Chem http://doi.org/cknh (2018)
Magnesium-ion batteries have been purported as one of the candidate technologies to surpass lithium-ion batteries. But with safety concerns less pressing and theoretical energy density about five times that of commercial Li-ion batteries, the most demanding problem in Mg-ion batteries research is the shortage of cathode materials that can reversibly intercalate and de-intercalate magnesium ions. Part of the issue resides in the greater charge-to-radius ratio of Mg2+ with respect to Li+. When Mg2+ ions intercalate they tend to polarize the cathode material, generating strong electrostatic interactions that limit Mg2+ diffusion. Andrews et al. have now shown that a metastable phase of V2O5 (ζ-V2O5) can reversibly intercalate and de-intercalate magnesium ions.
The ζ-V2O5 phase is a polymorph with an open tunnel framework that allows Mg2+ ions to diffuse within the material. Within this open framework there are several sites that magnesium can coordinate to, but the interactions remain weak at all of these sites. The researchers call this situation ‘frustrated coordination’, and it helps Mg2+ diffuse through the channels without needing to overcome large energy barriers. It is also worth noting that magnesation is accompanied by only a small volumetric change of <1%. Using this material, Andrews et al. show a Mg-ion battery with reversible capacity of 90 mAh g–1 over 100 cycles.