High Temperature Solid Electrolyte Research Articles

Enhanced performance of solid polymer electrolytes combining poly(vinylidene fluoride-co-hexafluoropropylene), metal-organic framework and ionic liquid for advanced solid state lithium-ion batteries

The search for sustainable and high-performance materials for lithium-ion batteries is leading to significant advances in solid polymer electrolyte (SPE) technology. However, the current drawbacks of this approach prove the need for further research and development in the field. Herein, novel ternary solid polymer electrolytes have been developed using varying loads of MOF-808 metal-organic framework and [BMIM][SCN] ionic liquid (IL) incorporated in a poly(vinylidene fluoride-co-hexafluoropropylene) matrix. The solid polymer electrolytes were evaluated at morphological, structural, thermal, mechanical and electrochemical levels, and their performance in cycling battery testing was assessed. The results showed a homogeneous structure throughout all the samples and a good dispersion of the distinct components. The polymer polar phase and degree of crystallinity of the samples are increased with increasing IL content, and the thermal and mechanical properties are appropriate for battery application. The ionic conductivity of the samples reaches maximum values of 4.68 × 10−5 S‧cm−1 at room temperature, lithium transference numbers up to 0.65, and high electrochemical stability, making them well-suited for battery applications. The assembled stability after 50 cycles at C/10 with a discharge capacity value of 150 mAh‧g−1 at room temperature was tested/derived. The obtained results show the potential of this system for high performance room temperature solid polymer electrolytes.

High Temperature Solid Oxide Electrolyte Fuel Cell Formulation: Non-Steady State Utilization of Fuel and Oxidant

The formulation presented in this paper was developed with the objective of its application to investigate the transient behavior of a high temperature solid oxide fuel cell (SOFC); especially with respect to the non-steady state consumption of fuel and oxidant reactants. Specifically, the chemical species transient amounts, their mole fractions, and total pressures in the cell anode-side fuel- (hydrogen) and cathode-side oxidant- (oxygen of the air) chambers can be predicted under the isothermal condition at a fixed cell-current level. The developed formulation is also capable of predicting the transient mole fraction profiles of fuel (hydrogen) and oxidant (oxygen) in the cell porous anode and cathode, respectively; thus, providing insight into the reactant species' effective transport and their utilization, via electrochemical reactions, in the cell porous electrodes. The presented formulation can be adapted for any fuel and oxidant combinations in any high temperature SOFC.

Synthesized by coprecipitation method for controlled phase structures of 5YSZ

Yttria-stabilized zirconia (YSZ), which exhibits a tetragonal phase, finds widespread application in the realm of high-temperature solid electrolytes. In the context of this research endeavor, a concerted effort was undertaken to procure a stable and controlled tetragonal phase structure within 5 mol% yttria-stabilized zirconia (5 YSZ) by modulating the precipitation rate of YSZ sols in three distinct precipitation environments, namely acidic (AC), near to neutral (NE), and alkaline (AL) conditions. Through the characterization of 5 YSZ compounds synthesized in these various environments, encompassing an assessment of their elemental composition, phase structure, local structure, and microscale morphology, it was discerned that under acidic conditions, the product exhibited non-uniform elemental distribution, pronounced agglomeration, and an abundance of hydroxyl groups, all of which proved detrimental to the stability of the tetragonal phase, resulting in the presence of 40.63% monoclinic phase. Conversely, under alkaline conditions, substantial agglomeration and hydroxyl group presence were also noted, with 34.7% monoclinic phase in the product. In stark contrast, under the condition which is near to neutral, the product demonstrated uniform elemental distribution, excellent dispersion characteristics, and a virtual absence of hydroxyl groups. The tetragonal phase structure remained stable and homogeneous, with almost negligible monoclinic phase content. Subsequent ceramic processing resulted in the highest attainable density (99.7%), coupled with the highest ionic conductivity at 850 °C (35.2 mS/cm). This study underscores that pH control during coprecipitation reactions stands as a robust and effective methodology for achieving a stable tetragonal phase structure.

