7Li NMR Research Articles

A Synthetic, Structural, Spectroscopic, and Computational Study of Alkali Metal-Thioether, -Selenoether, and -Telluroether Interactions.

The rigid thioether- and selenoether-containing pro-ligands, 4,5-bis(phenylsulfido)-2,7,9,9-tetramethylacridan (H[AS2Ph2] (1)) and 4,5-bis(phenylselenido)-2,7,9,9-tetramethylacridan (H[ASe2Ph2] (2)), were deprotonated with one equiv of nBuLi to afford dimeric lithium complexes [Li(AE2Ph2)]2 (E = S (3), Se (4)) or with one equiv of KCH2Ph to afford the previously reported potassium complexes [K(AS2Ph2)(dme)]x (5) and [K(ASe2Ph2)(dme)2] (6). Attempts to prepare a direct telluroether analogue of compounds 1-2 were unsuccessful. However, the bulky selenoether- and telluroether-containing pro-ligands 4,5-bis(2,4,6-triisopropylphenylselenido)-2,7,9,9-tetramethylacridan (H[ASe2Tripp2] (7)) and 4,5-bis(2,4,6-triisopropylphenyltellurido)-2,7,9,9-tetramethylacridan (H[ATe2Tripp2] (8)) were accessed via the reaction of 4,5-dibromo-2,7,9,9-tetramethylacridan with three equiv of nBuLi, followed by the addition of two equiv of the corresponding diaryl dichalcogenide and quenching with dilute HCl(aq). The new selenoether- and telluroether-containing pro-ligands were subsequently deprotonated using KCH2Ph to afford [K(AE2Tripp2)(dme)2] (E = Se (9), Te (10)). Compounds 1-10 were characterized by 1H, 13C{1H}, 77Se{1H}, 125Te{1H}, and 7Li NMR spectroscopy, where applicable, and single-crystal X-ray structures were obtained for all lithium and potassium complexes (3-6 and 9-10). DFT calculations were also performed to assess the nature of bonding between the hard group 1 cations and the soft chalcogenoethers.

(Invited) Confirmation of Na-O-Li Configuration for P2-Type Cathode Materials

Oxygen-redox-based cathode materials for sodium-ion batteries (SIBs) have attracted considerable attention in recent years owing to their possibility of delivering additional capacity in the high-voltage region. However, they still suffer from not only fast capacity fading but also poor rate capability. Herein, we introduce P2-Na0.75[Li0.15Ni0.15Mn0.7]O2, an oxygen-redox-based layered oxide cathode material for SIBs. The effect of Ni doping on the electrochemical performance was investigated by comparison with Ni-free P2-Na0.67[Li0.22Mn0.78]O2. The Na0.75[Li0.15Ni0.15Mn0.7]O2 delivered a specific capacity of ~160 mAh g-1 in the voltage region of 1.5–4.6 V at 0.1C in Na cells. Combined experiments (galvanostatic cycling, neutron powder diffraction (NPD), X-ray absorption spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (7Li NMR)) and theoretical studies (density functional theory, DFT calculations) confirmed that Ni substitution not only increases the operating voltage and decreases voltage hysteresis but also improves the cycling stability by reducing Li migration from transition metal (TM) to Na layers. This research demonstrates the effect of Li and Ni co-doping in P2-type layered materials and suggests a new strategy of using Mn-rich cathode materials via oxygen redox with optimization of doping elements for SIBs.

