Electrolyte Grains Research Articles

In-Situ Construction of Electronically Insulating and Air-Stable Ionic Conductor Layer on Electrolyte Surface and Grain Boundary to Enable High-Performance Garnet-Type Solid-State Batteries.

Lithophobic Li2CO3/LiOH contaminants and high-resistance lithium-deficient phases produced from the exposure of garnet electrolyte to air leads to a decrease in electrolyte ion transfer ability. Additionally, garnet electrolyte grain boundaries (GBs) with narrow bandgap and high electron conductivity are potential channels for current leakage, which accelerate Li dendrites generation, ultimately leading to short-circuiting of all-solid-state batteries (ASSBs). Herein, a stably lithiophilic Li2ZO3 is in situ constructed at garnet electrolyte surface and GBs by interfacial modification with ZrO2 and Li2CO3 (Z+C) co-sintering to eliminate the detrimental contaminants and lithium-deficient phases. The Li2ZO3 formed on the modified electrolyte (LLZTO-(Z+C)) surface effectively improves the interfacial compatibility and air stability of the electrolyte. Li2ZO3 formed at GBs broadens the energy bandgaps of LLZTO-(Z+C) and significantly inhibits lithium dendrite generation. More Li+ transport paths found in LLZTO-Z+C by first-principles calculations increase Li+ conductivity from 1.04×10-4 to 7.45×10-4Scm-1. Eventually, the Li|LLZTO-(Z+C)|Li symmetric cell maintains stable cycling for over 2000h at 0.8mAcm-2. The capacity retention of LiFePO4|LLZTO-(Z+C)|Li battery retains 70.5% after 5800 ultralong cycles at 4C. This work provides a potential solution to simultaneously enhance the air stability and modulate chemical characteristics of the garnet electrolyte surface and GBs for ASSBs.

Role of Fe3+ doping vis-à-vis secondary phases on the electrical transport of LiTi2(PO4)3 solid electrolyte

Fast ion conducting solid-electrolytes, with diverse technological applications, have been studied critically in recent years. Among various prototype structures, NASICON structured materials are known for their comparatively high bulk conductivities, which could be further improved by selective substitution at cationic sites. Present work reports the effect of Fe3+ doping at the Ti4+ sites vis-à-vis secondary phases on the ionic conductivity of NASICON structured lithium titanium phosphate (LiTi2(PO4)3 or LTP) solid electrolyte. Li1+xTi2−xFex(PO4)3 (x = 0.0, 0.1 and 0.2) was synthesized using the solid-state reaction method. Crystal structure, morphology, chemical composition, and ionic conductivity were studied using room-temperature powder X-ray diffraction (p-XRD), field emission scanning (FESEM) and high-resolution transmission (HRTEM) electron microscopy, and temperature-dependent impedance spectroscopy. Very low bulk activation energies were found for all the samples, attributed to interstitial diffusion via a concerted migration. The room-temperature ionic conductivity initially increased upon Fe3+ doping (x = 0.1) and dropped subsequently (x = 0.2). The aberrant growth of electrolyte grains, associated gas pores, and cracks formed during sintering were successfully reduced by the LiTiOPO4 phase formation upon Fe doping, initially raising the grain boundary conductivity. However, doped samples also showed segregation of another secondary phase, Li2FeTi(PO4)3, whose larger weight fraction at x = 0.2 severely restricted the Li-ion migration resulting in sudden conductivity loss. These results suggest the need to optimise the microstructure, especially the amount of secondary phases, which contribute to the grain boundary resistance, affecting the ionic conductivity of the samples.

Optimizing the Microstructure of Composite Cathodes in Garnet-Based All Solid-State Batteries By Continuum Modeling and Simulation

