Li Magic Angle Spinning Research Articles

Go in and Go out — Change in Local Structure and Diffusivity in Monoclinic Li3+X V2(PO4)3 upon Li Insertion and Extraction

The use of Li-ion batteries in our daily life has become vital and is going to increase further as the demand for portable energy storage systems will continue to rise in the future. Considering advanced anode and cathode materials a fundamental understanding is needed to visualize the electrochemical processes, local changes in structure and diffusivity upon insertion and extraction of Li ions. Monoclinic α-Li3+x V2(PO4)3 (LVP), crystallizing with the space group P21 /n, serves as a very attractive model compound to study these changes. As a chameleon-like electrode material it can be used as both the anode and cathode active material [1]. The Li ions in LVP (x = 0) are equally distributed over 3 crystal sites, which are clearly resolved in high-resolution 7Li magic angle spinning (MAS) nuclear magnetic resonance (NMR). As has been shown earlier by the Goward group [2], 1D and 2D exchange NMR spectroscopy is an excellent tool to identify site-specific ion mobilities and to identify the electrochemically active Li positions. Less attention has, however, been paid to LVP with x > 0. Although the topic has been addressed earlier [2,3], a complete picture about the correlation of local magnetic structures with macroscopic phase transitions is still missing. Here, we used 7Li MAS NMR, combined with both X-ray and neutron diffraction to throw some light on the changes LVP undergoes during Li uptake and release (− 2 < x < 2). As an example, Li insertion causes a drastic change of the original 7Li NMR spectrum of LVP. For Li3.5V2(PO4) the spectrum recorded at ambient bearing gas temperature consists of at least 4 distinct NMR signals being sharper than those of the starting materials with x = 0. Further increase of x to values larger than 1 reveals a second change leading a quite complex NMR signal with many overlapping lines. For Li3.5V2(PO4) and Li4.0V2(PO4) 2D 6Li MAS NMR will help us to understand the elementary hopping processes in the vanadium phosphate. Financial support by the Austrian Federal Ministry for Science, Research and Economy as well as the Christian-Doppler Forschungsgesellschaft is highly appreciated. [1] W.-F. Mao, H.-Q. Tang, Z.-Y. Tang, J. Yan, and Q. Xu, ECS Electrochem. Lett., 2 (7), A69-A71, (2013). [2] L. S. Cahill, R. P. Chapman, J. F. Britten, and G. R. Goward, J. Phys. Chem. B, 110, 7171-7177, (2006). [3] C. Liu, R. Massé, X. Nan, G. Cao, Energy Storage Mater., 4, 15-58, (2016). [4] S.-C. Yin, P. S. Strobel, H. Grondey, L. F. Nazar, Chem. Mater., 16, 1456-1465, (2004).

Synthesis and Characterization of the Lithium-Rich Phosphidosilicates Li10Si2P6 and Li3Si3P7.

The lithium phosphidosilicates Li10Si2P6 and Li3Si3P7 are obtained by high-temperature reactions of the elements or including binary Li-P precursors. Li10Si2P6 (P21/n, Z = 2, a = 7.2051(4) Å, b = 6.5808(4) Å, c = 11.6405(7) Å, β = 90.580(4)°) features edge-sharing SiP4 double tetrahedra forming [Si2P6]10- units with a crystal structure isotypic to Na10Si2P6 and Na10Ge2P6. Li3Si3P7 (P21/m, Z = 2, a = 6.3356(4) Å, b = 7.2198(4) Å, c = 10.6176(6) Å, β = 102.941(6)°) crystallizes in a new structure type, wherein SiP4 tetrahedra are linked via common vertices and which are further connected by polyphosphide chains to form unique ∞2[Si3P7]3- double layers. The two-dimensional Si-P slabs that are separated by Li atoms can be regarded as three covalently linked atoms layers: a defect α-arsenic type layer of P atoms sandwiched between two defect wurzite-type Si3P4 layers. The single crystal and powder X-ray structure solutions are supported by solid-state 7Li, 29Si, and 31P magic-angle spinning NMR measurements.

