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Lithium splashing from flowing liquid lithium limiter and its effect on high confinement plasma performance in EAST tokamak
To study the potential applications of liquid lithium (Li) as plasma facing material, the third generation of flowing liquid Li (FLiLi) limiter has been designed and successfully tested in EAST tokamak H-mode discharges in the 2018 run campaign. Here, the stability of liquid Li on FLiLi surface, and Li splashing and its effect on the plasma performance are investigated in detail. Li splashing was observed in L-mode and H-mode discharges due to Rayleigh-Taylor (R-T) instability, resulting from electromagnetic forces J → x B → . Li splashing in low-parameter plasma decreased both core and edge electron temperatures, resulting in the degradation of plasma energy confinement and even H-L back transition, however, it almost did not influence plasma confinement performance in high-parameter plasma. These findings indicate that high-parameter plasma has higher tolerance to Li impurities than low-parameter plasma. By contrast, tungsten splashing from the melted layer on the upper divertor was also induced by the R-T instability but generally resulted in plasma disruption, which suggests lower tolerance to tungsten impurities in EAST tokamak.
Electrochromic performance of nanocomposite nickel oxide counter electrodes containing lithium and zirconium
Nickel oxide materials are suitable for counter electrodes in complementary electrochromic devices. The state-of-the-art nickel oxide counter electrode materials are typically prepared with multiple additives to enhance peformance. Herein, nanocomposite nickel oxide counter electrodes were fabricated via RF magnetron co-sputtering from Ni-Zr alloy and Li2O ceramic targets. The as-deposited nanocomposite counter electrodes were characterized with inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). It was found that the stoichiometry, crystal structure and electronic structure of the nickel oxide-based materials could be readily tuned by varying the Li2O sputter deposition power level. Comprehensive electrochromic evaluation demonstrated that the performance of the nickel oxide-based materials was dependent on the overall Li stoichiometry. Overall, the nanocomposite nickel oxide counter electrode containing lithium and zirconium synthesized with a Li2O deposition power of 45 W exhibited the optimal performance with an optical modulation of 71% and coloration efficiency of 30 cm2/C at 670 nm in Li-ion electrolyte.
Thermodynamics, Kinetics and Structural Evolution of ε-LiVOPO 4 over Multiple Lithium Intercalation
ε -Li x VOPO 4 is a promising multi-electron cathode for rechargeable lithium-ion bat- teries that has an extremely high theoretical capacity of 318 mAh/g. In this w ork, we demonstrate the stable cycling of more than one Li in solid-state-syn thesized ε - LiVOPO 4 over more than 20 cycles for the first time. Using a combination of densit y functional theory (DFT) calculations, X-ray pair distribution funct ion (PDF) analy- sis and X-ray Absorption Near Edge Structure (XANES) measurements, we pre sent a comprehensive analysis of the thermodynamics, kinetics and stru ctural evolution of ε -Li x VOPO 4 over the entire lithiation range. We identify two intermediate ph ases at x = 1 . 5 and 1.75 in the low-voltage regime using DFT calculations, and the comput ed and electrochemically measured voltage profiles are in excellent agree ment. Operando PDF techniques show a reversible hysteretic change in the short ( < 2° A) V-O bond lengths coupled with an irreversible extension of the long V-O bond ( > 2.4 °A) dur- ing low-voltage cycling. These observations are confirmed with EXAFS spe ctra. We identify hydrogen intercalation from the electrolyte decomposition as a likely explana- tion for the ~ 2 . 4°A V-O bond and its irreversible extension. In terms of electronic conductivity, we find Li x VOPO 4 to be a large band gap insulator across the entire lithiation range, and calculated small polaron migration barriers are similar to those of the olivine LiMPO 4 cathodes. Finally, we demonstrate that ε -LiVOPO 4 is likely to be a one-dimensional diffuser using climbing-image nudged elastic ban d calculations. These results highlight the importance of nano-sizing and carbon coating in achieving good electrochemical performance in this material.