Due to their potentially higher energy densities and advantages in safety, all solid-state batteries (ASSBs) are being considered to replace conventional Li-ion batteries in a number of applications. Ceramic garnet-type electrolytes are promising candidates for the solid electrolyte in ASSBs because they provide high ionic conductivity and a wide electrochemical stability window.To improve battery performance, the optimization of the composite cathode in ASSBs is crucial. The microstructure of the cathode as well as interface phenomena occurring between active material particles and electrolyte grains are performance-limiting factors which need to be improved.In our contribution, we present microstructure resolved simulations in the 3D simulation framework BEST [1] demonstrating the effects of characteristic properties of the microstructure on the cell performance. By simulation studies using composite cathode microstructures with different particle size, active material fraction, and sinter density, we are able to identify advantageous properties which can serve as a target for the cell production.In the experiments, a large polarization of garnet-based ASSBs is observed which is commonly attributed to secondary phase formation between the active material and electrolyte in the production process [2]. Therefore, a new electrochemical interface model is introduced to account for the hindered transport of Li and electrons due to secondary phases. This model is based on physical parameters of the interface and, thus, can be used to get insights into the interface properties which are still subject of intensive research [3].[1] Latz, A.; Zausch, J. Thermodynamic consistent transport theory of Li-ion batteries. J. Power Sources 2011, 196, 3296-3302.[2] Finsterbusch, M.; Danner, T.; Tsai, C.-L.; Uhlenbruck, S.; Latz, A.; Guillon, O. High Capacity Garnet-Based All-Solid-State Lithium Batteries: Fabrication and 3D-Microstructure Resolved Modeling. ACS Applied Materials & Interfaces 2018, 10, 22329-22339.[3] Vardar, G.; Bowman, W. J.; Lu, Q.; Wang, J.; Chater, R. J.; Aguadero, A.; Seibert, R.; Terry, J.; Hunt, A.; Waluyo, I.; Fong, D. D.; Jarry, A.; Crumlin, E. J.; Hellstrom, S. L.; Chiang, Y.-M.; Yildiz, B. Structure, chemistry, and charge transfer resistance of the interface between Li7La3Zr2O12 electrolyte and LiCoO2 cathode. Chem. Mater. 2018, 30, 6259–6276.

Insights into the local structure, microstructure and ionic conductivity of silicon doped NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12

NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12 (LATP) is attractive because of the cheap raw materials, excellent air stability, and high ionic conductivity. Silicon doping is generally adopted to improve its conductivity further, but the corresponding mechanism is vacant. Herein, we synthesize the silicon doped LATP electrolyte with a simple solution-based method and systemically investigate the effects of different silicon doping level on the local structure, microstructure and ionic diffusion kinetics of the solid electrolytes. We firstly put forward the octahedral occupation of silicon in Li1.3Al0.3Ti1.7P3O12 electrolyte instead of tetrahedral sites. Silicon doping is found to be negative for the ionic transportation in grain bulk, however, the grain boundary conductivity can be increased after a small amount of silicon doping due to the modification of micro-structure, i, e., the silicon doping induces the segregation of LiTiOPO4 in the grain boundary, which can effectively suppress the abnormal growth of electrolyte grains and concomitant gas pores and cracks during sintering. As a result, the total conductivity can reach ∼10−3 S⋅cm−1 after silicon doping with this simple method. Our results demonstrate the critical importance of adjusting secondary phase on the micro-structure and ionic conductivity of electrolyte during the development of inorganic fast ionic conductors.

All‐Solid‐State Batteries: Nano‐Scale Complexions Facilitate Li Dendrite‐Free Operation in LATP Solid‐State Electrolyte (Adv. Energy Mater. 26/2021)

In article number 2100707, Christoph Scheurer and co-workers stabilize solid state electrolyte grains against Li dendrite nucleation and growth with a nanometer thin complexion. This naturally forming encapsulating layer serves as an effective electronic barrier while being permeable for Li ions. Future interfacial engineering could exploit a corresponding local separation of electronic and ionic flux at solid-solid interfaces for rational advances in all-solid-state batteries.

Rational Identification of Doping Strategy to Achieve a Highly Conductive and Reliable Protonic Electrolyte for Electrochemical Cells

While protonic ceramics are being utilized as electrolyte materials in electrochemical cells for hydrogen or electricity production, the higher proton conductivity and chemical stability under realistic operating conditions are required to deliver fast proton flux. For widely used Y or/and Yb doped Ba(Ce,Zr)O3 electrolytes, there are still some concerns with indistinct doping mechanism and uncertain element precipitation problem during sintering, which raise practical problem on electrolyte selection. In this work, the strategy of single element doping and co-element doping has been investigated to understand how they behave differently in proton conductivity and chemical instability. Three compositions, BaCe0.4Zr0.4Y0.2O3-δ, BaCe0.4Zr0.4Yb0.2O3-δ and BaCe0.4Zr0.4Y0.1Yb0.1O3-δ, are chosen to study the overall conductivity as function of B-site environment and gas conditions to provide experimental evidences for composition optimization. More importantly, the Y or/and Yb precipitation in each composition under various sintering conditions is extensively studied to explore the safe window for sintering the electrolyte with minimal element diffusion. In addition, the diffusion of nickel element into the electrolyte grain is also studied to understand the detrimental effects on grain boundary conductivity and consequently the electrochemical performance in the cells. This study will provide some insights into protonic electrolyte selection based on technical considerations on both excellence and stability.

