7Li Nuclear Magnetic Resonance Research Articles

NMR Study of LiCo0.96Al0.04O2 As a Positive Electrode Material for Li-Ion Batteries: Homogeneity and Role of Doping on Mechanisms

LiCoO2 (LCO) is one of the most widely used positive electrode materials in lithium-ion batteries due to its high volumetric energy density which can be further improved by charging at high voltages. However, working at high potential (above 4.3 V vs. Li+/Li) causes a deterioration in cycling performance induced by structural instabilities, electrolyte oxidation and Co dissolution. Extensive studies have been devoted to increasing energy density by increasing the cutoff voltage. The substitution of cobalt with various metals is one of the classic methods, the choice of aluminum as dopant for example is based on several criteria: low cost and non-toxicity, a similar radius for Al3+ compared to Co3+ (0.535 Å vs. 0.545 Å) facilitates the replacement of the latter and maintains the structure leading to the complete solid solution LiCo1-yAlyO2.We will focus here on LiCo0.96Al0.04O2, synthesized by the solid route and characterized by 7Li, 27Al and 59Co Nuclear Magnetic Resonance (NMR) and synchrotron X-Ray Diffraction (XRD). In addition to the characterization of the mean structure by XRD, the NMR allows us to study the local environments of the different nuclei. 27Al MAS NMR and synchrotron XRD studies revealed that the Al-doping in this material is homogeneous. 7Li MAS NMR indicates that its stoichiometry (Li/M=1.00) is ideal. The electrochemical study has shown that the phase transitions occurring during delithiation of LiCoO2, were partially eliminated by aluminum doping even with a low doping amount and the high potential mechanisms appear to be different. In order to better understand the role of Al-doping on the mechanisms involved during cycling, several phases LixCo0.96Al0.04O2 were prepared by electrochemical deintercalation and studied by 7Li, 59Co, and 27Al NMR and by XRD.During lithium deintercalation, Co3+ is oxidized to Co4+ then one unpaired electron is generated in the t2g band of Co atoms (t2g 5eg 0). For 0.8 ≤ x ˂ 1.00 the 7Li MAS NMR shows that the system behaves locally as two phase domain: domain with localized electrons and domain with delocalized ones on Con+ ions (Knight shift), even for very low amount of deintercalation (x=0.98), thus the XRD results confirm the existence of the biphasic domain. Whereas, a single phase domain is observed for the deintercalated materials with 0.4 ≤ x ≤ 0.8 and also at the NMR time of scale a single signal (Knight shift) is observed. This signal increases in intensity at the expense of 0 ppm and shifts to the higher isotropic displacement values up to x=0.5 then decreases, thus the evolution of the chex lattice parameter is correlated with the signal shift. For x = 0.3 and x = 0.2: a new broad signal appears probably due to formation of new Li environment in stacking faulted layers (O1 type). These different contributions will be more detailed on the presentation.

Further Improving Coulombic Efficiency and Discharge Capacity in LiNiO2 Material by Activating Sluggish ∼3.5 V Discharge Reaction.

The electrochemical activity of LiNiO2 at the initial cycle and factors affecting its activity were understood. Even though LiNiO2 can achieve almost theoretical charge capacity, it cannot deliver the theoretical discharge capacity that would result in low 1st Coulombic efficiency (CE). For different upper cut-off voltages at 4.3 and 4.1 V, the 1st CE barely increases. Given that the H2-H3 phase transition occurs at ∼4.2 V, the low 1st CE is not caused by this phase transition but is a result of the additional 3.5 V discharge reaction, which is kinetically limited and thereby not activated even at a reasonable current density. We found out that the several phase transitions during charge/discharge in LiNiO2 barely affect the 3.5 V reaction. Under galvanostatic intermittent titration technique (GITT) conditions, LiNiO2 can achieve ∼250 mAh/g of discharge capacity and 100% CE even with the 4.3 V cut-off voltage by fully activating the 3.5 V reaction. Using neutron diffraction and 6Li nuclear magnetic resonance (NMR) measurements, the sluggish kinetics of the 3.5 V reaction can be ascribed to difficult insertion of Li at the end of the discharge because this reaction can be accompanied by the rearrangement of cations or local structure change in the structure. To achieve high discharge capacity in LiNiO2 with the 4.3 V cut-off voltage, this 3.5 V sluggish reaction should be improved. The finding and understanding underlying the mechanism of the electrochemical activity will stimulate further research on high-capacity Ni-rich layered materials for high-performance Li-ion batteries.

