| 1. |
- Sun, Bing, et al.
(författare)
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Ion transport in polycarbonate based solid polymer electrolytes : experimental and computational investigations
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:14, s. 9504-9513
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Tidskriftsartikel (refereegranskat)abstract
- Among the alternative host materials for solid polymer electrolytes (SPEs), polycarbonates have recently shown promising functionality in all-solid-state lithium batteries from ambient to elevated temperatures. While the computational and experimental investigations of ion conduction in conventional polyethers have been extensive, the ion transport in polycarbonates has been much less studied. The present work investigates the ionic transport behavior in SPEs based on poly(trimethylene carbonate) (PTMC) and its co-polymer with epsilon-caprolactone (CL) via both experimental and computational approaches. FTIR spectra indicated a preferential local coordination between Li+ and ester carbonyl oxygen atoms in the P(TMC20CL80) co-polymer SPE. Diffusion NMR revealed that the co-polymer SPE also displays higher ion mobilities than PTMC. For both systems, locally oriented polymer domains, a few hundred nanometers in size and with limited connections between them, were inferred from the NMR spin relaxation and diffusion data. Potentiostatic polarization experiments revealed notably higher cationic transference numbers in the polycarbonate based SPEs as compared to conventional polyether based SPEs. In addition, MD simulations provided atomic-scale insight into the structure-dynamics properties, including confirmation of a preferential Li+-carbonyl oxygen atom coordination, with a preference in coordination to the ester based monomers. A coupling of the Li-ion dynamics to the polymer chain dynamics was indicated by both simulations and experiments.
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| 2. |
- Björklund, Erik, et al.
(författare)
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Influence of state-of-charge in commercial LiNi0.33Mn0.33Co0.33O2/LiMn2O4-graphite cells analyzed by synchrotron-based photoelectron spectroscopy
- 2018
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Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 15, s. 172-180
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Tidskriftsartikel (refereegranskat)abstract
- Degradation mechanisms in 26 Ah commercial Li-ion battery cells comprising graphite as the negative electrode and mixed metal oxide of LiMn 2 O 4 (LMO) and LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) as the positive electrode are here investigated utilising extensive cycling at two different state-of-charge (SOC) ranges, 10–20% and 60–70%, as well as post-mortem analysis. To better analyze these mechanisms electrochemically, the cells were after long-term cycling reassembled into laboratory scale “half-cells” using lithium metal as the negative electrode, and thereafter cycled at different rates corresponding to 0.025 mA/cm 2 and 0.754 mA/cm 2 . The electrodes were also analyzed by synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES) using two different excitation energies to determine the chemical composition of the interfacial layers formed at different depth on the respective electrodes. It was found from the extensive cycling that the cycle life was shorter for the cell cycled in the higher SOC range, 60–70%, which is correlated to findings of an increased cell resistance and thickness of the SEI layer in the graphite electrode as well as manganese dissolution from the positive electrode.
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| 3. |
- Kotronia, Antonia, et al.
(författare)
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Nature of the Cathode–Electrolyte Interface in Highly Concentrated Electrolytes Used in Graphite Dual-Ion Batteries
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:3, s. 3867-3880
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Tidskriftsartikel (refereegranskat)abstract
- Dual-ion batteries (DIBs) generally operate beyond 4.7 V vs Li+/Li0 and rely on the intercalation of both cations and anions in graphite electrodes. Major challenges facing the development of DIBs are linked to electrolyte decomposition at the cathode–electrolyte interface (CEI), graphite exfoliation, and corrosion of Al current collectors. In this work, X-ray photoelectron spectroscopy (XPS) is employed to gain a broad understanding of the nature and dynamics of the CEI built on anion-intercalated graphite cycled both in highly concentrated electrolytes (HCEs) of common lithium salts (LiPF6, LiFSI, and LiTFSI) in carbonate solvents and in a typical ionic liquid. Though Al metal current collectors were adequately stable in all HCEs, the Coulombic efficiency was substantially higher for HCEs based on LiFSI and LiTFSI salts. Specific capacities ranging from 80 to 100 mAh g–1 were achieved with a Coulombic efficiency above 90% over extended cycling, but cells with LiPF6-based electrolytes were characterized by <70% Coulombic efficiency and specific capacities of merely ca. 60 mAh g–1. The poor performance in LiPF6-containing electrolytes is indicative of the continual buildup of decomposition products at the interface due to oxidation, forming a thick interfacial layer rich in LixPFy, POxFy, LixPOyFz, and organic carbonates as evidenced by XPS. In contrast, insights from XPS analyses suggested that anion intercalation and deintercalation processes in the range from 3 to 5.1 V give rise to scant or extremely thin surface layers on graphite electrodes cycled in LiFSI- and LiTFSI-containing HCEs, even allowing for probing anions intercalated in the near-surface bulk. In addition, ex situ Raman, SEM and TEM characterizations revealed the presence of a thick coating on graphite particles cycled in LiPF6-based electrolytes regardless of salt concentration, while hardly any surface film was observed in the case of concentrated LiFSI and LiTFSI electrolytes.
