BU-401a: Fast and Ultra-fast Chargers

Learn about the good and bad on ultra-fast charging

Ultra-fast Chargers

Nowhere is ultra-fast charging in bigger demand than with the electric vehicle. Recharging an EV in minutes replicates the convenience of filling 50 liters (13 gallons) of fuel into a tank that delivers 600kWh of energy. Such large energy storage in an electrochemical device is not practical as a battery with such a capacity would weigh 6 tons. Most Li-ion only produces about 150Wh per kg; the energy from fossil fuel is roughly 100 times higher. (See BU-1007: Net Calorific Value).

Charging an EV will always take longer than filling a tank, and the battery will always deliver less energy per weight than fossil fuel. Breaking the rule of law and forcing ultra-fast charging adds stress, even if the battery is designed for such a purpose. We must keep in mind that a battery is sluggish in nature. Like an aging man, its physical condition becomes less ideal with use and age. So is the ability to fast-charge.

One assumes that all charge energy goes into the battery, whether charged slowly, rapidly or by ultra-fast method. Batteries are nonlinear devices and most chemistry accepts a fast charge from empty up to about 50% state-of-charge (SoC) with little losses. NiCd does best and suffers the least amount of strain. Stresses occur in the second half of the charge cycle towards top charge when acceptance of lithium ions in the anode of Li-ion becomes labored. An analogy is irate drivers fighting for the last parking spot in a shopping mall to catch a sale special.

Applying an ultra-fast charge when the battery is empty and then tapering off the current when reaching 50% SoC and higher is called step charging. The laptop industry has been applying step charging for many years. The charge currents must harmonize with the battery type as different battery systems have dissimilar requirements in charge acceptance. Battery manufacturers do not publish charge rates as a function of SoC. Much of this is proprietary information.

Research companies claim to achieve benefits with pulse-charging Li-ion instead applying the regular CCCV charge as described in BU-409: Charging Lithium-ion. The scientific community is skeptical to alternative charging and takes the “wait-and-see” approach.

As our bodies work best at 37ºC (98ºF), so does the transport mechanism improve when a battery is warm. Modern EVs will enable the “pre-charge” feature to prepare the battery temperature for the pending fast-charge while driving. (See also BU-410: Charging at High and Low Temperatures.)

Whether you own an EV, e-bike, a flying object, a portable device or a hobby gadget, the following conditions must be respected when charging a battery the ultra-fast way:

  1. The battery must be designed to accept an ultra-fast charge and must be in good condition. Li-ion can be designed for a fast charge of 10-minutes or so but the specific energy of such a cell will be low.
  2. Ultra-fast charging only applies during the first charge phase. The charge current should be lowered after the battery reaches 70 percent state-of-charge (SoC).
  3. All cells in the pack must be balanced and have ultra-low resistance. Aging cells often diverge in capacity and resistance, causing mismatch and undue stress on weaker cells.
  4. Ultra-fast charging can only be done under moderate temperatures, as low temperature slows the chemical reaction. Unused energy turns into gassing, metal-plating and heat.

An ultra-fast charger can be compared to a high-speed train (Figure 1) traveling at 300km per hour (188 mph). Increasing power is relatively simple. It’s the track that governs the permissible speed of a train and not the machinery. In the same manner, the condition of the battery dictates the charging speed.


High Speed Train
Figure 1: Ultra-fast charging can be compared to a high-speed train.
Powerful machinery is easy to build, but it’s the track that limits the speed.
 

A well-designed ultra-fast charger evaluates the condition of the “chemical battery” and makes adjustments according to the ability to receive charge. The charger should also include temperature compensations and other safety features to lower the charge current when certain conditions exist and halt the charge if the battery is under undue stress.

A “smart” battery running on SMBus or other protocols is responsible for the charge current. The system observes the battery condition and lowers or discontinues the charge if an anomaly occurs. Common irregularities are cell imbalance or the need for calibration. Some “smart” batteries stop functioning if the error is not corrected.
 

