The charge-discharge behavior of LiNi_0.5Mn_1.5O₄, having both the ordered and disordered spinel structures, had been investigated by several research groups [1–5]. However, there are discrepancies with regard to the suitability of the disordered or ordered spinel for better battery performance [3–5]. It is also not clearly understood whether the rate performance of the material is limited by bulk transport properties or interfacial charge transfer reaction kinetics. The purpose of the present work is to elucidate the role of the electrochemical charge transfer kinetics at the electrode/electrolyte interface of Li_1-xNi_0.5Mn_1.5O₄ in determining the rate performance of the spinel cathode. The measurements have been carried out on additive free sintered dense plate in order to exclude any extrinsic effect. The exchange current density at the electrode/electrolyte interface is found to be continuously increased with increasing the degree of delithiation for ordered phase (~0.21-6.5mA/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 4V plateau regime (x=0.01-0.04) and again monotonously increases (0.65-6.8mA/cm²) with further delithiation at (x=0.04-0.60). The ionic diffusivity of ordered and disordered phase is found to be ~5x10^-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.

 

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