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Asymmetrically coated LAGP/PP/PVDF-HFP composite separator film and its effect on the improvement of NCM battery
Tian Liang1,2, Jian-Hua Cao1, Wei-Hua Liang1
1Technical Institute of Physics and Chemistry, Chinese Academy of Science 29 zhongguancun east road, Haidian District Beijing 100190 P. R. China dayongwu@mail.ipc.ac.cn.
Abstract:
Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is an inorganic solid electrolyte with a Na superionic conductor (NASICON) structure that provides a channel for lithium ion transport. We coated LAGP particles on one side of a polypropylene (PP) separator film to improve the ionic conductivity of the separator, and water-dispersed polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) on the other side to reduce the interfacial resistance between the separator and the lithium metal anode. The results show that the LAGP/PP/PVDF-HFP separator has a high ionic conductivity (1.06 mS cm-1) at room temperature (PP separator: 0.70 mS cm-1), and an electrochemical window of 5.2 V (vs. Li+/Li). The capacity retention of a NCM|LAGP/PP/PVDF-HFP|graphite full cell is 81.0% after 300 charge-discharge cycles at 0.2C. When used in a NCM|LAGP/PP/PVDF-HFP|Li half-cell system, the initial discharge capacity is 172.5 mA h g-1 at 0.2C, and the capacity retention is 83.2% after 300 cycles. More significantly, the surface of the Li anode is smooth and flat after 200 cycles. The interface resistance increased from 7 to 109 Ω after 100 cycles at 0.2C. This indicates that the synergistic effect of the asymmetric coated LAGP and PVDF-HFP is beneficial to inhibiting the growth of lithium dendrites in the battery and reduces the interface resistance.
