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研究生:孫千媖
研究生(外文):Chien-Ying Sun
論文名稱:鹼金屬離子對薄膜電池氧化物電解質缺陷結構之影響
論文名稱(外文):Effect of Li Ion Doped in La1/3TaO3 on Structure Stability and Conductivity
指導教授:方冠榮
指導教授(外文):Kuan-Zong Fung
學位類別:碩士
校院名稱:國立成功大學
系所名稱:材料科學及工程學系碩博士班
學門:工程學門
學類:材料工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:中文
論文頁數:98
中文關鍵詞:鋰離子導體固態電解質鈣鈦礦結構
外文關鍵詞:electrolytePerovskite structureionic conductor
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由於現今科技產品的發達,攜帶式電子用品的普及,使得電源提供的元件越顯重要。自1980年代,鋰/鋰離子電池由於其高能量密度而受到重視,使得鋰/鋰離子電池的研究發展逐漸受到重視。為因應現今社會強調輕薄短小的潮流,鋰/鋰離子電池之薄膜化已是不可避免的趨勢。相較於液態電解質、高分子電解質而言,使用無機固態氧化物電解質是電池薄膜化之最佳方法。雖然其導電率低於液態電解質及高分子電解質,但在封裝可行性及安全性上卻是最具優勢的。
鈣鈦礦結構氧化物可利用異價離子的添加,使之形成離子缺陷,再加入適量之鋰離子,預期可形成具良好導電率之鋰離子導體。因此,本研究中採用具有高濃度陽離子缺陷的鈣鈦礦結構鑭鉭氧化物(La1/3-xLi3xTaO3)。在鈣鈦礦結構中,離子導體的導電機制是藉著A-site中所存在的空缺與帶電離子的存在,使帶電離子在周遭A-site中所存在的空缺移動而造成離子導電。但是,在添加鋰離子的過程中,鋰離子濃度與陽離子空缺濃度之相對變化也將對晶體結構之穩定性及相轉變產生影響。
因此,本研究以鑭鉭氧化物(La1/3TaO3)為base material。再利用鋰離子的添加來改變帶電離子(即鋰離子)濃度與陽離子空缺濃度,並觀察鋰離子濃度對鈣鈦礦晶體結構變化及離子導電率之影響。
在本研究中是在鑭鉭氧化物之鈣鈦礦結構的A-site中,藉著改變不同的鋰離子添加量(由0%~100%)探討鈣鈦礦結構之變化。結果發現在未添加鋰離子前所形成的鑭鉭氧化物為La1/3TaO3,此結構中存在了66%的A-site陽離子空缺,如此高的缺陷濃度造成了超晶格的形成,其成因為陽離子的有序排列:在垂直c軸的方向上,A-site中鑭離子和鋰離子主要分佈於(001)面,空缺則全部集中在 (002)面,如此交錯排列使得鑭離子和鋰離子在兩度空間中分佈。當鋰離子添加量達到25%,此時A-site中所存在的陽離子已超過50%,理論上無法再滿足上述的排列方式,因此A-site的陽離子漸呈現任意排列,因而超晶現象逐漸消失。再者,也由於鋰離子的添加使得A-site的陽離子數增加,也使得氧離子與氧離子間的斥力受到遮蔽效應而降低,導致其結構也由tetragonal phase轉變為較為對稱之cubic phase。
當高於50%的鋰離子添加於A-site中時,由於鋰離子的半徑遠小於鑭離子的半徑,造成鈣鈦礦結構中大多數的A-site陽離子已無法再與周圍的氧離子構成穩定的緊密堆積排列,因而造成Li-rich相的形成及兩相分離的發生,因為此時的Tolerance factor已小於穩定立方鈣鈦礦結構所需的0.8,因此Li-rich相的LiTaO3析出。
在離子導電率方面,以鋰含量為20%時(La0.266Li0.2TaO3),所得到的導電率值為最高。當鋰含量在20%以下的成份,由於陽離子空缺為二度空間的有序排列,使鋰離子僅限於平面傳導機制,因此導電率較低。至於鋰含量在20%以上的試片,因bottleneck的大小隨鋰離子的添加而逐漸縮小,使離子的傳導較為困難,因此在鋰含量為20%時,由於具適當的離子濃度、空缺濃度與最大的Bottleneck,可獲得最佳離子導電率。
Since 1980s, lithium/lithium ion batteries have emerged as one of the most important power sources for portable electronics due to their high energy density. In order to reduce weight and volume for portable electronics, the demand for lighter and thinner batteries is increasing. To reduce the battery size to micrometer range, using inorganic solid electrolyte is inevitable.
In search for Li ion conducting solid electrolyte, cation-deficient perovskite, La1/3-2XLi3XTaO3 has received considerable attention due to its better ionic conductivity. In ABO3 structure, ionic conduction originates from the migration of lithium ion via vacancies among the A-sites. It was found that the conductivity in La1/3-XLi3XTaO3 is strongly influenced not only by the carrier concentration, the size of bottleneck but also by the ordered arrangement of skeletal A-site ions.
In this study, the concentration of lithium ions added varied from 0% to 100% of the A-site cation sublattice in the lanthanum tantalate perovskite structure. La1/3TaO3 was found to exhibit perovskite structure in which two-third of A-cation sites were vacant. Such a high defect concentration causes an ordered arrangement of vacancies that formed a superstructure with doubled c axis compared with a standard perovskite structure.
