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Organic electrodes are advantageous for rechargeable lithium-ion batteries owing to their high theoretical capacities, diverse functionalities, and environmental compatibility. Understanding the working mechanism of organic electrodes is vital to strategic materials design. However, due to lack of suitable characterization tools, it has been challenging to probe the reaction processes of organic electrodes in real-time. Here, non-destructive in situ electron paramagnetic resonance (EPR) was performed on a model organic electrode, 7,7,8,8-tetracyanoquinodimethane (TCNQ) used in rechargeable lithium-ion batteries, to directly follow the redox reactions in real-time. In order to minimize interfering signals from other parts of the batteries than the TCNQ electrode of interest, two sets of batteries are fabricated and studied with in situ EPR: (1) a LiCoO2//Li4Ti5O12 full-cell battery to determine the EPR signal evolution of additives and electrolytes; (2) a LiCoO2//TCNQ battery, and the difference in the observed EPR signals reflects purely the redox reactions of TCNQ upon lithiation and delithiation. A two-electron reversible redox reaction is delineated for TCNQ. TCNQ dimers form during the first electron injection upon lithiation and followed by the break-down of the dimers and associated electron coupling to produce massive delocalized electrons, resulting in increased EPR signal during the 2nd electron injection. Reversible trends are observed during electron ejection upon delithiation. In situ EPR is very sensitive to electron activities, thus is a powerful tool to follow redox reactions of organic electrodes, allowing for improved fundamental understanding of how organic electrodes work and for informed design of high-performance organic materials for energy storage.

Lithium chalcogenide materials have been studied less than other alkali metal analogs and are of interest as ion conductors and semiconductors capable of thermal neutron detection. Herein, we descr...

Manganese-rich layered oxide materials hold great potential as low-cost and high-capacity cathodes for Na-ion batteries. However, they usually form a P2 phase and suffer from fast capacity fade. In this work, an O3 phase sodium cathode has been developed out of a Li and Mn-rich layered material by leveraging the creation of transition metal (TM) and oxygen vacancies and the electrochemical exchange of Na and Li. The Mn-rich layered cathode material remains primarily O3 phase during sodiation/desodiation and can have a full sodiation capacity of ca. 220 mAh g-1 . It delivers ca. 160 mAh g-1 specific capacity between 2-3.8 V with >86 % retention over 250 cycles. The TM and oxygen vacancies pre-formed in the sodiated material enables a reversible migration of TMs from the TM layer to the tetrahedral sites in the Na layer upon de-sodiation and sodiation. The migration creates metastable states, leading to increased kinetic barrier that prohibits a complete O3-P3 phase transition.

Argyrodites, with fast lithium-ion conduction, are promising for applications in rechargeable solid-state lithium-ion batteries. We report a new compositional space of argyrodite superionic conduct...

Polymer-based hybrid electrolytes are a promissing class of materials for solid-state batteries due to their mechanical, physico-chemical and electrochemical properties. This paper gives an in-depth overview of possible ionic conduction mechanisms essential for good battery performance, and related relevant contemporary materials. The materials' preparation and characterization techniques are given in the light of necessity for deeper understanding of the structure–property relationship in such composites.

We report the discovery of a new superprotonic compound, Cs7(H4PO4)(H2PO4)8, or CPP, which forms at elevated temperatures from the reaction of CsH2PO4 and CsH5(PO4)2. The structure, solved using high-temperature single-crystal X-ray diffraction and confirmed by high-temperature 31P NMR spectroscopy, crystallizes in space group Pm3n and has a lattice constant of 20.1994(9) A at 130 °C. The unit cell resembles a 4 × 4 × 4 superstructure of superprotonic CsH2PO4, but features an extraordinary chemical moiety, rotationally disordered H4PO4+ cations, which periodically occupy one of every eight cation sites. The influence of this remarkable cation on the structure, thermodynamics, and proton transport properties of the CPP phase is discussed. Notably, CPP forms at a temperature of 90 °C, much lower than the superprotonic transition temperature of 228 °C of CsH2PO4, and the compound does not appear to have an ordered, low-temperature form. Under nominally dry conditions, the material is stable against dehydration to ∼151 °C, and this results in a particularly wide region of stability of a superprotonic material in the absence of active humidification. The conductivity of Cs7(H4PO4)(H2PO4)8 is moderate, 5.8 × 10-4 S cm-1 at 140 °C, but appears nevertheless facilitated by polyanion (H2PO4-) group reorientation.

