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A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), is a
rechargeable battery A rechargeable battery, storage battery, or secondary cell (formally a type of Accumulator (energy), energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to ...
of
lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also sees ...
technology using a
polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
instead of a liquid electrolyte. High conductivity semisolid (
gel A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still di ...
) polymers form this electrolyte. These batteries provide higher
specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, sto ...
than other lithium battery types and are used in applications where
weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a Euclidean vector, vector quantity, the gravitational force acting on the object. Others define weigh ...
is a critical feature, such as
mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...
s,
radio-controlled aircraft A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ( ...
and some
electric vehicle An electric vehicle (EV) is a vehicle that uses one or more electric motors for propulsion. It can be powered by a collector system, with electricity from extravehicular sources, or it can be powered autonomously by a battery (sometimes cha ...
s.


History

LiPo cells follow the history of
lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also sees ...
and lithium-metal cells which underwent extensive research during the 1980s, reaching a significant milestone with
Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
's first commercial cylindrical Li-ion cell in 1991. After that, other packaging forms evolved, including the flat pouch format.


Design origin and terminology

Lithium polymer cells have evolved from
lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also sees ...
and lithium-metal batteries. The primary difference is that instead of using a liquid
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
-salt
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
(such as LiPF6) held in an
organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...
(such as EC/ DMC/ DEC), the battery uses a solid polymer electrolyte (SPE) such as
poly(ethylene oxide) Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...
(PEO),
poly(acrylonitrile) Poly, from the Greek πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong incorporated Chinese property developer ** Poly Real ...
(PAN),
poly(methyl methacrylate) Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite, ...
(PMMA) or poly(vinylidene fluoride) (PVdF). In the 1970s the original polymer design used a solid dry polymer electrolyte resembling a plastic-like film, replacing the traditional porous separator that is soaked with electrolyte. The solid electrolyte can typically be classified as one of three types: dry SPE, gelled SPE and porous SPE. The dry SPE was the first used in prototype batteries, around 1978 by
Michel Armand Michel Armand (born 1946) is a French scientist who is best known for helping with the invention of Lithium batteries. Lithium batteries are electrochemical devices that are widely used as power sources. The history of their development has con ...
, and 1985 by ANVAR and Elf Aquitaine of France, and
Hydro-Québec Hydro-Québec is a public utility that manages the generation, transmission and distribution of electricity in the Canadian province of Quebec, as well as the export of power to portions of the Northeast United States. It was established by the ...
of Canada. From 1990 several organisations like Mead and Valence in the United States and
GS Yuasa is a Kyoto-based Japanese company specializing in the development and production of lead acid and lithium-ion batteries, used in automobiles, motorcycles and other areas including aerospace and defense applications. History Yuasa In 1909, ...
in Japan developed batteries using gelled SPEs. In 1996, Bellcore in the United States announced a rechargeable lithium polymer cell using porous SPE. A typical cell has four main components: positive
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
, negative electrode, separator and
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
. The separator itself may be a
polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
, such as a microporous film of
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
(PE) or
polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene. Polypropylene belongs to the group of polyolefins and ...
(PP); thus, even when the cell has a liquid electrolyte, it will still contain a "polymer" component. In addition to this, the positive electrode can be further divided into three parts: the lithium-transition-metal-oxide (such as LiCoO2 or LiMn2O4), a conductive additive, and a polymer binder of poly(vinylidene fluoride) (PVdF). The negative electrode material may have the same three parts, only with
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
replacing the lithium-metal-oxide. The main difference between lithium ion polymer cells and lithium ion cells is the physical phase of the electrolyte, such that LiPo cells use dry solid, gel-like electrolytes whereas Li-ion cells use liquid electrolytes.


Working principle

Just as with other lithium-ion cells, LiPos work on the principle of intercalation and de-intercalation of lithium ions from a positive electrode material and a negative electrode material, with the liquid electrolyte providing a conductive medium. To prevent the electrodes from touching each other directly, a microporous separator is in between which allows only the ions and not the electrode particles to migrate from one side to the other.


