USB powered Switch Mode Li-ion Charger
The inductor in the circuit can be used to create a higher voltage than you had to start with. It stores energy when you put a current through it. When you remove that current, a voltage will appear across its terminals. This can be very much higher than the original voltage.

Circuits which provide a higher DC voltage from the original are known as step-up DC to DC converters. There are also step-down converters.

A feature of switch-mode supplies (and chargers) is they are quite efficient when converting the voltage (up or down), often 90% efficiency or more.