Why current flows from possitive terminal of battery to negative terminal?

Current is defined as flow of electrons. The direction of current is always given as opposite to the flow of electrons. In a battery at the negative terminal, it is rich in electron and when it is connected to the positive terminal through a load, it experiences the force due to the potential difference between cathode and the anode, and so electrons start moving from negative to the positive terminal and hencec current starts flowing from positive to negative terminal.