Limitations to ultra-fast charging Li-ion

The maximum charge current a Li-ion can accept is governed by cell design, and not the cathode material, as is commonly assumed. The goal is to avoid lithium-plating on the anode and to keep the temperature under control. A thin anode with high porosity and small graphite particles enables ultra-fast charging because of the large surface area. Power Cells can be charged and discharged at high currents, but the energy density is low. Energy Cells, in comparison, have a thicker anode and lower porosity and the charge rate should 1C or less. Some hybrid Cells in NCA (nickel-cobalt-aluminum) can be charged above 1C with only moderate stress.

Apply the ultra-fast charge only when necessary. A well-designed ultra-fast charger should have charge-time selection to give the user the option to choose the least stressful charge for the time allotted. Figure 2 compares the cycle life of a typical lithium-ion battery when charged and discharged at 1C, 2C and 3C rates. The longevity can further be prolonged by charging and discharging below 1C; 0.8C is the recommended rate.
 

Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge
Figure 2: 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 rule applies to most batteries.


Lithium deposition

Lithium deposition forms if the charge rate exceeds the ability by which lithium can be intercalated into the negative graphite electrode of Li-ion. A film of metallic lithium forms on the negative electrode that spreads uniformly over the host material or gravitates to one region in planar, mossy or dendritic format. The dendritic form is of concern because it may increase self-discharge that in extreme case can create a short and lead to venting with flame.

Environmental conditions affect the deposition of lithium as follows:

  1. Lithium deposit grows when Li-ion is ultra-fast charged at low temperature
  2. Deposition develops if Li-ion is ultra-fast charged beyond a given state-of-charge level 
  3. The buildup is also said to increase as Li-ion cells age due to raised internal resistance. 

Consumers demand fast charging at low temperature and this is especially critical with the electric vehicle. Solutions include special electrolyte additives and solvents, optimal negative to positive electrode ratios, and special cell design.

The question is often asked; “Why do ultra-fast chargers charge a battery to only 70 and 80 percent?” This may be done on purpose to reduce stress, but is also caused naturally by a lag between voltage and state-of-charge that amplifies the faster the battery is being charged. This can be compared to a rubber band lifting a heavy weight. The larger the weight, the wider the lag becomes. The ultra-fast charge forces the voltage to the 4.20V/cell ceiling quickly while the battery is only partially charged. Full charge will occur at a slower pace as part of saturation.

Lithium Titanate may be the exception and allow ultra-fast charging without undue stress. This feature will likely be used in future EVs; however, Li-titanate has a lower specific energy than cobalt-blended Li-ion and the battery is expensive. (See BU-205: Types of Lithium-ion) 

Nickel-cadmium is another battery chemistry that can be charged in minutes to 70 percent state-of-charge. Like with most batteries, the charge acceptance drops towards full-charge and the charge current must be reduced.

All ultra-fast methods need for high power. An ultra-fast EV charge station draws the equivalent electrical power of five households. Charging a fleet of EVs could dim a city.
 

Summary

All batteries perform best at room temperature and with a moderate charge and discharge. Such a sheltered life style does not always reflect real world situations where a compact pack must be charged quickly and deliver high currents. Such typical applications are drones and remote control devices for hobbyist. Expect a short cycle life when a small pack must give all it has.

If fast charging and high load requirements are prerequisites, the rugged Power Cell is ideal; however, this increases battery size and weight. An analogy is choosing a heavy diesel engine to run a large truck instead of a souped-up engine designed for a sports car. The big diesel will outlive the light engine even if both have identical horsepower. Going heavier will be more economical in the long run. Table 3 summarizes the charge characteristics of lead, nickel and lithium-based batteries.
 

Type Chemistry C rate Time Temperatures Charge termination
Slow charger NiCd
Lead acid		 0.1C 14h 0ºC to 45ºC
(32ºF to 113ºF)		 Continuous low charge or fixed timer. Subject to overcharge. Remove battery when charged.
Rapid charger NiCd, NiMH,
Li-ion		 0.3-0.5C 3-6h 10ºC to 45ºC
(50ºF to 113ºF)		 Senses battery by voltage, current, temperature and time-out timer.
Fast charger NiCd, NiMH,
Li-ion		 1C 1h+ 10ºC to 45ºC
(50ºF to 113ºF)		 Same as a rapid charger with faster service.
Ultra-fast charger Li-ion, NiCd, NiMH 1-10C 10-60 minutes 10ºC to 45ºC
(50ºF to 113ºF)		 Applies ultra-fast charge to 70% SoC; limited to specialty batteries.

