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Sulfurized polyacrylonitrile (SPAN) is a promising high-capacity cathode material. In this work, we use spatially resolved X-ray absorption spectroscopy combined with X-ray fluorescence (XRF) microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy to examine the structural transformation of SPAN and the critical role of a robust cathode-electrolyte interface (CEI) on the electrode. LiSx species forms during the cycling of SPAN. However, in carbonate-based electrolytes and ether-based electrolytes with LiNO3 additives, these species are well protected by the CEI and do not dissolve into the electrolytes. In contrast, in an ether-based electrolyte without the LiNO3 additive, LiSx species dissolve into the electrolyte, resulting in the shuttle effect and capacity loss. Examination of the Li anode by XRF and SEM reveals dense spherical Li morphology in ether-based electrolytes, but sulfur is present in the absence of the LiNO3 additive. In contrast, porous dendritic Li is found in the carbonate electrolyte. These analyses established that an ether-based electrolyte with LiNO3 is a superior choice that enables stable cycling of both electrodes. Based on these insights, we successfully demonstrate the stable cycling of high areal loading SPAN cathode (>6.5 mA h cm-2) with lean electrolyte amounts, showing promising Li∥SPAN cell performance under practical conditions.

A novel electrolyte system with an excellent low-temperature performance for lithium-ion batteries (LIBs) has been developed and studied. It was discovered for the first time, in this work, that when isoxazole (IZ) was used as the main solvent, the ionic conductivity of the electrolyte for LIBs is more than doubled in a temperature range between -20 and 20 °C compared to the baseline electrolyte using ethylene carbonate-ethyl methyl carbonate as solvents. To solve the problem of solvent co-intercalation into the graphite anode and/or electrolyte decomposition, the lithium difluoro(oxalato)borate (LiDFOB) salt and fluoroethylene carbonate (FEC) additive were used to form a stable solid electrolyte interphase on the surface of the graphite anode. Benefitting from the high ionic conductivity at low temperature, cells using a new electrolyte with 1 M LiDFOB in FEC/IZ (1:10, vol %) solvents demonstrated a very high reversible capacity of 187.5 mAh g-1 at -20 °C, while the baseline electrolyte only delivered a reversible capacity of 23.1 mAh g-1.

The development of phase change material (PCM) for battery thermal management poses key limitations on its reliability caused by leakage and shape deformation under high temperature. In this work, ...

Metal anodes represent as a prime choice for the coming generation rechargeable batteries with high energy density. However, daunting challenges including electrode volume variation and inevitable side reactions preclude them from becoming a viable technology. Here, a facile replacement reaction was employed to fabricate a three-dimensional (3D) interdigitated metal/solid electrolyte composite electrode, which not only provides a stable host structure for buffering the volume change within the composite but also prevents side reactions by avoiding the direct contact between active metal and liquid electrolyte. As a proof-of-concept demonstration, a 3D interdigitated zinc (Zn) metal/solid electrolyte architecture was fabricated via a galvanic replacement reaction between Zn metal foil and indium (In) chloride solution followed by electrochemical activation, featuring the interdigitation between metallic Zn and amorphous indium hydroxide sulfate (IHS) with high Zn2+ conductivity (56.9 ± 1.8 mS cm-1), large Zn2+ transference number (0.55), and high electronic resistivity [(2.08 ± 0.01) × 103 Ω cm]. The as-designed Zn/IHS electrode sustained stable electrochemical Zn plating/stripping over 700 cycles with a record-low overpotential of 8 mV at 1 mA cm-2 and 0.5 mAh cm-2. More impressively, it displayed cycle-stable performance with low overpotential of 10 mV under ultrahigh current density and areal capacity (20 mA cm-2, 20 mAh cm-2), which outperformed all the reported Zn metal electrodes in mild aqueous electrolyte. The fabrication of interdigitated metal/solid electrolyte was generalized to other metal pairs, including Zn/Sn and Zn/Co, which provide inspiration for next-generation Zn metal batteries with high energy density and reversibility.

It is highly desirable to realize high-energy-density lithium-ion batteries consisting of nickel-rich layered oxide cathodes (Ni-rich NMC) and Si-based anodes. A critical challenge for Ni-rich NMC ...

Recently, intrinsically conductive metal-organic frameworks (MOFs) have demonstrated promising performance in fast-charging energy storage applications and may outperform some current electrode materials (e.g., porous carbons) for supercapacitors in terms of both gravimetric and volumetric capacitance. In this report, we examine the mechanism of high capacitance in a nickel hexaaminobenzene-based MOF (NiHAB). Using a combination of in situ Raman and X-ray absorption spectroscopies, as well as detailed electrochemical studies in a series of aqueous electrolytes, we demonstrate that the charge storage mechanism is, in fact, a pH-dependent surface pseudocapacitance, and unlike typical inorganic systems, where transition metals change oxidation state during charge/discharge cycles, NiHAB redox activity is ligand-centered.

