Cathode Degradation Research Articles

Phase Transformation of Lithium‐rich Oxide Cathode in Full Cell and its Suppression by Solid Electrolyte Interphase on Graphite Anode

Lithium‐rich oxide is one of the most promising cathodes that meet high energy density requirement for batteries of the future, but its phase transformation from layer to spinel structure caused by the lattice instability presents severe challenge to cycling stability and the actually accessible capacity. The currently available approaches to suppress this undesired irreversible process often resort to limit the high voltages that lithium‐rich oxide is exposed to. However, cycling stability thus improved is at the expense of the eventual energy output. In this work, we identified a new mechanism that is directly responsible for the lithium‐rich oxide phase transformation and established a clear correlation between the successive consumption of Li+ on anode due to incessant interphase repairing and the over‐delithiation of lithium‐rich oxide cathode. This new mechanism enables a simple but effective solution to the cathode degradation, in which an electrolyte additive is used to build a dense and protective interphase on anode with the intention to minimize Li depletion at cathode. The application of this new interphase effectively suppresses both electrolyte decomposition at anode and the phase transformation of lithium‐rich oxide cathode, leading to high capacity and cycling stability.

The effect of calcium impurities of β″-alumina on the degradation of NaxCoO2 cathodes in all solid state sodium-ion batteries

β″-alumina is a promising solid electrolyte candidate for room-temperature all-solid-state sodium-ion batteries due to its high sodium ionic conductivity of up to 10−2 S cm−1 at room temperature. However, calcium impurities are known to be present in the Al2O3 precursors used to produce commercial β″-alumina. Here we present a study on the impact of the calcium impurities which are diffusing in a temperature controlled process from the β″-alumina substrates into the NaxCoO2 layered oxide cathode. The increasing calcium content in the NaxCoO2 cathode leads to a degradation due to the formation of the calcium-rich Ca3Co4O9 phase. The electrochemical performance of sodium-ion batteries is investigated with NaxCoO2/β″-alumina/Na solid-state model batteries. The thin-film cathodes were grown onto commercial β″-alumina ceramic substrates by pulsed laser deposition and cycled between 2.0 and 3.8 V with metallic sodium anodes.

Highly Selective Pt/TiOx Catalysts for the Hydrogen Oxidation Reaction

Reducing the cathode degradation in proton exchange membrane fuel cells during start-up and shut-down events (where the anode is filled with H2 and air) is crucial for its widespread automotive imp...

Characteristics of pulsed streamer discharge with MgO cathode and enhanced toluene degradation

Herein, characteristics of pulsed streamer discharge ignited by a MgO/stainless steel (MgO/SS) cathode and toluene degradation at atmospheric pressure are investigated. The voltage-current characteristics, spatiol-temporal distribution characteristics of streamer propagation and optical emission spectroscopy (OES) of the streamer discharge are inspected. The results show that the discharge peak current with MgO/SS cathode is 20% higher than that with stainless steel (SS) cathode at the optimal condition. Compared with the SS cathode, MgO/SS cathode will suppress the intensity of primary streamer but enhance the intensity of secondary streamer. The emission spectral intensity of N2C3∏u,υ'→B3∏g,υ'' with MgO/SS cathode is higher than that with SS cathode, implying that the MgO/SS cathode can increase the production of active species in the pulsed streamer discharge. The electron density can reach 6.364 × 1021 m−3 for the discharge with MgO/SS cathode, which is higher than that with SS cathode (4.799 × 1021 m−3). MgO/SS cathode can improve the O3 production, toluene removal efficiency and energy yield of pulsed streamer discharge.

Understanding Performance Degradation in Cation‐Disordered Rock‐Salt Oxide Cathodes

AbstractThe collective redox activities of transition‐metal (TM) cations and oxygen anions have been shown to increase charge storage capacity in both Li‐rich layered and cation‐disordered rock‐salt cathodes. Repeated cycling involving anionic redox is known to trigger TM migration and phase transformation in layered Li‐ and Mn‐rich (LMR) oxides, however, detailed mechanistic understanding on the recently discovered Li‐rich rock‐salt cathodes is largely missing. The present study systematically investigates the effect of oxygen redox on a Li1.3Nb0.3Mn0.4O2 cathode and demonstrates that performance deterioration is directly correlated to the extent of oxygen redox. It is shown that voltage fade and hysteresis begin only after initiating anionic redox at high voltages, which grows progressively with either deeper oxidation of oxygen at higher potential or extended cycling. In contrast to what is reported on layered LMR oxides, extensive TM reduction is observed but phase transition is not detected in the cycled oxide. A densification/degradation mechanism is proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation‐disordered rock‐salts can lead to performance degradation in these newer cathodes with 3D Li migration pathways. Design strategies to achieve balanced capacity and stability are also discussed.

