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Fluoride-ion conducting solid materials are applicable as solid electrolytes for sensing devices and next generation rechargeable batteries. Most of the previously reported materials have limited to the single-anion compounds such as fluorite-type, tysonite-type, and perovskite-type structures. These are suffered from further improvements by crystal structure modification which derives a paradigm shift in the material tailoring. Fluoride and sulfide ions prefer respective coordination environments because of the different ionic radii and electronegativity. This feature implies that fluorosulfide mixed-anion compounds have potential to form anion-ordering crystal structures with new fluoride-ion conducting layers. Herein, we have found that the fluorosulfide La2+xSr1−xF4+xS2 exhibits fluoride ion conduction. The presence of multiple anions results in the formation of anion-ordering two-dimensional crystal lattice with triple fluorite layers, which cannot be realized for metal fluorides. Sulfide ions in the crystal structure increases the number of interstitial sites of fluoride ions, forming fluoride ion conduction pathway.

Intensive research is underway to further enhance the performance of lithium-ion batteries (LIBs). To increase the capacity of positive electrode materials, Li-rich layered oxides (LLO) are attracting attention but have not yet been put to practical use. The structural mechanisms through which LLO materials exhibit higher capacity than conventional materials remain unclear because their disordered phases make it difficult to obtain structural information by conventional analysis. The X-ray total scattering analysis reveals a disordered structure consisting of metal ions in octahedral and tetrahedral sites of Li layers as a result of cation mixing after the extraction of Li ions. Metal ions in octahedral sites act as rigid pillars. The metal ions move to the tetrahedral site of the Li layer, which functions as a Li-layer pillar during Li extraction, and returns to the metal site during Li insertion, facilitating Li diffusion as an adaptive pillar. Adaptive pillars are the specific structural features that differ from those of the conventional layered materials, and their effects are responsible for the high capacity of LLO materials. An essential understanding of the pillar effects will contribute to design guidelines for intercalation-type positive electrodes for next-generation LIBs.

Amorphous transition-metal polysulfides are promising positive electrode materials for next-generation rechargeable lithium-ion batteries because of their high theoretical capacities. In this study, sulfur anion redox during lithiation of amorphous TiS₄ (a-TiS₄) was investigated by using experimental and theoretical methods. It was found that a-TiS₄ has a variety of sulfur valence states such as S²⁻, S⁻, and S[δ−]. The S²⁻ species became the main component in the Li₄TiS₄ composition, indicating that sulfur is a redox-active element up to this composition. The simulated a-TiS₄ structure changed gradually by lithium accommodation to form a-Li₄TiS₄: S–S bonds in the disulfide units and polysulfide chains were broken. Bader charge analysis suggested that the average S valency decreased drastically. Moreover, deep lithiation of a-TiS₄ provided a conversion reaction to metallic Ti and Li₂S, with a high practical capacity of ∼1000 mAh g⁻¹ when a lower cutoff voltage was applied.

An archetypical Li-rich layered oxide, Li2MnO3, shows a large initial charge capacity of ~350 mAh g-1 with little oxidation of the constituent Mn ions, yet, the crystal structure of delithiated Li2MnO3 is still unclarified because the structural disorder induced by the considerable Li extraction makes the analysis challenging. X-ray pair distribution function (PDF) analysis is a powerful tool to experimentally elucidate the structure of the disordered phase. Here, we conducted a comprehensive analysis with a focus on PDF analysis in combination with the X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) to reveal the disordered crystalline structure of the electrochemically delithiated Li2MnO3. The XRPD and TEM analyses clarified the formation of a low-crystallinity phase in the light of the average structure. The XAS and PDF analyses further revealed that the MnO6–based framework was rearranged with maintaining the MnO6 octahedral coordination after the initial charge. The difference pair distribution function (d-PDF) technique was therefore employed to extract the structural information of the low-crystallinity disordered phase. The delithiated phase was found to have a structure similar to the cubic spinel, LiMn2O4, rather than that of delithiated LiMn2O4 (λ-MnO2). In addition, the middle-range order of the delithiated phase deteriorated after the charge, indicating a decrease of coherent domain size to a single nm order. The composite structure formed after the first charge, therefore, consists of the disordered cubic spinel structure and unreacted Li2MnO3. The formation of the composite structure “activates” the electrode material structurally and eventually induces characteristic large capacity of this material.

Lithium- and manganese-rich layered oxides (LMRs) are promising positive electrode materials for next-generation rechargeable lithium-ion batteries. Herein, the structural evolution of Li1.2Ni0.2Mn0.6O2 during the initial charge–discharge cycle was examined using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy to elucidate the unique delithiation behavior. The pristine material contained a composite layered structure composed of Ni-free and Ni-doped Li2MnO3 and LiMO2 (M = Ni, Mn) nanoscale domains, and Li ions were sequentially and inhomogeneously extracted from the composite structure. Delithiation from the LiMO2 domain was observed in the potential slope region associated with the Ni2+/Ni4+ redox couple. Li ions were then extracted from the Li2MnO3 domain during the potential plateau and remained mostly in the Ni-doped Li2MnO3 domain at 4.8 V. In addition, structural transformation into a spinel-like phase was partly observed, which is associated with oxygen loss and cation migration within the Li2MnO3 domain. During Li intercalation, cation remigration and mixing resulted in a domainless layered structure with a chemical composition similar to that of LiNi0.25Mn0.75O2. After the structural activation, the Li ions were reversibly extracted from the newly formed domainless structure.

The charge/discharge reaction mechanisms of graphite negative electrodes in Li ion batteries were investigated via operando synchrotron X-ray diffraction at 0 °C and 25 °C. The intercalation of Li ions at 25 °C formed the stage 1 compound with an in-plane structure of LiC6; while intercalation at 0 °C only formed stage 2, with in-plane structures of LiC9 and LiC6. The degree of graphite expansion in the a, b-axes and c-axis directions by intercalation at 0 °C was less than that at 25 °C. Hence, it was difficult to form the stage 1 structure by further increases in the Li ion concentration, and the charging reaction at low temperature became difficult. De-intercalation at 0 °C did not follow the Daumas–Hérold model and proceeded discretely in the order: stage 1 → stage 2 → stage 4 → graphite, without going through stages 3, 5–8 and dilute stage 1.