Insights into Boron-Based Polyanion-Tuned High-Nickel Cathodes for High-Energy-Density Lithium-Ion Batteries
Ultrahigh-Ni layered oxide cathodes (Ni content > 90%) are at the forefront for potentially enabling higher-energy density lithium-ion batteries. Unfortunately, they suffer from rapid capacity fade, poor thermal stability, and increased air sensitivity. Introduction of boron-based polyanion into layered cathodes has been found to be effective in stabilizing high-Ni cathodes, but the mechanism behind it is not yet fully understood. To develop a better understanding, we present here an extensive characterization of the ultrahigh-Ni cathode LiNi 0.94 Co 0.06 O 2 (NC) and B 2 O 3 -LiNi 0.94 Co 0.06 O 2 (B-NC). The B-NC delivers a capacity of 223 mA h g -1 with 80% capacity retention after 400 cycles in full cells with graphite anodes, superior to 61% retention for NC. In-depth interphase investigations reveal that the improved cyclability is attributed to the development of a well-passivated boron/phosphorus-rich cathode-electrolyte interphase in B-NC. Moreover, B-NC demonstrates a considerably enhanced air-exposure and thermal stability. A 30-day air-stored B-NC delivers a discharge capacity of 125 mA h g -1 at 10C rate, in sharp contrast to 65 mA h g -1 for the stored NC. Finally, this work advances the understanding of the effect boron-based polyanion insertion into layered oxides has on battery performance and offers a viable strategy for developing practically viable ultra-high-Ni cathodes with high-energy density.
Calculated Reduction Potentials of Electrolyte Species in Lithium–Sulfur Batteries
In this work, reduction potentials of electrolyte molecules in the lithium–sulfur (Li/S) battery and their variations in several solvent environments are studied using the density functional theory method with Dunning’s triple-ζ correlation consistent basis set. Reliable reduction potential values are key for electrolyte additive design needed for suppressing polysulfide dissolution shuttle mechanism, resulting in poor cycle performance and severe self-discharge of the Li/S battery. Although isolated electrolyte molecules have reduction potentials outside the operating voltage range of the Li/S battery, complexation with other electrolyte species enables the electrolyte molecules to be reduced within the operating voltage range. Among the electrolyte species considered in this study, bis(fluorosulfonyl)imide (FSI – ) and fluoroethylene carbonate (FEC) yield reduction potentials within the expected range, suggesting the development of fluorine-containing additives as a promising line of research.
Probing the Formation of Cathode-Electrolyte Interphase on Lithium Iron Phosphate Cathodes via Operando Mechanical Measurements
Interfacial instabilities in electrodes control the performance and lifetime of Li-ion batteries. While the formation of solid-electrolyte interface (SEI) on anodes has received much attention, there is still lack of understanding about the formation of cathode-electrolyte interface (CEI) on the cathodes. To fill this gap, we report on dynamic deformations on lithium iron phosphate, LiFePO 4 cathodes during charge / discharge by utilizing in-operando digital image correlation, impedance spectroscopy and Cryo X-ray photoelectron spectroscopy. LiFePO4 cathodes were cycled in either LiPF 6 , LiClO 4 or LiTFSI- containing organic liquid electrolytes. Beyond the first cycle, Li-ion intercalation results in a nearly linear correlation between electrochemical strains and the state of (dis)-charge, regardless of the electrolyte chemistry. However, during the first charge in LiPF 6 - containing electrolyte, there is a distinct irreversible positive strain evolution at the onset of anodic current rise as well as current decay at around 4.0V. Impedance studies show the increase in surface resistance in the same potential window, suggesting the formation of CEI layers on the cathode. The chemistry of the CEI layer was characterized by X-ray photoelectron spectroscopy. LiF is detected in CEI layer starting as early as 3.4 V and Li $x$ PO $y$ F $z$ appeared at voltages higher than 4.0 V during the first charge. In conclusion, our approach offers new insights into the formation mechanism of CEI layers on the cathode electrodes, which is crucial for the development of robust cathode and electrolyte chemistries for higher performance batteries.
Ammonium Additives to Dissolve Lithium Sulfide through Hydrogen Binding for High-Energy Lithium–Sulfur Batteries
In rechargeable Li-S batteries, the uncontrollable passivation of electrodes by highly insulating Li2S limits sulfur utilization, increases polarization and decreases cycling stability. Dissolving Li2S in organic electrolyte is a facile solution to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Herein, ammonium salts are demonstrated as effective additives to promote the dissolution of Li2S to 1.25 M in DMSO solvent at room temperature. NMR measurements show that the strong hydrogen binding effect of N-H groups plays a critical role in dissolving Li2S by forming complex ligands with S2- anions coupled with the solvent’s solvating surrounding. Ammonium additives in electrolyte can also significantly improve the oxidation kinetics of Li2S, therefore enables the direct use of Li2S as cathode material in Li-S battery system in the future. This provides a new approach to manage the solubility of lithium sulfides through cation coordination with sulfide anion.
