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1.
Nature ; 627(8003): 301-305, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38448596

RESUMO

Solid-state Li-S batteries (SSLSBs) are made of low-cost and abundant materials free of supply chain concerns. Owing to their high theoretical energy densities, they are highly desirable for electric vehicles1-3. However, the development of SSLSBs has been historically plagued by the insulating nature of sulfur4,5 and the poor interfacial contacts induced by its large volume change during cycling6,7, impeding charge transfer among different solid components. Here we report an S9.3I molecular crystal with I2 inserted in the crystalline sulfur structure, which shows a semiconductor-level electrical conductivity (approximately 5.9 × 10-7 S cm-1) at 25 °C; an 11-order-of-magnitude increase over sulfur itself. Iodine introduces new states into the band gap of sulfur and promotes the formation of reactive polysulfides during electrochemical cycling. Further, the material features a low melting point of around 65 °C, which enables repairing of damaged interfaces due to cycling by periodical remelting of the cathode material. As a result, an Li-S9.3I battery demonstrates 400 stable cycles with a specific capacity retention of 87%. The design of this conductive, low-melting-point sulfur iodide material represents a substantial advancement in the chemistry of sulfur materials, and opens the door to the practical realization of SSLSBs.

2.
Nature ; 556(7700): 185-190, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29643482

RESUMO

There is an urgent need for low-cost, resource-friendly, high-energy-density cathode materials for lithium-ion batteries to satisfy the rapidly increasing need for electrical energy storage. To replace the nickel and cobalt, which are limited resources and are associated with safety problems, in current lithium-ion batteries, high-capacity cathodes based on manganese would be particularly desirable owing to the low cost and high abundance of the metal, and the intrinsic stability of the Mn4+ oxidation state. Here we present a strategy of combining high-valent cations and the partial substitution of fluorine for oxygen in a disordered-rocksalt structure to incorporate the reversible Mn2+/Mn4+ double redox couple into lithium-excess cathode materials. The lithium-rich cathodes thus produced have high capacity and energy density. The use of the Mn2+/Mn4+ redox reduces oxygen redox activity, thereby stabilizing the materials, and opens up new opportunities for the design of high-performance manganese-rich cathodes for advanced lithium-ion batteries.

3.
J Am Chem Soc ; 144(13): 5795-5811, 2022 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-35325534

RESUMO

In the pursuit of urgently needed, energy dense solid-state batteries for electric vehicle and portable electronics applications, halide solid electrolytes offer a promising path forward with exceptional compatibility against high-voltage oxide electrodes, tunable ionic conductivities, and facile processing. For this family of compounds, synthesis protocols strongly affect cation site disorder and modulate Li+ mobility. In this work, we reveal the presence of a high concentration of stacking faults in the superionic conductor Li3YCl6 and demonstrate a method of controlling its Li+ conductivity by tuning the defect concentration with synthesis and heat treatments at select temperatures. Leveraging complementary insights from variable temperature synchrotron X-ray diffraction, neutron diffraction, cryogenic transmission electron microscopy, solid-state nuclear magnetic resonance, density functional theory, and electrochemical impedance spectroscopy, we identify the nature of planar defects and the role of nonstoichiometry in lowering Li+ migration barriers and increasing Li site connectivity in mechanochemically synthesized Li3YCl6. We harness paramagnetic relaxation enhancement to enable 89Y solid-state NMR and directly contrast the Y cation site disorder resulting from different preparation methods, demonstrating a potent tool for other researchers studying Y-containing compositions. With heat treatments at temperatures as low as 333 K (60 °C), we decrease the concentration of planar defects, demonstrating a simple method for tuning the Li+ conductivity. Findings from this work are expected to be generalizable to other halide solid electrolyte candidates and provide an improved understanding of defect-enabled Li+ conduction in this class of Li-ion conductors.