Higher energy densities in rechargeable batteries can be achieved using thicker cathode films, though this is a challenging endeavor since the electrochemical performance of thick electrodes is sub...

LiNi0.8Co0.15Al0.05O2 (NCA) has been proven to be a good cathode material for lithium-ion batteries (LIBs), especially in electric vehicle applications. However, further elevating energy density of...

Sustainable water-splitting hydrogen production has long been considered one of the most promising energy conversion technologies, but enormous challenges remain: for instance, water electrolysis suffers from high overpotential and over energy consumption under neutral pH conditions. Here, taking advantage of the memory effect of layered double hydroxide (LDH), we report an energy-efficient neutral water electrolyzer material based on LDH with multiple vacancy defects. Benefiting from the improved electrical conductivity, larger electrochemical surface area (ECSA), and faster charge transfer, the NiFe LDH with O, Ni, and Fe vacancies exhibits a low overpotential of 87 mV at 10 mA/cm2 for hydrogen evolution reaction (HER) in a pH 7 buffer electrolyte. Impressively, the as-fabricated vacancy-containing NiFe LDH (v-NiFe LDH) splits water with a current density of 10 mA/cm2 at ∼1.60 V in a two-electrode device, outperforming most other water-splitting catalysts in neutral media. Such an electrolyzer setup cou...

Scanning electrochemical microscopy (SECM) was applied for in situ visualization of solid electrolyte interface (SEI) evolution on the TiO2 anode in a concentrated aqueous electrolyte during cyclin...

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....

Layered δ-MnO2 (birnessites) are ubiquitous in nature and have also been reported to work as promising water oxidation catalysts or rechargeable alkali-ion battery cathodes when fabricated under appropriate conditions. Although tremendous effort has been spent on resolving the structure of natural/synthetic layered δ-MnO2 in the last few decades, no conclusive result has been reached. In this Article, we report an environmentally friendly route to synthesizing homogeneous Cu-rich layered δ-MnO2 nanoflowers in large scale. The local and average structure of synthetic Cu-rich layered δ-MnO2 has been successfully resolved from combined Mn/Cu K-edge extended X-ray fine structure spectroscopy and X-ray and neutron total scattering analysis. It is found that appreciable amounts (∼8%) of Mn vacancies are present in the MnO2 layer and Cu2+ occupies the interlayer sites above/below the vacant Mn sites. Effective hydrogen bonding among the interlayer water molecules and adjacent layer O ions has also been observed ...

Li3VP3O9N was for the first time synthesized from its sodium analogue Na3VP3O9N using a solid–solid Li+/Na+ ion-exchange method. This lithium variant of nitridophosphate is found to possess similar crystal structure (space group P213) as its sodium analogue Na3VP3O9N (a = 9.4507(1) A) but with much smaller lattice parameter (a = 9.1237(1) A). The crystal structure of Li3VP3O9N was solved and refined using combined synchrotron X-ray and time-of-flight neutron powder diffraction data, allowing the three distinct lithium-ion sites to be identified. A lithium bond valence sum difference map calculation suggests the existence of isotropic three-dimensional lithium-ion-conducting pathways with a minimum valence threshold |ΔV| of 0.02. Li3VP3O9N behaves as a promising reversible cathode material for rechargeable lithium-ion batteries with an average V3+/V4+ redox potential of 3.8 V (vs Li+/Li). Both cyclic voltammetry tests and chemical delithiation (using NO2BF4) indicate it is possible to partially remove the ...

The rechargeable lithium-ion battery (LIB) is the most promising energy storage system to power electric vehicles with high energy density and long cycling life. However, in order to meet customers' demands for fast charging, the power performances of current LIBs need to be improved. From the cathode aspect, layer-structured cathode materials are widely used in today's market and will continue to play important roles in the near future. The high rate capability of layered cathode materials during charging and discharging is critical to the power performance of the whole cell and the thermal stability is closely related to the safety issues. Therefore, the in-depth understanding of structural changes of layered cathode materials during high rate charging/discharging and the thermal stability during heating are essential in developing new materials and improving current materials. Since structural changes take place from the atomic level to the whole electrode level, combination of characterization techniques covering multilength scales is quite important. In many cases, this means using comprehensive tools involving diffraction, spectroscopy, and imaging to differentiate the surface from the bulk and to obtain structural/chemical information with different levels of spatial resolution. For example, hard X-ray spectroscopy can yield the bulk information and soft X-ray spectroscopy can give the surface information; X-ray based imaging techniques can obtain spatial resolution of tens of nanometers, and electron-based microcopy can go to angstroms. In addition to challenges associated with different spatial resolution, the dynamic nature of structural changes during high rate cycling and heating requires characterization tools to have the capability of collecting high quality data in a time-resolved fashion. Thanks to the advancement in synchrotron based techniques and high-resolution electron microscopy, high temporal and spatial resolutions can now be achieved. In this Account, we focus on the recent works studying kinetic and thermal properties of layer-structured cathode materials, especially the structural changes during high rate cycling and the thermal stability during heating. Advanced characterization techniques relating to the rate capability and thermal stability will be introduced. The different structure evolution behavior of cathode materials cycled at high rate will be compared with that cycled at low rate. Different response of individual transition metals and the inhomogeneity in chemical distribution will be discussed. For the thermal stability, the relationship between structural changes and oxygen release will be emphatically pointed out. In all these studies being reviewed, advanced characterization techniques are critically applied to reveal complexities at multiscale in layer-structured cathode materials.