Lithium ion conductivity and dielectric relaxation in dendritic nanostructured LiTaO3 glass–nanocrystal composites

Lithium tantalate in single-crystalline and coarse-grained configurations is a poor ionic conductor and does not qualify as a solid electrolyte for lithium-based batteries. In this work, ionic conductivity was sought to be enhanced by the use of nanocrystals of LiTaO3 embedded in a borate-based glass matrix. Glasses of composition 3Li2O–4B2O3–Ta2O5 were formed by melt-quenching. The crystallization process was described by using isothermal crystallization kinetics, invoking the Johnson–Mehl–Avrami–Kolmogorov equation, which indicated a three-dimensional growth with an Avrami exponent of 3.5 and an effective activation energy for crystallization of 735 ± 65 kJ mol–1. Heat treatment of the as-quenched glasses was performed between 530 and 560 °C, and the evolution of LiTaO3 phase was studied by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The heat treatment yielded coalesced LiTaO3 nanocrystals of 18–32 nm size, forming dendritic structures in the glass matrix. Impedance analyses of the as-quenched and heat-treated glasses showed a dramatic improvement in dc conductivity (σdc), with a maximum around 3 × 10–3 S m−1 at 200 °C (σdcT = 1.5 S m−1 K) and activation energy of 0.54 eV for 530 °C/3 h heat-treated glasses. The values of σdc of the as-quenched glasses and of the 530 °C/3 h and 540 °C/3 h heat-treated glasses were about seven orders of magnitude higher than those of the single crystalline LiTaO3. Furthermore, the effect of heat treatment on lithium ion dynamics in the 40–200 °C temperature range was investigated by modulus formalism invoking the stretched exponential Kohlrausch–Williams–Watts function. The 7Li magic angle spinning NMR was used to investigate lithium self-diffusion in the nanostructured glass nanocrystal composites as a function of temperature between −10 °C and 60 °C.

La3Li3W2O12: Ionic Diffusion in a Perovskite with Lithium on both A- and B-Sites

The structure and Li+ ion dynamics of a new class of ABO3 perovskite with Li on both the A- and B-sites are described. La3Li3W2O12 is synthesized by solid state reaction at 900 °C and shown by powder X-ray diffraction to adopt the structure of a monoclinic double perovskite (A2)BB′O6, (La1.5Li0.5)WLiO6, with rock salt order of W6+ and Li+ on the B-site. High resolution powder neutron diffraction locates A-site Li in a distorted tetrahedron displaced from the conventional perovskite A-site, which differs considerably from the sites occupied by Li in the well studied La2/3–xLi3xTiO3 family. This is confirmed by the observation of a lower coordinated Li+ ion in the 6Li magic angle spinning nuclear magnetic resonance (NMR) spectra, in addition to the B-site LiO6, and supported computationally by density functional theory (DFT), which also suggests local order of A-site La3+ and Li+. DFT shows that the vacancies necessary for transport can arise from Frenkel or La excess defects, with an energetic cost of ∼0.4 eV/vacancy in both cases. Ab initio molecular dynamics establishes that the Li+ ion dynamics occur by a pathway involving a series of multiple localized Li hops between two neighboring A-sites with an overall energy barrier of ∼0.25 eV, with additional possible pathways involving Li exchange between the A- and B-sites. A similar activation energy for Li+ ion mobility (∼0.3 eV) was obtained from variable temperature 6Li and 7Li line narrowing and relaxometry NMR experiments, suggesting that the barrier to Li hopping between sites in La3Li3W2O12 is comparable to the best oxide Li+ ion conductors. AC impedance-derived conductivities confirm that Li+ ions are mobile but that the long-range Li+ diffusion has a higher barrier (∼0.5 eV) which may be associated with blocking of transport by A-site La3+ ions.