4.
Nat Mater ; 20(2): 214-221, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33046857

RESUMO

High-entropy (HE) ceramics, by analogy with HE metallic alloys, are an emerging class of solid solutions composed of a large number of species. These materials offer the benefit of large compositional flexibility and can be used in a wide variety of applications, including thermoelectrics, catalysts, superionic conductors and battery electrodes. We show here that the HE concept can lead to very substantial improvements in performance in battery cathodes. Among lithium-ion cathodes, cation-disordered rocksalt (DRX)-type materials are an ideal platform within which to design HE materials because of their demonstrated chemical flexibility. By comparing a group of DRX cathodes containing two, four or six transition metal (TM) species, we show that short-range order systematically decreases, whereas energy density and rate capability systematically increase, as more TM cation species are mixed together, despite the total metal content remaining fixed. A DRX cathode with six TM species achieves 307 mAh g-1 (955 Wh kg-1) at a low rate (20 mA g-1), and retains more than 170 mAh g-1 when cycling at a high rate of 2,000 mA g-1. To facilitate further design in this HE DRX space, we also present a compatibility analysis of 23 different TM ions, and successfully synthesize a phase-pure HE DRX compound containing 12 TM species as a proof of concept.

5.
Nat Mater ; 19(10): 1088-1095, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32424371

RESUMO

In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is a fundamental step towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na0.67MO2 (M = Co, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3' and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally unconstrained reactions between powder precursors favour the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solid-state synthesis of ceramic materials, and constitutes a step forward in unravelling the complex interplay between thermodynamics and kinetics during materials synthesis.

6.
Phys Chem Chem Phys ; 23(36): 20052-20064, 2021 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-34231590

RESUMO

Sodium (Na)-ion batteries are the most explored 'beyond-Li' battery systems, yet their energy densities are still largely limited by the positive electrode material. Na3FeF6 is a promising Earth-abundant containing electrode and operates through a conversion-type charge-discharge reaction associated with a high theoretical capacity (336 mA h g-1). In practice, however, only a third of this capacity is achieved during electrochemical cycling. In this study, we demonstrate a new rapid and environmentally-friendly assisted-microwave method for the preparation of Na3FeF6. A comprehensive understanding of charge-discharge processes and of the reactivity of the cycled electrode samples is achieved using a combination of electrochemical tests, synchrotron X-ray diffraction, 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, magnetometry, and 23Na/19F solid-state nuclear magnetic resonance (NMR) complemented with first principles calculations of NMR properties. We find that the primary performance limitation of the Na3FeF6 electrode is the sluggish kinetics of the conversion reaction, while the methods employed for materials synthesis and electrode preparation do not have a significant impact on the conversion efficiency and reversibility. Our work confirms that Na3FeF6 undergoes conversion into NaF and Fe(s) nanoparticles. The latter are found to be prone to oxidation prior to ex situ measurements, thus necessitating a robust analysis of the stable phases (here, NaF) formed upon conversion.

7.
J Am Chem Soc ; 139(13): 4835-4845, 2017 04 05.
Artigo em Inglês | MEDLINE | ID: mdl-28271898

RESUMO

Large-scale electric energy storage is fundamental to the use of renewable energy. Recently, research and development efforts on room-temperature sodium-ion batteries (NIBs) have been revitalized, as NIBs are considered promising, low-cost alternatives to the current Li-ion battery technology for large-scale applications. Herein, we introduce a novel layered oxide cathode material, Na0.78Ni0.23Mn0.69O2. This new compound provides a high reversible capacity of 138 mAh g-1 and an average potential of 3.25 V vs Na+/Na with a single smooth voltage profile. Its remarkable rate and cycling performances are attributed to the elimination of the P2-O2 phase transition upon cycling to 4.5 V. The first charge process yields an abnormally excess capacity, which has yet to be observed in other P2 layered oxides. Metal K-edge XANES results show that the major charge compensation at the metal site during Na-ion deintercalation is achieved via the oxidation of nickel (Ni2+) ions, whereas, to a large extent, manganese (Mn) ions remain in their Mn4+ state. Interestingly, electron energy loss spectroscopy (EELS) and soft X-ray absorption spectroscopy (sXAS) results reveal differences in electronic structures in the bulk and at the surface of electrochemically cycled particles. At the surface, transition metal ions (TM ions) are in a lower valence state than in the bulk, and the O K-edge prepeak disappears. On the basis of previous reports on related Li-excess LIB cathodes, it is proposed that part of the charge compensation mechanism during the first cycle takes place at the lattice oxygen site, resulting in a surface to bulk transition metal gradient. We believe that by optimizing and controlling oxygen activity, Na layered oxide materials with higher capacities can be designed.

