Cathode Degradation Research Articles

Understanding the Relationship between State-of-Charge and Structural Fragility in Ni-Rich Layered Materials for Lithium Batteries

Lithium batteries are at the frontier of energy storage. Co-free, Ni-rich layered transition metal oxide (TMO) materials have gained interest within the past decade due to their low cost and increased practical capacity. The challenge with employing these layered oxide cathodes is their inherent structural fragility, facilitated by metal cation migration and lattice oxygen loss. Upon charging, the redox center becomes oxidized, generating thermodynamically favorable electron transfer pathways between the electrolyte and the layered oxide. This transfer pathway is mainly due to the TM3d-O2p orbital hybridization perturbation during battery charging.Surface reconstruction and the structural reordering that accompanies it can undesirably influence the cathode – electrolyte interphase, leading to enhanced electrolyte degradation pathways that can minimize Coulombic efficiency. Electrolyte decomposition occurs at the oxide cathode surface, but can lead to bulk electronic and structural changes of the layered oxide, chemomechanical breakdown, and irreversible phase transformations.In this study, we focus on understanding the interplay between bulk phase transitions and surface instability with respect to electrolyte chemical decomposition. We use novel galvanostatic cycling parameters, extensive electron microscopy, and synchrotron X-ray techniques to decouple chemical and electrochemical electrolyte decomposition pathways to understand their role in Co-free, Ni-rich oxide cathode degradation. This work allows us to decouple surface and bulk chemistries at the cathode – electrolyte interphase to inform further insight into optimal Ni-rich oxide cathode design.

Cross-Talk-Suppressing Electrolyte Additive Enabling High Voltage Performance of Ni-Rich Layered Oxides in Li-Ion Batteries.

Control of electrode-electrolyte interfacial reactivity at high-voltage is a key to successfully obtain high-energy-density lithium-ion batteries. In this study, 2-aminoethyldiphenyl borate (AEDB) is investigated as a multifunctional electrolyte additive in stabilizing surface and bulk of both Ni-rich LiNi0.85 Co0.1 Mn0.05 O2 (NCM851005) and graphite electrodes in a cell operated with elevated upper cutoff voltage of 4.4 V vs. Li+ /Li. The presence of AEDB in a full-cell inhibits structural degradation of both cathode and anode materials, suppressing crack formation, and reduces metal dissolution at the cathode and metal deposition at the anode. As a consequence, the interfacial resistance is significantly reduced. Moreover, this is a case where "the whole is greater than the sum of the parts": the effect of AEDB in half-cells is rather modest, whereas in full-cells its addition results in tremendous performance improvement. The graphite‖NCM851005 full-cell in the presence of AEDB has a capacity retention of 88 % after 100 cycles, even when the upper cutoff voltage is set to 4.35 V, corresponding to 4.4 V vs Li+ /Li, whereas with standard electrolyte under the same conditions it is only 21 %. The study shows a simple and easy approach to using Ni-rich cathodes in an extended voltage window and demonstrates the importance of full-cell testing for electrolyte additive selection.

TEM Study of Oxygen Partial Pressure Effect on Early LSM-YSZ Surface Interactions in Solid Oxide Fuel Cells

Abstract Long-term stability studies indicate that cathode degradation is one of the main failure mechanisms in anode-supported SOFCs. In order to better understand the microstructural degradation mechanisms of the cathode and the influence of oxygen partial pressure at relevant operating temperatures, the authors of this article acquired TEM samples from technological cells to study cation interdiffusion mechanisms and LSM-YSZ interactions, particularly in areas where LSM grains are in contact with YSZ electrolyte. Here they present and interpret the results.

