Lithium Polymer History Brief
09-18-2003, 09:01 AM
#1
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Lithium Polymer History Brief
The following is a brief history of Lithium battery technology from Fred Marks of FMA Direct and JJ Hong of Kokam.
Fred Marks:
[/i] Lithium Polymer batteries are a new generation of batteries. They are different from other batteries used for RC. In 1959 when I became involved in RC, we had only carbon-zinc batteries. Lead-acid batteries were used with a converter to generate 180 V for the tubes used in transmitters, but about all else was done with carbon zinc.
The first time I ever saw anything other than carbon zinc used in RC was when the great Walt Good came to a meet in the early 1960s with some extraordinary cells he had sourced via Johns Hopkins Applied Physics lab where he worked. The small Silver Cadmium cells were of great interest but far out of the reach of the average modeler.
Surplus wet Nickel Cadmium cells began to appear from the Nike missile program as they had to be replaced periodically and found good use for glow plug lighters. In 1962, I obtained my first Ni Cd button cells from the ABC Battery Company. In due time, cylindrical Ni Cd cells came on the market with General Electric and Gulton as the first mass producers. It wasn’t long until the Japanese acquired the technology and rapidly drove down the price of Ni Cds.
Ni Cd technology has seen steady if slow growth over the ensuing 40 years. Ni Mh became a new technology only in the early nineties and has seen growth a bit faster than Ni Cd. The primary attraction for Ni Mh was lighter weight and better environmental characteristics.
About 1980, Lithium Ion (Li Ion) cells began to see use for light duty, lightweight applications. Li Ion began to be modified for RC from retired cell phones and surplus only about two years ago. Li Ion cells can tolerate only modest discharge rates but found some use to power electric airplanes.
Lithium Polymer (Li Po) cells began to see use in 2001 in a small way. The “small way†was primarily in the form of the Kokam Engineering Co., Ltd. 145 mAh cell. [/i]
Fred Marks:
[/i] Lithium Polymer batteries are a new generation of batteries. They are different from other batteries used for RC. In 1959 when I became involved in RC, we had only carbon-zinc batteries. Lead-acid batteries were used with a converter to generate 180 V for the tubes used in transmitters, but about all else was done with carbon zinc.
The first time I ever saw anything other than carbon zinc used in RC was when the great Walt Good came to a meet in the early 1960s with some extraordinary cells he had sourced via Johns Hopkins Applied Physics lab where he worked. The small Silver Cadmium cells were of great interest but far out of the reach of the average modeler.
Surplus wet Nickel Cadmium cells began to appear from the Nike missile program as they had to be replaced periodically and found good use for glow plug lighters. In 1962, I obtained my first Ni Cd button cells from the ABC Battery Company. In due time, cylindrical Ni Cd cells came on the market with General Electric and Gulton as the first mass producers. It wasn’t long until the Japanese acquired the technology and rapidly drove down the price of Ni Cds.
Ni Cd technology has seen steady if slow growth over the ensuing 40 years. Ni Mh became a new technology only in the early nineties and has seen growth a bit faster than Ni Cd. The primary attraction for Ni Mh was lighter weight and better environmental characteristics.
About 1980, Lithium Ion (Li Ion) cells began to see use for light duty, lightweight applications. Li Ion began to be modified for RC from retired cell phones and surplus only about two years ago. Li Ion cells can tolerate only modest discharge rates but found some use to power electric airplanes.
Lithium Polymer (Li Po) cells began to see use in 2001 in a small way. The “small way†was primarily in the form of the Kokam Engineering Co., Ltd. 145 mAh cell. [/i]
09-18-2003, 09:02 AM
#2
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RE: Lithium Polymer History Brief
JJ Hong - President of Kokam
“Early in 1980, Motorola and Sony decided to apply lithium ion technology to the mobile phone to reduce weight and (improve) energy density even though there were safety issues as (there are) now. They developed (the) safety module, so called PCM (protection circuit module). Up to now there have been few accidents only from Li Ion.
Meanwhile Bellcore Lab in San Diego announced that they had developed the lithium polymer battery to increase energy density and safety by using plastic pouch packaging/stacking method (different than Kokam system) using (an) ion conductive separator named PVDF (poly vinyl di fluoride) which has (good) binding character at 100 degree C.
Sony/Toshiba/Panasonic/Samsung/Saft/Varta/Valence/Ultra-life/Polystar and perhaps 30 companies bought licenses to commercialize the Bellcore technology during the last 10 years. No one was successful due to the difficulties of mass production technology when using this technology. Everybody gave up or went bankrupt. Sony started a new method which modified conventional tech with PVDF material only, but closely related to winding technology. With this material (PVDF) it is very difficult to achieve high power drain due to the limit of ion conductive material itself.
