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 of lithium-ion technology using a polymerelectrolyte instead of a liquid electrolyte. Highly conductive semisolid (gel) polymers form this electrolyte. These batteries provide higher specific energy than other lithium battery types. They are used in applications where weight is critical, such as mobile devices, radio-controlled aircraft, and some electric vehicles.[2]
Lithium polymer cells follow the history of lithium-ion and lithium-metal cells, which underwent extensive research during the 1980s, reaching a significant milestone with Sony's first commercial cylindrical lithium-ion cell in 1991. After that, other packaging forms evolved, including the flat pouch format.[3]
In the 1970s, the original polymer design used a solid dry polymer electrolyte resembling a plastic-like film, replacing the traditional porous separator soaked with electrolyte.
The solid electrolyte can typically be classified into three types: dry SPE, gelled SPE, and porous SPE. The dry SPE was the first used in prototype batteries, around 1978 by Michel Armand,[4][5] and 1985 by ANVAR and Elf Aquitaine of France, and Hydro-Québec of Canada.[6] Since 1990, several organisations, such as Mead and Valence in the United States and GS Yuasa in Japan, have developed batteries using gelled SPEs.[6] In 1996, Bellcore in the United States announced a rechargeable lithium polymer cell using porous SPE.[6]
A typical cell has four main components: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator itself may be a polymer, such as a microporous film of polyethylene (PE) or polypropylene (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).[7][8] The negative electrode material may have the same three parts, only with carbon replacing the lithium-metal-oxide.[7][8] 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.
Like other lithium-ion cells, LiPos work on the 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.
The voltage of a single LiPo cell depends on its chemistry and varies from about 4.2V (fully charged) to about 2.7–3.0V (fully discharged). The nominal voltage is 3.6 or 3.7 volts (about the middle value of the highest and lowest value) for cells based on lithium-metal-oxides (such as LiCoO2). This compares to 3.6–3.8V (charged) to 1.8–2.0V (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 or 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 per cell so that all cells are brought to the same state of charge (SOC).
Applying pressure on lithium polymer cells
An experimental lithium-ion polymer battery made by Lockheed Martin for NASA
Unlike lithium-ion cylindrical and prismatic cells, with a rigid metal case, LiPo cells have a flexible, foil-type (polymer laminate) 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 and deformation is prevented, which is associated with increase of cell impedance and degradation. [9][10]
Hexagonal lithium polymer battery for underwater vehicles
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 devices and notebook computers can be met. They also have a low self-discharge rate of about 5% per month.[11]
LiPo batteries are now almost ubiquitous when used to power commercial and hobby drones (unmanned aerial vehicles), radio-controlled aircraft, radio-controlled cars, 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 per the instructions.[12]
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.[13]
LiPo packs also see widespread use in airsoft, where their higher discharge currents and better energy density than traditional NiMH batteries have very noticeable performance gain (higher rate of fire).
Lithium-ion batteries are becoming increasingly commonplace in Uninterruptible power supply (UPS) systems. They offer numerous benefits over the traditional VRLA battery, 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 backup, including data centers where space is often at a premium.[16] The longer cycle life, usable energy (Depth of discharge), and thermal runaway are also seen as a benefit of 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. So such products have mostly switched to LiPo batteries or sometimes lithium iron phosphate batteries.