Chemical and Structural Evolution of Layered Lithium-Transition Metal Oxide Cathode Material upon Cycling

With the rapid development of electronic devices and hybrid-electric/electric vehicles (H/EVs), lithium-ion batteries have become the most promising electrical storage system due to its high volumetric and gravimetric energy density. However, the high energy density of lithium-ion batteries is difficult to maintain after extended cycles due to capacity fading, which can be attributed to multiple possible reasons including SEI formation,[1] electrolyte decomposition,[2] and structural changes in electrode materials.[3] These issues generate important concerns to the stability and lifetime of the battery. Layered lithium-transition metal oxides represent a major type of cathode materials that are widely used in the commercial market. However, these materials are suggested to suffer structural transformation during electrochemical cycling. Previous studies suggest the possible surface structural transitions from the layered structure to spinel[4], and/or rock-salt structures,[5] or possible further decomposition of the transformed phase.[6]A clear explanation of these surface phenomenon is still under debate. An in-depth investigation of the structural reconstruction is necessary to elucidate the degradation mechanisms of the layered cathode materials. In the present study, we investigated the chemical evolution and structural transformation of a prominent layered cathode material for lithium-ion batteries, LiNi1/3Mn1/3Co1/3O2 (NMC). The redox reaction of NMC cathode during charge-discharge process was analyzed in detail using high-resolution electron-energy loss spectroscopy (EELS) and 7Li magic-angle spinning (MAS) NMR. Our results suggest that the charge compensation of the NMC cathode during the delithiation-lithiation process is mainly achieved by the oxidation and reduction of Ni2+↔Ni4+, whereas Mn4+ and Co3+ remain mostly unchanged. This is consistent with the NMR findings, from which a trend to lower chemical shift upon lithium extraction is well-correlated with the oxidation change from paramagnetic Ni2+ to diamagnetic Ni4+. Furthermore, the electronic structure of the NMC cathode during initial charging process is found to be inhomogeneous from the particle surface to the bulk using spatially resolved STEM-EELS technique (Figure 1a-1d). It is revealed that the particle surface is at lower oxidation state compared with the bulk region, indicating that the surface evolution of NMC cathode material occurs during the initial cycle. This surface evolution is further analyzed at different numbers of cycles using atomic-resolution high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) imaging combined with EELS and nano-beam electron diffraction (NBED). Figure 1e shows a HAADF-STEM image of the NMC particle after 50 cycles. It can be clearly seen from the image that the bulk of the cycled NMC particle shows identical layered structure symmetry, the NBED (Figure 1h) obtained from the bulk can be indexed to the R-3m space group. In contrast, the Li layers are occupied by transition metal ions at the particle surface, and this surface reconstruction layer thickens with extended cycles. When probing to the outer-most surface, the corresponding NBED can be indexed to an Fm-3m rock-salt structure, as shown in Figure 1f. The valence change of the transition metal cations is analyzed using STEM-EELS. The results indicate that the transition metal ions are reduced to divalent states at the surface. In addition, the TM:O ratio increases almost twice at the surface than the bulk. The results indicating that the surface layer is a MO-type rock-salt phase with small amount of residual Li ions and/or vacancies. In addition, a transition zone is observed (Figure 1e) between the bulk layered region and the surface rock-salt layer, where the Li sites are partially occupied by the transition metal ions (some are marked by the red arrows), and the diffraction spots corresponding to the alternating arrangement of Li-containing layers and transition metal layers (some are marked with arrows) become weaker (Figure 1g). 7Li NMR studies of the local Li-environments, following ten cycles and ending at the top of charge, indicate that the order of the TM layers remains unchanged in the bulk of the material. This highlights the importance of complementary studies that are sensitive to different length scales. Further data, including EELS and NMR of the NMC cathode at different cycling state and electrolyte effect will be discussed in the presentation. [1] K. Edström, T. Gustafsson, J. Thomas, Electrochim. Acta 2004, 50, 397. [2] L. Terborg, S. Weber, F. Blaske, et al. J. Power Sources 2013, 242, 832. [3] B. Xu, C.R. Fell, M. Chi, et al. Energy Environ. Sci. 2011, 4, 2223. [4] A. Boulineau, L. Simonin, J.F. Colin, et al. Chem. Mater. 2012, 24, 3558. [5] F. Lin, I. M. Markus, D. Nordlund, et al. Nat. Commun. 2014, 5, 3529. [6] J. Zheng, M. Gu, J. Xiao, et al. Nano Lett. 2013, 13, 3824. Figure 1