8.
J Am Chem Soc ; 136(49): 17243-8, 2014 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-25397400

RESUMO

There is much interest in Na-ion batteries for grid storage because of the lower projected cost compared with Li-ion. Identifying Earth-abundant, low-cost, and safe materials that can function as intercalation cathodes in Na-ion batteries is an important challenge facing the field. Here we investigate such a material, ß-NaMnO2, with a different structure from that of NaMnO2 polymorphs and other compounds studied extensively in the past. It exhibits a high capacity (of ca. 190 mA h g(-1) at a rate of C/20), along with a good rate capability (142 mA h g(-1) at a rate of 2C) and a good capacity retention (100 mA h g(-1)after 100 Na extraction/insertion cycles at a rate of 2C). Powder XRD, HRTEM, and (23)Na NMR studies revealed that this compound exhibits a complex structure consisting of intergrown regions of α-NaMnO2 and ß-NaMnO2 domains. The collapse of the long-range structure at low Na content is expected to compromise the reversibility of the Na extraction and insertion processes occurring upon charge and discharge of the cathode material, respectively. Yet stable, reproducible, and reversible Na intercalation is observed.

9.
ACS Energy Lett ; 9(6): 3027-3035, 2024 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-38911531

RESUMO

Disordered rocksalt oxide (DRX) cathodes are promising candidates for next-generation Co- and Ni-free Li-ion batteries. While fluorine substitution for oxygen has been explored as an avenue to enhance their performance, the amount of fluorine incorporated into the DRX structure is particularly challenging to quantify and impedes our ability to relate fluorination to electrochemical performance. Herein, an experimental-computational method combining 7Li and 19F solid-state nuclear magnetic resonance, and ab initio cluster expansion Monte Carlo simulations, is developed to determine the composition of DRX oxyfluorides. Using this method, the synthesis of Mn- and Ti-containing DRX via standard high temperature sintering and microwave heating is optimized. Further, the upper fluorination limit attainable using each of these two synthesis routes is established for various Mn-rich DRX compounds. A comparison of their electrochemical performance reveals that the capacity and capacity retention mostly depend on the Mn content, while fluorination plays a secondary role.

10.
ACS Macro Lett ; 13(3): 341-347, 2024 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-38428022

RESUMO

The influence of the water content on ion and water transport mechanisms in polymer membranes under low to moderate hydration conditions remains poorly understood. In this study, we combine ion and water diffusivity (PFG-NMR) measurements with atomistic molecular dynamics simulations to better understand transport processes in hydrated salt-doped poly(ethylene glycol). Above the water percolation threshold, the experimental and simulated diffusivities are in good agreement with the free volume transport models. At low hydration levels, unlike dry systems, ion diffusion cannot be described by polymer segmental dynamics alone. We rationalize such observations by the interplay between ion-water and ion-polymer solvation of cations and between ion-water and cation-anion interactions for anions. Further, we demonstrate that a two-state model combining ion-water solvation and free volume transport can describe water dynamics across the entire hydration range of interest. Our findings provide a more encompassing analysis of ion and water transport in hydrated polyelectrolytes, specifically in the low hydration regime.

11.
Chem Mater ; 36(8): 3643-3654, 2024 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-38681087

RESUMO

Disordered rock salt oxides (DRX) have shown great promise as high-energy-density and sustainable Li-ion cathodes. While partial substitution of oxygen for fluorine in the rock salt framework has been related to increased capacity, lower charge-discharge hysteresis, and longer cycle life, fluorination is poorly characterized and controlled. This work presents a multistep method aimed at assessing fluorine incorporation into DRX cathodes, a challenging task due to the difficulty in distinguishing oxygen from fluorine using X-ray and neutron-based techniques and the presence of partially amorphous impurities in all DRX samples. This method is applied to "Li1.25Mn0.25Ti0.5O1.75F0.25" prepared by solid-state synthesis and reveals that the presence of LiF impurities in the sample and F content in the DRX phase is well below the target. Those results are used for compositional optimization, and a synthesis product with drastically reduced LiF content and a DRX stoichiometry close to the new target composition (Li1.25Mn0.225Ti0.525O1.85F0.15) is obtained, demonstrating the effectiveness of the strategy. The analytical method is also applied to "Li1.33Mn0.33Ti0.33O1.33F0.66" obtained via mechanochemical synthesis, and the results confirm that much higher fluorination levels can be achieved via ball-milling. Finally, a simple and rapid water washing procedure is developed to reduce the impurity content in as-prepared DRX samples: this procedure results in a ca. 10% increase in initial discharge capacity and a ca. 11% increase in capacity retention after 25 cycles for Li1.25Mn0.25Ti0.50O1.75F0.25. Overall, this work establishes new analytical and material processing methods that enable the development of more robust design rules for high-energy-density DRX cathodes.

