I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30357]
Open Access
Abstract: The development of flame-retarding battery electrolytes may be achieved by the inclusion of non-flammable solvents in existing conventional electrolyte formulations. Here the use of one such promising solvent, bis(2,2,2-trifluoroethyl) carbonate (TFEC), mixed with conventional lithium-ion battery solvents ethylene carbonate and ethyl methyl carbonate, achieves comparable or superior electrochemical performance to a state-of-the-art benchmark (up to 90 % capacity retention between 5th and 200th cycle, compared with 76 % for the benchmark). Further electrochemical analysis indicates comparable cell resistance and rate capability, though a TFEC content beyond 90 vol.% leads to increased resistance and rapid capacity fading. This was found to be caused by lithium trapping in the graphite electrodes and formation of a thinner solid electrolyte interphase with a distinct chemistry, as determined by X-ray photoelectron spectroscopy. TFEC’s low Li+-solvating ability likely significantly influences these electrolytes’ physico-chemical and electrochemical behaviour.
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Feb 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[33024]
Open Access
Abstract: With the increasing attention to energy storage solutions, a growing emphasis has been placed on environmentally compatible electrolytes tailored for lithium-ion batteries. This study investigates the surface behavior of Si wafers as model systems cycled with a fluorine-free electrolyte based on lithium bis(oxalato)borate (LiBOB), with and without the additive vinylene carbonate (VC). By utilizing operando X-ray reflectivity (XRR) and ex situ X-ray photoelectron spectroscopy (XPS), the intricate processes involved in solid electrolyte interphase (SEI) formation is elucidated, SiO2/Si (de)lithiation, and the impact of the VC additive. Three distinct stages in SEI evolution during lithiation and delithiation are identified: SEI formation, subsequent densification and growth, and decrease in SEI thickness during delithiation, which collectively demonstrate the breathing behavior of the SEI during cycling. The addition of VC is found to mitigate LiBOB decomposition during cycling and promote a smoother SEI layer. Moreover, lithium trapping within the Si wafer post-delithiation is observed for both electrolytes but to a lesser extent with the addition of VC. This study offers structural and chemical insights into the fundamental processes governing SEI formation and Si wafer (de)lithiation in LiBOB-based electrolytes, with implications for designing environmentally friendly lithium-ion batteries.
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Jan 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[33024]
Open Access
Abstract: Intrinsic self-healing chemistries based on dynamic bonds have been shown to solve many issues in advanced applications, not the least batteries. Herein, we investigate the interactions within a polymer system containing dynamic covalent bonds as cross-linkers and their role when they are used as binders in silicon electrodes. We introduce 1,4-benzenediboronic acid (BDBA) as a cross-linking agent forming boronic ester groups and sodium tetraborate (borax) forming borate ester bonds with poly(vinyl alcohol) (PVA). Silicon electrodes with the cross-linked binders show improved electrochemical performance with a capacity of 1500 mA h g–1 after 200 cycles compared to PVA alone featuring 1000 mA h g–1. In contrast, another hydroxyl-containing polymer, carboxymethyl cellulose, able to form the same cross-linking functionalities, showed poorer performance with the addition of BDBA. The choice of polymer and cross-linker not only impacted the cell performance but also the electrode fabrication and morphology. The presence of cross-linkers decreased the electrode cracking of the pristine and cycled electrodes while having little effect on the solid electrolyte interphase composition. Hence, the properties of the polymeric binder system as a whole and the electrode manufacturing process have a significant impact on the cell performance. Solid-state NMR is shown to be a powerful technique to investigate the interaction between the different components and to confirm the formation of boronic ester bonds via the hydroxyl groups of PVA. Furthermore, the presence of silicon particles changes the chemical environment of the boron in BDBA favoring the formation of borate species, which are not present with PVA only, indicating interactions between BDBA and the silicon particles. Hence, PVA in combination with the boron-based cross-linkers, BDBA and borax, provide higher capacity and cycling stability than PVA alone, showing a promising approach to overcome the challenges of silicon anodes using binders with dynamic covalent bonds.
