**Abstract**

As on today the main power sources of lithium-ion batteries (LIBs) research developments gradually approach their theoretical limits in terms of energy density. Therefore, an alternative next-generation of power sources is required with highenergy densities, low cost, and environmental safety. Alternatively, the chalcogen materials such as sulfur, selenium, and tellurium (SSTs) are used due to their excellent theoretical capacities, low cost, and no toxicity. However, there will be some challenges to overcome such as sluggish reaction of kinetics, inferior cycling stability, poor conductivity of S, and "shuttle effect" of lithium polysulfides in the Li-S batteries. Hence, several strategies have been discussed in this chapter. First, the Al-SSTs systems with more advanced techniques are systematically investigated. An advanced separators or electrolytes are prepared with the nano-metal sulfide materials to reduce the resistance in interfaces. Layered structured cathodes made with chalcogen ligand (sulfur), polysulfide species, selenium- and tellurium-substituted polysulfides, Se1-xSx uniformly dispersed in 3D porous carbon matrix were discussed. The construction of nanoreactors for high-energy density batteries are discussed. Finally, the detailed classification of flexible sulfur, selenium, and tellurium cathodes based on carbonaceous (e.g., carbon nanotubes, graphene, and carbonized polymers) and their composite (polymers and inorganics) materials are explained.

**Keywords:** sulfur, selenium, tellurium (SSTs) electrodes, polysulfides, nano-metal chalcogen and flexible batteries, nanoreactors, electrochemical properties
