Two-dimensional molecular brush-functionalized porous bilayer composite separators toward ultrastable high-current density lithium metal anodes

Chuanfa Li,Ganghao Liang,Shaohong Liu,Dingcai Wu,Chenguang Shi,Zhitao Lu,Ruowen Fu

doi:10.1038/s41467-019-09211-z

Abstract

Lithium metal batteries have been considerably limited by the problems of uncontrolled dendritic lithium formation and the highly reactive nature of lithium with electrolytes. Herein, we have developed functional porous bilayer composite separators by simply blade-coating polyacrylamide-grafted graphene oxide molecular brushes onto commercial polypropylene separators. Our functional porous bilayer composite separators integrate the lithiophilic feature of hairy polyacrylamide chains and fast electrolyte diffusion pathways with the excellent mechanical strength of graphene oxide nanosheets and thus enable molecular-level homogeneous and fast lithium ionic flux on the surfaces of electrodes. As a result, dendrite-free uniform lithium deposition with a high Coulombic efficiency (98%) and ultralong-term reversible lithium plating/stripping (over 2600 h) at a high current density (2 mA cm−2) are achieved for lithium metal anodes. Remarkably, lithium metal anodes with an unprecedented stability of more than 1900 h cycling at an ultrahigh current density of 20 mA cm−2 are demonstrated.

Highlights

Lithium metal batteries have been considerably limited by the problems of uncontrolled dendritic lithium formation and the highly reactive nature of lithium with electrolytes
The Fourier transform infrared (FTIR) spectra in Fig. 2b reveal that the PAM chains are successfully grafted from the GO nanosheets, as demonstrated by the presence of two new characteristic peaks of methylene groups at 2922 and 2853 cm−1 and the increased peak intensity of C = O bonds at 1720 cm−1 for GO-g-PAM
The results demonstrate that the molecular-level uniform distribution of polar functional groups enabled by the GO-g-PAM molecular brushes is crucial for achieving dendritefree deposition of Li metal, which results in stable solid electrolyte interphase (SEI) layers with minimized side reactions between the deposited Li and the electrolyte

Summary

Introduction

Lithium metal batteries have been considerably limited by the problems of uncontrolled dendritic lithium formation and the highly reactive nature of lithium with electrolytes. Li dendrite growth is accelerated at the exposed sites, and Li metal and electrolyte are continuously consumed through the formation of SEI layers over repeated plating/stripping processes, giving rise to a low Coulombic efficiency and poor cycling stability. These issues are more severe under the high-current densities that are needed due to the increasing demand of high-power devices.

Methods

Results

Conclusion