In Situ Observation and Evaluation of Electrodeposited Lithium by Means of Optical Microscopy with Alternating Current Impedance Spectroscopy

Abstract

Electrodeposited lithium was evaluated by ac impedance measurement and optical microscopy in two solutions con-taining LiC104; a propylene carbonate (PC) solution and a blended solution consisting of PC and 1,2-dimethoxyethane (DME) (volume ratio = 1:1). The ac impedance data were analyzed in the higher frequency region, where the charge-transfer resistance (Rct) Of Li + + e- ~ Li can be evaluated. The value of Rct was always larger in the PC electrolyte solution than in the PC-DME(I:I) electrolyte solution, and R~t depended on the lithium deposition charge. Microscopic observation i di-cated that lithium deposited more uniformly in PC-DME (1:1) than in PC solution. The results of morphological evaluation of the electrodeposited lithium using optical microscopy corresponded to the variations in the value of R~t obtained from ac impedance measurements, showing that the behavior of Rct accurately represented the morphological state. The cy-cleability of the lithium anode was investigated by charge-discharge testing. The cycle efficiency was worse in PC than in PC-DME (1:1) solution; this seems to be related to the morphological properties of the lithium deposits. Lithium batteries are some of the best candidates for use as high energy density batteries and have been widely stud-ted. 1'2 However, there is a major obstacle to the develop-ment of rechargeable lithium batteries, in that a lithium