Effect of H2O and CO2 on LSCF-GDC Composite Cathodes

Polarization losses associated with the cathode oxygen reduction reaction (ORR) and degradation of cathode materials remain as hurdles for widespread implementation of solid oxide fuel cells (SOFC). Rates of degradation depend significantly on the operating temperature and gas conditions, such as the presence of unwanted oxygen-containing compounds, namely H2O and CO2. In this study, we explore H2O and CO2 degradation mechanisms for a common composite cathode material, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) - Ce0.90Gd0.10O1.95 (GDC) using electrochemical impedance spectroscopy (EIS) under various temperatures, oxygen partial pressure, and contaminant conditions to determine the effect of H2O and CO2 on LSCF-GDC. Our results suggest that CO2 and H2O compete with the ORR, and a strong correlation between blocking, degradation, and sintering effects caused by CO2 and H2O is directly observed. The interactions of CO2 and H2O with the cathode surface changes as a function of operating temperature, resulting in different short-term or long-term degradation mechanisms.

Dependence of La0.57Sr0.38Co0.2Fe0.8O3-δ Cathode Degradation Rate on Electrode Thickness

The degradation factor of the La0.57Sr0.38Co0.2Fe0.8O3-δ (LSCF) cathode is investigated based on the relationship between its electrochemical performance and effective thickness. When the decrease in bulk diffusion coefficient D is assumed as the dominant factor of degradation, the effective thickness of LSCF electrode will decrease. On the other hand, the decrease in surface exchange coefficient k is the dominant factor, effective thickness will increase. From the 100 hrs experiments using LSCF electrodes with various thicknesses, degradation became severe as the LSCF thickness is decreased. This implies that the decrease in k can be the dominant factor in LSCF degradation.

Numerical Model of Sulfur Poisoning on LSCF Cathode and Its Application to a 2-D Single Cell Simulation

The progress of LSCF cathode degradation by sulfur poisoning is numerically investigated. A few degradation models are developed on the bases of different assumptions and available material properties and applied to 1D simulations. The results of 1D simulations are compared with the experimental data to see if the model can phenomenologically reproduce them. The model which gives a reasonable prediction is applied to 2D CFD simulations of a single planar-type anode-supported SOFC. The 2D simulation model consists of the conservation equations of mass, momentum, energy, species and charge carriers, which are coupled by the electrochemical reaction models. A volume-averaging method is applied to the porous electrodes. The simulation results show that the developed model fairly predicts the formation of SrSO4 near the cathode–electrolyte interface particularly in the upstream region of the air channel.

Dependence of Proton Conductivity on Cathode Degradation in PEFC

Based on our previous finding that there is a correlation between proton conductivity of ionomers and carbon oxidation degradation in the cathode, we have focused on further investigating the correlation between proton conductivity of ionomers and carbon oxidation by varying ionomers. Carbon oxidation was evaluated in terms of increase in pore volume using a FIB-SEM technique followed by reconstructing to three-dimensional images. We have considered degradation under both the high RH condition, where the difference in proton conductivity of ionomers is less effective, and the low RH condition, where difference in proton conductivity of ionomers is more effective, by using different kinds of ionomers with different proton conductivity. Consequently, dependence of proton conductivity on carbon oxidation degradation in the low humidity condition was observed, and controlling the proton conductivity of ionomers was found to be important especially under low humidity.