Solid electrolytes with high ionic conductivity and good stability are advantageous over the current liquid electrolytes in rechargeable Li-ion batteries. Argyrodites, Li6PS5X (X ​= ​Cl, Br, or I), with ionic conductivities on the order of mS/cm have attracted tremendous attention. However, the high potential of argyrodites in fast ion conduction is far from being reached. Significant enhancement in ion conduction relies on the fundamental understanding of the contributing factors for fast ion transport. Here, we have systematically prepared highly conductive Li-deficient Li6−xPS5−xCl1+x and examined the influence of Li-deficiency and Cl substitution of S on ion transport using impedance spectroscopy, solid-state NMR, and first-principles calculations. With increased Cl content, the amount of Cl− at S2− (4d) sites increases, forming a dominant 1S3Cl (4d) configuration. In addition, Li+ redistributes with significantly higher mobility. As a result, the activation energy for Li-ion transport decreases, and the conductivity increases to 17 ​mS/cm at 25 ​°C when x equals 0.7 (Li5.3PS4.3Cl1.7). This work not only reports a record ionic conductivity of Cl-containing argyrodites-type fast Li-ion conductors, but also provides new insights into anion disorder-induced ion transport, which has a wide and universal appeal in the development of fast ion conductors and mixed-anion functional materials.

Establishing structure–property correlations is of paramount importance to materials research. The ability to selectively detect observable magnetization from transitions between quantized spin states of nuclei makes nuclear magnetic resonance (NMR) spectroscopy a powerful probe to characterize solids at the atomic level. In this article, we review recent advances in NMR techniques in six areas: spectral resolution, sensitivity, atomic correlations, ion dynamics, materials imaging, and hardware innovation. In particular, we focus on the applications of these techniques to materials research. Specific examples are given following the general introduction of each topic and technique to illustrate how they are applied. In conclusion, we suggest future directions for advanced solid-state NMR spectroscopy and imaging in interdisciplinary research.

The frequency-dependent capacitance of low-temperature solution-processed metal oxide (MO) dielectrics typically yields unreliable and unstable thin-film transistor (TFT) performance metrics, which hinders the development of next-generation roll-to-roll MO electronics and obscures intercomparisons between processing methodologies. Here, capacitance values stable over a wide frequency range are achieved in low-temperature combustion-synthesized aluminum oxide (AlOx) dielectric films by fluoride doping. For an optimal F incorporation of ∼3.7 atomic % F, the F:AlOx film capacitance of 166 ± 11 nF/cm2 is stable over a 10-1-104 Hz frequency range, far more stable than that of neat AlOx films (capacitance = 336 ± 201 nF/cm2) which falls from 781 ± 85 nF/cm2 to 104 ± 4 nF/cm2 over this frequency range. Importantly, both n-type/inorganic and p-type/organic TFTs exhibit reliable electrical characteristics with minimum hysteresis when employing the F:AlOx dielectric with ∼3.7 atomic % F. Systematic characterization of film microstructural/compositional and electronic/dielectric properties by X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry, cross-section transmission electron microscopy, solid-state nuclear magnetic resonance, and UV-vis absorption spectroscopy reveal that fluoride doping generates AlOF, which strongly reduces the mobile hydrogen content, suppressing polarization mechanisms at low frequencies. Thus, this work provides a broadly applicable anion doping strategy for the realization of high-performance solution-processed metal oxide dielectrics for both organic and inorganic electronics applications.

The centrosymmetric polymorph of KNaNbOF5 undergoes a reconstructive transition from a rare A-site vacancy ordered perovskite to a unique nonperovskite high-temperature phase. Previously, the high ...

High ionic conductivity of solid electrolytes is key to achieving high-power all-solid-state rechargeable batteries. The superionic argyrodite family is among the most conductive Li-ion conductors....

Li1+2xZn1–xPS4 was computationally predicted to have superionic conductivity of over 50 mS/cm. However, experimental efforts so far have only yielded ionic conductivities on the order of 10–4 S/cm,...