Li2Ru0.5Mn0.5O3, a high capacity lithium-rich layered cathode material for lithium-ion batteries, was subject to comprehensive diagnostic studies, including in situ/ex situ X-ray diffraction, X-ray absorption spectroscopy (XAS), pair distribution function, and high resolution scanning transmission electron microscopy analysis, to understand the correlations between transition-metal chemistry, structure, and lithium storage electrochemical behavior. Ru–Ru dimers were identified in the as-prepared sample and found to be preserved upon prolonged cycling. Presence of these dimers, which are likely caused by the delocalized nature of 4d electrons, is found to favor the stabilization of the structure in a layered phase. The in situ XAS results confirm the participation of oxygen redox into the charge compensation at high charge voltage, and the great flexibility of the covalent bond between Ru and O may provide great reversibility of the global structure despite the significant local distortion around Ru. In co...

Motivated by predictions made using a bond valence sum difference map (BVS-DM) analysis, the novel Li-ion conductor Li2Mg2P3O9N was synthesized by ion exchange from a Na2Mg2P3O9N precursor. Impedance spectroscopy measurements indicate that Li2Mg2P3O9N has a room temperature Li-ion conductivity of about 10–6 S/cm (comparable to LiPON), which is 6 orders of magnitude higher than the extrapolated Na-ion conductivity of Na2Mg2P3O9N at this temperature. The structure of Li2Mg2P3O9N was determined from ex situ synchrotron and time-of-flight neutron diffraction data to retain the P213 space group, though with a cubic lattice parameter of a = 9.11176(8) A that is significantly smaller than the a = 9.2439(1) A of Na2Mg2P3O9N. The two Li-ion sites are found to be very substantially displaced (∼0.5 A) relative to the analogous Na sites in the precursor phase. The non-molten salt ion exchange method used to prepare Li2Mg2P3O9N produces a minimal background in powder diffraction experiments, and was therefore exploite...

For designing new battery systems with higher energy density and longer cycle life, it is important to understand the degradation mechanism of the electrode material, especially at the individual particle level. Using in situ transmission X-ray microscopy (TXM) coupled to a pouch cell setup, the inhomogeneous Li distribution as well as the formation, population, and evolution of inactive domains in a single LiCoO2 particle were visualized as it was cycled for many times. It is found that the percentage of the particle that fully recovered to the pristine state is strongly related to the cycling rate. Interestingly, we also observed the evolution of the inactive region within the particle during long-term cycling. The relationship between morphological degradation and chemical inhomogeneity, including the formation of unanticipated Co metal phase, is also observed. Our work highlights the capability of in situ TXM for studying the degradation mechanism of materials in LIBs.

The phase transition, charge compensation, and local chemical environment of Ni in LiNiO2 were investigated to understand the degradation mechanism. The electrode was subjected to a variety of bulk and surface-sensitive characterization techniques under different charge–discharge cycling conditions. We observed the phase transition from the original hexagonal H1 phase to another two hexagonal phases (H2 and H3) upon Li deintercalation. Moreover, the gradual loss of H3-phase features was revealed during the repeated charges. The reduction in Ni redox activity occurred at both the charge and the discharge states, and it appeared both in the bulk and at the surface over the extended cycles. The degradation of crystal structure significantly contributes to the reduction of Ni redox activity, which in turn causes the cycling performance decay of LiNiO2.

The mechanism of the sulfur cathode in Li–S batteries has been proposed. It was revealed by the real-time quantitative determination of polysulfide species and elemental sulfur by means of high-performance liquid chromatography in the course of the discharge and recharge of a Li–S battery. A three-step reduction mechanism including two chemical equilibrium reactions was proposed for the sulfur cathode discharge. The typical two-plateau discharge curve for the sulfur cathode can be explained. A two-step oxidation mechanism for Li2S and Li2S2 with a single chemical equilibrium among soluble polysulfide ions was proposed. The chemical equilibrium among S52–, S62–, S72–, and S82– throughout the entire oxidation process resulted for a single flat recharge curve in Li–S batteries.

With the correlation between Li+ solvation and interphasial chemistry on anodes firmly established in Li-ion batteries, the effect of cation–solvent interaction has gone beyond bulk thermodynamic and transport properties and become an essential element that determines the reversibility of electrochemistry and kinetics of Li-ion intercalation chemistries. As of now, most studies are dedicated to the solvation of Li+, and the solvation of anions in carbonate-based electrolytes and its possible effect on the electrochemical stability of such electrolytes remains little understood. As a mirror effort to prior Li+ solvation studies, this work focuses on the interactions between carbonate-based solvents and two anions (hexafluorophosphate, PF6–, and tetrafluoroborate, BF4–) that are most frequently used in Li-ion batteries. The possible correlation between such interaction and the interphasial chemistry on cathode surface is also explored.

