I'm a F2P player and I want to ask about "Energy Credit cap increase" from c-store.

Description:
Silver Players, increase your maximum Energy Credits from 10 million to 1 billion!

Note: Purchase of this option increases the Energy Credit cap for all characters on an account. Both Federation and Klingon Empire characters may use this option. Once this option is unlocked, you will need to log out and log back in for the change to take effect.

F2P players can buy it too, not only Silver?

*Sorry for my bad english but is not my native language

F2P players are Silver. Gold players are those who play the Subscritpion, either monthly or LTS. Silver players are those who play for free.

It doesn't automatically give it to you when you're gold. It just doesn't. As soon as your gold sub expires you'll go back to being silver.

That is about 100,000 dilithium, or 12.5 days worth of daily dilithium refinement on one character. You've made it sound like F2P players never buy anything. I just bought a Kar'fi today, I bought the AHCR and the Veranus, I got the enterprise and Quorgh for free during the second anniversary event, I'd buy the Corsair if I could get the fleet version for one FSM after I did that, I'd buy a FSM for a fleet Kar'fi, I'd buy two FSM for a AHCR, and I'm eagerly awaiting the next Klingon ship release (the uh, Bortas, just isn't quite my speed.)