Ternary Poly(ethylene oxide)/Poly(l,l-lactide) PEO/PLA Blends as High-Temperature Solid Polymer Electrolytes for Lithium Batteries

Lithium batteries are in high demand in different technological fields. However, the operating temperature is required to be below 70 °C, and this limits their use in applications demanding high-energy rechargeable batteries that are able to operate at temperatures above 100 °C. Poly(ethylene oxide) (PEO) is, currently, the reference solid polymer electrolyte (SPE) employed in solid-state lithium batteries. However, the application of PEO at higher temperatures is restricted due to the loss of mechanical properties. In this article, we show that the polymer blending strategy of blending PEO with poly(l,l-lactide) (PLA) allows extending its use in batteries at high temperatures (100 °C). This improvement is due to the mechanical reinforcement of PEO solid electrolytes associated with the presence of PLA crystals. Thus, two solid electrolyte systems based on PEO/PLA blends with either a LiTFSI salt or a lithium single-ion polymer (poly(lithium-1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide), PLiMTFSI) were investigated and compared. Differential scanning calorimetry (DSC) results indicate that regardless of the concentration of LiTFSI or PLiMTFSI in the blend, crystals of PLA are present with melting peaks at 160–170 °C and the lithium salt distributes preferentially in the PEO-rich amorphous phases. The ionic conductivity is negatively affected by the incorporation of PLA in the blends. However, at high temperatures (>70 °C), ionic conductivities of ∼10–4 S cm–1 were obtained for both systems. DMTA results showed that PLA addition increases the mechanical properties of the electrolytes, yielding storage modulus values of ∼106 Pa for the PEO/PLA/LiTFSI blend and ∼107 Pa or higher for the PEO/PLA/PLiMTFSI blend at high temperatures (100 °C). Finally, both ternary blends were compared in a symmetrical lithium battery at 100 °C, and the single-ion conducting PEO/PLA/PLiMTFSI system presented lower overpotentials, which is reflected in a lower polarization inside the lithium battery.

(Invited) Intermediate Temperature Direct Ammonia Fuel Cell Using Alkaline Electrolyte System

Ammonia is a very attractive carbon-neutral fuel due to its low cost, high energy density, and existing transportation infrastructure. However, the viable commercial application of direct ammonia fuel cells (DAFC) has not been realized, largely due to materials challenges that lead to poor cell performance. Generally, DAFCs either use low temperature polymer electrolytes, which are limited by low reaction rates and severe ammonia crossover, or use high temperature solid oxide electrolytes, which suffer from severe material thermal degradation. We have developed an intermediate temperature alkaline electrolyte-based DAFC that operates at 400-600 °C, enabling high reaction rates while limiting thermal degradation. This DAFC is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. The DAFCs uses state-of-the-art ammonia oxidation catalysts and ammonia-tolerant oxygen reduction reaction catalysts. Our DAFC has demonstrated an OCV of 1.2 V and can achieve 300 mA/cm2 at 0.86 V at 550 ⁰C, and 0.98 V at 600 ⁰C, or >450 mW/cm2 power from pure humidified ammonia. It has low ammonia crossover, thus enabling the high OCV and high power density without catalyst poisoning. Further work on catalyst development and cell design is underway to achieve higher power densities and reduce PGM catalyst loading and operation temperature, making this a more commercially viable technology.

