That is not correct. The battery chemistry Nissan use is stable. Telsa are / were the only ones using batteries prone to thermal runaway. Oh and Boeing but they don't build carsLithium ion batteries in cars must be cooled or could lethal when they ignite.
LEAF 24 'lizard battery' and LEAF 30 do just fine without active cooling.
The upcoming 60kWh LEAF ePower is on a different chemistry that may require some cooling. We will have to wait and see.