Revealing the effect of electrolyte coordination structures on the intercalation chemistry of batteries

In-depth understanding of the electrolyte-dependent intercalation chemistry in batteries through direct operando/in situ characterizations is crucial for the development of the high-performance batteries. Herein, taking the Al/graphite battery as a model system, the effect of electrolyte coordination structure on the intercalation processes has been investigated over the batteries with either 1-hexyl-3-methylimidazolium chloride (HMICl)-AlCl3 or 1-ethyl-3-methylimidazolium chloride (EMICl)-AlCl3 ionic liquid electrolyte using operando X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. With a weaker anion-cation interaction in HMI-based electrolyte, the XPS-derived atomic ratio between co-intercalated N and intercalated Al is 0.9, which is lower than 1.6 for EMI-based electrolyte. Attributed to the additional de-solvation process, the batteries with the HMI-based electrolyte show a lower ionic diffusion rate, capacity, and cycling performance, which agree with the operando characterization results. Our findings highlight the critical role of the electrolyte coordination structure on the (co–)intercalation chemistry.