D.I.Y.

Is fast charging a smartphone harmful to its battery?

To answer this question there are 3 factors to consider:

• First factor: Battery chemistry and its limitations.

  • Smartphones most commonly use Li-Ion and Li-Pol batteries, which are very similar in terms of their design and chemical processes, although Li-Pol batteries may have slightly higher voltages (up to 4.35V). These two types of batteries are often referred to by the generic term, lithium batteries. There are also LiFePo4 batteries, also related to lithium, but they have a different voltage (3.65V max), lower energy density and therefore are not yet used for smartphones.

  • For a long time there was a rule for Li-Ion batteries that the charge/discharge current should not exceed 0.5-1C, i.e. a current of 0.5-1A per 1000mAh of the battery capacity. Over time, the chemistry of batteries has changed, other electrolytes and materials for electrodes are used, which allowed some manufacturers to create high-current batteries capable of withstanding currents up to 6C (OPPO), 8-12C (Infinix) and even up to 15C (Xiaomi, vivo) per cell without damage.

• The second factor: Temperature.

  • Temperature is perhaps the primary factor affecting the longevity and consistent performance of batteries.

  • Temperature is generated:

    • in the battery itself during charging and depends on its chemistry and the perfection of battery manufacturing technology (see the first factor above)

    • in the charge controller during the voltage conversion as a voltage coming from the charger is different compare to the battery voltage.

    • in the components of the smartphone during their operation (processor, memory, etc.).

  • Temperature dissipation (cooling) is an important engineering task and often the metal smartphone housing acts as a heat sink.

  • Controlling the temperature of internal components and especially the battery is very important, so a manufacturer are always installing temperature sensors on the battery and in case of exceeding a temperature threshold, the charging current is reducing or even stopping, and in especially critical cases, the smartphone is turning off.

• Third factor: battery charging technology/protocol.

  • There are many different fast charging protocols that have emerged and evolved as battery technology and charge controllers have evolved. The first protocols such as DCP, QC2.0, PD provide a fixed set of voltages from the charger to the device being charged. What voltage will be and how much current will be pulled (within the available fixed options offered by the charging adapter) is determined by the charge controller of the smartphone. For example 5V1.5A or 9V3A.

  • Over time, more efficient charging protocols have emerged, such as PPS (used by Samsung smartphones, Google Pixel) and similar ones (QC3,4,5, UFCS), as well as proprietary ones (Samsung SFC, OPPO VOOC/SuperVOOC, Xiaomi Hypercharge). These fast charging protocols favorably differ from the previous protocols in that they allow charging controller of a smartphone to flexibly change the voltage and current within the authorized range, such as 3.3-21V-5A and transmit energy directly to the battery without its conversion, which significantly reduces the overall heating of the device (losses on voltage conversion can be up to 10%, which significantly heating the smartphone, including its battery). Using such fast charging protocols allows noticeably increase the charging power while maintaining an acceptable temperature of the battery while charging.

  • The battery is charged according to the CC/CV scheme, i.e. when the battery is depleted, it is charging with the highest current allowed for the battery (with constant temperature control), and after reaching the maximum voltage allowed for a particular battery (e.g. 4.2V), the charging current voltage is fixed, and the current gradually decreases. At the end of the charge cycle, the charging current drops almost completely and a constant voltage level is maintained, with a very little energy consumption.

  • It is important to note that the charging protocol is determined during the protocol negotiation between the charging adapter and the device being charged. Not only must the charging adapter and smartphone support the desired protocol (and its version), but in some cases the cable must allow it. For example, to maximize the charge of top Samsung devices requires UsbC-UsbC cable with e-maker chip and rating of 100W or 240W because the charging current can reach 5A, while the usual UsbC-UsbC cable without e-maker chip (60W) allows a current of only 3A, which does not allow you to fully realize the potential of fast charging a smartphone.

• Conclusions:

  • Using charging protocols that utilize direct charging of the battery without voltage conversion (PPS and its like) is much more efficient, generates the least amount of heat during charging and is the most preferred charging method in terms of extending battery life.

  • The battery charge controller is as important a component of the system as the battery itself and is responsible for its health and longevity. The controller selects the best available charge protocol, selects the optimal charge current based on the battery charge level, and takes into account the battery's characteristics and limitations, as well as its operating temperature range, to ensure acceptable results even with simpler and older fast charge protocols.

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