7Li Nuclear Magnetic Resonance Spectroscopy Research Articles

7Li NMR Spectroscopy: A Tool for Determining Dimerization Constants and Averaged Dimerization Constants of the Monomer/Dimer Equilibrium of Hierarchical Helicates.

7Li nuclear magnetic resonance (NMR) spectroscopy is an ideal tool to study hierarchically assembled helicates of the form Li[Li3L6Ti2]. Internally bound and external lithium ions can be well distinguished by solution- or solid-state NMR spectroscopy and dimerization constants of the monomer/dimer equilibrium can be easily determined in solution. Averaged dimerization constants can be estimated in case of statistical mixtures of helicates formed from mixtures of ligands.

Novel Operando Nuclear Magnetic Resonance Approach for Tracking the Electrode State of Charge in Li/Na-Ion Batteries

Lithium and sodium-ion batteries have become the focal point of interest for the energy transition due to their promising applications for electric cars and energy grid storage. Operando characterization of batteries is critical to understand the degradation processes and increasing their electrochemical performance, especially in abusive conditions like during fast charges. Knowledge of the redox state of each electrode is essential to identify the origins of capacity loss in full batteries. Among the methods used for these investigations, operando Nuclear Magnetic Resonance (NMR) methods are promising since, without destroying the battery, they enable monitoring in real-time the electrochemical processes and the formation of short-lived metastable or reactive phases [1,2].Up to now, most operando NMR studies have focused on 7Li NMR spectroscopy to follow the lithiation and degradation processes in the solid electrodes of lithium-ion batteries. However, the large shifts and broadenings of the NMR spectra, which result from the redox-active paramagnetic ions (Ni2/3+, Co4+, Mn3/4+) or from the metallicity of the electrodes [3], complicate operando NMR spectra acquisition and interpretation for full batteries.Herein, we demonstrate that the 1H operando NMR signal of the liquid electrolyte solvent can be used to spy on the positive electrode evolution while benefitting from the high sensitivity of 1H liquid-state NMR compared to 7Li NMR. So far, operando NMR using the liquid electrolyte signal was mainly exploited to follow electrolyte decomposition [4] or to image indirectly dendrite formation [5]. Contrary to the lithium or sodium atoms composing the electrodes, hydrogen atoms in the electrolyte solvent are not a direct probe of the state of charge of the electrode. We demonstrate that the 1H NMR signal of the electrolyte molecules in the battery is, however, highly sensitive to the magnetic susceptibility (and therefore the redox state) of the neighboring particles of positive electrode active material.The state-of-charge (SOC) of the positive electrodes in the charging battery can be tracked indirectly through distortion in the spectrum of the dimethyl carbonate (DMC) solvent near the positive electrode. The effect of the other battery components such as current collectors, separators, or even negative electrodes is shown to be negligible compared to the perturbations induced by the positive electrode. We define specific descriptors to track the changes in the distorted 1H NMR spectrum of the battery and we correlate these changes with the state-of-charge of the positive electrode inside the battery as it is charged and discharged. This approach will enable measuring, operando, the redox state of positive electrodes in batteries, even when their 7Li signals cannot be detected by NMR. Exact knowledge of the redox state will contribute to a better exploitation of the electrochemical curves in full batteries.[1] Bagheri, K.; Deschamps, M.; Salager, E. Nuclear Magnetic Resonance for Interfaces in Rechargeable Batteries. Current Opinion in Colloid & Interface Science 2023, 64, 101675. https://doi.org/10.1016/j.cocis.2022.101675.[2] Liu, X.; Liang, Z.; Xiang, Y.; Lin, M.; Li, Q.; Liu, Z.; Zhong, G.; Fu, R.; Yang, Y. Solid‐State NMR and MRI Spectroscopy for Li/Na Batteries: Materials, Interface, and in Situ Characterization. Advanced Materials 2021, 33 (50), 2005878. https://doi.org/10.1002/adma.202005878.[3] Grey, C. P.; Dupré, N. NMR Studies of Cathode Materials for Lithium-Ion Rechargeable Batteries. Chemical Reviews 2004, 104 (10), 4493–4512. https://doi.org/10.1021/cr020734p.[4] Wiemers-Meyer, S.; Winter, M.; Nowak, S. NMR as a Powerful Tool to Study Lithium Ion Battery Electrolytes. Annual Reports on NMR Spectroscopy 2019, 121–162. https://doi.org/10.1016/bs.arnmr.2018.12.003.[5] Ilott, A. J.; Mohammadi, M.; Chang, H. J.; Grey, C. P.; Jerschow, A. Real-Time 3D Imaging of Microstructure Growth in Battery Cells Using Indirect MRI. Proceedings of the National Academy of Sciences 2016, 113 (39), 10779–10784. https://doi.org/10.1073/pnas.1607903113.

