<p>Based on Al³⁺-modified Li_1.3Al_0.3Ti_1.7(PO₄)₃, a NASICON-type Li_1.3Al_0.3Ti_1.7(PO₄)₃- <i>x</i>ZnO (<i>x</i> = 0 − 4 wt.%) solid electrolyte was prepared by introducing Zn²⁺ into the Ti⁴⁺ site for nonequivalent substitution. Through the mechanism of ion diameter difference and charge compensation, Schottky defects are formed while broadening the ion transmission channel, thereby optimizing the crystal structure and improving the conductivity of the material. The results demonstrate that, when the larger ion radius of Zn²⁺ (0.074&#xa0;nm) replaces Ti⁴⁺ (0.068&#xa0;nm), the lattice parameters increase and the lithium-ion transmission channel widens. The unequal substitution of Zn²⁺ promotes the generation of more oxygen vacancies in the lattice and weakens the binding of O²⁻ to Li⁺. Simultaneously, Zn²⁺ acts as a sintering aid, where an appropriate amount of Zn²⁺ can promote uniform grain growth, improve intergranular contact, and reduce the formation of the LiTiPO₅ impurity phase. At <i>x</i> = 2 wt.%, the total conductivity increases to 0.32 mS/cm, 228% higher than that of the undoped sample, while the activation energy decreases to 0.20 eV. After 100 cycles at 0.1 C current density, the specific discharge capacity reaches 123.73 mAh/g with 87.26% capacity retention rate and 96.56% average coulomb efficiency.</p>