BU-401a: Fast and Ultra-fast Chargers
Nowhere is fast-charging in higher demand than with the electric car. Recharging an EV in minutes replicates the convenience of filling up 50 liters (13 gallons) of gasoline into a tank that is capable of delivering 600kWh of energy. Such large storage of energy in an electrochemical system is difficult to fathom and a battery holding this capacity would weigh 6 tons. However, electric energy from a battery delivers far more efficient and cleaner propulsion than the internal combustion engine.
Charging an EV will always take longer than filling a tank with liquid fuel, and the battery will always deliver less energy per weight than fossil fuel. This ratio with current battery technology is roughly 1:100 in favor of fossil fuel. Read more about Net Calorific Value. Breaking the rule and forcing ultra-fast charging would cause undue stress to the battery and strain the power grid by dimming the city. When talking about ultra-fast charging we must remember that the battery is an electrochemical device that is sluggish and loses performance with use and aging. Charging a battery cannot be compared to filling a tank with fuel that contains 12,000Wh of calorific value per liter. Furthermore, while a fuel tank keeps its volumetric dimensions, a battery begins to fade by the time it leaves the factory.
Ultra-fast Chargers
Ultra-fast chargers have been around for many years. Most NiCd and specialty types of Li-ion batteries, can be charged at a very high rate up to 70 percent state-of-charge (SoC). At a rate of 10C (see What is the C-rate?) or 10 times the rated current, a 1A battery could theoretically be charged in six minutes, but there are limits. To apply an ultra-fast charge, the following conditions must be observed:
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The battery must be designed to accept an ultra-fast charge. Current handing poses limitation with many pack designs.
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Ultra-fast charging only applies during the first charge phase. The charge current must be lowered when the 70 percent state-of-charge threshold is reached.
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All cells in the pack must be balanced and in good condition. Older batteries with high internal resistance will heat up; they are no longer suitable for ultra-fast charging.
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Ultra-fast charging can only be done under moderate temperatures. Low temperature slows the chemical reaction, and energy that cannot be absorbed causes gassing and heat buildup.
- The charger must include temperature compensations and other safety provisions to halt the charge if the battery gets unduly stressed. Failure to heed to these conditions could cause rapid disintegration of the battery and fire.
An ultra-fast charger can be compared to a high-speed train that is capable to travel 300km per hour (188 mph) on a track built for it. The tracks, and not the machinery, govern the maximum speed. Adding power to a charger is relatively simple; the intelligence lies in assessing the condition of the battery and applying the right amount of maximum charge. A properly designed ultra-fast charger will lower the current when certain conditions occur. In essence, only newer batteries can be ultra-fast charged.
Do not ultra-fast charge batteries if possible and charge at a more moderate rate of 1C or less. (A maker of the 18650 Li-ion recommends 0.7C.) Makers of electric cars prefer if EV owners charge at an eight-hour or 16-hour charge, both of which are below 1C. The 30-minute charge with a three-phase 440V outlet charges the battery at above 1C and this method should only be used if no other option exists (1C is the current rating of a battery. A 1C charge or discharge of a battery rated at 1Ah is 1A.)
Figure 1 compares the cycle life of a lithium-ion battery when charged and discharged at 1C, 2C and 3C. A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting a decrease to 84 percent. A 2C accelerates capacity fade to 310mAh, representing a decrease to 47 percent, and with 3C the battery fails after only 360 cycles with 26 percent remaining capacity.
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Figure 1: Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge Charging and discharging Li-ion above 1C reduces service life. Use a slower charge and discharge if possible. This applies to most batteries. |
Although the battery performs best at a gentle rate of 1C and less, we must keep in mind that some applications require high charge and discharge rates, and the user must take shorter life expectation into account. If full cycles with rapid charge and discharge are the norm, consider using a larger battery. This will not only provide more reserve capacity but it will also lower the C-rate in that a given charge and discharge current is less intrusive on the larger pack. An analogy can be made with an underpowered engine pulling a large vehicle; the stress is too large and the engine will not last.
Comments
Thanks pakopako, just corrected that.