Fluorine-Substituted Lithium Chloride Solid Electrolytes for High-Voltage All-Solid-State Lithium-Ion Batteries
Lithium ternary halides are promising solid electrolytes, owing to their high ionic conductivity and reasonably high oxidative and chemical stability. Recently, fluorine substitution in Li 3 MCl 6 has been suggested as a promising approach for further enhancing oxidation stability. Accordingly, this study outlines a material design strategy for F-substituted Li 3 MCl 6 through systematic theoretical analyses. Calculations reveal that the mixing limit of F in Li 3 MCl 6–x F x is in the range of 0.5–1.5, and the resulting Li 3 MCl 6–x F x phases can retain ionic conductivity above 1 mS/cm up to x = 1.0. Additionally, the calculations also predict that the formation of F-containing passivating phases could increase the oxidation potential for Li3MCl5F to ~6.3 V. The proposed material design strategy is validated through the synthesis of Li 3 YCl 5 F, which is confirmed to show both high ionic conductivity and enhanced oxidation stability. The design guidelines presented herein can accelerate the potential use of halide-based electrolyte chemistries in high-voltage all-solid-state batteries.
Surface-Coating Regulated Lithiation Kinetics and Degradation in Silicon Nanowires for Lithium Ion Battery
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Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition
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Multielectron, Cation and Anion Redox in Lithium-Rich Iron Sulfide Cathodes
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Collapse of LiNi 1– x–y Co x Mn y O 2 Lattice at Deep Charge Irrespective of Nickel Content in Lithium-Ion Batteries
Volume variation and the associated mechanical fracture of electrode materials upon Li extraction/insertion are a main cause limiting lifetime performance of lithium-ion batteries. For LiNi 1-x-y Co x Mn y O 2 (NCM) cathodes, abrupt anisotropic collapse of the layered lattice structure at deep charge is generally considered characteristic to high Ni content and can be effectively suppressed by elemental substitution. Herein, we demonstrate the lattice collapse is a universal phenomenon almost entirely dependent on Li utilization, and not Ni content, of NCM cathodes upon delithiation. With Li removal nearing 80 mol%, very similar c-axis lattice shrinkage of around 5% occurs concurrently for NCMs synthesized in-house regardless of nickel content (90, 70, 50, or 33 mol%); meanwhile, the a-axis lattice contracts for high-Ni NCM, but it expands for low-Ni NCM. We further reveal Co-Mn co-substitution in NCM barely, if at all, affects several key structural aspects governing the lattice distortion upon delithiation. Finally, our results highlight the importance of evaluating true implications of compositional tuning on high-Ni layered oxide cathode materials to maximize their charge-storage capacities for next-generation high-energy Li-ion batteries.
Visualizing nanoscale 3D compositional fluctuation of lithium in advanced lithium-ion battery cathodes
The distribution and concentration of lithium in Li-ion battery cathodes at different stages of cycling is a pivotal factor in determining battery performance. Non-uniform distribution of the transition metal cations has been shown to affect cathode performance; however, the Li is notoriously challenging to characterize with typical high-spatial-resolution imaging techniques. Here, for the first time, laser–assisted atom probe tomography is applied to two advanced Li-ion battery oxide cathode materials—layered Li 1.2 Ni 0.2 Mn 0.6 O 2 and spinel LiNi 0.5 Mn 1.5 O 4 —to unambiguously map the three dimensional (3D) distribution of Li at sub-nanometer spatial resolution and correlate it with the distribution of the transition metal cations (M) and the oxygen. The as-fabricated layered Li 1.2 Ni 0.2 Mn 0.6 O 2 is shown to have Li-rich Li 2 MO 3 phase regions and Li-depleted Li(Ni 0.5 Mn 0.5 )O 2 regions while in the cycled layered Li 1.2 Ni 0.2 Mn 0.6 O 2 an overall loss of Li and presence of Ni rich regions, Mn rich regions and Li rich regions are shown in addition to providing the first direct evidence for Li loss on cycling of layered LNMO cathodes. The spinel LiNi 0.5 Mn 1.5 O 4 cathode is shown to have a uniform distribution of all cations. These results were additionally validated by correlating with energy dispersive spectroscopy mapping of these nanoparticles in a scanning transmission electron microscope. Thus, we have opened the door for probing the nanoscale compositional fluctuations in crucial Li-ion battery cathode materials at an unprecedented spatial resolution of sub-nanometer scale in 3D which can provide critical information for understanding capacity decay mechanisms in these advanced cathode materials.