(Invited) Synthesis of Ion-Endohedral Fullerenes by Plasma Implantation

Endohedral metallofullerenes (EMFs), which are the hybrid materials consisting of fullerene cage and encapsulated metal(s), are one of the well-studied nanocarbon materials during the past 3 decades.[1] As a result of significant progress in the development of synthetic procedures and purification processes, a variety of different types of EMFs, such as mono-metallofullerenes, di-metallofullerenes and metal-cluster-fullerenes with various carbon-cage sizes, are currently available. We previously reported development of an efficient method to access EMFs, so-called plasma implantation.[2] This approach allowed us to achieve scalable synthesis of lithium-ion-encapsulated [60]fullerene Li+@C60 X−, a stable ionic form of lithium encapsulated fullerene. The compound can be regarded as “ion-endohedral fullerene” consisting of encapsulated ion, neutral fullerene cage and external counter anion X−, and it should not be categorized into general metallofullerenes because of its ion-pair structure. Despite the unique properties arising from its ionic natures, no other ionic metallofullerenes have been well studied so far.[3] For systematic and deeper studies on ion-endohedral fullerenes, we focused on Li+-endohedral [70]fullerene (Li+@C70) because C70 is the second abundant and therefore widely studied fullerene next to C60. The Li+@C70 was synthesized as PF6 − and TFSI− (TFSI=bis(trifluoromethanesulfonyl)imide) salts using our improved plasma implantation method followed by oxidative purification process. 7Li NMR spectrum showed a sharp singlet signal at −32.81 ppm (vs LiCl/D2O standard) indicating that the Li+ was encapsulated in the C70 cage. 13C NMR spectrum showed 5 aromatic peaks, which evidenced the defectless C70 structure. In addition to the NMR signals originated from the Li+@C70 core, 19F and 31P NMR spectra showed clear signals assigned to each external counter anion. The structure of Li+@C70 was unambiguously confirmed by X-ray crystal structure analysis of the TFSI− salt. The crystal structure showed encapsulation of Li+ by C70 cage as well as the 1:1 ion-paired structure of the cationic Li+@C70 core and external TFSI− anion.Moreover, we also performed collision experiments using sodium plasma to synthesize sodium-ion-endohedral [60]fullerene. Laser desorption ionization (LDI) mass spectrum of the crude products showed signals at m/z= 720 and 743 assignable to the molecular ion of empty C60 and the Na+@C60, respectively. The target compound was isolated as TFSI− salt by oxidative purification process followed by electrolyte-added HPLC. There was only a mass peak at m/z= 743 after the purification, which evidenced the complete removal of empty C60. 23Na NMR spectrum showed a sharp singlet signal at −59.6 ppm (vs NaCl/D2O standard), evidenced the formation of the target Na+@C60.

Revealing the Lithium Storage Mechanism of Sulfurized Polyacrylonitrile Cathode by Ex-Situ NMR and Ex-Situ Raman Spectroscopy

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for high-performance lithium-sulfur batteries.1-3 However, fundamental insights into its molecular structure and lithium storage mechanism are yet not clearly understood. Herein, we reveal the formation of N-S and C=N-S bonds in addition to the C-S and S-S bonds using high−resolution cross−polarization/magic angle spinning (CP−MAS) solid states nitrogen-15 and carbon-13 nuclear magnetic resonance spectroscopy (15N NMR and 13C NMR). Ex-situ 13C NMR, ex-situ 15N NMR, ex-situ 7Li NMR, and ex-situ Raman studies indicate the formation of Li-C-N-Li and Li-C-C-Li bonds. Li–C and Li–N bonds increase the electron density of the conjugated heterocyclic structure and benefit lowering the charge/discharge voltage hysteresis after the second cycle. These results confirm conjugated C=N and C=C double-bonds involved in the lithium-ion storage mechanism leading to higher practical discharge capacity than the theoretical capacity of elemental sulfur. References Weret, M. A. et al. Mechanistic understanding of the Sulfurized-Poly(acrylonitrile) cathode for lithium-sulfur batteries. Energy Storage Materials 26, 483-493 (2020). Weret, M. A., Su, W.-N. & Hwang, B. J. Strategies towards High Performance Lithium-Sulfur Batteries. Batteries & Supercaps 5, e202200059 (2022). Weret, M. A. et al. Fibrous organosulfur cathode materials with high bonded sulfur for high-performance lithium-sulfur batteries. Journal of Power Sources 541, 231693 (2022).

Lithium‐Filled Skutterudites by Intercalation at Ambient‐Temperature

AbstractThe incorporation of lithium as a filler species in Co1‐2xFexNixSb3 skutterudites was accomplished by intercalation at 60 °C, using n‐BuLi as a reducing agent. Solid state 7Li NMR and ICP‐MS analysis confirm the presence of lithium in the product phases and provide an estimate of the lithium content. The maximum uptake of lithium increases as cobalt is progressively substituted by an equimolar mixture of iron and nickel. Difference Fourier maps, calculated during Rietveld structure refinement using powder neutron diffraction data, locate the lithium cations at the 2a (0,0,0) sites within the cavities of the skutterudite framework. The intercalation of lithium results in reductions in thermal conductivity of up to 47 %, indicative of phonon glass electron crystal (PGEC) type behaviour. Charge transfer from lithium to the framework that accompanies intercalation results in a substantial decrease in electrical resistivity in lithiated phases and a more metal‐like temperature dependence. The increased carrier concentration also decreases the Seebeck coefficient, with the consequence that modest increases in the figure of merit occur, despite the reduced thermal conductivity.