Mesoscale Model for Ostwald Ripening of Catalyst Nanoparticles

A mesoscale model is proposed to characterize coarsening of platinum-based catalyst particles with the aim of understanding cathode degradation and power loss in proton exchange membrane fuel cells (PEMFC). The microstructure of a cathode catalyst layer is more complex than the ones typically described by Ostwald-ripening models, such as the Lifshitz and Slyozov and Wagner (LSW) theory or diffuse interface models. Our model captures the dissolution kinetics of the catalyst material, and the diffusivity of the ions in solution. The network structure of the model embeds the tortuosity of the microstructure and the effect of water content on Pt-ion mobility. Detailed diffusional interactions among catalyst particles are explicitly described with the aim of providing statistically averaged properties of coarsening ensembles. Through numerical tests, the scaling of coarsening kinetics is predicted as function of voltage. The effect of voltage cycling, and initial particle size distribution are also probed. The power-law exponents for the mean square radius vs time are affected by the reduced dimensionality of inter-particle diffusion, constrained by the carbon support and the surface wetting. This theoretical framework can be used to understand how material design influences the degradation pathways that are responsible for platinum surface area loss.

Highly Reversible Aqueous Zn‐MnO2 Battery by Supplementing Mn2+‐Mediated MnO2 Deposition and Dissolution

AbstractRechargeable Zn‐MnO2 batteries are boosted by the reversible intercalation reactions in mild aqueous electrolytes, but they still suffer from cathode degradation. Herein, Zn‐MnO2 batteries with high durability and high energy density are achieved by supplementing MnO2 deposition and dissolution in a mild aqueous electrolyte. The main finding is that adjusting Mn2+ concentration to a critical range enables a reversible MnO2/Mn2+ redox conversion without the involvement of oxygen evolution. This can recycle the by‐products from MnOOH disproportionation (MnOOH → MnO2 + Mn2+), resulting in a battery with extremely high durability (16 000 cycles without obvious capacity fading), high energy density (602 Wh kg−1 based on the active mass of the cathode), and high‐rate capacity (430 mAh g−1 at 19.5 A g−1). The utilization of a 3D carbon nanotube foam skeleton can accommodate the volume change during MnO2 deposition/dissolution and provide paths for efficient charge and mass transport. This work provides a feasible way to push the development of Zn‐MnO2 batteries in mild aqueous electrolytes.

Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteries

Summary Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.

Enhancing Oxygen Reduction Activity and Cr Tolerance of Solid Oxide Fuel Cell Cathodes by a Multiphase Catalyst Coating

AbstractIntermediate temperature solid oxide fuel cells (IT‐SOFCs) are cost‐effective and efficient energy conversion systems. The sluggish oxygen reduction reaction (ORR) and the degradation of cathodes are critical challenges to the commercialization of IT‐SOFCs. Here, a highly efficient multiphase (MP) catalyst coating, consisting of Ba1−xCo0.7Fe0.2Nb0.1O3−δ (BCFN) and BaCO3, to enhance the ORR activity and durability of the state‐of‐the‐art lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.2Fe0.8O3−δ, LSCF) cathode is reported. The conformal MP catalyst‐coated LSCF cathode shows a polarization resistance (Rp) of 0.048 Ω cm2 at 650 °C, about one order of magnitude smaller than that of the bare LSCF. In an accelerated Cr‐poisoning test, the degradation rate of the catalyst‐coated LSCF electrode is 10−3 Ω cm2 h−1 (0.59% h−1) over 200 h, only one fifth of the degradation rate of the bare LSCF electrode at 750 °C. In addition, anode‐supported single cells with the MP catalyst‐coated LSCF cathode show a dramatically enhanced peak power density (1.4 W cm−2 vs 0.67 W cm−2 at 750 °C) and increased durability against Cr and H2O. Both experimental results and density functional theory‐based calculations indicate that the BCFN phase improves the ORR activity while the BaCO3 phase enhances the stability of the LSCF cathode.

Understanding Degradation at the Lithium-Ion Battery Cathode/Electrolyte Interface: Connecting Transition-Metal Dissolution Mechanisms to Electrolyte Composition.

