Suppressing Cation Migration and Reducing Particle Cracks in a Layered Fe‐Based Cathode for Advanced Sodium‐Ion Batteries

Sodium‐ion batteries have huge potential in large‐scale energy storage applications. Layered Fe‐based oxides are one of the desirable cathode materials due to abundance in the earth crust and high activity in electrochemical processes. However, Fe‐ion migration to Na layers is one of the major hurdles leading to irreversible structural degradation. Herein, it is revealed that distinct Fe‐ion migration in cycling NaFeO₂ (NFO) should be mainly responsible for the strong local lattice strain and resulting particle cracks, all of which results in the deterioration of electrochemical performance. More importantly, a strategy of Ru doping could effectively suppress the Fe‐ion migration and then reduce the local lattice strain and the particle cracks, finally to greatly enhance the sodium storage performance. Atomic‐scale characterization shows that NFO electrode after cycling presents the intense lattice strain locally, accompanied by the remarkable particle cracks. Whereas, Ru‐doped NFO electrode maintains the well‐ordered layered structure by inhibiting the Fe–O distortion, so as to eliminate the resulting side effect. As a result, Ru‐doped NFO could greatly improve the comprehensive electrochemical performance by delivering a reversible capacity of 120 mA h g^?1, about 80% capacity retention after 100 cycles. The findings provide new insights for designing high‐performance electrodes for sodium‐ion batteries.     

Migration Characteristics under Long‐term Storage and a Combination of UV and Heat Exposure of Poly(Amide)/Poly(Ethylene) Composite Films for Food Packaging

The migration behaviour of polymer films in contact with food simulants is of high importance in terms of consumer protection. Legal regulations require compliance with specific and overall migration limits that are tested by standardized testing conditions. The testing of a polymer film generally takes place shortly after the manufacturing process and decides about the conformity or non‐conformity of the polymer film with the legal requirements. For film and food producers as well as for end users, it is of great interest that the conformity of a film is ensured over its complete lifetime and that environmental influences do not affect the migration behaviour inadequately. In this work, we have investigated (I) the long‐term storage behaviour of a poly(amide)/poly(ethylene) film over a storage period of 40 months with respect to the overall migration rate. This rate is decreasing over the storage period for the chosen food simulant. This means that the material characteristics concerning the overall migration of the poly(amide)/poly(ethylene) film were preserved over the lifetime of the film and even improved with regard to the overall migration potential. Additionally, (II) the migration behaviour was investigated under a combination of ultraviolet and heat exposure. A significant increase in the overall migration rate of 36.8% compared with the standardized migration conditions of 10 days at 40°C was observed. The specific migration of caprolactam, however, did not show a significantly different migration behaviour compared with the standardized migration conditions.