Stabilization of xLi[sub 2]MnO[sub 3]⋅(1−x)LiMO[sub 2] Electrode Surfaces (M=Mn, Ni, Co) with Mildly Acidic, Fluorinated Solutions

Abstract

It has been demonstrated previously that Li2MnO3Li2MnO3 -stabilized LiMO2LiMO2 electrodes [ xLi2MnO3⋅(1−x)LiMO2xLi2MnO3⋅(1−x)LiMO2 , M=MnM=Mn , NiNi , CoCo ] can provide anomalously high electrochemical capacities (∼250mAh∕g)(∼250mAh∕g) if charged to high potentials (4.6V)(4.6V) . High-voltage charging results in an irreversible capacity loss on the initial charge/discharge cycle; it also damages the electrode surface, leading to a high cell impedance. In this paper, we report that preconditioning 0.1Li2MnO3⋅0.9LiMn0.256Ni0.372Co0.372O20.1Li2MnO3⋅0.9LiMn0.256Ni0.372Co0.372O2 electrode powders [alternatively Li1.048(Mn0.333Ni0.333Co0.333)0.952O2Li1.048(Mn0.333Ni0.333Co0.333)0.952O2 in Li1+xM1−xO2Li1+xM1−xO2 notation] with extremely mild acidic solutions of NH4PF6NH4PF6 , (NH4)3AlF6(NH4)3AlF6 , and NH4BF4NH4BF4 salts in water and methanol (pH 6–6.5) leads to remarkable cycling stability of both lithium half-cells and full lithium-ion cells when repeatedly charged to high voltages (≥4.5V)(≥4.5V) . The enhanced electrochemical performance is attributed to stabilized electrode surfaces that are etched and passivated by fluorinated species. The low-temperature behavior of unconditioned and preconditioned electrodes is presented.