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The diffusion of small molecules or ions within polymeric materials is critical for their applications, such as polymer electrolytes. Cross-linking has been one of the common strategies to modulate solute diffusivity and a polymer’s mechanical properties. However, various studies have shown different effects of cross-linking on altering the solute transports. Here, we utilized coarse-grained molecular dynamics simulation to systematically analyze the effects of cross-linking and polymer rigidity of solute diffusive behaviors. Above the glass transition temperature <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi mathvariant="normal">T</mi><mi mathvariant="normal">g</mi></msub></semantics></math></inline-formula>, the solute diffusion followed the Vogel–Tammann–Fulcher (VTF) equation, D = D<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>0</mn></msub></semantics></math></inline-formula> e<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mo>−</mo><msub><mi mathvariant="normal">E</mi><mi mathvariant="normal">a</mi></msub><mo>/</mo><mi mathvariant="normal">R</mi><mrow><mo>(</mo><mi mathvariant="normal">T</mi><mo>−</mo><msub><mi mathvariant="normal">T</mi><mn>0</mn></msub><mo>)</mo></mrow></mrow></msup></semantics></math></inline-formula>. Other than the conventional compensation relation between the activation energy <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi mathvariant="normal">E</mi><mi mathvariant="normal">a</mi></msub></semantics></math></inline-formula> and the pre-exponential factor D<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>0</mn></msub></semantics></math></inline-formula>, we also identified a correlation between <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi mathvariant="normal">E</mi><mi mathvariant="normal">a</mi></msub></semantics></math></inline-formula> and Vogel temperature T<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>0</mn></msub></semantics></math></inline-formula>. We further characterized an empirical relation between T<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>0</mn></msub></semantics></math></inline-formula> and cross-linking density. Integrating the newly identified correlations among the VTF parameters, we formulated a relation between solute diffusion and the cross-linking density. The combined results proposed the criteria for the optimal solute diffusivity in cross-linked polymers, providing generic guidance for novel polymer electrolyte design.