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Recharging battery‐powered electric vehicles (EVs) in a similar timeframe as those used for refueling gas‐powered internal combustion vehicles is highly desirable for rapid penetration of the EV market. It is well known that the electrolyte in a battery plays a critical role in fast‐charging capability of the battery because it determines the rate of ion transport together with its derived electrode/electrolyte interphases on both cathode and anode of the battery. In this study, the effects of contents of salt, coordinating solvent, and noncoordinating diluent on salt dissociation degree and electrolyte ionic conductivity are investigated, and a controlled solvation structure electrolyte is developed to improve the lithium ion mobility and conductivity in the electrolyte and to enhance the kinetics and stability of the electrode/electrolyte interphases in the battery. This electrolyte enables fast‐charging capability of high energy density lithium‐ion batteries (LIBs) at up to 5 C rate (12‐min charging), which significantly outperforms the state‐of‐the‐art electrolyte. The controlled solvation structure sheds light on the future electrolyte design for fast‐charging LIBs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

LiVOPO4 is a promising cathode material for Li-ion batteries due to its ability to intercalate up to two electrons per vanadium redox center. However, LiVOPO4 exhibits polymorphism, forming either the αI, β, or ε phase. A thorough comparison between the properties of these phases is difficult because they usually differ in synthesis methods. In this study, we synthesize all three polymorphs by annealing a single precursor, LiVOPO4·2H2O, thereby reducing the effect of synthesis on the properties of the materials. We show through in situ XRD with heating and DFT calculations that, in terms of stability, αI-LiVOPO4⋘ε-LiVOPO4≤β-LiVOPO4. We also show experimentally and through DFT calculations that the tolerance to O-interstitials and O-vacancies can explain the differences in stability, morphology, and electrochemical performance between β- and ε-LiVOPO4. β-LiVOPO4 is more stable in the presence of O-interstitials while ε-LiVOPO4 is favored in the presence of O-vacancies. These defects affect the surface energies and morphology of the products formed, which are confirmed in the Wulff shape calculations and transmission electron microscopy images. These imply that β-LiVOPO4 has an improved rate performance under an oxidizing atmosphere due to the increased presence of facets with superior ion diffusion at the surface. This improved performance is seen by the improved rate capability and capacity of β-LiVOPO4 in the high-voltage region. In contrast, synthesis conditions have little effect on improving the rate performance of ε-LiVOPO4. [ABSTRACT FROM AUTHOR]

Recent advances in materials syntheses have enabled ε-LiVOPO4 to deliver capacities approaching, and in some cases exceeding the theoretical value of 305 mA h g-1 for 2Li intercalation, despite its poor electronic and ionic conductivity. However, not all of the capacity corresponds to the true electrochemical intercalation/deintercalation reactions as evidenced upon systematic tracking of V valence through combined operando and rate-dependent ex situ X-ray absorption study presented herein. Structural disorder and defects introduced in the material by high-energy ball milling impede kinetics of the high-voltage V5+/V4+ redox more severely than the low-voltage V4+/V3+ redox, promoting significant side reaction contributions in the high-voltage region, irrespective of cycling conditions. The present work emphasizes the need for nanoengineering of active materials without compromising their bulk structural integrity in order to fully utilize high-energy density of multi-electron cathode materials. [ABSTRACT FROM AUTHOR]

Although the determination of site occupancies is often a major goal in Rietveld refinement studies, the accurate refinement of site occupancies is exceptionally challenging due to many correlations and systematic errors that have a hidden impact on the final refined occupancy parameters. Through the comparison of results independently obtained from neutron and synchrotron powder diffraction, improved approaches capable of detecting occupancy defects with an exceptional sensitivity of 0.1% (absolute) in the class of layered NMC (Li[NixMnyCoz]O2) Li-ion battery cathode materials have been developed. A new method of visualizing the diffraction parameter space associated with crystallographic site scattering power through the use of f* diagrams is described, and this method is broadly applicable to ternary compounds. The f* diagrams allow the global minimum fit to be easily identified and also permit a robust determination of the number and types of occupancy defects within a structure. Through a comparison of neutron and X-ray diffraction results, a systematic error in the synchrotron results was identified using f* diagrams for a series of NMC compounds. Using neutron diffraction data as a reference, this error was shown to specifically result from problems associated with the neutral oxygen X-ray atomic form factor and could be eliminated by using the ionic O2− form factor for this anion while retaining the neutral form factors for cationic species. The f* diagram method offers a new opportunity to experimentally assess the quality of atomic form factors through powder diffraction studies on chemically related multi-component compounds. [ABSTRACT FROM AUTHOR]

