鈉超離子導體結構固態電解質之界面化學探討

Investigation of Interfacial Chemistry of Na Superionic Conductor (NASICON)-structured Solid-state Electrolytes

仝梓正(Zizheng Tong)

指導教授 ： 劉如熹

國立臺灣大學/理學院/化學研究所/博士(2022年)

https://doi.org/10.6342/NTU202200972

摘要

固態二次鹼金屬電池因其於電動汽車與消費電子產品中潛在應用而受廣泛關注。具高離子電導率、低電子電導率及優異化學與電化學穩定性之固態電解質為製造固態電池之關鍵，其中鈉超離子導體 (Na superionic conductor, NASICON) 結構之鈉/鋰離子導體因其高離子電導率與空氣穩定性而被廣泛研究為固態電解質。然NASICON 結構固態電解質並不完美，界面接觸不良、寄生反應、枝晶等界面問題為限制NASICON結構固態電池之實際應用之挑戰。本研究專注於 NASICON 結構固態電解質之界面化學，其中涵蓋以Na3Zr2Si2PO12 (NZSP) 為代表之鈉離子導體與Li1.5Al0.5Ge1.5(PO4)3 (LAGP) 為代表之與鋰離子導體。 NZSP因其高離子電導率與空氣穩定性而被用於固態Na–CO2電池，而後將 NZSP 之經驗擴展至 LAGP 之界面化學，並製造固態鋰離子電池。
以NZSP為固態電解質製造固態Na–CO2電池，然由界面接觸不良引起之界面Na+擴散動力學緩慢導致固態Na–CO2電池無法實現放電。故此，將塑膠晶體離子導電框架嵌入多孔催化陰極中，以促進 NZSP 與催化劑之間界面處離子擴散。於離子導電框架之幫助下， 以Ru 奈米顆粒修飾之多壁碳納米管 (Ru/CNT) 為陰極之固態 Na–CO2電池於 100 mA g−1 下可循環50週期。基於實驗結果，建立“三擴散”模型以描述金屬–空氣電池之理想陰極，當離子、電子與氣體於多孔陰極處之擴散具相當之“佈線長度”時，金屬–空氣電池表現最佳性能。基於“三擴散”模型之理論，離子導電骨架之作用為減少鈉離子擴散之“佈線長度”，以利電池之室溫放電。
同時研究NZSP負極側之界面化學，發現靠近 Na 離子擴散通道 Na1-Na3 之 (200) 與 (−111) 晶面為 NZSP 與 Na金屬間之界面寄生反應之優先蝕刻晶面。此外，通過飛行時間二次離子質譜與透射電子顯微鏡檢測出富鈉界面層，表明額外鈉離子注入。因此，NZSP對金屬鈉腐蝕可歸因於鈉離子注入，它破壞（200）與（−111）晶面上之SiO4/PO4四面體。破碎之 SiO4/PO4 重組產生新矽酸鹽/磷酸鹽。 NZSP 與Na金屬之間形成界面動力學穩定之界面層， Na|NZSP|Na界面電阻於4小時後不再增加。
為提高固態Na–CO2電池之循環穩定性，採用鈉碳複合負極 (Na@C) 以改善鈉金屬負極與 NZSP 間界面接觸。以無序結構之炭黑用為碳源，將炭黑與熔化之Na金屬混合以製備Na@C。Na@C 複合負極之於NZSP之潤濕性提升以構建緊密接觸，從而將界電阻自918 Ω cm2降至98 Ω cm2。以Na@C 複合負極組成對稱電池於 0.1 mA cm−2 下穩定循環超1100 h。此外，具 Na@C 之固態 Na–CO2電池於0.015 mA cm−2下循環壽命延長至 68 次。
此外，將 NZSP 經驗擴展至研究 NASICON 結構鋰離子導體 LAGP 界面化學。鋰金屬負極對LAGP界面腐蝕中，由 Li1 與 O2 位組成之(012)晶面為優先蝕刻晶面。 (012)晶面之快速腐蝕乃因額外鋰離子注入造成，其破壞共頂角之GeO6八面體與PO4四面體。其中Ge4+被還原為金屬態，PO43−重組生成 P2O74−。鋰離子注入侵蝕 LAGP 並留下由分解產物隨機堆疊構成之富鋰界面，鋰離子與電子於界面中不同途徑擴散。此外，當電子與離子傳輸方向相同時，界面層增長更快。由此結果可得知離子與電子傳輸於 LAGP 之電化學腐蝕中具同等之重要作用。
為解決界面副反應問題，塑膠晶體電解質（plastic crystal electrolyte, PCE）與具三維主體結構之複合負極用於提升界面穩定性。 丁二腈、鋰鹽與Li6.4La3Zr1.4Ta0.6O12 (LLZTO)粉末共同構建PCE界面，以增強LAGP與鋰金屬陰極之界面穩定性。 為保護柔軟之PCE層免受枝晶穿刺，將高度石墨化之 KS6 與熔化之鋰金屬混合以製造複合負極。 受益於PCE與Li@C之研究成果，固態電池呈現增強之循環穩定性。
本研究探討LAGP與NZSP固態電解質與鹼金屬負極之穩定性，並利用適當之方式穩定其界面以提升固態電池之電化學性能。此外，基“三擴散”模型設計之固態 Na–CO2電池可於室溫實現充放電。此一理論模型為固態金屬空氣電池之陰極設計指明方向。本研究之相關工作為實現鹼金屬固態電池之實際應用奠定基礎。