Ionic conductivity of Li3TaO4 depending on polymorphism and non-stoichiometric defects

Ionic conductivity of complex rock-salt Li3TaO4 was studied using low-temperature (LT; disordered) and high-temperature (HT; ordered) polymorphs modified with Li/Ta non-stoichiometry. For each of LT and HT derivatives, samples were prepared with four different nominal compositions of Li3.05Ta0.99O4, Li3TaO4, Li2.99Ta1.002O4, and Li2.98Ta1.004O4. The synchrotron X-ray diffraction analysis showed that the ordered HT phases have larger lattice volume than the disordered LT phases by ≈0.5%. Among both LT and HT sample groups, the lattice volume was smallest in the stoichiometric phases Li3TaO4. The X-ray diffraction line broadening analysis implied that the disordered LT phases contain local distortions that resemble the ordered HT phases. The solid-state magic-angle-spinning 7Li nuclear magnetic resonance spectroscopy revealed that LT phases have the larger LiO6 octahedra and the shorter Li–Li distances than HT phases. According to the ac impedance measurement and equivalent circuit analysis, the disordered LT phases had higher ionic conductivities (σi) than the ordered HT phases, by more than two orders of magnitudes. Particularly, the σi of Li2.98Ta1.004O4 (at ≈390 °C) was evaluated to be 10−2.4 S/cm and 10−4.8 S/cm for LT and HT phases, respectively. Meanwhile, the Li/Ta non-stoichiometry contributed to increase the σi of Li3TaO4, by more than an order.

Localized lithium plating under mild cycling conditions in high-energy lithium-ion batteries

Conditions such as the temperature and pressure experienced by lithium-ion battery components are dependent on cell geometry and can vary widely within a large cell. The resulting uneven degradation is challenging to study at the full cell level but can be revealed upon disassembly and post mortem analysis. In this work, we report localized lithium plating in automotive-grade, prismatic lithium-ion cells, also under cycling conditions generally considered to be mild (e.g., 5–65 %SOC, 23 °C, 0.5C cycle rate). Dead lithium content is quantified using 7Li nuclear magnetic resonance spectroscopy in both electrode and separator samples, corresponding to substantial capacity fade (26–46%) of the full cells. Severe lithium plating is typically initiated in regions near the positive tab, in which both the separators and negative electrodes are ultimately deactivated. High pressure arises during cycling, and we propose a deactivation mechanism based on high local stress due to electrode expansion and external constraint. Further, we develop a model to demonstrate that component deactivation can result in lithium plating even under mild cycling conditions. Notably, components harvested from regions with no detected lithium plating maintained adequate electrochemical performance.