Kokam, as well, evaluated Bellcore technology as an alternative but realized that it is not a practical technology for commercialization due to the processing difficulty. (Thus) Kokam decided to develop new technology with (assistance from) the Korean government (agency) named KIST (Korea Institute of Science and Technology).
I invented a new system which (permits Kokam) to make the battery easier without losing any performance over Li Ion and (provides) better safety. Kokam acquired patents all over the world and started to design the full process and equipments which are suitable to productionize the Kokam system. German and Chinese companies bought our license.
With the Kokam technology, we have successfully reached the 20C rate Li Po battery commercially first in the world. All electric solar car champions are using Kokam batteries in 2002/2003. Wound cells cannot achieve high discharge rates because of high current drain from the anode tab. Winding has (a) longer electrode which increases the internal resistance at high current draw.â€
“Early in 1980, Motorola and Sony decided to apply lithium ion technology to the mobile phone to reduce weight and (improve) energy density even though there were safety issues as (there are) now. They developed (the) safety module, so called PCM (protection circuit module). Up to now there have been few accidents only from Li Ion.
Meanwhile Bellcore Lab in San Diego announced that they had developed the lithium polymer battery to increase energy density and safety by using plastic pouch packaging/stacking method (different than Kokam system) using (an) ion conductive separator named PVDF (poly vinyl di fluoride) which has (good) binding character at 100 degree C.
Sony/Toshiba/Panasonic/Samsung/Saft/Varta/Valence/Ultra-life/Polystar and perhaps 30 companies bought licenses to commercialize the Bellcore technology during the last 10 years. No one was successful due to the difficulties of mass production technology when using this technology. Everybody gave up or went bankrupt. Sony started a new method which modified conventional tech with PVDF material only, but closely related to winding technology. With this material (PVDF) it is very difficult to achieve high power drain due to the limit of ion conductive material itself.
Kokam, as well, evaluated Bellcore technology as an alternative but realized that it is not a practical technology for commercialization due to the processing difficulty. (Thus) Kokam decided to develop new technology with (assistance from) the Korean government (agency) named KIST (Korea Institute of Science and Technology).
I invented a new system which (permits Kokam) to make the battery easier without losing any performance over Li Ion and (provides) better safety. Kokam acquired patents all over the world and started to design the full process and equipments which are suitable to productionize the Kokam system. German and Chinese companies bought our license.
With the Kokam technology, we have successfully reached the 20C rate Li Po battery commercially first in the world. All electric solar car champions are using Kokam batteries in 2002/2003. Wound cells cannot achieve high discharge rates because of high current drain from the anode tab. Winding has (a) longer electrode which increases the internal resistance at high current draw.â€
09-18-2003, 11:52 AM
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RE: Lithium Polymer History Brief
Very interesting Mr. Marks and Mr. Hong! It seems that you are the persons who might be able to answer a question for me.
Do you know the failure profile for LiPo batteries when they are subjected to either an over current, or over voltage situation during recharge? Does the cell temperature rise at a slow rate for a period of time, or does it remain stable and then rise suddenly when the failure occurs?
Later;
D.W.
Do you know the failure profile for LiPo batteries when they are subjected to either an over current, or over voltage situation during recharge? Does the cell temperature rise at a slow rate for a period of time, or does it remain stable and then rise suddenly when the failure occurs?
Later;
D.W.
09-25-2003, 02:23 PM
#4
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Thread Starter
RE: Lithium Polymer History Brief
D.W.
Both of these guys have been traveling and have not been able to answer your questions. I expect that they will return soon so please be patient.
Regards.
Both of these guys have been traveling and have not been able to answer your questions. I expect that they will return soon so please be patient.
Regards.
09-25-2003, 02:25 PM
#5
Senior Member
Thread Starter
More History...
In June 2002, FMA, Inc. and Kokam Engineering Co., Ltd. signed an exclusive agreement for FMA to serve as the agent for Kokam in North and South America. In October 2002, FMA, Inc. began actively shipping Kokam Lithium Polymer (Li Po) cells.
At this time, FMA Direct has been actively promoting the use of Li Po cells and packs for a little over a year with gratifying results. In the past year, Li Po technology has advanced further than Ni Cd technology advanced in nearly forty years. In 2002, the standard Kokam cell was capable of continuous operation at three to four times the multiple of capacity (3-4C) with 5C the upper limit. In the past six months, Kokam has introduced and FMA now has on the market cells capable of sustaining up to 20C continuously with loss of but 12% capacity.
