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EspañolLITHIUM ION POLYMER BATTERY
(Redirected from Lithium polymer cell)
'Lithium-ion polymer batteries', or more commonly 'lithium polymer batteries' (abbreviated Li-poly or LiPo) are rechargeable batteries which have technologically evolved from lithium-ion batteries. Ultimately, the lithium-salt electrolyte is not held in an organic solvent as in the lithium-ion design, but in a solid polymer composite such as polyacrylonitrile. The advantages of Li-poly over the lithium-ion design include lower cost manufacturing and being more robust to physical damage. Lithium-ion polymer batteries started appearing in consumer electronics around 1996.
Cells sold today as polymer batteries have a different design from the older lithium-ion cells. Unlike lithium-ion cylindrical, or prismatic cells, which have a rigid metal case, polymer cells have a flexible, foil-type (polymer laminate) case, but they still contain organic solvent. The main difference between commercial polymer and lithium-ion cells is that in the latter the rigid case presses the electrodes and the separator onto each other, whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.
Since no metal battery cell casing is needed, the battery can be lighter and it can be specifically shaped to fit the device it will power. Because of the denser packaging without intercell spacing between cylindrical cells and the lack of metal casing, the energy density of Li-poly batteries is over 20% higher than that of a classical Li-ion battery and approximately three times better than nickel-cadmium (NiCd) and nickel metal hydride (NiMH) batteries.
The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. Overcharging a Li-poly battery will likely result in explosion and/or fire. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load.
Early in its development, lithium polymer technology had problems with internal resistance. Other challenges include longer charge times and slower maximum discharge rates compared to more mature technologies. Li-poly batteries typically require more than an hour for a full charge. Recent design improvements have increased maximum discharge currents from two times to 15 or even 30 times the cell capacity (discharge rate in amps, cell capacity in amp-hours). In March 2005 Toshiba announced a new design offering a much faster (about 1–3 minutes) rate of charge. These cells have yet to reach the market but should have a dramatic effect on the power tool and electric vehicle industries, and a major effect on consumer electronics.
When compared to the lithium-ion battery, Li-poly has a greater life cycle degradation rate. However, in recent years, manufacturers have been declaring upwards of 500 charge-discharge cycles before the capacity drops to 80% (see Sanyo). Another variant of Li-poly cells, the "thin film rechargeable lithium battery", has been shown to provide more than 10,000 cycles.
A compelling advantage of Li-poly cells is that manufacturers can shape the battery almost however they please, which can be important to mobile phone manufacturers constantly working on smaller, thinner, and lighter phones. Another advantage of lithium polymer cells over nickel-cadmium and nickel metal hydride cells is that the rate of self-discharge is much lower.
Li-poly batteries are also gaining favor in the world of radio-controlled aircraft, where the advantages of both lower weight and greatly increased run times can be sufficient justification for the price. However, lithium polymer-specific chargers are required to avoid fire and explosion. Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts take special precautions to ensure their battery leads are properly connected and insulated. Specially designed electronic motor speed controls are used to prevent excessive discharge and subsequent battery damage. This is achieved using a low voltage cutoff (LVC) setting that is adjusted to maintain cell voltage at (typically) 3 V per cell.
Li-poly batteries are also gaining ground in PDAs (including iPhone) and laptop computers, such as Apple's MacBook and Lenovo's Thinkpad (Ultrabay Batteries), Dell (D-bay Batteries) and small digital music devices such as iPods and other MP3 players, as well as portable gaming devices like the Sony PSP or Nintendo's Game Boy Advance SP, where small form factors and energy density outweigh cost considerations.
These batteries may also power the next generation of battery electric vehicles. The cost of an electric car of this type is prohibitive, but proponents argue that with increased production, the cost of Li-poly batteries will go down.
Canadian company BionX supplied electric bicycle conversion kits that used brushless motors and nickel metal hydride batteries for some years, but in 2006, they introduced batteries that used lithium-ion technology. During 2007 Urban Mover and PowaCycle, both in the United Kingdom, introduced the first commercially available Li-poly powered electric bikes, as opposed to just supplying conversion kits.
There are currently two commercialized technologies, both lithium-ion-polymer (where "polymer" stands for "polymer electrolyte/separator") cells. These are collectively referred to as "polymer electrolyte batteries".
The idea is to use an ion-conducting polymer instead of the traditional combination of a microporous separator and a liquid electrolyte. This promises not only better safety, as polymer electrolytes do not ignite as easily, but also the possibility of making battery cells very thin, as they do not require pressure to "sandwich" cathode and anode together. Polymer electrolytes seal both electrodes together like a glue.
