Investigation of particle isolation in Li-ion battery electrodes using 7Li NMR spectroscopy

Li-7 MAS NMR spectroscopy was used to study the failure mechanisms of LiNi0.8Co0.15Al0.05O2 electrodes in Li-ion cells. Three sets of electrodes with different degrees of power fade (0%, 9%, and 23%) were Studied. The three electrodes were charged to various states of charge (0%, 40%, 60%, 80% and 100%) in pouch cells which were Subsequently disassembled for NMR analysis. The lithium NMR shifts of the positive electrodes in the different states of charge were investigated. The results indicate that NMR spectroscopy can be used to probe particle isolation in these electrodes. Particle isolation is responsible for the capacity and power fades since some of the active material particles are disconnected from the matrix. This Study also clearly showed the loss of electrochemically active lithium as the power fade increased. (c) 2005 Elsevier B.V. All rights reserved.