Surface Energy and Reconstruction of Li and Na Based Transition Metal Oxides: A Computational Study

Interfaces between cathode particles and electrolyte have significant influence on performance and longevity of Li-ion batteries. Therefore, for further battery improvement deep understanding of cathode-electrolyte interface structure and its relationship with electrochemical processes inside the battery is strongly required. During the last few years, more and more studies are focused on the interfaces and surfaces of cathode particles, especially for layered transition metal oxides (TMO). For example, it was established that TMO surfaces experience reconstruction from layered to spinel and cubic structures, considerably affecting charge transfer through cathode/electrolyte interface and electrolyte and cathode stability [1]. Though initially reconstruction was considered mostly as a detrimental effect, resulting in increased barriers for Li insertion and cathode degradation, new studies show that reconstructed layer can serve as a natural protection from oxygen loss, preventing decomposition of electrolyte and insertion of water in cathode structure [2]. Though it is evident from experimental studies that the reconstructed layer resembles spinel and rock-salt structures, the exact ordering of atoms is controversial. More importantly, the governing factors for reconstruction are still not fully clear: in some cases, reconstruction occurs during synthesis and in others it proceeds under exposure to electrolyte and/or during cycling. Finally, surface reconstruction remains almost unexplored in promising Na-based TMO cathodes, where its role can be highly important, serving as a protective layer from water insertion [2]. In this work, we develop an algorithm for finding reconstructed structures of surface for transition metal oxides. The algorithm is based on the Monte-Carlo method used for a random swap of alkali atoms, transition atoms, and vacancies, while the density functional theory is used for atomic optimization after each Monte-Carlo step and accurate calculation of energies. The Metropolis method allows to take into account the influence of temperature and predict kinetically controlled surface structures. The algorithm is implemented in our SIMAN package for high-throughput materials modelling and available for free use [3]. Employing the developed algorithm, we consider several oxide compounds, such as LiNiO2, NaNiO2 and NaMnO2 used for pragmatic applications for rechargeable Li-ion and Na-ion batteries. We found that in LiNiO2 and NaNiO2 the formation of surface and subsurface anti-site defects is much easier than that in the bulk region. By making simulation at real synthesis temperatures, we observed kinetically controlled formation of spinel layers for both LiNiO2 and NaNiO2. Under oxidative conditions the transformation of the LiNiO2 surface to a rock-salt structure is thermodynamically favorable. The obtained results explain experimentally observed surface reconstruction to spinel and rock-salt structures in layered oxides. The undergoing study will identify the reasons that control the type of reconstruction depending on the chemical composition and synthesis conditions, providing useful guidelines for improving cathode materials.

Increasing Energy Density and Power Density in Hybridised Supercapacitor-Battery Devices

Research is presented aiming to increase both power and energy density of lithium batteries by applying composite cathodes containing sulphur, which has a high theoretical specific capacity of 1675 Ah/kgS and is an abundant and low-cost material, and increase the power density of the cells by creating battery-supercapacitor hybrids with the hybridisation carried out at electrode material level. The focus of current research worldwide has been to increase the cyclability of lithium-sulphur (Li-S) batteries, which has been accomplished by devising composite sulphur cathodes, to avoid cathode degradation due to the expansion of sulphur to accommodate the formation of sulphides, and various functionalisation approaches to trap the sulphides and avoid the ‘shuttle’ effect during charge. However, the theoretical capacity of sulphur has not been achieved even at first discharge, lowering the expected energy density, and this is further compounded by the fact that only a fraction of the composite cathode is sulphur. Modelling studies have shown that access of all sulphur by the Li+ ions in the micropores is critical and formation of sufficient amounts of higher order sulphides during the first stage of discharge is needed, to be able to obtain a long second stage discharge plateau. The first stage of our study is focused on demonstrating homogeneous and deep sulphur impregnation of porous carbonaceous material to create cathodes with more than 50 wt% sulphur in a supercapacitor-type, porous, host matrix. Repeated discharges are carried out after which we have achieved the theoretical specific capacity of sulphur at first discharge (cumulative curve in Figure 1). We shall continue with parametric studies to investigate the effect of different amounts of sulphur in the composite cathode on the pore size distribution and discharge capacity. The second part of this study includes the investigations into lithium battery-supercapacitor cells hybridised at electrode material level, in combinations of parallel and in series material parts in equivalent circuit models. The effect of the supercapacitor porous carbonaceous electrode materials on the voltage of the cell in galvanostatic charge-discharge curves will be presented in experimental investigations for half-cells of both sides and full cells. Some novel cell architectures will be presented aiming at minimising any detrimental reactions in the supercapacitor materials within the battery cell window. Figure 1