Since the rechargeable Li-ion battery was invented in the early 1990s, its performance has evolved continually and Li-ion batteries are now installed in most mobile devices. In these batteries, graphite is used as a negative electrode material. However, the detailed reaction mechanism between graphite and Li remains unclear. Here we apply synchrotron X-ray diffraction, 7Li-nuclear magnetic resonance and Raman spectroscopy to operando analysis of the charge/discharge mechanism of a graphite electrode. The spectrum of the graphite electrode is measured repeatedly during the reaction. The operando dataset obtained is then analyzed synchronously with the composition of x in LiCx estimated from the charge/discharge curves. We propose a synchronized operando analysis method that provides useful information about the behavior of the C–C bond vibration mode and the interactions between Li and carbon atoms due to structural change during the charge/discharge reaction. In addition, we determine details of the intercalation mechanism.

A high anionic conductivity of ∼3.5 × 10–3 S cm–1 at room temperature is achieved for PbxSn2–xF4 (x = 1.21) obtained by annealing a mechanically milled PbF2/SnF2 mixture at 400 °C. The observed syn...

Conversion-type iron trifluoride (FeF3) has attracted considerable attention as a positive electrode material for lithium secondary batteries due to its high energy density and low cost. However, t...

Graphite is widely used as an anode material in almost all Lithium (Li)-ion batteries. Li is easily absorbed into the layer structure of graphite, forming lithium-carbon intercalation compounds LixC between LiC6 and C. However, although they are simple binary compounds, their structures have been left unelucidated for a long time, especially for the compounds between LiC12 and C. This is probably because the Li concentrations are too low to make a big difference in diffraction pattern between these Li-intercalated graphites and pure graphite. It has been known, however, that they have stacked layer structures, which strongly suggests that they are very likely to form modulated structures. Structural analyses of these compounds based on the modulated structure model were successfully performed, comprehensively elucidating all the LixC structures lying between LiC6 and C.

Vanadium sulfide (VS4) is one of the promising positive electrode materials for next-generation rechargeable lithium-ion batteries because of its high theoretical capacity (1196 mA h g−1). Crystalline VS4 has a unique structure, in which the Peierls-distorted one-dimensional chains of V–V bonds along the c axis are loosely connected to each other through van der Waals interactions. In this study, an amorphous VS4 is prepared by mechanical milling of the crystalline material, and its lithiation/delithiation behavior is investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy. The amorphous VS4 shows a chain structure similar to that of crystalline VS4. The amorphous host structure is found to change drastically during the lithiation process to form Li3VS4: the V ions become tetrahedrally coordinated by S ions, in which the valence states of V and S ions simultaneously change from V4+ to V5+ and S− to S2−, respectively. When the Li insertion proceeds further, the valence state of V ions is reduced. After the 1st cycle, the amorphous VS4 recovers to the chain-like structure although it is highly disordered. No conversion to elemental V is observed, and a high capacity of 700 mA h g−1 is reversibly delivered between 1.5 and 2.6 V.

The graphite negative electrode for Li-ion batteries was subjected to precision charge/discharge measurements at low current loads. The derivatives of the potential vs capacity curve and the potential vs C/Li composition curve were used to analyze elementary charge/discharge reactions. The number of peaks in the potential-capacity derivative curve increased with decreasing current load, and the elementary reactions, based on the formation of an unconfirmed superlattice structure, could be clearly separated and analyzed. By synchronizing these results with operando synchrotron X-ray diffraction data, a phase diagram of the Li-graphite intercalation compound formed by the charge/discharge reaction in Li-ion battery was established.

Since the commercialization of rechargeable Li ion batteries in the early 1990 s, the performance of these devices has continually improved. In such batteries, graphite is typically used as the negative electrode and the present work examined the reaction mechanisms at graphite negative electrodes based on operando synchrotron X-ray diffraction analyses during charge/discharge. The resulting in-plane diffraction patterns of the Li-intercalated graphite permitted a detailed analysis of changes in the three-dimensional structure of the electrode. As the intercalation proceeded from a dilute stage 1 (with less Li intercalation) to a final stage 1 (the formation of LiC6), the material transitioned from a random in-plane structure to a p(√3 × √3)R30° in-plane structure via a superlattice based on a p(3 × 3)R0° in-plane structure. The data also indicate that a series of superlattices was formed during the reaction of the electrode as a result of successive rearrangements, depending on the amount of Li intercalated into the graphite.

Lithium sulfide (Li2S) is one of the promising positive electrode materials for next-generation rechargeable lithium batteries. To improve the electrochemical performance of electronically resistive Li2S, a Fe-doped Li2S-based positive electrode material (Li8FeS5) has been recently designed and found to exhibit excellent discharge capacity close to 800 mAh g−1. In the present study, we investigate the structural and dynamic behavior of Li8FeS5 during charge–discharge cycling. In Li8FeS5, Fe ions are incorporated into the Li2S framework structure. The Li2S-based structure is found to transform to an amorphous phase during the charge process. The delithiation-induced amorphization is associated with the formation of S-S polysulfide bonds, indicating charge compensation by S ions. The crystalline to non-crystalline structural transformation is reversible, but Li ions are extracted from the material via a two-phase reaction, although they are inserted via a single-phase process. These results indicate that the delithiation/lithiation mechanism is neither a topotactic extraction/insertion nor a conversion-type reaction. Moreover, the activation energies for Li ion diffusion in the pristine, delithiated, and lithiated materials are estimated to be in the 0.30–0.37 eV range, which corresponds to the energy barriers for local hopping of Li ions along the Li sublattice in the Li2S framework.

Li-rich type manganese oxides are one of the most promising cathodes for lithium-ion batteries in recent years; thanks to their high energy density. In these cathodes, partial substitution of manga...

Fluoride shuttle batteries (FSBs), which utilize F– ion migration in electrochemical reactions, have recently advanced in academic research as next-generation rechargeable batteries. Bismuth trifluoride (BiF3) and its relatives are expected to be promising positive electrode materials for FSBs because of their high theoretical capacity. Herein, the defluorination/fluorination reaction of a BaF2-doped BiF3, Bi0.8Ba0.2F2.8, positive electrode was investigated using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. The Bi0.8Ba0.2F2.8 electrode showed a higher reversible capacity in the first cycle and improved capacity retention compared to the BiF3 electrode. The pristine Bi0.8Ba0.2F2.8 showed a tysonite-type structure, and metallic Bi and BaF2 nanoparticles were observed in the fully defluorinated state. Moreover, we found that the (re-)fluorinated material consisted of BiF3 and BaF2 nanoparticles, indicating that bismuth is the only redox-active element, and that the tysonite structure is not recovered after the initial discharging. This suggests that the cycle performance of the Bi0.8Ba0.2F2.8 electrode may be improved due to the suppression of the coarsening of BiF3 nanoparticles by the adhesion of BaF2 nanoparticles formed after initial defluorination.