I have always found comparisons between fuel weight (like gasoline) and battery weight to be fraudulent. A gallon of gasoline contains around 33kWhrs of energy, but most of that is released in the form of heat (and light). The kinetic energy released is what powers the car and accounts for around 25% of the gasoline’s total energy (8 kWhrs). Range extending gas powered engines (as in the Chevy Volt) produce roughly this amount of juice per gallon (good for around 35 miles of driving). Gas may weigh less than a battery (which actually is not a fuel, but an energy storage container) but one cannot power a car from the fuel itself- to do that requires a very heavy gasoline engine, fuel tank, cooling and exhaust system, etc, etc. which can easily weigh over
1000 pounds. If one is worried about weight, then one needs to compare the weights of the entire propulsive systems required by the fuel being considered. Actually, weight is not as important as people think when regen is available, which all electric cars have.
Thanks, I enjoy BU articles to learn how things ACTUALLY work. But there’s a couple of errors here ... the graph is the wrong one, and “A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting an 84 percent decrease. ” should read “A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting a decrease to 84 percent. ” (It’s not an 84% decrease, it’s a 16% decrease).
U mean to say that battery life will increase if we use the slower charger than its capacity. I have 1200 mA battery and i am using 800 mA charger so can i use 350 mA charger for my battery ?
Unless I am totally off the mark, the description:
quote
Figure 1 compares the cycle life of a lithium-ion battery when charged and discharged at 1C, 2C and 3C. A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting a decrease to 84 percent. A 2C accelerates capacity fade to 310mAh, representing a decrease to 47 percent, and with 3C the battery fails after only 360 cycles with 26 percent remaining capacity.
endquote
does not match the figure.
The figure shows 4 plots (with no key!) and the cpacities start at around 1000mAh, not 650mAh
Andrew, thanks for pointing out the error. We had the wrong chart displayed and I have added the correct one.
Can i charge a 150mAh battery with a 420mA/4,2V charger?
@ANYONE: A charger that large for a battery that size would be considered an “ultra-Fast Charger.” Depending on the age of the cell and the particular chemistry, you may be able to get away with this a number of times. Eventually, your internal impedance of the cell will increase and could cause an excessive heat buildup within the cell (P=I ^2 * R) which, if not dissipated properly, could cause a breakdown of materials within the cell and a thermal event.
Also, rapid charge/discharge of standard lithium cells generates significant damage to the SEI layer within the cell (Wikipedia “SEI Layer”) which, when reforming, is an exothermic chemical process…not good. This could also create an unsafe thermal event condition.
In short: Don’t do it. If you have to, be VERY careful and put the cells in a fireproof/nomex bag designed to contain batteries if/when they catch fire…they eventually will.
I want to design ultra fast charger for my minor project…Which battery can I use for ultra charging?
Can you provide some other relevant information about it….
fast charging radically lowers the lifetime of batteries . this is ultimately a futile exercise in milking out the charge/minute efficiency of a system not yet ready to practically handle high speed charging on a retail industrial basis.
the bottom line is that our battery technology is not ready yet for fast charging.
major strides in battery tech are on the horizon, and when they arrive, they will truly usher in a revolution in electric vehicle production.
the first true revolution will be observed as small 2 stroke 50cc scooters go nearly extinct as that segment gets entirely replaced by electric 2 wheelers. this trend is already happening in china, but it has yet to take in the rest of the world. you will know the battery revolution has arrived when there aren’t any little gas mopeds around anymore at all, because the electric ones provide such superior performance that no factories can profiteably produce the small 2 stroke moped engines anymore.
very good
Does all this information also stand true to the “boom” of superfast charing that we are seeing in several smartphones these days or are they using different technology? I’m interested because considering that before starting to show loss of battery capacity, the lithium-ion batteries used will last a good 2-4 years (unless excessively charged all the time. Will the superfast charing introduced in models such as the One+ One or Nexus 6 mean that batteries will show a significantly shorter lifespan? Will the batteries start to heat up after being fast-charged for 1½ years? Are there safety mechanics that make sure they won’t overheat and cause potentially big issues?
How does Qualcomm’s Quick Charge 2.0 affect battery longevity?
Qualcomm’s had UL test and certify this product before being released. New flagship cell phones with this tech come with only this type of charger in the box. They assume that everybody will use the charger provided on the corresponding device. Have they developed a method that doesn’t significantly affect battery life when using it daily?
Does Qualcomm rely on users upgrading to a new device before the batteries get destroyed? Or have they modified the Li-Ion battery and/or charging tech so that the life of the battery is not drastically impacted?
The URL tab title reads: “Fats and Ultra-fast”