No abstract

Silicon nanoparticles are coated with the conductive polyaniline (PANI) using in situ polymerization method as anode materials to improve the electrochemical performance for lithium ion batteries. At first, the physicochemical and electrochemical properties of the doped polyaniline in the lithium ion electrolyte are investigated. After that, the effect of different contents of PANI for preparing Si/PANI composites on the composition and structure and thus the electrochemical performance are investigated. The structure and morphology of asprepared materials are characterized systematically by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). It is demonstrated that the silicon/polyaniline composite presents the core/shell structure. The Si/PANI composite with 12.3 wt% PANI exhibits the optimum electrochemical performance. The electrode still maintains better reversible capacity of 766.6 mAh g −1 , and the capacity retention of 72 % is retained after 50 cycles at current density of 2 A g −1 . The good electrochemical properties can be attributed to the PANI-coating layer, which can improve the electrical conductivity of the Si-based anode materials for lithium ion batteries and accommodate the volume change of silicon during the charge-discharge processes.

The hydroxyl modified Zr-based MOFs is used for photocatalytic reduction of hexavalent chromium existing in wastewater.

In the paper, the deformation and elastic modulus evolution in Si composite electrodes during electrochemical lithiation and delithiation cycles are investigated experimentally. An electrochemical cell and optical system for in situ deformation monitoring of an electrode cantilever are designed and developed. Real-time bending deformation measurements of the Si composite electrode cantilever are conducted during the lithiation and delithiation cycles to determine the deformation as a function of the capacity. Analyses of the deformation characteristics and the microscopic mechanisms during the lithiation and delithiation cycles are performed. It is found that the electrode cantilever deforms relatively slowly during the first lithiation half-cycle and exhibits nonlinear deformation characteristics during subsequent cycles. The material softening of the lithiated Si and the diffusion-inducedcompression limiting diffusion rate are main factors, causing the electrode deformation to ease with a gradually decreasing slope as Li concentration increases. Furthermore, we provide a new method combined experiments and the derived evolution equation of Li concentration-curvature-elastic modulus to characterize the elastic modulus evolution. Using the experimental results, the influence of Li concentration upon the elastic modulus of the Si composite electrode is quantitatively described. The electrode elastic modulus decreases significantly by about 90% when the capacity is about 770 mAh/g.

In this paper, the interfacial mechanical properties of large-sized monolayer graphene attached to a flexible polyethylene terephthalate (PET) substrate are investigated. Using a micro-tensile test and Raman spectroscopy, in situ measurements are taken to obtain the full-field deformation of graphene subjected to a uniaxial tensile loading and unloading cycle. The results of the full-field deformation are subsequently used to identify the status of the interface between the graphene and the substrate as one of perfect adhesion, one showing slide or partial debonding, and one that is fully debonded. The interfacial stress/strain transfer and the evolution of the interface from one status to another during the loading and unloading processes are discussed and the mechanical parameters, such as interfacial strength and interfacial shear strength, are obtained quantitatively demonstrating a relatively weak interface between large-sized graphene and PET.

a b s t r a c tThe size-dependent mechanical properties and the edge effect of the tangential interface between graphene and a polyethylene terephthalate substrate (PET) are investigated. The interfacial mechanical parameters of graphene with seven different lengths are measured by in-situ Raman spectroscopy experiments. New phenomena are observed, such as the existence of the edge effect in the interfacial stress/strain transfer process, and the length of the edge of the interface can be affected by the size of graphene. Additionally, the interfacial shear stress exhibits a size effect, with its value significantly decreasing with an increase of the length of graphene. However, the ultimate stiffness and failure strength of the interface are size-independent as they are constant regardless of the length of graphene.

The strain/stress of the electrode materials induced in the electrochemical process is the key factor for lithium-ion batteries. However, in situ experimental techniques to quantitatively measure the strain/stress response of electrode materials at different length and time scales are still lacking. In this paper, in situ measurement of strain evolution in the graphene electrode during lithiation/ delithiation was performed by micro-Raman spectroscopy. The Raman G and 2D peaks of the graphene electrode were obtained using a modified coin cell with an optical window. The stages of the Li-graphite intercalation compounds were characterized by the G peak, while the in-plane strain of the graphene electrode microstructure was characterized by the 2D peak. Evolution of the biaxial strain during the electrochemical cycles was obtained based on determination of the relationship between the Raman shift and the in-plane strain of the graphene electrode. The experimental results show that the biaxial tensile strain of the graphene electrode almost linearly increases during lithiation. The maximum biaxial tensile strain induced by lithiation is about 0.4%, corresponding to the Li-graphite intercalation compound at stage 3. This study provides an experimental basis for understanding the deformation mechanism of the graphene electrode and developing high-performance graphene-based batteries.

No abstract