Li2MnO3 is an important parent component in lithium- and manganese-rich layered oxides (LMRs), which are one of the promising positive electrode materials for next-generation lithium ion rechargeable batteries. Here, we report the layered-to-spinel phase transformation in Li2MnO3 during the initial charging process to characterise its unique delithiation behaviour, which gives an insight into the relationship between the structure, superior capacities and degradation of LMR electrodes. The atomic-scale observation using scanning transmission electron microscopy (STEM) techniques suggests that the structural transformation occurs in a biphasic manner within a single particle. The formed phase has a Li-defect spinel structure, indicating that the delithiation leads to Mn migration from the transition-metal layer to the Li layer, accompanied by some oxygen release. This layered-to-spinel phase transformation is an essential bulk process in the initial activation of Li2MnO3. During the lithiation in the 1st discharge, the Mn remigration occurs and the layered structure is again formed with significant disordering. During the multiple cycles, the defect spinel structure is stabilised and becomes more oxygen-deficient with a lower Mn valency. As a consequence, the amount of inserted Li decreases, which corresponds to the capacity and voltage fading observed in Li2MnO3 and LMRs.

Lithium- and manganese-rich layered oxides (LMRs) are promising positive electrode materials for next-generation rechargeable lithium-ion batteries. Herein, the structural evolution of Li1.2Ni0.2Mn0.6O2 during the initial charge–discharge cycle was examined using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy to elucidate the unique delithiation behavior. The pristine material contained a composite layered structure composed of Ni-free and Ni-doped Li2MnO3 and LiMO2 (M = Ni, Mn) nanoscale domains, and Li ions were sequentially and inhomogeneously extracted from the composite structure. Delithiation from the LiMO2 domain was observed in the potential slope region associated with the Ni2+/Ni4+ redox couple. Li ions were then extracted from the Li2MnO3 domain during the potential plateau and remained mostly in the Ni-doped Li2MnO3 domain at 4.8 V. In addition, structural transformation into a spinel-like phase was partly observed, which is associated with oxygen loss and cation migration within the Li2MnO3 domain. During Li intercalation, cation remigration and mixing resulted in a domainless layered structure with a chemical composition similar to that of LiNi0.25Mn0.75O2. After the structural activation, the Li ions were reversibly extracted from the newly formed domainless structure.

Vanadium sulfide (VS

Li2MnO3, an electrode material for Li ion batteries, belongs to the C2/m space group and is known to have a cubic-close-packed (ABC...) layered structure, in which the transition-metal layer is supposed to have an ordered atomic arrangement with Li atoms at the 2b site and Mn atoms at the 4g site. However, recently, it has been reported that this compound usually does not exhibit such an ideal structure and instead contains a large number of structural defects, not only stacking faults but also mixing of Li and Mn atoms between the 2b and 4g sites. To elucidate the effect of such structural defects on the electrochemical behavior, we examined the crystal structure of Li2MnO3 synthesized at various temperatures by simultaneously analyzing the stacking faults and cation mixing using FAULTS, a Rietveld code. Our examination showed that the crystals consist of both disordered and ordered domains; the disordered domains contain a large number of stacking faults along the c axis and have considerable Li/Mn atomic mixing within the transition-metal layer, whereas the ordered domains have almost no defects. At low synthesis temperatures, the disordered domains are dominant. However, the ordered domains increase at the expense of the disordered domains above 770 °C and become dominant at higher temperatures. It is also found that the degree of cation mixing in the disordered domains remains almost constant irrespective of synthesis temperature. The crystalline defects such as stacking faults or Li/Mn cation mixing are expected to promote the formation of smooth Li percolation paths. The decreasing of the disordered domains leads to dramatically decreased capacity. This indicates that the observed capacities of Li2MnO3 can be determined by the relative amounts of the ordered/disordered domains in the structure.

We examined the crystal structures of Li2(NixMn1-x)O3(-δ) (x = 0, 1/10, 1/6, and 1/4) to elucidate the relationship between the structure and electrochemical performance of the compounds using neutron and synchrotron X-ray powder diffraction analyses in combination. Our examination revealed that these crystals contain a large number of stacking faults and exhibit significant cation mixing in the transition-metal layers; the cation mixing becomes significant with an increase in the Ni concentration. Charge-discharge measurements showed that the replacement of Mn with Ni lowers the potential of the charge plateau and leads to higher charge-discharge capacities. From a topological point of view with regard to the atomic arrangement in the crystals, it is concluded that substituting Mn in Li2MnO3 with Ni promotes the formation of smooth Li percolation paths, thus increasing the number of active Li ions and improving the charge-discharge capacity.

Li-rich layered oxides have attracted attention as promising positive electrode materials for next-generation lithium-ion secondary batteries because of their high energy storage capacity. The participation of the oxygen anion has been hypothesized to contribute to these oxides' high capacity. In the present study, we used O K-edge and Mn L-edge X-ray absorption spectroscopy (XAS) to study the reversible redox reactions that occur in single-phase Li-rich layered manganese oxide, Li2MnO3. We semiquantitatively analyzed the oxygen and manganese reactions by dividing the charge/discharge voltage region into two parts. The O K-edge XAS indicated that the electrons at the oxygen site reversibly contributed to the charge compensation throughout the charge/discharge processes at operating voltages between 2.0 and 4.8 V vs. Li+/Li0. The Mn L-edge XAS spectra indicated that the Mn redox reaction occurred only in the lower-voltage region. Thus, at higher potentials, the electrons, mainly at the oxygen site, contributed to the charge compensation. Peaks whose energies were similar to peroxide appeared in and then disappeared from the O K-edge spectra obtained during the reversible redox cycles. These results indicate that the reorganization of the oxygen network in the crystal structure affects the redox components. By using two kinds of detection modes with different probing depths in XAS measurements, it was found that these redox reactions are bulk phenomena in the electrode.

