Mixed Metal‐Organic Frameworks as Efficient Semi‐Solid Electrolytes for Magnesium‐Ion Batteries

Abstract

AbstractOne of the main issues of metal organic framework (MOF)‐based solid electrolytes (SE) is their high guest solvent content reaching up to >50 wt% of the total mass of SE pellets. The presence of large solvent amounts reduces the SE hardness and the electrochemical stability in presence of a magnesium (Mg) anode. Moreover, this often leads to misleading ionic conductivity values. In the present work, a strategy to minimize the guest solvent in MOF‐based SE from 44–55 wt% to 20–30 wt% of the total SE's mass is presented. Moreover, mixed metal organic frameworks of different structures and crystallinity are demonstrated for the first time to enhance the ionic conductivity of Mg2+ ions inside the MOFs’ structures. The presence of both highly crystalline and amorphous MOFs increases the degree of disorder in the mixture and consequently opens up extra pathways for Mg2+ ion diffusion. The ionic conductivity of mixed MOFs [amorphous Mgbp3dc and crystalline α‐Mg3(HCOO)6] showed an enhanced value of 3.8×10−5 S cm−1 at 30 °C compared to 1.1×10−6 S cm−1 for α‐Mg3(HCOO)6. Mixed MOF‐SEs with a transference number (t+) of 0.335 showed a good stability in the presence of Mg electrodes with an enhanced reversibility upon galvanostatic cycling.