Nowadays, plenty of smart phones have the functionality of fast-charging. Most of phones use Qualcomm quick charge (QC), but some of manufactures have their own fast-charging technology such as VOOC from OPPO.

The Principle of Fast Charging
When charge the phone, the electrons in the positive electrode move towards the negative electrode, while the lithium ions in the positive electrode move towards the negative electrode through the insulating membrane in the middle and are stored in the graphite end. When all the positive lithium ions move to the negative, the battery is fully charged. When stop charging, the battery starts discharging, and the lithium ions stored in the negative electrode move to the positive electrode. When all the lithium ions move to the positive electrode, the battery is dead.
Above is the fundamental process when a cell phone battery is charged and discharged.

The speed of charging a phone depends on the power. The higher the power reaches, the faster it charge. [W(Power)=A(Current)*V(Voltage)] In words, quick-charge technology is to find solutions to increase voltage(V) or current(A). Well-known QC and Pump Express from Media Tek are high-voltage quick charge , while VOOC is high-current quick charge.
Although quick-charge has already been commonly used, it still has defects. For example, high-voltage quick charge faces the challenge that the highest voltage extreme is hard to break through. Also, quick charge has problems such as high temperature of the phone and shortened components of the phone led by heat effect. Furthermore, quick charge still relies on cable equipment, and therefore limits customer experience. Due to such limitation, many manufacturers start to develop wireless quick charger to better satisfy customers’ needs and wants.