Apple iPhone 3GS's Lithium-ion battery, which has expanded due to a short-circuit failure
All Li-ion cells expand at high levels of state of charge (SOC) or overcharge due to slight vaporisation of the electrolyte. This may result in delamination and, thus, bad contact with the internal layers of the cell, which in turn diminishes the reliability and overall cycle life.[9] This is very noticeable for LiPos, which can visibly inflate due to the lack of a hard case to contain their expansion. Lithium polymer batteries' safety characteristics differ 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).[17] In comparison to liquid electrolytes and solid organic electrolytes, polymer electrolytes 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 was initially defined as a polymer matrix swollen with lithium salts, now called dry solid polymer electrolyte.[17] Lithium salts are dissolved in the polymer matrix to provide ionic conductivity. Due to its physical phase, there is poor ion transfer, resulting in poor conductivity at room temperature. 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.[18] The conduction mechanism is similar for liquid electrolytes and polymer gels, but GPEs have higher thermal stability and a low volatile nature which also further contribute to safety.[19]
Schematic of a lithium polymer battery based on GPEs
Lithium cells with solid polymer electrolyte
Cells with solid polymer electrolytes have not been fully commercialised[21] and are still a topic of research.[22] Prototype cells of this type could be considered to be between a traditional lithium-ion battery (with liquid electrolyte) and a completely plastic, solid-state lithium-ion battery.[23]
Nishi mentions that Sony 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.[24] At that time, polymer batteries were promising, and it seemed polymer electrolytes would become indispensable.[25] Eventually, this type of cell went into the market in 1998.[24] 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.[23] Although these polymer electrolytes may be dry to the touch, they can still include 30% to 50% liquid solvent.[26] In this regard, how to define a "polymer battery" 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.[27] It was a system like this that Bellcore used to develop an early lithium-polymer cell in 1996,[28] which was called a "plastic" lithium-ion cell (PLiON) and subsequently commercialised in 1999.[27]
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) (PEO),[29] a high molecular weight poly(trimethylene carbonate) (PTMC),[30] polypropylene oxide (PPO), poly[bis(methoxy-ethoxy-ethoxy)phosphazene] (MEEP), etc.
PEO exhibits the most promising performance as a solid solvent for lithium salts, mainly due to its flexible ethylene oxide segments and other oxygen atoms that comprise a strong donor character, readily solvating Li+ cations. PEO is also commercially available at a very reasonable cost.[17]
The performance of these proposed electrolytes is usually measured in a half-cell configuration against an electrode of metallic lithium, making the system a "lithium-metal" cell. Still, 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 inorganicionic liquids such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) as a plasticizer in a microporous polymer matrix like poly(vinylidene fluoride-co-hexafluoropropylene)/poly(methyl methacrylate) (PVDF-HFP/PMMA).[31]
A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li+ ions into electronically conducting solids to store energy. In comparison with other commercial rechargeable batteries, Li-ion batteries are characterized by higher specific energy, higher energy density, higher energy efficiency, a longer cycle life, and a longer calendar life. Also noteworthy is a dramatic improvement in lithium-ion battery properties after their market introduction in 1991: over the following 30 years, their volumetric energy density increased threefold while their cost dropped tenfold. In late 2024 global demand passed 1 Terawatt-hour per year, while production capacity was more than twice that.
Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special electric vehiclesand for grid energy storage, to balance out intermittent renewable power sources such as solar panels and wind turbines.
In materials science, fast ion conductors are solid conductors with highly mobile ions. These materials are important in the area of solid state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. As solid electrolytes they allow the movement of ions without the need for a liquid or soft membrane separating the electrodes. The phenomenon relies on the hopping of ions through an otherwise rigid crystal structure.
The electrochemical window (EW) of a substance is the electrode electric potential range between which the substance is neither oxidized nor reduced. The EW is one of the most important characteristics to be identified for solvents and electrolytes used in electrochemical applications. The EW is a term that is commonly used to indicate the potential range and the potential difference. It is calculated by subtracting the reduction potential from the oxidation potential.
Rechargeable lithium metal batteries are secondary lithium metal batteries. They have metallic lithium as a negative electrode. The high specific capacity of lithium metal, very low redox potential and low density make it the ideal negative material for high energy density battery technologies. Rechargeable lithium metal batteries can have a long run time due to the high charge density of lithium. Several companies and many academic research groups are currently researching and developing rechargeable lithium metal batteries as they are considered a leading pathway for development beyond lithium-ion batteries. Some rechargeable lithium metal batteries employ a liquid electrolyte and some employ a solid-state electrolyte.
The thin-film lithium-ion battery is a form of solid-state battery. Its development is motivated by the prospect of combining the advantages of solid-state batteries with the advantages of thin-film manufacturing processes.
An Ion gel is a composite material consisting of an ionic liquid immobilized by an inorganic or a polymer matrix. The material has the quality of maintaining high ionic conductivity while in the solid state. To create an ion gel, the solid matrix is mixed or synthesized in-situ with an ionic liquid. A common practice is to utilize a block copolymer which is polymerized in solution with an ionic liquid so that a self-assembled nanostructure is generated where the ions are selectively soluble. Ion gels can also be made using non-copolymer polymers such as cellulose, oxides such as silicon dioxide or refractory materials such as boron nitride.
