Hi everyone! So I have 5V 2A receiver and transmitter coils but my robot consumes 4A and 12 Volt. Also I am looking for a fast charging solution.How can I do that?

 

You can't.
You are completely restricted by the "SIZE" and efficiency of the Antennas.

What You are asking for is a 60+VA "Air-Core"-Transformer, built in 2 separate halfs.
There are very good reasons why these are not manufactured.
It would be massive, and completely impractical.

Teach your Robot how to plug it's self in.
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Farnell has a choice of over a hundred
https://uk.farnell.com/abracon/awcc...coil-25uh-10-3-15x35mm/dp/2709585?ost=2709585
if you search through the data sheets, you might find one with application circuits.
You could use several in parallel if the robot has a large flat base.

 

This is not as simple as it looks,
and the amount of Power transferred to the other end can be very disappointing.

Getting 60-Watts of actual Power transferred to the Receiving-Coil is very tricky,
and requires virtually "zero" spacing, and near perfect alignment, between the Coils.
BIG Coils for ~60-Watts.
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https://www.powerelectronictips.com/measuring-wireless-charging-efficiency-in-the-real-world/
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