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Catalysts containing isolated single atoms have attracted much interest due to their good catalytic behavior, bridging the gap between homogeneous and heterogeneous catalysts. Here, we report an efficient oxygen reduction reaction (ORR) catalyst that consists of atomically dispersed single copper sites confined by defective mixed-phased TiO2−x. This synergistic catalyst was produced by introducing Cu2+ to a metal organic framework (MOF) using the Mannich reaction, occurring between the carbonyl group in Cu(acac)2 and the amino group on the skeleton of the MOF. The embedding of single copper atoms was confirmed by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and x-ray absorption fine structure spectroscopy. Electronic structure modulation of the single copper sites coupling with oxygen vacancies was further established by electron paramagnetic resonance spectroscopy and first-principles calculations. Significantly enhanced ORR activity and stability were achieved on this special Cu single site. The promising application of this novel electrocatalyst was demonstrated in a prototype Zn–air battery. This strategy of the stabilization of single-atom active sites by optimization of the atomic and electronic structure on a mixed matrix support sheds light on the development of highly efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

The huge volume change during cycling causes severe electrode pulverization and rapid capacity fading of Si-based anodes. So far, various carbon-coating methods have been explored to enhance the cycling stability of Si anodes. However, the mechanism behind this strategy receives little attention. In this work, the stability of the solid electrolyte interphase (SEI) formed on carbon-coated Si and its role in the fracture inhibition are verified using X-ray photoelectron spectroscopy with Ar ion sputtering and the amplitude modulation-frequency modulation mode of scanning probe microscopy. A comparative experimental study and density functional theory calculations of the adsorption energy of electrolyte components confirm that fluoroethylene carbonate is more apt to be adsorbed on the surface of the carbon-coating layer to form a robust SEI than on that of Si. The LiF-rich SEI with higher Young's modulus can withstand the volume change upon lithiation/delithiation of Si, and keep itself intact. Therefore, the enhanced SEI can inhibit the cracking of Si and suppress continuous decomposition of electrolyte. This study provides critical insights into the function of the SEI from the perspective of carbon coating/electrolyte interphase protection, and also gives valuable suggestions to the design of electrodes with large volume change. [ABSTRACT FROM AUTHOR]

Nickel-rich layered oxides are attractive cathode for lithium-ion batteries (LIBs) because of the high energy density and low cost. The critical problem is capacity fading caused by the highly reactive metastable phases under voltages of higher than 4.15 V. Herein, we find that facile Ar/H2 plasma treating could produce oxygen vacancies that will readily transform into homogeneous spinel layer (∼ 6 nm) on the LiNi0.8Co0.1Mn0.1O2 (NCM811) surface after a few cycles of lithiation/delithiation procedure. Owing to the structural matching between spinel and layered structure, the diffusion of Li ions could remain fast upon cycling. Besides, the spinel layer is electrochemically inert, which guarantees surface stabilization and inhibits the detrimental phase transition from H2 to H3 at high voltages. Under the protection of the homogeneous spinel layer, the NCM811 electrode shows superior capacity retention of 91.2% after 200 cycles at the current density of 100 mA·g−1. This work proposes a novel strategy of surface reconstruction to stabilize nickel-rich layered oxide materials for LIBs. [ABSTRACT FROM AUTHOR]

It is highly desirable to raise the charge cutoff voltage to realize the potential of LiCoO2 (LCO) with its ultra‐high theoretical capacity of 275 mAh g‐1. However, rapid fading due to structure collapse caused by the formation of the H1‐3 metastable phase and the release of surface lattice oxygen has largely hindered the operation of LCO under voltages of higher than 4.55 V. Here, stable cycling of LCO at 4.6 V through hierarchical doping engineering with inert P‐outside and active Ni‐inside dual doping is achieved. This ingenious outside‐in structure design enables Ni2+ occupation in the Li layer in the bulk layered phase and P gradient doping at the superficial lattice. Compared with the conventional inert element substitution strategy, the doped active Ni2+ can not only serve as a "pillar" to restrain the formation of the metastable H1‐3 phase, but also regulate the electronic structure of LCO and trigger the superexchange interaction of Ni2+‐O‐Co4+, together with strong P–O coordination to substantially suppress the lattice oxygen escape from the surface. Therefore, it considerably reduces the risk of layer structure collapse and consequently achieves stable and high‐capacity operation over 4.6 V. This hierarchical outside‐in doping strategy may serve as inspiration for stabilizing high energy electrode materials working under high voltages. [ABSTRACT FROM AUTHOR]

High‐voltage LiCoO2 is an attractive cathode for ultra‐high energy lithium‐ion batteries in the 5G era. However, the practical application of LiCoO2 is largely hindered by the unstable structure under high voltage. Herein, dextran sulfate lithium (DSL) is used as a versatile binder to improve the cycling stability of LiCoO2 at 4.6 V. A coulombic efficiency of almost 100% and 93.4% capacity retention after 100 cycles has been achieved. The aqueous DSL binder can be evenly coated onto the surfaces of LiCoO2 particles to function as an artificial interface, significantly preventing the decomposition of electrolyte and the dissolution of Co ions. More importantly, the superior interaction between the sulfate acid groups of DSL chains and the LiCoO2 particles enhances the stability of CoO chemical bonds, further suppressing the detrimental phase transition from O3 to H1‐3 above 4.55 V. The stabilization of high‐voltage LiCoO2 through the binder is facile and enlightening to design high energy battery materials. [ABSTRACT FROM AUTHOR]