Li+ -conducting oxides are considered better ceramic fillers than Li+ -insulating oxides for improving Li+ conductivity in composite polymer electrolytes owing to their ability to conduct Li+ through the ceramic oxide as well as across the oxide/polymer interface. Here we use two Li+ -insulating oxides (fluorite Gd0.1 Ce0.9 O1.95 and perovskite La0.8 Sr0.2 Ga0.8 Mg0.2 O2.55 ) with a high concentration of oxygen vacancies to demonstrate two oxide/poly(ethylene oxide) (PEO)-based polymer composite electrolytes, each with a Li+ conductivity above 10-4 S cm-1 at 30 °C. Li solid-state NMR results show an increase in Li+ ions (>10 %) occupying the more mobile A2 environment in the composite electrolytes. This increase in A2-site occupancy originates from the strong interaction between the O2- of Li-salt anion and the surface oxygen vacancies of each oxide and contributes to the more facile Li+ transport. All-solid-state Li-metal cells with these composite electrolytes demonstrate a small interfacial resistance with good cycling performance at 35 °C.

The unclear Li+ local environment and Li+ conduction mechanism in solid polymer electrolytes, especially in a ceramic/polymer composite electrolyte, hinder the design and development of a new composite electrolyte. Moreover, both the low room-temperature Li+ conductivity and large interfacial resistance with a metallic lithium anode of a polymer membrane limit its application below a relatively high temperature. Here we have identified the Li+ distribution and Li+ transport mechanism in a composite polymer electrolyte by investigating a new solid poly(ethylene oxide) (PEO)-based NASICON-LiZr2(PO4)3 composite with 7Li relaxation time and 6Li → 7Li trace-exchange NMR measurements. The Li+ population of the two local environments in the composite electrolytes depends on the Li-salt concentration and the amount of ceramic filler. A composite electrolyte with a [EO]/[Li+] ratio n = 10 and 25 wt % LZP filler has a high Li+ conductivity of 1.2 × 10-4 S cm-1 at 30 °C and a low activation energy owing to the additional Li+ in the mobile A2 environment. Moreover, an in situ formed solid electrolyte interphase layer from the reaction between LiZr2(PO4)3 and a metallic lithium anode stabilized the Li/composite-electrolyte interface and reduced the interfacial resistance, which provided a symmetric Li/Li cell and all-solid-state Li/LiFePO4 and Li/LiNi0.8Co0.1Mn0.1O2 cells a good cycling performance at 40 °C.

A novel glass-ceramic solid electrolyte Li10P3S12I is synthesized, which delivers a high ionic conductivity of 6.4 mS/cm at 25 °C and a low activation energy of 0.26 eV. Li10P3S12I also exhibits significantly enhanced stability and low interfacial resistance against Li metal compared with thiophosphates. Tracer-exchange Li NMR reveals that lithium ions transport preferably through the glass phase and glass-ceramic interface in Li10P3S12I. Careful control of the synthesis process to avoid complete crystallization helps stabilize the highly Li-conductive phase.

The nitroxyl radical 1-methyl-2-azaadamantane N-oxyl (Me-AZADO) exhibits magnetic bistability arising from a radical/dimer interconversion. The transition from the rotationally disordered paramagnetic plastic crystal, Me-AZADO, to the ordered diamagnetic crystalline phase, (Me-AZADO)2, has been conclusively demonstrated by crystal structure determination from high-resolution powder diffraction data and by solid-state NMR spectroscopy. The phase change is characterized by a wide thermal hysteresis with high sensitivity to even small applied pressures. The molecular dynamics of the phase transition from the plastic crystal to the conventional crystalline phase has been tracked by solid-state (1H and 13C) NMR and EPR spectroscopies.

The large-voltage hysteresis remains one of the biggest barriers to optimizing Li/Na-ion cathodes using lattice anionic redox reaction, despite their very high energy density and relative low cost....

While sodium-ion batteries (SIBs) hold great promise for large-scale electric energy storage and low speed electric vehicles, the poor capacity retention of the cathode is one of the bottlenecks in...