Lithium transition-metal oxides (LiMn2O4 and LiMO2 where M = Ni, Mn, Co, etc.) are widely applied as cathode materials in lithium-ion batteries due to their considerable capacity and energy density. However, multiple processes occurring at the cathode/electrolyte interface lead to overall performance degradation. One key failure mechanism is the dissolution of transition metals from the cathode. This work presents results combining scanning electrochemical microscopy with inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to examine cathode degradation products. Our effort employs a LiMn2O4 (LMO) thin film as a model cathode to monitor the Mn dissolution process without the potential complications of conductive additive and polymer binders. We characterize the electrochemical behavior of LMO degradation products in various electrolytes, paired with ICP and EPR, to better understand the properties of Mn complexes formed following metal dissolution. We find that the identity of the lithium salt anions in our electrolyte systems [ClO4-, PF6-, and (CF3SO2)2N-] appears to affect the Mn dissolution process significantly as well as the electrochemical behavior of the generated Mn complexes. This implies that the mechanism for Mn dissolution is at least partially dependent on the lithium salt anion.

A Study of Model‐Based Protective Fast‐Charging and Associated Degradation in Commercial Smartphone Cells: Insights on Cathode Degradation as a Result of Lithium Depositions on the Anode

AbstractThe ever expanding mobile consumer electronic market has accelerated the need for safe and efficient fast‐charging approaches that improve the overall speed of battery charging without hastened deterioration of the battery performance. Herein, the impact of a resource inexpensive, physics‐based, electrochemically optimized fast‐charging algorithm (charging time < 2 h) for mobile devices is investigated. A critical difference in the amount and morphology of lithium deposits on the anode for cells fast‐charged without an optimized algorithm is observed and found to be the main cause of capacity decay. An in‐depth study of the LiCoO2 cathode regions opposite to pronounced lithium deposits on the anode reveals a “mirroring” phenomenon, i.e., a frozen monoclinic phase, and inactivity to relithiation. In operando hard X‐ray absorption spectroscopy reveals that degraded spots on harvested cathodes seem to be activated again and participate in the intercalation process when lithiated at low rates from lithium foil counter electrodes. On the other hand, tests at higher C‐rates, closer to the actual fast‐charging rate, reveal only negligible oxidation state changes and therefore poor performance.

A Shrinking-Core Model for the Degradation of High-Nickel Cathodes (NMC811) in Li-Ion Batteries: Passivation Layer Growth and Oxygen Evolution

A degradation model for high-nickel positive electrode materials that undergo a structural reorganisation involving oxygen loss and the formation of a disordered (spinel or rock-salt structure) passivation layer is presented for the first time. The model is a thermally coupled continuum model based on the single-particle model and is based upon a LiNi0.8Mn0.1Co0.1O2 (NMC811) layered oxide in this instance. The theoretical framework assumes a shrinking core mechanism, where lattice oxygen, [O], release occurs at the interface between the bulk and the passivation layer, and the rate of reaction is controlled by either [O]-diffusion through the passivation layer or the reaction kinetics at the interface. As the passivation layer grows, the core of active positive electrode material shrinks giving rise to both loss in active material (LAM) and loss in lithium inventory (LLI) through trapping lithium in the passivation layer, giving rise to capacity fade. The slower diffusion of lithium through the passivation layer also gives rise to power fade. The model predicts two limiting cases, “diffusion dominated” if [O]-diffusion is slow, and “reaction dominated” if [O]-diffusion is fast, relative to the reaction rate of [O]-release and also the thickness of the passivation layer.