According to the formula of La1/3-XLi3X□2/3-2xTaO3, when lithium concentration(3x) is over 25%, the vacancies concentration in A-site is no longer above 50%. With the increase of lithium concentration, the ordering phenomenon decreased. From the experimental result, when the addition of Li is less than 20% of A-site sublattice, the superstructure with vacancies located at (002) plane was still observed. But when more than 20% of Li was added into A-site sublattice, Li ions started to occupy A sites located at (002) plane. Consequently, the superstructure disappeared and the perovskite structure also changed from tetragonal phase to near cubic phase. The main reason is that the repulsion between anions or cations along c axis is stronger than that along the plane perpendicular to c axis. Thus, (001) plane and (002) plane must keep in a further distance to reduce the repulsion between charged ions. This results in the appearance of tetragonal phase in which the c-axis is larger than twice of a-axis. With more and more lithium ions added into the structure, the lattice has become less distorted and more isotropic because the mobile Li ions were randomly distributed in the A-site sublattice and the repulsion between oxygen ions is no longer significant.
When more than 50% of A-sites were incorporated by Li ions, the phase separation of cubic perovskite La0.17Li0.5TaO3 and rhombohedral LiTaO3 was observed. The phase separation was caused by the considerable difference of ionic radius between La and Li ions. The radius of lithium ion located at the A site is so small that the tolerance factor no longer falls in the range between 0.8 and 1. When the tolerance factor is beyond this range, a stable cubic perovskite could not be maintained. Therefore, a phase separation occurred.
The ionic conductivity of La1/3-2XLi3XTaO3 was strongly influenced by the charge carrier concentration and vacancy concentration available in the lattice. With small doping of lithium (0.2<3x), the conductivity increased with increasing of lithium concentration. When lithium concentration(3x) reached 0.2, the maximum conductivity of 7.1*10-5 S/cm was obtained. When lithium concentration increased to 0.5, the conductivity drop to only 10-8 S/cm due to the reduction of lattice constant.
The microstructure of (La, Li)TaO3 was also affected by the amount of Li added. For undoped and light Li-doped (<20%) (La, Li)TaO3 samples, columnar grains with tetragonal superstructure were observed. With the addition 20-50% of Li in the A-site sublattice, a single-phase and equiaxed grains was obtained. When excess amount of Li (>60%) was added, a Li-rich phase, LiTaO3, was segregated from the perovskite matrix.
中文摘要…………………………………………………Ⅰ
英文摘要…………………………………………………………Ⅳ
總目錄……………………………………………………Ⅶ
圖目錄……………………………………………………Ⅹ
表目錄…………………………………………………ⅩⅢ
第一章 緒論………………………………………………1
第二章 原理及文獻回顧…………………………………3
2-1 電池的基本原理與分類……………………………3
2-1-1 基本原理………………………………………3
2-1-2 電池的分類…………………………………3
2-2 鋰二次電池的簡介…………………………………4
2-3 鋰二次電池的電解質材料種類……………………7
2-3-1 有機溶液………………………………………7
2-3-2 高分子電解質……………………………………13
2-3-3 無機固態電解質…………………………………20
2-4 電解質必需的特性…………………………………24
2-5 鑭鋰鈦氧化物之缺陷結構…………………………24
2-6 離子移動活化能理論………………………………24
2-7 離子導電度(歐姆定律) …………………………26
2-8 Perovskite結構特性-Tolerance factor……26
第三章 研究動機與目的………………………………29
第四章 實驗方法及步驟………………………………32
4-1 試片的製備………………………………………33
4-2 性質測試…………………………………………34
4-2-1 試片之結構性質分析……………………………34
4-2-2 導電性質測試……………………………………35
4-2-3 熱膨脹係數的測定……………………………37
第五章 不同鋰離子添加量下的(La1/3-xLi3xTaO3)之結構穩定性與導電性之探討…………………………38
5-1 La1/3-xLi3xTaO之晶體結構分析………………38
5-1-1 La1/3TaO3之結構穩定性…………………………38
5-1-2 空缺對結構的影響……………………………44
5-2 鋰離子的添加對於La1/3TaO3的結構效應………46
5-3 微量的鋰離子添加對於La1/3Li3xTaO3(0≦ 3x≦0.2)
晶體結構之影響………………………………………49
5-3-1 超晶格現象的發生……………………………49
5-3-2 超晶格排列方式的印證…………………………51
5-3-2-1 單位晶胞中各原子座標位置的決定………52
5-3-2-2繞射峰Miller-index的決定…………………53
5-3-3 鋰離子濃度與晶體結構之關係………………57
5-4 鋰離子的添加對於La1/3Li3xTaO3(0.2≦ 3x≦0.5)晶體結構之影響……………………………………………58
5-4-1 超晶格的消失…………………………………59
5-4-2鋰離子濃度對繞射峰強度的消長……………61
5-4-3 晶格常數的劇減………………………………63
5-5 鋰離子的添加對於La1/3-2xLi3xTaO3(0.6≦ 3x≦1.0)晶體結構之影響…………………………………66
5-5-1相分離的發生……………………………… 66
5-6 La1/3-xLi3xTaO3導電性質之研究………………79
5-6-1 鋰離子的添加對離子導電率的影響…………79
5-7 不同鋰離子濃度下其導電活化能的探討…………84
第六章、結論……………………………………………91
參考文……………………………………………………96
致謝…………………………………………………………98
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