Correlation Between Solvation Structure and Ion-Conductive Properties of Highly-Concentrated Poly(ethylene carbonate)-Based Electrolytes

Ion-conductive solid polymer electrolytes (SPEs) are of great interest as key materials to realizing safe and flexible rechargeable batteries, particularly Li batteries. Since the discovery of ionic conductions in poly(ethylene oxide) (PEO)/metal salt complexes, numerous efforts have been made to improve their electrochemical properties. However, it is difficult to increase Li-ion conductivity that is the product of overall conductivity and Li transference number (t +). This drawback mainly arises from excessively tight complex structures between polar polymers and Li ion. To overcome the drawback and create all-solid-state batteries based on SPEs, we specifically focus on poly(alkylene carbonate)s derived from CO2/epoxide copolymerization as SPE polymer hosts [1,2]. Consequently, we have found an unusual ion-conductive behavior of poly(ethylene carbonate) (PEC)-based electrolyte, including high ionic conductivity of highly-concentrated electrolytes and extremely high t +, which in some cases is above 0.8 [3,4]. In this PEC-based electrolyte system, ionic conductivity continues to increase with increasing salt concentration, which is a behavior scarcely shown in conventional electrolyte systems. In addition, we have already confirmed operations of prototype Li/LiFePO4 cells based on PEC-based electrolytes combined with plasticizing and reinforcing additives [5,6]. In this context, we considered that elucidation of salt solvation structure is a key to better understanding the origin of the particular ion-conductive behavior, and improving the performance further. In the present study, we adopted spectroscopic studies including FT-IR, Raman spectroscopy, and solid-state 7Li magic angle spinning (MAS) NMR for PEC/lithium bis(fluorosulfonyl)imide (LiFSI) electrolytes with varying concentration. The FT-IR and Raman spectroscopy indicate that most FSI ions interact with more than one Li ion at high concentration region, which is referred to as aggregates, while C=O groups dissociates the salt. The 7Li MAS NMR suggested that a relatively weak contact between Li ions and FSI ions withdraws Li ions from a strong interaction with C=O groups. We conclude that this moderate complex structure, where C=O groups allows the highly concentrated ions to remain amorphous and mobile, leads to reasonable conductivity with extremely high t +. We believe that this finding will provide a new insight for developing SPEs having both high conductivity and high t + simultaneously.

Effects of Relaxation on Conversion Negative Electrode Materials for Li-Ion Batteries: A Study of TiSnSb Using 119Sn Mössbauer and 7Li MAS NMR Spectroscopies

Conversion materials were recently considered as plausible alternatives to conventional insertion negative electrode materials in lithium-ion batteries due to their large gravimetric and volumetric energy densities. The ternary alloy TiSnSb was recently proposed as a suitable negative electrode material due to its large capacity (550 mA h g–1) and rate capability over many cycles. TiSnSb has been investigated at the end of lithiation (discharge) using 119Sn Mossbauer and 7Li magic-angle spinning (MAS) NMR spectroscopies to determine the species formed, their relative stabilities and their behavior during relaxation. During discharge, TiSnSb undergoes a conversion reaction to produce a mixture of phases believed to consist of lithium antimonides, lithium stannides, and titanium metal. In situ 119Sn Mossbauer spectroscopy indicates the presence of Li7Sn2 at the end of discharge, while 7Li NMR experiments suggest the formation of two distinct Sn-containing species (tentatively assigned to Li7Sn2 and Li7Sn3), in addition to two Sb-containing species (tentatively assigned as Li3Sb and a non-stoichiometric phase of Li2Sb, Li2–xSb). To gain insight into the relative stabilities of the species formed, experiments have been completed under open circuit voltage conditions. A new Sn-based species has been identified via 119Sn Mossbauer spectroscopy at the end of relaxation. Similar changes are observed in the 7Li NMR spectra obtained during relaxation. The species created at the end of discharge are extremely unstable and spontaneously evolve towards delithiated phases. Surprisingly, it is possible to resume electrochemical cycling after relaxation. It is likely that this behavior can be extended to this family of electrode materials that undergo the conversion reaction.

