A GOOGLE-search on 2010 hyundai i20 key programming will retrieve a fair amount of useful information.

If you obtained a 'blank' key that's suitable for your 2010 i20, you'd need to have that key's 'blade' cut to match your present key. Then you'd need to have that key's transponder programmed to communicate with your car's security system. Realistically, it won't be practicable for either of those tasks to be performed by a car's owner.

This webpage quotes from £99 to £239 for a new Hyundai key

Hyundai Key Replacement | Oak Auto Locksmith

and a Hyundai dealership's charge could well be considerably higher.

Keys can be reproduced at many Timpson outlets and there are some prices quoted here

Autokeys Online | Key Found

 

Thanks DLUi20 for that info. I know on a another car I had which was a Ford Focus MK1 I was able to programme it via a sequence using the buttons on the key and turning it back and fourth in the ignition.
I was hoping this might have been an option for the Hyundai?

 

A 1996 Ford Transit Mk 4 I owned was similar and the DIY procedure for programming a new ignition key was very easy and described in the owner handbook. (A Ford dealer cut me a new key and I programmed it myself in the Transit's cab.)

There's plenty of on-line discussion about DIY programming Ford keys, but nothing I can find about doing this for Hyundai cars. A Hyundai dealership might be prepared to tell you if there's a 'magic' technique, but I'm pretty sure that - if you want a 2nd key - it will need to be programmed by a specialist.