Molten Lithium Battery for Space Applications

Solid-state electrolytes (SEs) have gained much interest lately as a potential for mitigating the various issues inherent in a most energy dense lithium metal (anode) based batteries such as lithium ion, lithium sulfur (Li-S), and lithium oxygen. Notable high energy next generation cathodes such as sulfur have their own issues with a liquid electrolyte based system, where the polysulfides discharge product dissolve into the electrolyte causing both: a loss of cathode active material and an unwanted shuttling of the polysulfides over the polymer separator to the lithium anode limiting their practical use. Moreover, the formation of lithium dendrites in lithium batteries is yet another challenging issue that not only limits battery cycle-life but also poses safety risks. The use of SEs can potentially address most of the issues related to next generation lithium batteries such as Li-S batteries, but getting rid of dendrite issues may not be addressed completely. One way to eliminate the dendrite issue is to use molten lithium as an anode.The National Aeronautics and Space Administration (NASA) has an ambitious plan to explore one of the most challenging planets in our solar system: Venus. The surface temperature of Venus can reach as high as 465°C and at same time, the Venus atmosphere is filled with corrosive gases such as carbon dioxide, sulfur dioxide, carbon monoxide, etc. A battery for such a challenging space mission can be built only if battery components (especially the electrolyte) is stable beyond 500°C and must be stable with molten lithium and sulfur electrodes for at least hours or days if not months—longer is better. Last but not the least, yet another challenge is containment of gaseous sulfur inside the battery container at such a high temperature. The potential to replace sulfur with selenium may mitigate the issue but at cost of reduced energy density.Under a NASA funded project, the University of Dayton Research Institute (UDRI) is developing molten lithium sulfur (Li-S) or lithium-selenium (Li-Se) batteries with the help of a high temperature solid ceramic electrolyte (SCE) that can enable a operating temperature >465°C for several hours. UDRI has been working on a high temperature SCE such as phosphate-based Li1+ xAlxGe2- x(PO4)3 (LAGP) ceramic electrolyte material1 that is stable beyond 500°C and also shows broad electrochemical window (up to 5V) that is sufficient for a molten Li-S or Li-Se battery operation; provided LAGP is stable with Li and S or Se in such harsh conditions and temperature. Unfortunately, LAGP is not stable with Li (forms a highly resistive interface layer between LAGP and electrode) and its stability with sulfur or Se, needs to be determined.Under the NASA project, UDRI has been developing interface materials between LAGP and electrodes for Li-S and Li-Se cells that can be stable at wide temperature range (room temperature to 500°C). The presentation will include progress on high temperature (up to 465°C) i) SCE, ii) SCE/Li interface materials, iii) SCE/S interface material, iv) SCE/Se interface material, v) impedance and open circuit voltage of Li-S or Li-Se cells at 465°C, and vi) cycle-life of Li-S or Li-Se cells at 465°C. To the authors knowledge, there is no such report (molten Li-S or Li-Se cells that can function at 465°C) that exists in literature.B. Kumar, D. Thomas, J. Kumar, “Space-Charge-Mediated Superionic Transport in Lithium Ion Conducting Glass–Ceramics,” J. Electrochem. Soc. 156, A506 (2009)

(Invited) Intermediate Temperature Direct Ammonia Fuel Cell Using Alkaline Electrolyte System

Ammonia is a very attractive carbon-neutral fuel due to its low cost, high energy density, and existing transportation infrastructure. However, the viable commercial application of direct ammonia fuel cells (DAFC) has not been realized, largely due to materials challenges. Generally, DAFCs either use low temperature polymer electrolytes, which are limited by low reaction rates, or use high temperature solid oxide electrolytes, which suffer from severe material thermal degradation. We have developed an intermediate temperature alkaline electrolyte-based DAFC that operates at 400-600 °C, enabling high reaction rates while limiting thermal degradation. This DAFC is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. The DAFCs use state-of-the-art ammonia oxidation catalysts and ammonia-tolerant ORR catalysts developed in-house and by our collaborators at SUNY Buffalo and University of Delaware. Our DAFC has demonstrated an OCV of 1.2 V and can achieve 300 mA/cm2 at 0.86 V, or >250 mW/cm2 power from pure humidified ammonia. It is stable for days without loss of activity and has very low ammonia crossover, enabling the high OCV and high power density without catalyst poisoning. Further work on catalyst development and cell design is underway to achieve higher power densities and reduce PGM catalyst loading and operation temperature, making this a more commercially viable technology.Acknowledgements: This work is financially supported by the Department of Energy’s ARPA-E under the award# DE_AR000814

CFD-simulation-based optimization of superheater for steam production from waste heat of SRF combustor

ABSTRACTA superheater uses waste heat from a combustor or an incinerator to produce superheated steam through heat exchange between saturated steam and exhaust (flue) gas. Superheaters predominantly use thin tube-type pipes, which makes it difficult to experimentally determine internal phenomena such as the flow, pressure distribution, and temperature distribution. Computational fluid dynamics (CFD) has recently been used to successfully analyze superheaters. In this study, steam at 180°C and 3.4 bars was converted via a cylindrical superheater into superheated steam above 700°C and 3bars using exhaust gas at 900°C from a solid refuse fuel combustor. The superheated steam was then supplied to a high-temperature solid oxide electrolyte cell to increase the hydrogen production efficiency of water electrolysis. CFD analyses were also conducted using a commercial Fluent simulator to study the effects of the furnace size, superheater size, inlet and outlet diameters, and steam generation amount on the exit temperature. The CFD simulation results were determined to be valid by a pilot experimental apparatus, which showed that the error rate between the experimental measurements and the simulation results was less than 2%. For the same volume, the superheater with the largest surface area (0.4-m diameter and 1-m length) produced the highest exit temperature. For steam inlet and outlet diameters of 8 mm, the highest exit temperature was 652°C. By reducing the flow rate to 70 kg/h, steam at over 700°C and 3 bars could be obtained under these optimal conditions.