12.
ACS Macro Lett ; 13(5): 638-643, 2024 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-38709178

RESUMO

Next-generation batteries demand solid polymer electrolytes (SPEs) with rapid ion transport and robust mechanical properties. However, many SPEs with liquid-like Li+ transport mechanisms suffer a fundamental trade-off between conductivity and strength. Dynamic polymer networks can improve bulk mechanics with minimal impact to segmental relaxation or ionic conductivity. This study demonstrates a system where a single polymer-bound ligand simultaneously dissociates Li+ and forms long-lived Ni2+ networks. The polymer comprises an ethylene oxide backbone and imidazole (Im) ligands, blended with Li+ and Ni2+ salts. Ni2+-Im dynamic cross-links result in the formation of a rubbery plateau resulting in, consequently, storage modulus improvement by a factor of 133× with the introduction of Ni2+ at rNi = 0.08, from 0.014 to 1.907 MPa. Even with Ni2+ loading, the high Li+ conductivity of 3.7 × 10-6 S/cm is retained at 90 °C. This work demonstrates that decoupling of ion transport and bulk mechanics can be readily achieved by the addition of multivalent metal cations to polymers with chelating ligands.

13.
Chem Mater ; 36(13): 6535-6546, 2024 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-39005535

RESUMO

In situ carbon dioxide (CO2) outgassing is a common phenomenon in lithium-ion batteries (LiBs), primarily due to parasitic side reactions at the cathode-electrolyte interface. However, little is known about the chemical origins of the in situ CO2 released from emerging Li-excess cation-disordered rock salt (DRX) cathodes. In this study, we selectively labeled various carbon sources with 13C in cathodes containing a representative DRX material, Li1.2Mn0.4Ti0.4O2 (LMTO), and performed differential electrochemical mass spectrometry (DEMS) during galvanostatic cycling in a carbonate-based electrolyte. When charging LMTO cathodes, electrolyte solvent (EC) decomposition is the dominant source of the CO2 outgassing. The amount of EC-originated CO2 is strongly correlated with the total surface area of carbon black in the electrode, revealing the critical role of electron-conducting carbon additives in the electrolyte degradation mechanisms. In addition, unusual bimodal CO2 evolution during the first cycle is found to originate from carbon black oxidation. Overall, the underlying chemical origin of in situ CO2 release during battery cycling is highly voltage- and cycle-dependent. This work further provides insights into improving the stability of DRX cathodes in LiBs and is envisioned to help guide future relevant material design to mitigate parasitic reactions in DRX-based batteries.

14.
Nat Commun ; 15(1): 2991, 2024 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-38582753

RESUMO

All-solid-state batteries using Si as the anode have shown promising performance without continual solid-electrolyte interface (SEI) growth. However, the first cycle irreversible capacity loss yields low initial Coulombic efficiency (ICE) of Si, limiting the energy density. To address this, we adopt a prelithiation strategy to increase ICE and conductivity of all-solid-state Si cells. A significant increase in ICE is observed for Li1Si anode paired with a lithium cobalt oxide (LCO) cathode. Additionally, a comparison with lithium nickel manganese cobalt oxide (NCM) reveals that performance improvements with Si prelithiation is only applicable for full cells dominated by high anode irreversibility. With this prelithiation strategy, 15% improvement in capacity retention is achieved after 1000 cycles compared to a pure Si. With Li1Si, a high areal capacity of up to 10 mAh cm-2 is attained using a dry-processed LCO cathode film, suggesting that the prelithiation method may be suitable for high-loading next-generation all-solid-state batteries.