關鍵字

固態電解質 ； 鋰金屬電池 ； 鈉金屬電池 ； 界面化學

並列摘要

Solid-state secondary alkali-metal batteries have attracted widespread attention for their potential application in electric vehicles and consumer electronics. A solid-state electrolyte with high ionic conductivity, low electronic conductivity, and excellent chemical and electrochemical stability is the key to making a better solid-state battery. Na superionic conductor (NASICON) structured Na/Li-ion conductors are widely studied as solid-state electrolytes because of their high ionic conductivity and air stability. However, NASICON-structured solid-state electrolytes are not perfect. Interfacial issues such as poor interfacial contact, parasitic reaction, and heterogeneous metal plating have been found as the challenges, which restrict the practical application of the NASICON-based solid-state battery. In this research, we focus on the interfacial chemistry of NASICON-structured solid-state electrolytes, which include Na3Zr2Si2PO12 (NZSP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) as representative Na-ion conductor and Li-ion conductor, respectively. NZSP has been employed as the solid-state electrolyte to fabricate solid-state Na–CO2 batteries due to its high ionic conductivity and air stability. Then the experience on NZSP is extended to the interfacial chemistry of LAGP, which has been used to fabricate solid-state Li-ion batteries.
NZSP is employed as the solid-state electrolyte to fabricate solid-state Na–CO2 batteries. However, the sluggish interfacial Na+ diffusion kinetics induced by poor interfacial contact results in the failure of solid-state Na–CO2 batteries. Herein, a plastic crystal ionic conductive framework is embedded in the porous catalytic cathode to promote ion diffusion at the interface between NZSP and cathode. With the help of the ionic conductive framework, the as-proposed solid-state Na–CO2 battery with Ru nanoparticles decorated multi-wall carbon nanotube (Ru/CNT) cathode delivers a life span of 50 cycles at 100 mA g−1. Based on the experimental results, a “tri-diffusive” model has been established to describe the ideal cathode of the metal–air batteries. The metal–air batteries are supposed to show the best performance when ion, electron, and gas diffusion have comparable “wiring lengths” at the porous cathode. Based on the “tri-diffusive” model, the role of the ionic conductive framework is to decrease the “wiring length” of Na-ion diffusion, thus facilitating the room temperature discharge of the cell.
Simultaneously, the interfacial chemistry on the anode side of NZSP has also been studied. (200) and (−111) planes, near the Na-ion diffusion channel Na1-Na3, have been found as the preferentially etched crystal planes of the interfacial parasitic reaction between NZSP and Na-metal. Furthermore, Na-rich interphase is detected by time-of-flight secondary ion mass spectrometry and cross-section transmission electron microscope, indicating the extra Na-ion injection. Therefore, the corrosion of NZSP against Na-metal can be ascribed to the Na-ion injection, which breaks SiO4/PO4 tetrahedron on the (200) and (−111) planes. The rearrangement of the broken SiO4/PO4 generates new silicates/phosphates, which are detected by Fourier-transform infrared spectroscopy and extended X-ray absorption fine structure. The interphase between NZSP and Na-metal is kinetically stable, as the interfacial resistance of Na|NZSP|Na no longer increases after 4 h.
To improve the cycling stability of the solid-state Na–CO2 batteries, a Na-carbon composite anode (Na@C) has been employed to improve interfacial contact between the Na-metal anode and NZSP. Carbon black with a disordered structure is employed as the carbon source. The Na@C is prepared by simply mixing carbon black with melted Na-metal. The intimate contact is constructed using the Na@C composite anode, thus decreasing the interfacial resistance from 918 Ω cm2 to 98 Ω cm2. The symmetrical cell with Na@C composite anode stably cycled over 1100 h at 0.1 mA cm−2. Furthermore, the solid-state Na–CO2 battery with Na@C shows a prolonged cycling lifespan of 68 cycles at 200 mA g−1.
Furthermore, the experience in NZSP is extended to study the interfacial chemistry of NASICON-structured Li-ion conductor LAGP. The (012) plane, consisting of Li1 and O2 sites, has been found as the preferentially etched crystal plane in the interfacial corrosion of LAGP against Li-metal anode. The fast corrosion of the (012) plane results from the extra Li-ion injection, which breaks the connection of corner-shared GeO6 octahedron and PO4 tetrahedron. As the result, Ge4+ is reduced to the metallic state, and PO43− is rearranged to generate P2O74−. The Li-ion injection erodes the LAGP and left Li-rich interphase, which is constructed by the random stack of decomposition products. Li-ion and electron diffuse from the different pathways in the interphase. Furthermore, the interphase grows faster when the electron and ion transport in the same direction. These results show that ion and electron transport plays an equally important role in the electrochemical corrosion of LAGP.
To fix the problem of interfacial parasitic reaction, plastic crystal electrolyte (PCE) and composite anode with a three-dimensional (3D) host structure play the role of matchmaker in combining the solid-state electrolyte and Li-metal anode. Succinonitrile cooperated with Li salt and Li6.4La3Zr1.4Ta0.6O12 nano-size powder built a PCE interphase, which enhanced the interfacial stability between Li1.5Al0.5Ge1.5(PO4)3 and Li metal anode. To protect the soft PCE from the dendrite penetration, highly graphitized KS6 was mixed with the melted Li metal to fabricate the composite anode. Benefitting from the matchmakers, the solid-state batteries exhibit enhanced cycling stability.
In this research, the interfacial stability of NASICON-structured solid-state electrolytes against alkali metal anode is studied. And the rationally designed strategies are employed to stabilize the interface between the solid-state electrolytes and alkali metal anode. Furthermore, a “tri-diffusive” model is built to describe the ideal cathode of metal–air batteries. Based on the model, a rechargeable Na–CO2 battery with NZSP electrolyte is fabricated. This research paves an accessible route for solid-state alkali metal batteries.

