多數固態電解質都有導離率不佳的問題(<1 mS/cm)，但鋰鍺磷硫(LGPS)硫化物固態電解質在室溫下擁有與液態電解質相當的導離度(6~12 mS/cm)，使得全固態電池漸漸受到世人重視，但是此材料對負極的不穩定性以及硫化氫生成限制其商業化的發展。
本研究的第一個部分為LGPS合成，由於LGPS此材料合成困難，造成許多文獻所報導的導離率普遍不高(2~3 mS/cm)，本研究一開始也遇到合成出來的材料導離率不高的問題，但透過改變製程參數、組成和熱傳行為探討導離率與其材料結構的變化，始得到接近文獻所報導的導離率(6 mS/cm)。另一方面，合成此材料需要在手套箱外進行球磨的步驟，但台灣氣候普遍潮濕，在手套箱外進行球磨可能會造成水氣污染樣品導致結構被破壞，最後得到低導離率的樣品，本研究也發展一種無球磨的技術，能在不球磨的狀況且縮短合成時間的方式下得到高導離率的樣品(5.9 mS/cm)。
第二部分則是希望藉由氟的摻雜增強LGPS對負極的穩定性，透過在負極與電解質的介面生成LiF這種不導電子的物種，緩和Li-Ge合金的生長，而提升電化學穩定性。一開始進行摻雜發現LGPS對氟的溶解度並不高，會有明顯的thio-LISICON雜相生成，進而利用成分相圖來對此材料進行成分探索。在低氟摻雜(LixGeyPzS11.9F0.1)下，在增加Li2S比例下，其雜相生成會從thio-LISICON轉變Li7PS6，藉由後續成分相圖分析，最後得到組成 Li10.43Ge1.29P1.57S11.5F0.5(#12)。由鋰對鋰對稱電池發現其組成可在0.1mA/cm2下循環250小時; 而未摻雜的LGPS在200小時就有非常大的極化現象產生。進行全電池發現組成#12並不適合與NMC811正極材料接觸，會在電化學循環過程中產生導離率低的介面層，使得電池效能下降。在硫化氫測試方面為摻雜的LGPS 在30分鐘後所生成的硫化氫為20ppm，而組成#12的氟摻雜鋰鍺磷硫僅有15 ppm，推測可能是(P-F-/S2-)鍵結穩定整體結構降低硫化氫生成。本研究探討各種不同製程參數以及成分相圖對氟摻雜LGPS的結構影響。接近純相的Li10.43Ge1.29P1.57S11.5F0.5也成功被合成出來，具有高導度和良好濕度穩定性，對環境以及未來生產製程的影響有重大意義。

Solid state electrolyte generally faces the challenge of low ionic conductivity. Among all solid-state electrolytes, LGPS sulfide solid-state electrolyte exhibits very high ionic conductivity(6~8 mS/cm) comparable to liquid electrolyte at room temperature. However, this material suffers from anode instability, and hydrogen sulfide formation limit its commercialization.
The first part of this work is the LGPS synthesis. Due to the difficulty in synthesizing LGPS, many literature works report low ionic conductivity (2~3 mS/cm). At the beginning of this study, the as-synthesized LGPS also faced the problem of low ionic conductivity. After studying the material structure and ionic conductivity via different process parameters, composition and heat transfer behavior. Finally, the as-synthesized LGPS can achieve high ionic conductivity (6 mS/cm). This work also optimizes the process parameter with high ionic conductivity (5.9 mS/cm) and shorter synthesis time by removing the ball milling step outside of the glovebox due to Taiwan’s relatively high humidity climate.
The second part of this work utilizes lithium fluoride as a dopant to enhance the anode stability. At the beginning of doping, the fluorine solubility in the structure is not high enough, which makes the thio-LISICON phase formation. After this, using the composition phase diagrams were studied to explore the possible composition of this material. At the low extent of fluorine doping, we can observe a phase transition region from thio-LISICON to Li7PS6 in certain area in the composition diagram. After carefully analyzing the XRD patterns of specific compositions in the composition diagram. Finally, we successfully synthesized the fluorine-doped LGPS with the composition Li10.43Ge1.29P1.57S11.5F0.5(#12). Comparing composition #12 with pristine LGPS in a lithium symmetry cell configuration, the cell with composition #12 could be continuously cycled for 250 hr compared to 200 hr for pristine LGPS. In a full cell test, we learned an additional challenge that composition #12 would form a resistive layer during cycling when in contact with the NMC811 cathode, resulting in poor battery performance. In moisture stability measurement, the composition #12 has less H2S formation (less than 15ppm) compared to pristine LGPS (about 20ppm) which may be attributed to strong bonding of (P-S2-/F-) in the structure. This study investigates the feasibility of fluorine doped LGPS and demonstrates the effects of various synthesis parameters. Pure Li10.43Ge1.29P1.57S11.5F0.5 was prepared successfully with high ionic conductivity and excellent humidity resistance. The lesson learned paves the way for future production and mitigating the environmental concerns of sulfide solid-state electrolytes

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