Unidimensional Approximation of the Diffuse Electrical Layer in the Inner Volume of Solid Electrolyte Grains in the Absence of Background Ions.

In this paper we continue working on our theory of electrical double layers resulting exclusively from dissociation of a solid electrolyte, which we previously proposed as a medium for catalytic interaction between solid cellulose and solid acid catalysts of hydrolysis. Two theoretical unidimensional models of the inner grain volume are considered: an infinitely long cylindrical pore, and a gel electrolyte near a grain outer surface. Despite the model simplicity, the predictions for the cylindrical pore case are in semi-quantitative agreement with literature data on electroosmotic experiments, adequately explaining high proton selectivity of sulfonic membranes, and decline of such selectivity at high background acid concentration. The gel model predicts less concentrated diffuse layer in comparison to electrolytes with impenetrable skeleton (e. g., sulfonated carbons). This suggests limited suitability of gel electrolytes as catalysts if a substrate cannot diffuse into the gel bulk and the reaction is thereby spatially limited to the near-surface region, for example if a substrate is solid like aforementioned cellulose.

Fabrication of composite probe electrode used for localized impedance analysis of solid-state electrolyte LATP

A composite probe combining manganese-based active material with a tipless probe has been developed using a simplified dip-pen process for the localized impedance measurement (LIM) of a solid-state phosphate electrolyte. The active material is found to be composed of a spinel LiMn2O4 crystal phase, while the crystal structure of the solid-state electrolyte is indicated as lithium aluminum titanium phosphate (LATP). Compared with the impedance measurement of the LATP through a platinum/LATP/platinum (Pt/LATP/Pt) metal-insulator-metal (MIM) cell, in which only the overall bulk electrolyte resistance can be recognized, a LIM performed with a tipless probe enables discernment of the grain boundary resistance from the bulk electrolyte. It is seen that ion transport in the bulk electrolyte can be facilitated by applying external DC bias. The composite probe further allows us to detect the charge transfer resistance in the LiMn2O4/LATP interface in addition to the grain boundary resistance. It is also found that the charge transfer and grain boundary resistances increase with a similar trend when a specific high bias voltage (>1.5 V) is applied. This can be attributed to more ion extraction from LiMn2O4 into the LATP under the bias voltage. Consequently, the excess ions accumulated in the LATP would either inhibit further ion transport into LATP or retard ion transport across the electrolyte grain boundary.

In-operando observation of microstructural evolution in a solid oxide cell electrolyte operating at high polarization

In the present work a symmetric scandia yttria stabilized zirconia electrolyte based solid oxide cell is investigated in-operando by synchrotron X-ray diffraction as a function of time and position within the electrolyte while annealing at 700 °C in air and at a polarization of 2 V. In addition, scanning electron microscopy experiments are carried out on similar cells operating at temperatures of 700, 800 and 900 °C. Void formation in the grain boundaries of the electrolyte close to the anode/electrolyte interface is detected as early as 6 h. No clear trend is observed with respect to cell operation time and temperature in cells with equal grain size. However, grain boundary surface area may be inversely related to the frequency of void observations. A decrease of d-spacing in the anode interface region can be attributed to compressive stress associated with oxygen pressure build up. Decrease of d-spacing in the cathode/electrolyte region could be associated to oxide ion deficiency. Dark field X-ray microscopy is used to map for the first time the strain gradients within an electrolyte grain close to the anode region. Changes in strain domains after 10.5 h at operating conditions are assumed to be associated with early stages of void formation.