Discriminating the Mobile Ions from the Immobile Ones in Li4+xTi5O12: 6Li NMR Reveals the Main Li+ Diffusion Pathway and Proposes a Refined Lithiation Mechanism

One of the most widely known anode materials with excellent cycling performance in lithium-ion batteries is zero-strain lithium titanate Li4Ti5O12 (LTO). This is based on the highly reversible insertion and deinsertion of Li ions varying the composition of Li4+xTi5O12 from x = 0 to x = 3. The facile incorporation of Li is tightly connected with bulk Li ion dynamics. Although macroscopic electrochemical properties have been studied in great detail, bulk Li ion diffusion pathways have rarely been probed experimentally from an atomic scale point of view. Here, we evaluated 1D and 2D 6Li magic angle spinning (MAS) NMR spectra recorded as a function of x to make the local magnetic changes during Li insertion visible. This enabled us to directly show that rapid Li exchange involves the 8a and 16c sites, forming a 3D network throughout the LTO spinel structure. In contrast, considering the time scale set by our NMR experiments, the Li ions residing on the mixed occupied octahedral positions 16d are quite immobil...

Effect of Metal Ions Doping on the Structural and Electrochemical Properties of Olivine LiFePO4

Li ion rechargeable batteries have better performance over the other competitive rechargeable batteries due to their higher operative voltage (around 3-4 v range), high-energy storage capacity, low self-discharge, and high cycleability. For the application in high power devices (various consumer electronic products such as laptop, camcorder, etc.) the discharge capacity of Li ion batteries at higher current rate required is to be improved. As diffusion of lithium ions inside the active material particles is the rate-limiting step of intercalation process, faster Li+ diffusion in the electrode materials could improve the rate capabilities of Li ion batteries. Olive LiFePO4 is a very promising cathode material used in lithium ion batteries, due to its environmental friendliness, high theoretical capacity (170 mAhg-1), low cost of precursors, high reversibility of Li+ insertion/extraction, good thermal stability, and lack of toxicity. In spite of these attractive features, LiFePO4 requires further modifications to overcome limitations such as poor electronic conductivity and slow lithium ion diffusion. In this work we have synthesized olivine LiFe1-xMxPO4 (M = Nb, Yb, Sb, Mg)(LFMPO) powders by chemical synthesis and co-precipitation method. The synthesized powders were used to prepare cathodes for Li ion coin cells. The structural and electrochemical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared, Raman spectroscopy, cyclic voltammetry and charge-discharge studies, respectively. The phase pure and crystalline quality of the materials was studied from XRD peaks and their line widths respectively. 7Li magic angle spinning nuclear magnetic resonance were used to compare the cation arrangement in the undoped and doped powders. The cyclic voltammetry of both the cathodes revealed the reversible nature of Li-ion intercalation in the cell. The dopant induced structural and stoichiometric modifications were correlated with the voltage cycling and charge discharge characteristics of these cathode materials.

CEC and 7Li MAS NMR Study of Interlayer Li+ in the Montmorillonite—Beidellite Series at Room Temperature and After Heating

AbstractThe objective of the study was to contribute to the understanding of the influence of the structure and the 2:1 layer dimension of smectites on cation exchange capacity (CEC) reduction and the hydration behavior of Li-saturated smectites after heating. Five montmorillonites extracted from bentonites of different provenance were saturated with Li+ and heated to 300°C. Initial montmorillonites and montmorillonites with reduced layer charge (RCM) were characterized by comprehensive mineralogical analysis supplemented by CEC measurements, surface-area measurements by Ar adsorption, and 7Li, 27Al, and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The CEC of the initial montmorillonites varied between 89 and 130 cmol(+)/kg while the CEC of the RCM prepared at 300°C varied between 8 and 25 cmol(+)/kg. The lateral dimension of the 2:1 layers varied between 70 and 200 nm. The greatest decrease in CEC was observed for the montmorillonite with the largest diameter of the 2:1 layers and the smallest decrease was observed for the montmorillonite with the smallest diameter of the 2:1 layers. 7Li MAS NMR revealed an axially symmetric chemical environment of the hydrated interlayer Li+ with ηΔ = 0 for the chemical shift anisotropy tensor for unheated montmorillonites with &gt;33% tetrahedral layer charge (ξ). The chemical environment is typical of innersphere hydration complexes of interlayer Li+. An axially non-symmetric chemical environment of the interlayer Li+ with ηCS of close to one was observed for all RCM. While the remaining CEC of RCM prepared at 300°C reflected the variable CEC at the edges, and thus the lateral size or aspect ratio of the 2:1 layers, the hydration complex of interlayer Li+ was strongly determined by the isomorphic substitutions in the dioctahedral 2:1 layers.

