以生物原料輔助合成高比表面積二氧化鈦及其在鋰離子電池上的應用

Abstract

在此研究中，我們使用了幾種低成本、對環境無害的生物原料作為模板，和不同的二氧化鈦前驅物反應並產生各種形貌的二氧化鈦，分別有微球、片狀球、實心片狀球、channel孔洞狀及海綿孔洞狀二氧化鈦。其生成機制和在鋰離子電池上的效能都會在以下討論。 首先第一部分，使用溶劑熱法，正丁醇鈦作為前驅物，無水酒精作為溶劑，與鹼性胺基酸:精氨酸或麩胺酸鈉(味精)反應，水解縮合並進一步鍛燒而產生片狀球、實心片狀球和微球。產物的特性鑑定主要使用掃描式電子顯微鏡 (SEM)、穿透式電子顯微鏡 (TEM)、粉末型X光繞射技術 (XRD) 及氮氣吸脫附分析技術 (BET)。BET結果顯示其表面積約為30 ~122 m2/g。在鋰電池的表現方面，由表面積最大的片狀球表現最為優異，在高速充放電下5 C 和10 C分別達到167 mAh/g 及 132 mAh/g，電極在經由多次充放電後呈現不錯的穩定性。 第二部分，使用麵包酵母、葡萄糖和澱粉作為模板，異丙醇鈦為前驅物在水溶液條件下進行水解縮合反應。此部分反應酵母菌會在異丙醇鈦水溶液中生存數個小時，並在有氧的環境進行呼吸作用，分解葡萄糖或澱粉形成氣泡二氧化碳和水，二氧化碳在此反應為主要的大孔構造來源，形成channel狀的大孔。反應後的前驅物在氬氣及氧氣的環境下鍛燒400 °C而形成多孔洞二氧化鈦 (大孔範圍: 1–3 微米; 中孔範圍4–100 奈米)，比表面積範圍為34–125 m2/g。作為鋰電池的表現，以同時含有大孔中孔的channel孔洞狀二氧化鈦表現最佳。 第三部分，使用麵包酵母、葡萄糖作為模板，四氯化鈦為前驅物在乙醇水溶液條件下進行水解縮合反應。由於四氯化鈦遇水易形成強酸，故酵母菌在此條件下並不會存活下來。此條件的大孔來源為酵母菌本身。反應後的前驅物在真空及氧氣的環境下鍛燒400 °C而形成海綿狀多孔洞二氧化鈦 (大孔範圍: 2–3 微米; 中孔範圍4–70 奈米)。為了提升二氧化鈦的導電特性，此樣品進一步利用化學氣相沉積法，在樣品表面沉積上一層厚度約2奈米的碳層，同時具有大孔中孔結構，並且含有碳層的樣品在鋰電池上的表現極佳，在高速充放電下5 C 和10 C分別達到180 mAh/g 及 142 mAh/g，而材料在多次充放電後仍然保持穩定性。

In this study, microspheres (MS), nanosheet spheres (NS), solid spheres with nanosheets (S-NS), channel-like (CT) and spongy-like porous TiO2 (PT) were synthesized with the assistance of the bio-ingredients as templates. We have proposed reaction pathways and the battery performance were also investigated. First, facile route was established to synthesize high specific surface area TiO2 microspheres using basic amino acid (arginine or monosodium glutamate) as the templates. Titanium tetrabutoxide Ti(OBu)4 was used as the TiO2 precursor and absolute ethanol as the solvent. The solvothermal synthesis was carried out in a heated Teflon stainless-steel autoclave. The as-formed TiO2 precursor solid was further processed at 400 °C under air to generate the TiO2 microspheres (MS), nanosheet spheres (NS) and solid spheres with nanosheets (S-NS). They were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption analysis. The nitrogen adsorption-desorption isotherms revealed specific surface areas ranging from 30 to 122 m2/g. The products were used as an anode material for Li ion battery. The cells showed remarkable performance that the capacity of the the anode reached 167 mAh/g and 132 mAh/g under high charge/discharge rates, 5 C and 10 C respectively. They also demonstrated good cycling stability at varied charge/discharge rates. Second, we employed a simple sol−gel process to fabricate TiO2 precursors by reacting titanium tetraisopropoxide (TTIP, Ti(OiPr)4), instant yeast, and glucose/starch molecules in an aqueous solution. Remarkably, the yeast cells maintained their physiological activities and occurred respirations in the aerobic reaction. Their respirations produced CO2 and H2O as the metabolites. The evolution of CO2 produces numerous channels in the inorganic matrix. After further processing, porous channel-like TiO2 (CT) was prepared. (macropore size: 1 – 3 µm) The BET/BJH results revealed specific surface areas ranging from 34 to 125 m2/g, and mesoporous size distributions (4 – 100 nm). In addition, potential applications of the as-prepared TiO2 in Li ion batteries were explored. Finally, spongy-like porous TiO2 (PT) was synthesized by using yeast and glucose as the pore forming templates. TiCl4 in C2H5OH(l) containing NH4OH(aq.) was polymerized in the presence of instant yeast and glucose. The organic–inorganic hybrid precursor was further processed to generate macroporous anatase TiO2 (pore size: 2 – 3 µm) with mesopores (4 – 70 nm). The porous TiO2 was coated with a thin layer of carbon by chemical vapour deposition to generate the hierarchical C/TiO2 composite material. The porous products were investigated as anode materials for Li-ion batteries. The capacities of the hierarchical C/TiO2 electrode material remained 180 mAh/g and 142 mAh/g under high charge/discharge rates of 5 C and 10 C, respectively. It demonstrated good cycling stability of 318 mAh/g at 0.1 C at various discharge–charge rates. The excellent performance is attributed to the high specific surface areas and open spaces of the C/TiO2 allowing effortless intercalation/de-intercalation of Li ions.