To meet the energy demands of massive international cargo ships, which carry tens of thousands of tons of cargo and use dozens of gigawatts of energy we’re going to need more advanced batteries. Building battery-powered ships comes with two big problems. The first is that conventional lithium-ion batteries pose safety risks, because they use liquid electrolytes to carry lithium ions between the electrodes. If the components in a battery degrade, this can cause the cell to rapidly heat up and fail, a process known as thermal runaway. The battery’s heat can lead to a cascade of failures in nearby batteries. If these batteries release their chemicals as they fail, all it takes is one battery to catch on fire and cause a large explosion.