Detailed performance data will be presented later. With the introduction of this new level of technology to the power tool and recreation industry, there is real confidence that cell cost for RC will come down.
FMA has considered Li Po batteries in the system context from the beginning. First, Li Po batteries require a different charger than other chemistries. The fact that each cell is 3.7V means that the pack and ESCs need to be designed and sized differently. It was desired to make it as easy as possible for the Ni Cd/Ni Mh user to make the transition to Li Po as painlessly as possible. By providing all the elements needed, it is hoped that Li Po will continue the rapid rate of acceptance and success seen to date. Finally, there are unique safety and operating ground rules that must be observed.
At this time, FMA Direct has been actively promoting the use of Li Po cells and packs for a little over a year with gratifying results. In the past year, Li Po technology has advanced further than Ni Cd technology advanced in nearly forty years. In 2002, the standard Kokam cell was capable of continuous operation at three to four times the multiple of capacity (3-4C) with 5C the upper limit. In the past six months, Kokam has introduced and FMA now has on the market cells capable of sustaining up to 20C continuously with loss of but 12% capacity.
Detailed performance data will be presented later. With the introduction of this new level of technology to the power tool and recreation industry, there is real confidence that cell cost for RC will come down.
FMA has considered Li Po batteries in the system context from the beginning. First, Li Po batteries require a different charger than other chemistries. The fact that each cell is 3.7V means that the pack and ESCs need to be designed and sized differently. It was desired to make it as easy as possible for the Ni Cd/Ni Mh user to make the transition to Li Po as painlessly as possible. By providing all the elements needed, it is hoped that Li Po will continue the rapid rate of acceptance and success seen to date. Finally, there are unique safety and operating ground rules that must be observed.
09-30-2003, 01:39 PM
#6
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Thread Starter
Charging
D.W.,
Here is your answer from Fred Marks as he tries to solve his posting access issues.
Li Po cells are charged differently than NiCd/NiMh and all other chemistries except for Li Ion. The charge schedule is different and you cannot use a charger not meant for either Li Ion or Lithium Polymer cells.
The charge schedule is easily controlled. The proper charger limits current to 1C, where C=cell capacity, e.g., 145 mAh. As cell voltage increases, so must charge voltage in order to force current through the cell until the voltage applied to the cell reaches a maximum of 4.235 V. As cell voltage rises to 4.235V, current approaches zero. When charge current falls to 0.1 C, the cell is full.
The preferred charge rate is 1C such that the cell can be charged to 90 % capacity in one hour if the charger is designed to hold charge current at 1C but without exceeding 4.235 V/cell maximum charge voltage. Lower charge rates are acceptable if longer charge time is tolerable. Li Po cells cannot be charged at high rates such as 4C. The charge algorithm below shows that almost nothing is gained by charging at a rate higher than 2C.
The above chart is very important, so study it carefully. The following charging guidelines emanate from the chart:
- Never exceed a 2C charge rate and accept that cycle life will be maximized by charging at 1C.
- Never exceed a maximum charge voltage of 4.235 VDC.
Appropriate chargers are available from FMA Direct. Charger specifications may be viewed at the Kokam/FMA Web site. In addition, there are numerous vendors who sell appropriate chargers.
Avoid the use of chargers that automatically determine cell count. Li Po cells are nominally 3.7 V under load. Cell voltage at full charge is 4.235V. Two fully charged cells, for example, output 8.4V. Three partially discharged cells may be 2.8V/cell X 3 = 8.4V. If two nearly charged cells are put on charge to "top them off", the charger may sense them as three discharged cells and set the charge for three cells. The two cells will receive over voltage and definitely be damaged. It is the user,s responsibility to ensure that cell count is properly selected.
All high energy density cells used for RC, including NiCd, NiMH, Pb Acid, as well as Li Po, pose an electrical hazard. If wiring or interconnects are poor or become shorted, these cells are capable of delivering such high currents that the wiring can burn like a filament. Should the pack or wiring be in contact with flammable material, a fire will result.
Under conditions of abuse or error, Lithium cells can vent with flames. During charge, applying a charge voltage of more than six volts per cell for a period of 20 minutes can potentially cause venting and might cause flames depending on current setting.
Users of all high energy density cells, including Li Po cells, must follow strict precautions when handling and charging batteries. The precautions are listed on the next page, and are also provided on the FMA Direct Web site.
