Solid-state lithium ion electrolytes of lithium potassium tantalate based compounds are provided which contain an anionic framework capable of conducting lithium ions. An activation energy of the lithium metal silicate composites is from 0.12 to 0.45 eV and conductivities are from 10−3 to 40 mS/cm at 300K. Compounds of specific formulae are provided and methods to alter the materials with inclusion of aliovalent ions shown. Lithium batteries containing the composite lithium ion electrolytes are also provided. Electrodes containing the lithium potassium tantalate based materials and batteries with such electrodes are also provided.