並列關鍵字

solid-state electrolyte ； Li-metal battery ； Na-metal battery ； interfacial chemistry

參考文獻

(1) Yang, S.; Qiao, Y.; He, P.; Liu, Y.; Cheng, Z.; Zhu, J.-J.; Zhao, H., A Reversible Lithium–CO2 Battery with Ru Nanoparticles as a Cathode Catalyst. Energy Environ. Sci. 2017, 10, 972−978.

(2) Lu, Y.; Rong, X.; Hu, Y.-S.; Li, H.; Chen, L., Research and Development of Advanced Battery Materials in China. Energy Storage Mater. 2019, 23, 144−153.

(3) Zhang, H.; Li, C.; Eshetu, G. G.; Laruelle, S.; Grugeon, S.; Zaghib, K.; Julien, C.; Mauger, A.; Guyomard, D.; Rojo, T.; Gisbert-Trejo, N.; Passerini, S.; Huang, X.; Zhou, Z.; Johnson, P.; Forsyth, M., From Solid Solution Electrodes and the Rocking-chair Concept to Today’s Batteries. Angew. Chem. Int. Ed. 2020, 59, 534−538.

(4) Larcher, D.; Tarascon, J. M., Towards Greener and More Sustainable Batteries for Electrical Energy Storage. Nat. Chem. 2015, 7, 19−29.

(5) Armand, M.; Tarascon, J.-M., Building Better Batteries. Nature 2008, 451, 652−657.