15.
Adv Mater ; 36(24): e2311559, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38520395

RESUMO

It is shown that structural disorder-in the form of anisotropic, picoscale atomic displacements-modulates the refractive index tensor and results in the giant optical anisotropy observed in BaTiS3, a quasi-1D hexagonal chalcogenide. Single-crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS6 chains along the c-axis, and threefold degenerate Ti displacements in the a-b plane. 47/49Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from a low symmetry local environment around Ti atoms. Scanning transmission electron microscopy is used to directly observe the globally disordered Ti a-b plane displacements and find them to be ordered locally over a few unit cells. First-principles calculations show that the Ti a-b plane displacements selectively reduce the refractive index along the ab-plane, while having minimal impact on the refractive index along the chain direction, thus resulting in a giant enhancement in the optical anisotropy. By showing a strong connection between structural disorder with picoscale displacements and the optical response in BaTiS3, this study opens a pathway for designing optical materials with high refractive index and functionalities such as large optical anisotropy and nonlinearity.

16.
J Chem Phys ; 138(11): 114201, 2013 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-23534632

RESUMO

The nuclear magnetic resonance of paramagnetic solids is usually characterized by the presence of large chemical shifts and shift anisotropies due to hyperfine interactions. Frequently the resulting spectra cover a frequency range of several megahertz, which is greater than the bandwidth of commercially available radio-frequency (RF) probes, making it impossible to acquire the whole spectrum in a single experiment. In these cases it common to record a series of spectra, in which the probe is tuned to a different frequency for each, and then sum the results to give the "true" spectrum. While this method is very widely used on static samples, the application of frequency stepping under magic-angle spinning (MAS) is less common, owing to the increased complexity of the spin dynamics when describing the interplay of the RF irradiation with the mechanical rotation of the shift tensor. In this paper, we present a theoretical description, based on the jolting frame formalism of Caravatti et al. [J. Magn. Reson. 55, 88 (1983)], for describing the spin dynamics of a powder sample under MAS when subjected to a selective pulse of low RF-field amplitude. The formalism is used to describe the frequency stepping method under MAS, and under what circumstances the true spectrum is reproduced. We also present an experimental validation of the methodology under ultra-fast MAS with the paramagnetic materials LiMnPO4 and TbCsDPA.

17.
Chem Mater ; 35(9): 3614-3627, 2023 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-37181671

RESUMO

Weberite-type sodium transition metal fluorides (Na2M2+M'3+F7) have emerged as potential high-performance sodium intercalation cathodes, with predicted energy densities in the 600-800 W h/kg range and fast Na-ion transport. One of the few weberites that have been electrochemically tested is Na2Fe2F7, yet inconsistencies in its reported structure and electrochemical properties have hampered the establishment of clear structure-property relationships. In this study, we reconcile structural characteristics and electrochemical behavior using a combined experimental-computational approach. First-principles calculations reveal the inherent metastability of weberite-type phases, the close energetics of several Na2Fe2F7 weberite polymorphs, and their predicted (de)intercalation behavior. We find that the as-prepared Na2Fe2F7 samples inevitably contain a mixture of polymorphs, with local probes such as solid-state nuclear magnetic resonance (NMR) and Mössbauer spectroscopy providing unique insights into the distribution of Na and Fe local environments. Polymorphic Na2Fe2F7 exhibits a respectable initial capacity yet steady capacity fade, a consequence of the transformation of the Na2Fe2F7 weberite phases to the more stable perovskite-type NaFeF3 phase upon cycling, as revealed by ex situ synchrotron X-ray diffraction and solid-state NMR. Overall, these findings highlight the need for greater control over weberite polymorphism and phase stability through compositional tuning and synthesis optimization.

