Niobium-Doped Ultrahigh-Ni Single-Crystalline LiNi _0.95 Co _0.025 Mn _0.025 O ₂ Cathode Enabled by the Molten Salt Method for High-Energy Lithium-Ion Batteries

Growing demand for high-energy-density lithium-ion batteries (LIBs) has established high-nickel layered oxides as one of the most promising cathode candidates. Compared with commonly used high-nickel polycrystalline layered oxides, high-nickel single-crystalline layered oxides have attracted more attention due to their improved structural and cycling stability. However, the synthesis of high-nickel single-crystalline nickel cobalt manganese lithium oxide (NCM) particles requires a high calcination temperature, leading to particle agglomeration and aggravated Li⁺/Ni²⁺ cation mixing. In addition, high-nickel single-crystalline NCM could suffer from sluggish Li⁺ diffusion kinetics and structural degradation caused by severe phase transformation. Herein, we adopted the molten salt method to prepare a single-crystalline LiNi_0.95Co_0.025Mn_0.025O₂ cathode at a relatively low synthesis temperature to relieve particle agglomeration. Meanwhile, the Nb doping strategy is employed to broaden the interplanar spacing to facilitate Li⁺ diffusion, inhibit the Li⁺/Ni²⁺ cation mixing, and restrain the severe phase transformation. The obtained Nb-doped single-crystalline LiNi_0.95Co_0.025Mn_0.025O₂ (SC-NCM-N) cathode achieves a high reversible capacity of 216.4 mAh g^-1 at 0.1 C (1 C = 180 mAh g^-1), along with an improved capacity retention (88.7% after 100 cycles at 1 C) in comparison with the polycrystalline LiNi_0.95Co_0.025Mn_0.025O₂ (P-NCM, 66.8%) and pristine single-crystalline LiNi_0.95Co_0.025Mn_0.025O₂ (SC-NCM, 79.1%). This work offers insights into developing high-nickel single-crystalline cathodes for high-energy-density LIBs.