The design is: anode (Li or carbon-Li intercalation compound)/conducting polymer electrolyte-separator/cathode (LiCoO2 or LiMnO4)
Typical reaction:
★ Anode: carbon-Li(''x'') - ''x''Li+ - ''x''e−
★ Separator: Li+ conduction
★ Cathode: Li(1-''x'')CoO2 + ''x''Li+ + ''x''e−
Polymer electrolytes/separators can be solid polymers (e.g., polyethyleneoxide, PEO) plus LiPF6, or other conducting salts plus SiO2, or other fillers for better mechanical properties (such systems are not available commercially yet). Some manufacturers like Avestor are using metallic Li as the anode (these are the Lithium-metal-polymer batteries), whereas others wish to go with the proven safe carbon intercalation anode.
Both currently commercialized technologies use PVdF (a polymer) gelled with conventional solvents and salts, like EC/DMC/DEC. The difference between the two technologies is that one (Bellcore/Telcordia technology) uses LiMnO4 as the cathode, and the other the more conventional LiCoO2.
Other, more exotic (although not yet commercially available) Li-polymer batteries use a polymer cathode. For example, Moltech is developing a battery with a plastic conducting carbon-sulfur cathode. However, as of 2005 this technology seems to have had problems with self-discharge and manufacturing cost.
Yet another proposal is to use organic sulfur-containing compounds for the cathode in combination with an electrically conducting polymer such as polyaniline. This approach promises high power capability (i.e., low internal resistance) and high discharge capacity, but has problems with cycleability and cost.
★ BatteryUniversity.com
★ World's First Electric Powered Paraglider - running on Lipo.
★ A sailplane with auxilary electric power, running on lipos.
★ Overcharging a lithium polymer battery
★ 2004.4.20 - [1] Altair Nanotechnologies Announces Initial Shipment of Lithium Titanate Spinel Electrode Nanomaterials
★ 2005.11.02 - A123Systems Launches New Higher-Power, Faster Recharging Li-Ion Battery Systems [2]
★ :2006.05.19 - Hybrid vehicle application note
 A prototype Lithium-Ion Polymer Battery at NASA Glenn Research Center. |
'Lithium-ion polymer batteries', or more commonly 'lithium polymer batteries' (abbreviated Li-poly or LiPo) are rechargeable batteries which have technologically evolved from lithium-ion batteries. Ultimately, the lithium-salt electrolyte is not held in an organic solvent as in the lithium-ion design, but in a solid polymer composite such as polyacrylonitrile. The advantages of Li-poly over the lithium-ion design include lower cost manufacturing and being more robust to physical damage. Lithium-ion polymer batteries started appearing in consumer electronics around 1996.
| Contents |
| Overview |
| Applications |
| Technology |
| References |
| External links |
Overview
Cells sold today as polymer batteries have a different design from the older lithium-ion cells. Unlike lithium-ion cylindrical, or prismatic cells, which have a rigid metal case, polymer cells have a flexible, foil-type (polymer laminate) case, but they still contain organic solvent. The main difference between commercial polymer and lithium-ion cells is that in the latter the rigid case presses the electrodes and the separator onto each other, whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.
Since no metal battery cell casing is needed, the battery can be lighter and it can be specifically shaped to fit the device it will power. Because of the denser packaging without intercell spacing between cylindrical cells and the lack of metal casing, the energy density of Li-poly batteries is over 20% higher than that of a classical Li-ion battery and approximately three times better than nickel-cadmium (NiCd) and nickel metal hydride (NiMH) batteries.
The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. Overcharging a Li-poly battery will likely result in explosion and/or fire. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load.
Early in its development, lithium polymer technology had problems with internal resistance. Other challenges include longer charge times and slower maximum discharge rates compared to more mature technologies. Li-poly batteries typically require more than an hour for a full charge. Recent design improvements have increased maximum discharge currents from two times to 15 or even 30 times the cell capacity (discharge rate in amps, cell capacity in amp-hours). In March 2005 Toshiba announced a new design offering a much faster (about 1–3 minutes) rate of charge. These cells have yet to reach the market but should have a dramatic effect on the power tool and electric vehicle industries, and a major effect on consumer electronics.
When compared to the lithium-ion battery, Li-poly has a greater life cycle degradation rate. However, in recent years, manufacturers have been declaring upwards of 500 charge-discharge cycles before the capacity drops to 80% (see Sanyo). Another variant of Li-poly cells, the "thin film rechargeable lithium battery", has been shown to provide more than 10,000 cycles.
