| 摘要: | 在2050淨零碳排的推動下，轉向更加環保和可再生的能源來源已成為當務之急，太陽能發電、水力發電或是風力發電等可再生能源雖然潔淨環保，但存在著間歇性和不穩定性的挑戰。因此，如何有效管理和儲存這些間歇性能源成為一個重大的目標，能源儲存技術的重要性也日益顯著。
鋰離子電池作為應用最廣泛的二次電池，在儲能領域的應用也得到了大量的關注。高熵氧化物(High entropy oxide, HEO)為一種新興材料，以其獨特的性能如高結構穩定性和優異的離子電導率等優勢，被視為極具潛力的鋰離子電池電極材料。相較於傳統材料，高熵氧化物具有多個元素，為其提供了更多活性位點，從而提高理論電容。然而，多元素的組成也增加了材料內部反應的複雜性，在電池充放電過程中，鋰離子與高熵氧化物材料之間的反應機制，以及對於電池性能的影響，仍需要進行深入研究。
本研究採用噴霧造粒法，分別以三種不同的燒結參數，合成岩鹽結構的高熵氧化物((Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O)，並用作鋰離子電池的負極活性材料，並以半電池形式測試性能。在三種材料中，燒結溫度最高者表現出最佳的電化學性能，於小電流(0.05C)充放電下，具有311.54mAh g-1的電容；在100次的長時間循環性能測試中，也能達到84.01%的高電容保持率。相較之下，燒結溫度較低、時間較短的樣品，在100次的長時間循環性能測試中，僅有60.28%的電容保持率。
此外，使用X射線光電子能譜儀(X-ray photoelectron spectroscopy, XPS)，分析不同循環狀態下的電極表面，探討固態電解質介面(Solid electrolyte interphase, SEI)的成分組成及電極活性物質之化學組態變化。藉由分析，我們推測了SEI層的生長機制，並發現高熵氧化物中，鈷(Co)、銅(Cu)及鋅(Zn)在充放電過程中會發生不可逆的還原反應，可能是此組成之高熵氧化物電極主要的老化原因之一。而鎂(Mg)元素不參與反應，推測其為材料穩定結構的主要元素。另外，也藉由化學組態變化，分析出不同燒結參數下的高熵氧化物材料中，各元素的轉化反應對於電化學性能的影響。
;In order to achieve net-zero carbon emissions by 2050, lithium-ion batteries have garnered significant attention in the field of energy storage. High entropy oxides (HEO) are considered highly promising as electrode materials for lithium-ion batteries due to their unique properties, such as high structural stability and excellent ionic conductivity. They are consist of multiple elements, providing more active sites and potentially increasing their theoretical capacity. However, a fully understanding of electrochemical behavior of HEO in lithium-ion battery is still lacking. The storage mechanism is complicated due to the multiple electroactive centers. Especially, the degradation mechanism of HEO electrode is debating.
In this research, we employed the spray granulation method with three different sintering parameters to synthesize HEO with rock-salt structures. The synthesized (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O HEO is used as an active material for the anode electrode of the lithium-ion batteries. Among three materials, the one sintered at the highest temperature exhibited the best electrochemical performance, delivering a capacity of 311.54mAh g-1 at 0.05C, and achieving a high capacity retention of 84.01% after 100 cycles of long-term cycling tests. In contrast, the samples sintered at lower temperatures and shorter times showed only 60.28% capacity retention after 100 cycles. Furthermore, we used X-ray photoelectron spectroscopy to analyze the surface of the electrodes at different cycling states, investigating the composition of the solid electrolyte interphase and the chemical state changes of the active materials. We proposed a growth mechanism for the SEI layer and discovered that cobalt, copper, and zinc undergo irreversible reduction reactions during the charging and discharging process, which may be one of the main causes of anode degradation. Magnesium, on the other hand, did not participate in the reactions, suggesting that it plays a crucial role in stabilizing the material′s structure. |