Interfacial Ion‐Transport Mechanism of Li7(Al0.1)La3Zr2O12 Solid Electrolyte Modified by using a Spark Plasma Sintering Method

AbstractA novel interfacial in situ modification for Li7(Al0.1)La3Zr2O12 is designed and prepared by using a spark plasma sintering method. The modified interface with most grain boundary area exhibits excellent interfacial electrochemical properties. The X‐ray diffraction (XRD) and scanning electron microscope (SEM) data indicate that the interfacial modified specimen (spark plasma sintering method, 1000 °C, 5 min) with 38.2(6) nm grain diameter and 32,134 cm2/g grain boundary specific surface area has the highest ionic conductivity (8.84×10−4 S/cm−1). The lithium‐ion transmission mechanism in grain‐internal and grain boundaries is revealed by ab initio theory, using Materials Studio software. Furthermore, the first‐principles calculation data indicate that the migration barrier of Li+ at the Li7(Al0.1)La3Zr2O12 solid electrolyte grain boundary is 0.21 eV, which is only 2/3 of that in the grain internal (0.33 eV). As a result, SPS interfacial in situ processing technology can increase the grain boundary area, thereby reducing the ion transport barrier and the interfacial impedance of the material.

Composite cathode material LSCF-Ag for solid oxide fuel cells obtained in one step sintering procedure

The lanthanum strontium cobalt ferrite (LSCF)-Ag composite cathode material was prepared in aqueous solution by new one-step method. In this method silver nanoparticles obtained by the reduction of [Ag(NH3)2]+ complex with sucrose were directly deposited onto the surface of LSCF powder. UV–Vis spectra of supernatant solution taken during synthesis showed the presence of a sharp excitation band near 397 nm attributed to the surface plasmon excitation of silver nanoparticles. Obtained composite powder was sintered to samaria doped ceria electrolyte in one step sintering procedure at 1000 °C. The presence of silver in LSCF cathode facilitates the oxygen reduction. The comparison of impedance spectra of LSCF-Ag cathodes with spectra reported in literature for similar LSCF cathodes shows that this effect is important at lower oxygen partial pressures. The analysis of the electrochemical impedance spectra recorded in the range 10−2–1010 Hz reveals that the second high frequency semicircle ascribed to the electrolyte grain boundary impedance is distorted due to process belonging to oxygen reduction reaction.

Porous ceramics based on yttrium and scandium-cerium doped ZrO2 with fluorite structure: Impact of chromium on conductivity

The total conductivity of the compositions containing Zr0.89Sс0.1Ce0.01О2 or Zr0.92Y0.08О2 powders and Cr2O3 was studied to evaluate a potential impact of the chromium deposition on the surface of electrolyte grains in the porous composite cathode. The compositions were fabricated in the corresponding ratios: (100-х) mol% Zr0.89Sс0.1Ce0.01О2 - х mol% CrO1.5 (10Sc1CeSZ-Cr) and (100-х) mol% Zr0.92Y0.08О2 - х mol% CrO1.5 (8YSZ-Cr) with х = 0.25, 0.5, 1, and 2. Porous ceramic Zr0.89Sс0.1Ce0.01О2 with 49% relative density exhibits higher conductivity than Zr0.92Y0.08О2. In general, a small addition of chromium decreases the conductivity of Zr0.89Sс0.1Ce0.01О2 and Zr0.92Y0.08О2, although the values of the conductivity change in a non-linear way, reaching minimum for 10Sc1CeSZ-Cr1 and 8YSZ-Cr0.25 compositions. This is accompanied by the decrease in the activation energy of the conductivity from 1.35 eV to 1.19 eV in the 10Sc1CeSZ-Cr series and from 1.28 eV to 1.19 eV in the 8YSZ-Cr series with the rise in the chromium content. Evolution of the conductivity values is associated with the interstitial incorporation of chromium into the fluorite structure as well as with its segregation on the surface of grains and grain boundaries. Chromium coexists in the multivalent states (Cr3+ and Cr6+) on the surface of grains. Considering a long-term operation of the SOFC system, one could suggest that Zr0.89Sс0.1Ce0.01О2 will show more promising transport characteristics in the presence of the chromium containing interconnects.

Improved Sr0.6La0.4Co0.8Fe0.2O3−δ/Ce0.8Y0.2O2−δ interface for IT-SOFC applications

One of the remaining challenges for the solid oxide fuel cell (SOFC) technology is decreasing its operation temperature to the 500–800 °C range in a cost-effective way without diminishing the cell performance. In this work, we studied a symmetrical cell composed of Sr0.6La0.4Co0.8Fe0.2O3−δ (LSCFO) cathodes deposited on a Ce0.8Y0.2O2−δ (CYO) substrate by the simple, cost-effective and scalable spin coating technique. The nanostructured cathode is composed of agglomerated ∼100–200 nm particles with ∼50 nm crystallite size. Electrochemical impedance spectroscopy (EIS) analysis indicates that electrolyte grain boundary conductivity strongly depends on the cathode nature. The detailed high resolution transmission electron microscopy (HR-TEM) characterization of the LSCFO/CYO interface reveals that the LSCFO cathode is well adhered to the CYO electrolyte. The improved nano/microstructure of the cathodes and the cathode/electrolyte interface yields to cathode area specific resistance (ASR) values as low as 0.4 Ωcm2 at 550 °C, being these values even lower than those previously reported in literature for cathodes in optimized LSCFO/CYO/YSZ/CYO/LSCFO cells.

