Improving the structural stability of Ni-rich LiNi0.81Co0.15Al0.04O2 cathode materials with optimal content of trivalent Al ions doping for lithium ions batteries

To synthesize and optimize stoichiometric Li(Ni0.84Co0.16)1-xAlxO2 (NCA, 0 < x < 0.1) cathode materials with enhanced structural stability, different contents of nano Al(OH)3 powders are employed to co-calcine with home-made Ni0.84Co0.16(OH)2 precursor and LiOH·H2O by ball milling and followed by being co-calcined at 750 °C for 15 h. The results characterized by energy dispersive spectrometer, X-ray diffraction, and transmission electron microscope demonstrate that the as-prepared stoichiometric LiNi0.81Co0.15Al0.04O2 (NC-A4) sample presents a slightly decreasing Al atom concentration from the surface to the core, a lowering cationic disorder degree of 1.69% and an enlarged interplanar distance of the (003) phase of 0.482 nm when the content of the doped nano Al(OH)3 powders is up to 4% based on the precursor. Moreover, the coin cell assembled with NC-A4 can deliver an initial discharge specific capacity of 196.3 mAh g−1 and retain 170.7 mAh g−1 after 100 cycles at 1.0 C at 30 °C with a remarkable capacity retention of 95.5%. Even though at a high current density of 5.0 C, it can also present a superior rate capacity of 162.1 mAh g−1. The enhanced electrochemical performance of NC-A4 is primarily attributed to the significant improvement in the structural stability with trivalent Al ions doping, which can not only maintain a stable lattice structure during the lithiation/delithiation process, but also alleviate the increasement of polarization degree and Rct value. Hence, the presented method would be a simple and effective way to construct stoichiometric and high-performance NCA cathode materials with excellent structural stability for lithium ions batteries.