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Cold Sintering of of Solid-State Sodium-Ion Battery Composites

Author
Grady, Zane
Published
[University Park, Pennsylvania] : Pennsylvania State University, 2023.
Physical Description
1 electronic document
Additional Creators
Maria, Jon-Paul
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Open Access.
Summary
Solid-state sodium-ion batteries (NaSSBs) have been proposed as one of the potential partial solutions to the future of energy storage. One of the most significant obstacles to the fabrication of NaSSBs is the processing of the ceramic sodium-ion solid-state electrolytes (SSEs), requiring solid-state sintering temperatures nearing 1200°C in order to obtain the high densities which yield high conductivity polycrystalline ceramics. These high temperatures preclude careful control of light element stoichiometry and prohibit the co-processing of these SSEs with composite solid-state electrodes. Thus, the primary objective of this thesis was to investigate the application of a low temperature sintering technique termed cold sintering, (which combines a transient solvent, uniaxial pressure, and temperature during sintering) to the fabrication of NaSSBs. First, the cold sintering process was applied to the archetypal "NASICON-structured" ceramic SSE, Na3Zr2Si2PO12 (NZSP). Using an NaOH transient solvent, cold sintering proved capable of achieving relative densities greater than 90% with a sintering temperature of 375°C, a uniaxial pressure of 350 MPa, and a dwell time of three hours. These cold sintered NZSP ceramics attained high conductivities, in excess of 10-4 S.cm-1, which is competitive with NZSP sintered at 1200°C. This process was then extended to the densification of a the refractory [beta]''-Al2O3 SSE, demonstrating a reduction in sintering temperature from 1600°C to 375°C. In the case of the [beta]''-Al2O3 SSE, the relative density was once again in excess of 90% and the ionic conductivity at high temperature neared that of solid-state sintered SSEs but required a post-annealing step to remove defects in the as-cold-sintered [beta]''-Al2O3. These results demonstrated the effectiveness of cold sintering for distinct NaSSB SSEs at unprecedent temperatures. The same cold sintering process was then applied to composites of the NASICON NZSP SSE, a chemically similar Na3V2(PO4)3 ceramic active material, and carbon. It was shown that the low sintering temperature avoided major decomposition and interaction between the phases, the onset of which is shown to be ca. 600°C, allowing for one of the first demonstrations of ceramic matrix triphasic solid-state electrode composites containing such thermally fragile conductive agents. By varying the composite composition, it was shown that the ionic and electronic conductivity on the composites could be increased significantly and systematically. The properties of the carbon-ceramic and ceramic-ceramic were investigated within the context of a percolation model and mixing law behavior respectively. The cold sintered triphasic composites demonstrated fair electrochemical performance in a half-cell configuration. The limited electrochemical performance was revealed to originate from a previously unreported interaction between the NZSP SSE and carbon, which has important implications potential future NaSSB solid-state electrode design. Despite this interaction, multilayer structures composed of solid-state composite electrodes and dense NZSP SSE layers were cold sintered in a single step at 375°C. In a symmetric cell configuration, the all-solid-state batteries demonstrated reversible electrochemical cycling in a temperature range of 50°C to 120°C, serving as a proof-of-concept cold sintered NaSSB system. Based on the limitations observed in this proof-of-concept system, a sodium layered oxide cathode material was selected as a future improvement towards practical performance. The NaOH mediated cold sintering process was shown to be effective in densifying this material as well, especially when the powder surface was desodiated using a solvent wash prior to the cold sintering process. While this work overtly focuses on the study of cold sintering for NaASSBs, interpretation of the findings requires a distinctly multidisciplinary scientific approach, ranging from the thermal processing of ceramics, oxide surface-solvent interactions, the ac response of novel composite systems, the relationship between mixed conduction and electrochemical performance, and the formation/characterization of solid-solid interfaces for electrochemical applications. In turn, the findings described herein may be similarly broad in the scope of their scientific usefulness.
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Dissertation Note
Ph.D. Pennsylvania State University 2023.
Reproduction Note
Microfilm (positive). 1 reel ; 35 mm. (University Microfilms 30551198)
Technical Details
The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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