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The effect of Li-salt concentration on the anion intercalation/de-intercalation reaction is studied. In LiN(CF3SO2)2 –or LiClO4/propylene carbonate cases, the interfacial activation energy for (E a) does not show the concentration dependency in the case of dilute solutions, while higher E a is obtained in the concentrated solutions. The result means that the activation barrier changes from the electrode side to the solution side by increasing the salt concentration. In addition, E a for the concentrated solutions continuously increase with the Li-salt concentration, although the activation barrier by the cleavage of the ion pair should be independent from the salt concentration. From the results, it is concluded that the charge of anion will not be shielded enough and the interaction from the wide range will influence the activation barrier.

Intermetallic compounds are expected to be used as the negative electrode for Mg-ion batteries, due to their relatively large capacity and the excellent electrochemical performance in the non-ethereal solutions. In the present study, the reaction mechanism of Mg3Bi2 is focused. By comparing the reactivity towards the same electrode sheet in various electrolyte solutions, it is found that the effect of MgF2 based surface film, which is formed by the decomposition of Mg(N(CF3SO2)2)2 (Mg(TFSA)2), is not large necessarily. The reactivity in Mg(TFSA)2+crown ether/acetonitrile solution fairly varies by the size of crown ethers. From the results, it is indicated that the de-solvation process will also be the critical factor for the Mg2+-ion insertion/extraction into the Mg3Bi2 electrode.

The effect of the coordination ability of the solvent species on the Mg plating/stripping behavior was investigated. The Mg plating reaction in Mg(N(CF3SO2)2)2/diglyme was inhibited by the equimolar of 15-crown-5 ether (15C5) to Mg2+-ion. On the other hand, Mg plating took place in the solution by reducing the amount of 15C5 less than that of Mg2+-ion. FT-IR spectra showed that 15C5 preferentially solvated Mg2+-ion in the glyme based solutions. The theoretical calculation indicated the interaction between Mg2+-ion and each O atom in 15C5 was stronger than that with diglyme or larger sized crown ether. The results showed that the coordination ability of the solvent species could be the critical for the Mg plating reaction.

The inherent high resistance of electrolyte/electrode interface in all-solid-state-lithium-secondary batteries (SSLB) poses a significant hurdle for the SSLB development. The interfacial resistivity between Li7La3Zr2O12 (LLZ) and LiCoO2 is decreased by introducing a thin Nb layer (∼10 nm) at this interface. The interface modification approach using a Nb interlayer dramatically improves the discharge capacity and rate capability of a SSLB.

A lithium insertion reaction in a Li + conductive glass ceramics solid electrolyte (lithium aluminum titanium phosphate: LATP) sheet produces an in-situ formed electrode active material, which operates at 2.35 V vs. Li/Li + in the vicinity of the LATP-sheet/current–collector interface. Electron energy loss spectroscopy clarifies that titanium in the LATP sheet in the vicinity of the current collector/LATP-sheet interface is preferentially reduced by this lithium insertion reaction. Charge transfer resistance between the in-situ-formed-electrode and the LATP-sheet is less than 100 Ω cm 2 , which is smaller than that of the common LiPON/LiCoO 2 interface. A thin film of LiCoO 2 is deposited on one side of the LATP-sheet as a Li + source for developing the in-situ formed electrode material. Eventually, a Pt/LATP-sheet/LiCoO 2 /Au multilayer is fabricated. The multilayer structure successfully works as an all-solid-state lithium-ion battery operating at 1.5 V. A redox peak of the battery is observed even at 100 mV s −1 in the potential sweep curve. Additionally, charge–discharge reactions are repeated stably even after 25 cycles.

Lithium metal (Li) is electrochemically-grown at the lithium phosphorus oxynitride glass electrolyte (LiPON)/copper (Cu) thin film interface. The plated lithium morphology depends on the current densities, and larger current densities bring about smaller-sized precipitation of Li with larger coverage ratio by the precipitates. Both scanning electron microscopy and in-situ optical microscopy observations reveal that the lithium tends to grow at the lithium pre-plated place. Large potential drop was observed at the initial lithium plating process, suggesting that the nucleation process requires large activation energy at the initial lithium plating process at the LiPON/Cu interface. The resultant morphology-controlled in-situ prepared Li provides stable and low-resistive Li/LiPON interface compared with the vacuum-evaporated Li thin film.

