研發以二氧化錫為負極材料的鈉離子電池： 電解液、輔助性碳材料與黏著劑的優化;Development of Tin Oxide Anode for Sodium-Ion Batteries: Optimization of Electrolytes, Carbon Supports, and Binders

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Title:	研發以二氧化錫為負極材料的鈉離子電池：電解液、輔助性碳材料與黏著劑的優化;Development of Tin Oxide Anode for Sodium-Ion Batteries: Optimization of Electrolytes, Carbon Supports, and Binders
Authors:	潘卓督;Patra, Jagabandhu
Contributors:	材料科學與工程研究所
Keywords:	钠离子电池;为负极材料的;SnO2;電解液;輔助性碳材料;與黏著;Sodium-ion batterie;Anode;SnO2;Electrolytes;Carbon Support;Binders
Date:	2018-08-17
Issue Date:	2018-08-31 13:11:49 (UTC+8)
Publisher:	國立中央大學
Abstract:	鈉離子電池在後鋰電池時代的儲能裝置中極具競爭力，鈉在地殼中豐富的含量更使其適合應用於大型儲能設備。不過鈉離子電池的發展仍在初期階段。近期已有許具潛力的正極材料被提出，已獲得突破性的成果，並達到接近鋰離子電池的電容量。尋找適用的負極材料是極具挑戰性的，主要原因在於傳統的石墨（graphite）儲存鈉離子的能力相對不佳。近期，擁有高穩定性、易取得、低毒性、高理論電容量（1398 mA h g−1）等性質的二氧化錫獲得研究人員高度重視。然而，二氧化錫作負極材料的鈉離子電池，仍有以下四大缺點代改善：（1）較低的首圈充放電庫倫效率、（2）未達預期的充放電電容量、（3）不佳的高速充放電電容維持率以及（4）不佳的循環穩定性。本研究論文著眼於電解液、輔助型碳材料、黏著劑的最佳化，研發出有良好電化學表現的二氧化錫負極鈉離子電池。整體目標為克服二氧化錫負極遭遇的困境。第一部分為系統性地研究電解液，應用於超臨界二氧化碳系統合成二氧化錫/石墨烯負極系統中。我們研究以NaClO4 為鈉鹽的propylene carbonate (PC)、PC/fluoroethylene carbonate (FEC)、PC/ethylene carbonate (EC) 與 PC/EC/FEC 電解液系統，藉以了解FEC和EC 對於二氧化錫/石墨烯負極的庫倫效率、可逆電容量、高速維持率與循環穩定性的影響。此外，上述的性質研究也應用於N-Propyl-N-methylpyrrolidinium (PMP)–FSI 的離子液體系統，不同溫度的影響（25 °C 與 60 °C）也納入研究範疇。此部分的研究結果顯示電解液的成分調和對於充放電性質有極大的影響。第二部分研究注重輔助型碳材料的研發。二氧化錫奈米顆粒（直徑2 nm左右）被包覆於CMK-8碳材，其中CMK-8具有三維多向性的連結孔道。此系統可獲得傑出的可逆電容量（800 mAh g−1）、高速維持率（約10分鐘的放電時限達到 330 mAh g−1 的電容量）與循環穩定性（充放電300圈後維持80% 的電容量）。此外，SnO2-Sn 的嵌合轉化反應與Sn-Na合金化反應也獲得提升。此處提出的電極材料微結構形式，能大幅提升儲鈉性質，亦可作為其它正/負極電池材料的應用參考。第三部分研究注重於最佳化SnO2/CMK-8系統的黏著劑條件。我們導入polyvinylidene difluoride (PVDF)、sodium carboxymethylcellulose (NaCMC)、sodium polyacrylate (NaPAA)、與 NaCMC/NaPAA混和系統以提升鈉化/去鈉化的電化學性質。NaCMC與NaPAA之間的協和作用在電極生成有效的保護層，此保護層不僅能提升充放電庫倫效率，也有限制SnO2於CMK-8當中，避免金屬氧化物的聚集，進而影響循環維持率。在此混和系統中，20 mA g–1 與 2000 mA g–1 充放電速率下的電容量分別達到 850 mAh g–1 與 425 mAh g–1。更甚者，在300圈的循環充放電測試下，電容維持率仍高達90%。在電化學性質以外，黏著劑對於鈉離子電池熱失控的影響也透過示差掃描量熱儀分析。 ;Sodium-ion batteries (NIBs) are appealing as post-lithium energy storage devices, especially for large-scale energy storage applications owing to its abundance and global distribution. However, NIBs are still in the early stages of development. There have been many decent breakthroughs in developing stable and low-cost cathodes, with the performance being close to that of Lithium-ion batteries (LIB) cathodes. Finding a suitable anode is comparatively challenging since the commonly used LIBs graphite anode has poor Na+ storage capability. Recently, tin oxide (SnO2) has attracted much attention as the NIB anode because it is chemically stable, readily available, and environmentally benign, and has ability to deliver a very high theoretical specific capacity of 1398 mA h g−1. However, this anode currently encounters four major obstacles, which are low first-cycle coulombic efficiency, unsatisfactory charge–discharge capacities, poor high rate performance, and insufficient cyclic