【研究背景】
【工作簡介】
單獨表面包覆或體相摻雜均無法同時解決超高鎳正極的界面失穩與體相開裂問題。Mg2+傾向于偏析至顆粒表層，可在表面誘導生成無序巖鹽相充當化學鈍化層；Nb5+可均勻摻入體相，誘導共格尖晶石類相并通過"交叉固定"效應緩解晶格應變，同時促進一次晶粒細化。二者協同還可通過輕微缺鋰設計誘導體相陽離子無序（Ni占據Li位），充當"支柱"抑制c軸過度收縮并提升氧空位形成能。因此Mg/Nb共摻雜可實現"外防內強"的表面–體相一體化微結構重構。
① 集成微結構確認
Figure 1 (a) The schematic diagram of the local microstructure regulation strategy for NCM95-MN. (b1–b4) EPMA images of morphology and elements (Ni, Mg, and Nb) distribution in the NCM95-MN. The HAADF-STEM images for (c) surface gradient structure, (d) coherent spinel-like phase, and (e) cation-disordered structure in the NCM95-MN. The ND patterns of (f) NCM95 and (g) NCM95-MN.
EPMA證實Mg表面富集、Nb體相均勻分布；HAADF-STEM+EELS顯示NCM95-MN表層存在~5 nm無序巖鹽相（Ni價態降低），體相觀察到共格尖晶石雙晶面（交角110°）及Li層內Ni2+占位（陽離子混排升至3.1%）。ND與XRD精修定量驗證了體相陽離子無序結構的引入——說明表面鈍化層與體相釘扎結構均已成功構建。
② 電化學性能
Figure 2 (a) The galvanostatic charge–discharge curves and (b) the dQ/dV curves of NCM95 and NCM95-MN at the first cycle within 2.8–4.3 V at 0.1C at 30°C. (c) The cycling performance of two samples within 2.8–4.3 V at 1C at 30°C. The dQ/dV curves of (d) NCM95 and (e) NCM95-MN at different cycles within 2.8–4.3 V at 1C at 30°C. (f) The rate performance of two samples within 2.8–4.3 V at 30°C. (g) The high temperature cycling performance of two samples within 2.8–4.3 V at 1C at 60°C. (h) The rapid charge performance of NCM95-MN within 2.8–4.3 V at 3C at 30°C.
改性樣品0.1C容量240.11 mAh·g-1，首效93.24%；1C/100圈保持97.37%，3C/500圈81.65%，15C仍達147.43 mAh·g-1，60℃/100圈＞80%——證明一體化微結構顯著提升循環、倍率及高溫性能。
③ 結構演變追
Figure 3 (a) The variation of (003) peak for NCM95 and NCM95-MN obtained from in situ XRD. (b) The variation of c-axis lattice parameters, volume, and sheer stress c/a in the NCM95 and NCM95-MN. (c) The R space curves and (d) the wavelet transform of NCM95 and NCM95-MN obtained by the EXAFS spectrum before and after cycling.
原位XRD顯示NCM95-MN的c軸收縮率和體積變化（6.26% vs 8.08%）及c/a剪切速率顯著降低，H2–H3相變更平緩；XAFS表明循環后Ni K邊位移更小，Ni–O/Ni–TM配位環境保留更好——說明體相釘扎效應有效抑制了各向異性應變與不可逆Ni4+生成。
④ 裂紋與界面表征
Figure 4 The SEM images of cycled (a, b) NCM95 and (e, f) NCM95-MN. (c) The TEM image of NCM95, in which region I and region II were analyzed by fast Fourier transform (FFT) maps, and the strain distribution in the region of (c1) was indicated by GPA analysis in (c2). (d) The CEI generated on the surface of cycled NCM95. (g) The TEM image of NCM95-MN, in which region I was analyzed by fast Fourier transform (FFT) map, and the strain distribution in the region of (g1) was indicated by GPA analysis in (g2). (h) The CEI generated on the surface of cycled NCM95-MN. (i) The load-depth curve and (j) the elastic modulus and hardness of the materials obtained from the nanoindentation test of cycled NCM95 and NCM95-MN.
循環后NCM95出現嚴重晶間裂紋及厚巖鹽相/CEI，NCM95-MN裂紋極少、表面鈍化層保留、CEI薄且均勻；納米壓痕測得循環后NCM95-MN彈性模量6.43 GPa、硬度0.0865 GPa（高于未改性5.20/0.0556 GPa）；TOF-SIMS顯示CEI副產物減少；ICP-MS中TM溶解量降低約60%——從力學與化學雙維度證實微結構工程的抗裂與界面鈍化效果。
⑤ 氧穩定性與熱安全
Figure 5 (a) The 2D contour maps of in situ Raman spectra for NCM95 and NCM95-MN during cycling within OCV-4.3 V at 0.2C. (b) The comparison of Raman spectra at different stages (OCV, charge to 4.3 V and discharged to OCV) in the NCM95 and NCM95-MN. (c) The EPR spectroscopy of NCM95 and NCM95-MN. (d) The TG-MS curves of NCM95 and NCM95-MN. (e) The DSC curves of NCM95 and NCM95-MN. (f) The schematic diagram of the relationship between oxygen stability and thermal stability.
原位Raman證明晶格氧振動可逆恢復，EPR顯示充電態活性氧物種減少；TGA-MS氧釋放溫區延遲≈20℃，DSC放熱峰升至235℃、產熱降至22.5 J/g——證實晶格氧過氧化被抑制，熱安全性顯著增強。
⑥ 動力學分析
Figure 6 (a) C 1s, O 1s, and F 1s XPS spectra of the cycled NCM95 and NCM95-MN. (b) 3D rendering TOF-SIMS fragments of C2HO, Li2F3 and PO2 in the cycled NCM95 and NCM95-MN. The 2D contour maps of DRT for the cycled (c) NCM95 and NCM95-MN. (d) The GITT curves of cycled NCM95 and NCM95-MN at high voltage.
DRT顯示電荷轉移與Li+擴散阻抗降低，GITT得出更高Li+擴散系數，尤其在＞4.2 V——共格尖晶石相提供了低能Li+遷徑通道。
Mg/Nb共摻雜在超高鎳NCM95中構建了表面無序巖鹽鈍化層 + 體相共格尖晶石相 + 陽離子無序釘扎結構的一體化微結構：表面層阻斷界面寄生反應，體相微結構釘扎晶格畸變、緩解H2–H3相變應變與微裂紋，二者耦合打斷"體相開裂→電解液滲透→表面惡化"惡性循環。改性正極兼具高容量（210.44 mAh·g?1@1C）、長循環（97.37%/100圈，81.65%/500圈@3C）、優異倍率/高溫性能及高熱安全性。該一體化局部微結構工程策略可拓展至其他高鎳/高電壓層狀正極，為實用化高能量密度鋰電正極設計提供了重要指導。