Bio-inspired construction of ion conductive pathway in covalent organic framework membranes for efficient lithium extraction

Summary As the most sophisticated separation system, biological membranes have served as natural prototypes for the design of artificial membranes because they provide high permeability and solute selectivity, owing to the presence of specialized ion channels. However, developing stable and selective artificial ion channels remains a formidable challenge. Herein, we demonstrate the construction of lithium nanochannels in two-dimensional covalent organic frameworks (COFs) to create biomimetic membranes. Implanted lithiophilic oligoethers conferred specificity and facilitated Li+ diffusion along the pore pathway of the COF. The ion channel characteristics were indicated by reversal potential measurements, showing that the relative permeability decreased in the order Li+ > K+ > Na+ > Ca2+ > Mg2+. The Li+ transfer was enhanced, while other ions were obstructed, allowing for high selectivity and permeability. A Li+/Mg2+ separation factor of 64 was achieved, confirming high lithium affinity. This study may serve as a design principle to develop selective artificial membranes for effective ion separation.

Tailoring Slurries Using Cosolvents and Li Salt Targeting Practical All‐Solid‐State Batteries Employing Sulfide Solid Electrolytes

AbstractPolymeric binders that can undergo slurry fabrication and minimize the disruption of interfacial Li+ contact are imperative for sheet‐type electrodes and solid electrolyte films in practical all‐solid‐state Li batteries (ASLBs). Although dry polymer electrolytes (DPEs) are a plausible alternative, their use is complicated by the severe reactivity of sulfide solid electrolytes and the need to dissolve Li salts. In this study, a new scalable fabrication protocol for a Li+‐conductive DPE‐type binder, nitrile‐butadiene rubber (NBR)‐LiTFSI, is reported. The less‐polar dibromomethane and more‐polar hexyl butyrate in cosolvents work synergistically to dissolve NBR and LiTFSI, while preserving Li6PS5Cl0.5Br0.5. It is found that the dispersion of NBR can be controlled by the fraction of the antisolvent (hexyl butyrate), which in turn affects the corresponding performance of the ASLBs. Sheet‐type LiNi0.70Co0.15Mn0.15O2 electrodes tailored using NBR‐LiTFSI outperform those prepared using the conventional insulating binder (NBR) in terms of capacity (163 vs 147 mA h g−1) and initial Coulombic efficiency (78.9 vs 70.4%), which is attributed to the facilitated interfacial Li+ transport, as confirmed by 6Li nuclear magnetic resonance and electrochemical measurements. Moreover, NBR‐LiTFSI is functional at 70 °C and in a graphite anode. Finally, the promising performance of pouch‐type LiNi0.70Co0.15Mn0.15O2/graphite ASLBs is also demonstrated.

Tracking Ions the Direct Way: Long-Range Li+ Dynamics in the Thio-LISICON Family Li4MCh4 (M = Sn, Ge; Ch = S, Se) as Probed by 7Li NMR Relaxometry and 7Li Spin-Alignment Echo NMR.

