Chemical synthesis of unconventional topologically close-packed intermetallic nanocrystals (NCs) remains a considerable challenge due to the limitation of large volume asymmetry between the components. Here, a series of unconventional intermetallic Frank-Kasper C15 phase Ir2M (M = rare earth metals La, Ce, Gd, Tb, Tm) NCs is successfully prepared via a molten-salt assisted reduction method as efficient electrocatalysts for hydrogen evolution reaction (HER). Compared to the disordered counterpart (A1-Ir2Ce), C15-Ir2Ce features higher Ir-Ce coordination number that leads to an electron-rich environment for Ir sites. The C15-Ir2Ce catalyst exhibits excellent and pH-universal HER activity and requires only 9, 16, and 27 mV overpotentials to attain 10 mA cm-2 in acidic, alkaline, and neutral electrolytes, respectively, representing one of the best HER electrocatalysts ever reported. In a proton exchange membrane water electrolyzer, the C15-Ir2Ce cathode achieves an industrial-scale current density of 1 A cm-2 with a remarkably low cell voltage of 1.7 V at 80 °C and can operate stably for 1000 h with a sluggish voltage decay rate of 50 µV h-1. Theoretical investigations reveal that the electron-rich Ir sites intensify the polarization of *H2O intermediate on C15-Ir2Ce, thus lowering the energy barrier of the water dissociation and facilitating the HER kinetics.

Polycrystalline Ni-rich layered lithium transition metal oxides are one of the most promising cathode materials for next-generation high energy density lithium-ion batteries, yet they are still facing many challenges, especially for the cycling induced structural degradations. Intergranular cracking has been identified as one of the most crucial degradations, and grain boundary (GB) engineering has been demonstrated to be an effective countering strategy. Herein, we report a GB modification protocol that can realize not only improved GB stability but also interfacial reaction kinetics, realizing much improved cycling performance of NCM811. The simple and effective solution method can incorporate Ti-dopant into GBs and secondary particle surface, realizing the increase of the capacity retention from 79.5% to 93.5% at 3.0-4.5 V after 100 cycles, and its high voltage (4.7 V) and high temperature (55 degrees C) cycling stability are also significantly improved. Comprehensive microstructure and electrochemical characterizations of the samples before and after cycling are conducted to reveal the underlying mechanisms, validating that both interfacial degradations and bulk failures have been effectively mitigated. This work provides an effective protocol in the modification of GBs and interfaces of polycrystalline battery materials, which is promising and feasible for industrial mass-production application.

Interfacial degradations dominate the performance decay of O3-layered cathode during low-voltage cycling; high voltage cycling induced bulk failures cause rapid performance decay due to transition metal cation migration.

Constructing robust surface and bulk structure is the prerequisite for realizing high performance high voltage LiCoO2 (LCO). Herein, we manage to synthesize a surface Mg-doping and bulk Al-doping core-shell structured LCO, which demonstrates excellent cycling performance. Half-cell shows 94.2% capacity retention after 100 cycles at 3-4.6 V (vs. Li/Li+) cycling, and no capacity decay after 300 cycles for full-cell test (3.0-4.55 V). Based on comprehensive microanalysis and theoretical calculations, the degradation mechanisms and doping effects are systematically revealed. For the undoped LCO, high voltage cycling induces severe interfacial and bulk degradations, where cracks, stripe defects, fatigue H2 phase, and spinel phase are identified in grain bulk. For the doped LCO, Mg-doped surface shell can suppress the interfacial degradations, which not only stabilizes the surface structure by forming a thin rock-salt layer but also significantly improves the electronic conductivity, thus enabling superior rate performance. Bulk Al-doping can suppress the lattice “breathing” effect and the detrimental H3 to H1-3 phase transition, which minimizes the internal strain and defects growth, maintaining the layered structure after prolong cycling. Combining theoretical calculations, this work deepens our understanding of the doping effects of Mg and Al, which is valuable in guiding the future material design of high voltage LCO.

