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A series of Li4/3–2x/3ZnxTi5/3–x/3O4(LZTO) with 0 ≤ x≤ 0.5 have received considerable interest as a negative electrode material for long-cycle-life lithium-ion batteries. However, their dynamic structural transformations under operating conditions have remained unknown, making an in-depth understanding essential for further improving the electrochemical performance. We, thus, performed almost simultaneous operandoX-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies on x= 0.125, 0.375, and 0.5. The x= 0.5 sample, Li2ZnTi3O8, indicated differences in the cubic lattice parameter between the discharge and charge reactions (δacs), corresponding to the reversible movement of Zn2+ions between the tetrahedral and octahedral sites. δacwas also observed for x= 0.125 and 0.375, although the capacity region exhibiting δacdecreased with a decrease in x. For all of the samples, there is no significant difference in the nearest-neighbor distance of the Ti–O bond (dTi–O) between the discharge and charge reactions. We also demonstrated different structural transformations between the micro- (XRD) and atomic (XAS) scales. In the case for x= 0.5, for instance, the maximum microscale change in acwas within +0.29(3)%, whereas at the atomic scale, dTi–Ochanged by up to +4.8(3)%. Combined with our previous results for ex situ XRD and operando XRD/XAS measurements on other xcompositions, the whole structural nature of LZTO, such as correspondence between acand dTi–O, origins for voltage hysteresis, and zero-strain reaction mechanisms, has been unveiled.

Negative electrode materials with high thermal stability are a key strategy for improving the safety of lithium-ion batteries for electric vehicles without requiring built-in safety devices. To search for crucial clues into increasing the thermal stability of these materials, we performed differential scanning calorimetry (DSC) and in situhigh-temperature (HT)-X-ray diffraction (XRD)/X-ray absorption (XAS) up to 450 °C with respect to a solid-solution compound of Li4/3–2x/3ZnxTi5/3–x/3O4with 0 ≤ x≤ 0.5. The DSC profile of fully discharged x= 0.5 (Li2ZnTi3O8) with a LiPF6-based electrolyte could be divided into three temperature (T) regions: (i) T≤ 250 °C for ΔHaccumi, (ii) 250 °C < T≤ 350 °C for ΔHaccumii, and (iii) T> 350 °C for ΔHaccumiii, where ΔHaccumnis the accumulated change in enthalpy in region n. The HT-XRD/XAS analyses clarified that ΔHaccumiand ΔHaccumiioriginated from the decomposition of solid electrolyte interphase (SEI) films and the formation of a LiF phase, respectively. Comparison of the DSC profiles with x= 0 (Li[Li1/3Ti5/3]O4) and graphite revealed the operating voltage, i.e., amount of SEI films, and stability of the crystal lattice play significant roles in the thermal stability of negative electrode materials. Indeed, the highest thermal stability was attained at x= 0.25 using this approach.

Pore structure of (NH4)4SiW12O40sponge crystal was successfully elucidated by means of Ar adsorption isotherm analysis combined with molecular probe method and molecular modeling. The pores consist of spherical voids or “cages” with diameter of ca. 12 Å and these are connected by smaller “windows”. These “cages” and “windows” are clearly resolved in the pore size distribution analysis for the first time. Molecular probe method elucidated the diameter of the “windows” is larger than 8.5 Å and smaller than 10.2 Å, being consistent with molecular modeling.Pore structure of (NH4)4SiW12O40sponge crystal was successfully elucidated by means of Ar adsorption isotherm analysis combined with molecular probe method and molecular modeling for the first time. Spherical voids or “cages” with diameter of ca. 13 Å are connected by smaller “windows”. The size of the “window” was elucidated to be larger than 8.5 Å and smaller than 10.2 Å.

An in-depth understanding of the thermal behavior of lithium-ion battery materials is valuable for two reasons: one is to devise strategies for inhibiting the risk of catastrophic thermal runaway and the other is to respond to the increasing demand for sustainable batteries using a direct regeneration method. Li1+x[Li1/3Ti5/3]O4(LTO) is regarded as a suitable negative electrode under the type of severe conditions that cause this thermal runaway, such as in ignition systems for automobiles. Thus, in this study, we used differential scanning calorimetry to systematically analyze lithiated LTO combined with ex situand in situhigh-temperature X-ray diffraction measurements. The observed thermal reactions with a LiPF6-based electrolyte were divided into three processes: (i) the decomposition of the initially formed solid electrolyte interphase below 200 °C, (ii) the formation of a LiF phase at 200 °C ≤ T≤ 340 °C, and (iii) the formation of a TiO2phase at T> 340 °C. Because the enthalpy change in process (ii) mainly contributed to the total heat generation, fluorine-free Li salts and/or stabilization of the LTO lattice may be effective in coping with the thermal runaway. Even in various lithiated states, a direct regeneration method returned the discharge capacity of LTO to ∼90% of its initial value, if we ignore the contributions from the electrochemically inactive LiF and TiO2rutile phases. Hence, it can be concluded that the recycling performance of LTO is far superior to those of lithium transition metal oxides for a positive electrode, whose delithiated states easily convert into electrochemical-inactive phases at high temperatures.

Lithium overstoichiometric cobalt oxide, Li(LiδCo1−δ)O2−δ, still occupies a privileged position as a positive electrode material for lithium-ion batteries. However, despite its widespread applications in commercial lithium-ion batteries, little is known about its reaction mechanisms and the effects of δ on cyclability at deep charge. We herein revisited this material through a recently developed in operandotechnique, i.e., rapid, alternating measurements of X-ray diffraction and X-ray absorption spectroscopy. The cyclability degraded when the charge cutoff voltage was >4.4 V versus Li+/Li, which corresponds to the Li composition exhibiting a minimum (maximum) lattice parameter along the ah(ch) axis. Differences in the structural parameters such as lattice parameters and bond distances clearly appeared between the charge and discharge reactions at a capacity below ∼220 mAh g–1. These changes occurred because deep charge and/or increasing the amount of δ induced a local distortion in the CoO6octahedra. We found a critical Li extraction content that satisfied the need for both high capacity and cyclability for Li(LiδCo1−δ)O2−δ, which can be applied to other layered materials.

Negative electrode materials with lower operating voltages are urgently required to increase the energy density of lithium-ion batteries. In this study, LiMgVO4with a Na2CrO4-type structure, LiZnVO4with a phenacite structure, and their mixture were treated under a high pressure of 12 GPa and a high temperature of 1273 K, and their electrochemical reactivities were examined in a nonaqueous lithium cell. Synchrotron X-ray diffraction (XRD) measurements and Raman spectroscopy revealed that the LiMg1–xZnxVO4samples with 0 ≤ x≤ 1 are in a single phase of the inverse spinel structure that forms a solid solution compound over the whole xrange. All of the samples were brown or light black due to the presence of a small amount of V4+ions with S= 1/2 and oxygen deficiencies. Since the majority of the vanadium ions are located at the route of the Li+ion conduction pathway, no rechargeable capacity (Qrecha) would be expected. Nevertheless, all LiMg1–xZnxVO4samples exhibited a Qrechavalue of more than 200 mAh g–1with an operating voltage of ∼0.8 V. This operating voltage is ∼1.6 V lower than that of LiV2O4with a normal spinel structure. Furthermore, the x= 0.5 sample demonstrated an extremely stable cycle performance over 1 month. Ex situ XRD measurements clarified that the reversible electrochemical reaction can be attributed to the movement of vanadium ions from the tetrahedral 8a to octahedral 16c sites during the initial discharge reaction. Details regarding the crystal structure, magnetism, and electrochemistry of LiMg1–xZnxVO4are presented.