Central banks once started charging banks to hold their money, not paying them

From June 2014 the European Central Bank pushed its deposit rate below zero, and the Bank of Japan and others followed, effectively fining banks for parking cash with them instead of lending it out. The goal was to force money out into the economy during years of weak growth and inflation stuck near zero. It was a tool textbooks had never described as usable, since interest rates were assumed to hit a hard floor at zero.

— European Central Bank, Why has the ECB introduced negative interest rates? — ECB Explainer