Rheo-impedance is the joint use of a rheological measurement and an electrical, electrochemical, or dielectric measurement to follow how a soft material or complex fluid reorganizes as it is processed or as it changes state. The two answer different questions about the same sample: rheology reports how the material flows and how stiff or elastic it is, while impedance, conductivity, and dielectric data report how well charge moves through it and what is happening at its interfaces. Because the mechanical and the electrical responses often depend on different parts of the microstructure, and need not change at the same moment, measuring both can separate states that look identical to either method alone. In this review, “rheo-impedance” is used as an organizing term rather than the name of a single standardized technique. The literature is grouped into three configurations—simultaneous, separate-but-linked, and correlation-based—and five material classes: carbon-black and conductive-colloid suspensions, lithium-ion battery slurries, polymer-electrolyte fuel-cell catalyst inks, gelation and stimuli-responsive systems, and drying, curing, and sintering. Four observations recur across these systems: the mechanical and electrical changes may be linked to the same process yet appear at different stages; a stiffer structure does not necessarily carry charge better; the structure present under flow is not always the one retained after processing; and both agreement and disagreement between the two responses can be informative. Throughout, we try to separate what has been shown experimentally from what is still system-dependent interpretation or future prospect. The main open problems are the ambiguity of equivalent-circuit interpretation, the limited transfer of descriptors between the flowing and the finished state, and the absence of standard geometries, frequency windows, and reporting conventions.
In lithium–oxygen batteries (LOBs), the chemical stability of electrolyte solvents is a critical factor determining cell performance. While sulfonamides represent a promising class of solvents for LOB electrolytes, systematic investigations into the structure–stability relationship of their analogs remain limited. In particular, although reactions involving the α-hydrogen (i.e., hydrogen abstraction and/or deprotonation of the hydrogen atom α to the sulfonyl group) have been widely considered to be initiating steps of solvent decomposition in various electrolytes, their actual impact on solvent decomposition and subsequent battery performance remain unclear. In this study, we performed a comparative analysis to elucidate the structure–stability relationships of sulfonamides with the general structure R1–SO2–NCH3(C4H9). Differential electrochemical mass spectrometry (DEMS) measurements revealed that the presence of α-hydrogens is not the dominant factor in solvent decomposition. Instead, the decomposition of the N-alkyl (butyl) chain plays a major role. These results suggest that longer alkyl chains lower the corresponding C–H bond dissociation energies through stabilization of the resulting alkyl radicals, thereby enhancing susceptibility to hydrogen abstraction by reactive oxygen species generated during the discharge/charge process. Our findings indicate that considering only the presence or absence of α-hydrogens is insufficient for designing chemically stable solvents. Rather, minimizing the number of C–H bonds susceptible to hydrogen abstraction is crucial for improving solvent stability.
Rechargeable zinc batteries (RZBs) have received much attention due to high theoretical specific capacity and high hydrogen overpotential of zinc, low cost, and safety. However, the electrolyte leakage, dendritic zinc deposition, some side reactions, and zinc hydroxide sulfate (ZHS) byproduct formation on the zinc negative electrode cause the deterioration of RZBs. Hydrogel electrolytes retaining large quantities of electrolytes can suppress leakage and regulate the transport of zinc ions via a three-dimensional host polymer network, overcoming these drawbacks. In this study, flexible alginate hydrogel electrolyte membranes (AHEMs) were successfully prepared by combining the formation of hydrogel membranes using 1,3-propanediol as a plasticizer with subsequent immersion in a Zn2+-containing aqueous solution. The AHEM exhibited ionic conductivity comparable to that of corresponding Zn2+-containing solution. Zinc deposition proceeded uniformly in AHEM, and the formation of ZHS was effectively suppressed. The symmetric Zn/AHEM/Zn cell showed a stable voltage profile without short-circuits for more than 2000 h in a charge-discharge test at 4 mA cm−2 for 30 min. The pouch-type quasi-solid-state Zn/AHEM/MnO2 cell maintained approximately 70 % of its maximum discharge capacity even after 300 cycles in the charge-discharge cycle test at a 3 C-rate (= 924 mA g−1).
Li metal has a high theoretical capacity (3860 mAh g−1) and the lowest electrochemical potential (−3.04 V vs. the standard hydrogen electrode). Li deposition/dissolution at the interface between the current collector (CC)/sulfide solid electrolyte (SSE), with Li+ ion supply from the positive electrode, is important for fabricating all-solid-state cells with high energy density. However, repeated inhomogeneous Li deposition/dissolution at the CC/SSE interface leads to short-circuiting of the cells. In this study, to promote homogeneous Li deposition, all-solid-state cells with a composite of SnF2 and acetylene black (SnF2–AB) at the interface between the CC and SSE were fabricated, and the Li deposition behavior was investigated. Li3PS4 (LPS) and 54Li3PS4·46LiI (LPSI) glasses were used as SSE. During Li deposition, the cell without the SnF2–AB layer short-circuited immediately because of inhomogeneous Li deposition. In contrast, in the cell with the SnF2–AB layer, SnF2 reacted with Li to form Li17Sn4 and LiF, which mainly remained within the SnF2–AB layer, promoting homogeneous Li deposition at the CC/SnF2–AB interface and suppressing short-circuiting of the cell. The use of LPSI instead of LPS in a cell with a SnF2–AB layer suppressed the formation of Li2S during reductive decomposition of the solid electrolyte, resulting in improved Li deposition capacity. The insertion of the SnF2–AB layer effectively promotes homogeneous Li deposition and is useful for applications in anode-free all-solid-state batteries.