stability. This thesis is focused on the development of high-performance SnO2 anode through optimization of electrolytes, carbon supports, and binders. The sole objective of the thesis is to overcome the limitations of SnO2 anode. The third chapter of the thesis deals with the systematic study to optimize the electrolyte formulation for a SnO2/graphene anode, which is prepared via a supercritical-CO2-assisted synthesis method. Herein, we study various electrolytes like propylene carbonate (PC), PC/fluoroethylene carbonate (FEC), PC/ethylene carbonate (EC), and PC/EC/FEC electrolytes (with NaClO4 salt) to clarify the effects of FEC and EC on the columbic efficiency, reversible capacity, rate capability, and cycle life of a SnO2/graphene. Moreover, the above properties are compared to those of an N-Propyl-N-methylpyrrolidinium (PMP)–FSI ionic liquid (IL) electrolyte. The temperature effects (25 and 60 °C) for both the carbonate-based and IL electrolytes are also examined. The results obtained point out the importance of the electrolyte formulation, which affects the charge–discharge performance of the electrode to a great extent. The fourth chapter of the thesis deals with the development of unique carbon support for SnO2. Nanosized SnO2 particles (~2 nm in diameter) are embedded in ordered mesoporous CMK-8 carbon with three-dimensional interconnected pore channels. With the unique SnO2/CMK-8 architecture, exceptional reversible capacity (800 mA h g−1), rate capability (delivering 330 mA h g−1 in ~10 min.), and cyclic stability (80% retention after 300 cycles) is achieved. Also, the SnO2−Sn conversion reaction and Sn−Na alloying reaction were effectively promoted. The proposed microstructure/architecture of the electrode material is highly effective in boosting Na+ storage properties and should be applicable to other anodes and cathodes in various battery applications. The fifth chapter deals with the optimization of binders for SnO2/CMK-8. Herein, we employed polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and NaCMC/NaPAA mixed binders to enhance the electrode sodiation/desodiation properties. Synergistic effects between NaCMC and NaPAA lead to the formation of an effective protective film on the electrode. This coating layer not only increases the charge–discharge Coulombic efficiency, suppressing the accumulation of solid-electrolyte interphases, but also keeps the SnO2 nanoparticles in the CMK-8 matrix, preventing oxide agglomeration and falling off upon cycling. With NaCMC/NaPAA binder, exceptional electrode capacities of 850 and 425 mA h g–1 are obtained at charge–discharge rates of 20 and 2000 mA g–1, respectively. After 300 cycles, 90% capacity retention is achieved. The thermal reactivity of the sodiated electrodes is studied using differential scanning calorimetry. The binder effects on NIB safety, in terms of thermal runaway, are investigated.
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