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| 4. |
- Pereira de Carvalho, Rodrigo, et al.
(författare)
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Exploring Metastable Phases During Lithiation of Organic Battery Electrode Materials
- 2022
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Ingår i: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the Li-ion insertion mechanism in organic electrode materials is investigated through the lens of atomic-scale models based on first-principles theory. Starting with a structural analysis, the interplay of density functional theory with evolutionary and potential-mapping algorithms is used to resolve the crystal structure of the different (de)lithiated phases. These methods elucidate different lithiation reaction pathways and help to explore the formation of metastable phases and predict one- or multi-electron reactions, which are still poorly understood for organic intercalation electrodes. The cathode material dilithium 2,5-oxyterephthalate (operating at 2.6 V vs. Li/Li+) is investigated in depth as a case study, owing to its rich redox chemistry. When compared with recent experimental results, it is demonstrated that metastable phases with peculiar ring-ring molecular interactions are more likely to be controlling the redox reactions thermodynamics and consequently the battery voltage.
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| 5. |
- Nilsson, Viktor, 1985, et al.
(författare)
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Critical evaluation of the stability of highly concentrated LiTFSI - Acetonitrile electrolytes vs. graphite, lithium metal and LiFePO4 electrodes
- 2018
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 384, s. 334-341
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Tidskriftsartikel (refereegranskat)abstract
- Highly concentrated LiTFSI - acetonitrile electrolytes have recently been shown to stabilize graphite electrodes in lithium-ion batteries (LIBs) much better than comparable more dilute systems. Here we revisit this system in order to optimise the salt concentration vs. both graphite and lithium metal electrodes with respect to electrochemical stability. However, we observe an instability regardless of concentration, making lithium metal unsuitable as a counter electrode, and this also affects evaluation of e.g. graphite electrodes. While the highly concentrated electrolytes have much improved electrochemical stabilities, their reductive decomposition below ca. 1.2 V vs. Li + /Li° still makes them less practical vs. graphite electrodes, and the oxidative reaction with Al at ca. 4.1 V vs. Li + /Li° makes them problematic for high voltage LIB cells. The former originates in an insufficiently stable solid electrolyte interphase (SEI) dissolving and continuously reforming – causing self-discharge, as observed by paused galvanostatic cycling, while the latter is likely caused by aluminium current collector corrosion. Yet, we show that medium voltage LiFePO 4 positive electrodes can successfully be used as counter and reference electrodes.
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| 6. |
- Elbouazzaoui, Kenza, et al.