Solid electrolytes are key elements for next-generation energy storage systems. To design powerful electrolytes with high ionic conductivity, we need to improve our understanding of the mechanisms that are at the heart of the rapid ion exchange processes in solids. Such an understanding also requires evaluation and testing of methods not routinely used to characterize ion conductors. Here, the ternary Li4MCh4 system (M = Ge, Sn; Ch = Se, S) provides model compounds to study the applicability of 7Li nuclear magnetic resonance (NMR) spin-alignment echo (SAE) spectroscopy to probe slow Li+ exchange processes. Whereas the exact interpretation of conventional spin–lattice relaxation data depends on models, SAE NMR offers a model-independent, direct access to motional correlation rates. Indeed, the jump rates and activation energies deduced from time-domain relaxometry data perfectly agree with results from 7Li SAE NMR. In particular, long-range Li+ diffusion in polycrystalline Li4SnS4 as seen by NMR in a dynamic range covering 6 orders of magnitude is determined by an activation energy of Ea = 0.55 eV and a pre-exponential factor of 3 × 1013 s–1. The variation in Ea and 1/τ0 is related to the LiCh4 volume that changes within the four Li4MCh4 compounds studied. The corresponding volume of Li4SnS4 seems to be close to optimum for Li+ diffusivity.

Revealing the Impact of Film-Forming Electrolyte Additives on Lithium Metal Batteries via Solid-State NMR/MRI Analysis

Because of the high specific capacity and low redox potential, lithium metal constitutes a promising material and might be an option for high energy density next-generation battery technologies, though application of lithium metal batteries (LMBs) is currently limited by poor long-term performance and severe safety issues when liquid electrolytes are used. These challenges arise from formation of “dead” lithium or inhomogeneous lithium deposits as well as ineffective solid electrolyte interphase (SEI) layers on lithium metal electrodes. Notably, lithium consumed by SEI formation and fractions of “dead” lithium was derived from in situ 7Li nuclear magnetic resonance (NMR) of pouch-type cells, while 19F 1D magnetic resonance imaging (MRI) profiling along with operando optical microscopy analysis revealed the nature of lithium deposits, considering the impact of electrode kinetics on the occurrence of dendritic lithium microstructures, governed by processes of electrodeposition and electrodissolution. Various electrolyte formulations were compared in view of different cell configurations, including Li||Li symmetric cells as well Li||Cu cells, Cu||NMC cells, and finally NMC||Li full cell systems, establishing the origin and likely contributions to irreversible capacity losses while systematically evaluating different active materials (including electrolyte formulations, cathode material, and lithium metal anodes). Indeed, a mixture of film-forming additives—fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2)—was demonstrated to afford both “better” interfacial/interphasial properties and more homogeneous lithium deposition, thus exhibiting promising electrochemical performance.

Unveiling the stability of Sn/Si/graphite composites for Li-ion storage by physical, electrochemical and computational tools.

Complex materials composed of two and three elements with high Li-ion storage capacity are investigated and tested as lithium-ion battery (LiB) negative electrodes. Namely, anodes containing tin, silicon, and graphite show very good performance because of the large gravimetric and volumetric capacity of silicon and structural support provided by tin and graphite. The performance of the composites during the first cycles was studied using ex situ magic angle spinning (MAS) 7Li Nuclear Magnetic Resonance (NMR), density functional theory (DFT) calculations, and electrochemical techniques. The best performance was obtained for Sn/Si/graphite in a 1 : 1 : 1 proportion, due to an emergent effect of the interaction between Sn and Si. The results suggest a stabilization effect of Sn over Si, providing a physical constraint that prevents Si pulverization. This mechanism ensures good cyclability over more than one hundred cycles, low capacity fading and high specific capacity.