Electrolyte contact changes nano-Li4Ti5O12 bulk properties via surface polarons

It is of general interest to combine the faradaic processes based high energy density of a battery with the non-faradaic processes based high power density of a capacitor in one cell. Surface area and functional groups of electrode materials strongly affect these properties. For the anode material Li4Ti5O12 (LTO), we suggest a polaron based mechanism that influences Li ion uptake and mobility. Here we show electrolytes containing a lithium salt induce an observable change in the bulk NMR relaxation properties of LTO nano particles. The longitudinal 7Li NMR relaxation time of bulk LTO can change by almost an order of magnitude and, therefore, reacts very sensitively to the cation and its concentration in the surrounding electrolyte. The reversible effect is largely independent of the used anions and of potential anion decomposition products. It is concluded that lithium salt containing electrolytes increase the mobility of surface polarons. These polarons and additional lithium cations from the electrolyte can now diffuse through the bulk, induce the observed enhanced relaxation rate and enable the non-faradaic process. This picture of a Li+ ion equilibrium between electrolyte and solid may help with improving the charging properties of electrode materials.

Enhanced Electrochemical Properties and Optimized Li+ Transmission Pathways of PEO/LLZTO‐Based Composite Electrolytes Modified by Supramolecular Combination

Poly(ethylene oxide) (PEO) and Li6.75La3Zr1.75Ta0.25O12 (LLZTO)‐based composite polymer electrolytes (CPEs) are considered one of the most promising solid electrolyte systems. However, agglomeration of LLZTO within PEO and lack of Li+ channels result in poor electrochemical properties. Herein, a functional supramolecular combination (CD‐TFSI) consisting of active β‐cyclodextrin (CD) supramolecular with self‐assembled LiTFSI salt is selected as an interface modifier to coat LLZTO fillers. Benefiting from vast H‐bonds formed between β‐CD and PEO matrix and/or LLZTO, homogeneous dispersion and tight interface contact are obtained. Moreover, 6Li NMR spectra confirm a new Li+ transmission pathway from PEO matrix to LLZTO ceramic then to PEO matrix in the as‐prepared PEO/LLZTO@CD‐TFSI CPEs due to the typical cavity structure of β‐CD. As a proof, the conductivity is increased from 5.3 × 10−4 S cm−1 to 8.7 × 10−4 S cm−1 at 60 °C, the Li+ transference number is enhanced from 0.38 to 0.48, and the electrochemical stability window is extended to 5.1 V versus Li/Li+. Li‖LiFePO4 CR2032 coin full cells and pouch cells prove the practical application of the as‐prepared PEO/LLZTO@CD‐TFSI CPEs. This work offers a new strategy of interface modifying LLZTO fillers with functional supramolecular combination to optimize PEO/LLZTO CPEs for solid lithium batteries.

Hybrid coating SnO2 for enhanced Li ions storage

Anode SnO2 in lithium-ion batteries suffers from volume expansion and agglomeration. Here, the SnO2 nanoparticles are hybrided with ZrO2 particles by the support of carbon nanotube networks. The obtained SnO2/C/ZrO2 composite shows improved electrochemical performances. Investigations reveal that the carbon nanotubes shorten the transmission path of electrons and Li+ ions. Ball milling with ZrO2 promotes the formation of nanosized SnO2 to weaken the internal strain change, being beneficial to buffering volume change during electrochemical cycling afterwards. High-resolution 6,7Li NMR investigations indicate that conversion and alloying reactions are stepwise involved for SnO2/C/ZrO2 anode. The strategy of designing SnO2/C/ZrO2 composite from the morphology-controlled metal-organic frameworks for energy storage widens the possibility to fabricate promising materials with enhanced performances.