Table 3: Charger characteristics. Each chemistry uses a unique charge termination.
 

Simple Guidelines Regarding Chargers


Last Updated 2019-04-12
 

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Comments (49)

On June 13, 2012 at 7:19am
pakopako wrote:

The URL tab title reads: “Fats and Ultra-fast”

On June 13, 2012 at 9:47am
Cadex Electronics Inc. wrote:

Thanks pakopako, just corrected that.

On July 11, 2012 at 1:38pm
ramon leigh wrote:

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.

On September 1, 2012 at 3:18pm
Jullian wrote:

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).

On September 7, 2012 at 11:25pm
Jignesh Patel wrote:

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 ?

On October 4, 2012 at 3:33am
Andrew Ashton wrote:

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

On October 5, 2012 at 9:19am
Cadex Electronics Inc. wrote:

Andrew, thanks for pointing out the error. We had the wrong chart displayed and I have added the correct one.

On December 26, 2012 at 7:33am
ANYONE wrote:

Can i charge a 150mAh battery with a 420mA/4,2V charger?

On February 6, 2013 at 3:18pm
Walker wrote:

@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.

On August 27, 2013 at 8:32am
Pooran Chand wrote:

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….

On August 6, 2014 at 2:13pm
teslark wrote:

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.

On September 14, 2014 at 4:21pm
mahmood wrote:

very good

On October 15, 2014 at 3:14pm
akselic wrote:

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?

On November 19, 2014 at 12:10pm
Masheen wrote:

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?

On January 8, 2015 at 4:46am
Bunu Zahra wrote:

What are the effects of fast and slow charging to a battery

On January 21, 2015 at 7:04am
Dave wrote:

I second Masheen’s question. Any insight on how Qualcomm’s Quick Charge 2.0 will effect battery longevity?

On February 3, 2015 at 6:09am
ravishankar b.k. wrote:

I am sure it will be helpful.

On February 3, 2015 at 6:11am
ravishankar b.k. wrote:

I sure it will be a great help.

On February 3, 2015 at 6:18am
Danielus wrote:

http://www.androidauthority.com/quick-charge-explained-563838/

Apparently, basically this “technology” does is provide more amp/power by the charger, so I think the cycles of the battery and capacity is also reduced over time. Too good to be true, it’s just marketing…

On March 1, 2015 at 12:37pm
Masheen wrote:

I think we can deduce that the batteries in our phones only get a numbered amount of cycles in their life, and the rapid charging technology would only impact its life by speeding up these limited cycles.

There is sufficient information supporting the technology behind the quick charge which states that the battery’s temperature is carefully monitored by software and overheating will not be a cause of battery degradation.

A good comparison is: just like 4G allows us to use our data plans faster, Quick-Charge allows us to use our battery’s cycles faster. However, if we stick to one cycle per day, it will be no different than the slower chargers in terms of battery health.

On March 21, 2015 at 8:01am
Troy Giorshev wrote:

Great article, typo on the third last point under simple guidelines.  “Foe nickel” is written instead of “for nickel”

On April 11, 2015 at 9:13am
Nick wrote:

Has anyone heard of the silex chreos? How on earth is that possible? Are they using polymer batteries?

On October 4, 2015 at 5:47pm
Kristian wrote:

My guess is - super capacitor in conjunction with a battery pack. Use the kV charger (say at 11 kV) to dump a huge amount of power into the super capacitor. Advantage is very fast charge and due to low internal resistance - a low heat generation (and higher efficiency). Disadvantage with a super capacitor is that it eventually looses its charge over time - so you cant leave the car standing for a month - where as batteries will hold their charge.

Put both together and you have a solution with a small weight/space penalty.

On October 25, 2015 at 5:00pm
DOROTHEA SCHALL wrote:

Would like to try superb FASTER CHARGER

On November 1, 2015 at 3:35pm
anthony m velleca wrote:

I want to try it

On December 19, 2015 at 10:47am
Bill Moore wrote:

What would be required to build a fast-charge 36 or 48V electric bicycle battery in terms of not only the cells used, presumably li-ion, but also the BMS and the battery charger?

