Analysis of Cathode Interfaces in Solid State Lithium Batteries
出版項
2021
說明
1 online resource (134 pages)
文字
text
無媒介
computer
成冊
online resource
附註
Source: Dissertations Abstracts International, Volume: 82-11, Section: B
Advisor: Holewinski, Adam
Thesis (Ph.D.)--University of Colorado at Boulder, 2021
Includes bibliographical references
Interfaces between electrodes and the electrolyte in solid state lithium batteries frequently involve disparate materials in contact with one another under the effect of a large electrochemical potential-rather extreme conditions that can often lead to interfacial reaction and degradation, ultimately resulting in cell failure. Here, methodologies and analyses for probing the fundamental behavior at solid-solid interfaces for solid state lithium batteries are developed and explored, specifically investigating cathode interfaces with the solid electrolyte Li7La3Zr2O12 (LLZO).To investigate of cathode compatibility with LLZO from a primarily electrochemical perspective, LiMn2O4 (LMO) was chosen as a model cathode due to its wide operable voltage window and the extensive body of literature in other electrolyte systems available for comparison. Thus, LMO LZO i full cells are constructed and galvanostatic cycling combined with electrochemical impedance spectroscopy (EIS) is used to assess changes in cell capacity and resistances as a function of cycle number. A series of symmetric cells isolating individual electrode- electrolyte interfaces aids in pinpointing the specific sources of cell capacity fade. Combined with X-ray photoelectron spectroscopy (XPS) depth-profiling, these analyses indicate a region of interdiffusion occurs at the LMO-LLZO interface, thereby suggesting their incompatibility as a cathode-electrolyte pairing.To further explore behavior at the buried solid-solid interfaces, a novel electrochemical mass spectrometry (EC-MS) system is developed and implemented to probe gas-evolution from these interfaces under electrochemical load. It is commonly accepted, that despite extensive mitigation procedures, Li2CO3 is able to re-form on the surface of LLZO after its removal. Li2CO3 can therefore become a contaminant present at cell interfaces during synthesis, Interfacial Li2CO3 oxidation occurs in LMO LZO i cells starting at charging potentials relevant for the operation of common cathode materials. Evolution of CO2 and O2 from Li2CO3 decomposition is detected by EC-MS, and further confirmed via its detection under the same conditions in blocking Au LZO i cells. The decomposition of interfacial Li2CO3 is shown to cause large increases in cell impedance alongside significant capacity loss.The techniques developed in the proceeding studies are then applied to a solid state Li-O2 system, where patterned gold electrodes deposited onto LLZO act as cathodes, providing a conductive-network for the nucleation of the discharge product. The use of a carbon-free cathode and the absence of liquid electrolytes-two cell common cell components that result in parasitic side reactions-facilitates direct assessment of the Li-O2 chemistry in a solid state system. It is found that by cycling these cells at high temperatures, which is permitted through the use of solid electrolytes, the thermally-enhanced electronic conductivity of the discharge products permits much thicker discharge product film growth than in traditional aprotic electrolyte Li-O2 cells
Electronic reproduction. Ann Arbor, Mich. : ProQuest, 2021