Observation of Li+ jumps in solid inorganic electrolytes over a broad dynamical range: A case study of the lithium phosphidosilicates Li8SiP4 and Li14SiP6

7Li NMR spectroscopy is known to be very sensitive to translational motion in solids and therefore highly suited for investigating temperature-dependent Li+ dynamics. A number of different NMR methods are available for choosing the dynamical range of the observed Li+ jump frequencies present in inorganic solid-state electrolytes. This includes 7Li spin-alignment echo NMR spectroscopy, static 7Li lineshape analysis, and 7Li spin-lattice relaxometry that can be used to detect Li+ jumps in the Hz, kHz, and MHz range, respectively. We introduce and discuss these NMR techniques with respect to their theoretical description and practical application to investigate the Li+ dynamics at different time scales for the two solid-state electrolytes Li8SiP4 and Li14SiP6. The data evaluation for all methods is discussed in detail, focusing on the determination of Li+ jump frequencies and activation energies for the investigated self-diffusion processes in a given structure.

Lithium‐ion Mobility in Li6B18(Li3N) and Li Vacancy Tuning in the Solid Solution Li6B18(Li3N)1−x(Li2O)x

AbstractAll‐solid‐state batteries are promising candidates for safe energy‐storage systems due to non‐flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open‐framework boron structure. The host–guest structure Li6B18(Li3N) comprises large hexagonal pores filled with Li7N] strands that represent a perfect cutout from the structure of α‐Li3N. Variable‐temperature 7Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol−1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O.

Lithium-ion Mobility in Li6 B18 (Li3 N) and Li Vacancy Tuning in the Solid Solution Li6 B18 (Li3 N)1-x (Li2 O)x.

All-solid-state batteries are promising candidates for safe energy-storage systems due to non-flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open-framework boron structure. The host-guest structure Li6 B18 (Li3 N) comprises large hexagonal pores filled with Li7 N] strands that represent a perfect cutout from the structure of α-Li3 N. Variable-temperature 7 Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol-1 and thus much lower than pristine Li3 N. The formation of the solid solution of Li6 B18 (Li3 N) and Li6 B18 (Li2 O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3 N and Li2 O.

Novel PEO-based composite electrolyte for low-temperature all-solid-state lithium metal batteries enabled by interfacial cation-assistance

Non-flammable succinonitrile (SN) is a promising plasticizer for lowering the working temperature of poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes. However, its application is greatly impeded by the inherent instability interface toward the Li anode. Here, we report a novel PEO/SN-based composite solid-state electrolyte with a durable interface and high room-temperature ionic conductivity of 6.74×10−4 S cm−1. By taking advantage of cation-assistance between La3+ cation in LLZTO and N atom in SN, reducing the active -CN groups or converting them to less reactive -C = N- groups, preventing the corrosion of lithium anode from SN. As a result, PEO/SN-based electrolyte displays highly stable Li plating/stripping cycling for over 1000 h at 0.1 mA cm−2 at RT. Furthermore, the all-solid-state lithium metal batteries (ASSLBs) based on LiFePO4 cathode deliver admirable cycling stability with a discharge capacity of 133 mAh g−1 and high-capacity retention of 92.6% after 240 cycles at 0.5C at RT. Even at -10 °C, the batteries still can achieve excellent electrochemical performance. The unique Li+ ion conduction pathway is investigated by tracer-exchange 6Li NMR. This work proposes new insight via cation assistance to build a durable interface for the real application of PEO/SN-based electrolytes system in ASSLBs.

Investigating structural properties and reaction mechanism of non-stoichiometric spinel LNMO via solid state NMR

By applying solid-state 6,7Li NMR, we reveal a redox reaction sequence of solid solution and biphasic transition and highlight the existence of intermediate species in non-stoichiometric transition metal-ordered high-voltage LNMO cathode reaction vs. Li.

Entropy stabilized cubic Li7La3Zr2O12 with reduced lithium diffusion activation energy: studied using solid-state NMR spectroscopy.

Stabilizing cubic polymorph of Li7La3Zr2O12 at low temperatures is challenging and currently limited to mono- or dual-ion doping with aliovalent ions. Herein, a high-entropy strategy at the Zr sites was deployed to stabilize the cubic phase and lower the lithium diffusion activation energy, evident from the static 7Li and MAS 6Li NMR spectra.

Lithium isotope tracing in silicon-based electrodes using solid-state MAS NMR: a powerful comprehensive tool for the characterization of lithium batteries.