Performance of All Solid Li-Air Battery

The Li–Air battery converts the electrochemical reactions of lithium and O2 into electrical energy and has been receiving attention as the next generation battery because of its high theoretical specific energy of 3400 Wh kg-1. The high specific energy of the Li–Air battery can be attributed to the reaction in the cathode where only Li and O2 are needed, and it is an order of magnitude higher than that of the future generation Li ion battery that is predicted to reach at most 400 Wh kg-1. In the cathode, the carbon particles are used to provide electron conductivity as well as the surface area for the reactions, and the electrolytes are necessary to transport Li+ ions between the anode and cathode [1]. The pore distribution of the cathode is reported to influence the capacity [2], and the lifetime of the battery is reported to be limited by the stability of electrolyte [3]. To ensure higher stability against the oxidative conditions, the ionic liquid-based electrolytes are often used [4]. However, even the ionic liquid is known to decompose at the oxidative environment of the Li-Air battery operation conditions. To increase the cycle lifetime of the Li-Air battery, more stable form of electrolyte in cathode is desired. By constructing an all solid Li-Air battery which consists of Li metal, solid electrolyte, and oxide cathode, the source of cathode degradation can be greatly reduced by eliminating the liquid electrolyte and carbon in the cathode. The oxide material which showed both electronic and ionic conductivity in the order of 10-4 S/cm was used as the cathode. The cathode material was ball milled to obtain sub-micron sized particles and the surface area in the order of 10 m2/g. The cathode was coated to obtain a 10 μm cathode layer, and the layer was sintered onto a LATP (Lithium aluminum titanium phosphate) electrolyte layer. The Li metal was then attached to the cathode/electrolyte to form an all solid Li-Air battery. To operate the Li-Air battery, the Li metal was isolated from the O2 environment to which the cathode was exposed. The performance of the battery was evaluated in a O2 filled chamber which had the relative humidity up to 100%. The discharge and charge curves were analyzed to evaluate the feasibility and the cycle lifetime of the all solid Li-Air battery. The composition of the discharge product and the possible reaction mechanism will be presented. The strategy to increase the specific energy and cycle lifetime of the battery will be also discussed. [1] D. Aurbach, B. D. McCloskey, L. F. Nazar and P. G. Bruce, Nat . Energy , 2016, 1, 1–11. [2] N. Ding, S. W. Chien, T. S. A. Hor, R. Lum, Y. Zong and Z. Liu, J. Mater. Chem. A , 2014, 2, 12433–12441. [3] S. A. Freunberger, Y. Chen, Z. Peng, J. M. Griffin, L. J. Hardwick, F. Barde, P. Novak and P. G. Bruce, J. Am. Chem. Soc., 2011, 133, 8040–8047. [4] N. Mozhzhukhina, A. Y. Tesio, L. P. Mendez De Leo and E. J. Calvo, J. Electrochem. Soc., 2017, 164, A518–523.

Non-flammable LiNi0.8Co0.1Mn0.1O2 cathode via functional binder; stabilizing high-voltage interface and performance for safer and high-energy lithium rechargeable batteries

Demands of increased energy density and high-safety of lithium-ion and lithium metal batteries are growing for advanced electronics, electric vehicles and energy storage systems. Nickel-rich layered oxides such as LiNi0.8Co0.1Mn0.1O2 (NCM811) are appealing as promising high-capacity cathode materials. Their reversible capacity increases further by charging to higher voltages than conventional 4.2 V, which is however difficult to make because of unstable cathode-electrolyte interface and structural degradation. Herein, we report the combination of NCM811 cathode active material with non-aqueous functional polyimide binder to imparts enhanced thermal stability and highly stable interface originating from in situ building-up of surface protective polyimide layer at cathode through monodentate metal-carboxylate chemical bonds during slurry preparation, which permits to charge to 4.4 V despite in commercial electrolyte without any additive. This unique active material-binder combination not only suppresses metal-dissolution and cathode degradation and produces increased reversible capacity higher than 200 mAh g−1 but also provides unprecedented non-flammable characteristics contrary to the case of conventional binder, enabling a stable operation of higher energy and safer batteries.

