Ion Flux Self-Regulation Strategy with a Volume-Responsive Separator for Lithium Metal Batteries

Abstract

Lithium metal batteries (LMBs) are regarded as one of the most promising next-generation energy storage devices due to their high energy density. However, the conversion of LMBs from laboratory to factory is hindered by the formation of lithium dendrites and volume change during lithium stripping and deposition processes. In this work, a volume-responsive separator with core/ shell structure thermoplastic polyurethane (TPU)/polyvinylidene fluoride (PVDF) fibers and SiO 2 coating layers is designed to restrict dendrite growth. The TPU/PVDF−SiO 2 separator can accommodate the volume change like an artificial lung and keep intimate contact with the electrodes, which leads to the formation of a uniform and high-density solid−electrolyte interphase. Meanwhile, the separator can regulate the transport channels and diffusion coefficients (D) of lithium ions with the change of porosity from both experimental and ab initio molecular dynamic analysis. The Li symmetric cells assembled with the TPU/ PVDF−SiO 2 can run for 1000 h at the current of 1.0 mA cm −2 without a short circuit. Moreover, the low melting point of PVDF can shut the ionic conduction down at 170 °C, guaranteeing the thermal safety of the batteries. With the above advantages, the TPU/PVDF−SiO 2 separator presents great potential to promote the commercial and industrial application of LMBs.

Functional Composite Separators with Cation-Trapping Abilities

“…SEM images of PES and HES after 30 min at 160 °C confirm the macroscopic observations: while fibers completely melted for PES, the microstructure of HES did not change (Figure b). This improvement of PVDF-HFP nanofibers’ thermal stability matches the best value recently reported by Shi et al (see Table S1 for a comparison of representative composite separators) . This enhanced thermal stability most probably comes from the high content of silica and the organization of the silica domains.…”

“…Besides their composition, the morphology of the inorganic entities is also of importance: the smaller the inorganic particles, the better the mechanical properties, and 1D nanowires or nanotubes showed even better enhancement of performances than particles. , This can be explained by a larger interface between the polymer and silica domains, further improving the mechanical properties. In addition, the coating of PVDF-HFP fibers with SiO 2 nanoparticles improves the wettability and conductivity of the separators, as recently illustrated by Shi et al Yet, it should be noted that these approaches are based on mixing or adding the inorganic particles or coating to the separators, strategies that may lead to the leaching of particles into the electrolyte. , …”

“…14,15 This can be explained by a larger interface between the polymer and silica domains, further improving the mechanical properties. In addition, the coating of PVDF-HFP fibers with SiO 2 nanoparticles improves the wettability and conductivity of the separators, as recently illustrated by Shi et al 16 Yet, it should be noted that these approaches are based on mixing or adding the inorganic particles or coating to the separators, strategies that may lead to the leaching of particles into the electrolyte. 8,17 Furthermore, designing functional separators able to trap impurities in the liquid electrolyte allows for a lower degradation rate of the battery and an increased lifespan.…”

“…This improvement of PVDF-HFP nanofibers' thermal stability matches the best value recently reported by Shi et al (see Table S1 for a comparison of representative composite separators). 16 This enhanced thermal stability most probably comes from the high content of silica and the organization of the silica domains. Differential scanning calorimetry (DSC) analyses were performed to gain more insight into the separators' thermal properties.…”

ZnO@C Coated Cellulose‐Based Separators Control Lithium Deposition Direction to Stable Lithium Metal Batteries

“…We were able to conclude that ZnO@C/cellulose plays an effective role. A comparison of the long cycle of Li||Li symmetric cells with the previous worth of literature in the separator area is shown in Figure 3c, [ 16,33–48 ] confirming the possibility of our work to optimize performance in LMBs. We additionally examined at the Li||Cu half cells with PP, cellulose, and ZnO@C/cellulose separators to illustrate Li deposition behavior.…”