以硫醇添加劑控制電鍍銅的動⼒學與微結構及其在鋰⾦屬電池負極的應⽤

Using thiol additive to control the kinetics and microstructure of copper electrodeposition and its application as the anode of lithium metal batteries

林浚丞(Chun-Cheng Lin)

指導教授 ： 胡啟章

國立清華大學/工學院/化學工程學系/博士(2020年)

摘要

本篇論文研究主旨是銅與鋰金屬的基礎電鍍行為，並以新穎的合成方法製備具特殊晶形的銅箔，與探討其在可充放電式鋰金屬中的應用。本論文的研究主題可分為三大方向：
1. 硫醇類型添加劑對電鍍銅還原動力學的影響及其老化失效原因
在新穎的半導體及印刷電路板銅製程中，以電鍍法將奈米或微米級的孔洞或溝槽填滿作為內連導線使用，已被廣泛應用於微型晶片及電路板的製程中。為使微奈米級填孔製程達到超級填充的電鍍成果，必須添加適當的有機添加劑以輔助電鍍銅的沉積，其中含硫醇官能基的物質時常被使用為鍍銅的光澤劑。為了提高填孔製程的操作穩定性，我們針對硫醇類添加劑對電鍍銅的基礎動力學影響進行研究，成果發現光澤劑對硫酸銅電鍍的還原機制有著顯著影響。相對於僅含有銅離子、硫酸、氯離子與抑制劑的電解液中，其具備顯著的去極化能力，並能將銅離子還原的機制由類雙電子轉移、一步驟反應途徑轉為單電子轉移、兩步驟反應的途徑。但此去極化能力會在電鍍過程中逐步失效並喪失填孔能力，本研究亦對造成其老化的原因進行探討，並發現在陽極表面直接氧化是造成其裂解的最主要原因。而在不溶性陽極的電鍍體系中，挑選具低活性的混合金屬氧化物塗層，可有效延長硫醇添加劑的壽命，維持填孔電鍍的操作穩定性。
2. 在直流電高速電鍍模式下以硫醇類型添加劑誘使奈米雙晶銅結構生成
增強電鍍銅膜的物理性質，如機械強度、導電性、及抗電遷移能力等，是下一世代半導體電鍍製程的關鍵之一，而製備具高密度奈米雙晶缺陷的銅被認為是一個有潛力的方向。然而，目前能誘使奈米雙晶銅的生長的電鍍條件中，多仰賴脈衝電鍍的模式，藉由調控適當的電流密度與電鍍週期來達成。因為有無可避免的停滯時間，以脈衝電鍍製備奈米雙晶銅的速率皆低於10奈米每秒，因此很難應用於商用電鍍的場域。本研究提出了一個新的方法，利用高濃度的硫醇類型添加劑，成功誘使高密度奈米雙晶銅生長，且其成長速率可高於150奈米每秒，可滿足許多商用電鍍製程所要求的成長速度。且應用電化學分析方法，探討高濃度硫醇添加劑對電鍍銅還原動力學的影響，發現二價銅與一價銅的反應速率被大幅提升，單位時間內吸附於陰極表面的一價銅核種大幅增加，使奈米雙晶銅成功在高速直流電鍍的條件下被生成。
3. 應用具單一晶面的奈米雙晶銅於可充電式鋰金屬電池的集電層
由於可充電式鋰金屬電池具備高能量密度與極低還原電位的特質，其被認為是有潛力應用於下一世代鋰電池的設計中。在充電過程中，鋰離子會被電鍍至負極集電層上，並以鋰金屬的形式存在。銅箔是最常被使用的負極集電層，但當使用現今商用的電解液系統時，鋰金屬在銅箔表面的成長通常呈現晶枝狀且結構鬆散，循環效率低。因為商用銅箔通常為具多種晶相的材料，當鋰離子在此異質材料成核與成長時，其可能受到銅晶面的表面能量不同影響，造成局部的成核速度不均，進而加劇鋰晶枝生長的現象。本研究測試了實驗室自行合成，具單一(111)晶面的奈米雙晶銅箔，做為鋰金屬電池的集電層，以改善晶面能差異可能對鋰金屬成長的負面影響。成果發現相較於商用多晶銅箔，鋰金屬在奈米雙晶銅箔上生長的結構更為緊實，且多以較大的橢圓形晶粒存在，大幅減少了鋰晶枝的生長。為驗證其在高電壓、無負極鋰電池中的效應，研究測試了奈米雙晶銅箔與鎳鈷錳酸鋰三元材料匹配的全電池。實驗成果亦證實，在操作電壓高達4.3伏特的情況下，奈米雙晶銅箔能有效提升電池的循環效率，減少無活性鋰金屬生成的比例，有效增加鋰金屬的應用效率。

