Superior Mg2+ storage properties of VS2 nanosheets by using an APC-PP14Cl/THF electrolyte

The difficult Mg2+ desolvation of chloride-based electrolytes and slow Mg2+ diffusion in the cathode seriously hinder the electrochemical performance of Mg-ion batteries (MIBs). To solve these problems, a high performance MIB cell was built using a VS2 nanosheet cathode and with 0.4 M (PhMgCl)2-AlCl3/tetrahydrofuran (APC/THF) and 50 wt.% 1-butyl-1-methylpiperidinium chloride (PP14Cl) as the electrolyte. The resulting system showed a large capacity of 348 mA h g−1 at 20 mA·g−1 current density and excellent rate capability with a 214 mA h g−1 capacity at 2.0 A·g−1 current density. A thorough experimental and theoretical study showed that Mg2+ desolvation energy was reduced from 3.0 to 0.67 eV under the catalytic effects of PP14+. Moreover, large-sized PP14+ was inserted into the VS2 interlayer during the first discharge and permanently resided in the material. As a result, the interlayer spacing of VS2 was largely expanded, which improved the Mg2+ diffusion coefficient by three orders of magnitude to 10−10–10−12 cm−2 s. The reduced Mg2+ desolvation energy by the catalytic effects of PP14+, together the improved Mg2+ diffusion kinetics by the interlayer expansion effect of PP14+, provided a significant implement way towards development of high performance and practical MIBs by electrolyte regulation.