| 摘要: | 富鋰層狀鋰鎳錳鈷正極材(Lithium-rich layered lithium nickel manganese cobalt oxide, Li1.2Mn0.54Ni0.13Co0.13O2, LRO) ，由於其擁有最高的能量密度、最寬的電壓窗口以及良好的工作電壓，被認為有前途的正極材料，此外同時作為一種高錳的正極材料，具備低成本以及較好的環性友善性。然而，Li1.2Mn0.54Ni0.13Co0.13O2的結構不穩定性導致循環性能差、容量衰減，限制了富鋰正極材料的發展。
為了解決這些挑戰，我們提出了一種創新方法，使用基於對苯二甲酸（PTA）的金屬有機框架（MOFs）之前驅物合成Li1.2Mn0.54Ni0.13Co0.13O2。在此過程中，有機配體作為模板，使金屬離子的均勻排列並大幅縮小顆粒尺寸，提升材料的Li+傳導率。另外直接讓鐵參與配位反應，形成鐵摻雜 Li1.2Mn0.54-xNi0.13Co0.13FexO2，進一步提升材料的穩定性，此外，我們分析不同充放電樣本的結構變化，建立起材料與電化學性能之間的關聯性。我們的研究揭示了正極材料在長期循環中的詳細結構重組，並為理解電池材料再生現象提供了理論支持與新的研究方向。
從結果可以發現在有機金屬框架製程中，正極材料會自動生成Li2Co3 均勻包覆在Li1.2Mn0.54Ni0.13Co0.13O2表面，保護材料減少電解液劣化反應，提升 Li+ 擴散。通過適當的鐵摻雜，控制Li2MnO3相態，提升材料的穩定性，其中Li1.2Mn0.54-xNi0.13Co0.13FexO2 (x =0.03) 樣品擁有最佳的性能表現，在 0.2 C 下，具有 250mAh/g 之實際電容量，在 1 C條件下進行 200 次與500次循環下，分別維持189 mAh/g和179 mAh/g的電容量，並且在不同倍率測試中，顯示2 C和5 C下能夠擁有170 mAh/g與127 mAh/g，揭示以有機金屬框架與鐵摻雜之結合，所合成出來的Li1.2Mn0.54Ni0.13Co0.13O2，其綜合性能遠超過其他製程。
;Lithium-rich layered lithium nickel manganese cobalt oxide Li1.2Mn0.54Ni0.13Co0.13O2 (LRO) has been recognized as a promising cathode material. Due to its highest energy density, widest voltage window, and excellent operating voltage. Furthermore, as a high-manganese cathode material, it possesses low cost and good environmental compatibility. However, the structural instability of LRO leads to poor cycling performance, capacity decay, limiting the development of lithium-rich materials.
To address these challenges, we propose an innovative approach to synthesize LRO cathode materials from precursors using metal-organic frameworks (MOFs) based on purified terephthalic acid (PTA). In this process, organic ligands serve as templates, facilitating uniform arrangement of metal ions and significantly reducing particle size to prepare cathode materials with high cycling stability and energy density. With Fe doping into the PTA-Mn-Ni-Co precursor. We successfully using XRD, XPS, and TEM confirm the incorporation of Fe into the material structure. In addition, we established a direct correlation between material structural changes and electrochemical performance and observed the microscopic structure of the samples through HR-TEM. Our research reveals detailed structural reorganization of cathode materials during long-term cycles and provides a microscopic mechanism for capacity increase, offering theoretical support for understanding battery material regeneration phenomena. The in-situ generate a Li2CO3 coating layer on the surface of LRO during the MOFs process, protecting the material from degradation reactions with the electrolyte and enhancing Li+ diffusion. Furthermore, by appropriate Fe doping, we control the ratio of Li2MnO3 phase to improve material stability. Among the different Fe doping sample, the Li1.2Mn0.54-xNi0.13Co0.13FexO2 (x=0.03) sample exhibits the best performance, achieving an actual capacity of 250 mAh/g at 0.2 C, and discharge capacity of 189 mAh/g and 179 mAh/g after 200 and 500 cycles at 1 C rate, respectively. Moreover, it maintains capacity of 170 mAh/g and 127 mAh/g at 2 C and 5 C rates, respectively. Compared with LRO from other literature, it reveals that the LRO combined with metal-organic frameworks and Fe doping exhibits significantly greater cycling stability than LRO produced by other processes. |