The introduction of lithiated components with different 7Li/6Li isotopic ratios, also called isotopic tracing, can give access to better understanding of lithium transport and lithiation processes in lithium-ion batteries. In this work, we propose a simple methodology based on high-resolution solid-state NMR for the determination of the 7Li/6Li ratio in silicon electrodes following different strategies of isotopic tracing. The 6Li and 7Li MAS NMR experiments allow obtaining resolved spectra whose spectral components can be assigned to different moieties of the materials. In order to measure the ratio of the 6Li/7Li NMR integrals, a silicon electrode with a natural 7Li/6Li isotope abundance was used as a reference. This calibration can then be used to determine the 7Li/6Li ratio of any similar samples. This method was applied to study the phenomena occurring at the interface between a silicon electrode and a labeled electrolyte, which is an essential step for isotopic tracing experiments in systems after the formation of the solid electrolyte interphase (SEI). Beyond the isotopic exchanges between the SEI and the electrolyte already observed in the literature, our results show that isotopic exchanges also involve Li-Si alloys in the electrode bulk. Within a 52-hour contact, the electrolyte labeling disappeared: isotopic concentrations of the electrolyte and electrode become practically homogenized. However, at the electrode level, different silicides are characterized by rather different isotopic enrichment. In the present work, ToF SIMS and liquid state NMR were also used to cross-check and discuss the solid-state NMR method we have proposed.

Ordered state of the intrinstic two-component magnetoelectric material Li2CuZrO4 according to 7Li NMR data

Ordered state of the intrinstic two-component magnetoelectric material Li2CuZrO4 according to 7Li NMR data

Schlenks Vermächtnis – Methyllithium unter der Lupe

AbstractKommerziell erhältliche Stammlösungen von Organolithiumverbindungen sind vielfach eingesetzte Reagenzien in der Organischen und Metallorganischen Chemie. Solche Lösungen sind jedoch von “Natur aus” mit Lithiumhalogenidsalzen verunreinigt, die viele Syntheseprotokolle und Aufreinigungsprozesse erheblich einschränken. In dieser Arbeit beschreiben wir die Isolierung von chloridfreiem Methyllithium mithilfe von K[N(SiMe3)2] als Halogenidfällungsreagenz. Der Einfluss von definierten LiCl‐Verunreinigungen auf die 7Li‐NMR chemische Verschiebung wurde systematisch untersucht und quantifiziert. Die strukturellen Parameter des neuen chloridfreien Methyllithiumkomplexes [(Me3TACN)LiCH3] wurden mit der halogenidverunreinigten Variante und monomerem Lithiumchlorid [(Me3TACN)LiCl] verglichen.

Toward Understanding of the Li-Ion Migration Pathways in the Lithium Aluminum Sulfides Li3AlS3 and Li4.3AlS3.3Cl0.7 via 6,7Li Solid-State Nuclear Magnetic Resonance Spectroscopy.

Li-containing materials providing fast ion transport pathways are fundamental in Li solid electrolytes and the future of all-solid-state batteries. Understanding these pathways, which usually benefit from structural disorder and cation/anion substitution, is paramount for further developments in next-generation Li solid electrolytes. Here, we exploit a range of variable temperature 6Li and 7Li nuclear magnetic resonance approaches to determine Li-ion mobility pathways, quantify Li-ion jump rates, and subsequently identify the limiting factors for Li-ion diffusion in Li3AlS3 and chlorine-doped analogue Li4.3AlS3.3Cl0.7. Static 7Li NMR line narrowing spectra of Li3AlS3 show the existence of both mobile and immobile Li ions, with the latter limiting long-range translational ion diffusion, while in Li4.3AlS3.3Cl0.7, a single type of fast-moving ion is present and responsible for the higher conductivity of this phase. 6Li-6Li exchange spectroscopy spectra of Li3AlS3 reveal that the slower moving ions hop between non-equivalent Li positions in different structural layers. The absence of the immobile ions in Li4.3AlS3.3Cl0.7, as revealed from 7Li line narrowing experiments, suggests an increased rate of ion exchange between the layers in this phase compared with Li3AlS3. Detailed analysis of spin-lattice relaxation data allows extraction of Li-ion jump rates that are significantly increased for the doped material and identify Li mobility pathways in both materials to be three-dimensional. The identification of factors limiting long-range translational Li diffusion and understanding the effects of structural modification (such as anion substitution) on Li-ion mobility provide a framework for the further development of more highly conductive Li solid electrolytes.