The sluggish kinetic in electrode materials is one of the critical challenges in achieving high-power sodium ion storage. We report a coaxial core–shell nanostructure composed of carbon nanotube (CNT) as the core and TiO2@MoO2@C as shells for a hierarchically nanoarchitectured anode for improved electrode kinetics. The 1D tubular nanostructure can effectively reduce ion diffusion path, increase electrical conductivity, accommodate the stress due to volume change upon cycling, and provide additional interfacial active sites for enhanced charge storage and transport properties. Significantly, a synergistic effect between TiO2 and MoO2 nanostructures is investigated through ex situ solid-state nuclear magnetic resonance. The electrode exhibits a good rate capability (150 mAh g–1 at 20 A g–1) and superior cycling stability with a reversibly capacity of 175 mAh g–1 at 10 A g–1 for over 8000 cycles.

While the behavior of polyelectrolyte chains in aqueous salt solutions has been extensively studied, little is known about polar polymer chains in solvents with extremely high concentrations of inorganic ions, such as those found in ionic liquids (ILs). Here, we report on expansion, solvation and diffusion of poly(vinyl alcohol), PVA, chains in dilute solutions of a hydrated inorganic IL phase change material (PCM), lithium nitrate trihydrate (LNH). This solvent has an extremely high concentration of inorganic ions (≈18 M) with a low concentration of water molecules largely forming solvation shells of Li+ and NO3− ions, as shown using ATR-FTIR spectroscopy. Diffusion and hydrodynamic size of PVA chains of different molecular weights in this unusual solvent were studied using fluorescence correlation spectroscopy (FCS). A higher scaling exponent obtained from the molecular weight dependences of the diffusion coefficients of PVA chains as well as a lower overlap concentration (c*) of PVA in LNH solutions as measured by FCS suggest an expansion of the polymer coils in this solvent. We argue that enhanced solubility of PVA in LNH solutions is likely a result of increased rigidification of polymer chains due to the binding of solvated Li+ ions, which is demonstrated using 7Li NMR spectroscopy. We believe that an understanding of solvation and ion-binding capability can offer crucial insight into designing polymer-based shape stabilization matrices for inorganic PCMs.

Thermoelectric generators can convert heat directly into usable electric power but suffer from low efficiencies and high costs, which have hindered wide-scale applications. Accordingly, an important goal in the field of thermoelectricity is to develop new high performance materials that are composed of more earth-abundant elements. The best systems for midtemperature power generation rely on heavily doped PbTe, but the Te in these materials is scarce in the Earth's crust. PbSe is emerging as a less expensive alternative to PbTe, although it displays inferior performance due to a considerably smaller power factor S2σ, where S is the Seebeck coefficient and σ is electrical conductivity. Here, we present a new p-type PbSe system, Pb0.98Na0.02Se- x%HgSe, which yields a very high power factor of ∼20 μW·cm-1·K-2 at 963 K when x = 2, a 15% improvement over the best performing PbSe- x%MSe materials. The enhancement is attributed to a combination of high carrier mobility and the early onset of band convergence in the Hg-alloyed samples (∼550 K), which results in a significant increase in the Seebeck coefficient. Interestingly, we find that the Hg2+ cations sit at an off-centered position within the PbSe lattice, and we dub the displaced Hg atoms "discordant". DFT calculations indicate that this feature plays a role in lowering thermal conductivity, and we believe that this insight may inspire new design criteria for engineering high performance thermoelectric materials. The high power factor combined with a decrease in thermal conductivity gives a high figure of merit ZT of 1.7 at 970 K, the highest value reported for p-type PbSe to date.

All-solid-state rechargeable batteries embody the promise for high energy density, increased stability, and improved safety. However, their success is impeded by high resistance for mass and charge transfer at electrode–electrolyte interfaces. Li deficiency has been proposed as a major culprit for interfacial resistance, yet experimental evidence is elusive due to the challenges associated with noninvasively probing the Li distribution in solid electrolytes. In this Letter, three-dimensional 7Li magnetic resonance imaging (MRI) is employed to examine Li distribution homogeneity in solid electrolyte Li10GeP2S12 within symmetric Li/Li10GeP2S12/Li batteries. 7Li MRI and the derived histograms reveal Li depletion from the electrode–electrolyte interfaces and increased heterogeneity of Li distribution upon electrochemical cycling. Significant Li loss at interfaces is mitigated via facile modification with a poly(ethylene oxide)/bis(trifluoromethane)sulfonimide Li salt thin film. This study demonstrates a power...