Morphology variations during electrochemical lithium plating–stripping reactions at the lithium phosphorus oxynitride glass electrolyte (LiPON)/copper current collector (Cu) interface are observed in-situ by scanning electron microscopy (SEM). This in-situ SEM observation shows dynamically that the plating reactions at 50 μA cm −2 distribute initial lithium growth sites sparsely at the LiPON/Cu interface, later, local lithium growth occurs from the pre-plated sites through the Cu film, and finally, most of the precipitated lithium grows to be needle-shape with the height of micron order. This local growth rate attains to be 6.8 mA cm −2 , about 100 times higher value than applied one. When those precipitated lithium are stripped at 50 μA cm −2 , core region of each precipitate is mostly stripped but its degree depends on the length of the precipitate. This dependency will arise from the diffusivity of Li. When this stripping current density is increased to 500 μA cm −2 , the coulomb efficiency is further decreased. In-situ SEM observation shows that plated lithium around the interface becomes thin preferentially while that far away from the interface (upper side of plated lithium) remains unchanged. This will isolate most of precipitate lithium from LiPON film electrically, leading to further decreasing of the coulomb efficiency.

Sodium-ion transfer through the interface between ceramic and organic electrolytes was studied by AC impedance spectroscopy. Na 3 Zr 1.88 Y 0.12 Si 2 PO 12 (NASICON) and Na-β″-alumina were used as ceramic electrolytes, and propylene carbonate (PC) and dimethyl sulfoxide (DMSO) containing 0.05 mol dm −3 NaCF 3 SO 3 were used as organic electrolytes. The semi-circle ascribed to interfacial charge transfer resistance ( R ct ) was observed. The activation energies for sodium-ion transfer at the interface between ceramic and organic electrolytes were evaluated by the temperature dependency of R ct . As a result, the activation energies depended on the ceramic electrolytes but not on the solvents. These results suggest that sodium-ion transfer from ceramic to organic electrolytes should be responsible for the activation energies, which is contrary to the case in a lithium-ion transfer system. Based on these results, the mechanism of interfacial sodium-ion transfer was discussed.

In this study, lithium-ion transfer through the electrode/electrolyte interface was examined using a model interface composed of a lithium-ion-conductive ceramic and liquid electrolytes to focus on lithium-ion transfer. Lithium-ion transfer resistances at the interface and their activation energies were evaluated by impedance spectroscopy. The activation energies were quite large and consistent with the interaction between lithium-ion and solvents in an electrolyte as determined by a theoretical calculation.

Li + -ion and Na + -ion transfer at interfaces composed of inorganic solid electrolytes and polymer or organic liquid electrolytes were compared. La 0.55 Li 0.35 TiO 3 and Na 3 Zr 1.88 Y 0.12 Si 2 PO 12 , which are conductive for Li + and Na + , were selected for use as inorganic solid electrolytes. PC solution and PEO-based polymer electrolytes were added to Li salt or Na salt to give ionic conductivity. Using these electrolytes, solid electrolyte/liquid electrolyte or solid electrolyte/polymer electrolyte interfaces were constructed. The resistivities of Li + or Na + transfer through these interfaces were estimated based on the results of ac impedance measurements. In both solid/liquid and solid/polymer systems, the activation energies of Na + -ion transfer at the interface were smaller than those of Li + -ion. The Lewis acidity of both ions, Li + and Na + , clearly explains this difference and supports the idea that the interaction between ion and solvents plays a major role in interfacial ion-transfer processes.

Lithium-ion transfer at the interface between the lithium-ion-conductive ceramic of La 0.55 Li 0.35 TiO 3 (LLT) and the polymer electrolyte of polyethylene oxide (PEO) complexed with LiCF 3 SO 3 (PEO-LiCF 3 SO 3 ) was studied by ac impedance spectroscopy for the system of Li/PEO-LiCP 3 SO 3 /LLT/PEO-LiCF 3 SO 3 /Li. The impedance ascribed to ion transfer through the interface was observed. The resistance due to the lithium-ion transfer at the interface was larger than those through phases of LLT and PEO-LiCF 3 SO 3 , and the temperature dependence of the interfacial resistances showed Arrhenius-type behavior. The activation energy of the interfacial resistances was larger than those for lithium-ion conduction in LLT and PEO-LiCF 3 SO 3 . The design of the ion-conductive ceramic and the polymer composite electrolytes is discussed based on the results.