Is there are any requirement of team leader, if all the employees are co-operating with each other?

May be NO at the operational level if the employees are cooperating with each other as you say, and ... there is a clear mandatory system that determines what to be done and obliges the employees to adhere to this system..However, this is NOT enough and NOT applicable at hihger levels involved in decision making in highly unknown/unpredictible environments ... this where leadership is an absiute necessary !!