What is Fast Charging?

While choosing a smartphone, we often consider different parameters: camera, screen size, processor and memory etc. In today’s life, where the schedule is tight for most people, it is preferred to charge mobile phone’s battery fast to keep up with the pace of life. Fast charging is of utmost importance in today’s phones as well as other charging devices or electric vehicles. Basically, fast charging is the capability to power up your device in few minutes rather than hours.

How does a fast charger work?

Faster charging can be done either by increasing the voltage or by increasing the current. The increase in voltage or current increases the potential energy. Voltage is said to be strength of electrical current whereas current is the flow of electrical charges from a battery to the device connected on the other end. By multiplying current and voltage, we get power that’s why we can increase either of them to increase wattage. We need to keep one thing in mind that there exist operating limits for any kind of battery. These limits are particularly regarding the voltage ratings which are necessary to be followed while charging the battery safely.

Let me make it clear that fast charging does not mean that you have to increase the voltage and current as much as you can to charge the battery fast.  We can break down the charging of battery into two phases i.e. constant current and constant voltage. We can observe the change in voltage while charging the battery through the figure provided below. From this figure, we can also interpret about the amount of current that flows through the battery.

Fast charging technologies harm the constant current phase by pushing the current to the battery as much as possible before its peak voltage arrives. So, we can say that fast charging methods work best when your battery is less than 50% full. Also, it has minute impact on the charge time, if the battery percentage exceeds 80%. Current charging is by the way the least damaging to the long-term health of the battery. In combination with heat, more continuous voltage is harmful for the longer life of battery.

When current passes through a smartphone, battery is charged. Battery is charged fast when greater amount of current and voltage is applied but it is applicable to specific limit.  The charge controller IC is used to control the excessive current and safeguards from hazardous surges. The controller chip controls the power flow into and out of the battery. In general, lithium-ion controls the current at which the battery is charged (in amps) by using measurements of the cell’s current and voltage of the battery. Some of them employ DC-to-DC to modify the input voltage and fancier integrated circuits can alter the resistance. These are connected between terminal of battery and charger’s input to control the flow of current.

Expensive batteries have more capability to withstand higher temperatures and currents due to higher C- rate and presence of new materials. Multi-anode batteries with cathode tabs can reduce the inner resistance of the battery and enhance its current. Dual cell batteries divide the electricity into two parallel batteries and hence provide a fast charging appearance.

Types of Fast Charging

USB Power Delivery

In the smartphones market, USB PD has become the most used charging standard since 2020. Most of the phones now support USB PD via their USB-C connector. USB PD has obtained a significant position among both android and iOS systems for charging the smartphones. It has provided consumers a single standard for fast charging for different types of gadgets. The table bellows lists devices on the basis of their wattage, current range and fixed voltage required by particular devices and gadgets.

Table 1 USB PD Power and Current Range of Different Devices

Qualcomm Quick Charge

Qualcomm's Quick Charge cannot be as dominant as it was a few years ago, because both proprietary and USB PD standards have been growing. However, it is currently in its fifth generation and still supports a number of devices on a regular basis.

The newest Quick Charge 5 has been retrograded to all prior Quick Charge and USB PD versions. The USB PD Specification is also compatible and can deliver up to 100 W of power for even more challenging devices. This is significantly more power than the previous versions, which often give compatible devices 18W and 27W power.

Quick Charge 5 is quite similar to rapid charging capabilities in USB PD PPS with increasing operating voltages up to 20V, 3A to 5A current. With charger identification capabilities and voltage, current and thermal safety protocols Qualcomm enhances its standard. It's even safer than regular USB PD according Qualcomm's words.

Table 2 Characteristics of Different Quick Charge

Wireless fast charging

It is convenient to use wireless charging although it can be slow. Most wireless chargers without fans or cooling systems can only charge at 5V/1A. However, a number of businesses now provide rapid wireless charging pads with built-in fans to disperse heat. Such chargers allow you to charge at speeds comparable to those of a cable.

Wireless charging follows the same ideas and challenges as cable rapid charging. Devices still need a fast-charging battery and a way to communicate data from the gadget to the charger. Then there's the extra challenge of efficiently delivering a significant amount of power over air.

References

[1] S. Ahmed et al., "Enabling fast charging–A battery technology gap assessment," Journal of Power Sources, vol. 367, pp. 250-262, 2017.

[2] G. L. Zhu et al., "Fast charging lithium batteries: recent progress and future prospects," Small, vol. 15, no. 15, p. 1805389, 2019.

[3] Y. Liu, Y. Zhu, and Y. Cui, "Challenges and opportunities towards fast-charging battery materials," Nature Energy, vol. 4, no. 7, pp. 540-550, 2019.

[4] A. Tomaszewska et al., "Lithium-ion battery fast charging: A review," ETransportation, vol. 1, p. 100011, 2019.