Structure and Optical Properties of LixAg1–xGaSe2 and LixAg1–xInSe2

Complete substitution of Li atoms for Ag atoms in AgGaSe2 and AgInSe2 was achieved, resulting in the solid solutions LixAg1-xGaSe2 and LixAg1-xInSe2. The detailed crystal structures were determined by single-crystal X-ray diffraction and solid-state 7Li nuclear magnetic resonance spectroscopy, which confirm that Li atoms occupy unique sites and disorder only with Ag atoms. The tetragonal CuFeS2-type structure (space group I4̅2d) was retained within the entirety of the Ga-containing solid solution LixAg1-xGaSe2, which is noteworthy because the end-member LiGaSe2 normally adopts the orthorhombic β-NaFeO2-type structure (space group Pna21). These structures are closely related, being superstructures of the cubic sphalerite and hexagonal wurtzite prototypes adopted by diamond-like semiconductors. For the In-containing solid solution LixAg1-xInSe2, the structure transforms from the tetragonal to orthorhombic forms as the Li content increases past x = 0.50. The optical band gaps increase gradually with higher Li content, from 1.8 to 3.4 eV in LixAg1-xGaSe2 and from 1.2 to 2.5 eV in LixAg1-xInSe2, enabling control to desired values, while the second harmonic generation responses become stronger or are similar to those of benchmark infrared nonlinear optical materials such as AgGaS2. All members of these solid solutions remain congruently melting at accessible temperatures between 800 and 900 °C. Electronic structure calculations support the linear trends seen in the optical band gaps and confirm the mostly ionic character present in Li-Se bonds, in contrast to the more covalent character in Ga-Se or In-Se bonds.

Coupling Particle Ordering and Spherulitic Growth for Long-Term Performance of Nanocellulose/Poly(ethylene oxide) Electrolytes

Development of lithium-ion batteries with composite solid polymer electrolytes (CPSEs) has attracted attention due to their higher energy density and improved safety compared to systems utilizing liquid electrolytes. While it is well known that the microstructure of CPSEs affects the ionic conductivity, thermal stability, and mechanical integrity/long-term stability, the bridge between the microscopic and macroscopic scales is still unclear. Herein, we present a systematic investigation of the distribution of TEMPO-oxidized cellulose nanofibrils (t-CNFs) in two different molecular weights of poly(ethylene oxide) (PEO) and its effect on Li+ ion mobility, bulk conductivity, and long-term stability. For the first time, we link local Li-ion mobility at the nanoscale level to the morphology of CPSEs defined by PEO spherulitic growth in the presence of t-CNF. In a low-MW PEO system, spherulites occupy a whole volume of the derived CPSE with t-CNF being incorporated in between lamellas, while their nuclei remain particle-free. In a high-MW PEO system, spherulites are scarce and their growth is arrested in a non-equilibrium cubic shape due to the strong t-CNF network surrounding them. Electrochemical strain microscopy and solid-state 7Li nuclear magnetic resonance spectroscopy confirm that t-CNF does not partake in Li+ ion transport regardless of its distribution within the polymer matrix. Free-standing CSPE films with low-MW PEO have higher conductivity but lack long-term stability due to the existence of uniformly distributed, particle-free, spherulite nuclei, which have very little resistance to Li dendrite growth. On the other hand, high-MW PEO has lower conductivity but demonstrates a highly stable Li cycling response for more than 1000 h at 0.2 mA/cm2 and 65 °C and more than 100 h at 85 °C. The study provides a direct link between the microscopic dynamic, Li-ion transport, bulk mechanical properties and long-term stability of the derived CPSE and, and as such, offers a pathway towards design of robust all-solid-state Li-metal batteries.

Exposing Heterogeneous Degradation in Prismatic Lithium-Ion Cells

The energy density and lifetime of lithium-ion cells for automotive applications have both substantially improved in recent years. This enables electric vehicles in both the consumer and commercial sectors that have greater range, better reliability, and longer service lives [1]. These factors all contribute to the widespread adoption of electric vehicles. However, inhomogeneities exist within cells that contribute to uneven internal degradation and, when severe, can trigger rapid failure. These inhomogeneities can be related to manufacturing tolerances or distributions of component parameters [2], as well as gradients in internal or external conditions. As such, the reality of heterogeneous aging is a complex, multivariate problem to solve.In this latest work, we cycle automotive-grade prismatic cells for several thousand cycles (until 10-30 % capacity fade) and harvest components for post mortem aging characterization and experimental parameter identification. The constituent electrodes are a Ni-rich layered oxide (approximately LiNi0.76Mn0.15Co0.09O2) and graphite. In addition to microscopy and electrochemical testing on harvested electrodes, we quantify local lithium plating on graphite with our recently developed method utilizing ex-situ, 7Li nuclear magnetic resonance spectroscopy [3]. We believe this to be the first report of spatially-resolved lithium plating quantification in commercial lithium-ion cells. Clear patterns emerge (see Figure 1), reflecting the geometry of the cell and showing reproducible heterogeneity that cannot be attributed solely to defects in manufacture. Several tests even confirm local lithium plating and unusually rapid degradation at comparatively mild cycle conditions (slow charge/discharge, low state-of-charge, and room temperature).The wound jellyroll design in contemporary prismatic cells enables very high packing efficiency and energy density, but includes inherently weak points from where lithium plating and internal stresses [4] can propagate. In some cases, cells achieve satisfactory lifetimes without accelerated aging. In others, heterogeneities cause extreme local degradation that triggers end-of-life even though other regions may remain relatively intact. We explore the causes of these patterns and question how such damage can occur, even under cycling conditions usually considered safe.

