Investigation of the cyclic aging characteristics and degradation mechanism of LiNi1/3Co1/3Mn1/3O2 batteries by non-invasive methodologies

Abstract

Cyclic aging tests of LiNi1/3Co1/3Mn1/3O2 batteries are performed at 25℃, 45℃ and 60℃. Several non-invasive electrochemical techniques, such as incremental capacity analysis, differential voltage analysis and capacity difference analysis, are employed to deduce degradation mechanism. The degradation mechanism of batteries is similar at different temperatures. Loss of active positive material follows a linear function at all conditions and increases by elevating temperature. Due to the graphite's volume expansion and contraction, loss of active negative material is observed at the first 100 full cycle equivalents. Then, it disappears until the appearance of a dense lithium-containing passivation layer. This covering layer is mainly from lithium deposition on the negative electrode surface. With this lithium-impermeable covering layer's growth, the homogeneity of active lithium distribution is successively reduced, and loss of negative material increases gradually. Moreover, a worst cyclic performance is found at 45℃, where the homogeneity of electrodes reduces rapidly. All results reveal that loss of active materials and lithium inventory loss only influence capacity loss. The evolution of the covering layer on the negative electrode surface is the deciding factor for cycle life.