Cycle performance of a Li/Li-rich half-battery with N-allyl-N-methylpiperidinium bis(trifluoromethanesulfonyl) imide protected by a high-temperature solid electrolyte interface membrane

We report a highly promising electrolyte based on N-allyl-N-methylpiperidinium bis(trifluoromethanesulfonyl) imide (PP13*TFSI) and lithium difluoro(oxalato)borate (LiDFOB) to greatly improve the cycle performance of a Li/Li1.1Ni0.25Mn0.65O2 battery at 2.5 V–4.6 V and 55 °C, which shows an initial discharge capacity of 181.7 mAh g−1 and a capacity retention of 90.9% after 150 cycles. A multiphase bilayer membrane structure is observed, which inhibits the decomposition of carbonate components and structure destruction. Physical characterization demonstrates the chemical interaction between PP13*+ and DFOB−, which prevents the cathode particle from structure degradation at 55 °C under high voltage.

High-temperature solid electrolyte interphases (SEI) in graphite electrodes

Thermal fragility of the solid electrolyte interphase (SEI) is a major source of performance decay in graphite anodes, and efforts to overcome the issues offered by extreme environments to Li-ion batteries have had limited success. Here, we demonstrate that the SEI can be extensively reinforced by carrying the formation cycles at elevated temperatures. Under these conditions, decomposition of the ionic liquid present in the electrolyte favored the formation of a thicker and more protective layer. Cells in which the solid electrolyte interphase was cast at 90 °C were significantly less prone to self-discharge when exposed to high temperature, with no obvious damages to the formed SEI. This additional resilience was accomplished at the expense of rate capability, as charge transfer became growingly inefficient in these systems. At slower rates, however, cells that underwent SEI formation at 90 °C presented superior performances, as a result of improved Li+ transport through the SEI, and optimal wetting of graphite by the electrolyte. This work analyzes different graphite hosts and ionic liquids, showing that this effect is more pervasive than anticipated, and offering the unique perspective that, for certain systems, temperature can actually be an asset for passivation.

Influence of elastic wave on electrochemical properties in high temperature solid electrolyte

Influence of elastic wave on electrochemical properties in high temperature solid electrolyte

A Safe High-Performance All-Solid-State Lithium-Vanadium Battery with a Freestanding V2O5 Nanowire Composite Paper Cathode.

The electronic conductivity and structural stability are still challenges for vanadium pentoxide (V2O5) as cathode materials in batteries. Here, we report a V2O5 nanowire-reduced graphene oxide (rGO) composite paper for direct use as a cathode without any additives for high-temperature and high-safety solid polymer electrolyte [PEO-MIL-53(Al)-LiTFSI] lithium-vanadium batteries. The batteries can show a fast and stable lithium-ion-storage performance in a wide voltage window of 1.0-4.0 V versus Li+/Li at 80 °C, in which with an average capacity of 329.2 mAh g-1 at 17 mA g-1 and a stable cycling performance over 40 cycles are achieved. The excellent electrochemical performance is mainly ascribed to integration of the electronic conductivity of rGO and interconnected networks of the V2O5 nanowires and solid electrolyte. This is a promising lithium battery for flexible and highly safe energy-storage devices.