Fast Li Ion Dynamics in the Mechanosynthesized Nanostructured Form of the Solid Electrolyte Li3YBr6

The Y-halides Li3YBr6 and Li3YCl6 have recently gained considerable attention as they might be used as ceramic electrolytes in all-solid-state batteries. Such materials need to show sufficiently high ionic conductivities at room temperature. A thorough investigation of the relationship between ion dynamics and morphology, defect structure, and size effects is, however, indispensable if we want to understand the driving forces behind Li ion hopping processes in these ternary compounds. Li3YBr6 can be prepared by conventional solid-state synthesis routes. Nanostructured Li3YBr6 is, on the other hand, directly available by mechanosynthesis under ambient conditions. The present study is aimed at shedding light on the question of whether (metastable) mechanosynthesized Li3YBr6 might serve as a sustainable alternative to annealed Li3YBr6. For this purpose, we studied the impact of structural disorder on ionic transport by combining mechanosynthesis with soft-annealing steps to prepare Li3YBr6 in two different morphologies. While structural details were revealed by X-ray powder diffraction and by high-resolution 6Li and 79Br magic angle spinning nuclear magnetic resonance (NMR) spectroscopy, broadband impedance measurements in conjunction with time-domain 7Li NMR relaxation measurements helped us to characterize Li+ dynamics over a wide temperature range. Interestingly, for Li3YBr6, annealed at 823 K, we observed a discontinuity in conductivity at temperatures slightly below 273 K, which is almost missing for nano-Li3YBr6. This feature is, however, prominently seen in NMR spectroscopy for both samples and is attributed to a change of the Li sublattice in Li3YBr6 Although a bit lower in ionic conductivity, the nonannealed samples, even if obtained after a short milling period of only 1 h, shows encouraging dynamic parameters (0.44 mS cm–1, Ea = 0.34 eV) that are comparable to those of the sample annealed at high temperatures (1.52 mS cm–1, Ea = 0.28 eV). 7Li nuclear magnetic relaxation, being solely sensitive to Li+ hopping processes on shorter length scales, revealed highly comparable Li+ self-diffusion coefficients on the order of 10–12 m2 s–1, which we extracted directly from purely diffusion-controlled 7Li NMR rate peaks. Spin-lock 7Li NMR reveals a change from uncorrelated to correlated dynamics at temperatures as low as 220 K.

Structural Characterization of Amorphous VS4 and Its Amorphous Phase Transformation during Li Insertion

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

Combination of Li Isotopic Tracing and Ex-Situ Characterizations for Imaging Li Dynamics in the SEI: Benefits and Issues

The Solid Electrolyte Interphase (SEI) has been considered as “the Most Important and the Least Understood Solid Electrolyte in Rechargeable Li Batteries” by Winter in 2009 [1]. Being aware that its stability has a significant impact on their performance, lifespan and safety, the scientific community tries to improve knowledge on this interface. Experimental studies have been achieved to observe the global composition of the SEI on common anodes (lithium, graphite and silicon) [2], [3]. LiF, Li2CO3, polyolefins and semicarbonates detected in the SEI derives from electrolyte compounds degradation. Several SEI models have been discussed (mosaic, super capacitor, multi-layers, etc), but they are still being debated. Finding the “perfect” model is challenging because this model should be able to explain conductive (ions) and resistive (electrons) properties of the SEI, as well as its formation and ageing. As of today, most of the knowledge concerning Li transport properties and SEI formation comes from theoretical studies and are based on simulations.Li isotopic tracing has already been successfully employed to study the Li dynamics in components of Li-ions accumulators. Since 2011 [4], Li isotope tracing has been used about 10 times in this field. In all literature, isotopes are introduced in specific parts of a cell (anode, cathode or electrolyte). In our study, we have added them at different states of charge (100% or 0%) in order to label selectively the SEI.This study aims at investigating the lithium dynamics within the SEI during the first cycles of charge and discharge. Trapped lithium (in the SEI) can be distinguished from active lithium by using its natural isotopes 6Li and 7Li. Two specific systems have been studied: SEI on graphite and SEI on silicon. During a first step, the SEI have been generated in 7Li. Then, the electrode has been recovered and re-used in a new cell in front of a 6Li-enriched counter electrode and electrolyte. By using time-of-flight secondary ion mass spectrometry (ToF-SIMS), we have been able to track 7Li and 6Li distribution in the electrode. First results on graphite electrode have shown that “trapped” Li is eventually highly mobile, even when the system is down (without polarization of the electrode). Indeed, when electrolyte and electrode are in contact without any electric field, lithium initially present in the electrolyte have been detected in the SEI.The same kind of experiments have been carried out on silicon-based electrodes. In addition to ToF-SIMS characterization, 7Li and 6Li Solid State Nuclear Magnetic Resonance (NMR) analyses have been performed. ToF-SIMS allows probing the surface chemistry on a small sample of the electrode (~1000 µm²), while NMR spectroscopy investigates the whole sample and allows knowing the chemical environment of the probed nucleus. The same observation has been made in these experiments: lithium “trapped” in the SEI is highly mobile. As no self-discharge has been observed, it is probably mainly related to isotope exchanges.These results paves the way for calculations of diffusion coefficients, as well as for the estimation of a characteristic length and thickness of the probed SEI. Other isotope experiments have also been carried out. However, natural isotope exchanges, even without polarization of the electrode, tend to hide information by homogenizing isotope concentrations. Optimization of experiments and operando measurements may overcome such issues.[1] M. Winter, Zeitschrift für Physikalische Chemie, 223, 1395–1406 (2009).[2] E. Peled and S. Menkin, Journal of The Electrochemical Society, 164, A1703–A1719 (2017).[3] S. J. An et al., Carbon, 105, 52–76 (2016).[4] P. Lu and S. J. Harris, Electrochemistry Communications, 13, 1035–1037 (2011). Figure 1