Voltage and state of charge

The voltage of a single LiPo cell depends on its chemistry and varies from about 4.2 V (fully charged) to about 2.7–3.0 V (fully discharged), where the nominal voltage is 3.6 or 3.7 volts (about the middle value of highest and lowest value) for cells based on lithium-metal-oxides (such as LiCoO2). This compares to 3.6–3.8 V (charged) to 1.8–2.0 V (discharged) for those based on lithium-iron-phosphate (LiFePO4). The exact voltage ratings should be specified in product data sheets, with the understanding that the cells should be protected by an electronic circuit that won't allow them to overcharge nor over-discharge under use. LiPo battery packs, with cells connected in series and parallel, have separate pin-outs for every cell. A specialized charger may monitor the charge on a per-cell basis so that all cells are brought to the same state of charge (SOC).


Applying pressure on LiPo cells

Unlike lithium-ion cylindrical and prismatic cells, which have a rigid metal case, LiPo cells have a flexible, foil-type (polymer
laminate Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materials ...
) case, so they are relatively unconstrained. Moderate pressure on the stack of layers that compose the cell results in increased capacity retention, because the contact between the components is maximised and
delamination Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling and ...
and deformation is prevented, which is associated with increase of cell impedance and degradation.


Applications

LiPo cells provide manufacturers with compelling advantages. They can easily produce batteries of almost any desired shape. For example, the space and weight requirements of
mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...
s and
notebook computers A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a clam shell form factor with the screen mounted on the inside of the upper li ...
can be met. They also have a low self-discharge rate, which is about 5% per month.


Drones, Radio controlled equipment and aircraft

LiPo batteries are now almost ubiquitous when used to power commercial and hobby drones (
unmanned aerial vehicle An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...
s),
radio-controlled aircraft A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ( ...
,
radio-controlled car 'Radio-controlled cars'' (or RC cars for short) are miniature model cars, vans, buses, trucks or buggy (automobile), buggies that can be controlled from a distance using a specialized transmitter or remote. The term "RC" has been used to mean bo ...
s and large scale model trains, where the advantages of lower weight and increased capacity and power delivery justify the price. Test reports warn of the risk of fire when the batteries are not used in accordance with the instructions. The voltage for long-time storage of LiPo battery used in the R/C model should be 3.6~3.9V range per cell, otherwise it may cause damage to the battery. LiPo packs also see widespread use in
airsoft Airsoft is a team game in which participants eliminate opposing players by tag (game), tagging them out of play with airsoft pellets, spherical plastic projectiles shot with mock air gun, air weapons(usually powered by an electronic motor) call ...
, where their higher discharge currents and better energy density compared to more traditional
NiMH NIMH may refer to: *Nickel–metal hydride battery (NiMH), a type of electrical battery *National Institute of Mental Health, an agency of the United States government *National Institute of Medical Herbalists, a professional organisation in the Un ...
batteries has very noticeable performance gain (higher rate of fire).


Personal electronics

LiPo batteries are pervasive in
mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...
s,
power bank A battery charger, recharger, or simply charger is a device that stores energy in a battery by running an electric current through it. The charging protocol (how much voltage or current for how long, and what to do when charging is complete) depen ...
s, very thin laptop computers,
portable media players A portable media player (PMP) (also including the related digital audio player (DAP)) is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. The data is typically stored o ...
, wireless controllers for video game consoles, wireless PC peripherals,
electronic cigarette An electronic cigarette is an electronic device that simulates tobacco smoking. It consists of an atomizer, a power source such as a battery, and a container such as a cartridge or tank. Instead of smoke, the user inhales vapor. As such ...
s, and other applications where small form factors are sought and the high energy density outweighs cost considerations.


Electric vehicles

Hyundai Motor Company Hyundai Motor Company, often abbreviated to Hyundai Motors ( ) and commonly known as Hyundai (, ; ), is a South Korean multinational automotive manufacturer headquartered in Seoul, South Korea, and founded in 1967. Currently, the company o ...
uses this type of battery in some of its battery electric and
hybrid vehicles A hybrid vehicle is one that uses two or more distinct types of power, such as submarines that use diesel when surfaced and batteries when submerged. Other means to store energy include pressurized fluid in hydraulic hybrids. The basic princip ...
, as well as
Kia Motors Kia Corporation, commonly known as Kia (, ; formerly known as Kyungsung Precision Industry and Kia Motors Corporation), is a South Korean multinational automobile manufacturer headquartered in Seoul, South Korea. It is South Korea's second lar ...
in their battery electric Kia Soul. The
Bolloré Bluecar The Bolloré Bluecar is a small four-seat, three-door electric car supplied by Bolloré, designed by Pininfarina and manufactured by Cecomp in Bairo, Italy, under a joint venture owned by Bolloré and Pininfarina called Véhicule Électriques Pini ...
, which is used in car sharing schemes in several cities, also uses this type of battery.


