Lithium Cobalt Oxide Electrodes Research Articles

High-fidelity reconstruction of porous cathode microstructures from FIB-SEM data with deep learning

Accurate modeling of lithium-ion battery (LIB) electrode microstructures provides essential references for understanding degradation mechanisms and optimizing materials. Traditional segmentation methods often struggle to accurately capture the complex microstructures of porous LIB electrodes in focused ion beam scanning electron microscopy (FIB-SEM) data. In this work, we develop a deep learning model based on the Swin Transformer to segment FIB-SEM data of a lithium cobalt oxide electrode, utilizing fused secondary and backscattered electron images. The proposed approach outperforms other deep learning methods, enabling the acquirement of 3D microstructure with reduced particle elongated artifacts. Analyses of the segmented microstructures reveal improved electrode tortuosity and pore connectivity crucial for ion and electron transport, emphasizing the necessity of accurate 3D modeling for reliable battery performance predictions. These results suggest a path toward voxel-level degradation analysis through more sensible battery simulation on high-fidelity microstructure models directly twinned from real porous electrodes.

Regulating solvated sheath with anion chelant enables 4.6 V ultra-stable commercial LiCoO2.

Increasing cut-off voltage of lithium cobalt oxide (LCO) (> 4.6 V) is an effective strategy to satisfy the ever-increasing demand for high energy density. However, the irreversible phase transition significantly destroys the structure of high-voltage LCO, especially the surface lattice. Considering that the structural stability of LCO is primarily dominated by the intrinsic merits of electrode-electrolyte interface (EEI), we explored and disclosed the operating mechanism of anion chelating agent tris(pentafluorophenyl) borane (TPFPB) and regulate the CEI layer on LCO electrode. Benefiting from the high HOMO energy level and preferential decomposition of TPFPB-PF6-, a robust LiF-rich CEI layer is constructed and greatly improves the stability of electrode/electrolyte interface. The well-designed electrolyte composed of 1 mol L-1 LiPF6 in EC/EMC with TPFPB additives endows Li/LCO half cells and 4 Ah Gr/LCO pouch cell with enhanced cycling stability under a high voltage condition. This work provides pave a new direction for the development of economical high-voltage LIBs.

Failure Modes of Flexible LiCoO2 Cathodes Incorporating Polyvinylidene Fluoride Binders with Different Molecular Weights.

Understanding the mechanical failure modes of lithium-ion battery [Li-ion batteries (LIBs)] electrodes is exceptionally important for enabling high specific energy and flexible LIB technologies. In this work, the failure modes of lithium cobalt oxide (LCO) cathodes under repeated bending and the role of the polymer binder in improving the mechanical durability of the LCO electrodes for use in flexible LIBs are investigated. Mechanical and electrochemical evaluations of LCO electrodes (areal capacity of ≥2.5 mA h cm-2) employing poly(vinylidene fluoride) (PVDF) binder were carried out, followed by extensive optical and electron microscopies. We find that the molecular weight (MW) of the PVDF significantly influenced the surface and bulk microstructure of the LCO electrodes, particularly the distribution of carbon additive and binder, which plays a crucial role in affecting the mechanical and electrochemical properties of the electrodes. Multiple mechanical failure modes (e.g., surface scratches and microcracks) observed in the LCO electrodes subjected to repeated bending originated from the use of low MW PVDF; these failure modes were successfully mitigated by using a high MW PVDF. Remarkably, the optimized flexible LCO electrode incorporating high MW PVDF showed comparable discharge capacity retention during galvanostatic cycling after repeated bending (7000 cycles at 50 mm bending diameter) to electrodes not subjected to the repeated bending. This study highlights the importance of carrying out a comprehensive investigation of the failure mechanisms in flexible electrodes, which identified the pivotal role of the PVDF MW in the electrode microstructure and its effects on the electrode resilience to failure during repeated bending.

Thin-Film Lithium Cobalt Oxide for Lithium-Ion Batteries

Lithium cobalt oxide (LCO) cathode has been widely applied in 3C products (computer, communication, and consumer), and LCO films are currently the most promising cathode materials for thin-film lithium batteries (TFBs) due to their high volumetric energy density and favorable durability. Most LCO thin films are fabricated by physical vapor deposition (PVD) techniques, while the influence of preparation on the materials’ properties and electrochemical performance has not been highlighted. In this review, the dominant effects (heating, substrate, power, atmosphere, etc.) on LCO thin films are summarized, and the LCO thin films fabricated by other techniques (spin coating, sol–gel, atomic layer deposition, pulsed laser deposition, etc.) are outlined. Moreover, the modification strategies including bulk doping and surface coating for powder and thin-film LCO electrodes are discussed in detail. This review may pave the way for developing novel, durable, and high-performance LCO thin films by versatile methods for TFB and other energy storage devices.