(Battery Division Postdoctoral Associate Research Award Address Sponsored by MTI Corporation and the Jiang Family Foundation) Extending Battery Life - Studies within the Faraday Institution on NMC811/Graphite Full Cells

To support the rapidly growing adoption of electric vehicles and renewable grid-storage systems, it is desirable to develop lithium-ion batteries with higher energy density and improved rate capability. However, the design of such energy-dense cell chemistries is impeded by a trade-off with cycling and calendar lifetimes. A key goal for the automotive and utilities industries is therefore to better understand the causes and mechanisms of degradation. This will enable improved control and prediction of the state of health of battery systems.As part of the Faraday Institution, the UK’s independent institute for electrochemical energy storage technology, the Battery Degradation Programme is building new understanding of the underlying physical and chemical processes that can lead to degradation in energy-dense NMC811/graphite lithium-ion cells as a model system. Led by the University of Cambridge (Clare Grey PI) in collaboration with 11 UK universities and institutions, the research consortium is working closely with industry partners to create a new hub for lithium-ion battery research and to address key challenges and opportunities in the field. This presentation will give an overview of the research consortium’s membership, key milestones, and technical progress.To date, the consortium has been applying a variety of analytical techniques to study degradation processes in NMC811/graphite cells. For example, electrochemical testing, operando synchrotron X-ray diffraction (XRD) and ex situ solid-state 7Li nuclear magnetic resonance spectroscopy (NMR) were combined to understand how changes in lithium dynamics correlate with the interlayer spacing changes that occur during delithiation.1 The method is now being applied to understand how the dynamics are affected by long-term structural damage to the NMC811 material. New spectroscopic methods are also being developed, including Kerr-gated Raman, which allows sensitive measurements of electrode materials and electrolytes with lower background signal than conventional Raman spectroscopy.2 X-ray computed tomography methods have been developed for in situ and operando studies of particle cracking during charging, cycling, or storage.3 Finally, Gaussian process machine learning is being applied to correlate electrochemical impedance spectral features with degradation patterns and to consider the value of EIS signals in battery management systems.4 Reference s: 1. K. Märker, P. J. Reeves, C. Xu, K. J. Griffith, and C. P. Grey, Chem. Mater., 31, 2545–2554 (2019).2. L. Cabo-Fernandez, A. R. Neale, F. Braga, I. V. Sazanovich, R. Kostecki, and L. J. Hardwick, Phys. Chem. Chem. Phys., 21, 23833–23842 (2019).3. T. M. M. Heenan, C. Tan, A. J. Wade, R. Jervis, D. J. L. Brett, and P. R. Shearing, Mater. Des., 191, 108585 (2020).4. Y. Zhang, Q. Tang, Y. Zhang, J. Wang, U. Stimming, and A. A. Lee, Nat. Commun., 11, 1706 (2020).

