可逆高熵氧化物陽極應用於 鋰離子全電池之研究;Study on Reversible High Entropy Oxides as Anode in Lithium-Ion Batteries

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Title:	可逆高熵氧化物陽極應用於鋰離子全電池之研究;Study on Reversible High Entropy Oxides as Anode in Lithium-Ion Batteries
Authors:	黃力朋;Huang, Li-Peng
Contributors:	材料科學與工程研究所
Keywords:	高熵氧化物;溶膠凝膠法;鋰離子電池;陽極材料;失效機制;High entropy oxide;sol-gel method;lithium-ion batteries;anode materials;failure mechanism
Date:	2023-08-15
Issue Date:	2024-09-19 15:51:31 (UTC+8)
Publisher:	國立中央大學
Abstract:	高熵氧化物 (HEO) 由於其出色的性能，如高溫熱穩定性和高離子導電性，對於鋰離子電池 (LIBs) 中的應用具有潛在的前景。本研究成功利用溶膠凝膠法合成一種新型的高熵氧化物 (Co0.2Ni0.2Cu0.2Mg0.2Zn0.2)O，該氧化物具有岩鹽結構，並將其作為LIBs的陽極活性材料。在50mA g-１ (0.1C)定電流充放電率 (C-rate) 條件下，可達到了450mAh g-1的比容量。為了解決高熵氧化物陽極反應初期不可逆容量損失的問題，會在與鎳鈷錳氧化物 (NCM811) 陰極組裝成全電池之前，通過預鋰化處理對高熵氧化物陽極表面進行改質。透過預鋰化改質成功將不可逆容量比從 50％降至 15％；在反應過程中，陽極/電解液界面也會形成磷酸鋰 (Li3PO4) 薄膜，可增強導電性並抑制鋰枝晶的生長。全電池的電化學測試結果顯示，高熵氧化物陽極在20mA g-1(0.1C)的C-rate條件下，實現了121mAh g-1的比容量，其工作電壓約2.4V，全電池的能量密度可達到292Wh kg-1。此外，為了探討高熵氧化物陽極的老化機制，透過拆解不同循環次數的HEO/Li袋裝型半電池及分析陽極表面形貌和元素價態的改變。以下提出了兩點造成老化的原因：1) HEO 材料結構中的鎂離子 (Mg2+) 還原為金屬鎂 (Mg) ，產生了氧(O) 造成電池膨脹；2) 鋰離子 (Li+) 與氧 (O) 結合形成氧化鋰 (Li2O) ，然後與電解液中的六氟磷酸鋰 (LiPF6) 反應，最終導致陽極表面上的 (Li3PO4)不斷增厚，造成界面阻抗增加。本研究通過對高熵氧化物陽極的效能測試及反應過程形貌與價態的變化深入研究，致力於推動高熵材料作為輕量、安全的活性材料應用在未來的儲能系統。;High entropy oxides (HEOs) have great potential for lithium-ion batteries (LIBs) applications due to the exceptional properties, such as high-temperature stability and high ionic conductivity. This study successfully synthesized a novel HEO (Co0.2Ni0.2Cu0.2Mg0.2Zn0.2) O with a rock-salt structure with the sol-gel method and utilized it as the anode in LIBs. The HEO anode achieved a specific capacity of 450mAh g-1 at a constant current charging-discharging rate (C-rate) of 50mA g-1 (0.1C). To solve the issue of irreversible capacity loss during the initial stage of the electrocatalysis reaction, the HEO anode surface was optimized through the pre-lithiation modification before assembling with the high-nickel cobalt manganese oxide (NCM811) cathode to form full cells. This process successfully reduced the irreversible capacity ratio from 50% to 15% and formed a lithium phosphate (Li3PO4) thin film at the anode/ electrolyte interface, enhancing conductivity and inhibiting the growth of the lithium dendrites. Electrochemical measurements of the full cells showed that the HEO anode achieved a specific capacity of 121mAh g-1 at 20mA g-1 (0.1C) with a working voltage of around 2.4V. The energy density can reach 292Wh kg-1. Furthermore, in order to investigate the aging mechanism of the HEO anodes, this study also analyzed the morphology and elemental valence changes of the HEO anode. Two degradation mechanisms were proposed: 1) Reduction of magnesium ions (Mg2+) in the HEO material system to metallic magnesium (Mg), resulting in the generation of oxygen (O) and cell expansion; 2) Migration of lithium ions (Li+) combined with O to form lithium oxide (Li2O), which then reacted with the lithium hexafluorophosphate (LiPF6) in the electrolyte, eventually leading to the continuous thickening of Li3PO4 deposits on the anode surface and increased interface impedance. Through in-depth research and analysis of the HEO anode′s performance, morphology changes, and valence states, this study aims to promote the application of HEO as a lightweight and safe active material in future energy storage systems.
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