Four-Dimensional Identical-Location X-ray Imaging of Fuel Cell Degradation during Start-Up/Shut-Down Cycling

In this work, local electrode degradation effects from start-up/shut-down cycling of polymer electrolyte fuel cells are visualized using X-ray tomographic imaging of specialized, miniature fuel cell hardware. This combination enables non-invasive in situ tracking of the same cathode catalyst layer domain throughout various degradation stages in four dimensions. Critical, localized regions are identified within the cathode catalyst layer where progressive structural deterioration occurs from carbon support corrosion leading to thinning and collapse of the material. A greater structural change is observed under the landing area than under the channels due to delayed resident gas purge. This finding differs from the results of voltage cycling accelerated stress test, where more structural change was observed under the channel area than the landing area. However, overall similarities in degradation and performance loss supports the use of voltage cycling for accelerated degradation studies. A direct correlation between the structural deterioration and the electrochemical performance reduction of the fuel cell is found. In addition, reduced reactant gas flow in a restricted anode flow channel enhances the local cathode degradation due to delayed gas purge. However, no influence on the degradation is observed in a cell with intentional anode/cathode channel misalignment, compared to generic test cells.

Layered oxides with solid-solution reaction for high voltage potassium-ion batteries cathode

The development of high-performance potassium-ion batteries (PIBs) is challenged by the availability of stable cathode materials, which are known to undergo complex phase transitions and irreversible structural degradation especially charged to high voltage. Here, we reported a P2-type cathode in formula of K0.6Mn0.8Ni0.1Ti0.1O2 (KMNT), which exhibited a highly reversible K+ (de)intercalation capability up to 4.2 V. We demonstrated that the coexistence of Ni and Ti was able to not only suppress the structural damage related to the Jahn-Teller effect of Mn3+, a critical factor accounting for the performance degradation of Mn-based PIBs cathodes, but also restrain the detrimental lattice sliding of transition metal layers at high voltage. Accordingly, the structurally engineered KMNT showed a much favored solid-solution reaction with a successful elimination of the destructive phase degradation at deep depotassiation state. Our results highlighted the essential role played by the lattice design of cathode materials in modulating their electrochemical behavior for stable and high-performance PIBs.

Impact of the temperature on calendar aging of an open cathode fuel cell stack

This paper deals with calendar aging of a proton exchange membrane open-cathode fuel cell. Calendar aging is already developed for energy sources as supercapacitor and batteries but the literature is very poor for fuel cell stacks. However, this kind of test is necessary to determine the actual lifetime of the system without running it and to define the aging impact of the storage of such a system. One possible outcome for fuel cells is to provide electricity in remote areas without connection to the grid. This issue becomes even more challenging under hard environmental conditions, especially in areas with possible negative ambient temperatures. Experimental research on the degradation of open cathode fuel cells under these tricky conditions is needed to investigate the impact of resting states on the fuel cell lifetime and to evaluate the impact of the sub-zero temperatures on the performance losses.

Visualizing Lithium Distribution and Degradation of Composite Electrodes in Sulfide-based All-Solid-State Batteries Using Operando Time-of-Flight Secondary Ion Mass Spectrometry.

Understanding the electrochemical reactions taking place in composite electrodes during cell cycling is essential for improving the performance of all-solid-state batteries. However, comprehensive in situ monitoring of Li distribution, along with measurement of the evolution of degradation, is challenging because of the limitations of the characterization techniques commonly used. This study demonstrates the observation of Li distribution and degradation in composite cathodes consisting of LiNi0.8Co0.15Al0.05O2 (NCA) and 75Li2S·25P2S5 (LPS) during cell operation using operando time-of-flight secondary ion mass spectrometry. The evolution of the nonuniform reaction of NCA particles during charge and discharge cycles was successfully visualized by mapping fragments containing Li. Furthermore, degradation of the NCA/LPS interface was investigated by mapping POx- and SOx- fragments, which are related to the solid electrolyte interphase. We found that during the charge-discharge cycle and application of a high-voltage stress to the composite electrodes, the PO2- and PO3- fragments increased monotonically, whereas the SO3- fragment exhibited a reversible increase-decrease behavior, implying the existence of a redox-active component at the NCA/LPS interface. The demonstrated technique provides insights into both the optimized structures of composite electrodes and the underlying mechanisms of interfacial degradation at active material/solid electrolyte interfaces.

