Journal Article lithium-sulfur batteries graphene Research Support, Non-U.S. Gov't dendrites layered double hydroxides lithium metal anodes lithium-sulfur battery polysulfide electrocatalysis polysulfides shuttle effect aligned carbon nanotubes atomic doping bifunctional perovskite promoters carbon nanotubes composite cathodes current density dilute alloy electrochemical reactions energy storage hollow spheres hybrid materials lithium batteries mesoporous carbon metal nitride nanostructure nitrogen doping polar functional groups polysulfide redox reactions porphyrin organic frameworks