Sodium ion batteries have attracted much attention in recent years, due to the higher abundance and lower cost of sodium, as an alternative to lithium ion batteries. However, a major challenge is their lower energy density. In this work, we report a novel multi-electron cathode material, KVOPO4, for sodium ion batteries. Due to the unique polyhedral framework, the V3+ ↔ V4+ ↔ V5+ redox couple was for the first time fully activated by sodium ions in a vanadyl phosphate phase. The KVOPO4 based cathode delivered reversible multiple sodium (i.e. maximum 1.66 Na+ per formula unit) storage capability, which leads to a high specific capacity of 235 Ah kg-1. Combining an average voltage of 2.56 V vs. Na/Na+, a high practical energy density of over 600 Wh kg-1 was achieved, the highest yet reported for any sodium cathode material. The cathode exhibits a very small volume change upon cycling (1.4% for 0.64 sodium and 8.0% for 1.66 sodium ions). Density functional theory (DFT) calculations indicate that the KVOPO4 framework is a 3D ionic conductor with a reasonably, low Na+ migration energy barrier of ≈450 meV, in line with the good rate capability obtained. [ABSTRACT FROM AUTHOR]

By controlling the morphology and particle size of the epsilon polymorph of vanadyl phosphate, ε-VOPO4, it can fully reversibly intercalate two Li-ions and reach the theoretical capacity of 305 mA h g−1 over two voltage plateaus at about 4.0 and 2.5 V. [ABSTRACT FROM AUTHOR]

Abstract: Sodium ion batteries have attracted much attention in recent years, due to the higher abundance and lower cost of sodium, as an alternative to lithium ion batteries. However, a major challenge is their lower energy density. In this work, we report a novel multi‐electron cathode material, KVOPO4, for sodium ion batteries. Due to the unique polyhedral framework, the V3+ ↔ V4+ ↔ V5+ redox couple was for the first time fully activated by sodium ions in a vanadyl phosphate phase. The KVOPO4 based cathode delivered reversible multiple sodium (i.e. maximum 1.66 Na+ per formula unit) storage capability, which leads to a high specific capacity of 235 Ah kg−1. Combining an average voltage of 2.56 V vs. Na/Na+, a high practical energy density of over 600 Wh kg−1 was achieved, the highest yet reported for any sodium cathode material. The cathode exhibits a very small volume change upon cycling (1.4% for 0.64 sodium and 8.0% for 1.66 sodium ions). Density functional theory (DFT) calculations indicate that the KVOPO4 framework is a 3D ionic conductor with a reasonably, low Na+ migration energy barrier of ≈450 meV, in line with the good rate capability obtained. [ABSTRACT FROM AUTHOR]

Hybrid supercapacitors using asymmetric, LiFePO4 (LFP) lithium intercalation and electric double layer activated carbon (AC) electrodes combining the high energy battery ability and high power supercapacitor ability in one device are reported. In AC/Li half-cell, AC electrode has 44.5 mAh g−1 capacity and operative voltage > 2 V (Li/Li+) to exhibit supercapacitor-like ion adsorption mechanism. The cyclic voltammetry (CV) and charge/discharge (CD) analysis on AC||LFP hybrid cells with AC/LFP mass ratio, 0.33, 1.2, 1.93, and 3.19, show the transformation from a redox reaction dominated like in battery to a system in which both faradaic redox and the physical electrostatic adsorption processes forming electric double layer are fully balanced in terms of stored charges on both electrodes. The capacity analysis by discharge at different rates shows the high capacity of 125 and 70 mAh g−1 with steep fall at high rates for AC/LFP mass ratios 0.33 and 1.2, respectively. With a specific capacity of ~ 40 mAh g−1, the hybrid cells with AC/LFP mass ratios 1.93 and 3.19 show significant capacity retention at high rates. Optimized by charge balance, the AC||LFP hybrid cell exhibits a high specific energy of 35 Wh kg−1, a high specific power of 1.69 kW kg−1, and a long cycling life. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) provide high-energy-density electrochemical energy storage, which plays a central role in advancing technologies ranging from portable electronics to electric vehicles (EVs). However, a demand for lighter, more compact devices and for extended range EVs continues to fuel the need for higher energy density storage systems. Li2VO2F, which is synthesized in its lithiated state, allows two-electron transfer per formula during the electrochemical reaction providing a high theoretical capacity of 462 mAh/g. Herein, the synthesis and electrochemical performance of Li2VO2F are optimized. The thermal stability of Li2VO2F, which is related to the safety of a battery is studied by thermal gravimetric analysis. The structure and vanadium oxidation state evolution along Li cycling are studied by ex-situ X-ray diffraction and absorption techniques. It is shown that the rock-salt structure of pristine Li2VO2F is stable up to at least 250°C, and is preserved upon Li cycling, which proceeds by the solid-solution mechanism. However, not all Li can be removed from the structure upon charge to 4.5 V, limiting the experimentally obtained capacity. [ABSTRACT FROM AUTHOR]