CONDUCTIVITY AND IONIC MOBILITY STUDIES ON Li2WO4-LiI- Al2O3 BY EIS AND NMR TECHNIQUES

Li2WO4-LiI-Al2O3 solid electrolytes have been found to be a potential electrolyte for battery applications due to its high electrical conductivity at ambient temperature. The binary solid electrolyte with incorporation Al2O3 was prepared in solid state reaction and characterized by Electrical Impedance Spectroscopy (EIS) and 7Li Magic Angle Spinning (MAS) solid state Nuclear Magnetic Resonance (ssNMR) technique. Maximum electrical conductivity of 3.35x10-3 Scm-1 was recorded for the sample containing 20 wt.% of LiI. The conductivity improved up to 3.92x10-3Scm-1 as 5wt.% of Al2O3 was added into the optimum composition of the binary system. Mobility of the charge carrier in the sample was investigated and NMR result showed that the electrolyte with high ionic mobility contribute into high electrical conductivity.

Physical properties of the nonlinear optical material Li2B4O7 studied by static NMR and MAS NMR

The mechanisms behind the nonlinear optical (NLO) properties of Li2B4O7 are characterized by 7Li static nuclear magnetic resonance (NMR) and magic-angle spinning (MAS) NMR. Furthermore, the structural nature of 3-coordinate BO3 and 4-coordinate BO4 groups is also characterized by the same method. For 7Li and 11B, the spin-lattice relaxation time T1 in laboratory frame gradually decreases with increasing temperature, whereas the spin-lattice relaxation time T1ρ in rotating frame, which differs from T1, is nearly constant. In addition, the activation energies of 7Li and 11B, which are obtained via the values of T1 and T1ρ, are also compared.

Highly conductive Li garnets by a multielement doping strategy.

Highly conductive Li7La3Zr2O12 (LLZ) garnet-type solid electrolytes were further optimized to improve Li-ion conduction by La(3+)-sites substitution with Ba(2+) and Zr(4+)-sites substitution with Ta(5+) and Nb(5+). Garnet-structured metal oxides of the nominal chemical compositions Li6.65La2.75Ba0.25Zr1.4Ta0.5Nb0.1O12, Li6.4La3Zr1.4Ta0.6-xNbxO12 (x = 0, 0.1, 0.2, and 0.3), and the parent LLZ, as a reference, were prepared via conventional solid-state reaction to investigate the effect of multielement doping on ionic conductivity. The phase formation, morphology, and Li ion conductivity were characterized using powder X-ray diffraction (PXRD), scanning electron microscopy, and alternating current impedance spectroscopy methods, respectively. In addition, solid-state (27)Al and (7)Li magic-angle spinning (MAS) NMR was used to study the effect of "Al doping" on the investigated multielement doped Li-stuffed garnet metal oxides. All the prepared samples obtained the cubic garnet-type structure (space group: Ia3̅d; No. 230) at 1150 °C, similar to that of cubic LLZ. Except for Li6.4La3Zr1.4Ta0.6O12, all the members show Al content by Al MAS NMR. However, it was not possible to detect Al-based impurity phases using PXRD in any of the investigated garnets. Among the samples investigated in this work, "Al-free" Li6.4La3Zr1.4Ta0.6O12 demonstrated a bulk Li ion conductivity of 0.72 mS cm(-1) at 25 °C, with apparent activation energy of 0.26 eV, significantly higher than the parent LLZ.

Re-entrant lithium local environments and defect driven electrochemistry of Li- and Mn-rich Li-ion battery cathodes.