Applications
A rechargeable lithium polymer Nokia mobile phone battery.
A compelling advantage of Li-poly cells is that manufacturers can shape the battery almost however they please, which can be important to mobile phone manufacturers constantly working on smaller, thinner, and lighter phones. Another advantage of lithium polymer cells over nickel-cadmium and nickel metal hydride cells is that the rate of self-discharge is much lower.
Li-poly batteries are also gaining favor in the world of radio-controlled aircraft, where the advantages of both lower weight and greatly increased run times can be sufficient justification for the price. However, lithium polymer-specific chargers are required to avoid fire and explosion. Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts take special precautions to ensure their battery leads are properly connected and insulated. Specially designed electronic motor speed controls are used to prevent excessive discharge and subsequent battery damage. This is achieved using a low voltage cutoff (LVC) setting that is adjusted to maintain cell voltage at (typically) 3 V per cell.
Li-poly batteries are also gaining ground in PDAs (including iPhone) and laptop computers, such as Apple's MacBook and Lenovo's Thinkpad (Ultrabay Batteries), Dell (D-bay Batteries) and small digital music devices such as iPods and other MP3 players, as well as portable gaming devices like the Sony PSP or Nintendo's Game Boy Advance SP, where small form factors and energy density outweigh cost considerations.
These batteries may also power the next generation of battery electric vehicles. The cost of an electric car of this type is prohibitive, but proponents argue that with increased production, the cost of Li-poly batteries will go down.
Canadian company BionX supplied electric bicycle conversion kits that used brushless motors and nickel metal hydride batteries for some years, but in 2006, they introduced batteries that used lithium-ion technology. During 2007 Urban Mover and PowaCycle, both in the United Kingdom, introduced the first commercially available Li-poly powered electric bikes, as opposed to just supplying conversion kits.
Technology
There are currently two commercialized technologies, both lithium-ion-polymer (where "polymer" stands for "polymer electrolyte/separator") cells. These are collectively referred to as "polymer electrolyte batteries".
The idea is to use an ion-conducting polymer instead of the traditional combination of a microporous separator and a liquid electrolyte. This promises not only better safety, as polymer electrolytes do not ignite as easily, but also the possibility of making battery cells very thin, as they do not require pressure to "sandwich" cathode and anode together. Polymer electrolytes seal both electrodes together like a glue.
The design is: anode (Li or carbon-Li intercalation compound)/conducting polymer electrolyte-separator/cathode (LiCoO2 or LiMnO4)
Typical reaction:
★ Anode: carbon-Li(''x'') - ''x''Li+ - ''x''e−
★ Separator: Li+ conduction
★ Cathode: Li(1-''x'')CoO2 + ''x''Li+ + ''x''e−
Polymer electrolytes/separators can be solid polymers (e.g., polyethyleneoxide, PEO) plus LiPF6, or other conducting salts plus SiO2, or other fillers for better mechanical properties (such systems are not available commercially yet). Some manufacturers like Avestor are using metallic Li as the anode (these are the Lithium-metal-polymer batteries), whereas others wish to go with the proven safe carbon intercalation anode.
Both currently commercialized technologies use PVdF (a polymer) gelled with conventional solvents and salts, like EC/DMC/DEC. The difference between the two technologies is that one (Bellcore/Telcordia technology) uses LiMnO4 as the cathode, and the other the more conventional LiCoO2.
Other, more exotic (although not yet commercially available) Li-polymer batteries use a polymer cathode. For example, Moltech is developing a battery with a plastic conducting carbon-sulfur cathode. However, as of 2005 this technology seems to have had problems with self-discharge and manufacturing cost.
Yet another proposal is to use organic sulfur-containing compounds for the cathode in combination with an electrically conducting polymer such as polyaniline. This approach promises high power capability (i.e., low internal resistance) and high discharge capacity, but has problems with cycleability and cost.
References
External links
★ BatteryUniversity.com
★ World's First Electric Powered Paraglider - running on Lipo.
★ A sailplane with auxilary electric power, running on lipos.
★ Overcharging a lithium polymer battery
★ 2004.4.20 - [1] Altair Nanotechnologies Announces Initial Shipment of Lithium Titanate Spinel Electrode Nanomaterials
★ 2005.11.02 - A123Systems Launches New Higher-Power, Faster Recharging Li-Ion Battery Systems [2]
★ :2006.05.19 - Hybrid vehicle application note
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