Soft X-ray Ptychography Chemical Imaging of Degradation in a Composite Surface-Reconstructed Li-Rich Cathode.

The capability in spatially resolving the interactions between components in lithium (Li)-ion battery cathodes, especially correlating chemistry and electronic structure, is challenging but critical for a better understanding of complex degradation mechanisms for rational developments. X-ray spectro-ptychography and conventional synchrotron-based scanning transmission X-ray microscopy image stacks are the most powerful probes for studying the distribution and chemical state of cations in degraded Li-rich cathodes. Herein, we propose a chemical approach with a spatial resolution of around 5.6 nm to imaging degradation heterogeneities and interplay among components in degraded Li-rich cathodes. Through the chemical imaging reconstruction of the degraded Li-rich cathodes, fluorine (F) ions incorporated into the lattice during charging/discharging processes are proved and strongly correlate with the manganese (Mn) dissolution and oxygen loss within the secondary particles and impact the electronic structure. Otherwise, the electrode-electrolyte interphase component, scattered LiF particles (100-500 nm) along with the MnF2 layer, is also visualized between the primary particles inside the secondary particles of the degraded cathodes. The results provide direct visual evidence for the Li-rich cathode degradation mechanisms and demonstrate that the low-energy ptychography technique offers a superior approach for high-resolution battery material characterization.

Tetracycline inhibition and transformation in microbial fuel cell systems: Performance, transformation intermediates, and microbial community structure

Tetracycline (TC) transformation in the anode of an air cathode microbial fuel cell (MFC) and in the cathode of an MFC-Fenton system was investigated. TC at 10 mg/L in the anolyte was removed by 43–74% in 14-d cycles, mainly attributed to adsorption. The electrochemical activity, COD and acetate consumption of the anodic biofilm were inhibited by TC; inhibition was reversed when TC addition was stopped. Over 84 d of MFC operation with TC, Geobacter and Mycobacterium in the anode biofilm decreased, while Janthinobacterium and Comamonas increased. Over 99% of TC at 10–40 mg/L was removed within 8 h in the MFC-Fenton cathode. O2−•/HO2• and •OH were responsible for the cathodic TC degradation. The maximum current was 0.93 mA (at 250 Ω) and increased by 36.3% by the MFC-Fenton reaction. Cathodic MFC-Fenton is an efficient and energy-saving process for TC removal, compared to slow and problematic anodic TC bio-oxidation.

Beneficial Effect of Li5FeO4 Lithium Source for Li-Ion Batteries with a Layered NMC Cathode and Si Anode

The energy density of lithium-ion batteries can be increased by replacing the traditional graphite anode with a high capacity silicon anode. However, volume changes and interfacial instabilities cause a large irreversible capacity and a continual loss of lithium during cycling, which lead to rapid capacity loss. In this work, we add Li5FeO4 (LFO) to a LiNi0.5Mn0.3Co0.2O2 (NMC) cathode as a pre-lithiation additive, which increases the lithium inventory and extends the cycle life of Si-graphite/NMC full cells, and decreases the NMC particle degradation. LFO delivers a large 764 mAh g−1 LFO capacity below 4.7 V vs Li/Li+. By tuning the LFO content in Si-graphite/LFO-NMC full cells, we show higher capacity, improved retention, lower impedance, and superior rate performance compared to full cells without LFO. Post-test characterizations demonstrate that LFO inclusion in the cathode matrix leads to less NMC secondary particle segregation/cracking and a thinner surface reduced layer on the NMC particles. The beneficial effects of LFO endure after the lithium reserve has been exhausted, highlighting a lasting synergy between the lithium source and electrode active materials. This study introduces a new approach to simultaneously increase lithium inventory and reduce cathode degradation, and makes critical advances toward enabling Si anodes for lithium-ion batteries.

