The present disclosure relates to a lithium ion-conducting glass ceramic which comprises a residual glass phase that is also ion-conducting, a process for the production thereof as well as its use in a battery. The glass ceramic according to the present disclosure comprises a main crystal phase which is isostructural to the NaSICon crystal phase, wherein the composition can be described with the following formula: Li1+x−yMy5+Mx3+M2−x−y4+(PO4)3, wherein x is greater than 0 and at most 1, as well as greater than y. Y may take values of between 0 and 1. Here, the following boundary condition has to be fulfilled: (1+x−y)>1. Here, M represents a cation with the valence of +3, +4 or +5. M3+ is selected from Al, Y, Sc or B, wherein at least Al as trivalent cation is present. Independently thereof, M4+ is selected from Ti, Si or Zr, wherein at least Ti as tetravalent cation is present. Independently thereof, M5+ is selected from Nb, Ta or La.