a) Spinel structure with Li sitting in tetrahedral 8a positions (in purple) and transition metals sitting in octahedral 16d positions. b) Targeted solid solution compounds along the tie line LiNi0.5Mn1.5O4–LiFe0.5Mn1.5O4 (substitution of Fe by Ni with a step of x = 0.1 mol per formula unit). c) Obtained PXRD patterns of the powder samples after synthesis. d–i) SEM images of obtained powder samples after synthesis: d) x = 0.5; e) x = 0.4; f) x = 0.3; g) x = 0.2; h) x = 0.1; i) x = 0.

Major Contributions
 

1.Demonstrated that moderate nickel substitution (x = 0.2) in Fe-rich high-voltage spinels LiNixFe0.5–xMn1.5O4 significantly enhances cycling stability, achieving 97% capacity retention after 35 cycles compared to rapid degradation in the unsubstituted Fe-rich spinel. This improvement is achieved without sacrificing the high-voltage capacity, enabling practical application of Fe-rich spinels in next-generation Li-ion batteries.

2.Provided comprehensive structural analysis using Rietveld refinement, pair distribution function (PDF) analysis, and advanced electron microscopy, revealing that both average and local structures remain similar across the series, but local Fe clustering and nanoscale Li2MnO3 formation are present. These subtle local structural features do not directly account for the electrochemical differences, highlighting the complexity of defect chemistry in these materials.

3.Uncovered the mechanism behind capacity fading in Fe-rich spinels by combining in situ X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that nickel incorporation shifts the Fe4+/3+ redox activity to lower voltages, suppresses large concentration polarization, and leads to the formation of a more stable cathode–electrolyte interphase (CEI). This stabilization mitigates oxidative side reactions and Li inventory loss, which are the predominant failure mechanisms in Fe-rich spinels without nickel.

主要貢獻
 

1.證實在富鐵高壓尖晶石 LiNixFe0.5–xMn1.5O4 中，適度的鎳取代（x = 0.2）能顯著提升循環穩定性，在35次循環後達到97%容量保持率，遠優於未摻鎳富鐵尖晶石的快速衰退，且不影響高壓容量，展現富鐵尖晶石於次世代鋰離子電池實用化的潛力。

2.透過Rietveld精修、配對分布函數（PDF）分析及先進電子顯微鏡，全面解析系列材料的平均與局部結構，發現雖然平均結構相近，但局部存在鐵聚集與奈米級Li2MnO3相分離。這些細微的局部結構特徵無法直接解釋電化學性能差異，突顯材料缺陷化學的複雜性。

3.結合原位X光繞射與原位漫反射紅外傅立葉轉換光譜（DRIFTS），揭示富鐵尖晶石容量衰退的機制。鎳的引入能將Fe4+/3+氧化還原反應電壓下移，抑制濃度極化，並促進形成更穩定的正極-電解液界面層（CEI），有效減緩氧化副反應與鋰存量流失，這是未摻鎳富鐵尖晶石主要的失效機制。