Sputtering Coating of Lithium Fluoride Film on Lithium Cobalt Oxide Electrodes for Reducing the Polarization of Lithium-Ion Batteries.

Lithium cobalt oxide (LCO) is the most widely used cathode materials in electronic devices due to the high working potential and dense tap density, but the performance is limited by the unstable interfaces at high potential. Herein, LiF thin film is sputtered on the surface of LCO electrodes for enhancing the electrochemical performance and reducing the voltage polarization. The polarization components are discussed and quantified by analyzing the relationship between electrochemical polarization and charger transfer resistance, as well as that between concentration polarization and Li-ion diffusion coefficients. In addition, the decreased charge transfer resistance, increased lithium-ion diffusion coefficients, and stabilized crystal structure of LiF-coated LCO are confirmed by various electrochemical tests and in-situ XRD experiments. Compared to that of pristine LCO, the capacity and cycling performance of LiF-coated LCO is improved, and the overpotential is reduced upon cycling. This work provides reference for quantifying the various polarization components, and the strategy of coating LiF film could be applied in developing other analogous cathode materials.

Regeneration of Al-doped LiNi1/3Co1/3Mn1/3O2 cathode material via a sustainable method from spent Li-ion batteries

The increase in the use of lithium-ion batteries has led to a rapid increase in the number of used Li-ion batteries. If these used lithium-ion batteries are not handled properly, they will result in environmental pollution and waste of valuable metal resources. In this study, spent lithium cobalt oxide electrode sheets were directly leached using d, l-malic acid and H2O2, and LiNi1/3-xCo1/3Mn1/ 3AlxO2 (x = 0.02, 0.04) was resynthesized by sol-gel method. Results show that the prepared materials exhibit typical layered structure, and the doping of Al3+ has a certain effect on inhibiting the mixing of cations. The synthesized LiNi1/3-0.04Co1/3Mn1/3Al0.04O2 maintains an excellent reversible discharge capacity of 148.1 mAhg−1 at a current density of 0.2 C after 100 cycles, which is higher than that of LiNi1/3Co1/3Mn1/3O2. The good performance of the regenerated positive electrode material indicates that the simple recovery and recycling process is feasible.

Design of lithium cobalt oxide electrodes with high thermal conductivity and electrochemical performance using carbon nanotubes and diamond particles

Thermal management remains one of the major challenges in the design of safe and reliable Li-ion batteries. We show that composite electrodes assembled from commercially available 100 μm long carbon nanotubes (CNTs) and LiCoO2 (LCO) particles demonstrate the in-plane thermal conductivity of 205.8 W/m*K. This value exceeds the thermal conductivity of dry conventional laminated electrodes by about three orders of magnitude. The cross-plane thermal conductivity of CNT-based electrodes is in the same range as thermal conductivities of conventional laminated electrodes. The CNT-based electrodes demonstrate a similar capacity to conventional laminated design electrodes, but revealed a better rate performance and stability. The introduction of diamond particles into CNT-based electrodes further improves the rate performance. Our lightweight, flexible electrode design can potentially be a general platform for fabricating polymer binder- and aluminum and copper current collector-free electrodes from a broad range of electrochemically active materials with efficient thermal management.

Decomposition of Non-Aqueous Electrolytes on High-Voltage Cathodes of Lithium-Ion Batteries

