Preparation and Electrochemical Performance of High Rate Spherical Layered LiNi0.5Co0.2Mn0.3O2 Cathode Material for Lithium-Ion Batteries

Abstract

Layered Ni-rich compound LiNi0.5Co0.2Mn0.3O2 has drawn considerable attention recently because high Ni content contributes to the improvement of specific capacity and the reduction of cost. However, it is a challenge to obtain the Ni-rich LiNi0.5Co0.2Mn0.3O2 cathode with both high rate performance and high tap density because the rate capability is often improved at the expense of volumetric energy density, which is mostly dependent on the tap density. In our work, an uniform Ni-rich LiNi0.5Co0.2Mn0.3O2 microsphere with an average diameter of ca. 5 μm and tap density of 2.1 g·cm-3 was successfully prepared using carbonate co-precipitation method, which can meet the commercial requirement for lithium-ion batteries (tap density≥2.1 g·cm-3, Lithium Nickel Cobalt Manganese Oxides from CETC International Co., Ltd). In this synthetic route, the 2 mol·L-1 mixture of NiSO4·6H2O, MnSO4·H2O and CoSO4·7H2O (Ni:Co:Mn=5:2:3, molar ratio) are the starting materials, 2 mol·L-1 Na2CO3 and 4 mol·L-1 NH3·H2O are the precipitant and chelating agent, respectively. In order to achieve high tap density, the stirring speed of continuous stirred tank reactor (CSTR) is as high as 1500 r/min, and the powder was preheated at 550℃ for 6 h and then calcined at 850℃ for 14 h in flowing oxygen. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicate that the microsphere LiNi0.5Co0.2Mn0.3O2 material has a well-ordered α-NaFeO2 structure with stable in-plane [√3×√3]R30° ordering in the transition-metal layers. Electrochemical results also confirm that this cathode has excellent cycling stability and high rate capability. Specifically, it exhibits a discharge capacity of 150 mAh·g-1 between 2.7 and 4.3 V at 1C after 100 cycles, with outstanding capacity retention of 94.6%. At 30C rate, it can still deliver a high discharge capacity of 96 mAh·g-1. Meanwhile, the energy storage capacity for this cathode is also encouraging. At 0.1C rate, the specific energy (Es) is 687.83 Wh·kg-1 (volumetric energy density is 1444.45 Wh·L-1); at 30C rate, the specific energy (Es) is 335.27 Wh·kg-1(volumetric energy density is 704.07 Wh·L-1). These excellent features will make this microsphere LiNi0.5Co0.2Mn0.3O2 material as a potential positive electrode material for commercial high energy density lithium-ion batteries.