The oxidation/reduction behaviours of lattice oxygen and transition metals in a Li-rich manganese-based layered oxide Li[Li0.25Ni0.20Mn0.55]O1.93 are investigated by using hard X-ray photoelectron spectroscopy (HAX-PES). By making use of its deeper probing depth rather than in-house XPS analyses, we clearly confirm the formation of O- ions as bulk oxygen species in the active material. They are formed on the 1st charging process as a charge compensation mechanism for delithiation and decrease on discharging. In particular, the cation-anion dual charge compensation involving Ni and O ions is suggested during the voltage slope region of the charging process. The Ni ions in the material are considered to increase the capacity delivered by a reversible anion redox reaction with the suppression of O2 gas release. On the other hand, we found structural deterioration in the cycled material. The O- species are still observed but are electrochemically inactive during the 5th charge-discharge cycle. Also, the oxidation state of Ni ions is divalent and inactive, although that of Mn ions changes reversibly. We believe that this is associated with the structural rearrangement occurring after the activation process during the 1st charging, leading to the formation of spinel- or rocksalt-like domains over the sub-surface region of the particles.

We investigated the oxygen contributions on delithiation process of different types of layered 3d transition metal oxides, Li2TiO3, Li2MnO3, and LiCoO2, using X-ray spectroscopies with the aid of density functional theory calculations. In delithiatied LiCoO2, electrons are extracted from highly hybridized Co 3d and O 2p orbitals without O2 loss. In Li2TiO3, the hybridized Ti 3d and O 2p orbitals at the valence band is mainly contributed by O 2p orbitals, and delithiated Li2TiO3 loses oxygen as the electrons are extracted. Li2MnO3 exhibits some hybridization. In delithiated Li2MnO3, a certain amount of oxygen is lost, but the large amount of oxidized O anions remains as peroxide and superoxide-like states, which would work as the redox active species. Therefore, the degree of hybridization between metal 3d and O 2p orbitals is a key factor to influence the stability of O anion redox during the oxidation process, which determines the electrode performance.

An archetypical Li-rich layered oxide, Li2MnO3, shows a large initial charge capacity of ~350 mAh g-1 with little oxidation of the constituent Mn ions, yet, the crystal structure of delithiated Li2MnO3 is still unclarified because the structural disorder induced by the considerable Li extraction makes the analysis challenging. We have performed X-ray pair distribution function (PDF) analysis in combination with the X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) to reveal the disordered crystalline structure of the electrochemically delithiated Li2MnO3. The XRPD and TEM analyses clarified the formation of a low-crystallinity phase in the light of the average structure. The XAS and PDF analyses revealed that the MnO6–based framework was rearranged with maintaining the MnO6 octahedral coordination after the initial charge. The difference pair distribution function (d-PDF) technique was therefore employed to extract the structural information of the low-crystallinity disordered phase. The delithiated phase was found to have a structure similar to the cubic spinel, LiMn2O4, rather than that of delithiated LiMn2O4 (l-MnO2). In addition, the middle-range order of the delithiated phase deteriorated after the charge, indicating a decrease of coherent domain size to a single nm order. The composite structure formed after the first charge, therefore, consists of the disordered cubic spinel structure and unreacted Li2MnO3. The formation of the composite structure “activates” the electrode material structurally and eventually induces characteristic large capacity of this material.

Vanadium sulfide (VS4) is one of the promising positive electrode materials for high capacity lithium ion secondary batteries. In this study, we prepared an amorphous VS4 (a-VS4) by mechanical treatment of the crystalline VS4 (c-VS4) and characterize its local structure. Furthermore, its lithium insertion/extraction behavior was investigated using solid-state nuclear magnetic resonance (NMR), X-ray pair distribution function (PDF), and Raman spectroscopy analyses. Crystalline VS4 was synthesized from V2S3 (99%, Kojundo Chemical Lab.) and S (99.9%, Wako).1 The mixture was heated in a sealed glass tube under vacuum at 400 °C for 12 h. Then, the amorphous VS4 was prepared from the crystalline sample by mechanical milling for 40 h at 270 rpm. A working electrode was prepared from a mixture of the active material (a-VS4), conductive carbon, and Teflon binder in a weight ratio of 59:29:12. Coin-type or laminate-type cells were assembled in an Ar-filled glove box. The cells were cycled between 1.5 and 2.6 V at a constant current density of 59.8 mA g–1 using a TOSCAT-3100 battery-testing system (Toyo System). They were then carefully disassembled at selected discharge/charge states in the glove box and rinsed with dimethyl carbonate (DMC) to remove the residual electrolyte solution. Local structures of c-VS4 and a-VS4 were characterized and the structural changes of the electrode samples were examined by NMR spectroscopy, X-ray PDF analyses, and Raman spectroscopy. Operando 7Li NMR measurements were performed to study the Li insertion/extraction process under electrochemical operation.2 It is known that c-VS4 has a unique structure, in which the Peierls-distorted one-dimensional chains of V-V bonds along the c axis are loosely connected to each other through van der Waals interactions. We confirmed that a-VS4 shows a chain structure similar to that of c-VS4. The chain structure is found to change drastically during the Li insertion process to form amorphous Li3VS4, where the V ions become tetrahedrally coordinated by S ions. The valence states of V and S ions simultaneously change from V4+ and S– (a-VS4) to V5+ and S2– (a-Li3VS4), respectively. When the Li insertion proceeds further (i.e., a-Li3+d VS4), the valence state of V ion is reduced, and a broad 7Li NMR peak shifts to higher frequencies (Fig. 1). After the 1st cycle, the amorphous VS4 recovers the chain-like structure although it is highly disordered. It is also found that the conversion reaction to metallic V and Li2S are observed when the cell is discharged to 0.2 V. This study indicates that the Li insertion/extraction process of the amorphous sulfur-rich transition metal (TM) sulfides such as a-VS4 and a-TiS4 3 involves the amorphous-amorphous phase transformation, which is related to the changes in the bonding nature of sulfide species and the coordination number of TM ions. The amorphous host structure can accommodate these modifications, which is clearly different from the Li insertion/extraction mechanism in crystalline electrode materials. This work is based on results obtained from a project, “Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2)”, JPNP16001, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Koganei et al., Solid State Ionics, 323, 32-36 (2018). Shimoda et al., RSC adv. 9, 23979-23985 (2019). Sakuda et al., J. Am. Chem. Soc., 139, 8796-8799 (2017). Figure 1