Kinetic studies of cathode degradation on PEM fuel cell short stack level undergoing freeze startups with different states of residual water and current draws

One of the biggest challenges for a wide spread introduction of polymer electrolyte membrane fuel cells in automotive applications is the freeze start at subzero temperatures as this poses a severe threat to fuel cell performance and overall lifetime. Therefore, the impact of current draw during stack freeze startup at various rest water contents and current densities was investigated applying state of the art in-situ testing as quasi cyclic voltammetry.The results indicate a clear dependency between number of freeze startups and performance loss, whereas higher initial water content within the stack reduced its destructive impacts.In our earlier work we were able to show the dependency between residual water and degradation for non-freeze-startup-capable systems at the unit cell level [31]. With this work we confirm that the same physical relationship also applies to freeze-startup-capable systems on the short stack level.Furthermore, reversible performance losses that were encountered during this study can be assigned to oxidizable fuel contaminants, which are believed to be CO, and an easy cleansing procedure is being suggested.

Efficient Co-MoS2 electrocatalyst for cathodic degradation of halogenated disinfection by-products in water sample

The development of non-noble metal electrocatalysts that are efficient and low-cost are being sought as alternatives to noble metals for electrochemical degradation of organic halides. In this study, Co-MoS2, a non-noble metal electrocatalyst, was synthesized and deposited on graphite felt (GF) via the hydrothermal approach. The functionalized graphite felt was used as a cathode electrode for reductive degradation of halogenated disinfection products from water samples. Five halogenated disinfection byproducts (DBPs), CHBr2Cl, C3H5Br2Cl, CHBr3, CHCl3, and CCl4 were selected as model compounds, and electro-reductive degradation by the electrode was evaluated. The batch experiments performed with an undivided electrolytic cell revealed that the Co-MoS2-GF electrode exhibited superior electrocatalytic degradation towards the DBPs compounds compared to other reported electrodes in literature. Co-MoS2-GF electrode displayed a current efficiency of ̴ 13% and degradation efficiency of more than 90% for each of the DBPs after 60 min of electrolysis. The enhanced catalytic activity of the Co-MoS2 was ascribed to the synergistic role of CoS /MoS2 towards the accelerated Volmer step of hydrogen evolution reaction (HER), which aided the production of surface-bound atomic hydrogen *H. Cyclic voltammetry and scavenging experiments clarify the formation of *H during Co-MoS2-GF catalyzed water reduction and show its contribution to DBPs degradation. The prepared Co-MoS2-GF electrode also displayed substantial stability and reusability potential even after ten cycles of recurring operation.

Characterization of Cathode/Electrolyte Interfacial Processes By Scanning Electrochemical Microscopy

Lithium transition metal oxides (LiMn2O4 and LiMO2 where M=Ni, Mn, Co, etc.) are widely applied in lithium ion batteries due to their considerable capacity and energy density. Multiple processes occurring at the cathode/electrolyte interface lead to performance degradation, one of which is the dissolution of transition metals. While transition metal dissolution has been known to occur for some time, open questions remain about mechanistic details of these processes. This work uses the scanning electrochemical microscope (SECM) to observe active cathode degradation processes in situ and immediately at the cathode/electrolyte interface. These results are also paired with complementary analysis employing inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to yield insight into the properties of cathode degradation products and their reactivity.This work focuses on studies of LiMn2O4 thin films as model cathodes and characterizes products of the Mn dissolution process. The degradation process of binder-free LiMn2O4 thin films prepared by polymer assisted deposition was investigated in varied electrolytes. The properties of Mn dissolution products from cathode degradation is compared to Mn salt solutions introduced into complementary electrolytes. Our results appear to indicate substantial variations between the properties of dissolved Mn salts and actual cathode degradation products. Moreover, electrolyte composition appears to affect the electrochemical behavior of metal dissolution products significantly. This likely indicates that the LiMn2O4 degradation mechanism in differing electrolytes undergo different degradation reaction pathways.