Here is your answer from Fred Marks as he tries to solve his posting access issues.
Li Po cells are charged differently than NiCd/NiMh and all other chemistries except for Li Ion. The charge schedule is different and you cannot use a charger not meant for either Li Ion or Lithium Polymer cells.
The charge schedule is easily controlled. The proper charger limits current to 1C, where C=cell capacity, e.g., 145 mAh. As cell voltage increases, so must charge voltage in order to force current through the cell until the voltage applied to the cell reaches a maximum of 4.235 V. As cell voltage rises to 4.235V, current approaches zero. When charge current falls to 0.1 C, the cell is full.
The preferred charge rate is 1C such that the cell can be charged to 90 % capacity in one hour if the charger is designed to hold charge current at 1C but without exceeding 4.235 V/cell maximum charge voltage. Lower charge rates are acceptable if longer charge time is tolerable. Li Po cells cannot be charged at high rates such as 4C. The charge algorithm below shows that almost nothing is gained by charging at a rate higher than 2C.
The above chart is very important, so study it carefully. The following charging guidelines emanate from the chart:
- Never exceed a 2C charge rate and accept that cycle life will be maximized by charging at 1C.
- Never exceed a maximum charge voltage of 4.235 VDC.
Appropriate chargers are available from FMA Direct. Charger specifications may be viewed at the Kokam/FMA Web site. In addition, there are numerous vendors who sell appropriate chargers.
Avoid the use of chargers that automatically determine cell count. Li Po cells are nominally 3.7 V under load. Cell voltage at full charge is 4.235V. Two fully charged cells, for example, output 8.4V. Three partially discharged cells may be 2.8V/cell X 3 = 8.4V. If two nearly charged cells are put on charge to "top them off", the charger may sense them as three discharged cells and set the charge for three cells. The two cells will receive over voltage and definitely be damaged. It is the user,s responsibility to ensure that cell count is properly selected.
All high energy density cells used for RC, including NiCd, NiMH, Pb Acid, as well as Li Po, pose an electrical hazard. If wiring or interconnects are poor or become shorted, these cells are capable of delivering such high currents that the wiring can burn like a filament. Should the pack or wiring be in contact with flammable material, a fire will result.
Under conditions of abuse or error, Lithium cells can vent with flames. During charge, applying a charge voltage of more than six volts per cell for a period of 20 minutes can potentially cause venting and might cause flames depending on current setting.
Users of all high energy density cells, including Li Po cells, must follow strict precautions when handling and charging batteries. The precautions are listed on the next page, and are also provided on the FMA Direct Web site.
09-30-2003, 01:41 PM
#7
Senior Member
Thread Starter
OverVoltage
Charging must be done such that no damage to life or property can occur if a short in wiring, cells or venting with flames occurs. All lithium cells have the potential for "venting with flames" if mishandled. This is because lithium is a metal that, under abuse, can ignite and burn. Aluminum does also. Finely powdered aluminum is the "fuel" used in solid rocket motors. It takes a very strong ignitor to fire a solid rocket motor.
Li Po cells, as with any rechargeable battery, react to overcharge. Ni Cd and NI MH cells react to over current; Li Po reacts to over voltage. This is why the charge algorithm show above is carefully controlled to 4.2V/cell. The cell has some tolerance; it is not going to balloon and flame without a lot of provocation. In the above example, the charge voltage was set at a very high level; 6.8V right from the start. The cell did not react at all for 10 minutes, then began to swell. A plot of maximum dimension would follow the temperature curve as gasses that rise in temperature are generated. Those gasses, for any cell, come from break-down of the electrolytic as it begins to be vaporized. It took almost an hour of the overcharge before temperature and pressure rose enough to rupture the envelope.
NOTE: If the envelope is not ruptured to let oxygen in to provide oxidation for the lithium, Ignition of the Li does not occur. The safety precautions listed below include the warning not to charge batteries unattended. The cell under test held out for almost an hour. Leaving any battery on fast charge for an hour without checking it is a dereliction of responsibility. If a cell is found to be swelling during charge, remove the charge current immediately. Based on the precautions below, it must be assumed that the cell is in a safe charging station. Allow the cell to cool before taking any action. You can recognize that rupture of the cell could allow hot gasses and electrolytic to spew.
Once the cell has cooled handle it as a fully charged cell with full energy available. This means you do not "poke a hole in it" in preparation for disposal. First, the cell must be discharged at a reasonable rate. This can be done with the electric motor or a length of wire with clip leads can and a load such as a resistor can be used. There is no hurry about this; a slow, complete discharge to zero volts while still under load is a safe way to do the job. Once the cell is depleted, a small hole may be *****ed in the envelope to allow salt water to enter the envelope, and the cell dropped into salt water for a few hours. After that, the cell may be disposed of in the trash.
