Metal‐Organic Framework Glass as a Functional Filler Enables Enhanced Performance of Solid‐State Polymer Electrolytes for Lithium Metal Batteries

Abstract Polymers are promising candidates as solid‐state electrolytes due to their performance and processability, but fillers play a critical role in adjusting the polymer network structure and electrochemical, thermal, and mechanical properties. Most fillers studied so far are anisotropic, limiting the possibility of homogeneous ion transport. Here, applying metal‐organic framework (MOF) glass as an isotropic functional filler, solid‐state polyethylene oxide (PEO) electrolytes are prepared. Calorimetric and diffusion kinetics tests show that the MOF glass addition reduces the glass transition temperature of the polymer phase, improving the mobility of the polymer chains, and thereby facilitating lithium (Li) ion transport. By also incorporating the lithium salt and ionic liquid (IL), Li–Li symmetric cell tests of the PEO‐lithium salt‐MOF glass‐IL electrolyte reveal low overpotential, indicating low interfacial impedance. Simulations show that the isotropic structure of the MOF glass facilitates the wettability of the IL by enhancing interfacial interactions, leading to a less confined IL structure that promotes Li‐ion mobility. Finally, the obtained electrolyte is used to construct Li–lithium iron phosphate full batteries that feature high cycle stability and rate capability. This work therefore demonstrates how an isotropic functional filler can be used to enhance the electrochemical performance of solid‐state polymer electrolytes.

seen below each peak.The given number for the corresponding H-atom in chemical structural formula of benzimidazole and imidazole is displayed.From the area under the peak at 9 and 9.5 ppm, the benzimidazole/imidazole ratio can be determined.The ratio is then used to find the composition when assuming two linkers per zinc atom and no free linkers, which yields; ZnIm1.74bIm0.26 and ZnIm1.77bIm0.23 for crystal and glass, respectively.Interestingly, the water peak shifts between the two measurements.This may be caused by differences in solution concentration and/or pH change.
However, this is likely of little to no consequence for the determination of the chemical composition of the ZIF-62.very high viscosity, resulting in very limited fluidity.Therefore, the surface morphology of the ZIF-62 glass particle is partially inherited from the ZIF-62 crystal particle precursor, as also observed elsewhere. [1]   PEO-based electrolyte film, it is difficult for the indenter tip to locate the sample surface at the beginning of loading process, which is consistent with previous findings. [2]However, the values of hardness and modulus are calculated from the unloading curve, i.e., the hardness is determined by fitting the first one third of the unloading curve to a linear model.During the indentation tests, we observed some differences in the hardness and reduced modulus values obtained at different loading/unloading rates, indicating that the prepared electrolyte film has the time-dependent mechanical behavior, which is consistent with previously reportes. [3]

Figure S1 .
Figure S1.1H NMR spectra of (a) ZIF-62 crystal and (b) ZIF-62 glass.The area of the peaks can be

Figure S8 .
Figure S8.Schematic of the relevant parameters during indentation test.The stiffness, S, of the

Figure S13 .
Figure S13.Evolution of absorption energy of ILs on the surface of (a) ZIF-62 crystal and (b) ZIF-62 glass as a function of temperature.

Figure S15 .
Figure S15.Simulated MSD curves of Li + in the ionic liquid at different temperatures when subjected

Figure S19 .
Figure S19.(a) Cyclic performance and (b) the corresponding voltage-capacity curves of the PEO-

Figure S22 .
Figure S22.(a) Rate performance and (b) corresponding voltage-capacity curves of the PEO-LiTFSI-

Figure S23 .
Figure S23.(a) Cycle performance, (b) rate performance, and (c) long cycle stability of the PEO-

Figure S24 .
Figure S24.Atom types in ZIF-62 and calculated charges from DFT using the DDEC method.

Table S1 .
Hardness and modulus values obtained from indentation measurements.

Table S2 .
Comparison of the performance of solid-state electrolytes.