Phase transition-induced improvement in the capacity of fluorine-substituted LiFeBO3 as a cathode material for lithium ion batteries

Among polyanion-type cathode materials used for large-scale lithium-ion batteries (LIBs), LiFeBO3 (LFeB) has received attention due to its lowest weight framework with a larger theoretical capacity of 220 mAh g−1 compared with commercialized LiFePO4 (170 mAh g−1). The main drawback of LFeB, however, is its poor specific discharge capacity as a cathode material for LIBs. Herein, the fluorine-substituted LFeB at the oxygen site, LiFeBO3-xF2x (LFeBF, x = 0.05, 0.1, 0.2, 0.3, and 0.5), has been prepared as a cathode material for LIBs via a solid-state reaction to improve the electrochemical behavior accompanied by phase transition. Morphological change as increasing x and well-distributed fluorine element of LFeBF have been observed using a scanning electron microscope combined with an energy dispersive X-ray spectrometer. X-ray diffraction, X-ray photoelectron spectroscopy, and solid-state 7Li and 11B nuclear magnetic resonance spectroscopy studies of LFeBF as well as increasing x show a dramatic phase transition from monoclinic to vonsenite-type structure. The plausible atomic arrangement has been also investigated using density functional theory. Furthermore, the fluorine substitution at the oxygen site of LFeB leads to a remarkable improvement in discharge capacity, the highest value (361.15 mAh g−1 for LFeBF (x = 0.3)) of which is about five times larger than that of LFeB (73.43 mAh g−1) at 0.05 C rate, without any additional carbon source.

Recycling of graphite and metals from spent Li-ion batteries aiming the production of graphene/CoO-based electrochemical sensors

This work describes the synthesis of hybrid materials based on reduced graphene oxide (rGO) and cobalt oxide (CoO) from recycled Li-ion batteries. A hydrometallurgical route was employed in the recycling process, with citric acid and nitric acid used as the leaching agents for the cathode and anode materials, respectively. Graphene oxide (GO) was prepared from the recycled graphite by a modified Hummers method; the hybrid material was produced by mixing GO and the recycled metal oxides (mostly CoO) using a sol-gel route followed by heat treatment at 450 °C during 2 h. The physicochemical characterization of the hybrid material was conducted by X-ray diffraction, scanning electron microscopy and solid-state 7Li and 13C nuclear magnetic resonance (NMR) spectroscopy; the results indicated the formation of crystalline CoO (with face centered cubic structure) and rGO (with turbostratic structure), whereas lithium and manganese were also identified as minor components. The performance of this product as electrochemical sensor was evaluated by cyclic voltammetry. The study of the electrocatalytic oxidation of ascorbic acid using the hybrid material as electrode showed good linearity in the relationship between the oxidation current and the acid concentration. These results showed that the hybrid material produced from the recycled batteries is promising for applications as an enzyme-free electrochemical sensor.

Synthesis in Molten Salts and Characterization of Li6B18(Li2O)x Nanoparticles.