An added caution is due regarding shorting any high energy density battery. Li Po, if shorted can heat to the point that the envelope may be ruptured. When oxygen hits the lithium, it may ignite the Li if the battery is highly charged. The wiring harness, if shorted, can glow like a filament and cause ignition of flammable materials.
Li Po cells, as with any rechargeable battery, react to overcharge. Ni Cd and NI MH cells react to over current; Li Po reacts to over voltage. This is why the charge algorithm show above is carefully controlled to 4.2V/cell. The cell has some tolerance; it is not going to balloon and flame without a lot of provocation. In the above example, the charge voltage was set at a very high level; 6.8V right from the start. The cell did not react at all for 10 minutes, then began to swell. A plot of maximum dimension would follow the temperature curve as gasses that rise in temperature are generated. Those gasses, for any cell, come from break-down of the electrolytic as it begins to be vaporized. It took almost an hour of the overcharge before temperature and pressure rose enough to rupture the envelope.
NOTE: If the envelope is not ruptured to let oxygen in to provide oxidation for the lithium, Ignition of the Li does not occur. The safety precautions listed below include the warning not to charge batteries unattended. The cell under test held out for almost an hour. Leaving any battery on fast charge for an hour without checking it is a dereliction of responsibility. If a cell is found to be swelling during charge, remove the charge current immediately. Based on the precautions below, it must be assumed that the cell is in a safe charging station. Allow the cell to cool before taking any action. You can recognize that rupture of the cell could allow hot gasses and electrolytic to spew.
Once the cell has cooled handle it as a fully charged cell with full energy available. This means you do not "poke a hole in it" in preparation for disposal. First, the cell must be discharged at a reasonable rate. This can be done with the electric motor or a length of wire with clip leads can and a load such as a resistor can be used. There is no hurry about this; a slow, complete discharge to zero volts while still under load is a safe way to do the job. Once the cell is depleted, a small hole may be *****ed in the envelope to allow salt water to enter the envelope, and the cell dropped into salt water for a few hours. After that, the cell may be disposed of in the trash.
An added caution is due regarding shorting any high energy density battery. Li Po, if shorted can heat to the point that the envelope may be ruptured. When oxygen hits the lithium, it may ignite the Li if the battery is highly charged. The wiring harness, if shorted, can glow like a filament and cause ignition of flammable materials.
10-01-2003, 08:59 AM
#9
Senior Member
Thread Starter
RE: Lithium Polymer History Brief
Mr HC,
Assuming that you start with cells of equal lot and charge, it appears to be safe because they tend to balance each other out.
I have not had a problem charging cells in either series or parallel or a combination of both. The problems arise from excessive discharge (over stressing) of the cells and overcharging.
One way to overcharge them is to select the wrong voltage setting on the charger. Another, and more hidden way, is to not detect a cell failure so, for example, a 3-cell pack looks like a 2-cell pack with one cell shorted.
For now, sanity checking the pack voltage is a needed practice. The new generation chargers and pack designs that cross check measured pack voltage with settings and also tap into the pack's mid-cells will provide additional safety.
Finally, a visual check of the pack for cell emissions is also a good idea. Lithium looks brownish and has a distinct smell to it.
Regards.
Assuming that you start with cells of equal lot and charge, it appears to be safe because they tend to balance each other out.
I have not had a problem charging cells in either series or parallel or a combination of both. The problems arise from excessive discharge (over stressing) of the cells and overcharging.
One way to overcharge them is to select the wrong voltage setting on the charger. Another, and more hidden way, is to not detect a cell failure so, for example, a 3-cell pack looks like a 2-cell pack with one cell shorted.
For now, sanity checking the pack voltage is a needed practice. The new generation chargers and pack designs that cross check measured pack voltage with settings and also tap into the pack's mid-cells will provide additional safety.
Finally, a visual check of the pack for cell emissions is also a good idea. Lithium looks brownish and has a distinct smell to it.
Regards.
10-01-2003, 11:06 AM
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RE: Lithium Polymer History Brief
I appreciate your information very much! It appears that using cell temperature may not be a useful method for avoiding over charging. According to the second chart, temperature remains fairly constant well after the time damage (bulge) occurs. It might, however, be possible to avoid cell rupture and fires with a temperature sensor.
Later;
D.W.
Later;
D.W.
