Molten lithium-sulfur and lithium-selenium electrochemical cells are disclosed. A solid electrolyte separates a molten lithium metal or molten lithium metal alloy 106 from a molten sulfur or molten selenium. The molten lithium-sulfur and lithium-selenium cells have low over potential, no side reaction, and no dendrite growth. These cells have high Coulombic efficiency and energy efficiency and thus provide new chemistries to construct high-energy, high-power, long-lifetime, low-cost and safe energy storage systems.