Cathode electrolyte interphase (CEI) layer plays a crucial role in determining the electrochemical performance of lithium-ion batteries. Limited by the sensitive nature of CEI and the lack of characterization techniques, its dynamic evolution during cycling, its formation mechanism, and its specific impact on battery performance are not yet fully understood. Herein, we systematically investigate the dynamic evolution of CEI layer and its critical effect on the cycling performance of LiCoO2 cathode by diverse characterization techniques. We find that cycling voltage plays a key role in affecting CEI formation and evolution, and a critical potential (4.05 V vs. Li) is identified, which acts as the switching potential between CEI deposition and decomposition. We show that CEI starts deposition in the discharge process when the potential is below 4.05 V, and CEI decomposition occurs when the potential is higher than 4.05 V. When the battery is cycled below such a critical potential, a stable CEI layer is developed, which leads to superior cycling stability. When the battery is cycled above such a critical potential, a CEI-free cathode interface is observed, which also demonstrates good cycle stability. However, when the critical potential falls in the cycling voltage range, CEI deposition and decomposition are repeatedly switched on during cycling, leading to the dynamically unstable CEI layer. The unstable CEI layer causes continuous interfacial reaction and degradation, resulting in battery performance decay. Our work deepens the understanding of the CEI formation and evolution mechanisms, and clarifies the critical effect of CEI layer on cycling performance, which provides new insights into stabilizing the electrode–electrolyte interface for high-performance rechargeable batteries.

Surface modification is an effective approach for overcoming the interfacial degradations to enable high electrochemical performance of battery materials, yet it is still challenging to realize high-quality surface modification with simple processing, low cost, and mass production. Herein, a thermal-induced surface precipitation phenomenon is reported in a Ti-dopped LiCoO2 , which can realize an ultrathin (≈5 nm) and uniform surface modification by a simple annealing process. It is revealed that surface Li-deficiency enables bulk Ti to precipitate and segregate on the non-(003) surface facets, forming a Ti-enriched disordered layered structure. Such a surface modification layer can not only stabilize the interfacial chemistry but also significantly improve the charge/discharge reaction kinetics, leading to much-improved cycling stability and rate capability. Dopants surface precipitation is a unique outward diffusion process, which differs from the current surface modification techniques and further diversifies these approaches for realizing high-quality surface modification of battery materials.

Cycling-induced cathode interfacial degradations are usually attributed to chemical process, while the physical effect is overlooked to a large extent. Herein, we investigate the failure mechanism of LiCoO2 cathode and reveal that misfit strain plays a dominant role in the surface layer exfoliation process. We illustrate that highly strained LiCoO2 surface can initiate massive surface cracks, leading to the LiCoO2 surface layer broken and exfoliation. Mechanical cracking coupled with chemical etching aggravates the surface layer degradation, leading to a weathering-like degradation on LiCoO2 surface. Our work reveals that interfacial degradation of electrode materials is a complex physicochemical process. [GRAPHICS] .

It is known that uniformly dispersed rare earth oxide (RE2O3) nanoparticles in molybdenum matrix could improve the ductility of Mo. However, it is reported that the agglomeration of La2O3 was quite serious when the addition amount of La2O3 was over 2 wt%, which leaded to a dramatic decrease of the ductility of Mo. In this paper, a new type of uniformly dispersed Er2O3 doped Mo powder was prepared, with the amount of Er2O3 accounting for 4 wt%. It is found that the reduction temperature of MoO3 was higher and the grain size was smaller for the Mo powders doped with Er2O3 than those doped with La2O3. First-principles calculations illustrate that La2O3/Er2O3 had a strong trend to be absorbed on the surface of MoO3, and the inhibition capability for the reduction of MoO3 to MoO2 by Er3+ was larger than La3+ due to the stronger Er-O interactions. It gives a potential explanation of the higher reduction temperature of MoO3 doped with Er2O3 than that doped with La2O3. Furthermore, the formation energies of Er-O and La-O pairs within the bulk Mo were in the sequence: La-O > Er-O > 0 eV, indicating that these systems are unstable and La2O3 is easier to escape from the interior of Mo grains and agglomerate on the Mo surface than Er2O3. (C) 2019 Elsevier B.V. All rights reserved.

The alloying effect of cerium in low carbon granular bainitic steel has been studied. Cerium increases the incubation time of granular bainitic transformation, exerts an influence on the morphology of nucleation and growth of bainitic transformation, and refines the structure of normalized granular bainite.