A tailored ceramic composite separator with electron-rich groups for high-performance lithium metal anode

Ceramic composite separator is more competitive than traditional polyolefin separator in the field of power supply for superior thermal stability and wettability of liquid electrolyte. In this study, we develop a two-steps method that modifies SiO2 with acrylamide (AM) by grafting process and prepare a functional SiO2 composite separator (PE/SiO2-AM). This kind of composite separator exhibits similar size-shrinkage (8.8%) to that of PE/ SiO2 composite separator at the tested temperature, lower than 18.1% of bare PE separator, and is electrochemically stable below 4.5 V (vs. Li/Li+). In addition, the Li-symmetric cells employing PE/SiO2-AM composite separator have the lowest overpotential and an improved lithium-ion transference number of 0.44. It is demonstrated from DFT calculation that the electron-rich species of imide group is able to uniformly disperse lithium-ion flux at the interface of electrolyte/lithium anode, and contributes to lithium-ion transport process. After assembling the LiCoO2/Li half cells, the cell with PE/SiO2-AM composite separator displays better cycle performance and higher discharge capacity when compared with other separators. Therefore, functional ceramic separator would be more attractive for next-generation lithium metal battery with high energy density.