Recently I bought a 16Gb microSD card to expand the storage capability of my android device, my intencion was to be able to sync all my Spotify lists for offline playing.

Sadly Spotify won’t let you modify the path where it’s files are stored, but there is a way.

You must have a rooted phone and know how to use adb or a terminal emulator. Then, as root:

Open the Spotify config file in /data/data/com.spotify.mobile.android.ui/shared_prefs/spotify_preferences.xml

The file will look like this.

<?xml version='1.0' encoding='utf-8' standalone='yes' ?>
<map>
<string name="installation_id">qr8vlrvtatrokb0kmpj8gappn3</string>
</map>

you have to add one line.

<?xml version='1.0' encoding='utf-8' standalone='yes' ?>
<map>
<string name="installation_id">qr8vlrvtatrokb0kmpj8gappn3</string>
<string name="storage_location">/mnt/emmc</string>
</map>

Then you will have to close Spotify for the changes to apply, select Spotify  in the application manager and select “Force Close”.

Open Spotify again, now Spotify will store it’s data on /mnt/emmc/Android/data/com.spotify.mobile.android.ui, you can delete the old files, they are in /mnt/sdcard/Android/data/com.spotify.mobile.android.ui

Source: Spotify support forums