Separator is an essential component of batteries between anode and cathode, but the commonly used micro-porous polyolefin separator can hardly satisfy the continuously increasing battery energy densities due to its limited thermal stability, low wettability, and poor rate performance. Poly(vinylidene fluoride-hexafluoropropylene)(PVDF-HFP)-LiFePO4(LFP)/LiMn0.5Fe0.5PO4(LMFP)separators are synthesized and investigated for lithium-ion batteries. In addition to 2.7% energy capacity enhancement owing to the incorporation of cathode material, the separators have a robust structure with remarkable thermal stability. LiFePO4/Li cells with PVDF-HFP-LFP separator deliver a room temperature capacity up to 162 mAh g-1 at 0.1 C, and a capacity up to 141 mAh g-1 at 80 oC at 0.5 C. Only 4.7% capacity degradation is observed after 100 charge/discharge cycles, and a capacity of 84 mAh g-1 is achieved at 5 C. LiMn0.5Fe0.5PO4/Li cell with PVDF-HFP-LMFP separator also exhibits an electrochemical performance superior to that with pure PVDF-HFP and commercial Celgard 2400, which indicates that this research is effective to other element doped LFP-materials. The remarkable cyclic and rate capabilities are attributed to the atomic-level integrity of the separator-cathode interface and the electrochemical reaction of LFP and LMFP in the separators as verified by in-situ Raman spectroscopy. Calculations combined with Fourier-transform infrared spectroscopy analysis suggest that there exists a strong interaction between the -CF3 group in PVDF-HFP and the LiO surface of LFP and LMFP.

Incorporating cathode materials into polymeric separator for lithium-ion batteries: Beyond additional capacity

2019 Spring National Meeting

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