Lithium borides have been synthesized exclusively through classical solid-state chemistry processes that lead to bulk materials. Indeed, due to the lack of reactivity of the solid boron precursors usually employed and to the high covalent connectivity in such solids, high temperatures and long reaction times are necessary to obtain lithium borides. These conditions result in extensive crystal growth. Here we present the synthesis of nanoparticles of a lithium boride bearing tunnel-like cavities templated by neutral Li2O species, which have been reported to be labile. To reach this goal, a liquid-phase synthesis in inorganic molten salts has been developed. The Li6B18(Li2O)x nanoparticles have been characterized by scanning and transmission electronic microscopy (SEM and TEM), X-ray diffraction (XRD), and Raman spectroscopy. We provide an in-depth structural characterization by using 1H, 7Li, and 11B solid-state nuclear magnetic resonance (NMR) coupled with DFT modeling to provide the first assignment of 7Li and 11B solid-state NMR signals in lithium borides. We then assess the nanoparticle morphology oriented along the direction of the cavities. This feature shows similarities with structurally related hexagonal tungsten bronzes and could therefore affect the electrochemical and ion exchange properties.

Hidden magnetic order in the triangular-lattice magnet Li2MnTeO6

The manganese tellurate Li2MnTeO6 consists of trigonal spin lattices made up of Mn4+ (d3, S = 3/2) ions. The magnetic properties of this compound were characterized by several experimental techniques, which include magnetic susceptibility, specific heat, dielectric permittivity, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) measurements, and by density functional calculations (DFT). The magnetic susceptibility chi(T) demonstrates very unusual behavior. It isdescribed by the Curie-Weiss law at high temperature with Curie-Weiss temperature of Theta = -74 K, exhibits no obvious anomaly indicative of a long-range magnetic ordering at low magnetic fields. At high magnetic fields, however, the character of chi(T) changes showing a maximum at about 9 K. That this maximum of chi(T) reflects the onset of an antiferromagnetic order was confirmed by specific heat measurements, which exhibit a clear lambda-type anomaly at TN around 8.5 K even at zero magnetic field, and by 7Li NMR and dielectric permittivity measurements. The magnetic structure of Li2MnTeO6, determined by neutron powder diffraction measurements at 1.6 K, is described by the 120-degree non-collinear spin structure with the propagation vector k = (1/3, 1/3, 0). Consistent with this finding, the spin exchange interactions evaluated for Li2MnTeO6 by density functional calculations are dominated by the nearest-neighbor antiferromagnetic exchange within each triangular spin lattice. This spin lattice is strongly spin frustrated with f = |Theta|/TN around 8 and exhibits a two-dimensional magnetic character in a broad temperature range above TN.

Investigation of Transverse Relaxation Rate Distribution via Magnetic Resonance Imaging: Impact of Electrode Formation

The impact of electrode formation is studied by the spatially and time‐resolved distribution of transverse relaxation. In situ 7Li nuclear magnetic resonance experiments are performed on an experimental lithium‐ion battery cell to study the impact of electrode passivation via imaging and transverse relaxation in the interelectrode volume. The electrolyte in the battery, using technically relevant electrode material, i.e., graphite and lithium–nickel–cobalt–manganese–oxide, is studied by 2D magnetic resonance imaging. The electrolyte is 1 mol L−1 lithium hexafluorophosphate dissolved in a binary mixture of ethylene carbonate and dimethyl carbonate. 1D profiles are acquired and related to 7Li concentration during passivation and during a constant current/constant voltage cycle. The transverse relaxation rate R2(z,t) measured by multiecho profiles revealed changes within the electrolyte volume. The ongoing process changes the relaxation distribution. Indications for a defective electrode passivation are deduced from the data. During one charging cycle with constant current/constant voltage, the lithium concentration is measured spatially resolved, and the data are modeled by the Nernst–Planck equation.

Operando NMR of NMC811/Graphite Lithium-Ion Batteries: Structure, Dynamics, and Lithium Metal Deposition.

Lithium-ion batteries (LIBs) are of tremendous importance for our society, but their limited lifetime still poses a great challenge. For a better understanding of battery cycling and degradation, operando analytical measurements are invaluable. In this work, we demonstrate that operando 7Li nuclear magnetic resonance (NMR) spectroscopy can be applied to full LIBs. We exemplify this on LiNi0.8Mn0.1Co0.1O2 (NMC811)/graphite cells, which are typical high-energy LIBs. Employing industry-standard electrodes, our operando cells show realistic cycling performance at practical rates, which allows us to conduct experiments at different rates and temperatures and to draw conclusions on the performance of LIBs. The NMR experiments monitor processes in both electrodes individually, including Li-ion mobility and its changes with temperature. Moreover, Li metal deposition on graphite is observed at low temperature, which is an important degradation mechanism in LIBs and a severe safety hazard. Our experiments offer unique insights into this Li metal deposition process under different charging conditions.