Solid-state ionics is the study of ionic-electronic mixed conductor and fully ionic conductors and their uses. Some materials that fall into this category include inorganic crystalline and polycrystalline solids, ceramics, glasses, polymers, and composites. Solid-state ionic devices, such as solid oxide fuel cells, can be much more reliable and long-lasting, especially under harsh conditions, than comparable devices with fluid electrolytes.
A solid-state battery (SSB) is an electrical battery that uses a solid electrolyte for ionic conductions between the electrodes, instead of the liquid or gel polymer electrolytes found in conventional batteries. Solid-state batteries theoretically offer much higher energy density than the typical lithium-ion or lithium polymer batteries.
Nanoarchitectures for lithium-ion batteries are attempts to employ nanotechnology to improve the design of lithium-ion batteries. Research in lithium-ion batteries focuses on improving energy density, power density, safety, durability and cost.
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.
A separator is a permeable membrane placed between a battery's anode and cathode. The main function of a separator is to keep the two electrodes apart to prevent electrical short circuits while also allowing the transport of ionic charge carriers that are needed to close the circuit during the passage of current in an electrochemical cell.
Aluminium-ion batteries are a class of rechargeable battery in which aluminium ions serve as charge carriers. Aluminium can exchange three electrons per ion. This means that insertion of one Al3+ is equivalent to three Li+ ions. Thus, since the ionic radii of Al3+ (0.54 Å) and Li+ (0.76 Å) are similar, significantly higher numbers of electrons and Al3+ ions can be accepted by cathodes with little damage. Al has 50 times (23.5 megawatt-hours m-3) the energy density of Li-ion batteries and is even higher than coal.
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 reducing cost.
Lithium hybrid organic batteries are an energy storage device that combines lithium with an organic polymer. For example, polyaniline vanadium (V) oxide (PAni/V2O5) can be incorporated into the nitroxide-polymer lithium iron phosphate battery, PTMA/LiFePO4. Together, they improve the lithium ion intercalation capacity, cycle life, electrochemical performances, and conductivity of batteries.
Calcium (ion) batteries are energy storage and delivery technologies (i.e., electro–chemical energy storage) that employ calcium ions (cations), Ca2+, as the active charge carrier. Calcium (ion) batteries remain an active area of research, with studies and work persisting in the discovery and development of electrodes and electrolytes that enable stable, long-term battery operation. Calcium batteries are rapidly emerging as a recognized alternative to Li-ion technology due to their similar performance, significantly greater abundance, and lower cost.
A solid-state electrolyte (SSE) is a solid ionic conductor and electron-insulating material and it is the characteristic component of the solid-state battery. It is useful for applications in electrical energy storage (EES) in substitution of the liquid electrolytes found in particular in lithium-ion battery. The main advantages are the absolute safety, no issues of leakages of toxic organic solvents, low flammability, non-volatility, mechanical and thermal stability, easy processability, low self-discharge, higher achievable power density and cyclability. This makes possible, for example, the use of a lithium metal anode in a practical device, without the intrinsic limitations of a liquid electrolyte thanks to the property of lithium dendrite suppression in the presence of a solid-state electrolyte membrane. The use of a high capacity anode and low reduction potential, like lithium with a specific capacity of 3860 mAh g−1 and a reduction potential of -3.04 V vs SHE, in substitution of the traditional low capacity graphite, which exhibits a theoretical capacity of 372 mAh g−1 in its fully lithiated state of LiC6, is the first step in the realization of a lighter, thinner and cheaper rechargeable battery. Moreover, this allows the reach of gravimetric and volumetric energy densities, high enough to achieve 500 miles per single charge in an electric vehicle. Despite the promising advantages, there are still many limitations that are hindering the transition of SSEs from academia research to large-scale production, depending mainly on the poor ionic conductivity compared to that of liquid counterparts. However, many car OEMs (Toyota, BMW, Honda, Hyundai) expect to integrate these systems into viable devices and to commercialize solid-state battery-based electric vehicles by 2025.