Sodium-ion batteries (SIBs) are an emerging electrochemical energy storage technology that has high promise for electrical grid level energy storage. High capacity, long cycle life, and low cost cathode materials are very much desired for the development of high performance SIB systems. Sodium manganese oxides with different compositions and crystal structures have attracted much attention because of their high capacity and low cost. Here we report our investigations into a group of promising lithium doped sodium manganese oxide cathode materials with exceptionally high initial capacity of ∼223 mAh g−1 and excellent capacity retentions, attributed primarily to the absence of phase transformation in a wide potential range of electrochemical cycling, as confirmed by in-operando X-ray diffraction (XRD), Rietveld refinement, and high-resolution 7Li solid-state NMR characterizations. The systematic study of structural evolution and the correlation with the electrochemical behavior of the doped cathode materials provides new insights into rational design of high-performance intercalation compounds by tailoring the composition and the crystal structure evolution in electrochemical cycling.

Composite electrolytes are widely studied for their potential in realizing improved ionic conductivity and electrochemical stability. Understanding the complex mechanisms of ion transport within composites is critical for effectively designing high-performance solid electrolytes. This study examines the compositional dependence of the three determining factors for ionic conductivity, including ion mobility, ion transport pathways, and active ion concentration. The results show that with increase in the fraction of ceramic Li7La3Zr2O12 (LLZO) phase in the LLZO–poly(ethylene oxide) composites, ion mobility decreases, ion transport pathways transit from polymer to ceramic routes, and the active ion concentration increases. These changes in ion mobility, transport pathways, and concentration collectively explain the observed trend of ionic conductivity in composite electrolytes. Liquid additives alter ion transport pathways and increase ion mobility, thus enhancing ionic conductivity significantly. It is also...

A novel and efficient method is demonstrated to improve the electrochemical performance of Li4Ti5O12 and metal-oxide anodes. In contrast to other methods, inexpensive red phosphorus powder is used as a reducing reagent, and the reduction is conducted at a relatively low temperature of 400 °C. This method offers a low cost and effective way for Li4Ti5O12 and metal-oxide anode applications.

Nickel phosphide (Ni5P4) nanosheets are synthesized using in situ chemical vapor deposition of P on Ni foam. The thickness of the as-synthesized Ni5P4 film is determined to be ∼5 nm, using atomic force microscopy (AFM). The small thickness shortens the diffusion path of Li ions and results in fast ion transport. In addition, the 2D Ni5P4 nanosheets seamlessly connect to the Ni foam, which facilitates electron transfer between Ni5P4 and the Ni current collector. Therefore, the binder/carbon free-nickel supported Ni5P4 shows fast rate performance as an anode for lithium-ion batteries (LIBs). The specific capacity of 2D Ni5P4 is obtained as 600 mA h g−1 at a cycling rate of 0.1C, approaching the theoretical capacity of 768 mA h g−1. Even at a rate of 0.5C, the capacity remains as 450 mA h g−1 over 100 cycles. A capacity >100 mA h g−1 is retained at a very high rate of 20C. Ni5P4 also exhibits a low voltage of ∼0.5 V with respect to Li metal, which makes it a suitable negative electrode for LIBs. In operando31P NMR and 7Li NMR are employed to probe the lithiation and de-lithiation mechanisms upon electrochemical cycling.

Li in Li-rich cathodes mostly resides at octahedral sites in both Li layers (LiLi) and transition metal layers (LiTM). Extraction and insertion of LiLi and LiTM are strongly influenced by surrounding transition metals. pjMATPASS and operando Li nuclear magnetic resonance are combined to achieve both high spectral and temporal resolution for quantitative real time monitoring of lithiation and delithiation at LiLi and LiTM sites in Li2MnO3, Li1.2Ni0.2Mn0.6O2, and Li1.2Ni0.13Mn0.54Co0.13O2 cathodes. The results have revealed that LiTM are preferentially extracted for the first 20% of charge and then LiLi and LiTM are removed at the same rate. No preferential insertion or extraction of LiLi and LiTM is observed beyond the first charge. Ni and Co promote faster and more complete removal of LiTM. The recovery of the removed Li is 80% for LiLi upon first discharge. The study sheds light on the activity of LiLi and LiTM during electrochemical processes as well as their respective contributions ...

