Abstract
Although stoichiometric lithium cobalt dioxide LiCoO2 (ST-LCO) is the most common positive electrode material for Li-ion batteries, the magnetic nature of ST-LCO is still not fully understood. Therefore, we measured susceptibility (χ), electron paramagnetic resonance (EPR), and μSR for ST-LCO, particularly above 100 K. The temperature dependence of χ shows a Pauli paramagnetic behavior, supporting the previous conclusion that Co3+ ions are in a low-spin state with S = 0 (t62g). However, the EPR and μSR measurements reveal a "dynamical" magnetic phase in ST-LCO above 100 K. Because the volume fraction of this magnetic phase reaches about 50% at 300 K, the appearance of the magnetic phase is not caused by impurities and/or muonium formation but is an intrinsic characteristic of ST-LCO. By considering the time windows of the three measurement techniques used in this study, we conclude that the origin of the dynamical magnetism is most likely spin fluctuations of the Co ions.
Highlights
Since the discovery that Li+ ions are reversibly extracted and inserted by an electrochemical reaction [1], lithium cobalt oxide LiCoO2 (LCO) has been widely used as a positive electrode material for lithium-ion batteries (LIBs)
Susceptibility (χ) measurements indicate that the Co3+ ions are in a nonmagnetic low-spin (LS) state with S = 0 (t62g) [3], μSR measurements clarify the complex magnetic nature below 60 K
This supports that the appearance of localized moments at low T is an intrinsic feature for LiCoO2. This is quite different from NaCoO2 [7], which is an isostructural compound of stoichiometric lithium cobalt dioxide LiCoO2 (ST-LCO). We report another unique magnetic feature of ST-LCO, i.e., “dynamical magnetism” at 100 K ≤ T ≤ 500 K clarified by electron paramagnetic resonance (EPR) and μSR measurements up to 500 K
Summary
Since the discovery that Li+ ions are reversibly extracted and inserted by an electrochemical reaction [1], lithium cobalt oxide LiCoO2 (LCO) has been widely used as a positive electrode material for lithium-ion batteries (LIBs). Susceptibility (χ) measurements indicate that the Co3+ ions are in a nonmagnetic low-spin (LS) state with S = 0 (t62g) [3], μSR measurements clarify the complex magnetic nature below 60 K. We report another unique magnetic feature of ST-LCO, i.e., “dynamical magnetism” at 100 K ≤ T ≤ 500 K clarified by electron paramagnetic resonance (EPR) and μSR measurements up to 500 K.
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