Introduction : In order to promote development of electric vehicle, it is required to improve the capacity density, the low-temperature performance, and the high-rate property of the batteries. Understanding the lithium intercalation and de-intercalation mechanism at graphite electrode of the storage battery (LIB) is very important for this purpose. Crystal structure changes of lithium-intercalated graphite during charge and discharge processes were investigated by operando X-ray diffraction (XRD) measurements using a synchrotron radiation facility. Low-temperature operando XRD measurements were now available by the development of a new temperature-controlled cell jacket.1-2 This study confirmed in-plane structure change along a- and b-axis as well as stage structure change along c-axis.3 As a result, it was elucidated that crystallinity of graphitic carbon caused differences in phase transition during discharge and this phenomenon affected low-temperature and high-rate discharge performances. Experimental : Coin cells composed of carbon and NMC electrodes were firstly prepared and subjected to the evaluation of the battery performances from the low-temperature (0℃) to the room temperature. Coin cells of several graphitic carbon were evaluated. Crystal structures of lithium-intercalated graphite during discharge process were investigated by operando analysis using synchrotron radiation X-ray diffraction (SR-XRD) at BL28XU beam line of SPring-8. Al-laminated half-cells composed of graphitic carbon and Li electrodes were prepared and subjected to the analysis of operando measurement. The graphitic carbons of different crystallite sizes were analysed. Al-laminated half-cells conditioned by several cycles were used for the measurement. Operando XRD measurements were carried out during charge and discharge processes. X-ray of 25keV (its wavelength of 0.0496 nm) with a beam size of 0.2 mm ×0.5 mm was used to obtain diffraction patterns. The exposure time was set to 10 s. The diffraction patterns were obtained by two-dimensional detector, PILATUS 100K (DECTRIS). Two-dimensional image data were converted to one-dimensional 2q profiles, and the diffraction peaks were separated using the Lorentz functions. The test cell underwent an aging treatment was charged (Li insertion) at room temperature. Thereafter, structural transition were analyzed during the discharging process (Li de-intercalation) in 0.2C at room temperature and in 0.1C at 0℃. Results and Discussion : Figure 1 shows the SR-XRD patterns of lithium-intercalated graphite at the discharge process with current density of 0.2C at room temperature. The result showed the in-plane structure change along a- and b-axis as well as stage structure change along c-axis. The detailed analysis of in-plane structure change and stage structure change for each graphitic carbon was performed using the operando measurements. It was identified that the crystallinity of graphitic carbon caused differences in phase transition during discharge. These results showed that crystallite sizes influence the phase transition and give major effect on LIB performances of graphite negative electrode at low-temperature or high-rate discharge. The Li diffusivity in the graphitic carbon is likely dependent on the crystallite size. The battery reaction mechanism influenced by crystallite size was elucidated by operando XRD measurements. The present results confirm that the crystallinity of the graphitic carbon affects the low-temperature and high-rate discharge characteristics. The detail results will be shown in the conference. Acknowledgment: This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Battery 2 (RISING2) project administrated by the New Energy and Industrial Technology Development Organization (NEDO). References: S. Takagi et al., “Operando Structure Analysis of Graphite Electrode by Synchrotron Radiation Diffraction” The 59th Battery Symposium, 2E14 (2018). S. Takagi et al., “Operando Structure Analysis of Graphite Electrode by Synchrotron Radiation Diffraction” The 60th Battery Symposium, 1B20 (2019). H. Fujimoto et al., “Operando analysis of charge/discharge reaction mechanism of graphite anode of Li ion battery using synchrotron radiation diffraction, Second report”, The 59th Battery Symposium, 2E16 (2018). Figure 1

Introduction The rechargeable Li-ion battery (LIB) is a successful energy storage device because of its high energy density and long cycle life. In order to improve its performance, quantitative understanding of elementary reactions in the LIB such as the reaction of Li intercalation from electrolyte solution into graphite and crystal structure change in graphite during the reaction must be a great help. Structure change of Li-intercalated graphite during the charge/discharge processes was recently observed by operando X-ray diffraction measurements using a synchrotron radiation at SPring-8.1 The operando XRD data at LiC18 charge/discharge state exhibited two peaks corresponding two different C-C grid distances in the same plane of graphite, while no change in interlayer distance was detected during the appearance and disappearance of these peaks; it implies only in-plane structure transition such as Li/6C layer to Li/9C layer changes.1 An AA to AB stack transition in graphite was characterized by (101) peak disappearance in the XRD data at the composition between LiC63–LiC72.2 To interpret and discuss these experimental results, we conduct first-principles calculations for the phase stability of graphite. Methods and Models The formation enthalpy ∆H f of Li-intercalated graphite is defined as ∆H f (Li n C m ) = ( E DFT(Li n C m ) − nE DFT(Li) − mE DFT(C) ) / (m+n) (1), where E DFT are the total energies of Li-intercalated graphite Li n C m , simple metal Li, and AB stacked graphite C from density functional theory (DFT) calculations. Formation enthalpy as a function of C-ratio, x C = m / (m + n) (2), was used to investigate the phase stability of Li n C m . Quantum ESPRESSO with a plane-wave basis3 and van der Waals functional4 was used to obtain DFT energies. Our previous study using this functional well reproduced the experimental lattice constants and electromotive forces (EMFs) of Li-intercalated graphite.5 It is known that Li-intercalated graphite exhibits stages from 1 to 8. These stages may take different combination of in-plane configurations and interlayer configurations. In-plane configurations considered are Li/6C, Li/9C, Li/18C, and Li/24C, which means the ratios of Li/C atoms are located on a single layer as shown in Fig. 1 (a). Three interlayer structures are considered here; (1) graphite layers stacked with AA overlap, (2) with AB, and (3) mixed (Li including layers are AA stacked, the other layers are AB stacked). Conventional LiC6 intercalated phase corresponds to the stage 1 of Li/6C AA stack structure (denoted as s1-Li/6C-AA, here s1, s2, s3, ... represents stage 1, stage 2, stage 3, ..., respectively). Results The calculated formation enthalpies ∆H f are plotted as a function of x C in Fig. 1 (b). At the composition of LiC6 (x C = 0.857), LiC12 (x C = 0.923), and C (x C = 1), respective most stable phases are s1-Li/6C-AA, s2-Li/6C-AA, and AB stack graphite ones as we could expect. At the composition of LiC18 (x C = 0.947), s2-Li/9C-AA structure is more stable than the s3-Li/6C-AA structure, which is consistent with the experimental observation.1 AB stack structures are more stable than AA at x C > 0.97 from the theoretical calculation, while the AA-AB transition has been observed at 0.984 < x C < 0.986 by experiments. At higher stages (x C > 0.94), mixed stack structure is predicted to be more stable than simple AA and AB structures. The formation enthalpies of s2-Li/9C-mixed and s3-Li/6C-mixed are almost the same (within 0.01 meV/atom) and these configurations are predicted to be the most stable at LiC18. However, these mixed stackings have not been detected by experiments. In the presentation, we will also present the theoretical EMF values of the Li-intercalated graphite electrode and compare them with experimental results. Acknowledgments This work was supported in part by the Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 Project (RISING2) administrated by the New Energy and Industrial Technology Development Organization (NEDO). References S. Takagi, K. Shimoda, H. Fujimoto, H. Kiuchi, T. Naka, T. Murata, K.-I. Okazaki, T. Fukunaga, E. Matsubara, Z. Ogumi, and T. Abe, “Operando Structure Analysis of Graphite Electrode by Synchrotron Radiation Diffraction” The 60th Battery Symposium, 1B20 (2019). H. Fujimoto , S. Takagi , H. Kiuchi , K. Shimoda , K.-I. Okazaki, T. Murata , T. Abe, Z. Ogumi, and E. Matsubara, “Operando analysis of charge/discharge reaction mechanism of graphite anode of Li ion battery using synchrotron radiation diffraction, Second report”, The 59th Battery Symposium, 2E16 (2018). P. Giannozzi et al., J. Phys.: Condens. Matter 21, 395502 (2009); ibid. 29, 465901 (2017). I. Hamada, Phys. Rev. B 89, 121103(R) (2014). J. Haruyama, T. Ikeshoji, and M. Otani, J. Chem. Phys. C 122, 9804 (2018). Figure 1

