Proton-conducting solid-oxide electrolyzer and fuel cells (PC-SOECs/FCs) represent viable, intermediate-temperature green technologies for H2 production and conversion. While PC ceramics have been extensively investigated as electrolytes for PC-SOECs/FCs, the development of corresponding single-phase electrode components has been hindered by difficulties in finding efficient mixed proton-electron conductors (MPECs), with also effective catalytic activity toward oxygen reduction and evolution reactions (ORR/OER). To address this challenge, we applied first-principles methods (PBE+U) to design new perovskite-oxide MPEC electrodes based on the known BaZrO3 PC ceramic. Our strategy has been to modify the parent material by substituting Zr with earth abundant transition metals, namely Mn and Fe. We found Zr:Mn and Zr:Fe ratios of 0.75:0.25 to be sufficient to obtain electronic structural features that can enable electric conductivity. We also investigated other relevant processes for MPEC-based electrodes: hydration, proton migration, and ORR/OER electrocatalysis. From calculations of key descriptors associated with these processes, we found that Zr substitution with Mn or Fe delivers in both cases promising PC-SOEC/FC electrodes. Moreover, our first-principles results highlight the specific qualities of Mn and Fe: the first provides better electronic features and electrocatalytic activities, whereas the latter allows for better hydration and proton migration. In perspective, our findings present clear indications for the experimental implementation and test of new low-cost materials for solid-oxide electrochemical cells

Transition-metal (TM) layered oxides have been attracting enormous interests in recent decades because of their excellent functional properties as positive electrode materials in lithium-ion batteries. In particular LiCoO2 (LCO), LiNiO2 (LNO) and LiMnO2 (LMO) are the structural prototypes of a large family of complex compounds with similar layered structures incorporating mixtures of transition metals. Here, we present a comparative study on the phase stability of LCO, LMO and LNO by means of first-principles calculations, considering three different lattices for all oxides, i.e., rhombohedral (hR12), monoclinic (mC8) and orthorhombic (oP8). We provide a detailed analysis—at the same level of theory—on geometry, electronic and magnetic structures for all the three systems in their competitive structural arrangements. In particular, we report the thermodynamics of formation for all ground state and metastable phases of the three compounds for the first time. The final Gibbs Energy of Formation values at 298 K from elements are: LCO(hR12) −672 ± 8 kJ mol−1; LCO(mC8) −655 ± 8 kJ mol−1; LCO(oP8) −607 ± 8 kJ mol−1; LNO(hR12) −548 ± 8 kJ mol−1; LNO(mC8) −557 ± 8 kJ mol−1; LNO(oP8) −548 ± 8 kJ mol−1; LMO(hR12) −765 ± 10 kJ mol−1; LMO(mC8) −779 ± 10 kJ mol−1; LMO(oP8) −780 ± 10 kJ mol−1. These values are of fundamental importance for the implementation of reliable multi-phase thermodynamic modelling of complex multi-TM layered oxide systems and for the understanding of thermodynamically driven structural phase degradations in real applications such as lithium-ion batteries.

The development of cathode materials represents the key bottleneck to further push the performance of current Li-ion batteries (LIB) beyond the commercial benchmark. Li-rich transition-metal-layered oxides (LRLOs) are a promising class of materials to use as high-capacity/high-potential positive electrodes in LIBs thanks to the large lithium content (e.g., ∼1.2 Li equiv per formula unit) and the exploitation of multiple redox couples (e.g., Mn4+/3+, Co4+/3+, Ni4+/3+/2+). In this work, we propose and demonstrate experimentally a Co-free overlithiated LRLO material with a limited nickel content, i.e., Li1.25Mn0.625Ni0.125O2. This LRLO is able to exchange reversibly an outstanding practical specific capacity at room temperature, i.e., 230 mAh g–1 at C/10 for almost 200 cycles, and can sustain high current rates, i.e., 118 mAh g–1 at 2C. This material has been successfully prepared by a facile solution combustion synthesis and characterized by scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), X-ray diffraction (XRD), and Raman techniques. Overall, our positive electrodes based on Li1.25Mn0.625Ni0.125O2 overlithiated Co-free LRLO is a step forward in the development of the materials for batteries with improved performance and better environmental fingerprint.

Li-rich layered oxide (LRLO) materials are promising positive-electrode materials for Li-ion batteries. Antisite defects, especially nickel and lithium ions, occur spontaneously in many LRLOs, but their impact on the functional properties in batteries is controversial. Here, we illustrate the analysis of the formation of Li/Ni antisite defects in the layered lattice of the Co-free LRLO Li1.2Mn0.6Ni0.2O2 compound through a combination of density functional theory calculations performed on fully disordered supercells and a thermodynamic model. Our goal was to evaluate the concentration of antisite defects in the trigonal lattice as a function of temperature and shed light on the native disorder in LRLO and how synthesis protocols can promote the antisite defect formation.

In this manuscript, we report an extensive study of the physico-chemical properties of different samples of O3-NaMnO2, synthesized by sol–gel and solid state methods. In order to successfully synthesize the materials by sol–gel methods a rigorous control of the synthesis condition has been optimized. The electrochemical performances of the materials as positive electrodes in aprotic sodium-ion batteries have been demonstrated. The effects of different synthesis methods on both structural and electrochemical features of O3-NaMnO2 have been studied to shed light on the interplay between structure and performance. Noticeably, we obtained a material capable of attaining a reversible capacity exceeding 180 mAhg−1 at 10 mAg−1 with a capacity retention >70% after 20 cycles. The capacity fading mechanism and the structural evolution of O3-NaMnO2 upon cycling have been extensively studied by performing post-mortem analysis using XRD and Raman spectroscopy. Apparently, the loss of reversible capacity upon cycling originates from irreversible structural degradations.