(författare)
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Ionic transport in solid-state composite poly(trimethylene carbonate)-Li6.7Al0.3La3Zr2O12 electrolytes : The interplay between surface chemistry and ceramic particle loading
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 462
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Tidskriftsartikel (refereegranskat)abstract
- The ionic transport in solid-state composite electrolytes based on poly(trimethylene carbonate) (PTMC) with LiTFSI salt and garnet-type ion-conducting Li6.7Al0.3-La3Zr2O12 (LLZO) ceramic particles is here investigated for a range of different compositions. Positive effects on ionic conductivity have previously been reported for LLZO incorporated into poly(ethylene oxide) (PEO), but the origin of these effects is unclear since the inclusion of particles also affects polymer crystallinity. PTMC is, in contrast to PEO, a fully amorphous polymer, and therefore here chosen for the design of a more straight-forward composite electrolyte (CPE) system to study ionic transport. With LLZO loadings ranging from 5 to 70 wt%, the CPE with 30 wt% of LLZO exhibits the highest ionic conductivity with a cationic transference number of 0.94 at 60 degrees C. This is significantly higher than for the pristine PTMC polymer electrolyte. Generally, low to moderate LLZO loadings display a gradual increase of the ionic conductivity, transference number and also of the polymer-cation coordination number. The combined contributions of ionic transport along polymer-ceramic interfaces and Lewis acid-base interaction between the LLZO particles and the LiTFSI salt can explain this enhancement. With loadings of LLZO above 50 wt%, a detrimental effect on the ionic conductivity was however observed. This could be explained by agglomeration of ceramic particles, and by a partial coverage of LLZO particles with a Li2CO3 layer. Consequently, inner polymer-particle interfaces become more resistive, and Li+conduction is prevented along interfacial pathways. The presence of Li2CO3 has more detrimental impact at higher LLZO loadings, since inter-particle connectivity will be hampered, and this is vital for efficient ionic transport. This suggests that there is an interplay between the LLZO particle surface chemistry with its loading, which ultimately controls the Li-ion transport.
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| 7. |
- Jeschull, Fabian, 1989-
(författare)
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Functional Binders at the Interface of Negative and Positive Electrodes in Lithium Batteries
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, electrode binders as vital components in the fabrication of composite electrodes for lithium-ion (LIB) and lithium-sulfur batteries (LiSB) have been investigated.Poly(vinylidene difluoride) (PVdF) was studied as binder for sulfur-carbon positive electrodes by a combination of galvanostatic cycling and nitrogen absorption. Poor binder swelling in the electrolyte and pore blocking in the porous carbon were identified as origins of low discharge capacity, rendering PVdF-based binders an unsuitable choice for LiSBs. More promising candidates are blends of poly(ethylene oxide) (PEO) and poly(N-vinylpyrrolidone) (PVP). It was found that these polymers interact with soluble lithium polysulfide intermediates generated during the cell reaction. They can increase the discharge capacity, while simultaneously improving the capacity retention and reducing the self-discharge of the LiSB. In conclusion, these binders improve the local electrolyte environment at the electrode interface.Graphite electrodes for LIBs are rendered considerably more stable in ‘aggressive’ electrolytes (a propylene carbonate rich formulation and an ether-based electrolyte) with the poorly swellable binders poly(sodium acrylate) (PAA-Na) and carboxymethyl cellulose sodium salt (CMC-Na). The higher interfacial impedance seen for the conventional PVdF binder suggests a protective polymer layer on the particles. By reducing the binder content, it was found that PAA-Na has a stronger affinity towards electrode components with high surface areas, which is attributed to a flexible polymer backbone and a higher density of functional groups.Lastly, a graphite electrode was combined with a sulfur electrode to yield a balanced graphite-sulfur cell. Due to a more stable electrode-electrolyte interface the self-discharge of this cell could be reduced and the cycle life was extended significantly. This example demonstrates the possible benefits of replacing the lithium metal negative electrode with an alternative electrode material.
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| 8. |
- Wu, Liang-Ting, et al.
(författare)
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A method for modelling polymer electrolyte decomposition during the Li-nucleation process in Li-metal batteries
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Elucidating the complex degradation pathways and formed decomposition products of the electrolytes in Li-metal batteries remains challenging. So far, computational studies have been dominated by studying the reactions at inert Li-metal surfaces. In contrast, this study combines DFT and AIMD calculations to explore the Li-nucleation process for studying interfacial reactions during Li-plating by introducing Li-atoms close to the metal surface. These Li-atoms were added into the PEO polymer electrolytes in three stages to simulate the spontaneous reactions. It is found that the highly reactive Li-atoms added during the simulated nucleation contribute to PEO decomposition, and the resulting SEI components in this calculation include lithium alkoxide, ethylene, and lithium ethylene complexes. Meanwhile, the analysis of atomic charge provides a reliable guideline for XPS spectrum fitting in these complicated multicomponent systems. This work gives new insights into the Li-nucleation process, and experimental XPS data supporting this computational strategy. The AIMD/DFT approach combined with surface XPS spectra can thus help efficiently screen potential polymer materials for solid-state battery polymer electrolytes.
