Lithium-ion batteries can be recharged by placing them in sunlight, but only if there is a charger. This is because lithium-ion batteries may not be charged at all without a charger, and even if you have a charger, it must have an input from a power source.
“Li-ion (Lithium Iron) also performs better at high temperatures than at low ones. Heat lowers the internal resistance but this stresses the battery. Warming a dying flash-light or cellular phone battery in your jean pocket might provide additional runtime in the winter.” (Discharging at High and Low Temperatures)
Similarly if a battery is cold then warming it in the sun may provide some additional runtime, not by charging it, but by decreasing its internal resistance.