while charging. The charging procedure is performed at constant voltage with current-limiting circuitry (i.e., charging with constant current until a voltage of 4.2 V is reached in the cell and continuing with a constant voltage applied until the current drops close to zero). Typically, the charge is terminated at 3% of the initial charge current. In the past, lithium-ion batteries could not be fast-charged and needed at least two hours to charge fully. Current-generation cells can be fully charged in 45 minutes or less. In 2015 researchers demonstrated a small 600 mAh capacity battery charged to 68 percent capacity in two minutes and a 3,000 mAh battery charged to 48 percent capacity in five minutes. The latter battery has an energy density of 620 W·h/L. The device employed heteroatoms bonded to graphite molecules in the anode.
Performance of manufactured batteries has improved over time. For example, from 1991 to 2005 the energy capacity per price of lithium ion batteries improved more than ten-fold, from 0.3 Wh per dollar to over 3 Wh per dollar. In the period from 2011 to 2017, progress has averaged 7.5% annually. Overall, between 1991 and 2018, prices for all types of lithium-ion cells (in dollars per kWh) fell approximately 97%. Over the same time period, energy density more than tripled. Efforts to increase energy density contributed significantly to cost reduction. Differently sized cells with similar chemistry can also have different energy densities. The 21700 cell has 50% more energy than the 18650 cell, and the bigger size reduces heat transfer to its surroundings.
Price range: The cost of Li-ion batteries fell below $132 per KWhr in 2021.
Commercialization: Sony, Asahi Kasei
Use Cases: Automobile industry, portable devices like mobile phones, laptops, cameras, power tools
Theme: Battery Technology | Subtheme: Lithium-ion batteries (liquid electrolyte)
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