I don't believe there is a difference.
Actually there is a difference according to the Bible.
All demons are evil spirits, but not all evil spirits are demons.
They are all evil angels -- hence spirit beings -- but demons are spirits which (a) present themselves as gods and goddesses, (b) possess people and animals, (c) exercise evil influences over people including sickness, disease, and death, (d) oppress and attack Christians (but also others), (e) mastermind false doctrines, and (f) present themselves as ghosts. All of this is revealed in Scripture.
Evil spirits communicate through mediums, are involved with witchcraft, exercise influence over nations, work through false prophets and false teachers, produce counterfeit miracles, and oppose the Gospel and Christ at every opportunity. All these spirits are under the control of Satan, who is called "the prince of the power of the air". Just as the holy angles are ranked in hierarchies, the evil angels are also ranked in hierarchies. We see a glimpse of that when they are called thrones, dominions, principalities, powers, rulers of the darkness of this world, and spiritual wickedness in high places.
No demon, evil spirit, or Satan is outside of God's control and authority, but they are allowed a measure of freedom for a season. Demons cannot possess Christians, but can certainly oppress, attack, and sabotage Christians and churches. They can be cast out through prayer and fasting, but Christians should really hand over Satan and his evil angels to Christ, and let God deal with them. Even Michael the archangel said to Satan "the Lord rebuke thee" (Jude 1:9), because the LORD had first said to Satan "the LORD rebuke thee" (Zech 3:1,2).