A polymer electrolyte is a polymer matrix capable of ion conduction. Much like other types of electrolyte—liquid and solid-state—polymer electrolytes aid in movement of charge between the anode and cathode of a cell. The use of polymers as an electrolyte was first demonstrated using dye-sensitized solar cells. The field has expanded since and is now primarily focused on the development of polymer electrolytes with applications in batteries, fuel cells, and membranes.
Lithium aluminium germanium phosphate, typically known with the acronyms LAGP or LAGPO, is an inorganic ceramic solid material whose general formula is Li 1+xAl xGe 2-x(PO 4) 3. LAGP belongs to the NASICON family of solid conductors and has been applied as a solid electrolyte in all-solid-state lithium-ion batteries. Typical values of ionic conductivity in LAGP at room temperature are in the range of 10–5 - 10–4 S/cm, even if the actual value of conductivity is strongly affected by stoichiometry, microstructure, and synthesis conditions. Compared to lithium aluminium titanium phosphate (LATP), which is another phosphate-based lithium solid conductor, the absence of titanium in LAGP improves its stability towards lithium metal. In addition, phosphate-based solid electrolytes have superior stability against moisture and oxygen compared to sulfide-based electrolytes like Li 10GeP 2S 12 (LGPS) and can be handled safely in air, thus simplifying the manufacture process. Since the best performances are encountered when the stoichiometric value of x is 0.5, the acronym LAGP usually indicates the particular composition of Li 1.5Al 0.5Ge 1.5(PO 4) 3, which is also the typically used material in battery applications.
↑ Bruno Scrosati, K. M. Abraham, Walter A. van Schalkwijk, Jusef Hassoun (ed), Lithium Batteries: Advanced Technologies and Applications, John Wiley & Sons, 2013 ISBN1118615395,page 44
↑ M. B. Armand; J. M. Chabagno; M. Duclot (20–22 September 1978). "Extended Abstracts". Second International Meeting on Solid Electrolytes. St. Andrews, Scotland.{{cite book}}: CS1 maint: location missing publisher (link)
↑ M. B. Armand, J. M. Chabagno & M. Duclot (1979). "Poly-ethers as solid electrolytes". In P. Vashitshta; J.N. Mundy & G.K. Shenoy (eds.). Fast ion Transport in Solids. Electrodes and Electrolytes. North Holland Publishers, Amsterdam.
1 2 3 Murata, Kazuo; Izuchi, Shuichi; Yoshihisa, Youetsu (3 January 2000). "An overview of the research and development of solid polymer electrolyte batteries". Electrochimica Acta. 45 (8–9): 1501–1508. doi:10.1016/S0013-4686(99)00365-5.
1 2 Yazami, Rachid (2009). "Chapter 5: Thermodynamics of Electrode Materials for Lithium-Ion Batteries". In Ozawa, Kazunori (ed.). Lithium ion rechargeable batteries. Wiley-Vch Verlag GmbH & Co. KGaA. ISBN978-3-527-31983-1.
↑ Dunn, Terry (5 March 2015). "Battery Guide: The Basics of Lithium-Polymer Batteries". Tested. Whalerock Industries. Archived from the original on 16 March 2017. Retrieved 15 March 2017. I've not yet heard of a LiPo that burst into flames during storage. All of the fire incidents that I'm aware of occurred during charge or discharge of the battery. Of those cases, the majority of problems happened during charge. Of those cases, the fault usually rested with either the charger or the person who was operating the charger…but not always.
1 2 Scrosati, Bruno (2002). "Chapter 8: Lithium polymer electrolytes". In van Schalkwijk, Walter A.; Scrosati, Bruno (eds.). Advances in Lithium-ion batteries. Kluwer Academic Publishers. ISBN0-306-47356-9.
↑ Nishi, Yoshio (2002). "Chapter 7: Lithium-Ion Secondary batteries with gelled polymer electrolytes". In van Schalkwijk, Walter A.; Scrosati, Bruno (eds.). Advances in Lithium-ion batteries. Kluwer Academic Publishers. ISBN0-306-47356-9.
↑ Brodd, Ralf J. (2002). "Chapter 9: Lithium-Ion cell production processes". In van Schalkwijk, Walter A.; Scrosati, Bruno (eds.). Advances in Lithium-ion batteries. Kluwer Academic Publishers. ISBN0-306-47356-9.
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