7Li NMR Study on Irreversible Capacity of LiNi0.8-xCo0.15Al0.05MgxO2 Electrode in a Lithium-Ion Battery. Issue 7 (18th April 2015)

• Record Type: Journal Article
• Authors: Murakami, Miwa; Shimoda, Keiji; Ukyo, Yoshio; Arai, Hajime; Uchimoto, Yoshiharu; Ogumi, Zempachi
• Is Part Of: Journal of the Electrochemical Society. Volume 162:Issue 7(2015)
• Page Start: A1315
• Page End: A1318
• Publication Date: 2015-04-18
• Subjects: Lithium ion battery -- solid-state NMR -- ultra-fast MAS; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0781507jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Effects of magnesium and the charge/discharge process on the local structure of LiNi0.8-x Co0.15 Al0.05 Mg x O2 ( x = 0, 0.05, 0.10) were examined by 7 Li MAS NMR. Two distinct 7 Li signals were observed at ca. 660 ppm and at ca. 570 ppm for the x = 0 material by the combined use of ultra-fast MAS (100 kHz) and high magnetic field (14 T). We attributed these two signals to two Ni-rich domains for the x = 0 material; the former Li signal is assigned to the Li site, whose local structure is expressed formally as LiNiO2 and the latter to LiNi0.83 (Co/Al)0.17 O2 . The intensities of these Ni-rich domains reduce significantly upon slight addition of magnesium. This leads us to conclude that magnesium preferably replaces nickel in the Ni-rich domains. After the first charge/discharge process, the signal intensities at 500∼750 ppm assigned to the Ni-rich domains in the x = 0 material decrease appreciably. From this, we conclude that the lithium ions responsible for the irreversible capacity after the first cycle belong to the Ni-rich domains, and the reduction of the amount of the Ni-rich domains due to magnesium substitution is responsible for the improved cyclic performance of the x > 0 material as a positive electrode material.