Strengthened the structural stability of in-situ F− doping Ni-rich LiNi0.8Co0.15Al0.05O2 cathode materials for lithium-ion batteries

Layered Ni-rich oxides have always been considered as highly promising cathode materials for high-energy–density lithium-ion batteries, whereas they have been confronted with technical bottlenecks sprung from short cycle life and thermal instability. In this work, F− doping as one feasible approach has been introduced into LiNi0.8Co0.15Al0.05O2 for alleviating the limitations by stabilizing the layered structure. The stoichiometric LiNi0.8Co0.15Al0.05O2-xFx (0 ≤ x ≤ 0.1) composite powders doped with different amounts of NH4F powders are precisely synthesized by in-situ modified method, which are strictly identified by physicochemical methods. The characterization results demonstrate that F ions successfully enter into the lattice of LiNi0.8Co0.15Al0.05O2-xFx (0 ≤ x ≤ 0.1) and that the targeted LiNi0.8Co0.15Al0.05O1.96F0.04 composite powders possess the most ordered layered structure with compact surface morphology when the doping amount of F− is up to 4 % based on the weight of the precursor Ni0.8Co0.15Al0.05(OH)2 composite powders. Moreover, the half-cell assembled with the LiNi0.8Co0.15Al0.05O1.96F0.04 composite electrode presents a reversible discharge specific capacity of 157.8 mAh g−1 with remarkable capacity retention of 98.3 % after 100cycles at 2.0C at 25 °C. Even at an elevated temperature of 60 °C and a high current density of 5.0C, it still delivers an improved discharge specific capacity of 142.6 mAh g−1 with excellent capacity retention of 89.1 %. The outstanding improvements in the terms of the lithium storage performance are principally attributed to the stronger metal-F bonds substituting the metal-O bonds with introducing F ions into the lattice, which can not only effectively stabilize the host structure to preserve the structural integrity, but also prevent the erosion of HF and suppress the increment of the polarization degree during continuous cycling processes. Therefore, the F− doping strategy may provide a novel horizon to construct layered Ni-rich cathode materials with improved structural stability and durable electrochemical performance for lithium-ion batteries.