The solvation of Li+ with 11 nonaqueous solvents commonly used as electrolytes for lithium batteries was studied. The solvation preferences of different solvents were compared by means of electrospray mass spectrometry and collision-induced dissociation. The relative strength of the solvent for the solvation of Li+ was determined. The Lewis acidity of the solvated Li+ cations was determined by the preferential solvation of the solvent in the solvation shell. The kinetics of the catalytic disproportionation of the O2•- depends on the relative Lewis acidity of the solvated Li+ ion. The impact of the solvated Li+ cation on the O2 redox reaction was also investigated.

Li1.2Cr0.4Mn0.4O2 (0.4LiCrO2·0.4Li2MnO3) is an interesting intercalation-type cathode material with high theoretical capacity of 387 mAh g–1 based on multiple-electron transfer of Cr3+/Cr6+. In this work, it has been demonstrated that the reversible Cr3+/Cr6+ redox reaction can only be realized in a wide voltage range between 1.0 and 4.8 V. This is mainly due to large polarization during the discharge. The reversible migration of the Cr ions between octahedral and tetrahedral sites leads to large extent of cation mixing between lithium and transition metal layers, which does not affect the lithium storage capacity and stabilize the structure. In addition, a distorted spinel phase (Li3M2O4) is identified in the deeply discharged sample (1.0 V, Li1.5Cr0.4Mn0.4O2). The above results can explain the high reversible capacity and high structural stability achieved on Li1.2Cr0.4Mn0.4O2. These new findings will provide further in depth understanding on multielectron transfer and local structure stabilization mech...

Two-dimensional (2D) heteronanosheets are currently the focus of intense study due to the unique properties that emerge from the interplay between two low-dimensional nanomaterials with different properties. However, the properties and new phenomena based on the two 2D heteronanosheets interacting in a 3D hierarchical architecture have yet to be explored. Here, we unveil the surface redox charge storage mechanism of surface-exposed WS2 nanosheets assembled in a 3D hierarchical heterostructure using in situ synchrotron X-ray absorption and Raman spectroscopic methods. The surface dominating redox charge storage of WS2 is manifested in a highly reversible and ultrafast capacitive fashion due to the interaction of heteronanosheets and the 3D connectivity of the hierarchical structure. In contrast, compositionally identical 2D WS2 structures fail to provide a fast and high capacitance with different modes of lattice vibration. The distinctive surface capacitive behavior of 3D hierarchically structured heteronanosheets is associated with rapid proton accommodation into the in-plane W-S lattice (with the softening of the E2g bands), the reversible redox transition of the surface-exposed intralayers residing in the electrochemically active 1T phase of WS2 (with the reversible change in the interatomic distance and peak intensity of W-W bonds), and the change in the oxidation state during the proton insertion/deinsertion process. This proposed mechanism agrees with the dramatic improvement in the capacitive performance of the two heteronanosheets coupled in the hierarchical structure.

Application of high-voltage spinel LiNi0.5Mn1.5O4 cathode material is the closest and the most realistic approach to meeting the midterm goal of lithium-ion batteries for electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs). However, this application has been hampered by long-standing issues, such as capacity degradation and poor first-cycle Coulombic efficiency of LiNi0.5Mn1.5O4 cathode material. Although it is well-known that the structure of LiNi0.5Mn1.5O4 into which Li ions are reversibly intercalated plays a critical role in the above issues, performance degradation related to structural changes, particularly in the first cycle, are not fully understood. Here, we report detailed investigations of local atomic-level and average structure of LiNi0.5Mn1.5O4 during first cycle (3.5–4.9 V) at room temperature. We observed two types of local atomic-level migration of transition metals (TM) ions in the cathode of a well-prepared LiNi0.5Mn1.5O4//Li half-cell during first charge via an aberrati...

High-energy and high-power Li-ion batteries have been intensively pursued as power sources in electronic vehicles and renewable energy storage systems in smart grids. With this purpose, developing high-performance cathode materials is urgently needed. Here we report an easy and versatile strategy to fabricate high-rate and cycling-stable hierarchical sphered cathode Li(1.2)Ni(0.13)Mn(0.54)Co(0.13)O2, by using an ionic interfusion method. The sphere-shaped hierarchical cathode is assembled with primary nanoplates with enhanced growth of nanocrystal planes in favor of Li(+) intercalation/deintercalation, such as (010), (100), and (110) planes. This material with such unique structural features exhibits outstanding rate capability, cyclability, and high discharge capacities, achieving around 70% (175 mAh g(-1)) of the capacity at 0.1 C rate within about 2.1 min of ultrafast charging. Such cathode is feasible to construct high-energy and high-power Li-ion batteries.

