In the case of δ-V2O5, interlayer expansion was explored via ionic and/or molecular pillaring approaches. Clites et al. studied the chemical pre-intercalation of different sized alkali-and alkaline-earth ions as simple ionic pillars, resulting in a variation of the interlayer spacing between 0.96 -1.34 nm. The material with the largest initial interlayer spacing (δ-V2O5 preintercalated with Mg 2+ ) was found to exhibit the highest rate behavior for the electrochemical lithiation reaction. Wei et al. pre-intercalated δ-V2O5 with Fe 3+ -ions, which in turn improved the kinetics and stability of the electrochemical sodium intercalation reaction compared to pristine δ-V2O5. The authors attribute the effect to a large reduction in electrochemo- mechanical lattice breathing during (de-)sodiation. In the tunnel-structured polymorph ζ-V2O5, pre-intercalation of Na + or K + led to an expansion of the 1D tunnels, yielding higher reversible lithium intercalation capacity and diffusivity. Several ionic pillaring approaches of δ-V2O5 have also been reported to improve the capacity and stability of the electrochemical Zn 2+ intercalation reaction, demonstrating the viability of the approach also for multivalent electrochemical intercalants in an aqueous electrolyte environment. However, there is a need for a more systematic understanding of the impact of pillars on the charge storage mechanism, including the interaction between "pillaring ions" and mobile, electrochemically shuttled ions.