A comparative study was conducted on the electrochemical interaction between CO2 and various bipyridines, including 2,2′-, 3,3′-, and 4,4′-bipyridine (4,4′-BPy), as well as perfluoro-4,4′-bipyridine (PF-4,4′-BPy). Among these, 4,4′-BPy exhibited the most robust performance, particularly when paired with weakly coordinating quaternary ammonium cations, such as tetrabutylammonium (Bu4N+). The use of these bulky cations proved highly effective in facilitating the electrochemical interaction with CO2, likely due to their attenuated electrostatic interaction with the bipyridine anionic species, which facilitates reversible CO2 binding. In contrast, PF-4,4′-BPy exhibited no electrochemical interaction with CO2; its radical anion showed insufficient nucleophilicity to overcome the activation barrier for CO2 binding, while the corresponding dianion was highly unstable, leading to rapid decomposition potentially initiated by a reductive defluorination process.
In power-type lithium-ion batteries (LIBs), the reaction distribution formed during high-rate operation significantly influences their performance. The reaction distribution in the electrode cross-sectional direction has been studied; however, in-plane reaction distribution, which can be an issue for large cells, remains poorly understood. In this study, we applied an electrode-freezing technique that can preserve reaction inhomogeneity at high rates to investigate the relationship between the in-plane reaction distribution and electrode design. The reaction distributions of LiNi1/3Co1/3Mn1/3O2 positive and hard carbon negative electrodes were analyzed using synchrotron-based Ni K-edge X-ray absorption fine structure and ion chromatography, respectively. The results showed that reducing electrode thickness significantly increased the in-plane inhomogeneity, with preferential reaction progress near the current-collector tabs. On the other hand, such pronounced in-plane reaction distributions did not necessarily degrade the power performance of the cell, suggesting the importance of cross-sectional inhomogeneity. This study shows that the dominant direction of reaction distribution in power-type LIBs varies depending on electrode thickness and C-rate, providing useful insights for electrode design optimized for high-rate operation.
The charge-discharge behaviors of pillared carbon thin-films as an anode of all-solid-state lithium-ion batteries were investigated, using LiBH4 as the solid electrolyte. The reduced contact area between the pillared carbon thin films and the solid electrolyte resulted in the suppression of side reactions originating from the solid electrolyte. The capacity of the pillared carbon thin-film electrodes increased with the increase in the Si content and reached a very high value of 1278 mAh g−1. Lithium ions were intercalated into the interlayer space of the pillared carbon and the interlayer distance increased from 1.33 to 1.42 nm upon lithium storage. A slight change in the XANES spectrum of the pillared carbon in the Si K-edge region after the introduction of lithium ion indicated that lithium ions were introduced in the vicinity of silicon atom surrounded by 3 oxygen atoms and one methyl group. The present results indicate that pillared carbon is a promising anode material for all-solid-state lithium-ion batteries.
Amorphous powder in the Li2O-CaO-ZrO2-P2O5 system were prepared by using mechanochemical synthesis process at room temperature. Amorphous materials with the nominal composition of Li1+2xCaxZr2−x(PO4)3 (LCZP) (x = 0.05, 0.08, 0.1) were calcinated at 900 °C in air. The calcinated LCZP materials were sintered at 1100 °C. The NASICON-structured LCZP(x = 0.08) solid electrolytes after sintering exhibited relatively high lithium-ion conductivities of 1.2 × 10−5 S cm−1 at 25 °C. The activation energy (Ea) was 35 kJ mol−1. The LCZP solid electrolytes obtained via the crystallization of amorphous materials would be a potential candidate as lithium-ion conductors for all-solid-state battery applications.
It was found that when an Al substrate was anodized in 0.3 M oxalic acid containing 50 mM sulfuric acid, the growth rate of the anodic porous alumina film (APAF) formed was significantly higher than that formed in an electrolyte without sulfuric acid. In contrast, adding small amounts of sulfuric acid did not promote the dissolution of the APAF. In other words, adding a small amount of sulfuric acid to the oxalic acid electrolyte enables the formation of a thick APAF before the sample surface is dissolved. As a result, it was possible to produce an ordered APAF with a sub-millimeter-scale thickness using an oxalic acid electrolyte with a small amount of sulfuric acid. The thick APAF obtained using this process is expected to be a promising template for fabricating various one-dimensional nanomaterials, such as nanotubes and nanofibers.
All-solid-state lithium metal batteries have attracted significant attention as next-generation batteries with the potential to achieve substantial performance improvements over conventional lithium-ion batteries. However, achieving a higher energy density requires not only improving the performance of the Li metal anode but also overcoming the challenges posed by a thinner, lighter configuration. In this study, a vacuum deposition process is employed to prepare thin Li-Mg films with thicknesses of several micrometers, which are difficult to achieve using conventional processes. Subsequently, the electrochemical properties of these thin films are evaluated in all-solid-state lithium metal batteries, and the functional role of Mg is investigated. The results reveal that the cycle life is highly dependent on the Mg content. Specifically, the Li (5 & micro;m)-Mg (400 nm) configuration (similar to 7 at% Mg) exhibits the highest performance, achieving 87.7 % capacity retention after 100 cycles. Cross-sectional observations confirm uniform alloying of the prepared film. Furthermore, the optimal film exhibits a stable interface with the solid electrolyte (Li6PS5Cl), effectively suppressing void formation during repeated plating/stripping cycles. This improved cycling stability is attributed to increased elastic modulus of the films and the suppression of void formation, which is facilitated by the improved wettability induced by Mg.
