One misfeature of most "lithium ion" cells is that their cathodes produce oxygen under high temperatures. One very good reason for Segway (e.g.) to use lithium

One misfeature of most "lithium ion" cells is that their cathodes produce oxygen under high temperatures. One very good reason for Segway (e.g.) to use lithium-iron-phosphate cells - they're far less likely to burn, though their power density suffers over conventional cells.