Examining Hysteresis in Composite xLi₂MnO₃·(1–x)LiMO₂ Cathode Structures

Abstract

This paper reports the results of an initial investigation into the phenomenon of hysteresis in the charge−discharge profile of high-capacity, lithiumand manganese-rich "layered−layered" xLi 2 MnO 3 •(1−x)LiMO 2 composite cathode structures (M = Mn, Ni, Co) and "layered−layered-spinel" derivatives that are of interest for Li-ion battery applications. In this study, electrochemical measurements, combined with in situ and ex situ X-ray characterization, are used to examine and compare electrochemical and structural processes that occur during charge (lithium extraction) and discharge (lithium insertion) of preconditioned cathodes. Electrochemical measurements of the open-circuit voltage versus lithium content demonstrate a ∼1 V hysteresis in site energy for approximately 12% of the total lithium content during the early cycles, which is markedly different from the hysteresis commonly observed in other intercalation materials. X-ray absorption data indicate structural differences in the cathode at the same state of charge (i.e., the same lithium content) during lithium insertion and extraction reactions. The data support an intercalation mechanism whereby the total number of lithium ions extracted at the top of charge is not reaccommodated in the structure until low states of charge are reached. The hysteresis in this class of materials is attributed predominantly to an inherent structural reorganization after an electrochemical activation of the Li 2 MnO 3 component that alters the crystallographic site energies.

Oxygen Release and Surface Degradation of Li- and Mn-Rich Layered Oxides in Variation of the Li2MnO3Content

“…As oxygen release is hypothesized to be correlated to the voltage hysteresis and the hysteresis between charge and discharge, 11,45 one might pose the question whether the large differences in oxygen release shown in Figure 3 also have such a big influence onto the voltage fading of the different materials. The mean charge and discharge voltages are shown in Figure 4b.…”

“…Therefore, the oxygen release is a side reaction occurring at the HE-NCM nearsurface region, 25 while reversible and irreversible transition metal migration in the bulk material cause the main voltage fading and the high hysteresis. 35,45,46 Figure 5 depicts the dQ/dV plots for cycle 3, cycle 20, and cycle 48 extracted from the cycling data shown in Figure 4. Hereby, cycle 3 is the first C/5 cycle between 2.0 V and 4.7 V and therefore is subjected to the same cycling conditions as cycle 20 and 48.…”

Physical Theory of Voltage Fade in Lithium- and Manganese-Rich Transition Metal Oxides

“…The primary experiments are electrochemical; and often times extracting information on voltage fade phenomena relies on an interpretation of the voltage profile as a function of the number of charge/discharge cycles. Secondary experiments such as X-ray absorption fine structure spectroscopy, 4,11 X-ray diffraction, 4,11 Li nuclear magnetic resonance spectroscopy, 12 neutron diffraction, 8 and transmission electron microscopy, 5 can provide valuable information on cathode structure during the evolution of voltage fade phenomena. These studies provided evidence for a correlation between transition metal migration and voltage fade; leading to a qualitative mechanism of voltage fade as outlined in Ref.…”

Suppression of Manganese-ion Dissolution by SiO₂ Aerosol Addition from Spray Pyrolyzed Li₂MnO₃-LiMn_1/3Ni_1/3Co_1/3O₂

“…Croy et al have reported a correlation between voltage fade and hysteresis in the charge/discharge profiles. 6,7 The layered electrode materials such as 0.5Li 2 MnO 3 · 0.5LiMn 0.375 Ni 0.375 Co 0.25 O 2 exhibit a significant hysteresis loop, which is considerably different from other traditional lithium insertion electrode materials. 6 To account for this hysteresis, both the reversible and irreversible migration of transition metal ions were proposed.…”

“…6,7 The layered electrode materials such as 0.5Li 2 MnO 3 · 0.5LiMn 0.375 Ni 0.375 Co 0.25 O 2 exhibit a significant hysteresis loop, which is considerably different from other traditional lithium insertion electrode materials. 6 To account for this hysteresis, both the reversible and irreversible migration of transition metal ions were proposed. 7 Studies in the literature have so far revealed several important factors for the capacity fade of the layered materials, which include the dissolution of Mn ions into electrolytes, 8 the decomposition of electrolytes through side reactions of LiPF 6 with water molecules, 9 and structural transformations to, e.g.…”