Thermal stability of charged LiNixMnyCozO2 (NMC, with x + y + z = 1, x:y:z = 4:3:3 (NMC433), 5:3:2 (NMC532), 6:2:2 (NMC622), and 8:1:1 (NMC811)) cathode materials is systematically studied using combined in situ time-resolved X-ray diffraction and mass spectroscopy (TR-XRD/MS) techniques upon heating up to 600 °C. The TR-XRD/MS results indicate that the content of Ni, Co, and Mn significantly affects both the structural changes and the oxygen release features during heating: the more Ni and less Co and Mn, the lower the onset temperature of the phase transition (i.e., thermal decomposition) and the larger amount of oxygen release. Interestingly, the NMC532 seems to be the optimized composition to maintain a reasonably good thermal stability, comparable to the low-nickel-content materials (e.g., NMC333 and NMC433), while having a high capacity close to the high-nickel-content materials (e.g., NMC811 and NMC622). The origin of the thermal decomposition of NMC cathode materials was elucidated by the changes ...

Sodium-ion batteries utilize various electrode materials derived from lithium batteries. However, the different characteristics inherent in sodium may cause unexpected cell reactions and battery performance. Thus, identifying the reactive discrepancy between sodiation and lithiation is essential for fundamental understanding and practical engineering of battery materials. Here we reveal a heterogeneous sodiation mechanism of iron fluoride (FeF2) nanoparticle electrodes by combining in situ/ex situ microscopy and spectroscopy techniques. In contrast to direct one-step conversion reaction with lithium, the sodiation of FeF2 proceeds via a regular conversion on the surface and a disproportionation reaction in the core, generating a composite structure of 1-4 nm ultrafine Fe nanocrystallites (further fused into conductive frameworks) mixed with an unexpected Na3FeF6 phase and a NaF phase in the shell. These findings demonstrate a core-shell reaction mode of the sodiation process and shed light on the mechanistic understanding extended to generic electrode materials for both Li- and Na-ion batteries.

Lithium iron borate (LiFeBO3) has a high theoretical specific capacity (220 mAh/g), which is competitive with leading cathode candidates for next-generation lithium-ion batteries. However, a major factor making it difficult to fully access this capacity is a competing oxidative process that leads to degradation of the LiFeBO3 structure. The pristine, delithiated, and degraded phases of LiFeBO3 share a common framework with a cell volume that varies by less than 2%, making it difficult to resolve the nature of the delithiation and degradation mechanisms by conventional X-ray powder diffraction studies. A comprehensive study of the structural evolution of LiFeBO3 during (de)lithiation and degradation was therefore carried out using a wide array of bulk and local structural characterization techniques, both in situ and ex situ, with complementary electrochemical studies. Delithiation of LiFeBO3 starts with the production of LitFeBO3 (t ≈ 0.5) through a two-phase reaction, and the subsequent delithiation of this phase to form Lit-xFeBO3 (x0.5). However, the large overpotential needed to drive the initial two-phase delithiation reaction results in the simultaneous observation of further delithiated solid-solution products of Lit-xFeBO3 under normal conditions of electrochemical cycling. The degradation of LiFeBO3 also results in oxidation to produce a Li-deficient phase D-LidFeBO3 (d ≈ 0.5, based on the observed Fe valence of ∼2.5+). However, it is shown through synchrotron X-ray diffraction, neutron diffraction, and high-resolution transmission electron microscopy studies that the degradation process results in an irreversible disordering of Fe onto the Li site, resulting in the formation of a distinct degraded phase, which cannot be electrochemically converted back to LiFeBO3 at room temperature. The Li-containing degraded phase cannot be fully delithiated, but it can reversibly cycle Li (D-Lid+yFeBO3) at a thermodynamic potential of ∼1.8 V that is substantially reduced relative to the pristine phase (∼2.8 V).

It is demonstrated that Na ions are mobile at room temperature in the nitridophosphate compound Na3TiP3O9N, with a diffusion pathway that is calculated to be fully three-dimensional and isotropic. When used as a cathode in Na-ion batteries, Na3TiP3O9N has an average voltage of 2.7 V vs Na+/Na and cycles with good reversibility through a mechanism that appears to be a single solid solution process without any intermediate plateaus. X-ray and neutron diffraction studies as well as first-principles calculations indicate that the volume change that occurs on Na-ion removal is only about 0.5%, a remarkably small volume change given the large ionic radius of Na+. Rietveld refinements indicate that the Na1 site is selectively depopulated during sodium removal. Furthermore, the refined displacement parameters support theoretical predictions that the lowest energy diffusion pathway incorporates the Na1 and Na3 sites while the Na2 site is relatively inaccessible. The measured room temperature ionic conductivity of ...