FeF3 has attracted considerable attention as a positive electrode material for next-generation rechargeable lithium ion batteries, because of its low cost, low risk, and high energy density, which facilitate a conversion-type lithiation/delithiation reaction. However, the conversion reaction of the FeF3 electrode is known to suffer from capacity fading during repeated discharge–charge cycles. Herein, we find an interesting correlation between capacity fading behavior and spectral evolutions in electrochemical operando nuclear magnetic resonance (NMR) measurements. The operando 7Li NMR spectra demonstrate the reversible formation of metallic Fe by the conversion process during the early discharge–charge cycles. However, it is gradually suppressed after repeated cycles. Moreover, LiF is augmented at the fully charged states, indicating that FeF3 is no longer recovered after repeated cycles. The active material can converge into FeF2 and LiF in the degraded electrode. Another factor associated with capacity degradation is the electrolyte decomposition occurring at high voltages, which results in a resistive film coating the electrode surface. We therefore conclude that the film accumulation on repeated discharging inhibits the conversion reaction to metallic Fe and LiF, leading to a characteristic capacity fading behavior of FeF3.

1.Introduction In recent years, the development of innovative batteries that exceed the performance of lithium-ion batteries has been desired. One of the candidates is a fluoride shuttle battery (FSB). It is an anion-based, rechargeable batteries operating under fluoride shuttling, and rests upon the foundation of a redox-active fluoride ion transporting electrolyte of high electrochemical stability. To realize the FSB, we have developed a lactone-based Li+/F- hybrid electrolyte, in which Li+ and F- ions that normally cannot coexist in organic solvents form some complexes soluble in GBL. The thus reformed electrolyte, together with its delicate and unique anion accepting (AA) function, largely expands the negative potential window to or beyond the standard redox potential of Li+/Li. In this study, in order to clarify the electrochemical behaviors of BiF3/Bi electrode combined with the electrolyte, the operando analysis was carried out by the synchrotron radiation diffraction (SRD) measurement. 2. Experimental The BiF3 powder mixed with acetylene-black and PVdF was used as the working electrode. The activated carbon and Ag metal were used as the counter and reference electrodes, respectively. The Al-laminated half-cell composed of above-mentioned electrodes was assembled using a newly developed hybridized electrolyte. Thus prepared cell was pre-discharged (0th cycle) in advance in the potential range of -1.5 V – 1.0 V at ca. 0.04C. Then, several charge/discharge cycles were repeated with the same conditions. SRD was measured with BL28XU beam line at Super Photon ring-8, Japan during the whole charge/discharge process. High-energy X-ray with a wavelength of 0.049592 nm was used to obtain 2D diffraction patterns. The exposure time was set to 10 s, and several thousand diffraction profiles were obtained during the discharge/charge process. In order to analyze the obtained enormous profiles data in conjunction with the charge/discharge curves and their differential curves (V-dQ/dV), an analysis software called “Profile Chaser” was newly developed. By using the software, all the profiles of electrode during charge/discharge processes are loaded automatically in the computer. The profiles were successively displayed on a monitor as a series of profiles in conjunction of compositions estimated from the charge/discharge curves, so that the profile change was traced from the monitor. 3. Results and discussions Fig.1 shows the SRD profile changes in the discharge process of 0th and 1st cycles. In both cycles, the intensity of 111 diffraction of BiF3 decreased and that of 012 diffraction of Bi increased as the discharge reaction proceeded. However, the formation of BiF3 was hardly observed in the charge process. It indicates that the bismuth fluoride formed in the charge process is amorphous or solved in the electrolyte. Figure 1