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Oct 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36213]
Open Access
Abstract: Five different electrolyte salts, namely NaBF4, NaClO4, NaDFOB, NaFSI and NaPF6, were evaluated in non-flammable triethyl phosphate (TEP) based electrolyte solutions in sodium-ion full-cells using high-mass loading Prussian white and hard carbon electrodes. Their impact on the viscosity, ionic conductivity and solvation structure was analyzed, revealing that NaFSI-based electrolytes exhibited a stronger interaction with TEP and less ion-pairing than the other salts, resulting in the highest ionic conductivity at a concentration of 0.8 m (mol/kg). Galvanostatic cycling experiments showed that none of the electrolyte salts dissolved in TEP forms an efficient passivation layer. However, adding 1 wt.% vinylene carbonate (VC) significantly improved cycling performance for the cells with NaBF4, NaDFOB or NaFSI, but not with NaClO4 or NaPF6. Additionally, NaFSI in TEP with 1 wt.% VC electrolyte solution showed minimal gas evolution during the formation cycling (< 8 mbar). In a 1 Ah multilayer pouch cell, 0.8 m NaFSI in TEP with 1 wt.% VC showed promising results with 88% capacity retention after 200 cycles. X-ray photoelectron spectroscopy analysis revealed that the addition of VC results in the formation of a thin SEI and minimized TEP decomposition on hard carbon, especially for 0.8 m NaFSI TEP with 1 wt.% VC.
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Oct 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30357]
Open Access
Abstract: 1,1,1-trifluoroethyl methyl carbonate (FEMC) is a popular non-flammable solvent for lithium-ion battery electrolytes, although its high irreversible capacity means it can only be used with film-forming additives like fluoroethylene carbonate (FEC). This work studies the origin of the high irreversible capacity of FEMC-containing cells. Scanning electron microscopy and Raman spectroscopy of graphite anodes after charging and discharging in an FEMC electrolyte show evidence of significant physical and chemical graphite degradation, likely caused by solvent co-intercalation, which is probably responsible for a large portion of the capacity loss. X-ray photoelectron spectroscopy analysis of the anodes shows very low graphite signals, a sign of graphite degradation, formation of a thick solid electrolyte interphase (SEI), or both. When a small amount of FEC is added to FEMC, co-intercalation does not occur. FEC reduction occurs at a higher potential versus Li/Li+ than FEMC co-intercalation. It also forms a significantly different and thinner SEI containing more carbon, less fluorine, and no apparent FEMC decomposition products.
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Sep 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[31857]
Open Access
Abstract: Triethyl phosphate (TEP) is a cheap, environmentally benign, and non-flammable electrolyte solvent, whose implementation in lithium-ion batteries is held back by its co-intercalation into graphite anodes, resulting in exfoliation of the graphite structure. In this work, the electrode-electrolyte interface behaviour of electrolytes containing up to 100% TEP was investigated and correlated to electrochemical performance. High capacity and stable cycling are maintained with up to 30% TEP in carbonate ester-based electrolytes, but above this threshold the reversibility of Li+ intercalation into graphite drops sharply to almost zero. This represents a potential route to improved battery safety, while TEP can also improve safety indirectly by enabling the use of lithium bis(oxalato borate), a fluorine-free salt with limited solubility in traditional electrolytes. To understand the poor performance at TEP concentrations of >30%, its solvation behaviour and interfacial reaction chemistry were studied. Nuclear magnetic resonance spectroscopy data confirms changes in the Li+ solvation shell above 30% TEP, while operando gas analysis indicates extensive gas evolution from TEP decomposition at the electrode above the threshold concentration, which is almost entirely absent below it. X-ray photoelectron spectroscopy depth profiling of electrodes demonstrates poor passivation by the solid electrolyte interphase above 30% TEP and significant graphite exfoliation.