Layer-structured xLi2MnO3·(1 – x)LiMO2 are promising cathode materials for high energy-density Li-ion batteries because they deliver high capacities due to the stabilizing effect of Li2MnO3. However, the inherent disadvantages of Li2MnO3 make these materials suffer from drawbacks such as fast energy-density decay, poor rate performance and safety hazard. In this paper, we propose to replace Li2MnO3 with Li2MoO3 for constructing novel Li-rich cathode materials and evaluate its feasibility. Comprehensive studies by X-ray diffraction, X-ray absorption spectroscopy, and spherical-aberration-corrected scanning transmission electron microscopy clarify its lithium extraction/insertion mechanism and shows that the Mo4+/Mo6+ redox couple in Li2MoO3 can accomplish the task of charge compensation upon Li removal. Other properties of Li2MoO3 such as the nearly reversible Mo-ion migration to/from the Li vacancies, absence of oxygen evolution, and reversible phase transition during initial (de)lithiation indicate that ...

We explore structural changes of the carbon in MnO2/reduced graphene oxide (RGO) hybrid materials prepared by the direct redox reaction between carbon and permanganate ions (MnO4–) to reach better understanding for the effects of carbon corrosion on carbon loss and its bonding nature during the hybrid material synthesis. In particular, we carried out near-edge X-ray absorption fine structure spectroscopy at the C K-edge (284.2 eV) to show the changes in the electronic structure of RGO. Significantly, the redox reaction between carbon and MnO4– causes both quantitative carbon loss and electronic structural changes upon MnO2 deposition. Such disruptions of carbon bonding have a detrimental effect on the initial electrical properties of the RGO and thus lead to a significant decrease in electrical conductivity. Electrochemical measurements of the MnO2/reduced graphene oxide hybrid materials using a cavity microelectrode revealed unfavorable electrochemical properties that were mainly due to the poor electric...

The powdered crystalline samples of nominal composition Li1.07Mn1.93O4-δ have been investigated by transmission electron microscopy (TEM) combined with X-ray powder diffraction (XRD) at room temperature. As suggested by the TEM observation, the dominant phase of the particles is a cubic spinel Li1+αMn2-αO4-δ with space group Fd3̅m. A monoclinic Li2MnO3 phase with C2/m space group was also identified. Furthermore, the occurrence of nanoscale rotational twinning domains in Li2MnO3 with 120° rotation angles, stacked along the [103]m/[111]c ("m" and "c" represent the monoclinic and cubic descriptions, respectively) axis was also observed. These nanoscale rotational twining domains are responsible for the pseudo-3-fold axis and their formation is supported by the superstructure reflections in selected-area electron-diffraction (SAED) patterns. Similar patterns were reported in the literature but may have been misinterpreted without the consideration of such domains. Consistent with the TEM observation, the XRD results reveal the increasing percentage of monoclinic Li2MnO3 with increasing annealing time, associated with more oxygen vacancies. In addition, the electron beam irradiation during TEM studies may cause the nucleation of nanoscale cubic spinel Li-Mn-O crystallites on the monoclinic Li2MnO3 grains. These results provide the detailed structural information about the Li1.07Mn1.93O4-δ samples and advance the understanding of corresponding electrochemical properties of this material as well as other layer structured cathode materials for lithium-ion batteries.

The thermal stability of charged cathode materials is one of the critical properties affecting the safety characteristics of lithium-ion batteries. New findings on the thermal-stability and thermal-decomposition pathways related to the oxygen release are discovered for the high-voltage spinel LixNi0.5Mn1.5O4 (LNMO) with ordered (o-) and disordered (d-) structures at the fully delithiated (charged) state using a combination of in situ time-resolved X-ray diffraction (TR-XRD) coupled with mass spectroscopy (MS) and X-ray absorption spectroscopy (XAS) during heating. Both o- and d- LixNi0.5Mn1.5O4, at their fully charged states, start oxygen-releasing structural changes at temperatures below 300 °C, which is in sharp contrast to the good thermal stability of the 4V-spinel LixMn2O4 with no oxygen being released up to 375 °C. This is mainly caused by the presence of Ni4+ in LNMO, which undergoes dramatic reduction during the thermal decomposition. In addition, charged o-LNMO shows better thermal stability than...

A novel characterization technique using the combination of chemical sodiation and synchrotron based in situ X-ray diffraction (XRD) has been detailed illustrated. The power of this novel technique was demonstrated in elucidating the structure evolution of Li4Ti5O12 upon sodium insertion. The sodium insertion behavior into Li4Ti5O12 is strongly size dependent. A solid solution reaction behavior in a wide range has been revealed during sodium insertion into the nanosized Li4Ti5O12 (~44 nm), which is quite different from the well-known two-phase reaction of Li4Ti5O12/Li7Ti5O12 system during lithium insertion, and also has not been fully addressed in the literature so far. On the basis of this in situ experiment, the apparent Na(+) ion diffusion coefficient (DNa+) of Li4Ti5O12 was estimated in the magnitude of 10(-16) cm(2) s(-1), close to the values estimated by electrochemical method, but 5 order of magnitudes smaller than the Li(+) ion diffusion coefficient (D(Li+) ~10(-11) cm(2) s(-1)), indicating a sluggish Na(+) ion diffusion kinetics in Li4Ti5O12 comparing with that of Li(+) ion. Nanosizing the Li4Ti5O12 will be critical to make it a suitable anode material for sodium-ion batteries. The application of this novel in situ chemical sodiation method reported in this work provides a facile way and a new opportunity for in situ structure investigations of various sodium-ion battery materials and other systems.

