Investigation and Improvement of Metallic Aluminum as Alloying Electrode in Non-Aqueous Li Cells

Abstract

Aluminum metal is known to be one of attractive negative electrode materials for lithium-ion batteries because of its electrochemical alloying reaction with lithium. We investigate electrochemical properties of bare Al foil, double layered sheet of Al foil and graphite composite layer, and Al powder composite electrodes in non-aqueous Li cell. From comparing the electrochemical properties by using different binders, electrolyte additives, separators, current collectors, Al alloys of AlSb and AlNi, an Al powder composite electrode composed of Al powder, acetylene black, and poly(vinylidene fluoride) binder on Cu foil exhibits better reversibility and capacity retention on the basis of the electrochemical formation of LiAl alloy. Although the rapid capacity fading is observed in a conventional LiPF6 carbonate-ester solution, a highly concentrated electrolyte of 11 mol kg−1 lithium bis(fluorosulfonyl)imide dimethoxyethane solution demonstrates stable capacity retention of 940 mAh (g of Al mass)−1 for 15 cycles. Surface analyses and X-ray diffraction of tested electrodes revealed that dense structure of powdery Al layer can be maintained with uniform surface layer consisting of electrolyte decomposition products and residual Al oxide. The surface layer suppresses the electric isolation of Al particles resulting in the improved alloy/dealloy reversibility.