Effect of nanostructured carbon coatings on the electrochemical performance of Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x)-based cathode materials

Nanocomposites of Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x) and amorphous carbon were obtained by the pyrolysis of linear and cross-linked poly(vinyl alcohol) (PVA) in presence of Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x). In the case of linear PVA, the formation of nanostructured carbon coatings on Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x) particles is observed, while for cross-linked PVA islands of mesoporous carbon are located on the boundaries of Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x) particles. The presence of the carbon framework leads to a decrease of the polarization upon cycling and of the charge transfer resistance and to an increase in the apparent Li(+) diffusion coefficient from 10(−16) cm(2)·s(−1) (pure Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x)) to 10(−13) cm(2)·s(−1). The nanosized carbon coatings also reduce the deep electrochemical degradation of Li(1.4)Ni(0.5)Mn(0.5)O(2+)(x) during electrochemical cycling. The nanocomposite obtained by the pyrolysis of linear PVA demonstrates higher values of the apparent lithium diffusion coefficient, a higher specific capacity and lower values of charge transfer resistance, which can be related to the more uniform carbon coatings and to the significant content of sp(2)-hybridized carbon detected by XPS and by Raman spectroscopy.