A combination of soft and hard synchrotron-based spectroscopy with first-principles density functional theory within the GGA + U framework is used to investigate the distortion of the Mn local environment of LixMnPO4 as a function of electrochemical delithiation (x = 1.0, 0.75, 0.5, 0.25) and its effect on the electron and hole polaron formation. Analysis of the soft X-ray absorption spectroscopy (XAS) of the Mn L3,2-edges confirmed the evolution from the Mn2+ to the Mn3+ charge state as a two-phase reaction upon delithiation; the corresponding Mn K-edge extended X-ray fine structure measurements clearly revealed a splitting of the Mn–O nearest-neighbor distances with increasing Mn3+ character. In addition, the O K-edge absorption and emission spectra confirmed the corresponding orbital lifting of degeneracy accompanying the distortion of the MnO6 octahedra in the Mn3+ state. Our GGA + U calculations show that the distortion is not a strict Jahn–Teller distortion but is instead a preferential elongation o...

In this work, we present results from the application of a new in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy. We exploit this approach to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries. Results from charged LixNi0.8Co0.15Al0.05O2 cathode materials indicate that the evolution of both O2 and CO2 gases are strongly related to phase transitions that occur during thermal decomposition, specifically from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and finally to the rock-salt structure (Fm3m). The state of charge also significantly affects both the structural changes and the evolution of oxygen as the temperature increases: the more extensive the charge, the lower the temperature of the phase transitions and the larger the oxygen release. Ex situ X-ray absorption spectroscopy (XA...

Many researchers have focused in recent years on resolving the crucial problem of capacity fading in Li ion batteries when carbon anodes are replaced by other group-IV elements (Si, Ge, Sn) with much higher capacities. Some progress was achieved by using different nanostructures (mainly carbon coatings), with which the cycle numbers reached 100-200. However, obtaining longer stability via a simple process remains challenging. Here we demonstrate that a nanostructure of amorphous hierarchical porous GeO(x) whose primary particles are ~3.7 nm diameter has a very stable capacity of ~1250 mA h g(-1) for 600 cycles. Furthermore, we show that a full cell coupled with a Li(NiCoMn)(1/3)O(2) cathode exhibits high performance.

Vanadium is shown to substitute for iron in the olivine LiFePO4 up to at least 10 mol %, when the synthesis is carried out at 550 °C. In the solid solution LiFe1–3y/2VyPO4, the a and b lattice parameters and cell volume decrease with increasing vanadium content, while the c lattice parameter increases slightly. However, when the synthesis is performed at 650 °C, a NASICON phase, Li3V2(PO4)3, is also formed, showing that solid solution is a function of the synthesis temperature. X-ray absorption near-edge structure indicates vanadium is in the 3+ oxidation state and in an octahedral environment. Magnetic studies reveal a shift of the antiferromagnetic ordering transition toward lower temperatures with increasing vanadium substitution, confirming solid solution formation. The addition of vanadium enhances the electrochemical performance of the materials especially at high current densities.

U.S. Department of Energy, Office of Basic Energy Science; Energy Efficiency and Renewable Energy, Office of Vehicle Technologies [DEAC02-98CH10886]; Northeastern Center for Chemical Energy Storage; U.S. Department of Energy, Office of Science, Office of

Four boron-based anion receptors were investigated as electrolyte additives for lithium-ion batteries. The electrochemical performance of lithium-ion cells was found to strongly depend on the structure of the anion receptor added to the electrolyte. The capacity retention of the lithium-ion cell was slightly improved by adding 0.07 M bis(1,1,1,3,3,3-hexafluoroisopropyl)pentafluorophenylboronate additive, whereas the addition of 2,5-bis(trifluoromethylphenyl)tetrafluoro-1,3,2-benzodioxaborole dramatically deteriorated the electrochemical performance. The addition of a certain type of anion receptor can promote the electrochemical decomposition of the electrolyte, resulting in high interfacial impedance and accelerated capacity fading of lithium-ion cells. Ab initio calculations showed that the electrochemical performance of anion receptors had good correlation to the degree of localization of the lowest unoccupied molecular orbital at the boron center of anion receptors, which can potentially be used in th...

In situ hard X-ray absorption spectroscopy (XAS) at metal K-edges and soft XAS at O K-edge and metal L-edges have been carried out during the first charging process for the layered Li1-xCo1/3Ni1/3Mn1/3O2 cathode material. The metal K-edge XANES results show that the major charge compensation at the metal site during Li-ion deintercalation is achieved by the oxidation of Ni2+ ions, while the manganese ions and the cobalt ions remain mostly unchanged in the Mn4+ and Co3+ state. These conclusions are in good agreement with the results of the metal K-edge EXAFS data. Metal L-edge XAS results at different charge states in both the FY and PEY modes show that, unlike Mn and Co ions, Ni ions at the surface are oxidized to Ni3+ during charge, whereas Ni ions in the bulk are further oxidized to Ni4+ during charge. From the observation of O K-edge XAS results, we can conclude that a large portion of the charge compensation during Li-ion deintercalation is achieved in the oxygen site. By comparison to our earlier res...

