Depending on the model, some android smartphones might have hot swappable external sdcard, means you can remove the external sdcard without turn off the phone/remove the battery.
If you do have that kind of smartphone, normally you just take out/remove the sdcard from your phone, but that's wrong way and if you keep doing that, your sdcard might broken someday.
Before removing external sdcard from your phone, you need to eject/unmount first, it's very easy, go to "Settings" > "Storage" > "Unmount SD card".
After doing that, you can unplug/remove the external sdcard from your phone. So basically that's how you properly eject/remove external sdcard from your android phone.
~ see you later ~