Asymmetric Sodiophilic Host Based on a Ag-Modified Carbon Fiber Framework for Dendrite-Free Sodium Metal Anodes

Sodium (Na) metal is considered a promising anode material for high-energy Na batteries due to its high theoretical capacity and abundant resources. However, uncontrollable dendrite growth during the repeated Na plating/stripping process leads to the issues of low Coulombic efficiency and short circuits, impeding the practical applications of Na metal anodes. Herein, we propose a silver-modified carbon nanofiber (CNF@Ag) host with asymmetric sodiophilic features to effectively improve the deposition behavior of Na metal. Both density functional theory (DFT) calculations and experiment results demonstrate that Na metal can preferentially nucleate on the sodiophilic surface with Ag nanoparticles and uniformly deposit on the whole CNF@Ag host with a "bottom-up growth" mode, thus preventing unsafe dendrite growth at the anode/separator interface. The optimized CNF@Ag framework exhibits an excellent average Coulombic efficiency of 99.9% for 500 cycles during Na plating/stripping at 1 mA cm^-2 for 1 mAh cm^-2. Moreover, the CNF@Ag-Na symmetric cell displays stable cycling for 500 h with a low voltage hysteresis at 2 mA cm^-2. The CNF@Ag-Na//Na₃V₂(PO₄)₃ full cell also presents a high reversible specific capacity of 102.7 mAh g^-1 for over 200 cycles at 1 C. Therefore, asymmetric sodiophilic engineering presents a facile and efficient approach for developing high-performance Na batteries with high safety and stable cycling performance.

Critical Review of the Use of Reference Electrodes in Li-Ion Batteries: A Diagnostic Perspective

Use of a reference electrode (RE) in Li-ion batteries (LIBs) aims to enable quantitative evaluation of various electrochemical aspects of operation such as: (i) the distinct contribution of each cell component to the overall battery performance, (ii) correct interpretation of current and voltage data with respect to the components, and (iii) the study of reaction mechanisms of individual electrodes. However, care needs to be taken to ensure the presence of the RE does not perturb the normal operation of the cell. Furthermore, if not properly controlled, geometrical and chemical features of the RE can have a significant influence on the measured response. Here, we present a comprehensive review of the range of RE types and configurations reported in the literature, with a focus on critical aspects such as electrochemical methods of analysis, cell geometry, and chemical composition of the RE and influence of the electrolyte. Some of the more controversial issues reported in the literature are highlighted and the benefits and drawbacks of the use of REs as an in situ diagnostic tool in LIBs are discussed.

How reliable is the Na metal as a counter electrode in Na-ion half cells?

Despite the extensive research on Na-ion batteries little is known about the stability of the Na-metal counter electrode in a half-cell configuration.