Cobalt-free composite-structured cathodes with lithium-stoichiometry control for sustainable lithium-ion batteries
Abstract Lithium-ion batteries play a crucial role in decarbonizing transportation and power grids, but their reliance on high-cost, earth-scarce cobalt in the commonly employed high-energy layered Li(NiMnCo)O 2 cathodes raises supply-chain and sustainability concerns. Despite numerous attempts to address this challenge, eliminating Co from Li(NiMnCo)O 2 remains elusive, as doing so detrimentally affects its layering and cycling stability. Here, we report on the rational stoichiometry control in synthesizing Li-deficient composite-structured LiNi 0.95 Mn 0.05 O 2 , comprising intergrown layered and rocksalt phases, which outperforms traditional layered counterparts. Through multiscale-correlated experimental characterization and computational modeling on the calcination process, we unveil the role of Li-deficiency in suppressing the rocksalt-to-layered phase transformation and crystal growth, leading to small-sized composites with the desired low anisotropic lattice expansion/contraction during charging and discharging. As a consequence, Li-deficient LiNi 0.95 Mn 0.05 O 2 delivers 90% first-cycle Coulombic efficiency, 90% capacity retention, and close-to-zero voltage fade for 100 deep cycles, showing its potential as a Co-free cathode for sustainable Li-ion batteries.
Industrializable interlayer with catalytic conversion of dead lithium for Ah–level Nickel–rich lithium metal batteries
The growth of lithium (Li) dendrites and the accumulation of dead Li (i.e., Li metal regions which are electronically disconnected from the current collector) significantly undermine the safety and performance of Li metal batteries. This study employs kilogram-scale atomic layer deposition technology to construct zinc oxide with a preferential (002) crystal orientation, which homogeneously forms on commercial carbon nanotube papers. Our approach emphasizes the importance of achieving a moderate Li adsorption energy and low Li migration energy barriers to suppress Li dendrite growth. In this work, we introduce the concept of "catalytic" effect for dead Li reconversion, as validated through time-of-flight secondary ion mass spectrometry, leading to a Li plating/stripping efficiency of 99.89%. The Ah-level Li metal pouch cells with high-nickel positive electrodes achieve a specific energy of 380 Wh kg -1 (based on the mass of the whole pouch cell) and demonstrate stable cycling under demanding conditions. Analysis of the cycled pouch cells confirms the structural integrity and provides insights into the mechanism of the dead Li "catalytic" conversion.
Controlled large-area lithium deposition to reduce swelling of high-energy lithium metal pouch cells in liquid electrolytes
Lithium (Li) metal battery technology, renowned for its high energy density, faces practical challenges, particularly concerning large volume change and cell swelling. Despite the profound impact of external pressure on cell performance, there is a notable gap in research regarding the interplay between external pressure and the electroplating behaviours of Li+ in large-format pouch cells. Here we delve into the impact of externally applied pressure on electroplating and stripping of Li in 350 Wh kg –1 pouch cells. Employing a hybrid design, we monitor and quantify self-generated pressures, correlating them with observed charge–discharge processes. A two-stage cycling process is proposed, revealing controlled pouch cell swelling of less than 10%, comparable to state-of-the-art Li-ion batteries. Finally, the pressure distribution across the cell surface unveils a complex Li+ detour behaviour during electroplating, highlighting the need for innovative strategies to address uneven Li plating and enhance Li metal battery technology.
Revisiting metal fluorides as lithium-ion battery cathodes
Metal fluorides, promising lithium-ion battery cathode materials, have been classified as conversion materials due to the reconstructive phase transitions widely presumed to occur upon lithiation. We challenge this view by studying FeF 3 using X-ray total scattering and electron diffraction techniques that measure structure over multiple length scales coupled with density functional theory calculations, and by revisiting prior experimental studies of FeF 2 and CuF 2 . Metal fluoride lithiation is instead dominated by diffusion-controlled displacement mechanisms, and a clear topological relationship between the metal fluoride F- sublattices and that of LiF is established. Initial lithiation of FeF3 forms FeF2 on the particle's surface, along with a cation-ordered and stacking-disordered phase, A-Li x Fe y F 3 , which is structurally related to alpha-/beta-LiMn 2+ Fe 3+ F 6 and which topotactically transforms to B- and then C-Li x Fe y F 3 , before forming LiF and Fe. Lithiation of FeF 2 and CuF 2 results in a buffer phase between FeF 2 /CuF 2 and LiF. Overall, the resulting principles will aid future developments of a wider range of isomorphic metal fluorides.