Direct observations of structure-electrochemical activity relationships continue to be a key challenge in secondary battery research. (6)Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can quantitatively characterize local lithium environments on the subnanometer scale that dominates the free energy for site occupation in lithium-ion (Li-ion) intercalation materials. In the present study, we use this local probe to gain new insights into the complex electrochemical behavior of activated 0.5(6)Li2MnO3·0.5(6)LiMn(0.5)Ni(0.5)O2, lithium- and manganese-rich transition-metal (TM) oxide intercalation electrodes. We show direct evidence of path-dependent lithium site occupation, correlated to structural reorganization of the metal oxide and the electrochemical hysteresis, during lithium insertion and extraction. We report new (6)Li resonances centered at ∼1600 ppm that are assigned to LiMn6-TM(tet) sites, specifically, a hyperfine shift related to a small fraction of re-entrant tetrahedral TMs (Mn(tet)), located above or below lithium layers, coordinated to LiMn6 units. The intensity of the TM layer lithium sites correlated with tetrahedral TMs loses intensity after cycling, indicating limited reversibility of TM migrations upon cycling. These findings reveal that defect sites, even in dilute concentrations, can have a profound effect on the overall electrochemical behavior.

Pristine and coated LiNi1/3Mn1/3Co1/3O2 as positive electrode materials for li-ion batteries

Layered LiNi1/3Mn1/3Co1/3O2 (NMC) positive materials were synthesized by efficient, low cost and easy manageable methods such as oxalate co-precipitation and sol-gel processes. Preliminary electrochemical results show that sol-gel sample provide better results than co-precipitated samples. With the aim to improve the properties of the co-precipitated samples these were coated with carbon and alumina bearing in mind the co-precipitated method is suitable for large scale production. The subsequently performed local structure investigations revealed well crystallized layered cathode materials with α-NaFeO2-type structure (R-3m space group). Sample tests using both the scanning electron microscope (SEM) and the transmission electron microscope (TEM) showed submicron particles with a slight tendency to agglomerate and furthermore the existence of a thin film that encapsulates the oxide particles. 7Li magic angle spinning nuclear magnetic resonance (7LiMAS NMR) measurements were carried out for pristine and coated samples to compare the cation arrangement in the transition metal layers. Finally, electrochemical tests revealed a remarkable improvement in capacity retention of the coated oxides compared to the parent compounds.

Relationships between Mn3+ Content, Structural Ordering, Phase Transformation, and Kinetic Properties in LiNixMn2–xO4 Cathode Materials

Micrometer-sized LiNixMn2–xO4 (0.3 ≤ x ≤ 0.5) single crystals with (111) surface facets were synthesized and characterized by 6Li magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, and electrochemical studies. All three techniques were sensitive to cation disorder and the corroborated results showed that structural ordering improves with x. The transition from the ordered to the disordered spinel was triggered by an increase in Mn3+ content, which was accomplished either by a change in chemical composition or postsynthesis thermal treatment. Disordering led to increased solid solution behavior, reduced two-phase transformation domains, and improved transport properties during Li extraction and insertion. Further increasing Mn3+ content in already disordered structure extends the solid solution domain and eliminates the presence of phase II; however, this has limited effect on rate capability. The study demonstrates the dominant role of structural ordering in morpholo...

Lithium species in electrochemically lithiated and delithiated silicon oxycarbides.

The work described herein deals with efforts to make a persuasive correlation between structural characteristics and electrochemical lithium storage for a silicon oxycarbide prepared from poly(methylhydrogensiloxane) and divinylbenzene. Structural characterization reveals that the silicon oxycarbide includes excess free carbon in an amorphous network. The reversibility of lithiation and delithiation in the silicon oxycarbide reaches 74% between 0.005 and 3 V relative to lithium at the first cycle but falls to only ca. 30% between 0.4 and 3 V. We found two resonances at 0 and 2.4 ppm in the (7)Li magic angle spinning nuclear magnetic resonance spectrum of the silicon oxycarbide lithiated to 0.4 V, whose contributions are 67 and 33%, respectively, and thus are in good agreement with the reversibility observed between 0.4 and 3 V. The fully lithiated silicon oxycarbide shows a single resonance at ca. 3-9 ppm, which tends to broaden at lower temperatures to -120 °C, whereas the fully delithiated silicon oxycarbide has a single resonance at 0 ppm. These results indicate that both reversible and irreversible lithium species have ionic natures. The Li K edge in electron energy loss spectroscopy does not show clearly any identified near-edge fine structures in the inner part of the silicon oxycarbide after delithiation. Near the surface, on the other hand, LiF and oxygen- and phosphorus-containing compounds were found to be the major constituents of a solid electrolyte interface (SEI) layer. Over repeated lithiation and delithiation, the SEI layer appears to become thick, which should in part trigger capacity fading.

