Effect of outer layer thickness on full concentration gradient layered cathode material for lithium-ion batteries

Abstract

Full concentration gradient (FCG) layered cathode materials Li[Ni0.6−xCo0.15+xMn0.25]O2 (x = 0, 0.01, and 0.04) with different outer layer thicknesses are synthesized via a specially developed coprecipitation method. In the FCG cathode, the nickel concentration decreases linearly and the cobalt concentration increases from the center to particle surface throughout the particle at a fixed composition of Mn. The thickness of the FCG primary particle increases in the radial direction with an increasing outer layer thickness of the secondary particles and significantly affects the electrochemical performance. An increase in the stable outer layer thickness improves the cycle performance and thermal stability of the FCG materials at the expense of reversible capacity, whereas the rate capability and low temperature performance are significantly deteriorated by increasing outer layer thickness. All of the FCG materials exhibit superior electrochemical and thermal properties compared to the conventional cathode Li[Ni0.58Co0.17Mn0.25]O2 due to the unique microstructure of the FCG cathode.