Single Cubic Phase Scandia-Stabilized Zirconia: Stabilization and Aging at 600oC

Zirconia stabilized with 8-12 mol% scandia shows the highest value of oxide ion conductivity among zirconia-stabilized oxides. However, the cubic-rhombohedral phase transition at approximately 600°C prevents its use as high temperature solid electrolyte. To circumvent this problem, several additives have been proposed. In this work, ZrO2:10 mol% Sc2O3 was mixed to MnO2 to evaluate its effect on cubic phase stabilization, oxide ion conductivity and aging at 600oC. Pressed ceramic pellets of zirconia stabilized with 10 mol% scandia with addition of 1.0, 1.5, 2.0 and 2.5 mol% MnO2 were sintered at 1500 °C/2 h. X-ray fluorescence analysis was carried out to evaluate the manganese content. In situ high temperature X-ray diffraction data were collected to follow the rhombohedral-to-cubic transition. All specimens were analyzed by X-ray diffraction for structural phase evaluation and dilatometry for monitoring shrinkage. Polished and thermally etched surfaces of the sintered pellets were observed in scanning electron and scanning probe microscopes. Impedance spectroscopy measurements were carried out in the frequency range 5 Hz-13 MHz in the 300-500 °C temperature range. The single cubic structure is achieved for the specimen with 1 mol% MnO2 nominal addition, with no traces of the rhombohedral phase present in the ScSZ sintered pellets. The oxide ion conductivity of the YSZ + 1 mol%MnO2 specimen was monitored at 600 oC for 100 days by impedance spectroscopy measurements. After an initial decay, the ionic conductivity value of the solid electrolyte remained constant, suggesting its use as solid electrolyte in SOFCs operating at that temperature.

Study of reversible SOFC/SOEC based on a mixed anionic-protonic conductor

This paper deals with the fabrication and electrochemical study of a high temperature solid electrolyte supporting cell operating as SOFC (Solid Oxide Fuel Cell) and SOEC (Solid Oxide Electrolysis Cell). The cell is based on a dual membrane (DM) electrolyte design, advantageously separating the cell into three different chambers: hydrogen side, oxygen side, and dual membrane (DM), where H2O production or splitting takes place in SOFC or SOEC mode respectively. The supporting electrolyte consists of a dense/porous/dense tri-layer, exclusively made of BaCe0.85Y0.15O3−δ (monolithic design), which is a mixed anionic-protonic conductor. The assembly was fabricated by tape casting, adding pore formers to control porosity. The cell was then electrochemically studied under different operating conditions of temperature, overpotentials and gas feeding, either in SOFC and SOEC mode. From the results presented here, it can be observed that, in spite of dense and thick electrolyte layers and platinum electrodes, the electrochemical study of the cell showed: (i) promising power density, (ii) interesting SOFC/SOEC operating mode reversibility, (iii) proved H2O production in the porous dual membrane when the cell operates as a fuel cell, and proved splitting of the H2O molecules contained in the porous dual membrane when the cell operates as an electrolyser. Investigations of cell performance degradation were also conducted.

Graft copolymer electrolytes for high temperature Li-battery applications, using poly(methyl methacrylate) grafted poly(ethylene glycol)methyl ether methacrylate and lithium bis(trifluoromethanesulfonimide)

For successful hybridization of heavy vehicles, high temperature batteries might be the solution. Here, high temperature solid polymer electrolytes (SPE's) based on different ratios of poly(methyl methacrylate) (PMMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA), with LiTFSI salt (at a fixed ether oxygen (EO):Li ratio of 20:1) have been prepared and investigated. The copolymers comprise PMMA backbones with grafted PEGMA side-chains containing 9 EO units. The SPE systems were characterized using Raman spectroscopy, broadband dielectric spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, and electrochemical cycling in prototype cells, with a particular focus on the 83wt% PEGMA system. The electrolytes have good thermal stabilities and dissociate the LiTFSI salt easily, while at the same time maintaining low glass transition temperatures (Tg’s). Depending on the polymeric structure, ionic conductivities >1mScm−1 at 110°C are detected, thus providing ion transport properties for a broad range of electrochemical applications. Prototype Li|polymer electrolyte|LiFePO4 cells utilizing the SPE at 60°C showed surprisingly low capacities (<20mAhg−1 LiFePO4), which could be due to poor electrode/electrolyte contacts.

Electrochemical Performances of a Reversible High Temperature Fuel Cell Based on a Mixed Anionic-Protonic Conductor