關鍵字

電鍍銅 ； 硫醇添加劑 ； 奈⽶雙晶銅 ； 電鍍鋰 ； 鋰⾦屬電池

並列摘要

In this work, the electrodeposition behavior of copper and lithium was studied, and there are three major topics:
1. Effect of thiol additive on the reduction kinetic of copper and its degradation behavior during copper electrodeposition
In modern copper electrodeposition process, filling the nano- or microscale vias or trenches to serve as the copper interconnect is ubiquitous inside the integrated circuit (IC) and printed circuit board (PCB), which both are key components in miniature electronic devices. Using several types of organic additives to assist the electroplating process has been widely adopted, and chemical possessing thiol ligand is also one of an essential additives. In our work, we carefully investigated the role of thiol additive in copper electrodeposition, and it is found that such depolarizing additive can shift the copper reaction kinetic from the apparent two-electron-transfer, single step reduction route toward single-electron-transfer, two steps reduction mechanism. The genuine reason leading to the deactivation of thiol additive was also investigated, and it turns out the direct oxidation at the anode surface is responsible for the major oxidation source. In addition, the catalytic ability of mixed metal oxide coating on titanium anode has proven to possess significant influence on the oxidation rate of thiol additive, and using the rather inert coating can effectively prolong the lifetime of thiol additive.
2. Induce the growth of nanotwinned copper with thiol additive by high-speed direct-current electrodeposition
Improving the physical properties of electrodeposited copper film by introducing high-density nanotwinned interphases has been proven to be an effective approach. It can enhance the yield strength, maintain the conductivity, and retard the rate of electromigration phenomenon. To induce the growth of nanotwinned copper, current strategy relies on using pulsed electrodeposition with appropriate plating period and current density. However, the growth rate of copper within such method is restricted by the inevitable off-current period, and the growth rate is limited below 10 nm∙s-1, which is unacceptable for many copper plating process. In our work, we developed a novel method to induce the growth of nanotwinned copper with direct-current electrodeposition mode, and the critical factor is adding proper amount of thiol additive. The growth rate of copper is successfully promoted up to 150 nm∙s-1, which is the faster than any current reports, and is able to satisfy the production rate for most commercial copper plating process. The mechanism to induce such structure is also examined by electrochemical analyses, and we confirmed that the cuprous ion concentration during copper electrodeposition was greatly enhanced, leading to faster nucleation rate for Cu growth.
3. Employ nanotwinned Cu as the anode of lithium metal batteries
Lithium metal batteries (LMBs) have drawn wide attention owing to the very high potential capacity and low reduction potential. During the charge process of LMBs, lithium will be electrodeposited on anode current collector, which is normally copper foil, and store the energy as metallic lithium. When lithium nucleate and grow on the heterogeneous copper substrate, the deposition pattern was mostly dendritic and loose, and numerous approaches including modifying electrolyte composition, adding additives to ameliorate the Li deposition morphology have been proposed. However, the effect caused by the properties of copper foil is still unstudied, especially the contribution from the facet selectivity of copper. Therefore, we synthesize the nanotwinned copper foil by high-speed direct-current plating, and compare its effect on battery performance with the commercial foil. The result demonstrated the (111)-oriented surface can ameliorate the macroscopic lithium distribution, and allow larger granular Li grains growth, which can reduce the porosity of Li deposition. Supported by the full batteries cycling and material analysis result, nanotwinned copper foils can enhance the usage efficiency of lithium, and decrease the amount of dead Li accumulation.

並列關鍵字

copper electrodepositon ； thiol additive ； nanotwinned copper ； lithium electrodepositon ； lithium metal batteries

參考文獻

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