The volumetric energy density of today's lithium-ion batteries is limited mostly by the graphitic carbon anode. Silicon is a promising replacement but its excessive volume expansion on lithiation limits its long-term cyclability performance. A nano-sized aluminium containing silicon, leached in acid, with a porous structure is shown to maintain its capacity higher than pure bulk silicon or nano-sized silicon by over 700 mAh/g. The capacity of leached silicon is maintained at 1400 mAh/g for more than 60 cycles. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nuclear magnetic resonance spectroscopy have been used to correlate the electrochemical performance with the materials' morphology and composition. [ABSTRACT FROM AUTHOR]

Understanding the reaction mechanism of olivine compounds as electrode materials for lithium lithium-ion batteries have has received much attention recently. The question whether olivine LiFePO4 undergoes two-phase or non-nonequilibrium single-phase reaction during electrochemical processes has taken center stage in the understanding of the faster reaction kinetics observed in this material. Here, the lithiation/delithiation mechanism of Mg Mg-substituted LiFePO4 using high high-resolution X-ray diffraction(XRD), transmission electron microscopy(TEM), and electrochemical measurements is reported. Ex situ partially (de)lithiated olivine- LiMg0.2Fe0.8PO4 show the existence of stable equilibrium intermediate phases as characterized by the presence of more than two phases and broadness of diffraction peaks. Electron energy loss spectroscopy profiles across individual nanoparticles further confirm uniform lithiation with a constant Fe-L3 energy measured across each nanoparticle, suggestive of solid solution behavior in individual particles. In addition, a continuous shift in the diffraction peak position is observed even in the 'two-phase' region in the ex situ electrochemical (de)lithiated electrodes. [ABSTRACT FROM AUTHOR]

Understanding the reaction mechanism of olivine compounds as electrode materials for lithium lithium-ion batteries have has received much attention recently. The question whether olivine LiFePO4 undergoes two-phase or non-nonequilibrium single-phase reaction during electrochemical processes has taken center stage in the understanding of the faster reaction kinetics observed in this material. Here, the lithiation/delithiation mechanism of Mg Mg-substituted LiFePO4 using high high-resolution X-ray diffraction(XRD), transmission electron microscopy(TEM), and electrochemical measurements is reported. Ex situ partially (de)lithiated olivine- LiMg0.2Fe0.8PO4 show the existence of stable equilibrium intermediate phases as characterized by the presence of more than two phases and broadness of diffraction peaks. Electron energy loss spectroscopy profiles across individual nanoparticles further confirm uniform lithiation with a constant Fe-L3 energy measured across each nanoparticle, suggestive of solid solution behavior in individual particles. In addition, a continuous shift in the diffraction peak position is observed even in the 'two-phase' region in the ex situ electrochemical (de)lithiated electrodes. [ABSTRACT FROM AUTHOR]