Introduction Lithium-ion batteries play a key role in the future renewable energy society, and considerable effort has been devoted to improve the battery performance. High-voltage cathode materials mainly for EVs, which operate above electrochemical window of conventional non-aqueous electrolytes, have recently developed. However, the electrolytes are easily decomposed on the cathode and the reaction mechanism has not been clarified yet. In this study, we investigated the reaction products and their stereochemistry of decomposition of the conventional non-aqueous electrolytes on the high-voltage lithium cobalt oxide electrodes using gas chromatography and mass spectrometry to elucidate the decomposition mechanism. Experimental Cathode composite electrodes made of LiCoO2 powder, acetylene black, and PVDF were separated from cells charged at 4.2 V. The composite electrode powder including the Li x CoO2 (x≤ 0.5) was mixed with 1:1 (by volume) solution of EC and DMC, and then the mixture was kept at 50 °C. Reaction products in the mixture were analyzed using gas chromatograph (GC) and mass spectrometer. Results and discussion One of the main products from the EC, DMC, and Li x CoO2 mixture was identified as vinylene carbonate (VC). When EC and DMC mixed solution was heated without Li x CoO2, VC was not detected. The results indicate that EC was oxidized to VC by Li x CoO2 as shown in Figure 1a. It is well known that a typical way of organic chemical synthesis from EC to VC is radical reaction mechanism [1, 2]. To understand our EC oxidation reaction mechanism, the kinetic isotope effects (KIEs) were discussed. Reactions of EC and EC-d4 with DMC and Li x CoO2 were carried out and the amounts of VC-d2 and VC were measured by the GC, respectively. Figure 2 shows the time evolution of the amounts of VC-d2 and VC. Reaction ratios, k D and k H, were estimated by an equation as follows; k D = d[VC-d2]/dt or k H = d[VC]/dt The relative ratio of these independently determined reaction rate constant (k H/k D) was decided as 2.7 [3]. This value suggests that our reaction is not via a radical reaction, but via a new process; two–electron oxidative decomposition reaction, which will be a key to elucidate the mechanism for formation of VC. Ethylene glycol (EG) was formed in EC and DMC mixed solution without Li x CoO2, while it was not found in the EC, DMC, and Li x CoO2 mixture. When EG was added in the EC, DMC, and Li x CoO2 mixture, the amount of EG was decreased depending on reaction time, which indicates that EG is intermediate product of the reaction of EC on Li x CoO2. The results suggest that EG, which is hydrolyzate of EC, is oxidized on Li x CoO2as shown in Figure 1b. In the presentation, we discuss details of the oxidation reaction mechanism as well.

Analysis of geometric and electrochemical characteristics of lithium cobalt oxide electrode with different packing densities

Abstract To investigate geometric and electrochemical characteristics of Li ion battery electrode with different packing densities, lithium cobalt oxide (LiCoO2) cathode electrodes were fabricated from a 94:3:3 (wt%) mixture of LiCoO2, polymeric binder, and super-P carbon black and calendered to different densities. A synchrotron X-ray nano-computed tomography system with a spatial resolution of 58.2 nm at the Advanced Photon Source of the Argonne National Laboratory was employed to obtain three dimensional morphology data of the electrodes. The morphology data were quantitatively analyzed to characterize their geometric properties, such as porosity, tortuosity, specific surface area, and pore size distribution. The geometric and electrochemical analysis reveal that high packing density electrodes have smaller average pore size and narrower pore size distribution, which improves the electrical contact between carbon-binder matrix and LiCoO2 particles. The better contact improves the capacity and rate capability by reducing the possibility of electrically isolated LiCoO2 particles and increasing the electrochemically active area. The results show that increase of packing density results in higher tortuosity, but electrochemically active area is more crucial to cell performance than tortuosity at up to 3.6 g/cm3 packing density and 4 C rate.

Effect of an Electrolyte Additive of Vinylene Carbonate on the Electronic Structure at the Surface of a Lithium Cobalt Oxide Electrode under Battery Operating Conditions

Lifetimes of lithium-ion batteries are often affected by deterioration of positive electrodes. It is well-known that the deterioration of the positive electrodes can be reduced by using electrolyte additives; however, the mechanism underlying this cyclability improvement needs to be clarified. In this study, we investigate electronic structure at the electrode/electrolyte interface using in situ total-reflection fluorescence X-ray absorption spectroscopy to elucidate the mechanism underlying the cyclability improvement of a LiCoO2 electrode upon addition of vinylene carbonate (VC) to the electrolyte. The results indicate that the reduction of cobalt ions at the surface of the LiCoO2 electrode, which occurs upon soaking in the electrolyte in the absence of VC, is suppressed by the presence of the VC additive. The VC additive also suppresses irreversible change in the electronic structure of the cobalt ions at the LiCoO2 surface during successive charge/discharge processes. The effects of the VC additive can be attributed to the formation of a layer of decomposed VC molecules at the LiCoO2/electrolyte interface, which plays an important role in the suppression of the irreversibility at the LiCoO2 surface during the charge/discharge processes.

