Hi,
What exactly does the datasheet say? 1C is typical or recommended charge current, or maximum charge current?
(Why don't you post a link to the datasheet?)
Doesn't the manufacturer provide additional documents on how to charge the battery?
Usually Li-Ion need constant current charging, but only up to a given cell voltage (very tightly tolerated), then the current needs to be reduced.
If you don't follow this rule you risk explosion and fire.
There are many documemts from battery manufacturers, charger IC manufacturers, universities on how to correctly charge a battery.
Btw: there's a good reason why there are dedicated cgarger ICs. I'd use one of them.
Many (unexperienced) say they are complicated. But indeed many of them have optimized charging scheme, tight voltage references, power saving techniques and many other useful features included...
Klaus