This paper deals with the fabrication and study of a high temperature solid electrolyte supporting electrochemical cell operating as SOFC and SOEC. The cell is based on the idea of a dual membrane electrolyte, which has the advantage to separate the cell in three different chambers: hydrogen side, oxygen side and dual membrane (D.M.), where water production-SOFC or splitting-SOEC takes place. The tape casted supporting electrolyte is constituted by a dense/porous/dense tri-layer, made of BaCe0.85Y0.15O3-δ (BCY), which is a mixed ionic conductor. The electrolyte sandwich was formed by in-situ sintering of stacked green tapes with or without pore former. The process optimization (slurry formulation, lamination and thermal treatments) led to flat, crack-free, 580 µm thick BCY discs with a well-controlled microstructure. Platinum electrodes were deposited on both sides of the sandwich-structured electrolyte. The cell was then electrochemically studied under different operating conditions of temperature, overpotentials and gas feeding, either in SOFC and SOEC mode. From the presented results it can be highlighted that despite the dense electrolyte layers were kept thick and the electrodes were made of platinum, the electrochemical study of the cell show: i) a promising power density, ii) an interesting reversibility SOFC/SOEC, iii) a proved splitting of the water contained in the porous central membrane when the cell operates as an electrolyser (SOEC). Degradation of the cell performance is also focused.

Effect of Manganese Dioxide Addition on the Cubic Phase Stability, Densification and Electrical Conductivity of Scandia-Stabilized Zirconia

Zirconia stabilized with 8-12 mol% scandia shows the highest value of oxide ion conductivity among zirconia-based oxides. However, the cubic-rhombohedral phase transition at approximately 600 °C prevents its use as high temperature solid electrolyte. To circumvent this problem, additives have been proposed. In this work, ZrO2:10 mol% Sc2O3 was mixed to MnO2 and sintered at 1200 oC/2 h + 1450 °C/2 h with addition of 1, 1.5, 2 and 2.5 mol% MnO2. All specimens were analyzed by X-ray diffraction for structural phase evaluation and dilatometry for densification. Polished and thermally etched surfaces were observed in scanning electron microscope and scanning probe microscope. Impedance spectroscopy measurements were carried out in the frequency range 5 Hz-13 MHz in the 300-500 oC temperature range. The main results show that the manganese dioxide addition prior to sintering leads to the formation of single cubic phase, to the reduction of the maximum shrinkage temperature, and to an increase in the value of the total oxide ion conductivity.

ChemInform Abstract: Hydrogen Production via Solid Electrolytic Routes

AbstractReview: 61 refs.

Ionic conductivity of directionally solidified zirconia–mullite eutectics

Abstract The properties of directionally solidified eutectic (DSE) zirconia–mullite composites are presented. These materials combine two oxide ion conductors in eutectic microstructures stable over broad temperature (570–1415 °C) and pO2 (10− 20 to 105 Pa) ranges, which are pertinent for their application as high temperature (> 1200 °C) solid electrolytes, e.g. in Nernstian sensors. X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy results reveal a composite structure comprising eutectic crystals of mullite and zirconia, and an intergranular amorphous phase rich in Al–Y–Si–O. The amorphous phase is crystallised upon annealing at 1400 °C, and the resulting composites have a composition close to the nominal eutectic consisting of 79 vol.% mullite and 21 vol.% zirconia. The electrical conductivity of these materials is rationalized in terms of percolation, fraction and properties of each phase, attaining values in excess of 0.01 S/cm at 1370 °C and displaying Arrhenius behaviour with activation energy of 70 kJ/mol. The broad electrolytic domain of these solid electrolytes is demonstrated by conductivity measurements carried out from 600 °C to 1370 °C in O2, air, Ar and 10%H2 + 90%N2 atmospheres.

Mass spectrometric study of thermodynamic properties in the Yb2O3‐ZrO2 system at high temperatures

Materials based on the Yb2O3-ZrO2 system have many industrial applications such as high-temperature solid electrolytes, ceramics with special properties and most importantly for thermal barrier coatings. As their synthesis and use take place at high temperatures, information on the vaporization processes, thermodynamic properties and phase equilibria of this system at high temperatures is of great importance. Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using two tungsten effusion cells containing the sample under study and pure Yb2O3. The values of component activities in the Yb2O3-ZrO2 system were also calculated using the CALPHAD approach. The Yb and O vapor species were identified over the samples studied at 2400 K. Using these data the ZrO2 activities, chemical potentials of components and the Gibbs energies of the solid solution formation were calculated in this system. The thermodynamic values were also obtained as the result of modeling of the Yb2O3-ZrO2 system based on the CALPHAD approach using the data available on the phase diagram of this system and calorimetric measurements only. The thermodynamic functions found in the Yb2O3-ZrO2 system at 2400 K, such as the activities of components and the Gibbs energy of formation, displayed negative deviation from ideality. Mutual agreement was observed between the experimental thermodynamic values and the results of calculations based on the CALPHAD approach.