Double-sided conductive separators for lithium-metal batteries

Abstract

A novel double-sided conductive (DSC) separator consisting of two 5 μm-thick carbon nanotube (CNT)/cellulose nanofiber (CNF) composite layers coated on each side of a 20 μm-thick glass-fiber (GF)/CNF composite membrane is described. In a lithium-metal battery (LMB), the DSC separator exhibits a high ionic conductivity (i.e. 1.7 mS cm−1 using an LP40 electrolyte) due to the high porosity (i.e. 66%) of the GF/CNF membrane. More stable Li anodes can also be realized by depositing Li within the porous electronically conducting CNT/CNF matrix at the DSC separator anode side due to the decreased current density. The CNT/CNF layer of the DSC separator facing the cathode, which is in direct electric contact with the current collector, decreases the overpotential for the cathode and consequently improves its capacity and rate performance significantly. A Li/Li cell containing a DSC separator showed an improved cycling stability compared to an analogous cell equipped with a commercial Celgard separator at current densities up to 5 mA cm−2 for Li deposition and stripping capacities up to 5 mAh cm−2. A proof-of-concept LMB containing a lithium iron phosphate (LFP) composite cathode and a DSC separator showed a significantly improved rate capability, yielding capacities of about 110 mAh g−1 at 5 C and 80 mAh g−1 at 10 C. The LMB cell containing a DSC separator also exhibited a capacity retention of 80% after 200 cycles at a rate of 6 C indicating that the two-sided conductive separator design has significant potential in facilitating the development of well-functioning LMBs.