Multiple imaging mode X-ray computed tomography for distinguishing active and inactive phases in lithium-ion battery cathodes

This paper presents the use of nanometer scale resolution X-ray computed tomography (nano-CT) in the three-dimensional (3D) imaging of a Li-ion battery cathode, including the separate volumes of active material, binder plus conductive additive, and pore. The different high and low atomic number (Z) materials are distinguished by sequentially imaging the lithium cobalt oxide electrode in absorption and then Zernike phase contrast modes. Morphological parameters of the active material and the additives are extracted from the 3D reconstructions, including the distribution of contact areas between the additives and the active material. This method could provide a better understanding of the electric current distribution and structural integrity of battery electrodes, as well as provide detailed geometries for computational models.

Cycling-Induced Changes in the Entropy Profiles of Lithium Cobalt Oxide Electrodes

Entropy profiles of lithium cobalt oxide (LiCoO2) electrodes were measured at various stages in their cycle life to examine performance degradation and cycling-induced changes, or lack thereof, in thermodynamics. LiCoO2 electrodes were cycled at C/2 rate in half-cells (vs. lithium anodes) up to 20 cycles or C/5 rate in full cells (vs. MCMB anodes) up to 500 cycles. The electrodes were then subjected to entropy measurements (∂E/∂T, where E is open-circuit potential and T is temperature) in half-cells at regular intervals over the approximate range 0.5 ≤ x ≤ 1 in LixCoO2. Despite significant losses in capacity, the cycling did not result in any change to the overall shape of the entropy profile, indicating retention of the LiCoO2 structure, lithium insertion mechanism, and thermodynamics. This confirms that cycling-induced performance degradation in LiCoO2 electrodes is primarily caused by kinetic barriers that increase with cycling. Electrodes cycled at C/5 exhibited a subtle, quantitative, and gradual change in the entropy profile in the narrow potential range of the hexagonal-to-monoclinic phase transition. The observed change is indicative of a decrease in the intralayer lithium ordering that occurs at these potentials, and it demonstrates that a cycling-induced structural disorder accompanies the kinetic degradation mechanisms.

Coupling Between Stack Stress and Chemical Degradation in Lithium-Ion Pouch Cells

Knowledge of how stack-level mechanical stress affects cell aging is important for the long term performance of practical li-ion cells which spend their entire service lives under compressive stress. This compressive stress is set by an initial manufacturing stack pressure, fluctuates with electrode expansion/contraction during charge/discharge, and increases over time due to irreversible electrode expansion. In a previous aging study in which we monitored the stack stress of constrained li-ion cells during cycling, we observed that higher levels of stack stress led to higher rates of capacity fade [1]. Through a post mortem analysis, we determined that the primary source of capacity fade was cycleable lithium loss, such that higher levels of stack stress led to an increase in parasitic side reactions. This degradation occurred in a spatially non-uniform manner such that localized regions of the cell’s graphite anode were covered with a surface film. We also observed similar distributions of localized pore closure in the separator leading us to hypothesize that stack stress and chemical degradation are coupled through separator deformation [2-3].In this presentation we present a follow up study to the aforementioned aging study in which we present experimental evidence for the coupling of stack stress and chemical degradation through separator deformation. To isolate the effects of separator deformation on cell aging, coin cells are fabricated using conventional graphite and lithium cobalt oxide electrodes containing deformed separators. The deformed separators are deformed by applying high localized stresses to create controlled macroscopic patterns of pore closure as can be seen visually in Figure 1. Cells cycled with deformed separators show higher rates of capacity fade than cells cycled with pristine separators as seen from the capacity plot in Figure 2. Upon disassembly, localized visible surface films similar to those observed in [1] are found to be present on the graphite anode.We explain the observed surface film patterns by considering the relative rates of lateral transport that occur in the presence of separator pore closure which restricts normal transport through the separator membrane. Because the electrochemical potential of lithium in lithium cobalt oxide varies more strongly with concentration than it does in graphite, lateral ion transport is enhanced in the cathode. However, sluggish lateral transport in the anode results in high overpotentials which can result in temporary lithium plating and consequential chemical degradation. The proposed explanation is supported by three electrode measurements of a full cell in which the graphite electrode exhibits a negative potential vs. Li/Li+ for cells constructed with deformed separators as seen in Figure 3. We anticipate these issues to become increasingly important in next generation lithium-ion cells which are expected to make use of higher expansion electrode materials.REFERENCES[1]. J. Cannarella, C. B. Arnold, “Stress evolution and capacity fade in constrained lithium-ion pouch cells,” J. Power Sources 245 (2014) 745-751.[2]. J. Cannarella, C. B. Arnold, “Ion transport restriction in mechanically strained separator membranes,” J. Power Sources 226,(2013) 149-155.[3]. C. Peabody, C. B. Arnold, “The role of mechanically-induced separator creep in lithium-ion battery capacity fade,” J. Power Sources, 196 (2011) 8147-8153.ACKNOWLEDGEMENTSSupport was provided by the DoD through the NDSEG Program and by the Siebel Energy Challenge. J. C. also acknowledges the Rutgers-Princeton IGERT in Nanotechnology for Clean Energy.FIGURE CAPTIONSFigure 1. Photograph of a separator that has been deformed locally in a ring-shaped pattern.Figure 2. Capacity evolution of a cells constructed with a deformed and pristine separator.Figure 3. Three electrode measurements of a full cell cycled with a deformed separator showing anode voltage dropping below 0V vs. Li/Li+.