L transition metal phosphates, especially olivine LiFePO4, have been found to be promising rechargeable Li-ion battery cathode materials for many applications since they can safely deliver a good energy density utilizing only earth-abundant materials. However, the olivine materials have limitations which include a poor electrical conductivity and one-dimensional (1D) Li-ion diffusion pathways that can be easily blocked. The search for next-generation phosphate materials has broadened to include transition metal fluorophosphates which incorporate a second anion moiety of F− and which have good electrochemical performance and favorable intrinsic properties such as 2D ion diffusion channels and small volume changes during ion removal and insertion. Here we demonstrate the design of a battery cathode material incorporating N3− anions as a distinct structural building block. While the low mass/charge ratio of N3− is not surpassed by any other anionic group used in battery applications, the voltages previously measured for transition metal nitrides and oxynitrides were low and thus only suitable for anode applications. Electrodes with N3− which can deliver suitable voltages for cathode applications have never before been demonstrated. In the present work, it is shown that A2M II 2P3O9N compounds with M II = Fe and A = Li can be utilized as cathodes in rechargeable Li-ion batteries. In this structure type, N3− anions are present in the form of nitridophosphate PO3N tetrahedra that link together MO6 octahedra. The compound Na2Fe2P3O9N (Figure 1) belongs to a class of known compounds with general formula A2M II 2P3O9N which are known to exist for A = Na and for M = Mg, Fe, Mn, and Co. Compounds with A = Li are clearly of interest for battery applications but have not previously been prepared and could not be directly synthesized under conditions that we have tested due to the preferential formation of olivine LiFePO4, although methods for producing Li-containing nitridophosphate compounds through ion exchange will be demonstrated. Powders of Na2Fe2P3O9N were synthesized by reacting stoichiometric amounts of NaPO3, Fe2O3, and (NH4)2HPO4 at 625 °C under flowing NH3 (50 mL/min) in an open-ended quartz boat for 40 h with one intermediate grinding, similar to prior studies. The full crystal structure of Na2Fe2P3O9N was determined from the Rietveld refinement of high resolution synchrotron X-ray diffraction data (Figure 2a) and time-offlight neutron diffraction data (Supporting Information, Figure S1). The expected primitive cubic phase (P213, No. 198) was observed with a lattice parameter of 9.3459(1) A, substantially smaller than the 9.40 A reported originally. The structure of 2:2 Na2Fe2P3O9N shares the same framework of tetrahedral trimeric P3O9N 6− anionic blocks as 3:1 Na3MP3O9N analogues (M III = Ti, V, etc.). Although these two structural variants both maintain charge balance for the anionic groups using four cations that are found at the same crystallographic sites, they differ in their ratio of monovalent to multivalent cations (2:2 or 3:1). The additional divalent Fe cation in Na2Fe2P3O9N occupies an octahedral site that corresponds to the Na2 position in the 3:1 structure type. As a result, the two FeO6 octahedra in Na2Fe2P3O9N share a face, as illustrated in Figure 1. This close proximity of the two Fe ions (∼3.0 A) is expected to strongly influence redox potentials both through electrostatic repulsions and through potentially contradictory bond length preferences for the three shared oxygen ligands that occur when two Fe ions of different valence are found in a single dimer. Full crystallographic parameters (Tables S1−S5) and important bond distances (Table S6) are provided in the Supporting Information.

We have investigated the local electronic and atomic structure of the LiMn0.5Ni0.5O2 electrode during the first charge and discharge process using in situ X-ray absorption spectroscopy (XAS) of the Mn and Ni K-edges. The Ni K-edge structure in the XANES spectrum shifts to higher energy during charge and shifts back reversibly during discharge in the higher voltage region of ∼4 V, whereas the Mn K-edge structure does not appear to exhibit a rigid edge shift. Further Li-ion intercalation during extended discharge in the 1-V plateau leads to the reduction of Mn4+ ions suggesting that the charge compensation in this region is achieved via the reduction of Mn4+ ions to Mn2+. Mn K-edge EXAFS results indicate that a small amount of Li is found in the Ni2+/Mn4+ layers. These Li ions in the transition metal layers are primarily present in the second coordination shell of Mn and not around Ni. Ni K-edge EXAFS fitting results suggest that the oxidation process upon Li deintercalation takes place in two steps: Ni2+ ...

Etude de l'orientation sur le platine des films de Langmuir Blodgett constitues du melange acide stearique/poly(alkyl-3 thiophene) et d'un copolymere de pyrrole et d'alkyl-3 pyrrole