Investigation of Structural and Electronic Changes Induced by Postsynthesis Thermal Treatment of LiNiO2

Postsynthesis thermal treatments at various temperatures in air have been applied to LiNiO2, and the induced structural and electronic changes have been uncovered. Except for the familiar decomposition process at higher temperatures, a series of transformations also take place under mild conditions. To identify such subtle changes, ex situ and in situ synchrotron radiation diffraction, ex situ 7Li nuclear magnetic resonance spectroscopy, and ex situ measurements of magnetic properties have been performed. We show that the reaction between LiNiO2 and CO2 starts already at a temperature of 200 °C, forming Li1–zNi1+zO2 layers. If the thickness of this layer is well adjusted, the electrochemical performance of LiNO2 can be improved. A cation off-stoichiometry of [Li0.90Ni0.10]NiO2 is identified at 600 °C even before the decomposition occurs. We also investigate the interplay of the reaction between LiNiO2 and CO2 with the decomposition at 700 °C. The changes in the Ni oxidation state and local Li environments are also monitored during the whole process.

Battery Degradation and Lifetime – Studies within the Faraday Institution on NMC811/Graphite Full Cells

Lithium-ion batteries (LIBs) find use in a wide range of applications, each of which has its own design specifications and practical requirements. With regards to the role of LIBs in mitigating carbon emissions, and therefore climate change, it is desirable to support the rapidly growing adoption of electric vehicles and renewable grid-storage systems via development of higher energy density, lower cost, and improved rate capability. However, the design of energy-dense, low-cobalt, and/or high-rate cell chemistries is impeded by inherent trade-offs with cycling and calendar lifetimes. A key goal for the automotive and utilities industries is therefore to predict battery lifetime for new cell designs and chemistries at a very high level of confidence, for example through improved understanding of the physical and chemical processes that determine 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 Project has built 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 eight UK universities, 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 diverse 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 and operando solid-state 7Li nuclear magnetic resonance spectroscopy (NMR) were combined to monitor processes in both electrodes individually, including Li-ion mobility and its changes with temperature.1 The method is now being applied to understand how the dynamics are affected by long-term structural damage to the NMC811 material. A series of differential voltage analysis experiments have been paired with operando X-ray diffraction measurements to propose the mechanism behind a critical ‘turning point’ in NMC811/graphite cells, following which degradation accelerates significantly.2 New operando cell designs have been developed to measure changes in cell pressure,3 which are being paired with solution NMR spectroscopy,4 and differential electrochemical mass spectrometry to quantify electrolyte oxidation. The role and rate of transition-metal dissolution in cells under stressed cycling conditions, namely cycling at high temperature (60 °C) and high upper cut-off voltages (4.4, 4.6 V), has been investigated.5 Scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) measurements were coupled with time-of-flight secondary-ion mass spectrometry (Tof-SIMS) to observe the Al-containing phases at NMC811 surfaces and grain boundaries.7 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.6 Finally, X-ray computed tomography methods have been developed that enable operando imaging and spectroscopic mapping of heterogeneities at a sub-particle length scale and across large areas of electrodes, which are being applied to study the origins of microstructural defects, cracking, and redox activity during charging, cycling, or storage.8,9 Reference s: K. Märker, C. Xu, and C. P. Grey, J. Am. Chem. Soc., 142, 17447–17456 (2020). W. M. Dose, C. Xu, C. P. Grey, and M. F. L. De Volder, Cell Rep. Phys. Sci., 1, 100253 (2020). N. Ryall and N. Garcia-Araez, J. Electrochem. Soc., 167, 110511 (2020). B. L. D. Rinkel, D. S. Hall, I. Temprano, and C. P. Grey, J. Am. Chem. Soc., 142, 15058–15074 (2020). Z. Ruff, C. Xu, and C. P. Grey, J. Electrochem. Soc., 168, 060518 (2021). 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). J. Lee, H. Amari, M. Bahri, Z. Shen, C. Xu, Z. Ruff, C. P. Grey, O. Ersen, A. Aguadero, N. D. Browning, and B. L. Mehdi, Batter. Supercaps, 4, 1813–1820 (2021). T. M. M. Heenan, A. Wade, C. Tan, J. E. Parker, D. Matras, A. S. Leach, J. B. Robinson, A. Llewellyn, A. Dimitrijevic, R. Jervis, P. D. Quinn, D. J. L. Brett, and P. R. Shearing, Adv. Energy Mater., 10, 2002655 (2020). C. Tan, A. S. Leach, T. M. M. Heenan, H. Parks, R. Jervis, J. N. Weker, D. J. L. Brett, and P. R. Shearing, Cell Rep. Phys. Sci., 100647 (2021).