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Jul 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30357]
Open Access
Abstract: Novel lithium-ion battery electrolytes often exhibit poor electrochemical stability against typical commercial layered oxide and graphite electrodes. Pre-passivating the electrodes prior to cell assembly with an electrically insulating, ionically conductive solid-electrolyte interphase (SEI) is one innovative strategy for stabilising systems with otherwise unusable electrolytes. Here, methyl(2,2,2-trifluoroethyl) carbonate (FEMC), a promising non-flammable electrolyte solvent that is generally unstable against graphite, is utilised after pre-passivation of electrodes with a state-of-the-art carbonate-based electrolyte. A significant improvement in performance is observed compared with the untreated electrodes. Hard X-ray photoelectron spectroscopy was used to probe the interphase layer composition.
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Apr 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[26551]
Open Access
Abstract: For sodium-ion batteries, two pressing issues concerning electrolytes are flammability and compatibility with hard carbon anode materials. Non-flammable electrolytes that are sufficiently stable against hard carbon have—to the authors’ knowledge—previously only been obtained by either the use of high salt concentrations or additives. Herein, the authors present a simple, fluorine-free, and flame-retardant electrolyte which is compatible with hard carbon: 0.38 m sodium bis(oxalato)borate (NaBOB) in triethyl phosphate (TEP). A variety of techniques are employed to characterize the physical properties of the electrolyte, and to evaluate the electrochemical performance in full-cell sodium-ion batteries. The results reveal that the conductivity is sufficient for battery operation, no significant self-discharge occurs, and a satisfactory passivation is enabled by the electrolyte. In fact, a mean discharge capacity of 107 ± 4 mAh g−1 is achieved at the 1005th cycle, using Prussian white cathodes and hard carbon anodes. Hence, the studied electrolyte is a promising candidate for use in sodium-ion batteries.
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Oct 2021
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Nuria
Tapia-Ruiz
,
A. Robert
Armstrong
,
Hande
Alptekin
,
Marco A.
Amores
,
Heather
Au
,
Jerry
Barker
,
Rebecca
Boston
,
William R
Brant
,
Jake M.
Brittain
,
Yue
Chen
,
Manish
Chhowalla
,
Yong-Seok
Choi
,
Sara I. R.
Costa
,
Maria
Crespo Ribadeneyra
,
Serena A
Cussen
,
Edmund J.
Cussen
,
William I. F.
David
,
Aamod V
Desai
,
Stewart A. M.
Dickson
,
Emmanuel I.
Eweka
,
Juan D.
Forero-Saboya
,
Clare
Grey
,
John M.
Griffin
,
Peter
Gross
,
Xiao
Hua
,
John T. S.
Irvine
,
Patrik
Johansson
,
Martin O.
Jones
,
Martin
Karlsmo
,
Emma
Kendrick
,
Eunjeong
Kim
,
Oleg V
Kolosov
,
Zhuangnan
Li
,
Stijn F L
Mertens
,
Ronnie
Mogensen
,
Laure
Monconduit
,
Russell E
Morris
,
Andrew J.
Naylor
,
Shahin
Nikman
,
Christopher A
O’keefe
,
Darren M. C.
Ould
,
Robert G.
Palgrave
,
Philippe
Poizot
,
Alexandre
Ponrouch
,
Stéven
Renault
,
Emily M.
Reynolds
,
Ashish
Rudola
,
Ruth
Sayers
,
David O.
Scanlon
,
S.
Sen
,
Valerie R.
Seymour
,
Begoña
Silván
,
Moulay Tahar
Sougrati
,
Lorenzo
Stievano
,
Grant S.
Stone
,
Chris I.
Thomas
,
Maria-Magdalena
Titirici
,
Jincheng
Tong
,
Thomas J.
Wood
,
Dominic S
Wright
,
Reza
Younesi
Open Access
Abstract: Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.
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Jul 2021
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Open Access
Abstract: Na2Ti3O7 (NTO) is considered a promising anode material for Na‐ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na+/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na2Ti6O13. The enhanced electrochemical performance agrees with the higher Na+ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.
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Feb 2021
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