Synthesis of rock-salt type lithium borohydride and its peculiar Li+ ion conduction properties

The high energy density and excellent cycle performance of lithium ion batteries makes them superior to all other secondary batteries and explains why they are widely used in portable devices. However, because organic liquid electrolytes have a higher operating voltage than aqueous solution, they are used in lithium ion batteries. This comes with the risk of fire due to their flammability. Solid electrolytes are being investigated to find an alternative to organic liquid. However, the nature of the solid-solid point contact at the interface between the electrolyte and electrode or between the electrolyte grains is such that high power density has proven difficult to attain. We develop a new method for the fabrication of a solid electrolyte using LiBH4, known for its super Li+ ion conduction without any grain boundary contribution. The modifications to the conduction pathway achieved by stabilizing the high pressure form of this material provided a new structure with some LiBH4, more suitable to the high rate condition. We synthesized the H.P. form of LiBH4 under ambient pressure by doping LiBH4 with the KI lattice by sintering. The formation of a KI - LiBH4 solid solution was confirmed both macroscopically and microscopically. The obtained sample was shown to be a pure Li+ conductor despite its small Li+ content. This conduction mechanism, where the light doping cation played a major role in ion conduction, was termed the “Parasitic Conduction Mechanism.” This mechanism made it possible to synthesize a new ion conductor and is expected to have enormous potential in the search for new battery materials.

SOFC Durability against Standby and Shutdown Cycling

To simulate realistic operating conditions in SOFC systems, we investigate the influence of thermal cycling on the performance of electrolyte-supported planar SOFCs. Thermal cycling is often associated with interruption of fuel supply, with three main modes; hot standby, cold standby, and shutdown. Cell performance degradation is most significant during shutdown cycles. Nickel oxidation and agglomeration are more pronounced when SOFCs are subjected to lower temperatures for longer periods of time, leading to significant performance degradation. Ostwald ripening at the anode leads to degradation as Ni grains increase in size with cycling. Ni particle precipitation on the anode zirconia grains and along electrolyte grain boundaries is found for the first time in shutdown cycling tests. When H2S is mixed with the fuel, the internal reforming reactions and electrode reactions are inhibited by sulfur poisoning of the Ni anodes, accelerating degradation. The SOFC cycling degradation mechanisms are discussed in detail.

Computer simulation of positive electrode operation in lithium-ion battery: Optimization of active mass composition

The work of the positive electrode (cathode) of a lithium-ion battery is simulated. The model of equally sized grains of three types: the intercalating agent grains with a volume fraction g, the electrolyte grains with a volume fraction gi, and the carbon black grains with a volume fraction ge is studied. The optimal composition of cathode active mass providing maximum specific capacity of cathode is determined. It is shown that a fraction of carbon black grains should be as small as possible: ge = 0.35. The variation in the fraction of intercalating agent grains within the allowable limits (0 ≤ g ≤ 0.3) changes the main parameters of cathode active mass: a fraction of electrochemically active intercalating agent grains g* (g* < g); a specific surface area S, on which the electrochemical process proceeds; and the conductivity k* by lithium ions in the ionic percolation cluster, which forms in the cathode active mass. The parameters g* and S decrease and parameter k* steeply increases with decreasing g. Therefore, in the range of possible values of g, specific capacity of cathode reaches the maximum value at g = gopt. The value of gopt is determined under the galvanostatic mode of cathode discharge. The cathode working parameters: the active layer thickness, discharge time, specific capacity, and potential at the cathode active layer/interelectrode space interface at the instant of discharge completion are calculated in relation to a fraction of intercalating agent grains g.

