86 巻 (2018) 3 号 p. 116-121
The development of SIB has attracted attention as a substitute for LIB. Low-temperature-fired soft carbon (LFSC) has been the target of study as SIB’s useful negative electrode material. We estimated Na chemical diffusion coefficient Dchem using the same approach and samples of previous report on LIB. The approach was potential step chronoamperometry (PSCA) method, and the samples were mesophase-pitch-based carbon fiber fired at four different low temperatures (600, 700, 800 and 950°C). The PSCA measurements by using a single LFSC fiber electrode were performed in an electrolyte of propylene carbonate (PC) containing 1 M NaClO4 at room temperature in a glove box filled with dried Ar. The largest Dchem value we obtained with four pristine LFSC was about 10−9 cm2/sec. The Dchem values depended not only on firing temperature of LFSC but also on the nature of LFSC’s surface. The effective surface treatment promoted Na insertion/extraction reaction rate on the carbon surface. The largest Na Dchem value we obtained after surface treatment was 10−8 cm2/sec. This Na Dchem value was close to the Li Dchem value (10−7.5 cm2/sec) by previous report, which suggests possibility of SIB’s practical use.