Quantifying lithium lost to plating and formation of the solid-electrolyte interphase in graphite and commercial battery components

A key degradation mechanism in lithium-ion batteries (LIBs) is the irreversible loss of cyclable lithium during cycling. At the graphite negative electrode, this loss occurs through the deposition of lithium-containing compounds in the solid-electrolyte interphase (SEI) and through plating of metallic lithium, resulting in so-called dead lithium. The separate quantification of SEI and dead lithium has so far been a challenge in post mortem analysis of commercial LIBs. Here we report a simple and fast 7Li nuclear magnetic resonance spectroscopy (NMR) protocol applied to solid-state samples derived from lab-built batteries to independently quantify these and other lithium species in graphite electrodes without the need for specialized cell design nor knowledge of prior charging history. The metallic lithium content is corroborated by electrochemical calculations; the total amount of lithium is also determined from 7Li liquid-state NMR and inductively coupled plasma optical emission spectroscopy (ICP-OES) in suitably digested samples. Factors influencing accuracy like the sample handling process, the radiofrequency skin effect, and re-intercalation losses are investigated. Measurements on samples from commercial cells aged under realistic conditions demonstrate quantification of dead lithium and remaining ionic species (SEI), and further reveal lithium dendrites entrained in the separator following cell disassembly. The method uses conventional and widely available NMR instrumentation and is applicable to samples from lab-scale test cells or commercial batteries, thereby presenting a vast improvement over prior post mortem methods.

New Insights into Lithium Hopping and Ordering in LiNiO2 Cathodes during Li (De)intercalation

In situ 7Li and ex situ 6Li nuclear magnetic resonance (NMR) spectroscopy is applied to monitor lithium mobility in a LiNiO2 cathode during Li-ion (de)intercalation. In situ X-ray absorption spectroscopy and galvanostatic intermittent titration are also used to capture changes during the Li-ion deintercalation process. A considerable line broadening was first found by 7Li NMR spectroscopy. The Jahn–Teller distortion hinders the Li diffusion, thus broadening the NMR signal. The observed NMR shifts are compared to Li/vacancy ordering patterns described earlier by Arroyo y de Dompablo et al. Coupled motions of electrons and Li ions are also discovered by both in situ 7Li and ex situ 6Li NMR spectroscopy for the first time. They result in local Li environments with an enhanced number of Ni3+ neighbors at highly charged states. This opens a new perspective for understanding the highly delithiated structure.

