A Quest for the Faster Charging Batteries

The average number of hours that an average phone user spends on the phone is approximately 4 hours. That is approximately 120 hours or 5 days. The average daily charging time from 0% to 100% is about 2 hours that makes the number of hours spent charging phone per month is 60 hours or 2 1/2 days. That is about a month in a year. That number is high, and phone manufacturers are continually working on ways to make batteries charge faster with the introduction of Quick Charge technology.

This quick Charge was a technology pioneered by Qualcomm Snapdragon, a system on chip (SoC) manufacturers for various devices such as Android and Windows phone. Over time, other SoC manufacturers have come up with their proprietary fast charging technology.

How to charge a battery fast

Battery discharges when ions move from anode to cathode. Reversing the process requires passing current through the electrolyte to push the ions back to the anode. Batteries in small electronic devices such as phones, tablets and laptops usually have their rating in mAh or milliampere hour as against Ah in the deep cycle, golf cart, motor, motorcycle batteries, etc. The bigger a battery is, the longer the charging time. For instance, under same charging condition, a 2,000 mAh battery should charge twice faster than a 4,000 mAh batteries.

Also how fast you charge a battery is a function of both the charging voltage and charging current.

The standard USB charger is 5V at either 0.5A or 1A charging current. If a battery charger outputs 1A 5V, i.e. a 5w charger (power= current x voltage= 5 x 1= 5w), and another charger outputs 2A at same 5V, the latter will charge faster than the former.

Why can't we have a 20A 20V ( or 400w) or more mobile device charger and get the charge over in seconds?

The problem is the present lithium battery technology cannot handle such large amount of charging current. But the Quick Charge technology can cut down the time that it takes other conventional chargers to a quarter of the time- 30 minutes.

The Qualcomm 4.0 version can charge batteries up to a power of 28w. It does this by using a special chip to adjust the maximum current the battery can take plus top of the market heat dissipation technology to avoid battery's temperature from getting to a dangerous level while charging.

The Oliver Twist Effect

Even though with the present fast charging technology we can charge full or at least get to 50% of the mobile phone's capacity, users still complain on 61-watt charger's performance from Apple's iPhone which is commensurate with the steep cost of $69.

Can we have a phone that charge in seconds?

Yes, we can. But sadly the energy source won't be a battery but rather a supercapacitor.

The capacitor and battery have one thing in common - which is an ability to store charge. But all use a different method of storage; a battery makes use of chemical reactions between electrolyte and electrode to cause an electron to flow. Capacitors use electrostatic, the static electricity which occurs when the two plates, separated by a dielectric (an insulating material), takes on charge when an electric current passes through it. A thundercloud is a natural phenomenon that simulates the massive power storing potential of capacitors if the plates get increased to a substantial level.

The Supercapacitors

A supercapacitor is similar to a capacitor but with some distinguishing features which include a higher capacitance and hence can store more energy than ordinary capacitors, a different dielectric material and setup, plus high energy density.

Due to the slightly larger plates in the supercapacitor and the decreased separation between the plates, the capacitance of supercapacitors is bigger and can store more charge.

The farad (F) which is the basic unit of measuring capacitance of a capacitor is typically in μF, microfarad (microfarad, one millionth (10⁻⁶) of a farad) or picofarad, pF ( (picofarad, one trillionth (10⁻¹²) of a farad)) or nF (nanofarad, one billionth (10⁻⁹) of a farad) for a capacitor. In a supercapacitor, this ability to store charge is in Farads (F) which means it can store up to a million times more than those in conventional capacitors rated in μF.

Though some firms can pack thousands of farads in a supercapacitor, that amount is still small (around 20%) of what we can do with batteries.

How about portable devices like cell phones that require less power?

A supercapacitor has a lot of good associated with it; one is it can be recharged and discharged for more than 30,000 times without getting weak. That means we are looking at a lifetime of more than ten years. It can, more importantly, charge in seconds. But the drawback is the charge-discharge characteristics and the way the voltage depletes in both batteries and supercapacitors.

Look at the graph of voltage against time you will notice the difference between the behaviour of a supercapacitor and a conventional rechargeable battery. The supercapacitor charges as fast as it discharges with its voltage dipping with it. In most electronics, a steady voltage is what is required, for instance, most cellphone's lithium battery voltage is between 3.7v to 4.2v. This battery voltage remains more or less the same until about 90% or more discharged when it dips to cut off voltage of between 3.4v or 3.0v on which battery is assumed to be dead.

For us to use a supercapacitor, there will be more complexity for the added circuitry that will regulate this free fall of voltage.

Also developing a superconductor small enough to fit in a cellphone and with enough capacity as the conventional battery is still a design problem.

Though Eesha Khare, the then high school student of Lynbrook High School in California won an Intel's Young Scientist Award with cash prize of $50,000 in 2013 for developing a supercapacitor that has up to 10,000 cycles and scalable to fit in a phone, and is rechargeable under 20 to 30 seconds. Her demonstration shows the supercapacitor light an LED.

Five years on, the invention may well be on hold. But a new UK-based company called Zap&Go founded in 2013 may well be on the path to be the people to give us the fast charge we may need. They were able to use a nanocarbon-graphene supercapacitor which can charge under 5 minutes which is still a far cry from the 20 seconds charge of the supercapacitors. You can watch the CEO and investment director of Zap&Go talk about the exciting prospect of 5-minute full charge battery here.

But until we have these products available in the open markets, we may have to be content with the 30-minute 50% charge currently offered by the Quick Charge systems :)

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^REFERENCES

• ^{Qualcomm Quick Charge}
• ^{What exactly is Fast Charging? And how does it work?}
• ^{We Tested iPhone Fast-Charging and You Should Definitely Upgrade Your Charger}
• ^{How Much Time Do People Spend on Their Mobile Phones in 2017?}
• ^Zap&Go
• ^{High school student develops supercapacitor, wins Young Scientist Award}
• ^{Supercapacitors}

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