X‐ray Absorption Near‐Edge Structure and Nuclear Magnetic Resonance Study of the Lithium–Sulfur Battery and its Components

Understanding the mechanism(s) of polysulfide formation and knowledge about the interactions of sulfur and polysulfides with a host matrix and electrolyte are essential for the development of long-cycle-life lithium-sulfur (Li-S) batteries. To achieve this goal, new analytical tools need to be developed. Herein, sulfur K-edge X-ray absorption near-edge structure (XANES) and (6,7) Li magic-angle spinning (MAS) NMR studies on a Li-S battery and its sulfur components are reported. The characterization of different stoichiometric mixtures of sulfur and lithium compounds (polysulfides), synthesized through a chemical route with all-sulfur-based components in the Li-S battery (sulfur and electrolyte), enables the understanding of changes in the batteries measured in postmortem mode and in operando mode. A detailed XANES analysis is performed on different battery components (cathode composite and separator). The relative amounts of each sulfur compound in the cathode and separator are determined precisely, according to the linear combination fit of the XANES spectra, by using reference compounds. Complementary information about the lithium species within the cathode are obtained by using (7) Li MAS NMR spectroscopy. The setup for the in operando XANES measurements can be viewed as a valuable analytical tool that can aid the understanding of the sulfur environment in Li-S batteries.

Charge transfer in Li/CFx–silver vanadium oxide hybrid cathode batteries revealed by solid state 7Li and 19F nuclear magnetic resonance spectroscopy

Solid state 7Li and 19F magic angle spinning nuclear magnetic resonance (MAS NMR) experiments are conducted on several cathodes containing CFx–Silver vanadium oxide (CFx–Ag2V4O11) hybrid cathodes discharged to 50% depth of discharge (DoD) and stored at their open-circuit voltage for a period of one and three months. Three carbonaceous sources for the CFx phase are investigated: petroleum coke-based, fibrous, and mixed fibrous. For each hybrid cathode, a measurable increase in the relative amount of lithium fluoride is observed after a three month resting period in both the 7Li and 19F NMR spectra. These changes are attributed to lithium ion migration from the silver vanadium oxide to the CFx phase during the resting period, and help clarify the mechanism behind high power handling capability of this cathode.

Characterization of Lithium Storage in TiO2(B) by 6Li-NMR and X-Ray Diffraction Analysis

Lithium storage in TiO2(B) was investigated by 6Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and ex-situ X-ray diffraction (XRD) analysis combined with the entropy (ΔS) and galvanostatic intermittent titration technique (GITT) measurements. Lithium storage sites in TiO2(B) were characterized to be separated from four bands assigned to different lithium storage sites. Band A at 0 ppm vs. LiCl in the 6Li NMR spectra and ΔS measurements indicated that ionic lithium was stored at surface domain of LixTiO2(B) up to x = 0.18. Band B at 2.5 ppm significantly increased with lithium insertion in the region for 0.25 < x < 0.5, which indicated that lithium was mainly inserted into the site lying between bridging oxygens in LixTiO2(B). Additionally, the site on the lithium diffusion path along b-axis was also occupied by a small amount of lithium. The stepwise change of OCV and ΔS at around x = 0.45 indicated that lithium was inserted at the site in TiO2 layer in LixTiO2(B). In the region for x > 0.75, Band D was observed at more positive chemical shift than Band B. The lithium at the site distorted the local structure of LixTiO2(B), which leads to decrease of the lithium diffusivity in LixTiO2(B).