Understandingthe phase transformation behavior of electrode materialsfor lithium ion batteries is critical in determining the electrodekinetics and battery performance. Here, we demonstrate the lithiation/delithiationmechanism and electrochemical behavior of the simferite compound,LiMg0.5Fe0.3Mn0.2PO4.In contrast to the equilibrium two-phase nature of LiFePO4, LiMg0.5Fe0.3Mn0.2PO4undergoes a one-phase reaction mechanism as confirmed by ex situX-ray diffraction at different states of delithiation and electrochemicalmeasurements. The equilibrium voltage measurement by galvanostaticintermittent titration technique shows a continuous change in voltageat Mn3+/Mn2+redox couple with addition of Mg2+in LiMn0.4Fe0.6PO4olivinestructure. There is, however, no significant change in the Fe3+/Fe2+redox potential. [ABSTRACT FROM AUTHOR]

We have revealed the critical role of carbon coating in the stability and thermal behaviour of olivine MnPO4 obtained by chemical delithiation of LiMnPO4. (Li)MnPO4 samples with various particle sizes and carbon contents were studied. Carbon-free LiMnPO4 obtained by solid state synthesis in O2 becomes amorphous upon delithiation. Small amounts of carbon (0.3 wt%) help to stabilize the olivine structure, so that completely delithiated crystalline olivine MnPO4 can be obtained. Larger amount of carbon (2 wt%) prevents full delithiation. Heating in air, O2, or N2 results in structural disorder (<300 °C), formation of an intermediate sarcopside Mn3(PO4)2 phase (350-450 °C), and complete decomposition to Mn2P2O7 on extended heating at 400 °C. Carbon coating protects MnPO4 from reacting with environmental water, which is detrimental to its structural stability. [ABSTRACT FROM AUTHOR]

The crystal structure and delithiationmechanism of Li-site substitutedLiFePO4have been revealed by investigation of supervalentV3+substitution. The combined X-ray and neutron powderdiffraction data analysis surprisingly shows that the substitutingaliovalent vanadium ions occupy the Fe site while some of the Fe residesat the Li site, probably as sarcopside, which leads to an increasein the unit cell volume. Such substitution reduces the miscibilitygap at room temperature and also significantly lowers the solid solutionformation temperature in the two-phase region. The effect of the phasediagram modification results in improved kinetics, leading to betterrate performance. Such substitution, however, significantly lowersthe LiFePO4capacity at moderate current densities. [ABSTRACT FROM AUTHOR]

The impact of substitution at the Fe site in LiFePO4on reaction pathway, kinetics, and crystallographic changesuponelectrochemical delithiation has been determined. Substitution wasfound by X-ray diffraction to reduce the lattice mismatch betweenthe Li-rich and the Li-poor phases of the substituted samples as comparedto the unsubstituted one. Substitution was also found, by monitoringthe 200reflection peaks of both the triphylite andheterosite phases, to increase the composition width of the singlephase formed on lithium removal, Li1 – xFePO4. A single phase was observed ashigh as x= 0.15 in Li1 – xFe0.85V0.1PO4, whereasLiFePO4at the same state of charge and of similar particlesize show the existence of two phases. In addition, the temperatureat which a single phase is observed for the composition range 0 ≤ x≤ 1 is decreased from slightly above 300 °Cto ca. 200 °C. This increased single-phase-like behavior explainsthe enhanced kinetics of substituted LiFePO4and is consistentwith a pseudosingle-phase reaction mechanism. [ABSTRACT FROM AUTHOR]

The structures, electrochemical properties and thermal stability of Al-substituted lithium-excess oxides, Li1.2Ni0.16 Mn0.56Co0.08-yAlyO2 (y = 0, 0.024, 0.048, 0.08), are reported, and compared to the stoichiometric compounds, LiNizMnzCo1-2zO2. A solid solution was found up to at least y = 0.06. Aluminum substitution improves the poor thermal stability while preserving the high energy density of lithium-excess oxides. However, these high manganese compositions are inferior to the lithium stoichiometric materials, LiNizMnzCo1-2zO2 (z = 0.333, 0.4), in terms of both power and thermal stability. [ABSTRACT FROM AUTHOR]

Li1-3y[VyFe]PO4 (y = 0, 0.025, 0.05, 0.1, 0.2) is synthesized by solid state reaction of Li2CO3, FeC2O4, NH4H2PO4, and NH4VO3 (8.5% H2/He, 550 °C, 10 h). [ABSTRACT FROM AUTHOR]

