Abstract The relentless quest for sustainable and efficient energy storage solutions has propelled sodium‐ion batteries (SIBs) to the forefront of research and development in the realm of rechargeable batteries. This mini review delves into the intricate interfacial kinetics of Na ion transfer within SIBs, with a special focus on the carbon‐based negative electrode/electrolyte interfaces. By synthesizing insights from a myriad of studies encompassing experimental and theoretical analyses, we illuminate the critical role of electrode material properties and interfacial dynamics in dictating the kinetics of Na ion transfer for SIBs. Strategies for optimizing these parameters are scrutinized, revealing pathways to enhance the kinetic behavior of Na ions. Furthermore, emerging materials such as hard carbon, carbon nanospheres, and graphene‐like graphite are evaluated for their potential to surmount existing limitations.

Non-graphitizable carbon allows reversible sodium-ion intercalation and hence enables stable and high-capacity sodium storage, making it a promising material for achieving long-term cycling stability in sodium-ion batteries (SIBs). This study investigated the interfacial reactions between various electrolytes and a non-graphitizable carbon electrode for their use in SIBs. The morphology and particle diameter of the non-graphitizable carbon, HC-2000, remained unchanged after heat treatment, indicating its stability. The X-ray diffraction pattern and Raman spectrum suggested a disordered structure of HC-2000 carbon. The interlayer spacing, Brunauer–Emmett–Teller specific surface area, and density were determined to be 0.37 nm, 5.8 m² g⁻¹, and 1.36 g cm⁻³, respectively. Electrochemical impedance spectroscopy analysis showed that the charge transfer resistances differed between the Na salts and other electrolytes. Therefore, the use of a large amount of NaF in the solid electrolyte interphase (SEI) resulted in high charge transfer resistances at the non-graphitizable electrodes. However, there were no apparent differences in the activation energy or reversible capacity. In summary, NaF obstructs the penetration pathway of sodium ions into non-graphitizable carbon, impacting the charge transfer resistance and rate stability of SIBs. Charge–discharge measurements revealed reversible capacities of 260–290 mAh g⁻¹, and the rate performance varied depending on the electrolyte. Therefore, an SEI containing minimal inorganic species, such as NaF, is desirable for efficient sodium-ion insertion into non-graphitizable carbon.

With the growing interest in promising energy sources for high-energy-demand devices, the development of materials for use in rechargeable batteries based on electrochemical charge carrier storage, such as Li and Na, has attracted intensive attention. Among them, carbon materials (e.g., graphene, graphite, and disordered carbons) have been extensively used as electrode materials for battery systems because of their critical advantages, namely, relatively good charge carrier storage capability, low cost, abundant resources, and simple manufacturing process. In particular, various types of defects are indispensably formed in the carbon structure during the manufacturing processes, which significantly influence their electrochemical charge carrier storage mechanisms and thus determine the electrochemical properties of the carbon-based rechargeable battery systems. This comprehensive review summarizes the correlation between the fundamental properties of carbon defects and electrochemical Li and Na storage mechanisms for Li- and Na-based rechargeable batteries, representative cations using battery systems, with a special focus on atomic-scale science and technology, which have a notable role in investigating and understanding the interaction between the defect phases and charge carriers in carbon structures. First, various carbon defects are categorized for the purpose of this work; then, computational/experimental methods for analyzing them and their critical properties (especially electronic structure) are introduced because identifying defect types is critical. Next, the roles and influences of carbon defects on electrochemical charge carrier storage mechanisms (especially adsorption and intercalation [insertion], diffusion, and formation of metal clusters) are described for Li- and Na-based rechargeable batteries. This study focuses on the physicochemical and electrochemical properties, which are key characteristics of carbon defects that determine their optimal utilization in rechargeable battery systems.

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) is a promising electrocatalyst for the oxygen evolution reaction (OER) in alkaline solution. The OER activities of BSCF are gradually enhanced by prolonging the duration of electrochemical operation at OER potentials, but the underlying cause is not fully understood. In this study, we investigated the role of chemical operation, equivalent to immersion in alkaline solution, in the time-course of OER enhancement of BSCF. Interestingly, the time-course OER enhancement of BSCF was promoted not only by electrochemical operation, which corresponds to potential cycling in the OER region, but also by chemical operation. In situ Raman measurements clarified that chemical operation had a lower rate of surface amorphization than electrochemical operation. On the other hand, the leaching behavior of A-site cations was comparable between chemical and electrochemical operations. Since the OER activity of BSCF was stabilized by saturating the electrolyte with Ba²⁺, “chemical” A-site leaching was key to inducing the time-course OER enhancement on perovskite electrocatalysts. Based on these results, we provide a fundamental understanding of the role of chemical operation in the OER properties of perovskites.

Graphitic materials cannot be applied for the negative electrode of sodium-ion battery because the reversible capacities of graphite are anomalously small. To promote electrochemical sodium-ion intercalation into graphitic materials, the interfacial sodium-ion transfer reaction at the interface between graphitized carbon nanosphere (GCNS) electrode and organic electrolyte solutions was investigated. The interfacial lithium-ion transfer reaction was also evaluated for the comparison to the sodium-ion transfer. From the cyclic voltammograms, both lithium-ion and sodium-ion can reversibly intercalate into/from GCNS in all of the electrolytes used here. In the Nyquist plots, the semi-circles at the high frequency region derived from the Solid Electrolyte Interphase (SEI) resistance and the semi-circles at the middle frequency region owing to the charge-transfer resistance appeared. The activation energies of both lithium-ion and sodium-ion transfer resistances were measured. The values of activation energies of the interfacial lithium-ion transfer suggested that the interfacial lithium-ion transfer was influenced by the interaction between lithium-ion and solvents, anions or SEI. The activation energies of the interfacial sodium-ion transfer were larger than the expected values of interfacial sodium-ion transfer based on the week Lewis acidity of sodium-ion. In addition, the activation energies of interfacial sodium-ion transfer in dilute FEC-based electrolytes were smaller than those in concentrated electrolytes. The activation energies of the interfacial lithium/sodium-ion transfer of CNS-1100 in FEC-based electrolyte solutions were almost the same as those of CNS-2900, indicating that the mechanism of interfacial charge-transfer reaction seemed to be the same for highly graphitized materials and low-graphitized materials each other. Graphic abstract

平成28年度 京都大学化学研究所 スーパーコンピュータシステム 利用報告書

A carbonaceous thin-film electrode was prepared by plasma-assisted chemical vapor deposition, and used as a model carbon electrode to study the interfacial reactions between a electrode and electrolyte. Lithium-ion transfer at the interface between carbonaceous thin-film electrode and electrolyte was studied by electrochemical impedance spectroscopy. In the Nyquist plots, semi-circles assigned to charge-transfer resistance were observed in high frequency region. Activation energies for lithium-ion transfer at the interface between carbonaceous thin-film electrode and electrolyte were evaluated, and the values were found to be dependent on the electrolyte solutions. The effects of ion-solvent interaction on the activation energies for the interfacial lithium-ion transfer are discussed based on theoretical calculations.

Carbonaceous materials have been widely investigated as negative electrode materials of lithium-ion batteries (LIBs). In this review, the properties of nano-carbon materials for use as negative electrodes are summarized from the viewpoint of their morphology. As nano-carbon materials, carbon nanospheres (zero dimension), carbon nanotubes (one dimension), carbon nanofibers (one dimension), graphene (two dimension), and so on were covered. The advantages and disadvantages of nano-carbon materials as the negative electrode in LIBs are discussed.