0428同步年報-2021-全

024 ACTIVITY REPORT 2021 Fig. 1 : Illustrated Li-CO 2 battery for the APXPS study in situ at TLS 24A1 . The ionic liquid is composed of [Pyr14] + and [TFSI] - . [Reproduced from Ref. 1] Water vapor accounts for the third most abundant substance in the atmosphere; its concentration fluctuates temporally and geographically. The authors hypothesized that varied water content might be the primary cause of the capacity discrepancy reported in the literature. To examine, they studied the XPS behavior of a Li-CO 2 battery under 5 mbar of 2:1 CO 2 and H 2 O. They found that, when discharging at 1.7−1.2 V Li , a substantial accumulation of amorphous carbon species was accompanied by the growth of LiOH. This result indicated that H 2 O helps to reduce CO 2 to amorphous carbon in the presence of Li + . Further discharge to 1.0 V Li generated carbonate species from CO 2 and LiOH. This observation agrees with the authors' hypothesis that water vapor plays a critical role in promoting CRR in non-aqueous electrolytes. On the charging side of the cycle, the authors found a significantly decreased amorphous carbon and a mild loss of carbonate, of which the withdrawal exposed the subsurface LiOH. When charged to 4.9 V Li , a substantial amount of Li 2 CO 3 and LiOH remained on the electrode. This condition, unfortunately, indicated a poor rechargeability of the battery. The story became quite different with the presence of O 2 . In a 5-mbar 2:1 CO 2 -O 2 mixture, strongly solvated Li + in an ionic liquid bonded more weakly with O 2 – , the activated oxygen intermediate species that consequently initiated CRR. As a result, the dominating discharging carbon product became amorphous carbon instead of carbonate. To bridge the pressure gap between this APXPS model study and a battery working condition at 1 bar, the authors scaled up the CO 2 -O 2 mixture to 1 bar for an X-ray diffraction (XRD) experiment in situ . Although XRD is blind to amorphous carbon, it revealed that Li 2 O 2 and Li 2 O, also seen in the APXPS experiment, appeared in a potential range of no carbonate. The battery for the APXPS experiment resumed 90% of its capacity after a charge. This reversibility is attributed to the simultaneous decomposition of Li 2 O 2 , Li 2 O and amorphous carbon, in addition to the absence of side reactions. (reported by Bo-Hong Liu) This report features the work of Yi-Chun Lu and her co-workers published in Nano Energy 83 , 105830 (2021). TLS 24A1 XPS, UPS, XAS, APXPS • APXPS, XPS, NEXAFS, UPS • Materials Science, Chemistry, Surface, Interface and Thin-film Chemistry, Condensed-matter Physics Reference 1. Y. Wang, W. Wang, J. Xie, C.-H. Wang, Y.-W. Yang, Y.-C. Lu, Nano Energy 83 , 105830 (2021). ·