高電容量錫基奈米結構作為鋰離子電池之陽極

Abstract

此次研究中，我們提出在不使用模板與金屬催化劑的環境下，合成出錫基奈米結構，其中包含奈米棒、空球狀、奈米片狀之二氧化錫以及碳材包覆金屬錫之核殼一維奈米線作為陽極材料。此外，本研究也對錫基奈米結構的成長機制以及電化學性質作了詳細的探討。 首先，藉由氣固相反應，以氧化鈣及四氯化錫作為前驅物，氬氣作為載流氣體之環境，合成出具有相分離奈米棒之二氧化錫(短軸為10-20奈米長度；長軸為1-2微米長度)及氯化鈣鹽類。接著，藉由水熱法以不同的+4/+2價態錫之前驅物，合成出空球狀、奈米片狀之二氧化錫，其中空球之殼厚大約為200奈米厚度，球狀大小為1-3微米長度；片狀為40奈米厚度。根據實驗所觀察之結果，提出成長機制，藉其嘗試了解成長過程。並且進一步討論，在電化學性質上與不同形貌奈米棒、空球狀、奈米片狀之二氧化錫之間相關性。電池測試方面，以二氧化錫奈米結構作為電極(充放電速率為100 mA g-1)，奈米棒、空球狀、奈米片狀之二氧化錫經過100次循環充放電分別有435、522以及490 mA h g-1，其效能表現優異，主要原因為二氧化錫具有獨特之奈米形貌以及被非活性物質圍繞著，故此在充放電過程中，以至於能達到降低材料體積變化之壓力。 為了達到更佳效能以及減少不可逆現象，並以錫基為基礎的複合材料，故此設計一新穎之錫碳複合奈米材料作為電極材料。我們提出一簡單方式製備碳材包覆金屬錫之核殼一維奈米線材料。以二氧化錫作為前驅物，通入乙炔氣體及氬氣作為載流氣體之環境成長；其中短軸為100-350 奈米長度；長軸為數十微米長度；碳層為30-70 奈米厚度，並發現管壁中具有中空區域。根據實驗所觀察之結果，提出一氣固相反應的成長機制，藉其嘗試了解成長過程。電池測試方面，以碳錫材料作為電極 (充放電速率為100 mA g-1)，經過100次循環充放電仍有525 mA h g-1；甚至在快速充放電狀況(1000 mA g-1)，依然保有486 mA h g-1。因本材料具有獨特之一維形貌與中空區域作為體積膨脹之緩衝區域，故其效能之表現優異。

In this studies, we demonstrate the synthesis of tin-based nanostructures include SnO2 nanorods (NRs), hollow spheres (HSs), nanosheets (NSs) and Sn@C core-shell nanowires (NWs) without the usage of template and catalysts. Growth mechanism and electrochemical properties of tin-based samples were also investigated. First, phase-segregated SnO2 nanorods (NRs, length 1-2 m and diameter 10-20 nm) were developed in a matrix of CaCl2 salt by reacting CaO particles with a flowing mixture of SnCl4 and Ar gases at elevated temperatures via a vapor–solid reaction growth (VSRG) pathway. And developed a facile hydrothermal method to synthesize SnO2 hollow spheres (HSs) and nanosheets (NSs). The morphologies and structures of SnO2 could be controlled by Sn+4/+2 precursors. The shell thickness of the HSs was around 200 nm with diameter 1-3 μm, while thickness of the NSs was 40 nm. The correlation between the morphological characteristics and the electrochemical properties of SnO2 NRs, HSs and NSs were discussed. The SnO2 nanomaterials were investigated as a potential anode material for Li-ion batteries (LIBs). SnO2 NRs, HSs and NSs exhibit superior electrochemical performance and deliver 435, 522 and 490 mA h g−1 up to the one hundred cycles at a current density of 100 mA g-1 (0.13 C), which is ascribed to the unique structure of SnO2 which be surrounded in the inactive amorphous byproduct matrix. The matrix probably buffered and reduced the stress caused by the volume change of the electrode during the charge-discharge cyclings. Development tin-based nanocomposites containing suitably chosen matrix elements to achieve higher performance and reduce irreversibility processes. Designed strategy to fabricate a novel tin-carbon nanocomposites as electrodes of LIBs. Sn@C core-shell nanowires (NWs) were synthesized by reacting SnO2 particles with a flowing mixture of C2H2 and Ar gases at elevated temperatures. The overall diameter of the core–shell nanostructure was 100-350 nm. The C shell thickness was 30-70 nm. The NW length was several micrometers. Inside the shell, a void space was found. The reaction is proposed to be via a vapor–solid reaction growth (VSRG) pathway. The NWs were investigated as a potential anode material for Li-ion batteries (LIBs). The half-cell constructed from the as-fabricated electrode and a Li foil exhibited a reversible capacity of 525 mA h g-1 after one hundred cycles at a current density of 100 mA g-1. At a current density as high as 1000 mA g-1, the battery still maintained a capacity of 486 mA h g-1. The excellent performance is attributed to the unique 1D core-shell morphology. The core-shell structure and the void space inside the shell can accommodate large volume changes caused by the formation and decomposition of LixSn alloys in the charge-discharge steps.