Uninterruptible power supply systems

Lithium-ion batteries are becoming increasingly more commonplace in
Uninterruptible power supply An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system ...
(UPS) systems. They offer numerous benefits over the traditional
VRLA battery A valve regulated lead–acid (VRLA) battery, commonly known as a sealed lead–acid (SLA) battery, is a type of lead–acid battery characterized by a limited amount of electrolyte ("starved" electrolyte) absorbed in a plate separator or formed ...
and with stability and safety improvements confidence in the technology is growing. Their power to size and weight ratio is seen as a major benefit in many industries requiring critical power back up including data centers where space is often at a premium. The longer cycle life, usable energy (Depth of discharge), and thermal runaway are also seen as a benefit for using Li-po batteries over VRLA batteries.


Jump starter

The battery used to start a vehicle engine is typically 12V or 24V, so a portable jump starter or battery booster uses three or six LiPo batteries in series (3S1P/6S1P) to start the vehicle in an emergency, instead of the other jump-start methods. The price of a lead-acid jump starter is less but they are bigger and heavier than comparable lithium batteries, and so such products have mostly switched to LiPo batteries or sometimes lithium iron phosphate batteries.


Safety

All Li-ion cells expand at high levels of
state of charge State of charge (SoC) is the level of charge of an electric battery relative to its capacity. The units of SoC are percentage points (0% = empty; 100% = full). An alternative form of the same measure is the Depth of discharge, depth of discharge ...
(SOC) or over-charge, due to slight vaporisation of the electrolyte. This may result in
delamination Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling and ...
, and thus bad contact of the internal layers of the cell, which in turn brings diminished reliability and overall cycle life of the cell. This is very noticeable for LiPos, which can visibly inflate due to lack of a hard case to contain their expansion. The safety characteristics of Lithium Polymer batteries are different from those of lithium iron phosphate batteries.


Polymer Electrolytes

Polymer electrolytes can be divided into two large categories: dry solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE). In comparison to liquid electrolytes and solid organic electrolytes, polymer electrolyte offer advantages such as increased resistance to variations in the volume of the electrodes throughout the charge and discharge processes, improved safety features. excellent flexibility and processability. Solid polymer electrolyte is initially defined as a polymer matrix swollen with lithium salts, which is now referred to as dry solid polymer electrolyte. Lithium salts are dissolved im the polymer matrix to provide ionic conductivity. Due to its physical phase, there is poor ion transfer resulting in poor conductivity at room temperature. In order to improve the ionic conductivity at room temperature, gelled electrolyte is added resulting in the formation of GPEs. GPEs are formed by incorporating an organic liquid electrolyte in the polymer matrix. Liquid electrolyte is entrapped by a small amount of polymer network, hence the properties of GPE is characterized by properties between those of liquid and solid electrolytes. The conduction mechanism is similar for liquid electrolytes and polymer gels, but GPEs have higher thermal stability and low volatile nature which also further contribute to safety.


