雙金屬抑制4.6V高壓單晶高鎳氧釋放的策略

要點一：AN-SNCM的結構表征

Figure?1.?(a)?XRD patterns of SNCM and AN-SNCM. (b and c) SEM images of micron-sized SNCM and AN-SNCM particles. (d) HAADF-STEM image and corresponding SEAD patterns of AN-SNCM. (e-g) TEM of AN-SNCM particle surface. (h) HADDF image of AN-SNCM and TEM-EDS element mapping results of Ni, Al, Nb. (i-j) XPS patterns with a different etching time of Al 2p, Nb 3d for AN-SNCM.

要點二：AN-SNCM首圈的庫倫效率得到提高，在3-4.6V循環200圈后容量保持率達到89.1%（VS初始79.5%），DEMS的測試結果表明初始循環過程中的氧釋放問題得到了有效解決，防止了電池工作中潛在的安全隱患。

Figure 2. Electrochemical performance of coin type batteries with SNCM and AN-SNCM cathodes in the voltage range of 25 ℃, 3-4.6 V. (a)Initial charge discharge curves of original SNCM and AN-SNCM cathodes. (b) Performance curve for 200 cycles at 1C current density. (c) – (d) dQ/dV spectra of two cathodes derived from Figure 2b. (e) Cycling performance of two cathodes at 3C current density. (f)-(g) Gas evolution profiles of CO₂?and O₂during the second galvanostatic charge process of SNCM and AN-SNCM electrodes.

要點三：AN-SNCM正極在循環工作中的H₂-H₃相變過程緩和，晶包參數c和體積變化更小，有效地釋放了內部應變，防止了由于晶格畸變而導致的結構解體。

Figure 3. Phase transition during cyclic processes. Operando XRD characterization of the full contour plots and selected line patterns for (a) SNCM and (b) AN-SNCM cathodes during the initial cycle in the voltage range of 3-4.6 V, 0.2C. The variation of the c-axis and cell volume parameter during charging for pristine (c)SNCM and (d)AN-SNCM.

Figure 4. (a-h) HAADF-STEM images of SNCM and AN-SNCM particle cross-sections prepared by FIB after 200 cycles at 1C and 4.6V. (i-j) EELS line scanning of Ni and O elements from the surface to the interior of particles.

要點四：正極界面電解質界面處的C₂HO^–、磷化物（PO^3-、C₂P^–）、C₂F^–和LiF^2-等有機物含量顯著降低。

Figure 5. Normalized TOF-SIMS depth maps of SNCM and AN-SNCM cathode CEI after 150 cycles at 3-4.6 V and 1C, respectively. (a) TOF-SIMS depth maps of CH₂O^?, PO^3?, LiF^2??and NiF^3??species; (b) 3D rendering (CH₂O^?, PO^3?, LiF^2??and NiF^3?) concentration distribution composition; (c) Chemical imaging of TOF-SIMS on SNCM and AN-SNCM cathode surfaces (CH₂O^?, PO^3?,LiF^2??and NiF^3?). (d)Phase transition during the?In-situ?high-temperature XRD patterns, and (e)Differential scanning calorimetry profiles when charged to 4.6V of SNCM and AN-SNCM.

要點五：Al的摻雜可以有效緩解晶格氧的電荷損失，使得O:2p費米能級以上的未占據軌道顯著減少；其次，差分電荷密度結果表明，Al的加入增加了周圍過渡金屬元素的電荷密度，系統中的TM-O鍵得到了加強，結構變得更加穩定。由于在表面引入Nb，Nb-O鍵可以為O原子提供額外的負價態變化，并緩解O氧化以進行電荷補償，從而賦予強大的穩定作用。

Figure 6. DFT calculation of the effect of doping on the structure and electronic states of the system. (a) Formation energy for replacing Ni, Co, or Mn ions both surface (Sur.) and bulk layer (Bulk) with Al or Nb ions. (b-c) The calculated projected density of states of Ni:3d, O:2p and the total density of states plots of SNCM and AN-SNCM. (d-e) The calculated projected density of states of O 2p and 2D contour maps of charge density distribution.