Can Lithium-Ion batteries be recharged by placing them in sunlight?

No, Lithium Iron batteries can not be recharged without a charger (which may run off solar power) but “iones de litio (Lithium Iron batteries) 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.