We investigated the impact of high pressure and high-temperature annealing on lithium-vanadium-iron-phosphate (LiFe0.75V0.10PO4) glass materials, proposed for the use in cathodes for high-performance batteries. The treatment was carried out below the glass transition temperature (Tg ≈ 483 °C) at P = 1 GPa pressure, in an argon atmosphere. It led to the multifold electrical conductivity increase. Broadband dielectric spectroscopy (BDS) measurements before and after the process revealed the strong DC-conductivity increase across the whole studied frequency range by two orders of magnitude. The phenomenon is explained using Mott's theory of polaron hopping in disordered solids containing transition metal oxides. The pressure evolution of the glass transition temperature and the crystallisation temperature above Tg is shown.