18.
Chem Mater ; 35(16): 6364-6373, 2023 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-37637013

RESUMO

The development of new high-performing battery materials is critical for meeting the energy storage requirements of portable electronics and electrified transportation applications. Owing to their exceptionally high rate capabilities, high volumetric capacities, and long cycle lives, Wadsley-Roth compounds are promising anode materials for fast-charging and high-power lithium-ion batteries. Here, we present a study of the Wadsley-Roth-derived NaNb13O33 phase and examine its structure and lithium insertion behavior. Structural insights from combined neutron and synchrotron diffraction as well as solid-state nuclear magnetic resonance (NMR) are presented. Solid-state NMR, in conjunction with neutron diffraction, reveals the presence of sodium ions in perovskite A-site-like block interior sites as well as square-planar block corner sites. Through combined experimental and computational studies, the high rate performance of this anode material is demonstrated and rationalized. A gravimetric capacity of 225 mA h g-1, indicating multielectron redox of Nb, is accessible at slow cycling rates. At a high rate, 100 mA h g-1 of capacity is accessible in 3 min for micrometer-scale particles. Bond-valence mapping suggests that this high-rate performance stems from fast multichannel lithium diffusion involving octahedral block interior sites. Differential capacity analysis is used to identify optimal cycling rates for long-term performance, and an 80% capacity retention is achieved over 600 cycles with 30 min charging and discharging intervals. These initial results place NaNb13O33 within the ranks of promising new high-rate lithium-ion battery anode materials that warrant further research.

19.
ACS Appl Mater Interfaces ; 15(15): 18747-18762, 2023 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-37014990

RESUMO

Lithium-excess, cation-disordered rocksalt (DRX) materials have been subject to intense scrutiny and development in recent years as potential cathode materials for Li-ion batteries. Despite their compositional flexibility and high initial capacity, they suffer from poorly understood parasitic degradation reactions at the cathode-electrolyte interface. These interfacial degradation reactions deteriorate both the DRX material and electrolyte, ultimately leading to capacity fade and voltage hysteresis during cycling. In this work, differential electrochemical mass spectrometry (DEMS) and titration mass spectrometry are combined to quantify the extent of bulk redox and surface degradation reactions for a set of Mn2+/4+-based DRX oxyfluorides during initial cycling with a high-voltage charging cutoff (4.8 V vs Li/Li+). Increasing the fluorine content from 7.5 to 33.75% is shown to diminish oxygen redox and suppresses high-voltage O2 evolution from the DRX surface. Additionally, electrolyte degradation processes resulting in the formation of both gaseous species and electrolyte-soluble protic species are observed. Subsequently, DEMS is paired with a fluoride-scavenging additive to demonstrate that increasing fluorine content leads to increased dissolution of fluorine from the DRX material into the electrolyte. Finally, a suite of ex situ spectroscopy techniques (X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, and solid-state nuclear magnetic resonance spectroscopy) are employed to study the change in DRX composition during charging, revealing the dissolution of manganese and fluorine from the DRX material at high voltages. This work provides insight into the degradation processes occurring at the DRX-electrolyte interface and points toward potential routes of interfacial stabilization.

20.
J Am Chem Soc ; 134(41): 17178-85, 2012 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-23004936

RESUMO

Substituted lithium transition-metal (TM) phosphate LiFe(x)Mn(1-x)PO(4) materials with olivine-type structures are among the most promising next generation lithium ion battery cathodes. However, a complete atomic-level description of the structure of such phases is not yet available. Here, a combined experimental and theoretical approach to the detailed assignment of the (31)P NMR spectra of the LiFe(x)Mn(1-x)PO(4) (x = 0, 0.25, 0.5, 0.75, 1) pure and mixed TM phosphates is developed and applied. Key to the present work is the development of a new NMR experiment enabling the characterization of complex paramagnetic materials via the complete separation of the individual isotropic chemical shifts, along with solid-state hybrid DFT calculations providing the separate hyperfine contributions of all distinct Mn-O-P and Fe-O-P bond pathways. The NMR experiment, referred to as aMAT, makes use of short high-powered adiabatic pulses (SHAPs), which can achieve 100% inversion over a range of isotropic shifts on the order of 1 MHz and with anisotropies greater than 100 kHz. In addition to complete spectral assignments of the mixed phases, the present study provides a detailed insight into the differences in electronic structure driving the variations in hyperfine parameters across the range of materials. A simple model delimiting the effects of distortions due to Mn/Fe substitution is also proposed and applied. The combined approach has clear future applications to TM-bearing battery cathode phases in particular and for the understanding of complex paramagnetic phases in general.


Assuntos
Lítio/química , Fosfatos/química , Teoria Quântica , Elementos de Transição/química , Espectroscopia de Ressonância Magnética , Isótopos de Fósforo
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