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Sodium-ion batteries (SIBs) are promising candidates for largescale energy storage systems due to the abundance and wide distribution of sodium resources. Various solutions have been successfully applied to revolve the large-ionsize-induced battery issues at the mid-to-low current density range. However, the fast-charging properties of SIBs are still in high demand to accommodate the increasing energy needs at large to grid scales. Herein, a core−shell Co 2 VO 4 / carbon composite anode is designed to tackle the fast-charging problem of SIBs. The synergetic effect from the stable spinel structure of Co 2 VO 4 , the size of the nanospheres, and the carbon shell provide enhanced Na + ion diffusion and electron transfer rates and outstanding electrochemical performance. With an ultrahigh current density of 5 A g −1 , the Co 2 VO 4 @C anode achieved a capacity of 135.1 mAh g −1 and a >98% capacity retention after 2000 cycles through a pseudocapacitive dominant process. This study provides insights for SIB fastcharging material design and other battery systems such as lithium-ion batteries.

Four typical types of residual oil, residual oil trapped in dead ends, oil ganglia in pore throats, oil at pore corners and oil film adhered to pore walls, were studied. According to main pore structure characteristics and the fundamental morphological features of residual oil, four displacement models for residual oil were proposed, in which pore-scale fl ow behavior of viscoelastic fl uid was analyzed by a numerical method and micro-mechanisms for mobilization of residual oil were discussed. Calculated results indicate that the viscoelastic effect enhances micro displacement effi ciency and increases swept volume. For residual oil trapped in dead ends, the fl ow fi eld of viscoelastic fl uid is developed in dead ends more deeply, resulting in more contact with oil by the displacing fl uid, and consequently increasing swept volume. In addition, intense viscoelastic vortex has great stress, under which residual oil becomes small oil ganglia, and fi nally be carried into main channels. For residual oil at pore throats, its displacement mechanisms are similar to the oil trapped in dead ends. Vortices are developed in the depths of the throats and oil ganglia become smaller. Besides, viscoelastic fl uid causes higher pressure drop on oil ganglia, as a driving force, which can overcome capillary force, consequently, fl ow direction can be changed and the displacing fl uid enter smaller throats. For oil at pore corners, viscoelastic fl uid can enhance displacement effi ciency as a result of greater velocity and stress near the corners. For residual oil adhered to pore wall, viscoelastic fl uid can provide a greater displacing force on the interface between viscoelastic fl uid and oil, thus, making it easier to exceed the minimum interfacial tension for mobilizing the oil fi lm.

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In situ analysis of sweat provides a simple, convenient, costeffective, and noninvasive approach for the early diagnosis of physical illness in humans and is particularly useful in family care. In this study, a flexible and skin-attachable colorimetric sweat sensor for multiplexed analysis is developed using a simple, cost-effective, and convenient method. The obtained sweat sensor can be used to simultaneously detect glucose, lactate, urea, and pH value in sweat, as well as sweat loss and skin temperature. Only 2.5 μL of sweat is enough for the whole test, and the sweat loss and chemical-sensing results can be read out conveniently by naked eyes or a smartphone. In addition, body temperature can also be detected with an additional electrical circuit. Our sweat sensor provides a new, cost-effective, and convenient approach for in vitro diagnosis of multiple components in sweat, and the easy fabrication and cost-effectiveness make our sensor commercializable in the near future.

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