Mechanistic insights into the reversible lithium storage in an open porous carbon via metal cluster formation in all solid-state batteries

Porous carbons are promising anode materials for next generation lithium batteries due to their large lithium storage capacities. However, their highsloping capacity during lithiation and delithiation as well as capacity fading due to intense formation of solid electrolyte interphase (SEI) limit their gravimetric and volumetric energy densities. Herein we compare a microporous carbide-derived carbon material (MPC) as promising future anode for all solid-state batteries with a commercial high-performance hard carbon anode. The MPC obtains high and reversible lithiation capacities of 1000 mAh g−1carbon in half-cells exhibiting an extended plateau region near 0 V vs. Li/Li+ preferable for full-cell application. The well-defined microporosity of the MPC with a specific surface area of >1500 m2 g−1 combines well with the argyrodite-type electrolyte (Li6PS5Cl) suppressing extensive SEI formation to deliver high coulombic efficiencies. Preliminary full-cell measurements vs. nickel-rich NMC-cathodes (LiNi0.9Co0.05Mn0.05O2) provide a considerably improved average potential of 3.76 V leading to a projected energy density as high as 449 Wh kg−1 and reversible cycling for more than 60 cycles. 7Li Nuclear Magnetic Resonance spectroscopy was combined with ex-situ Small Angle X-ray Scattering to elucidate the storage mechanism of lithium inside the carbon matrix. The formation of extended quasi-metallic lithium clusters after electrochemical lithiation was revealed.

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.

(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).

Li+ conduction in air-stable Sb-Substituted Li4SnS4 for all-solid-state Li-Ion batteries

Development of new sulfide Li+ superionic conductors with mechanical sinterability is the key to the success of all-solid-state lithium batteries. While phosphorus-containing sulfide superionic conductor materials have been widely investigated, phosphorus-free materials showing good air-stability have been overlooked. Herein, the Li+ dynamics in Sb-substituted Li4SnS4 showing a high Li+ conductivity of max. 0.85 mS cm−1 at 30 °C and excellent dry-air stability as well as negligible H2S evolution is described. Structural analysis with X-ray and neutron diffraction reveals that Sb-substitution renders an expansion of the lattice volume and formation of Li vacancies. Additionally, 1D-preferable 3D Li+ diffusion channels in Li4-xSn1-xSbxS4 are disclosed. The fast Li+ diffusion in Li4-xSn1-xSbxS4 is rationalized by complementary analysis using AC impedance measurements, bond valence energy landscape calculation, and 7Li nuclear magnetic resonance spectroscopy. Excellent electrochemical performances of TiS2 electrodes employing Li3.85Sn0.85Sb0.15S4 in all-solid-state batteries are demonstrated.

In situ7Li-NMR analysis of lithium metal surface deposits with varying electrolyte compositions and concentrations.

A major challenge of lithium metal electrodes, in theory a suitable choice for rechargeable high energy density batteries, comprises non-homogeneous lithium deposition and the growth of reactive high surface area lithium, which eventually yields active material losses and safety risks. While it is hard to fully avoid inhomogeneous deposits, the achievable morphology of the occurring lithium deposits critically determines the long-term cycling behaviour of the cells. In this work, we focus on a combined scanning electron microscopy (SEM) and 7Li nuclear magnetic resonance spectroscopy (7Li-NMR) study to unravel the impact of the choice of conducting salts (LiPF6 and LiTFSI), solvents (EC : DEC, 3 : 7, DME : DOL, 1 : 1), as well as their respective concentrations (1 M, 3 M) on the electrodeposition process, demonstrating that lithium deposition morphologies may be controlled to a large extent by proper choice of cycling conditions and electrolyte constituents. In addition, the applicability of 7Li-NMR spectroscopy to assess the resulting morphology is discussed. It was found, that lithium deposition analysis based on the 7Li chemical shift and intensity should be used carefully, as various morphologies can lead to similar results. Still, our case study reveals that the combination of SEM and NMR data is rather advantageous and offers complementary insights that may provide pathways for the future design of tailored electrolytes.

