Uniform Ni-rich LiNi0.6Co0.2Mn0.2O2 porous microspheres: facile designed synthesis and their improved electrochemical performance
A facile two-step synthetic route, i.e., combining the carbonate co-precipitation method and impregnation method, to prepare uniform porous Ni-rich LiNi0.6Co0.2Mn0.2O2 microsphere with an average diameter of ∼3 μm and BET specific surface area of 13.4 m2 g-1 is proposed for the first time. The XRD and TEM results confirm that the porous microspheres LiNi0.6Co0.2Mn0.2O2 material has a well-ordered α-NaFeO2 structure with stable in-plane [3x3]R30° ordering in the transition-metal layers. The exquisite morphology and ideal structure endow this nanocrystal-assembled porous LiNi0.6Co0.2Mn0.2O2 microspheres enhanced electrochemical performance such as high capacity, good cycling stability and excellent rate capability. Specifically, the as-prepared porous LiNi0.6Co0.2Mn0.2O2 cathode delivers a high discharge capacity of 79 mAh g-1 even at the ultrahigh rate 50C (10 A g-1), and 138 mAh g-1 at 1C after 100 cycles with an excellent cycle life. Additionally, the fast-charging test results are indicative of the fact that this cathode has sufficiently stable structure, because it can still deliver a discharge capacity higher than 123 mAh g-1 after 100 cycles with capacity retention of 90.1% at 5C charge and 1C discharge. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) results demonstrate that the porous LiNi0.6Co0.2Mn0.2O2 cathode has a higher apparent lithium ion diffusion coefficient (insertion/extraction process are 8.67 x 10-8 and 3.78 x 10-8 cm2 s-1, respectively) and lower activation energy (29.3 KJ mol-1). Our results indicate that this preparation strategy may be facile and versatile for synthesis other high-capacity anode/cathode materials.