Development of advanced electrolytes in Na-ion batteries: application of the Red Moon method for molecular structure design of the SEI layer

Microscopic Analysis of the Mechanical Stability of an SEI Layer Structure Depending on the FEC Additive Concentration in Na-Ion Batteries: Maximum Appearance in Vickers Hardness at Lower FEC Concentrations

The stability of the solid electrolyte interphase (SEI) layer during the charging-discharging cycles is reasonably related to its microscopic elasticity. For the first time, it was theoretically revealed that each component of the elastic moduli takes a maximum at an optimal concentration of 1.0 vol % of fluoroethylene carbonate (FEC) for the SEI layer formed in the FEC-added NaPF₆/PC-based electrolyte. The elastic constants indicated that the SEI layer formed at lower FEC concentrations is more resistant to tensile and shear deformations. The optimal hardness is sensitive in the lower FEC concentrations although it simply decreases as the FEC concentration increases. This is due to the formation of a denser SEI structure with small cavities in the lower concentrations. The results are excellently consistent with the experimental one, justifying the microscopic understanding of the FEC additive effect on the mechanical stability of the SEI layers designed through the Red Moon simulation.

Effect of Carbon Nanotubes on the Na+ Intercalation Capacity of Binder Free Mn2V2O7-CNTs Electrode: A Structural Investigation

Improvements in sodium intercalation in sodium cathodes have been debated in recent years. In the present work, we delineate the significant effect of the carbon nanotubes (CNTs) and their weight percent in the intercalation capacity of the binder-free manganese vanadium oxide (MVO)-CNTs composite electrodes. The performance modification of the electrode is discussed taking into account the cathode electrolyte interphase (CEI) layer under optimal performance. We observe an intermittent distribution of the chemical phases on the CEI, formed on these electrodes after several cycles. The bulk and superficial structure of pristine and Na+ cycled electrodes were identified via micro-Raman scattering and Scanning X-ray Photoelectron Microscopy. We show that the inhomogeneous CEI layer distribution strongly depends on the CNTs weight percentage ratio in an electrode nano-composite. The capacity fading of MVO-CNTs appears to be associated with the dissolution of the Mn2O3 phase, leading to electrode deterioration. This effect is particularly observed in electrodes with low weight percentage of the CNTs in which the tubular topology of the CNTs are distorted due to the MVO decoration. These results can deepen the understanding of the CNTs role on the intercalation mechanism and capacity of the electrode, where there are variations in the mass ratio of CNTs and the active material.

P-doped porous carbon derived from walnut shell for zinc ion hybrid capacitors

Zinc ion hybrid capacitors (ZHCs) are expected to be candidates for large-scale energy storage products due to their high power density and large energy density. Due to their low cost and stability, carbon materials are generally the first choice for the cathode of ZHCs, but they face a challenge in the serious self-discharge behavior. Herein, zinc ion hybrid capacitors with high-performance are successfully assembled using a porous carbon cathode derived from low-cost p-doped waste biomass and a commercial zinc foil anode. The p-doped walnut shell ZHCs delivered a specific capacity of 158.9 mA h g⁻¹ with an energy density of 127.1 W h kg⁻¹ at a low current density. More importantly, the device had outstanding anti-self-discharge characteristics (retaining 77.98% of its specific capacity after a 72 h natural self-discharge test) and long-term cycle stability (retaining 88.2% of its initial specific capacity after 15 000 cycles at 7.5 A g⁻¹). This work presents guidance and support for the design and optimization of electrode materials for zinc ion supercapacitors and next-generation aqueous zinc ion energy storage performance.

A P-doped porous carbon cathode material from walnut shell is assembled with zinc foil to form typical ZHCs, which showed excellent energy storage characteristics and long-life cycle stability.