Lithium cells with solid polymer electrolyte

Cells with solid polymer electrolytes have not reached full commercialization and are still a topic of research. Prototype cells of this type could be considered to be between a traditional
lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also sees ...
battery (with liquid electrolyte) and a completely plastic,
solid-state lithium-ion battery A solid-state battery is a battery (electricity), battery technology that uses solid electrodes and a solid-state electrolyte, solid electrolyte, instead of the liquid or polymer gel electrolytes found in Lithium-ion battery, lithium-ion or Lithiu ...
. The simplest approach is to use a polymer matrix, such as
polyvinylidene fluoride Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. PVDF is a specialty plastic used in applications requiring the highest pur ...
(PVdF) or
poly(acrylonitrile) Poly, from the Greek πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong incorporated Chinese property developer ** Poly Real ...
(PAN), gelled with conventional salts and solvents, such as LiPF6 in EC/ DMC/ DEC. Nishi mentions that
Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
started research on lithium-ion cells with gelled polymer electrolytes (GPE) in 1988, before the commercialisation of the liquid-electrolyte lithium-ion cell in 1991. At that time polymer batteries were promising and it seemed polymer electrolytes would become indispensable. Eventually, this type of cell went into the market in 1998. However, Scrosati argues that, in the strictest sense, gelled membranes cannot be classified as "true" polymer electrolytes, but rather as hybrid systems where the liquid phases are contained within the polymer matrix. Although these polymer electrolytes may be dry to the touch, they can still contain 30% to 50% liquid solvent. In this regard, how to really define what a "polymer battery" is remains an open question. Other terms used in the literature for this system include hybrid polymer electrolyte (HPE), where "hybrid" denotes the combination of the polymer matrix, the liquid solvent and the salt. It was a system like this that Bellcore used to develop an early lithium-polymer cell in 1996, which was called "plastic" lithium-ion cell (PLiON), and subsequently commercialised in 1999. A solid polymer electrolyte (SPE) is a solvent-free salt solution in a polymer medium. It may be, for example, a compound of lithium bis(fluorosulfonyl)imide (LiFSI) and high molecular weight
poly(ethylene oxide) Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...
(PEO), a high molecular weight
poly(trimethylene carbonate) Poly(trimethylene carbonate) (PTMC) is an aliphatic polycarbonate synthesized from the 6-membered cyclic carbonate, trimethylene carbonate (1,3-propylene carbonate or 1,3-Dioxan-2-one). Trimethylene carbonate (TMC) is a colorless crystalline so ...
(PTMC), polypropylene oxide (PPO), poly
is(methoxy-ethoxy-ethoxy)phosphazene In linguistics, a copula (plural: copulas or copulae; abbreviated ) is a word or phrase that links the subject of a sentence to a subject complement, such as the word ''is'' in the sentence "The sky is blue" or the phrase ''was not being'' in ...
(MEEP), ''etc''. PEO exhibits most promising performance as a solid solvent for lithium salts, mainly due to its flexible ethylene oxide segments and other oxygen atoms that comprise strong donor character, readily solvating Li+ cations. PEO is also commercially available at a very reasonable cost. The performance of these proposed electrolytes is usually measured in a
half-cell In electrochemistry, a half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally occurring Helmholtz double layer. Chemical reactions within this layer momentarily pump electri ...
configuration against an electrode of metallic
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
, making the system a " lithium-metal" cell, but it has also been tested with a common lithium-ion cathode material such as lithium-iron-phosphate (LiFePO4). Other attempts to design a polymer electrolyte cell include the use of
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
ionic liquid An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...
s such as 1-butyl-3-methylimidazolium tetrafluoroborate (
MIM MIM or Mim may refer to: Places * Mim, Ahafo, Ghana * Mim Lake, Ghana * Mim Bour, or Mim Mountains, Ghana Education * Master of Management, a post-graduate master's degree * Master of Information Management, an interdisciplinary degree progra ...
F4) as a plasticizer in a microporous polymer matrix like poly(vinylidene fluoride-co-hexafluoropropylene)/poly(methyl methacrylate) (PVDF-HFP/PMMA).


See also

*
List of battery types This list is a summary of notable electric battery types composed of one or more electrochemical cells. Three lists are provided in the table. The primary (non-rechargeable) and secondary (rechargeable) cell lists are lists of battery chemistry ...
*
Lithium–air battery The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow. Pairing lithium and ambient oxygen can ...
*
Lithium iron phosphate battery The lithium iron phosphate battery (LFP (lithium ferro-phosphate), or Li-IP) is a type of lithium-ion battery using lithium iron phosphate () as the cathode material, and a graphitic carbon electrode with a metallic backing as the anode. Becaus ...
*
Research in lithium-ion batteries Research in lithium-ion batteries has produced many proposed refinements of lithium-ion batteries. Areas of research interest have focused on improving energy density, safety, rate capability, cycle durability, flexibility, and cost. Artifici ...


References


External links


Electropaedia on Lithium Battery Manufacturing


{{Use dmy dates, date=June 2020 Lithium-ion batteries