Introduction : In order to promote development of electric vehicle, it is required to improve the capacity density of a battery, the battery performance at a low temperature, and the high rate property of a battery. Characterization of the size distribution and the average size of carbon in the negative electrode significantly influence on the battery performance. We have studied clarification of graphitic carbon’s properties influencing on performance of LIB especially at low temperature. Firstly, the X-ray diffraction profiles of several graphitic carbons were analyzed by the fundamental parameter (FP) method. Further, the structure changes of lithium-intercalated graphite during the charge and discharge processes were investigated by operando measurement using synchrotron radiation at BL28XU of SPring-8 in Japan. The time resolution of the apparatus is the order of milliseconds for analyzing one diffraction pattern. Experimental : Crystallite size and its distribution of several graphitic carbons were analyzed by the fundamental parameter (FP) method using X-ray diffraction profiles. X-ray wavelength of 0.154 nm was used to obtain X-ray diffraction profiles. In order to analyze crystallite size and its distribution, X-ray diffraction profiles were calculated by using software called PDXL2 (Rigaku Corporation). Coin cells composed of carbon and NMC electrodes were prepared and subjected to the evaluation of the battery performances from the low temperature to the room temperature. Coin cells conditioned by several cycles were evaluated. Further, crystal structures of lithium-intercalated graphite during charge and discharge processes were investigated by operando analysis using synchrotron radiation diffraction at BL28XU beam line of SPring-8. Al-laminated half-cells composed of graphitic carbon and Li electrodes were prepared and subjected to the evaluation of operando measurement. The graphitic carbons of different crystallite sizes and their distributions were analysed. Al-laminated half-cells conditioned by several cycles were used for the measurement. Operando measurements were carried out during charge and discharge processes. X-ray of 25keV (its wavelength of 0.0496 nm) with a beam size of 0.2 mm ×0.5 mm was used to obtain diffraction patterns. The exposure time was set from 0.5 s to 10 s. The diffraction patterns were obtained by two-dimensional detector (Rigaku Corporation). Results and Discussion : The experimental X-ray diffraction profile of graphitic carbon and that calculated profile by the fundamental parameter (FP) method were obtained. The calculated profile showed a good fit with the measured one. The each plane of graphitic carbon was analyzed properly. The analysis of FP method revealed that crystallite sizes and their distributions of graphitic carbons influences on LIB performance especially at low temperature. The results indicate that the low temperature characteristics improve as the crystallite size and distribution of the graphite (102) plane decreases. The same results were also obtained for the relationship between the crystallite size distribution of the graphite (102) plane and the high-rate discharge characteristics of LIB. The crystallite size distribution of the graphite (102) plane is thought to express the Li diffusivity. Figure shows the result of synchrotron radiation diffraction pattern of lithium-intercalated graphite at the discharge process with current density of 0.2C. The stage change was analysed clearly as shown in Figure.The difference of stage change of each carbon was revealed in considerable detail by Operando measurement. The crystallite size and its distribution influencing on the battery performance at low temperature was examined in detail. The result showed that crystallite sizes and their distributions influence on the phase structure changes and give major effect on charge and discharge performances of graphite negative electrode at low temperature. Their battery reaction mechanism influenced by crystallite size distribution was elucidated by the Operando measurement. The detail results will be shown in the conference. Acknowledgment: This work was supported by the Research and Development Innovative for Scientific Innovation of New Generation Battery 2 (RISING2) project of the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Vanadium sulfide (VS4) is one of the promising positive electrode materials for high capacity lithium ion secondary batteries. In this study, we prepared an amorphous VS4 (a-VS4) by mechanical treatment of the crystalline VS4 (c-VS4) and characterize its local structure. Furthermore, its lithium insertion/extraction behavior was investigated using solid-state nuclear magnetic resonance (NMR), X-ray pair distribution function (PDF), and Raman spectroscopy analyses. Crystalline VS4 was synthesized from V2S3 (99%, Kojundo Chemical Lab.) and S (99.9%, Wako).1 The mixture was heated in a sealed glass tube under vacuum at 400 °C for 12 h. Then, the amorphous VS4 was prepared from the crystalline sample by mechanical milling for 40 h at 270 rpm. A working electrode was prepared from a mixture of the active material (a-VS4), conductive carbon, and Teflon binder in a weight ratio of 59:29:12. Coin-type or laminate-type cells were assembled in an Ar-filled glove box. The cells were cycled between 1.5 and 2.6 V at a constant current density of 59.8 mA g–1 using a TOSCAT-3100 battery-testing system (Toyo System). They were then carefully disassembled at selected discharge/charge states in the glove box and rinsed with dimethyl carbonate (DMC) to remove the residual electrolyte solution. Local structures of c-VS4 and a-VS4 were characterized and the structural changes of the electrode samples were examined by NMR spectroscopy, X-ray PDF analyses, and Raman spectroscopy. Operando 7Li NMR measurements were performed to study the Li insertion/extraction process under electrochemical operation.2 It is known that c-VS4 has a unique structure, in which the Peierls-distorted one-dimensional chains of V-V bonds along the c-axis are loosely connected to each other through van der Waals interactions. We confirmed that a-VS4 shows a chain structure similar to that of c-VS4. The chain structure is found to change drastically during the Li insertion process to form amorphous Li3VS4, where the V ions become tetrahedrally coordinated by S ions. The valence states of V and S ions simultaneously change from V4+ and S– (a-VS4) to V5+ and S2– (a-Li3VS4), respectively. When the Li insertion proceeds further (i.e., a-Li3+d VS4), the valence state of V ion is reduced, and a broad 7Li NMR peak shifts to higher frequencies (Fig. 1). After the 1st cycle, the amorphous VS4 recovers the chain-like structure although it is highly disordered. It is also found that the conversion reaction to metallic V and Li2S are observed when the cell is discharged to 0.2 V. This study indicates that the Li insertion/extraction process of the amorphous sulfur-rich transition metal (TM) sulfides such as a-VS4 and a-TiS4 3 involves the amorphous-amorphous phase transformation, which is related to the changes in the bonding nature of sulfide species and the coordination number of TM ions. The amorphous host structure can accommodate these modifications, which is clearly different from the Li insertion/extraction mechanism in crystalline electrode materials. References 1. Koganei et al., Solid State Ionics, 323, 32-36 (2018). 2. Shimoda et al., RSC adv. 9, 23979-23985 (2019). 3. Sakuda et al., J. Am. Chem. Soc., 139, 8796-8799 (2017). Figure 1

Li2TiO3 is a Li-rich cathode/anode material similar to Li2MnO3. These materials crystallize into monoclinic structures with ABC-stacked atomic layers, approximated by pseudo-trigonal cells. In these crystals, transition-metal layers are occupied not only by transition-metal atoms but also by Li atoms, forming ordered/disordered atomic arrangements. Faults Rietveld analysis was conducted, showing that Li2TiO3 crystalizes into a monoclinic structure with the space group C2/c, in which Li and Ti atoms are configured in an imperfectly ordered arrangement at the transition-metal layer and a large number of stacking faults are generated in the crystal. To precisely evaluate the site occupancies in such imperfect crystals, our structural analysis found that the structures should be analyzed by powder diffraction while taking stacking faults and atomic mixing into account. The atomic mixing at the transition-metal layer tends to gradually increase as the synthesis temperature is raised.

An investigation was made on the electronic structure of 4d transition metal layered oxide material of Li2RuO3 using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The intensity of O [Formula: see text] pre-edge peak increased for Li ion extracted samples, suggesting increased ligand holes. The Ru 3d XPS spectrum suggested the variation of local structure around Ru ions by extraction of Li ions. We conclude that the delithiation from Li2RuO3 is charge compensated by O anions, and that the creation of the ligand holes reorganizes electronic structures composed of highly hybridized Ru 4d and O 2p orbitals.