Capacity fading mechanism of conversion-type FeF3 electrode: Investigation by electrochemical operando nuclear magnetic resonance spectroscopy

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.

Li-Ion Diffusion in Nanoconfined LiBH4-LiI/Al2O3: From 2D Bulk Transport to 3D Long-Range Interfacial Dynamics.

Solid electrolytes based on LiBH4 receive much attention because of their high ionic conductivity, electrochemical robustness, and low interfacial resistance against Li metal. The highly conductive hexagonal modification of LiBH4 can be stabilized via the incorporation of LiI. If the resulting LiBH4-LiI is confined to the nanopores of an oxide, such as Al2O3, interface-engineered LiBH4-LiI/Al2O3 is obtained that revealed promising properties as a solid electrolyte. The underlying principles of Li+ conduction in such a nanocomposite are, however, far from being understood completely. Here, we used broadband conductivity spectroscopy and 1H, 6Li, 7Li, 11B, and 27Al nuclear magnetic resonance (NMR) to study structural and dynamic features of nanoconfined LiBH4-LiI/Al2O3. In particular, diffusion-induced 1H, 7Li, and 11B NMR spin–lattice relaxation measurements and 7Li-pulsed field gradient (PFG) NMR experiments were used to extract activation energies and diffusion coefficients. 27Al magic angle spinning NMR revealed surface interactions of LiBH4-LiI with pentacoordinated Al sites, and two-component 1H NMR line shapes clearly revealed heterogeneous dynamic processes. These results show that interfacial regions have a determining influence on overall ionic transport (0.1 mS cm–1 at 293 K). Importantly, electrical relaxation in the LiBH4-LiI regions turned out to be fully homogenous. This view is supported by 7Li NMR results, which can be interpreted with an overall (averaged) spin ensemble subjected to uniform dipolar magnetic and quadrupolar electric interactions. Finally, broadband conductivity spectroscopy gives strong evidence for 2D ionic transport in the LiBH4-LiI bulk regions which we observed over a dynamic range of 8 orders of magnitude. Macroscopic diffusion coefficients from PFG NMR agree with those estimated from measurements of ionic conductivity and nuclear spin relaxation. The resulting 3D ionic transport in nanoconfined LiBH4-LiI/Al2O3 is characterized by an activation energy of 0.43 eV.

Rapid Low-Dimensional Li+ Ion Hopping Processes in Synthetic Hectorite-Type Li0.5[Mg2.5Li0.5]Si4O10F2.

Understanding the origins of fast ion transport in solids is important to develop new ionic conductors for batteries and sensors. Nature offers a rich assortment of rather inspiring structures to elucidate these origins. In particular, layer-structured materials are prone to show facile Li+ transport along their inner surfaces. Here, synthetic hectorite-type Li0.5[Mg2.5Li0.5]Si4O10F2, being a phyllosilicate, served as a model substance to investigate Li+ translational ion dynamics by both broadband conductivity spectroscopy and diffusion-induced 7Li nuclear magnetic resonance (NMR) spin–lattice relaxation experiments. It turned out that conductivity spectroscopy, electric modulus data, and NMR are indeed able to detect a rapid 2D Li+ exchange process governed by an activation energy as low as 0.35 eV. At room temperature, the bulk conductivity turned out to be in the order of 0.1 mS cm–1. Thus, the silicate represents a promising starting point for further improvements by crystal chemical engineering. To the best of our knowledge, such a high Li+ ionic conductivity has not been observed for any silicate yet.