Surface coating with Li-Ti-O to improve the electrochemical performance of Ni-rich cathode material

Abstract LiNi0.8Co0.1Mn0.1O2 is a promising cathode material for lithium-ion batteries due to its high capacity, high energy density and low cost. However, LiNi0.8Co0.1Mn0.1O2 suffers from an aggressive side reaction with electrolyte, resulting in poor cycling performance, large polarization and fast voltage degradation. To overcome these drawbacks, we use an acid coprecipitation method to prepare rod-shaped LiNi0.8Co0.1Mn0.1O2, and introduce a thin and uniform lithium titanium oxide layer on the surface by a solvothermal method. The 3 mol% lithium titanium oxide-coated LiNi0.8Co0.1Mn0.1O2 exhibits a much higher capacity retention (88.6%) than the pristine material after 100 cycles, and the polarization and voltage degradation of the Ni-rich cathode are largely alleviated. Furthermore, at an elevated temperature of 65 °C, the capacity retention of lithium titanium oxide–coated LiNi0.8Co0.1Mn0.1O2 is 81.1% after 50 cycles, which is much higher than that of pristine LiNi0.8Co0.1Mn0.1O2 (only 52.0%). These results suggest that the surface doping of Ti4+ and the introduction of the lithium titanium oxide layer help to improve the structure stability and mitigate the side reactions on the electrode-electrolyte interface, resulting in good electrochemical performance.

Evolution and degradation phenomena of electrode for proton exchange membrane fuel cells (PEMFCs)

Electrode degradation is the main problem of the lifetime for proton exchange membrane fuel cell performance. The operating conditions with different parameters, as high and low flow rates, high and low pressures for hydrogen and oxygen and the aggressive operating which the results show the distribution of the catalyst in the cathode by scanning electron microscopic (SEM) and degradation, especially in the catalyst. This shows the detachment of catalyst from the support as shown by X-ray diffraction (XRD) peaks and transmission electron microscopy (TEM). The XRD showed the decrease in intensity peaks after operating, which increase in the degradation of cathode as crystallinities phases, and increasing the particle size of catalyst from 4.14 to 5.57 nm for more than 100 h operating in a single cell of 25 cm2 with different operating conditions as shown by the TEM.
 Keywords: Electrode fabrication, degradation; characterisation.

Development and Validation of Chromium Getters for Solid Oxide Fuel Cell Power Systems.

Degradation of cathode in solid oxide fuel cells (SOFC) remains a major concern for the long-term performance stability and operational reliability. The presence of gas phase chromium species in air has demonstrated significant cathode performance degradation during long-term exposure due to unwanted compound formation at the cathode and electrolyte interface which retards the oxygen reduction reaction (ORR). We have demonstrated a novel method to mitigate the cathode degradation using chromium getters which capture the gas phase chromium species before it is ingested in the cathode chamber. Low-cost getter materials, synthesized from alkaline earth and transition metal oxides, are coated on the cordierite honeycomb substrate for application in the SOFC power systems. As-fabricated getters have been screened by chromium transpiration tests for 500 h in humidified air atmosphere in presence of chromium vapor. Selected getters have been further validated utilizing electrochemical tests. Typically, electrochemical performance of SOFCs (lanthanum strontium manganite (LSM) ǁ yttria stabilized zirconia (YSZ) ǁ Pt) was measured at 850 °C in the presence and absence of Cr getter. For the 100 h cell tests containing getters, stable electrochemical performance was maintained, whereas the cell performance in the absence of Cr getters rapidly decreased in 10 h. Analyses of Nyquist plots indicated significant increase in the polarization resistance within the first 10 h of the cell operation. Characterization results from posttest SOFCs and getters have demonstrated the high efficiency of chromium capture for the mitigation of cell degradation.

Effects of Environmental Conditions on Cathode Degradation of Polymer Electrolyte Fuel Cell during Potential Cycle

We investigated the effects of cell temperature and the humidity of gas supplied to the cell during the load cycle durability test protocol recommended by The Fuel Cell Commercialization Conference of Japan (FCCJ). Changes in the electrochemically active surface area (ECA) and in the amount of carbon support corrosion were examined by using the JARI standard single cell. The ECA declined more quickly when the gas humidity was raised, and the carbon corrosion was at the same level. These results suggest that the agglomeration of platinum was accelerated by the same agglomeration mechanism, i.e., by raising the humidity of the gas supplied to the cell.

