A new type of protective surface layer for high-capacity ni-based cathode materials: Nanoscaled surface pillaring layer

摘要

A solid solution series of lithium nickel metal oxides, Li[Ni _(1-x)M_x]O_2 (with M = Co, Mn, and Al) have been investigated intensively to enhance the inherent structural instability of LiNiO_2. However, when a voltage range of Ni-based cathode materials was increased up to >4.5 V, phase transitions occurring above 4.3 V resulted in accelerated formation of the trigonal phase (P3ì...m1) and NiO phases, leading to and pulverization of the cathode during cycling at 60 C. In an attempt to overcome these problems, LiNi_(0.62)Co_(0.14)Mn _(0.24)O_2 cathode material with pillar layers in which Ni~(2+) ions were resided in Li slabs near the surface having a thickness of ～10 nm was prepared using a polyvinylpyrrolidone (PVP) functionalized Mn precursor coating on Ni_(0.7)Co_(0.15)Mn _(0.15)(OH)_2. We confirmed the formation of a pillar layer via various analysis methods (XPS, HRTEM, and STEM). This material showed excellent structural stability due to a pillar layer, corresponding to 85% capacity retention between 3.0 and 4.5 V at 60 C after 100 cycles. In addition, the amount of heat generation was decreased by 40%, compared to LiNi _(0.70)Co_(0.15)Mn_(0.15)O_2.