On February 19, 2016 at 1:19pm
Jeff wrote:

More an more phones are coming with Qualcomm Quick Charge 2.0 or 3.0 capability.  All I want to know is, will using Quick Charge 2.0 technology with a compatible device signficanly lower battery life/capacity over time compared to using the standard, slower charges to charge the device?  And is this answer a theoretical answer or an answer based on actual tests?

On March 26, 2016 at 9:17pm
Manaf wrote:

Would you please suggest Fast charger for LTO battery bank ( 580V 150Ah) ?

On May 24, 2016 at 12:12pm
Matteo Croce wrote:

Does this apply to Qualcomm Quick Charge too?

On June 10, 2016 at 5:00am
John wrote:

cubic foot of gasoline and a cu foot of battery. The gasoline contains 4 times as much energy storage. A vehicle using an internal combustion engines is approx 20% efficient. That means 80% of the energy in the tank is wasted. As modern electric motors are 90-95% efficient this puts a whole new angle on electric vehicles. They then become as equal to gasoline vehicles, or even better.  Add supercapacitors and regen braking and it is easy to see that EVs win.

On October 14, 2016 at 5:56am
Robert Gornall wrote:

I curious with the current state of battery technology why do all the current technology’s sufferer from fade, after all 500 charge discharge cycles is a very short life especially in the life of lets say, battery’s used in electric cars just how long can we expect a set of cells to last in a car.

as a final point if battery fade is so prevalent in all battery technology’s, is no way to overcome this problem at either the design or manufacturing stage.

finally what would the best battery technology to use to get the best of all worlds and what is the future of battery technology as we know it and where do we go from here.

R.C.Gornall

On October 21, 2016 at 3:39pm
Jesse wrote:

So i should avoid fast charging my phone? the charger
Delivers 5v @ 2amps
Delivers 9v @ 1.8 amps
Delivers 12v @ 1.5 amps
And to prolong the battery it i should slow charge my phone at 5v 1 amps?

On November 1, 2016 at 12:51pm
Gordon wrote:

Samsung just exceeded the Li ion battery physics/chemistry on storage capacity per volume and rate of charge in its latest smartphone.  Oops!

Where we go from here is Sodium Ion.

On April 19, 2017 at 12:34am
Philipp wrote:

Is there some similar Graph for values below 1C? I would be very interested in it as it is relevant for todays smartphones ...

On May 3, 2017 at 1:35am
zhaodaqin wrote:

Why 70% SOC stop ultra-fast charging? What will happen if keeping ultra-fast charging after 70% SOC? Have you got some data to verify this conclusion?

On September 24, 2017 at 8:40pm
Mr.Phil wrote:

I bought my Nexus 6 end of 2014. I mostly use a Q charger because it happens to be on the table next to my chair. I use the factory fast charger when the phone hits 15%. So, the phone is about 3 years old and still on the original battery. Not really sure how long a charge lasts but i still get by with it. Don’t think I have ever had a cell phone battery last this long. For me they got the charging/battery combination right.

On November 24, 2017 at 5:11pm
Kwabena Afrani wrote:

If fast charging a smartphone shortens life span of the battery, why should the manufacturers include only fast charging chargers? For instance, the recent galaxy note 8 supplied fast chargers.Both the charger & the wireless one are fast ones.

On November 30, 2017 at 7:58am
James Tomlinson wrote:

I have a Samsung S8. Look at the charger. It says “Adaptive Fast Charger”. I believe it will operate at the higher charge current/voltage up to a certain percent charge, then switch modes to a slower charge rate. Most of the makes describe “0 to 50% in 30 minutes”, or something like that. If you plug in a phone with 90% charge, it does NOT take 6 minutes to finish charging. It will probably take something like 15-20 minutes. It adapts and varies the charge rate based on the state of charge.

On April 13, 2018 at 3:34am
Bhavdipsinh Rathod wrote:

Hi,
I am using Li-SoCl2 battery (non-rechargeable) in our project whose nominal voltage 3.6V.
I received that battery and checked the voltage using DMM which is 3.6V.
Is it ok or It should be around 4.2V? (like in Li batteries)
Or doesn’t If fully charged?

