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High-entropy oxides based on transition metals, such as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (TM-HEO), have recently drawn special attention as potential anodes in lithium-ion batteries due to high specific capacity and cycling reversibility. However, the lithiation/delithiation mechanism of such systems is still controversial and not clearly addressed. Here, we report on an operando XAS investigation into TM-HEO-based anodes for lithium-ion cells during the first lithiation/delithiation cycle. This material showed a high specific capacity exceeding 600 mAh g-1 at 0.1 C and Coulombic efficiency very close to unity. The combination of functional and advanced spectroscopic studies revealed complex charging mechanisms, developing through the reduction of transition-metal (TM) cations, which triggers the conversion reaction below 1.0 V. The conversion is irreversible and incomplete, leading to the final collapse of the HEO rock-salt structure. Other redox processes are therefore discussed and called to account for the observed cycling behavior of the TM-HEO-based anode. Despite the irreversible phenomena, the HEO cubic structure remains intact for ∼60% of lithiation capacity, so proving the beneficial role of the configuration entropy in enhancing the stability of the HEO rock-salt structure during the redox phenomena.

Enhancing electrode areal capacity of lithium-ion batteries will result in cost saving and better electrochemical performances. Additive manufacturing (AM) is a very promising solution, which enables to build structurally complex electrodes with well-controlled geometry, shape and thickness. Here we report on 3D-printed cathodes based on LiMn2O4 (LMO) as the active material, which are fabricated by robocasting AM via aqueous processing. Such a technology is: i) environmentally friendly, since it works well with water and green binders; ii) fast, due to very short deposition times and rapid drying process because of low amount of solvent in the printable pastes; iii) easily scalable. The cathodes are produced by extruding pastes with higher solid loadings (>70 vol %) than those typically reported in literature. The printing efficiency is strongly affected by both the binder and the carbonaceous additive. The best cathode is composed by LMO, Pluronic as the binder, and a mixture of graphite/carbon black as the electronic conductor, which is critical for achieving optimal electrochemical performance. The cathode with thickness of 200 μm and mass loading of 13 mg cm−2 exhibits good electrochemical areal capacity (2.3 mAh cm−2) and energy density (>32 J cm−2). Our results may boost the development of greener, lower cost and more efficient new generation of LIBs for applications as household energy storage or even micro-battery technology.

High entropy oxides based on transition metals, as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (TM-HEO), have recently drawn special attention as potential anodes in lithium-ion batteries, due to high specific capacity and cycling reversibility. However, the lithiation/delithiation mechanism of such systems is still controversial and not clearly addressed. Here, we report on an operando XAS investigation on TM-HEO based anodes for lithium-ion cells during the first lithiation/delithiation cycle. This material showed high specific capacity exceeding 600 mAh g-1 at C/10 and Coulombic efficiency very close to unit. The combination of functional and advanced spectroscopic study revealed complex charging mechanisms, developing through an initial Li intercalation reaction during the first charging cycle, followed by the reduction of transition metal (TM) cations, which triggers the conversion reaction below 1.0 V. The conversion is irreversible and not completed, leading to the final collapse of the HEO rock-salt structure. Other redox processes are therefore discussed and called to account the observed cycling behavior of the TM-HEO based anode. Despite the irreversible phenomena, the HEO cubic structure remains intact for ~ 60% of lithiation delivered capacity, so proving the beneficial role of the configuration entropy to enhance the stability of the HEO rock-salt structure during the redox phenomena.