Anionic redox chemistry offers a transformative approach for significantly increasing specific energy capacities of cathodes for rechargeable Li-ion batteries. This study employs operando electron paramagnetic resonance (EPR) to simultaneously monitor the evolution of both transition metal and oxygen redox reactions, as well as their intertwined couplings in Li2MnO3, Li1.2Ni0.2Mn0.6O2, and Li1.2Ni0.13Mn0.54Co0.13O2 cathodes. Reversible O2–/O2n– redox takes place above 3.0 V, which is clearly distinguished from transition metal redox in the operando EPR on Li2MnO3 cathodes. O2–/O2n– redox is also observed in Li1.2Ni0.2Mn0.6O2, and Li1.2Ni0.13Mn0.54Co0.13O2 cathodes, albeit its overlapping potential ranges with Ni redox. This study further reveals the stabilization of the reversible O redox by Mn and e– hole delocalization within the Mn–O complex. The interactions within the cation–anion pairs are essential for preventing O2n– from recombination into gaseous O2 and prove to activate Mn for its increasing pa...

Composite polymer solid electrolytes (CPEs) containing ceramic fillers embedded inside a polymer-salt matrix show great improvements in Li+ ionic conductivity compared to the polymer electrolyte alone. Lithium lanthanum zirconate (Li7La3Zr2O12, LLZO) with a garnet-type crystal structure is a promising solid Li+ conductor. We show that by incorporating only 5 wt % of the ceramic filler comprising undoped, cubic-phase LLZO nanowires prepared by electrospinning, the room temperature ionic conductivity of a polyacrylonitrile-LiClO4-based composite is increased 3 orders of magnitude to 1.31 × 10–4 S/cm. Al-doped and Ta-doped LLZO nanowires are also synthesized and utilized as fillers, but the conductivity enhancement is similar as for the undoped LLZO nanowires. Solid-state nuclear magnetic resonance (NMR) studies show that LLZO NWs partially modify the PAN polymer matrix and create preferential pathways for Li+ conduction through the modified polymer regions. CPEs with LLZO nanoparticles and Al2O3 nanowire fi...

Excellent rate performance of Li4+xTi5O12 (0 < x < 3, LTO) electrodes results from mixed Li site occupancy and facile Li ion exchange at 8a and 16c sites. In this paper, we reveal that inter-particle connectivity within LTO electrodes affects 8a and 16c site occupancies upon discharge and impacts Li ion diffusion. LTO electrodes of the same primary crystal structure but of different grain boundary structures were prepared and they showed significantly different electrochemical performance. LTO electrodes with a percolated 3D structural network and bridged grain boundaries offered balanced 8a-16c occupancy, Li ion exchange at 8a and 16c sites upon discharge, high ionic conductivities, and good rate performance. While LTO electrodes with isolated clusters of particles showed strong rate dependence of 8a-16c occupancy, a lack of Li ion exchange at 8a and 16c sites, large over-potential, and substantial capacity decay upon fast charging. Bridged grain boundaries in LTO secondary particles facilitate apparent solid-solution process during electrochemical cycling by maintaining Li site exchange and thus enhance the rate performance of LTO electrodes.

Sodium borohydride (NaBH4) has been proposed as a potential hydrogen storage material for fuel cells, and the development of highly active and robust catalysts for hydrolyzing NaBH4 is the key for the practical usage of NaBH4 for fuel cells. Herein we report Co-nanocrystal assembled hollow nanoparticles (Co-HNP) as an active and robust catalyst for the hydrolysis of NaBH4. A hydrogen generation rate of 10.8 L·min–1·g–1 at 25 °C was achieved by using the Co-HNP catalyst with a low activation energy of 23.7 kJ·mol–1, which is among the best performance of reported noble and non-noble catalysts for hydrolyzing NaBH4. Co-HNP also showed good stability in the long term cycling tests. The mechanism of the catalytic hydrolysis of NaBH4 on Co-HNP was studied by using 1H and 11B solid-state NMR, which provided unambiguous experimental evidence of the Co–H formation. The systematically designed NMR experiments unveiled the key role of Co-HNP in the activation of borohydride and the subsequent transfer of H– to wate...