Lithium Storage Behavior of Three-Dimensional Graphene-like Ordered Microporous Carbon Synthesized in a Zeolite Template

Nanostructured carbons with high porosity are of great interest as high-performance anode materials for lithium-ion battery (LIB) applications. In the present work, we investigated the Li storage behavior of three-dimensional graphene-like ordered microporous carbon, which was synthesized via a zeolite-templating route. The microporous carbon exhibited an extremely high initial Li storage capacity as an anode for LIBs. Approximately 60% of the initial capacity was reversible during the subsequent cycles, while 40% was irreversible. The reversible capacity was comparable to the highest value reported so far with carbon alone. In order to investigate the chemical state of the Li species (i.e., ionic or metallic), the charged and discharged zeolite-templated carbon sample was characterized with 7Li nuclear magnetic resonance spectroscopy. The location of lithium was investigated using a transmission electron microscope equipped with an electron energy loss spectrometer and an energy-dispersive X-ray spectrometer. The result indicated that most of the reversible and irreversible lithium existed in nonmetallic +1 oxidation state inside the carbon micropores. The huge amount of Li storage is attributed to the three-dimensionally ordered microporous structure with a large surface area built with the single-layer graphene-like framework. In this study, we provides insights on the Li storage behavior in narrow carbon pore environment.

New insights into pre-lithiation kinetics of graphite anodes via nuclear magnetic resonance spectroscopy

Pre-lithiation of anode materials can be an effective method to compensate active lithium loss which mainly occurs in the first few cycles of a lithium ion battery (LIB), due to electrolyte decomposition and solid electrolyte interphase (SEI) formation at the surface of the anode. There are many different pre-lithiation methods, whereas pre-lithiation using metallic lithium constitutes the most convenient and widely utilized lab procedure in literature. In this work, for the first time, solid state nuclear magnetic resonance spectroscopy (NMR) is applied to monitor the reaction kinetics of the pre-lithiation process of graphite with lithium. Based on static 7Li NMR, we can directly observe both the dissolution of lithium metal and parallel formation of LiCx species in the obtained NMR spectra with time. It is also shown that the degree of pre-lithiation as well as distribution of lithium metal on the electrode surface have a strong impact on the reaction kinetics of the pre-lithiation process and on the remaining amount of lithium metal. Overall, our findings are highly important for further optimization of pre-lithiation methods for LIB anode materials, both in terms of optimized pre-lithiation time and appropriate amounts of lithium metal.

Li Metal Deposition during Low-Temperature Charge-Discharge Cycling of Li-Ion Batteries Observed by In Situ 7Li Nuclear Magnetic Resonance Spectroscopy

The influences of temperature and cell operation conditions on Li metal deposition were studied by in situ 7Li nuclear magnetic resonance (NMR) spectroscopy for cells cycled in continuous current (CC) and pulse current (PC) modes at –5, 0, and 5 °C. The above technique detected the growth of Li dendrites during low-temperature CC cycling, although electrochemical impedance spectroscopy failed to reveal any changes. Conversely, cells cycled in PC mode showed no Li dendrite signals in their 7Li NMR spectra even after 36000 cycles at –5 °C. The corresponding Li metal deposition rates were estimated and discussed, accounting for the capacity fading rate.

Lithium Bond Chemistry in Lithium–Sulfur Batteries

AbstractThe lithium–sulfur (Li–S) battery is a promising high‐energy‐density storage system. The strong anchoring of intermediates is widely accepted to retard the shuttle of polysulfides in a working battery. However, the understanding of the intrinsic chemistry is still deficient. Inspired by the concept of hydrogen bond, herein we focus on the Li bond chemistry in Li–S batteries through sophisticated quantum chemical calculations, in combination with 7Li nuclear magnetic resonance (NMR) spectroscopy. Identified as Li bond, the strong dipole–dipole interaction between Li polysulfides and Li–S cathode materials originates from the electron‐rich donors (e.g., pyridinic nitrogen (pN)), and is enhanced by the inductive and conjugative effect of scaffold materials with π‐electrons (e.g., graphene). The chemical shift of Li polysulfides in 7Li NMR spectroscopy, being both theoretically predicted and experimentally verified, is suggested to serve as a quantitative descriptor of Li bond strength. These theoretical insights were further proved by actual electrochemical tests. This work highlights the importance of Li bond chemistry in Li–S cell and provides a deep comprehension, which is helpful to the cathode materials rational design and practical applications of Li–S batteries.