Sn 2 Fe anode materials were synthesized by a solvothermal route, and their electrochemical performance and reaction mechanism were evaluated. The structural evolution in the first two lithium cycles was investigated by X-ray absorption spectroscopy (XAS), synchrotron X-ray diffraction (XRD), and magnetic studies. In the first cycle, progressive alloying of Sn with Li accompanied by metallic iron displacement occurs upon lithiation, and the delithiation proceeds by Li x Sn dealloying and recovery of the Sn 2 Fe phase. In the second cycle, both XRD and XAS identify Li-Sn alloying at earlier lithiation stages than in the first cycle, with low-Li-content alloys evident in the beginning of the lithiation process. In the fully lithiated state, XAS analysis reveals higher coordination numbers in both the Li x Sn and Fe phases, which points toward more complete reaction and higher crystallinity of the products. Upon second delithiation, the Sn 2 Fe phase is generally reformed as evidenced by XRD. However, XAS indicates somewhat reduced Sn-Fe coordination and shorter Fe-Fe distance, which indicates incomplete reconversion and metallic Fe retention, which is also evident in the magnetic studies. Thus, a combination of long-range (XRD, magnetic) and local (XAS) techniques has revealed differences between the first and the second Li cycles relevant to the understanding of the capacity fading mechanisms., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Sn-based alloy materials are strong candidates to replace graphitic carbon as the anode for the next generation lithium-ion batteries because of their much higher gravimetric and volumetric capacity. A series of nanosize Sn y Fe alloys derived from the chemical transformation of preformed Sn nanoparticles as templates have been synthesized and characterized. An optimized Sn 5 Fe/Sn 2 Fe anode with a core-shell structure delivered 541 mAh·g -1 after 200 cycles at the C/2 rate, retaining close to 100% of the initial capacity. Its volumetric capacity is double that of commercial graphitic carbon. It also has an excellent rate performance, delivering 94.8, 84.3, 72.1, and 58.2% of the 0.1 C capacity (679.8 mAh/g) at 0.2, 0.5, 1 and 2 C, respectively. The capacity is recovered upon lowering the rate. The exceptional cycling/rate capability and higher gravimetric/volumetric capacity make the Sn y Fe alloy a potential candidate as the anode in lithium-ion batteries. The understanding of Sn y Fe alloys from this work also provides insight for designing other Sn-M (M = Co, Ni, Cu, Mn, etc.) system., Competing Interests: The authors declare no competing financial interest.

ε-LiVOPO 4 is a promising multielectron cathode material for Li-ion batteries that can accommodate two electrons per vanadium, leading to higher energy densities. However, poor electronic conductivity and low lithium ion diffusivity currently result in low rate capability and poor cycle life. To enhance the electrochemical performance of ε-LiVOPO 4 , in this work, we optimized its solid-state synthesis route using in situ synchrotron X-ray diffraction and applied a combination of high-energy ball-milling with electronically and ionically conductive coatings aiming to improve bulk and surface Li diffusion. We show that high-energy ball-milling, while reducing the particle size also introduces structural disorder, as evidenced by 7 Li and 31 P NMR and X-ray absorption spectroscopy. We also show that a combination of electronically and ionically conductive coatings helps to utilize close to theoretical capacity for ε-LiVOPO 4 at C/50 (1 C = 153 mA h g -1 ) and to enhance rate performance and capacity retention. The optimized ε-LiVOPO 4 /Li 3 VO 4 /acetylene black composite yields the high cycling capacity of 250 mA h g -1 at C/5 for over 70 cycles., Competing Interests: The authors declare no competing financial interest.

ε- and β-LiVOPO 4 were synthesized from the same precursor at different temperatures in an air atmosphere. ε-LiVOPO 4 is obtained at 400 and 700 °C. The 700 °C sample has better purity and crystallinity, but the 400 °C sample has a little better electrochemical performance due to its smaller particle size and the conducting carbon residue in the sample. β-LiVOPO 4 is formed between the above two temperatures, which gives slightly lower capacity than that of the ε-LiVOPO 4 sample, indicating higher kinetics of the lithium reaction for the ε phase than those of the β one. The phase transformation from ε to β then back reversibly to ε was also observed by ex situ X-ray diffraction. This thermal study verifies that ε-LiVOPO 4 is the more stable phase for LiVOPO 4 ; however, reaction kinetics control the phases formed at lower temperatures.