Why can't we use diodes in place of batteries?
As originally asked, the question was:


1.why we cant use diodes in place of battery?we are getting 1.4v in a cheaper cost than battery.but why we dont use? 2.if electrons are moving in a single direction it releases many energies but why we are calling it as "current"?


Answer: 


Diodes are not an energy source.
They modify how energy may flow.
Their function is to allow current or electrons or charge to flow in one direction in a circuit much more readily than in the other direction.
A good analogy is to think of them as a non-return valve of one-way-valve in a water flow system. 
Batteries are energy sources - usually a means of converting chemical energy into electrical energy.
A good analogy is to think of them as a "pump" in a water flow system.
Just as a pump is NOT a pure energy source in its own right, but a way of converting some other form of energy to "flow", so a battery is a converter, turning some other form of energy into electrical energy. usually chenmical energy is the source.
Electron flow is termed "current flow" because of the traditional and useful analogy with flow of water in a water flow system. 
Many of the elements in a basic electrical system have equivalents in a water flow analogy. The comparisons are NOT EXACT but are useful.


Voltage: Pressure, water head.  
Current: Water flow
Resistance: obstruction to flow, pipe resistance,
Capacitance: inline chamber with a elastic diaphragm across it.
Inductance: inline chamber with walls made of elastic material. 
Diode: One way valve.