Computer simulation of the negative electrode operation in lithium ion battery: Galvanostatics, the problem of calculating working parameters

The work of the negative electrode (anode) of a lithium-ion battery operating in the galvanostatic discharge mode is simulated. Attention was focused on formulating the complete mathematical description of processes occurring on the anode. The most serious complication is associated with taking into account the diffusion limitation arising at the extraction of lithium atoms from grains of the active substance (intercalating agent). The analytical relationship is found between the average lithium concentration in the intercalator grain and the lithium concentration on the contact surface between the intercalator grains and the electrolyte grains. Algorithms of computer-assisted calculations are developed that allow the anode characteristics to be found. The following anode working parameters are determined: the active layer thickness, the complete discharge time, the specific electric capacity, and the final potential at the active layer/interelectrode space boundary. Calculations of the working parameters are carried out in the following two versions: for anodes with a thin active layer (imitation of processes occurring in an individual intercalator grain) and for anodes with the active layer of the optimal thickness. The procedure of selecting the reasonable discharge current, i.e., its maximum value at which virtually all lithium atoms can be removed from the active intercalator grain, is shown.

Computer simulation of negative electrode operation in lithium—ion battery: Galvanostatic discharge, porous electrode model and film model

Computer simulation of the structure and methods of operation (galvanostatic discharge) of the negative electrode of a lithium-ion battery is performed. Two possible models of the active anode layer were compared. 1. The model of porous active layer (mixture of active substance grains with grains of electrolyte). Here, the electrochemical process occurs within a porous active layer. 2. The film model (constant-thickness layer) of pure active substance (intercalating agent) grains without admixture of grains of electrolyte. In this case, the electrochemical reaction occurs only on the planar active electrode layer/interelectrode space interface. In both cases, the optimum working parameters of anode active layers were calculated: porous active layer thickness (in the film model, this was the calculation parameter), duration of full anode discharge, specific electric capacitance and finite difference between the intercalating agent/electrolyte potentials at the active anode layer/interelectrode space interface. It is found that each of these two models has its advantages and faults. Specific electric capacitance C cannot exceed the values of the order of magnitude of 10 C/cm2 when a porous active layer is used. Whereas in the film model, much higher values of C may be obtained: tens and even hundreds of C/cm2. On the other hand, in the case of anode discharge, the reasonable discharge current density value, its maximum value, at which practically full recovery of lithium atoms from active intercalating agent grains is still possible, proves to be by orders of magnitude higher in the case of an anode with a porous active layer, as compared with a film-type anode. Thus, in the case of development of electrode active layers of lithium-ion batteries, there is a possibility of choosing from two variants. There is the variant of an active film-type layer providing high capacitance values, but low discharge current density. Or there is another variant: a porous active layer with limited capacitance but then much higher values of discharge current density.

Computer modeling of positive electrode operation in lithium-ion battery: Model of equal-sized grains, percolation calculations

A computer simulation of the structure of the cathode active material in a lithium-ion battery is performed. The model of equal-sized grains of three types (active grains, grains of electrolyte, and carbon black grains) is studied. Acceptable bulk concentration of active grains g is estimated. It is in the range of zero to 0.3. Dependence of the key parameters of the electrode active material on its composition is determined: specific conductivity of electrolyte and specific surface area on which the electrochemical process occurs. It is shown that the average number of electrochemically active faces of active grains cannot be 100%, as usually assumed in the studies of diffusion processes occurring in an individual active grain. In the range of 0.0 ≤ g ≤ 0.3, the average number of active faces is in the approximate range of 2 ≤ n ≤ 3. The final choice of the optimum composition of components for the active material of a lithium-ion battery cathode (and, primarily, choice of the value for parameter g) requires performing an additional complex of computer simulations.

Solid Oxide Electrolysis Cells: Degradation at High Current Densities

The degradation of Ni/yttria-stabilized zirconia (YSZ)-based solid oxide electrolysis cells operated at high current densities was studied. The degradation was examined at , at current densities of −1.0, −1.5, and , with a 50:50 gas supplied to the Ni/YSZ hydrogen electrode and oxygen supplied to the lanthanum, strontium manganite (LSM)/YSZ oxygen electrode. Electrode polarization resistance degradation is not directly related to the applied current density but rather a consequence of adsorbed impurities in the Ni/YSZ hydrogen electrode. However, the ohmic resistance degradation increases with applied current density. The ohmic resistance degradation is attributed to oxygen formation in the YSZ electrolyte grain boundaries near the oxygen electrode/electrolyte interface.