Studies on mixed oxy-sulfide and mixed oxy-sulfide-nitride lithium glassy solid-state electrolytes
Date
2022-12
Authors
Hu, Guantai
Major Professor
Advisor
Martin, Steve
Jiang, Shan
Collins, Peter
Kovnir, Kirill
An, Qi
Committee Member
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Abstract
Lithium ion batteries have been widely used for portable devices to electric vehicles since 1990s. Solid-state lithium batteries (SSLBs) have been considered as promising candidate for next generation energy storage, since it can safely enable lithium anode, which will drastically improve energy density of batteries. Both sulfide glasses and oxide glasses can be used as ion-conducting electrolytes in SSLBs, however they are either unstable or poorly ion-conductive in most cases. Some inspiring studies on mixed oxy-sulfide (MOS) glasses have been reported, as they can sustain good stability and ionic conductivity at the same time, but none of them are good enough for commercial applications.
In this work, a number of new MOS and mixed oxy-sulfide-nitride (MOSN) glass compositions have been synthesized, processed and characterized. Structural information, thermal behavior and electrochemical performance have been revealed using a number of spectroscopies (IR, Raman, NMR, and XPS), x-ray diffraction, differential scanning calorimetry, and electrochemical stations. These results are helpful to understand structures and ion-mixing effects of those glassy solid-state electrolytes (GSSEs), and can provide insight to produce other high quality and high performance GSSEs.
First of all, an MOS glass composition, 0.67 Li2S + 0.33 [0.2P2O5 + 0.8SiS2)] GSSE has been synthesized via traditional planetary ball mill (PBM) method. However, it is found that unreacted raw material, Li2S, has not been fully incorporated into the glass powder even with 20h of energized milling process, and at the same time, the unfavorable elemental silicon ejection has been observed. A glass composition series, 0.56 Li2S+0.44 [(0.33-x) PS5/2 +x PO5/2 + 0.67 SiS2], have been then synthesized via melt-quench (MQ) method, and most of glasses made have been confirmed to be amorphous through a number of structural characterizations. Although these glasses are not yet capable to be make into high quality glass piece for battery tests, it still shows the advantage of MQ over PBM synthesis method. After a few trials on composition exploration, two GSSE compositions in 0.9[0.6Li2S + 0.4SiS2]-0.1[(1-y) LiPO3 + y LiPO3-3x/2Nx] have been successfully synthesized by MQ, and N incorporation has been confirmed through structure investigation. Using the same starting materials, high quality GSSEs, 0.56Li2S + 0.34SiS2 + (0.1-y) LiPO3 + y LiPO3-3x/2Nx, are finally synthesized, producing high quality glass pieces that are able to perform electrochemical tests. Results have shown N doping improved the ionic conductivity of GSSE, and good chemical and electrochemical stability are also revealed.
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dissertation