Interfacial Design on Graphene–Hematite Heterostructures for Enhancing Adsorption and Diffusion towards Superior Lithium Storage

Hematite (α-Fe2O3) is a promising electrode material for cost-effective lithium-ion batteries (LIBs), and the coupling with graphene to form Gr/α-Fe2O3 heterostructures can make full use of the merits of each individual component, thus promoting the lithium storage properties. However, the influences of the termination of α-Fe2O3 on the interfacial structure and electrochemical performance have rarely studied. In this work, three typical Gr/α-Fe2O3 interfacial systems, namely, single Fe-terminated (Fe-O3-Fe-R), double Fe-terminated (Fe-Fe-O3-R), and O-terminated (O3-Fe-Fe-R) structures, were fully investigated through first-principle calculation. The results demonstrated that the Gr/Fe-O3-Fe-R system possessed good structural stability, high adsorption ability, low volume expansion, as well as a minor diffusion barrier along the interface. Meanwhile, investigations on active heteroatoms (e.g., B, N, O, S, and P) used to modify Gr were further conducted to critically analyze interfacial structure and Li storage behavior. It was demonstrated that structural stability and interfacial capability were promoted. Furthermore, N-doped Gr/Fe-O3-Fe-R changed the diffusion pathway and made it easy to achieve free diffusion for the Li atom and to shorten the diffusion pathway.

Nanorod-like Ni-rich layered cathode with enhanced Li+ diffusion pathway for high-performance lithium-ion batteries

Ni-rich LiNixCoyMn1-x-yO2 (x 0.6) layered oxide cathodes are one of the most promising cathode materials for lithium-ion batteries owing to their superior capacity, prominent energy density and low cost. However,...

Designer Synthesis of Ultra-Fine Fe-LTL Zeolite Nanocrystals

Nanosized zeolites with larger external surface area and decreased diffusion pathway provide many potential opportunities in adsorption, diffusion, and catalytic applications. Herein, we report a designer synthesis of ultra-fine Fe-LTL zeolite nanocrystals under very mild synthesis conditions. We prepared Fe-LTL zeolite nanocrystals synthesized using L precursor. The precursor is aging at room temperature to obtain zeolite L nuclei. In order to investigate more details of Fe-LTL zeolite nanocrystals, various characterizations including X-ray diffraction (XRD), inductively coupled plasma (ICP), diffuse reflectance ultraviolet-visible (UV-Vis) spectroscopy, confirm the tetrahedral Fe3+ species in the zeolite framework. Besides, scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR), dynamic light scattering (DLS) indicate that the average particle size of Fe-LTL zeolite crystals is approximately 30 nm. Thus, ultra-fine Fe-LTL zeolite with large external surface area and shorter diffusion pathway to the active sites might have great potential in the near future.

Three-Dimensional Finite Element Study on Lithium Diffusion and Intercalation-Induced Stress in Polycrystalline LiCoO2 Using Anisotropic Material Properties

In this study, lithium (Li) intercalation-induced stress of LiCoO2 with anisotropic properties using three-dimensional (3D) microstructures has been studied systematically. Phase field method was employed to generate LiCoO2 polycrystals with varying grain sizes. Li diffusion and stresses inside the polycrystalline microstructure with different grain size, grain orientation, and grain boundary diffusivity were investigated using finite element method. The results show that the anisotropic mechanical properties and Li concentration-dependent volume expansion coefficient have a very small influence on the Li chemical diffusion coefficients. The low partial molar volume of LiCoO2 leads to this phenomenon. The anisotropic mechanical properties have a large influence on the magnitude of stress generation. Since the Young's modulus of LiCoO2 along the diffusion pathway (a–b axis) is higher than that along c–axis, the Li concentration gradient is larger along the diffusion pathway. Thus, for the same intercalation-induced strain, the stress generation will be higher (∼40%) than that with isotropic mechanical properties as discussed in our previous study (Wu, L., Zhang, Y., Jung, Y.-G., and Zhang, J., 2015, “Three-Dimensional Phase Field Based Finite Element Study on Li Intercalation-Induced Stress in Polycrystalline LiCoO2,” J. Power Sources, 299, pp. 57–65). This work demonstrates the importance to include anisotropic property in the model.