Ceramic–polymer hybrids carry the promise of forming composite electrolytes with high ionic conductivity, good stability and compatibility with electrodes, and excellent mechanical properties that cannot be achieved with conventional ceramic or polymer ion conductors. Small molecule additives often further enhance ion conduction. This work employs a representative composite comprising a ceramic Li-ion conductor, garnet-type Li7La3Zr2O12 (LLZO), a polymer Li-ion conductor, polyethylene oxide (PEO), and an additive, tetraethylene glycol dimethyl ether (TEGDME). All the Li sites in bulk LLZO, PEO, and TEGDME, and at the interfaces of PEO/LLZO, PEO/TEGDME, and LLZO/TEGDME, have been clearly identified with high-resolution Li NMR. It is determined using the 6Li → 7Li isotope replacement strategy that Li-ion transport in this composite occurs mainly via TEGDME-associated phases. Changes in the bulk and interfacial structures of the composite will likely alter Li-ion pathways and thus lead to variation in ionic conductivity. As an example, the composite structure evolves over time, which results in a decrease in active Li sites and degradation of ionic conductivity.

The Na 2 Si 2 O 5 in the amorphous state exhibits a fast Na + -conduction at elevated temperatures. However, it is metastable, gradually transforming into the insulating Na 2 Si 2 O 5 in the crystalline state with temperatures. The present work shows that the presence of H 2 and Al-doping can suppress the harmful amorphous-to-crystalline transformation in Na 2 Si 2 O 5 . A systematic investigation was carried out to understand the fundamental aspects of the amorphous-to-crystalline transformation through a suite of advanced experimental techniques including X-ray diffraction (XRD), differential scanning calorimetry (DSC) analysis, electrochemical impedance spectroscopy (EIS), Raman spectroscopy and multi-nucleus nuclear magnetic resonance spectroscopy (NMR).

Chromium oxide, Cr 2 O 5 , was synthesized by pyrolyzing CrO 3 at 350 °C and employed as a new cathode in rechargeable sodium ion batteries. Cr 2 O 5 /Na rechargeable batteries delivered high specific capacities up to 310 mAh/g at a current density of C/16 (or 20 mA/g). High-resolution solid-state 23 Na NMR both qualitatively and quantitatively revealed the reversible intercalation of Na ions into the bulk electrode and participation of Na ions in the formation of the solid-electrolyte interphase largely at low potentials. Amorphization of the electrode structure occurred during the first discharge revealed by both NMR and X-ray diffraction data. CrO 3 -catalyzed electrolyte degradation and loss in electronic conductivity led to gradual capacity fading. The specific capacity stabilized at >120 mAh/g after 50 charge-discharge cycles. Further improvement in electrochemical performance is possible via electrode surface modification, polymer binder incorporation, or designs of new morphologies.

Polymer-ceramic composite electrolytes are emerging as a promising solution to deliver high ionic conductivity, optimal mechanical properties, and good safety for developing high-performance all-solid-state rechargeable batteries. Composite electrolytes have been prepared with cubic-phase Li7 La3 Zr2 O12 (LLZO) garnet and polyethylene oxide (PEO) and employed in symmetric lithium battery cells. By combining selective isotope labeling and high-resolution solid-state Li NMR, we are able to track Li ion pathways within LLZO-PEO composite electrolytes by monitoring the replacement of (7) Li in the composite electrolyte by (6) Li from the (6) Li metal electrodes during battery cycling. We have provided the first experimental evidence to show that Li ions favor the pathway through the LLZO ceramic phase instead of the PEO-LLZO interface or PEO. This approach can be widely applied to study ion pathways in ionic conductors and to provide useful insights for developing composite materials for energy storage and harvesting.

Solid-oxide Li+ electrolytes of a rechargeable cell are generally sensitive to moisture in the air as H+ exchanges for the mobile Li+ of the electrolyte and forms insulating surface phases at the electrolyte interfaces and in the grain boundaries of a polycrystalline membrane. These surface phases dominate the total interfacial resistance of a conventional rechargeable cell with a solid-electrolyte separator. We report a new perovskite Li+ solid electrolyte, Li0.38 Sr0.44 Ta0.7 Hf0.3 O2.95 F0.05 , with a lithium-ion conductivity of σLi =4.8×10-4 S cm-1 at 25 °C that does not react with water having 3≤pH≤14. The solid electrolyte with a thin Li+ -conducting polymer on its surface to prevent reduction of Ta5+ is wet by metallic lithium and provides low-impedance dendrite-free plating/stripping of a lithium anode. It is also stable upon contact with a composite polymer cathode. With this solid electrolyte, we demonstrate excellent cycling performance of an all-solid-state Li/LiFePO4 cell, a Li-S cell with a polymer-gel cathode, and a supercapacitor.

