Insights into the Coating Integrity and its Effect on the Electrochemical Performance of Core-Shell Structure SiOx @C Composite Anodes.

Silicon-based anodes have been considered as ideal candidates for next-generation Li-ion batteries. However, the rapid cyclability decay due to significant volume expansion limits its commercialization. Besides, the instable interface further aggravates the degradation. Carbon coating is one effective way to improve the electrochemical performance.The coating integrity may be a critical index for core-shell structure electrode materials. Herein, the coating integrity of SiOx @C composite is tested by a developed selective alkali dissolution, further quantitatively depicted by a proposed index of alkali solubility α. The effect of coating integrity on electrochemical performance reveals that SiOx dissolution loss has a significant impact on the overall electrode structure stability and interface property. Because of the side reaction between uncoated active SiOx and electrolyte, the quadratic decrease of initial coulombic efficiency and increase of solid electrolyte interphase thickness with the rise of alkali solubility are closely related to the generated F content induced by active material loss, further supported by the obvious linear rise of Li2 SiF6 fraction, leads to the linear increase of interface impedance and volume expansion rate, which may take primarily responsibility for the performance decay. This work propels the fundamental understanding on the interface failure mechnism and inspires rational high-performance electrode material design.

Experimental and numerical study on DCB specimens bonded with similar and dissimilar materials.

In this paper, the influence of the bonding materials on the failure modes and the critical energy release rate (CERR) is studied through the double cantilever beam (DCB) test. The test results show that the failure mode and CERR of the bonded structure are closely related to the bonding materials, and three failure modes, i.e., the cohesive failure, the interface failure and the mixed-mode failure are identified on the bonding surface. The finite element method is used to simulate the interface debonding behavior of the DCB test specimens, and the influence of material randomness on the interface failure is introduced. A XFEM/CZM coupled approach is proposed to model the crack migration phenomena. The predicted results have a good agreement with the experimental results.

Strength of Graphene-Coated Ni Bi-Crystals: A Molecular Dynamics Nano-Indentation Study.

Nanoindentation simulations are performed for a Ni(111) bi-crystal, in which the grain boundary is coated by a graphene layer. We study both a weak and a strong interface, realized by a 30 ∘ and a 60 ∘ twist boundary, respectively, and compare our results for the composite also with those of an elemental Ni bi-crystal. We find hardening of the elemental Ni when a strong, i.e., low-energy, grain boundary is introduced, and softening for a weak grain boundary. For the strong grain boundary, the interface barrier strength felt by dislocations upon passing the interface is responsible for the hardening; for the weak grain boundary, confinement of the dislocations results in the weakening. For the Ni-graphene composite, we find in all cases a weakening influence that is caused by the graphene blocking the passage of dislocations and absorbing them. In addition, interface failure occurs when the indenter reaches the graphene, again weakening the composite structure.

Bone remodelling around the tibia due to total ankle replacement: effects of implant material and implant-bone interfacial conditions.

One of the major causes of implant loosening is due to excessive bone resorption surrounding the implant due to bone remodelling. The objective of the study is to investigate the effects of implant material and implant-bone interface conditions on bone remodelling around tibia bone due to total ankle replacement. Finite element models of intact and implanted ankles were developed using CT scan data sets. Bone remodelling algorithm was used in combination with FE analysis to predict the bone density changes around the ankle joint. Dorsiflexion, neutral, and plantar flexion positions were considered, along with muscle force and ligaments. Implant-bone interfacial conditions were assumed as debonded and bonded to represent non-osseointegration and fully osseointegration at the porous coated surface of the implant. To investigate the effect of implant material, three finite element models having different material combinations of the implant were developed. For model 1, tibial and talar components were made of Co-Cr-Mo, and meniscal bearing was made of UHMWPE. For model 2, tibial and talar components were made of ceramic and meniscal bearing was made of UHMWPE. For model 3, tibial and talar components were made of ceramic and meniscal bearing was made of CFR-PEEK. Changes in implant material showed no significant changes in bone density due to bone remodelling. Therefore, ceramic appears to be a viable alternative to metal and CFR-PEEK can be used in place of UHMWPE. This study also indicates that proper bonding between implant and bone is essential for long-term survival of the prosthetic components.