A lithium-ion battery or Li-ion battery is a type of rechargeable battery composed of cells in which lithium ions move from the negative electrode through an electrolyte to the positive electrode during discharge and back when charging.
Cells composed, of rechargeable battery Li-ion design, chemistry and uses are briefly illustrated by Pritish Kumar Halder.
Li-ion cells use an intercalated lithium compound as the material at the positive electrode and typically graphite at the negative electrode. Li-ion batteries have a high energy density, no memory effect and low self-discharge. Cells can be manufactured to prioritize either energy or power density. They can however be a safety hazard since they contain flammable electrolytes and if damaged or incorrectly charged can lead to explosions and fires.
Generally, the negative electrode of a conventional lithium-ion cell is made from carbon. The positive electrode is typically a metal oxide. The electrolyte is a lithium salt in an organic solvent. The electrochemical roles of the electrodes reverse between anode and cathode, depending on the direction of current flow through the cell.
The most common commercially used anode (negative electrode) is graphite, which in its fully lithiated state of LiC6 correlates to a maximal capacity of 1339 C/g (372 mAh/g). The positive electrode is generally one of three materials: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate) or a spinel (such as lithium manganese oxide). More experimental materials include graphene-containing electrodes, although these remain far from commercially viable due to their high cost.
Depending on materials choices, the voltage, energy density, life, and safety of a lithium-ion cell can change dramatically. Current effort has been exploring the use of novel architectures using nanotechnology to improve performance. Areas of interest include nano-scale electrode materials and alternative electrode structures.
The increasing demand for batteries has led vendors and academics to focus on improving the energy density, operating temperature, safety, durability, charging time, output power, elimination of cobalt requirements, and cost of lithium-ion battery technology.
The reactants in the electrochemical reactions in a lithium-ion cell are materials of anode and cathode, both of which are compounds containing lithium atoms. During discharge, an oxidation half-reaction at the anode produces positively charged lithium ions and negatively charged electrons. The oxidation half-reaction may also produce uncharged material that remains at the anode.
Both electrodes allow lithium ions to move in and out of their structures with a process called insertion (intercalation) or extraction (deintercalation), respectively.
As the lithium ions “rock” back and forth between the two electrodes, these batteries are also known as “rocking-chair batteries” or “swing batteries”.
The following equations exemplify the chemistry.
The positive electrode (cathode) half-reaction in the lithium-doped cobalt oxide substrate is
CoO2 + Li+ + e- <=> LiCoO2
The negative electrode (anode) half-reaction for the graphite is
LiC6 <=> C6 + Li+ + e^-
The full reaction (left to right: discharging, right to left: charging) being
LiC6 + CoO2 <=> C6 + LiCoO2
The overall reaction has its limits. Over discharging supersaturates lithium cobalt oxide, leading to the production of lithium oxide, possibly by the following irreversible reaction:
Li+ + e^- + LiCoO2 -> Li2O + CoO
Overcharging up to 5.2 volts leads to the synthesis of cobalt (IV) oxide, as evidenced by x-ray diffraction:
LiCoO2 -> Li+ + CoO2 + e^-
Li-ion cells (as distinct from entire batteries) are available in various shapes, which can generally be divided into four groups:
1)Small cylindrical (solid body without terminals, such as those used in older laptop batteries)
2)Large cylindrical (solid body with large threaded terminals)
3)Flat or pouch (soft, flat body, such as those used in cell phones and newer laptops; these are lithium-ion polymer batteries.
4)Rigid plastic case with large threaded terminals (such as electric vehicle traction packs)
Cells with a cylindrical shape are made in a characteristic “swiss roll” manner (known as a “jelly roll” in the US), which means it is a single long ‘sandwich’ of the positive electrode, separator, negative electrode, and separator rolled into a single spool. The shape of the jelly roll in cylindrical cells can be approximated by an Archimedean spiral. One advantage of cylindrical cells compared to cells with stacked electrodes is the faster production speed. One disadvantage of cylindrical cells can be a large radial temperature gradient inside the cells developing at high discharge currents.
The vast majority of commercial Li-ion batteries are used in consumer electronics and electric vehicles. Such devices include:
Portable devices: these include mobile phones and smartphones, laptops and tablets, digital cameras and camcorders, electronic cigarettes, handheld game consoles and torches (flashlights).
Power tools: Li-ion batteries are used in tools such as cordless drills, sanders, saws, and a variety of garden equipment including whipper-snippers and hedge trimmers.
Electric vehicles: electric vehicle batteries are used in electric cars, hybrid vehicles, electric motorcycles and scooters, electric bicycles, personal transporters and advanced electric wheelchairs. Also radio-controlled models, model aircraft, aircraft, and the Mars Curiosity rover.
More niche uses include backup power in telecommunications applications. Lithium-ion batteries are also frequently discussed as a potential option for grid energy storage, although they are not yet cost-competitive at scale.