Low-temperature crystallization and microwave dielectric properties of forsterite generated in MgO–SiO2 system following LiF addition

The crystallization and microwave dielectric properties of forsterite (Mg2SiO4) produced in (1-x)2MgO–SiO2(MS)-xLiF mixtures were characterized. High-temperature XRPD for a 0.91MS-0.09LiF specimen indicated the crystallization of forsterite above 800 °C, although MgSiO3, MgO and SiO2 were also detected due to the short heating duration. The XRPD patterns for (1-x)MS-xLiF ceramics sintered at 900 °C for 4 h in a covered crucible demonstrated the formation of forsterite as a single phase in compositions having x values less than 0.08. The activation energy for the crystallization fraction of forsterite was estimated from the DTA curves by using Kissinger-Akahira-Sunose method and decreased from 1382.4 to 474.0 kJ/mol, suggesting that the LiF addition enhances the nucleation and crystallization of forsterite. Refinement of the crystal structures of the (1-x)MS-xLiF ceramics by Rietveld analysis showed that the patterns acquired from samples having x values of 0.03–0.08 corresponded to a forsterite single phase with a decrease in the lattice parameters, confirming the substitution of Li and F for Mg and O in the forsterite. 7Li and 19F solid-state NMR spectroscopy analyses also confirmed the presence of 7Li and 19F signals for the sintered ceramics. The Q・f values for the ceramics increased from 22,800 to 104,800 GHz as x was increased to 0.08, due to the improvement in the crystallinity of forsterite. Although a near zero TCf value was achieved by CaTiO3 addition for (1-y)(0.92MS-0.08LiF)-yCaTiO3 ceramics at y = 0.10 (εr = 8.2, Q・f = 25,050 GHz, TCf = −5 ppm/°C), the Q・f values were drastically decreased due to the lower crystallinity of the forsterite and the presence of SiO2 and Li2MgSiO4 as secondary phases.

(Invited) Discovery of New Capacity Fade Mechanism in Lixsn Batteries with Derivativeoperando (dOp) NMR Spectroscopy

Tin, silicon and other intermetallic forming electrodes have large volumetric lithium capacities—nearly 10 times that of graphite. Such a high capacity combined with their low cost make intermetallics promising materials for the next generation of rechargeable batteries. Unfortunately, severe capacity fade remains the greatest obstacle in their commercial use. For example, in 2005 Sony introduced their NEXELION battery technology using nanostructured SnCo electrodes but eventually had to pull these batteries from the market due to substantial capacity loss with cycling. While a major reason for capacity fade in these electrodes is thought to be cracking from large volume changes during transitions between intermetallic phases, little evidence for cracking in nanostructured electrodes has been found; and the mechanism for capacity fade in nanostructured intermetallic electrodes has remained a mystery.Using derivative operando (dOp) 7Li NMR we have discovered a mechanism for capacity fade in LixSn nanoparticle electrodes that may solve this mystery. In short, the capacity fade in nanoparticle electrodes is the result of nanoparticles losing contact with the carbon/PVDF binder. Yet, it occurs in a peculiar way which causes the cell to reach full capacity at the end of every cycle on lithiation. In other words, capacity fade only occurs during delithiation. We present clear NMR evidence showing that particle disconnection occurs during the delithiation (volume contraction of the electrode particles) process. During lithiation (volume expansion of the electrode particles) our NMR data further reveals that connected particles are surprisingly pushed back into contact with the disconnected particles which then rejoin the circuit and allow the cell to reach full capacity on lithiation. Our dOp 7Li NMR spectra also reveal the structural transformation pathways between Li-Sn intermetallics during lithiation and delithiation of Sn nanoparticles. The disconnecting particles are associated with LixSn phases undergoing large decreases in diameters on delithiation, i.e., Sn, Li2Sn5, LiSn, and Li7Sn3. The Li–Sn phases observed are somewhat consistent with the structural evolution expected from the equilibrium binary phase diagram, but there are some notable exceptions with the observation of a metastable phase Li2Sn3, and two vacancy rich metastable phases, Li7−ζSn3, and Li13−δSn5 during delithiation.Although this new capacity fade mechanism is simple, we know no in-situ microscopy method capable of detecting and following such a disconnection-connection mechanism. Our approach clearly show the power of operando NMR spectroscopy for revealing such fundamental processes. These results point the way for future efforts in both industrial and academic research labs to reduce capacity fade in a wider range of nano-structured intermetallic electrodes, involving Si, Ge and Sb. Figure 1