Part-II: Exchange current density and ionic diffusivity studies on the ordered and disordered spinel LiNi 0.5 Mn 1.5 O 4 cathode

Additive-free pellets of Li1-xNi0.5Mn1.5O4 have been prepared for the purpose of performing ionic diffusivity and exchange current density studies. Here we report on the characterization of interfacial charge transfer kinetics and ionic diffusivity of ordered (P4332) and disordered (Fd3¯m) Li1-xNi0.5Mn1.5O4 as a function of lithium content at ambient temperature. The exchange current density at the electrode/electrolyte interface is found to be continuously increased with increasing the degree of delithiation for ordered phase (∼0.21–6.5 mA/cm2) at (x = 0.01–0.60), in contrast the disordered phase exhibits gradually decrease of exchange current density in the initial delithiation at the 4 V plateau regime (x = 0.01–0.04) and again monotonously increases (0.65–6.8 mA/cm2) with further delithiation at (x = 0.04–0.60). The ionic diffusivity of ordered and disordered phase is found to be ∼5 × 10−10cm2s−1 and ∼10−9cm2s−1, respectively, and does not vary much with the degree of delithiation. From the obtained results it appears that the chemical diffusivity during electrochemical use is limited by lithium transport, but is fast enough over the entire state-of-charge range to allow charge/discharge of micron-scale particles at practical C-rates.