Secondary batteries and capacitors are becoming more important in the society. In this report, the present status of secondary batteries and capacitors, as well as the importance of surface science on the field, is outlined.
An Electrochemical Atomic Force Microscope (EC-AFM) was used to observe the surface reaction of lead electrode in sulfuric acid electrolyte, when the reaction corresponding to what occurs at the electrode of a lead-acid battery takes place. At first, the morphology change at the surface of the lead electrode during Cyclic-Voltammetry measurement could be observed by using EC-AFM. After that, behavior of PbSO4 crystals during open-circuit standing after oxidation was observed by in-situ EC-AFM, and the degradation of charge acceptance performance of lead-acid batteries during open-circuit standing after discharge could be explained by this observation result. In this paper, we introduce some technique with using EC-AFM for understanding of the electrochemical reaction at solid/liquid interface in the lead-acid battery.
Alkali metal pyrophosphate, A2MP2O7 (A = Li, Na, M = Fe Mn, Co), have been recently reported as novel polyanionic cathode materials for rechargeable alkali-ion batteries with competent electrochemical properties with high rate durability. A closer look revealed they offer the highest operating voltage by M3+/M2+ redox couple among ever reported related compounds. Of particular interest is its much safer nature than olivine LiFePO4 currently recognized as the only practical option providing definitely safe large-scale lithium-ion battery. Scientific origins of these promising features will be unveiled in this article.
Electrode performance of hard-carbon electrodes in non-aqueous Na cells is examined with or without fluoroethylene carbonate (FEC) as an electrolyte additive. It is found that electrode performance is highly improved by using FEC as additives. To study the mechanisms for the improvement of electrode performance, solid electrolyte interphase (SEI) of hard-carbon electrodes is investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Surface analysis reveals that fluorine-containing SEI is formed at the hard carbon surface, which suppresses the decomposition of electrolyte solution in Na cells. From these results, the role and importance of SEI for the development of Na-ion batteries are also discussed.
Bis (trifluoromethanesulfonyl) amide (TFSA) based room-temperature ionic liquids (RTILs) were used as electrolytes for lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries. The discharge-charge cycle stability and coulombic efficiency of Li-S cells with TFSA-based RTILs were found to be surprisingly superior to those of a cell with a conventional organic electrolyte consisting of tetrahydrofuran (THF) and a Li slat. The poor cycle stability of the cell with the conventional organic electrolyte was attributed to the dissolution of lithium or sodium polysulfides (M2Sm, M = alkali metal, 2 ≤ m ≤ 8), which were generated as reaction intermediates through redox processes at the S cathode in the M-S cell. TFSA-based RTILs have low donor ability owing to the weak Lewis basicity of [TFSA]− anion, whereas conventional ether-based molecular solvents, such as THF, have high donor ability. The dissolution of M2Sm was significantly suppressed owing to the weak donor ability of RTILs.