Nanofiber separators are becoming increasingly popular in high-performance lithium-ion batteries (LIBs) due to their high porosity, high electrolyte uptake, and thinner thickness. So far, polypropylene (PP) materials occupy a large share of the LIB separator market due to their low cost and stable electrochemical properties. However, it is difficult to realize the preparation of PP nanofibers by solution electrospinning because there is no corresponding solvent for PP materials. Moreover, the large size of melt-blown PP fibers cannot reach the nanoscale. PP nanofibers produced by nanolayer coextrusion technology at mass can be processed into LIB separators. The tensile strength of PP nanofiber separators (PPNFS) treated with hot pressing at 120 °C (PPNFS-120) increases by 423%. PPNFS-120 has low interfacial impedance and high ionic conductivity (1.5 mS cm −1 ) and exhibits satisfactory thermal stability at 160 °C. In addition, the electrolyte uptake of PPNFS-120 (265%) is significantly enhanced due to the higher porosity (71.7%). More importantly, the PPNFS-120-based NCM811/graphite and LFP/graphite full cells exhibit excellent rate-performance and cycling stability. This work provides a new idea for the large-scale preparation of high-performance polyolefin nanofiber separators.
Commercial polyolefin separators in lithium batteries encounter issues of uncontrolled lithium-dendrite growth and safety incidents due to their low Li + transference numbers ( t Li + ${t}_{{\mathrm{Li}}^{+}}$ ) and low melting points. To address these challenges, this study proposes an innovative approach by upgrading conventional separators through the incorporation of metal-organic framework (MOF)-confined polyoxometalate (POM). The presence of POM restricts anion diffusion through electrostatic repulsion while facilitating Li + transport within MOF nanochannels through their affinity for lithium ions. Moreover, MOF confinement effectively mitigates the acidification of electrolytes induced by POM. As a proof-of-concept, the polypropylene separators decorated with phosphotungstic acid@UIO66 (denoted as PW 12 @UIO66-PP) exhibit remarkable lithium-ion conductivity of 0.78 mS cm −1 with a high t Li + ${t}_{{\mathrm{Li}}^{+}}$ of 0.75 at room temperature. The modified separators also display excellent thermal stability, preventing significant shrinkage even at 150°C. Furthermore, Li symmetric cells employing PW 12 @UIO66-PP separators exhibit stable cycling for 1000 h, benefiting from rapid Li-ion transport and uniform deposition. Additionally, the modified separator shows promising adaptability to industrial manufacturing of lithium-ion batteries, as evidenced by the assembly of a 4 Ah NCM811/graphite pouch cell that retains 97% capacity after 350 cycles at C/3, thus highlighting its potential for practical applications.
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