We have Lync 2010. We want to deploy an aditional Skype For Business Standard Pool (Mixed mode).

This URL indicates that I have to upgrade to Lync 2013 ???

https://technet.microsoft.com/en-us/library/dn951396.aspx

In place upgrade is possible only with Lync 2013. You can have Lync 2010 pool and deploy Skype for Business pool in coexistence, however you cannot upgrade Lync 2010 to SfB. 

You can move users homed on a Lync Server 2010 Front-End Pool directly to a Skype for Business 2015 FE Pool, followed by setting up Sfb counterpart to replace other Lync 2010 server roles in an inside-out fashion. Make sure that you have the latest patch applied though. Note that in-place upgrade (on- or offline mode) is designed to work with Lync Server 2013 Server roles only.

Please share if this helps. Thanks.