Metallic germanium is a promising anode material in secondary lithium-ion batteries (LIBs) due to its high theoretical capacity (1623 mAh/g) and low operating voltage, coupled with the high lithium-ion diffusivity and electronic conductivity of lithiated Ge. Here, the lithiation mechanism of micron-sized Ge anodes has been investigated with X-ray diffraction (XRD), pair distribution function (PDF) analysis, and in-/ex-situ high-resolution 7Li solid-state nuclear magnetic resonance (NMR), utilizing the structural information and spectroscopic fingerprints obtained by characterizing a series of relevant LixGey model compounds. In contrast to previous work, which postulated the formation of Li9Ge4 upon initial lithiation, we show that crystalline Ge first reacts to form a mixture of amorphous and crystalline Li7Ge3 (space group P3212). Although Li7Ge3 was proposed to be stable in a recent theoretical study of the Li–Ge phase diagram (Morris, A. J.; Grey, C. P.; Pickard, C. J. Phys. Rev. B: Condens. Matter Ma...

Hybrid organic-inorganic metal halide perovskites possess exceptional structural tunability, with three- (3D), two- (2D), one- (1D), and zero-dimensional (0D) structures on the molecular level all possible. While remarkable progress has been realized in perovskite research in recent years, the focus has been mainly on 3D and 2D structures, with 1D and 0D structures significantly underexplored. The synthesis and characterization of a series of low-dimensional organic tin bromide perovskites with 1D and 0D structures is reported. Using the same organic and inorganic components, but at different ratios and reaction conditions, both 1D (C4 N2 H14 )SnBr4 and 0D (C4 N2 H14 Br)4 SnBr6 can be prepared in high yields. Moreover, photoinduced structural transformation from 1D to 0D was investigated experimentally and theoretically in which photodissociation of 1D metal halide chains followed by structural reorganization leads to the formation of a more thermodynamically stable 0D structure.

Local dynamics and hydrogen bonding in CsH2PO4 have been investigated by 1H, 2H, and 31P solid-state NMR spectroscopy to help provide a detailed understanding of proton conduction in the paraelectric phase. Two distinct environments are observed by 1H and 2H NMR, and their chemical shifts (1H) and quadrupolar coupling constants (2H) are consistent with one strong and one slightly weaker H-bonding environment. Two different protonic motions are detected by variable-temperature 1H MAS NMR and T1 spin–lattice relaxation time measurements in the paraelectric phase, which we assign to librational and long-range translational motions. An activation energy of 0.70 ± 0.07 eV is extracted for the latter motion; that of the librational motion is much lower. 31P NMR line shapes are measured under MAS and static conditions, and spin–lattice relaxation time measurements have been performed as a function of temperature. Although the 31P line shape is sensitive to the protonic motion, the reorientation of the phosphate ...

Understanding the local structure and ion dynamics is at the heart of ion conductor research. This paper reports on high-resolution solid-state 29Si, 23Na, and 17O NMR investigation of the structure, chemical composition, and ion dynamics of a newly discovered fast ion conductor, Na-doped SrSiO3, which exhibited a much higher ionic conductivity than most of current oxide ion conductors. Quantitative analyses reveal that with a small dose ( 10 mol% Na doping, phase separation occurs, leading to the formation of an amorphous phase β-Na2Si2O5 and a crystalline Sr-rich phase. Variable-temperature 23Na and 17O magic-angle-spinning NMR up to 618 °C have shown significant changes in Na ion dynamics at high temperatures but little oxide ion motion, suggesting that Na ions are responsible for the observed high ionic conductivity. In addition, β-Na2Si2O5 starts to crystallize at temperatures higher than 480 °C with prolonged heating, resulting in reduction in Na+ motion, and thus degradation of ionic conductivity. This study has contributed critical evidence to the understanding of ionic conduction in Na-doped SrSiO3 and demonstrated that multinuclear high-resolution and high-temperature solid-state NMR is a uniquely useful tool for investigating ion conductors at their operating conditions.