The electrochemically-driven conversion reaction of BiF3 with Li+ ions is of interest for potential application as a positive electrode system in conversion type rechargeable batteries. Here, we use synchrotron radiation diffraction and 7Li nuclear magnetic resonance (NMR) for complementary operando observations of reversible or quasi-reversible conversion reactions of α-BiF3 nanocomposite electrode at room temperature. The nanocomposite electrode was fabricated by ball milling and subsequent heat treatments. A pronounced XRD peak broadening indicated a disordered fine crystalline state in the electrode. The operando synchrotron radiation diffraction measurements revealed a quasi-reversible smooth crystallographic transformation between α-BiF3 and metallic Bi. The operando 7Li NMR measurement quantitatively showed reversible conversion reactions. The series of in-situ 7Li NMR spectra contained sharp signals from Li+ ions in the electrolyte and a broad signal associated with a solid phase of LiF. These signals followed a stoichiometric relationship that conformed to a three-electron BiF3 conversion pathway.

To examine the dynamical origin of high ionic conductivity of (Li2S)70(P2S5)30 glass ceramic obtained by annealing (Li2S)70(P2S5)30 glass, we applied 6/7Li and 31P solid-state NMR. NMR line shapes and spin–lattice relaxation times (T1) were measured as a function of temperature. The results showed that dynamics of the PS4 tetrahedra and P2S7 ditetrahedra units in (Li2S)70(P2S5)30 glass ceramic is not appreciable at temperatures below ca. 310 K, where the ionic conductivity is low. At higher temperatures, however, significant motion especially for the P2S7 ditetrahedra unit is apparent in both of 31P-T1 and 31P MAS line shapes. Further, we applied the 31P–31P dipolar correlation experiment to examine the 31P line width, which is reduced by motion at higher temperatures. It was shown that the line width of the P2S7 unit is attributable to the distribution of local structures of and around the P2S7 ditetrahedra unit. With these, we concluded that the significant motional fluctuation of the P2S7 ditetrahedra ...

Delithiation and lithiation behaviors of ordered spinel LiNi0.5Mn1.5O4 and disordered spinel LiNi0.4Mn1.6O4 were investigated by using in situ (in operando) 7Li NMR and ex situ 6Li MAS NMR spectroscopy. The in situ 7Li monitoring of the ordered spinel revealed a clear appearance and subsequent disappearance of a new signal from the well-defined phase Li0.5Ni0.5Mn1.5O4, suggesting the two-phase reaction processes among Li1.0Ni0.5Mn1.5O4, Li0.5Ni0.5Mn1.5O4, and Li0.0Ni0.5Mn1.5O4. Also, for the disordered spinel, Li0.5Ni0.4Mn1.6O4 was identified with a broad distribution in Li environment. High-resolution 6Li MAS NMR spectra were also acquired for the delithiated and lithiated samples to understand the detailed local structure around Li ions. We suggested that the nominal Li-free phase Li0.0Ni0.5Mn1.5O4 can accommodate a small amount of Li ions in its structure. The tetragonal phases Li2.0Ni0.5Mn1.5O4 and Li2.0Ni0.4Mn1.6O4, which occurred when the cell was discharged down to 2.0 V, were very different in the Li environment from each other. It is found that 6, 7Li NMR is highly sensitive not only to the Ni/Mn ordering in LiNi0.5Mn1.5O4 but also to the valence changes of Ni and Mn on charge-discharge process.

1Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan 2Department Materials Structure Science, The Graduate University for Advanced Studies, Hayama 240-0193, Japan 3J-PARC Center, Japan Atomic Energy Agency, Naka-gun, Ibaraki 319-1195, Japan 4Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan 5Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan

The first preparation of Li-graphite intercalation compound (Li-GIC) was attempted by Hérold et al. in 1955. Since then, a lot of reports have been made mainly by the research groups in France, and with regard to the stage I and II compounds, it is clarified that they take the in-plane structures called by P(√3×√3)R30°. Though there have been many reports since 1970s, the detail discussion has not been done so far concerning the intercalation mechanism and in-plane structure of higher stage compounds. The first reason is that the concentration of Li species becomes smaller in the higher stages. The second reason is the strong preferred orientation of graphite. Such reasons make difficult to clarify the intercalation mechanism and in-plane structure. In order to improve the performance of Li-ion battery, it is essential to investigate the detail structure change of graphite electrode during the charge/discharge process. In this study, in order to elucidate the intercalation mechanism and structure change not only along c-axis, but also along the a,b-axes, we traced dynamically the intercalation reaction in Li-ion battery negative electrode by Operando measurement with synchrotron radiation diffraction.

Rechargeable lithium-ion batteries (LIBs) are currently accepted to be one of the most suitable energy storage resources in portable electronic devices because of their high gravimetric and volumetric energy density. To understand the behavior of Li^{+} ions on electrochemical lithium extraction/insertion process, we performed in situ^{7}Li nuclear magnetic resonance (NMR) measurements for LiC_{o}O_{2} cathode in a plastic cell battery, and the spectral evolutions of the ^{7}Li NMR signal of Li_{x}C_{o}O_{2} (0 ≤ x ≤ 1) were well investigated. Very narrow solid solution region of Li_{x}C_{o}O_{2} (∼0.99 ≤ x < 1) was explicitly defined from the large intensity reduction of Li_{x}C_{o}O_{2} signal at ∼0 ppm, which is related to the localized nature of the electronic spin of paramagnetic Co^{4+} ion formed at the very early delithiation stage. With further decreasing the signal intensity of LiC_{o}O_{2} , a Knight-shifted signal corresponding to an electrically conductive Li_{x}C_{o}O_{2} phase emerged atx = 0.97, which then monotonously decreased in intensity for x < 0.75 in accordance with the electrochemical lithium de-intercalation from Li_{x}C_{o}O_{2}. These observations acquired in situ fully confirm the earlier studies obtained in ex situ measurements, although the present study offers more quantitative information. Moreover, it was shown that the peak position of the NMR shift for Li_{x}C_{o}O_{2} moved as a function of lithium content, which behavior is analogous to the change in its c lattice parameter. Also, the growth and consumption of dendritic/mossy metallic lithium on the counter electrode was clearly observed during the charge/discharge cycles.