Coating versus Doping: Understanding the Enhanced Performance of High-Voltage Batteries by the Coating of Spinel LiNi0.5Mn1.5O4 with Li0.35La0.55TiO3

Li0.35La0.55TiO3 (LLTO) coated spinel LiNi0.5Mn1.5O4 (LNMO) as cathode material is fabricated by a new method using hydrogen-peroxide as activating agent. The structure of the obtained active materials is investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes are probed by the charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles is investigated by the SEM, which shows a fully dense and homogeneous coating (thickness approximate to 7 nm, determined by TEM) on the surface of active material. XRD studies of the coated active materials treated at different temperatures (between 300 degrees C and 1000 degrees C) reveal expansion or contraction of the unit cell in dependence of the coating concentration and degree of Ti diffusion. It is concluded, that for the LNMO particles calcined at low temperatures, the LLTO coating layer is still intact and protects the active material from the interaction with the electrolyte. However, for the coated particles treated at high temperatures, Ti ions migrate into the structure of LNMO during the modification process between 500 degrees C and 800 degrees C, resulting in "naked" and unprotected particles.