Sodium ion batteries (SIBs) are promising candidates for large-scale energy storage owing to the abundant sodium resources and low cost. The larger Na + radius (compared to Li + ) usually leads to sluggish reaction kinetics and huge volume expansion. One of the efficient strategies is to reduce the size of electrode materials or the components of electrolytes to a suitable scale where size effect begin to emerge, leading to the improved or varied thermodynamics, kinetics, and mechanisms of sodium storage. However, only a few systematic reviews address size effects in SIBs, which requires further attention urgently. Herein, after a brief discussion of the general size effect, the size-related kinetics, thermodynamics (equilibrium voltage and morphology), and sodium storage mechanisms (phase transition, conversion reaction, interfacial, and nanopore storage) of electrode materials are presented. The size effect on liquid, polymer, and inorganic solid-state electrolytes are discussed as well, including the size of solvent molecules, Na salts, and inorganic fillers. Finally, neutral and adverse size effects are discussed, and some useful strategies are proposed to overcome them. The deep insights into the size effect will provide instructive guidelines for developing SIBs and other new energy storage systems.

A flexible Fe3N@C/3DNCF anode is fabricated via a green and scalable strategy, which exhibits highly reversible crystalline-phase transformation and superior cycling performance during sodium storage.

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To improve the osteointegration property of biomedical titanium, nano-architectured electroactive coating was synthesized through the electrochemical polymerization of dopamine and pyrrole. The highly binding affinity of Ca2+ to the catechol moiety of doped dopamine enabled efficient interaction between polypyrrole/polydopamine nanowires and mineral ions. The results indicate that the PPy/PDA nanowires preserved its efficient electro-activity and accelerated the hydroxyapatite deposition in a simulated body fluid. The PPy/PDA nanowires coating could be applied to promote the osteointegration of titanium implant.

Construction of functional porous titanium scaffold is drawing ever growing attention, due to its effectiveness in solving the mechanical mismatch between titanium implant and bone tissue. However, the poor water permeability as well as the problem in achieving uniform surface modification inside scaffold hinders the further biomedical application of porous titanium scaffold. In this study, largescale functional TiO 2 nanostructures (nanonetwork, nanoplate and nanowire) were constructed on three-dimensional porous titanium scaffolds surface via an effective hydrothermal treatment method. These nanostructures increase the hydrophilicity of the titanium scaffold surface, facilitating the cell culture medium to penetrate into the inner pore of the scaffold. Zeta potential analyses indicate that the surface electrical properties depend on the nanostructure, with nanowire exhibiting the lowest potential at pH 7.4. The influence of the nano-functionalized scaffold on protein adsorption and cell adhesion was examined. The results indicate that the nano-functionalized surface could modulate protein adsorption and bone marrow derived mesenchymal stem cells (BMSCs) adhesion, with the nanowire functionalized porous scaffold homogeneously promoting protein adsorption and BMSCs adhesion. Our research will facilitate future research on the development of novel functional porous scaffold.