Unraveling the Origin of Performance Degradation in High-Capacity Cation-Disordered Oxide Cathodes

Due to the substantial energy gap between state-of-the-art cathodes and anodes, development of new-generation Li ion batteries (LIBs) critically depends on cathode material discovery and improvement. In recent years, a combination of reversible redox activities of both transition-metal cations and oxygen anions were found to be feasible in a number of transition-metal (TM) oxides, such as the layered Li- and Mn-rich, lithium nickel manganese cobalt oxides (LMR-NMCs) and Li-rich rock-salt compounds. Such combination allows a significant enhancement in the charge storage capacity of LIB cathodes. However, challenges exist in these LIB cathodes with both cationic and anionic redox activities. After extensive cycling, performance issues such as capacity fade, voltage decay, hysteresis, and impedance rise often occur. Understanding the chemical origin of these issues in LMR-NMC has been on-going for well over a decade. Various degradation mechanisms, such as TM migrations, have been proposed. However, the effect of oxygen redox in cation-disordered cathode is largely unknown. In this work, we performed detailed studies on one of the most promising cation-disordered rock-salt cathodes, Li1.3Nb0.3Mn0.4O2 (LNMO). Systematic evaluation on the electrochemical behavior as a function of oxygen redox revealed that the performance deterioration is directly correlated to the extent of oxygen redox involvement. On the fundamental side, we performed a series of hard and soft X-ray absorption spectroscopic (XAS) studies to analyze the changes in Mn and oxygen activities due to cycling, and illustrated the chemical and structural origin for the observed voltage decay and capacity fade. It was found that electrochemical cycling with large contribution of oxygen redox significantly decrease the redox activity of oxygen itself as well as Mn redox activity. In contrast to what was reported on layered LMR oxides, extensive TM reduction was observed but phase transition resulting from cation site migration was not detected in the cycled oxide. A densification/degradation mechanism was proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation-disordered rock-salts can lead to performance degradation in these newer cathodes with 3-dimentional Li migration pathways. On the basis of these studies, cation site chemistry of Li-Nb-Mn rock salt system was systematically tailored to tune the contribution of oxygen redox. Opportunities in balancing capacity and cycling stability will be discussed.

Computational Insights to Charge Transfer Kinetics at the Cathode/Electrolyte Interface

The charge transfer reaction is the fundamental reaction for rechargeable batteries. The energy landscape of this reaction depicts the equilibrium and kinetics of the electrochemical process. Many transition metal oxide surfaces in a high oxidation state have been found to be unstable against common Li-ion electrolytes. It undergoes a spontaneous reduction upon immersion in the electrolyte in open circuit. This process involves the reduction of the cathode surface and degradation of the electrolyte to form a cathode electrolyte interphase (CEI), forming a complex cathode/CEI/electrolyte interface. However, the mechanism of this interaction remains unclear. In this work, a modeling framework was developed to predict the energy landscape of the charge transfer reaction at a LiCoO2/LiF/EC-electrolyte interface, with combined density functional theory (DFT) and molecular dynamics (MD) calculations. The energy profile of this reaction was simulated under different voltage. The mechanism of the interaction between LiCoO2 and EC-electrolyte would be discussed.

Interface and Grain Boundary Degradation of Cathode from Commercial Cells Induced By Electrochemical Operation in Humidified Air

Electrode performance degradation is a major obstacle for the development of SOFC technologies. Among different causes of electrode performance degradation, variation of operating gas environment could impact durability of SOFCs and lead to degradation. For the cathode, certain degree of humidity is always present in ambient air. It has been consistently reported that the degradation rate is accelerated when the cell is operated in the humidified air. This work presents nanostructure analyses of operated commercial SOFCs with either LSM/YSZ cathode or with mixed conducting LSCF/SDC cathode exposed to humidified air. For the cell with LSM/YSZ cathode, three commercial button cells were operated in humidified air for various time at 800 °C. Microscopy work reveals nanostructure degradation occurred within the cathode active layer, and it is most pronounced in the region next to the electrolyte. Newly grown Mn-rich nano-precipitates accompanied with nano-voids and cracking propagate at the LSM/YSZ interface. Additionally, prolonged operation in humidified air promotes the formation of the Mn-enriched precipitates at the YSZ/YSZ grain boundaries. By contrast, for the cell with LSCF/SDC cathode, upon long term operation of 2600 hours, Co and Fe enriched Spinel nano-grains were found accumulated at the original pore region of the cathode. The formation mechanism of Mn-enriched nano-precipitates and Co-enriched nanograins for the LSM/YSZ and LSCF/SDC cathode are discussed.