Thanks for your support.
BR,
Bhavdipsinh

On April 13, 2018 at 3:36am
Bhavdipsinh Rathod wrote:

Hi,

I am searching for battery with fast charging rate (4C or 5C). Can you suggest the battery types or manufacturer reference?

Thanks
Bhavdipsinh

On April 18, 2018 at 9:54am
Thomas Earle Moore wrote:

The rustic analogies are helpful, but a University really should provide more technical details on this subject. Where is the nonlinearity in a battery, and how does it’s internal impedance vary with temperature and state of charge or other factors? What is the differential equation for charging/discharging and what do the solutions look like for representative cases?

Also, some topical discussion of practical implications would be appreciated. For example, current fast chargers may be reaching practical limits in view of the amount of cooling capacity that is normally available in a vehicle. What, then are the prospects for future systems suggesting power levels up to 350 kW and higher, for charging batteries of 100 kWh capacity? Are we really going to see 15 min charging times to 80%? You are in a position to shed quite a bit of light on these issues and I recommend that you do, by providing some practical engineering considerations.

On April 18, 2018 at 12:07pm
Thomas Earle Moore wrote:

I mistakenly clicked on the link to stop notifications, so I’m starting them up again with this post.

On October 27, 2018 at 11:27am
Dan Smith wrote:

Thank you for maintaining such an informative web site.

You seem to be suggesting that fast charging tends to reduce battery life.

My Plug-in Hybrid came with a level 1 charger, but the manufacturer indicates that Level 2 charging is preferable for maximum battery life, without explaining why.  Is it possible to damage a battery by charging it too slowly?  Are there conditions where charging faster help to improve battery life?

On December 15, 2018 at 3:43am
Eske Rahn wrote:

Would it be possible to offer us a variant of figure two, where the discharge is fixed at say 1C, and only the charge differs?

This would make it easier to see the effect of different charging patterns for the same usage pattern.

Great site BTW smile

On August 4, 2019 at 7:30am
Dan at OCoil.com wrote:

Thanks for the great summary. We have a solution is designed to keep the charging and discharging rates below 0.5C - while still allowing for reenergizing in less than 5 minutes.

Dan at OCoil.com

U.S. Patent Number 10355254 OCoil.com

OCoil.com
https://ocoil.com/blog/f/imagine-an-electric-vehicle-that-costs-thousands-of-dollars-less

On August 20, 2019 at 9:51pm
Mike Thielvoldt wrote:

If the charging current is applied for only a short duration, will a higher charging current be possible before Lithium deposition occurs? 

As an example, imagine a small EV like an electric skateboard, where the motor delivers a charging current to the battery during braking that would be high enough to cause plating if it were applied for minutes, but this current is only delivered for 10 seconds or less.  Is Lithium plating on the anode still a given, or does the electrolyte have some ability to momentarily hold Lithium ions and delay the onset of Lithium deposition for a few seconds?

- long-time fan of BU.

On September 2, 2019 at 9:29am
Abdel Rahman Elsayed wrote:

I love your analogies! Great job!

“Stresses occur in the second half of the charge cycle towards top charge when acceptance of lithium ions in the anode of Li-ion becomes labored. An analogy is irate drivers fighting for the last parking spot in a shopping mall to catch a sale special.”

On November 15, 2019 at 8:17am
Daniel Mitchell wrote:

Someone mentioned the energy/weight comparison of fuel vs battery.  Another important aspect of the combustion engine is: the heat byproduct is used in the HVAC system of a vehicle.  For colder climates, a battery vehicle would have to generate this heat.

On March 16, 2021 at 10:24pm
Vishwesh Bhat wrote:

What would be the charging time of a 7.4V 5000mAh (Nominal/Rated values) Li-Po battery, if I used a fast charger?

Would I still have to use the same formula:
Charging time = Batt. Cap(Ah)/Applied Current(A).

Or would the formula change, since the Li-ion/Li-Po batteries charges in stages(CC-CV)...?

If I can no longer use the same formula in case of fast charging, then what should be my revised approach?