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| 9. |
- Wu, Liang-Ting, et al.
(författare)
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Role of copper as current collectors in the reductive reactivity of polymers for anode-free lithium metal batteries : Insights from DFT and AIMD studies
- 2023
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Ingår i: Materials Today Physics. - : Elsevier. - 2542-5293. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the role of current collectors (CCs) in the reductive reactivity of polymers on Li metal and the resultant solid electrolyte interphase (SEI) formation is essential for improving the performance of anode-free lithium metal batteries (AFLMBs). In this study, we have examined the reactivity of three polymeric hosts: poly(ethylene oxide) (PEO), poly(epsilon-caprolactone) (PCL), and poly(trimethylene carbonate) (PTMC) at Li metal supported on Cu surfaces (Li/Cu) using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. In particular, the effect of copper (Cu) CCs on polymer stability, electronic structure, and their reduction reactions is investigated and compared to that of pure Li (100) surface. Through time-dependent Bader charge transfer analysis, electron transfer is identified as the triggering factor for polymer reduction. Based on the simulations, we find that the Cu CCs have a significant influence on the charge distribution of the Li metals, which increases electron transfer to the polymers and thereby accelerates polymers reduction. This thereby leads to different reaction mechanisms as compared to on Li-metal. The findings suggest that utilization of Cu CCs avoids the production of CO molecules and improves the quality of the formed SEI layer.
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| 10. |
- Carvalho, Rodrigo P.
(författare)
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Organic Electrode Battery Materials : A Journey from Quantum Mechanics to Artificial Intelligence
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Batteries have become an irreplaceable technology in human life as society becomes progressively more dependent on electricity. The demand for novel battery technologies has increased fast, especially with the popularisation of different portable devices. However, the current battery industry relies heavily on non-renewable resources that are also prone to provoke environmental harm. Among the possible candidates for the next generation of batteries, organic electroactive materials (OEMs) have become attractive due to a series of advantages: vastly accessible from renewable raw materials; highly versatile due to the possible functionalisation mechanisms; possibly lower production costs; reduced environmental impacts; etc. Nevertheless, some drawbacks need to be overcome before OEMs become competitive. Issues with energy density, rate capability and cycling stability hinder their final technological application. This thesis thereby discusses fundamental aspects of OEMs and proposes novel techniques to accelerate the materials discovery process.The first part of this thesis presents a pathway to systematically investigate organic materials by combining quantum mechanics calculations and crystal structure predictions. An evolutionary algorithm predicts the crystal structure of several OEMs, enabling an initial assessment of the electronic structure and the thermodynamics of the ionic insertion mechanism in these compounds. Furthermore, this first part also suggests an approach to tailor OEMs, identifying their charge storage limits and the possible occurrence of metastable phases during the ion insertion process. However, the presented strategy, while accurate, is seriously limited by its high computational demands, which are unrealistic for high-throughput screening of novel materials.Since organic materials represent a possibly limitless universe of compounds, alternative techniques are needed. Thus, the second part of this thesis combines quantum mechanics and artificial intelligence (AI), rendering a powerful platform to aid this task. An “AI-\textit{kernel}” was employed to analyse millions of organic compounds, discovering novel possible organic battery materials. Moreover, the AI accurately identified common functional groups associated with higher-voltage electrodes and suggested features that may aid future materials design. Furthermore, the kernel can also identify materials suitable for Na- and K-ion batteries and anticipate their redox stability.In conclusion, this thesis has focused on investigating fundamental properties of organic electroactive materials, particularly the ionic insertion process in batteries. Furthermore, AI-driven methodologies have also been proposed, accurately evaluating OEMs and enabling fast access to the gigantic organic realm when searching for novel battery electrode materials.
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