PbZrO₃-based antiferroelectric (AFE) ceramics are promising dielectrics for high-energy-density capacitors due to their reversible phase transitions during charge–discharge cycles. In this work, a new composition series, [Pb${}_{0.93-x}$La${}_{0.02}$(Li${}_{1∕2}$Bi${}_{1∕2}{)}_x$Sr${}_{0.04}$][Zr${}_{0.57}$Sn${}_{0.34}$Ti${}_{0.09}$]O₃, with Li${}^{+}$ and Bi${}^{3+}$ substitution of Pb${}^{2+}$ at $x=0$, 0.04, 0.08, 0.12, 0.16 is investigated for the microstructure evolution, ferroelectric (FE) and dielectric properties. It is found that Li${}^{+}$ and Bi${}^{3+}$ substitution can significantly reduce the sintering temperature and simultaneously enhance the dielectric breakdown strength. An ultrahigh energy efficiency (94.0%) and a large energy density (3.22$$J/cm${}^3)$ are achieved in the composition of $x=0.12$ with a low sintering temperature (1075^∘C).