Study on the Process Optimization of Synthesizing Co<sub>3</sub>O<sub>4</sub> Nanoparticles by Homogeneous Precipitation Based on Support Vector Regression

The Co3O4 is the major raw material for fabricating lithium cobalt oxide electrode of lithium ion battery. According to the experimental dataset on grain diameter of Co3O4 nanoparticles synthesized by homogeneous precipitation under four main process parameters including the concentration of Co(NO3)2•6H2O solution, mole ratio of reactants, reaction temperature and reaction time, support vector regression (SVR) combined with particle swarm optimization (PSO) for its parameter optimization, is introduced to establish a model for estimating grain diameter of Co3O4 nanoparticles. The comparison of prediction results strongly support the prediction and generalization abilities of SVR are superior to those of multivariable gradual regression (MGR). Meanwhile, the index of grain diameter of Co3O4 nanoparticles under an independent combination of process parameters predicted by SVR model is more accurate than that by MGR model. The multi-factors analysis results based on SVR model are consistent with that of the literatures. This study suggests that SVR is a theoretical significance and potential practical value in development of smaller grain diameter of Co3O4 nanoparticles via guiding experiment.

Strategic dispersion of carbon black and its application to ink-jet-printed lithium cobalt oxide electrodes for lithium ion batteries

The effects of surface-modified carbon black induced by UV/ozone and triethylenetetramine on the microstructure and electrochemical properties of ink-jet-printed LiCoO2 electrodes for lithium ion batteries are observed. The dispersion properties of surface-modified carbon black and LiCoO2 ink are evaluated using particle size distribution measurements, surface pressure calculations, and scanning electron microscopy. Modifications to the surface of carbon black result in improved dispersion properties, which in turn enhance the compactness and homogeneity of the microstructure of ink-jet-printed LiCoO2 electrodes compared to those printed with as-received carbon black. Electrochemical experiments indicate that LiCoO2 electrodes ink-jet-printed with surface-modified carbon black exhibit improved initial specific discharge capacities compared to those printed with as-received carbon black due to the better electrical contact between the carbon black and the LiCoO2, as evidenced by the analysis of the area-specific impedance of the electrode as a function of the depth of discharge.

Is 3-methyl-2-oxazolidinone a suitable solvent for lithium-ion batteries?

3-Methyl-2-oxazolidinone (MeOx) has been mixed to ethylene carbonate (EC) or dimethyl carbonate (DMC) in presence of lithium tetrafluoroborate (LiBF 4) or lithium hexafluorophosphate (LiPF 6) for use as electrolyte in lithium batteries. The optimized electrolytes in term of conductivity and viscosity are MeOx:EC, x(MeOx) = 0.5 and MeOx:DMC, x(MeOx) = 0.4 in presence of LiBF 4 (1 M) or LiPF 6 (1 M). MeOx:EC electrolytes have a better thermal stability than MeOx:DMC electrolytes but the low wettability of the Celgard separator by MeOx:EC prevents its use in lithium batteries. No lithium insertion–deinsertion occurs when LiPF 6 is used as salt in MeOx-based electrolytes. MeOx:DMC, x(MeOx) = 0.4 + LiBF 4 (1 M) exhibits a good cycling ability at a graphite electrode but all the investigated electrolytes containing MeOx have a low stability in oxidation at a lithium cobalt oxide electrode (Li x CoO 2).

A laboratory-scale lithium-ion battery recycling process

A laboratory process based on simple and environmentally compatible operations, aimed to the treatment and recycling of spent lithium-ion batteries, is described in its various steps. The validity of the process has been evaluated by testing as cathode in a common lithium-ion battery configuration, a lithium cobalt oxide electrode prepared from recycled precursors.