Direct Elimination of Detrimental Surface Phases Parasitic to LiNi_xCo_1−xO₂ (x = 0.8 and 0.9) with Unique 3D Porous Structures during Synthesis

Abstract Detrimental rock‐salt and/or spinel surface phases parasitic to Ni‐rich layered oxides with high theoretical capacity are quite formidable which are reported to be eliminated only through alien element dopings and/or surface modifications. Herein, these surface phases are directly eliminated successfully during the synthesis of pristine LiNi_0.8Co_0.2O₂ and LiNi_0.9Co_0.1O₂ using an expanded graphites (EGs) template approach, accompanied by the formation of unique 3D porous structures. The elimination of surface phases may be ascribed to the 3D porous structures formed during the calcination processes at both low and high temperatures, which enables the access of sufficient oxygen to individual nanoparticles and thus promotes the oxidization of Ni²⁺ to Ni³⁺ to reduce Li/Ni disordering. Both LiNi_0.8Co_0.2O₂ and LiNi_0.9Co_0.1O₂ show excellent rate capability, long‐term cycling stability, and high initial Coulombic efficiencies (ICEs), such as 210.4 (149) and 222.6 (133) mAh g⁻¹, ICEs of 94.9% and 93.8% at 0.1 C (20 C), and capacity retentions of 74% after 500 cycles at 1 C and 76% after 300 cycles at 1 C, respectively, far better than those synthesized using a conventional sol–gel recipe. This study provides a simple and novel platform for directly synthesizing detrimental surface phases free and chemically stoichiometric Ni‐rich layered oxides with high performance.