Abstract
All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and energy-dispersive X-ray spectroscopy data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300 °C. La2Zr2O7 and Li2CO3 were identified as decomposition products after annealing at 500 °C by synchrotron X-ray diffraction. X-ray absorption spectroscopy results indicate the presence of also LaCoO3 in addition to La2Zr2O7 and Li2CO3. On the basis of electrochemical impedance spectroscopy and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500 °C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode|electrolyte interfaces that enable fast Li transfer and high capacity.
Original language | English |
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Pages (from-to) | 6259-6276 |
Number of pages | 18 |
Journal | Chemistry of Materials |
Volume | 30 |
Issue number | 18 |
DOIs | |
State | Published - Sep 25 2018 |
Externally published | Yes |
Funding
The authors acknowledge the support of the Bosch Energy Research Network (BERN) grant, the MIT Energy Initiative, and MISTI MIT-Imperial College grant. This work made use of the MRSEC Shared Experimental Facilities at MIT, supported by the National Science Foundation under Award DMR 14-19807. D.D.F. was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the 23-ID-2 beamline of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors thank Zhan Zhang, Jon Tischler, Joshua Wright, John Katsoudas, Fatih Piskin, and Maximilian Jensen for their help with experiments at beamlines.